"uuid","repository link","title","author","contributor","publication year","abstract","subject topic","language","publication type","publisher","isbn","issn","patent","patent status","bibliographic note","access restriction","embargo date","faculty","department","research group","programme","project","coordinates"
"uuid:28542c6f-1e32-4beb-87eb-d4080ed4647d","http://resolver.tudelft.nl/uuid:28542c6f-1e32-4beb-87eb-d4080ed4647d","VoNA The Visualisation of Neuronal Activation: To observe and shape electrode-generated outputs for electrical stimulation in the brain using a Finite Element Model","van Lith, Niels (TU Delft Mechanical, Maritime and Materials Engineering)","Lopes Marta da Costa, T.M. (mentor); Remis, R.F. (graduation committee); Delft University of Technology (degree granting institution)","2024","The development of neural prostheses, especially those directly targeting the brain, requires extensive research and modelling before clinical trials can be performed. Currently, the resolution of artificial vision is not sufficient for everyday tasks. By studying the expected spatial extent of stimulation, we aim to provide insights to researchers that can be used to improve the resolution of artificial vision. The goal of this MSc thesis was to visualise the shape and intensity of electric fields in the cortex as a response to intracortical microelectrode stimulation to observe the expected regions of neuronal activation considering electrode design parameters. To do this, parameters that can influence the generated electric field and the regions of activated tissue have been defined. Implementing these parameters in a Finite Element Model (FEM) allows the computation of the generated electric field in 3D of a stimulating electrode to observe the spatial extent of activated tissue. The spatial extent of activated tissue can be estimated using simplified methods such as the activating function (AF) or current density threshold. The result is a parameterised framework that creates a Visualisation of Neuronal Activation (VoNA) that can be used to assess activated tissue regions for varying scenarios by defining material properties and dimensions of the model, and allows for the adjustment of the stimulation configuration, electrode contact spacing, customisation of electrode size and modulation of stimulation current. It enables the user to tune the model settings towards their specific needs and explore the possibilities by visualising the results from different angles by defining subsets of the entire solution. In line with expectations, the presented models show that the model parameters can influence factors such as the generated electric field, the current density and electric potential, which are indicators of neuronal activation. The findings support the hypothesis that these parameters should be considered during electrode design to achieve accurate stimulation.","FEM; Activating Function; Parameterised model; COMSOL; Intracortical; Neuronal activiy; spatial extent of stimulation","en","master thesis","","","","","","","","","","","","Biomedical Engineering","",""
"uuid:eab57f33-09be-4185-b612-7eb3b5a35235","http://resolver.tudelft.nl/uuid:eab57f33-09be-4185-b612-7eb3b5a35235","Fatigue design investigation of the main- to cross-girder connection in steel railway bridges: A study on the beam railway bridges of the Oostertoegang in Amsterdam","Romijn, Kasja (TU Delft Civil Engineering & Geosciences)","Veljkovic, M. (mentor); Malschaert, D.H. (graduation committee); den Besten, J.H. (graduation committee); Langedijk, W.P.J. (graduation committee); Delft University of Technology (degree granting institution)","2023","Over the past few decades, the Netherlands has built numerous steel railway bridges to improve its infrastructure. The repeated loading from railway traffic makes steel bridges susceptible to fatigue damage. The stress ranges at fatigue-prone locations are generally higher in railway bridges than in road traffic bridges. Due to the limited space available due to road and rail alignment, the connection between the main girder and cross-girder is often identified as a critical fatigue location.
The main- to cross-girder connection can be designed for fatigue using different design principles. Designing the connection with a certain rotational stiffness leads to higher fatigue stresses at this location. Meeting the fatigue requirements at the connection can often be achieved by local adjustments, such as welding extra steel plates to the fatigue-induced location to evenly distribute stresses from the cross-girder to the main girder. This can be a costly solution. Designing a connection that is flexible could reduce stresses at the main- to cross-girder connection. Solving fatigue issues can be done by making global adaptations to the structure. The question arises: which aspects can be adjusted such that slight changes can notably improve fatigue resistance in a cost-effective manner?
A literature study and a finite element investigation of the main- to cross-girder connection are performed. A reference model is made after which parameters are altered to investigate their impact on the fatigue response of the connection. The reference model is based on the design of the bridges from project Oostertoegang. However, instead of considering a connection with a certain rotational stiffness, the design is made more flexible for this study. Ansys 2022 R2 is used to create a finite element model of the bridge with shell elements. The hot spot stress method is used to conduct the fatigue assessment. In total four critical fatigue locations are researched for six parameters. The parameters researched are: the center-to-center distance between the cross-girders, the height of the cross-girder and main girder, the thickness of the inner web plate of the main girder, the diaphragm, and the steel deck plate.
From the analysis, it can be concluded that for one detail (M3) local measures should be applied to meet fatigue criteria. The three other details can satisfy requirements within feasible limits. The most cost-effective and realistic way is to increase the thickness of the inner web of the main girder. Other cost-effective but less feasible solutions to optimize the flexible design for fatigue are: decreasing the thickness of the diaphragm and increasing the height of the cross-girder. These parameters show the best ratio between the costs needed to alter the parameter and the total fatigue damage change of the critical detail.
Furthermore, it is determined that the fatigue assessment using finite element analysis with shell elements can be optimized by using the hot spot stress method in combination with modeling the weld using an increased thickness.
There is a lack of knowledge on dynamic effects of bending moments on steel cylindrical shells (monopiles). While the dynamic axial buckling capacity of cylindrical shells has been researched extensively, there is little known on the dynamic bending buckling capacity of such shells. This thesis investigates the influence of loading rate on the dynamic buckling capacity of monopiles subjected to bending moments. For this, a finite element model is constructed which is validated by analytical models. Later on, the finite element model is used to conduct a parametric study to investigate the effect of loading rate on buckling capacity.
The scope of this study excludes factors such as soil dynamics, fluid structure interactions, residual stresses, and lateral forces. The focus is solely on the cylindrical shell of monopiles, excluding secondary steel from consideration. Initial geometric imperfections are considered as local perturbations necessary to initiate buckling, while other factors that may affect lateral forces or overall structural capacity are excluded.
This study will show that different parameters play part in the dynamic bending buckling behavior of cylindrical shells. The natural frequency of the cylinder, as well as the non-dimensional length together with the yield stress of the material play an important role in the dynamic buckling capacity. This research concludes that cylindrical shells with higher natural periods are more influenced by dynamic bending moments than cylinders with shorter periods. Next, shorter, stocky cylinders exhibit higher dynamic buckling capacities than slender cylinders. Also, imperfections are found to decrease the buckling capacity of cylindrical shells, but this effect diminishes for increasing loading rates.
Keywords: Offshore wind energy; Cylindrical shells; Dynamic buckling; Loading rate; Imperfections; FEM;","Offshore wind; Cylindrical shell; Dynamic buckling; Loading rate; Imperfections; FEM","en","master thesis","","","","","","","","","","","","Mechanical Engineering","",""
"uuid:8e0f9eda-6a94-4c33-94e6-65de25a4b8c9","http://resolver.tudelft.nl/uuid:8e0f9eda-6a94-4c33-94e6-65de25a4b8c9","Settlement Predictions of The Noordtunnel: A Numerical Simulation","Prabendra Ardhan Atmakusuma, Prabendra Ardhan (TU Delft Civil Engineering & Geosciences)","Broere, W. (mentor); Dekker, Harry (graduation committee); Voorendt, M.Z. (graduation committee); Zhang, X. (graduation committee); Delft University of Technology (degree granting institution)","2023","The Noordtunnel is an immersed tunnel open to roadway service since 1990 in The Netherlands. Over the past thirty years of its operation time, a significant differential settlement behaviour has been observed, and this ongoing settlement potentially imposes safety concerns to the tunnel, such as joint leakage. However, the underlying factor triggering this differential settlement behavior remains unknown. To ensure the tunnel's serviceability, this thesis aims to investigate the underlying causes of the occurring excessive settlement, predict future settlements, and assess its impact on tunnel structural safety within its designed lifetime.
The analysis starts by reconstructing the settlement time history of the Noordtunnel. The process involves determining the most reliable reference point and performing back analysis to estimate the settlement magnitude during the unmeasured period. Further, the settlement history is reconstructed by combining all the settlement data of all the periods. It is found that the settlement history at all immersion joints show a logarithmic trendline, with a maximum estimated settlement of about 94.36 mm occurring at immersion joint 2. Subsequently, the soil profile and geotechnical parameters were determined for the simulation. The provided Cone Penetration Test (CPT)s data and borehole ensure the soil profile depicted in the given situation map. Additionally, in the absence of laboratory data, the Hardening Soil Model (HS Model) and Soft Soil Creep Model (SSC) parameters are estimated based on CPT - NEN Table 2b correlations.
Afterward, the Two Dimensions (2D) Finite Element Method (FEM) simulations were carried out in PLAXIS (a commercial simulation software), while considering the variations of load acting on top of the subsoil. Two types of soil constitutive law were chosen to simulate the settlement in the Noordtunnel: HS Model and SSC Model. The optimum model, which can simulate the settlement behaviour in the field, was selected by aligning the simulation outcomes to the reconstructed historical settlement. The simulation results show that only settlement at immersion joint 2 has the same tendency as the SSC Model, while the other immersion joints tend to have a similar tendency to the HS Model. The simulation outcomes also indicate that excessive settlement at immersion joint 2 occurs due to the soft soil underneath the tunnel and the natural sedimentation on top of it. The soft soil is responsible for at least 20 mm of settlement, while the sedimentation contributes to a minimum of 8 mm of settlement during 30 years of tunnel operation. Subsequently, the sensitivity analysis is conducted to examine how much the simulation outcomes may deviate when accounting for soil variability in the field. Due to the narrow distribution of the reference values, adjusting the most sensitive parameter will only deviate the results by a maximum of 5.48% at immersion joint 2 and 4% at the other immersion joints. These results indicate that the model is robust enough and expected to generate reasonable future settlement predictions. An additional settlement of 15.13 mm of settlement is predicted to occur at immersion joint 2, while 4 to 5 mm of additional settlement is anticipated at the other immersion joints over the tunnel's remaining lifespan.
The differential settlement at the tunnel longitudinal direction has triggered element tilting and further induced compression and decompression to the GINA gasket at immersion joints. It has been observed that while uneven settlement contributes to joint decompression, the external forces acting on the GINA gasket remain considerably lower in magnitude compared to the overall friction force. Therefore, the impact of uneven settlement on the water tightness is generally minimal. Additionally, considering the limitations of the current monitoring procedure, an optimized monitoring plan based on the Distributed Optical Fiber Sensor (DOFS) system is proposed. Finally, future recommendations to improve the current thesis are also put forward.","Immersed Tunnel; Settlement; FEM; Predictions; Immersion joints; Leakage","en","master thesis","","","","","","","","","","","","Geo-Engineering","","51.85759576993236, 4.654055303002794"
"uuid:c61d6c66-5552-47a5-a432-eb9fe2e42cab","http://resolver.tudelft.nl/uuid:c61d6c66-5552-47a5-a432-eb9fe2e42cab","Influence of geometric imperfections and increasing turbine sizes on validity load transfer functions in bolted ring-flange connections","Korthals Altes, Ruth (TU Delft Civil Engineering & Geosciences)","Veljkovic, M. (mentor); El Bamby, H. (mentor); Sluys, Lambertus J. (mentor); Wesarg, B. (mentor); Delft University of Technology (degree granting institution)","2023","The global focus on climate change and the transition away from fossil fuels has highlighted the importance of renewable energy sources. Offshore wind turbines are being optimized and are therefore growing in size and power.
This research focuses on bolted ring-flange connections, a connection type that plays a crucial role in the design of offshore wind turbines, as they transfer the external force between parts of a turbine. The objective of this thesis is to analyze how the increasing dimensions from current to future offshore wind turbines and geometric imperfections impact the reliability of analytical approaches for load transfer functions (LTFs) for these connections. Two components of this objective are considered: examining the influence of different dimensions of ring-flange connections and analyzing the impact of various gaps between flanges on LTFs for 'current generation' and 'next generation' turbines. Analytical calculations are compared to results obtained with finite element analyses, which are assumed to represent an actual connection.
Based on the research findings, the following conclusions are made. Firstly, the widely used tri-linear approach by Schmidt/Neuper [18] for obtaining the LTF in bolted ring-flange connections is found to be unreliable for current and future turbine sizes. This method highly underestimates the forces in the bolts when initial gaps are present between the flanges. Calculations performed with this approach could lead to an overestimation of the turbine's lifetime compared to reality by multiple years, possibly causing more maintenance or early failure. Alternative approaches, such as a very new and not yet approved polynomial approach, show reliable results, providing accurate estimations of bolt forces for large connection diameters. Additionally, currently verified tolerances for gaps between flanges (1 mm over 30° and 2 mm over entire circumference) are outdated, and larger gap heights or smaller gap lengths are expected in practice, especially for future turbines. These gaps lead to a larger bolt force in practice, decreasing the fatigue resistance and lifetime of the structure. Even though very small gaps are expected to occur often, lower bolt forces are obtained compared to larger gaps, both with an expected height to length ratio of 𝑢𝑔𝑎𝑝/𝑙𝑔𝑎𝑝= 0.53 ∗ 10^−3. In analytical design calculations, it therefore is recommended to consider larger sized gaps with a gap length of approximately 1600 mm with its expected gap height.","Master Thesis; Offshore; Offshore energy; offshore wind; Offshore Wind; Windenergy; Structural Engineering; Civil Engineering; Sustainability; Steel design; bolted joints; FEM; FEA Simulation","en","master thesis","","","","","","","","","","","","Civil Engineering | Structural Engineering","",""
"uuid:76c71b4c-9f09-4250-9415-069226efff5e","http://resolver.tudelft.nl/uuid:76c71b4c-9f09-4250-9415-069226efff5e","Thermal shrinkage cracking in steel fibre reinforced underwater concrete floors: A probabilistic finite element approach","Slockers, Dennis (TU Delft Civil Engineering & Geosciences; TU Delft Concrete Structures)","Hendriks, M.A.N. (mentor); Nunes, Sandra (graduation committee); Morales Napoles, O. (graduation committee); van der Meer, L.J. (graduation committee); de Boer, Ane (graduation committee); Delft University of Technology (degree granting institution)","2023","This thesis explores a suitable method and appropriate input to determine the failure probability of thermal shrinkage cracking in a steel fibre-reinforced underwater concrete floor by examining the factors that influence this failure probability.
An underwater concrete (UWC) floor is a common construction type in the Netherlands that is often applied to create building pits under the groundwater table. Usually, these (generally unreinforced) UWC floors only function as a watertight bottom layer of the building pit with only a temporary sealing function. Water tightness and crack prevention are very important aspects of this type of construction. A permanent reinforced structural top floor is frequently used on top of the temporary UWC floor to make a completely watertight construction, which is not the most sustainable and cost-efficient solution. Advances in concrete technology such as fibre-reinforced concrete have made it possible to integrate both the UWC and structural top floor or even use the UWC floor as the permanent structural floor. In these cases, the UWC floor should already function as a watertight barrier and controlling leakage by limiting the crack width becomes even more important. The addition of fibres to concrete may prevent through crack formation in the UWC slab and the possible consequent leakage. An important cause of cracking in UWC floors is thermal shrinkage during the cooling phase of the hardening reaction shortly after casting the UWC floor.
Currently, there are no guidelines for the construction of fibre-reinforced concrete (FRC) floors and the prevention or limitation of thermal shrinkage cracking. A CROW-committee ""Steel fibre reinforced underwater concrete (SFRUWC) floor as permanent structural floor"" has been formed. This committee aims to set up a design recommendation and part of that is addressing the thermal shrinkage cracking problem. There is a lot of uncertainty in geometry, material properties and boundary conditions associated with SFRUWC floor design and construction. Because of this, there is a need for a probabilistic approach to investigate the influence of these uncertainties and tolerances on crack formation in SFRUWC floors during the hardening phase. This research aims to determine a suitable probabilistic method to investigate the failure probability of SFRUWC floors and the parameters that influence this.
In order to achieve this, a finite element model was developed that determines the shrinkage cracking behaviour in a part of a UWC floor in a building pit. Before this model could be developed, all the necessary input parameters and design equations were collected from literature and existing guidelines. To set up a model, first the behaviour of UWC floors was studied, followed by the development of a finite element model that includes the hardening behaviour and strength development of young concrete. An important aspect of this finite element model is the use of random fields to introduce spatial variation in the strength properties of the SFRUWC floor, which is a first step to include stochastic variation in the model for the probabilistic analysis. A probabilistic sensitivity study was performed with the finite element model by calculating multiple samples for each set of input parameters. Separate input parameters were varied and the influence on the results was investigated. The parameters that were considered, include the random field properties, material properties and thermal properties. Finally, a full Monte Carlo analysis was performed to give a proof of concept on how to calculate the failure probability regarding thermal shrinkage cracking in SFRUWC floors.
In order to prevent leaking cracks and satisfy the crack width criterion, the tension-hardening behaviour of FRC has to be utilised. Tension hardening behaviour will lead to a distributed cracking pattern, consisting of multiple small cracks which can satisfy the crack width criterion as opposed to a single large separation crack which does not satisfy the maximum allowable crack width criterion. It was found that the tensile behaviour of FRC and the use of random fields to model this tensile behaviour were major parameters that influenced the crack width and the occurrence of a distributed crack pattern. An important parameter is the standard deviation of the random field, which influences the difference between the maximum and minimum tensile strength in different locations in the slab. Looking at material behaviour, the main conclusion was that the introduction of a small hardening branch in the tensile material model was the governing influence factor. Both the standard deviation of the random field and the introduction of a hardening branch in the tensile behaviour affect the ratio between the tensile strength of the ordinary concrete and the residual tensile strength of the fibre-reinforced concrete. These two factors in combination with the model that was used, turned out to be dominating the results in such a way that the other input parameters only had a relatively small influence on the crack widths.
To determine maximum crack widths in SFRUWC floor it is essential to consider multiple samples with different random fields to find out if only a distributed crack pattern is possible or whether also single localised cracks can occur. The possibility of both these results being able to occur, leads to a large possible error in the maximum crack width. The results of this thesis have shown that the random field parameters remain uncertain and experimental research is needed to determine these correctly. Until then, it is important to investigate how significantly these parameters influence the results. It is recommended to extend this research by improving the model by making it more realistic and finding out if these two factors are still the dominating input parameters.
How can the determination of the location of the first fatigue crack in the deck, at a stiffener to deck plate weld toe, be parameterized?
To answer the research question, the (in the Netherlands active) regulations are studied. Based on the regulations the process of determining fatigue damage of a point in the bridge can be understood. As well as the reason why, this process is too computational demanding and complex to be able to be applied to all points in all welds.
In response to this an alternative method is proposed. This method reduces the complexity and the computational budget that is needed, by using 1D elements instead of the currently prescribed 2D elements. To determine if this method can be used it was decided to apply it on a case study. The bridge which served as the case study was the Goereese bridge. The alternative method was applied to determine the expected distribution of fatigue damages in all welds in the case study. Based on this obtained distribution a limited number of interesting locations in the deck could be identified. At these points to regulatory required method was used to obtain results which can be compared with the alternative method.
It is concluded that the predicted location of the first fatigue crack of both methods is directly next to each other. However, the distribution of the remaining points suggest by the alternative method does not agree with the obtained results of the regulatory method. Remarkable enough, both these methods predict a location which is counter intuitive to the structural engineers participating in the research.
Therefore, the following general recommendations are given:- Research if the regulatory method, to determine the location of the first fatigue crack, can be simplified. - Research the cause(s) of the differences between the regulatory method and the alternative method. - Increase the awareness of structural engineers regarding their intuition on the location of the first fatigue crack.","Orthotropic Steel Deck; Fatigue crack location; FEM","en","master thesis","","","","","","","","","","","","Civil Engineering","",""
"uuid:7a610fee-7d3b-44a9-82b5-64779daba2f7","http://resolver.tudelft.nl/uuid:7a610fee-7d3b-44a9-82b5-64779daba2f7","Two raft wave energy converters: A combined optimisation of annual energy conversion and stability","Kluwer, Thomas (TU Delft Civil Engineering & Geosciences)","Colomes, Oriol (mentor); Antonini, A. (graduation committee); Delft University of Technology (degree granting institution)","2023","Global warming has caused an increasing demand for renewable energy. Currently, 50% of the renewable energy is provided by wind and solar combined. However, these renewable energy sources are highly volatile. Wave energy converters can provide a stable renewable energy source. Previous research has contributed to understanding various combined effects of length, aspect ratio, hydro-elasticity and PTO damping on the optimisation of peak power absorption for regular waves. However, research on optimising the combined effects on annual energy production and especially power stability is missing. This thesis aims to better understand these effects by answering the following research question: ""How can the combined effects of total length, aspect ratio, raft stiffness and PTO damping influence yearly energy conversion and energy stability of a pitching raftWEC""
To do this, a novel formulation for a monolithic finite element model containing Timoshenko beam theory and Linear potential flow is developed. This FEM consists of a two-dimensional domain, where the water is excited by linear irregular waves. The wave energy converter is modelled as two floating Timoshenko beams connected by a damped joint. The model is verified by proving that the solution converges according to the polynomial order +1 for decreasingmesh size. Additionally, it is proven that energy is conserved which shows that there is no wave reflection resulting from the domain boundaries. Finally, the model is validated by comparing the results of the structure with and without joint to previous research.
Two experiments are developed to understand the combined effects. Initially, an eigenmode analysis of the undamped structure is performed. This gives insight into the influence of individual parameters on the eigenfrequencies and shapes. Moreover, the real eigenmodes are used to decompose the real part of the complex resonance shapes of the relative rotation response amplitude operator (RAO). This provides a coupling between the performance according to the relative rotation RAO and the eigenmodes and frequencies. A limitation of this method is that phase differences cannot be considered.
The second experiment maximises the annual energy conversion and energy stability of thewave energy converter with three sets of variable parameters: (total length, aspect ratio, damping parameter), (total length, symmetrical raft stiffness, damping parameter) and (stiffness fore-aft, stiffness aft-raft, damping parameter). This is done in three steps. First, the RAO for the relative rotation at the joint is constructed. This is converted to a power spectrum. Secondly, the power spectrum is scaled by the JONSWAP energy density spectra. These
spectra are constructed using the annual wave conditions, significant wave heights and peak periods from a wave scatter diagram. Subsequently, the results per spectrum are scaled by the number of occurrences of the wave conditions to obtain the annual energy conversion. Third, The optimum damping parameter per configuration is determined by calculating the annual energy conversion for a set of damping parameters. These results are interpolated to select the damping parameter that maximises annual energy conversion.
Finally, the performance of each configuration with their respective optimum damping parameter is assessed on annual energy conversion and capture width per peak wave period to give insight into the energy conversion and stability. The optimisation results are clarified with the results of the eigenmode analysis.
It was found that the optimal total length, considering raft stiffness, aspect ratio and PTO damping can be determined by matching the dimensionless wavelength corresponding to the third mode, and the annual significant wavelength.
Furthermore, It is proven that an aspect ratio of 0.2 to 0.3 increases the performance in high-frequency waves without compromising on low-frequency waves. The capture width is more evenly distributed over peak wave periods, indicating a higher energy stability. This results in an increase of annual energy conversion of 31% with respect to an aspect ratio of 0.5. Besides the aspect ratio, it was found that an asymmetrical raft stiffness, with a moderately flexible fore raft and a rigid aft-raft increase energy stability without compromising annual energy conversion.","Wave energy converters; WEC; Optimisation energy; Hydro elasticity; hydro-elasticity; Eigenvalue analysis; eigenvalue-eigenvector decomposition; Annual energy conversion; Energy stability; FEM; Finite element model; Gridap; energy conversion; Irregular waves; Annual optimisation; Frequency domain","en","master thesis","","","","","","","","","","","","Civil Engineering | Hydraulic Engineering","",""
"uuid:1591759f-539e-44a1-887d-5ea8d6fb8f0b","http://resolver.tudelft.nl/uuid:1591759f-539e-44a1-887d-5ea8d6fb8f0b","Soil-Structure Interaction Modelling of High-Rise Building Settlements due to Compressible Soil Layers below Foundation Level","Hartman, Illona (TU Delft Civil Engineering & Geosciences)","Gavin, Kenneth (mentor); Korff, M. (graduation committee); Crielaard, R. (graduation committee); de Jong, F. K. (graduation committee); Teeuwen, A. S. (graduation committee); Delft University of Technology (degree granting institution)","2023","In the field of structural and geotechnical engineering, a uniform approach to predict and model foundation settlements during the design phase of a high-rise building appears to be missing. In the Netherlands, pile foundations of tower structures underlain by compressible soil layers are challenging to model due to different stiffness and load distribution effects. As a result, the Dutch building code currently used for foundation design, the NEN9997-1, does not include realistic soil-structure interaction (SSI) effects. Instead, the NEN defines a simplified approach for high-rise buildings as the sum of two types of foundation settlements: individual pile head settlements (s1) and pile group settlements (s2) due to compressible layers below pile tip level.
Numerical models were used in this thesis to predict the individual contribution of different soil layers to measured subsidence of tower structures. By running several simulations using Tomlinson’s load spread method and the new embedded beam formulation (EB-I) in Plaxis 3D, it was found that approximately 65% of the total (s2) settlements are caused by the compression of clay layers below foundation level. Moreover, the effects of different pile factors (αs, αp) on the load distribution (more pile shaft resistance versus base resistance) from superstructure to subsurface were investigated. This research concluded that updated pile factors - in accordance with recent pile load tests on the Maasvlakte (Gavin, 2020) - influenced the predicted and modelled pile head settlements (s1) slightly for a Fundex 560 pile. Nonetheless, the change in load distribution due to different pile factors did not affect the vertical effective stresses or resulting (s2) settlements at depth.
Further, to accomplish a more uniform modelling approach for high-rise building settlements, this thesis provides insights for an automated soil-structure interaction mattress methodology as illustrated in Figure 1. A model verification is proposed for the mattress model approach using finite element software commonly used by geotechnical (Plaxis 3D) and structural engineers (SCIA Engineer) in daily practice. In essence, it is based on a simplified (s2) settlement analysis from Plaxis 3D (step 1) and mattress fit model in SCIA Engineer (step 2) consisting of multiple springs with linear stiffness (k_bedding) connected by a plate (E_plate) and a simplified surface load on top. The surface load represents the quasi-permanent building loads. An apparent limitation of the Plaxis 3D model (step 1) was the missing building stiffness or load redistribution within the superstructure due to differential settlements over time. However, a modelling discrepancy of only 1% was found for both the peak and differential settlements between SCIA Engineer (step 3) and Plaxis 3D (step 4) for a theoretical, symmetric high-rise building of 69 m in the North of Amsterdam. Thus, a model verification was accomplished by comparing the settlements from Plaxis 3D with the building on top of EB-I embedded beams (step 4) to the deformations of the fitted mattress model (k_bedding + E_plate) representing the compressible soils underneath the structure in SCIA Engineer (step 3). Altogether, this thesis provides a solid foundation towards a more universal design methodology between multiple stakeholders while including SSI effects for settlement predictions of high-rise buildings in daily practice.
As a result of this project, practitioners can use the upside of stochastic analysis using RFEM to derive new insights about the behavior of their system, such as potential soil-related asymmetries, all while obtaining a better picture of the risks associated with a certain design. As with any technological advancement, responsible use of the framework is required to ensure the upside is attained and computational concerns do not hinder the use of the model, feature which still requires further research and improvement.","Heterogeneity; RFEM; PLAXIS; User-Defined Soil Model (UDSM; scale of fluctuation; probability of failure; FEM; spatial variability","en","master thesis","","","","","","","","","","","","Geo-Engineering","",""
"uuid:17a22b0d-8e66-4caf-be7a-292822ed63ef","http://resolver.tudelft.nl/uuid:17a22b0d-8e66-4caf-be7a-292822ed63ef","Modelling the finite strain response of PEEK with strain-dependent viscosity within the EGP model","Aarsen, Mark (TU Delft Civil Engineering and Geosciences; TU Delft Materials- Mechanics- Management & Design)","van der Meer, F.P. (mentor); Kasbergen, C. (graduation committee); Kovacevic, D. (graduation committee); Delft University of Technology (degree granting institution)","2022","The University of Twente performed experimental uniaxial compression tests of Poly(ether-ether-ketone) (PEEK) and the TU Delft made a comparison with a numerical model; the viscoplastic Eindhoven Glassy Polymer (EGP) model. A higher strain-rate dependency and a higher yield stress at lower temperatures are observed in the experimental results. It is of importance to correctly model the stress-strain behaviour of PEEK for future research in long term behaviour of fibre reinforced PEEK by adapting the EGP model to account for these differences. The viscosity of the EGP model is based on the Ree-Eyring equation in which the three Ree-Eyring parameters (activation volume, activation energy and initial viscosities) are constants within the EGP model. It is observed that all three Ree-Eyring parameters are not constant over the strain when the original Ree-Eyring equation is fitted to the experimental data. Thus, non-constant Ree-Eyring parameters should be included in the EGP model. Evolving all three Ree-Eyring parameters leads to accurate stress-strain results, except for the pre-yield regime. The EGP model does not behave as stiff as the experiment in this region. Thus, a higher stiffness is included by evolving the shear moduli over the pre-yield regime. The evolution of the Ree-Eyring parameters is expressed by a $\tanh()$ function and quadratic function, while the evolution of the shear moduli is only expressed by a $\tanh()$ function. The evolution based on the $\tanh()$ function mostly influences the behaviour at small strains and the evolution based on the quadratic function mostly influences the behaviour at large strains. The evolution of the Ree-Eyring parameters at large strains leads to the insertion of viscous strain hardening in the EGP model. The viscous strain hardening qualitatively describes the Bauschinger effect for a cyclic loading case. The Bauschinger effect can be explained as the change of material behaviour when stresses are present. What occurs when the loading direction reverses within a cyclic loading case. An invariant function that is proportional to the strain determines the strain dependency of the evolution of the Ree-Eyring parameters and shear moduli. This invariant function is prevented from reducing for the evolution based on the $\tanh()$ function when the loading direction is reversed but does reduce for the evolution based on the quadratic function to correctly model cyclic loading. Furthermore, the linearization of the stiffness tensor is updated for the changes to the EGP model and a part of the stiffness tensor which was omitted in the original implementation is added.
Including the evolution of the Ree-Eyring parameters and shear moduli with the mentioned characteristics in the EGP model makes the EGP model correspond very well with the experimental results for all investigated temperatures and strain-rates.","FEM; EGP model; PEEK; constitutive model","en","master thesis","","","","","","","","","","","","Civil Engineering","",""
"uuid:50809368-b160-492e-ae33-0b0de2bedbac","http://resolver.tudelft.nl/uuid:50809368-b160-492e-ae33-0b0de2bedbac","Implementations of a Compact Drilling System (CDS) for bone","Schots, Joost (TU Delft Mechanical, Maritime and Materials Engineering)","van Ostayen, R.A.J. (mentor); Spronck, J.W. (graduation committee); Goosen, J.F.L. (graduation committee); Delft University of Technology (degree granting institution)","2022","Bone drilling is a surgical action required for bone fixation using plates. The holes are currently drilled using a large, conventional drill. This causes problems when limited space is available, de to the size of the drill. For that reason a new, small Compact Drilling System is proposed. In earlier research a compact self-feeding mechanism was introduced, various implementations of that mechanism are presented here. A module, to be used in combination with a conventional drill, is used as a bridging step towards a fully redesigned device. An example locking mechanism is designed, used to lock the module in place during the drilling. FEM techniques are used to validate the design, and adapt it where necessary.
The PBX is predicted to react if it has satisfied a certain reaction criterion based on the hot spot theory of ignition. This theory poses that known chemical properties of the material, the plastic shear strain rate and the hydrostatic pressure can predict the occurrence of a reaction. A finite element model was used to find the plastic strain rate and hydrostatic pressure in the energetic material subjected to a case-crushing loading. Next, the reaction criterion is computed in a separate script. The energetic material was modelled as a homogeneous continuum with a Drucker-Prager yield criterion. This material model did not include any post-yielding behaviour, like strain hardening.
First, a finite element model was constructed that was used as the baseline model throughout the thesis. The combined FEM and post-processing model was shown to be more sensitive than the model in the reference paper. The combined model also predicted a reaction at a lower velocity, which, according to tests in the reference paper, should have not produced a reaction.
The baseline model, and consequent models in the parameter study, also showed excessive deformation. This can be attributed to the use of a simpler Drucker-Prager material model for the PBX as opposed to a more complex material model. The absence of any hardening behaviour, and the resulting deformation, also contributed to the instability of the finite element model.
A parameter study was conducted by adapting the baseline model. Varying the velocity of the projectile was the most impactful change.
In conclusion: the developed model gives a first indication of parameters that contribute to the sensitivity of certain munition articles to case crushing. However, the material model used should be improved to create a more stable finite element model. An improved material model could also better capture the mechanical behaviour of the complex energetic material. It is recommended that future research should focus on this improvement.
The first novelty introduced by this Master Thesis is the use of the Olivine flow viscosity model, with a wet rheology, to study GIA in Greenland. The second main novelty in this Master Thesis, is the use of a unified ice history from 122000 years from present till 2019 in one GIA model; while using a resolution of 10 [𝑘𝑚], which is an improvement, compared to for instance Milne et al. (2018), Simpson et al. (2011) or Lecavalier et al. (2014) which use resolutions ranging from 15 to 75 [𝑘𝑚], which is found to still not be sufficient enough to properly model modern elastic and viscous deformation.
The following conclusions were made through analysing the final results. First, the simulations which use 3D viscosity models are more sensitive regionally and react, to ice load changes with larger amplitudes of solid Earth deflections in shorter time spans. Second, 3D varying viscosity models, with the same ice loads as the 1D varying viscosity models, have a pattern of deflection which is more explicitly linked to the changes in viscosity across Greenland, whereas the 1D viscosity profiles deflection rates are clearly positive in the present day on land and negative in the sea, and hence are more explicitly linked to the coastal limits of Greenland. Last, the inability of the model to properly model elastic uplifts in recent times, is made evident by the constant under estimation of total uplift rates.
The natural frequency is a parameter which is largely influenced by the mass and the stiffness of the structure. One would think that after the completion of structure, that the magnitudes of parameters can be determined with a high level of certainty, and that the natural frequency can be calculated accurately, but this is not the case. When comparing the measured natural frequencies of several high-rise structures in the Netherlands, to their natural frequencies determined in the design phases, an underestimation of between 20\% to 50\% was seen. Although the likelihood that these underestimations will lead to structural failure are small, it does lead to larger design forces and higher peak accelerations, which are used in determining occupant comfort in the structures. The aim of this research is to find the reasons for the discrepancies between the measured and the calculated natural frequencies.
A literature study was performed to determine what the most common methods of determining the natural frequency are during the design phase. There are three main methods which are used throughout different stages of the design phase to approximate the natural frequencies. At the start of the design phase, when structural parameters have not yet been determined, the natural frequency is approximated using empirical formulae. These formulae mostly only depend on 1 or 2 spatial parameters.
As the design progresses and the structural parameters are specified, dynamic beam theory can be used to determine the natural frequency. These calculations take the stiffness of the super- and substructure, and the mass of the structure, into account. As the design nears completion, the structure is modelled in a FE software package. The natural frequency can then be calculated by the software to give a final impression of the natural frequency.
The main parameters influencing the natural frequency of a system are the stiffness and the mass. This is no different for high-rise structures, but how do these parameters affect the natural frequency, and which of these parameters has the greatest effect on the natural frequency? A sensitivity study, looking at 5 existing high-rise structures in the Netherlands, was performed. Each structure was represented by 5 different beam models. One structural parameter was added to each subsequent beam model as to be able to quantify the influence of the added parameter. Lower and upper bounds were determined for each structural parameter. By varying these parameters and calculating the natural frequencies, the effect this variation has on the natural frequency can be determined. It was found that there are 3 parameters which have significant influence on the natural frequencies, namely, the superstructure stiffness, the superstructure density and the rotational stiffness of the foundation.
For all cases with a flexible foundation, the measured natural frequencies could not be reached, even after determining the natural frequencies using the extreme parameter combination, the natural frequencies were still underestimated. The analyses were done for both uniform beam models and multibeam models. The general trend was that the multibeam model produced higher frequencies. This is due to more of the overall stiffness and mass of the structure being situated in the bottom sections of the structure. Using a multibeam can lead to an increase in natural frequency of up to 15\%. Although the natural frequencies were increased, they were still nowhere near the measured natural frequencies.
The underestimation of the natural frequencies using the beams models, led to the question if there are other factors which are not yet taken into account when determining the natural frequencies. In the calculation of the stiffness of the new Erasmus Medical Centre (NEMC), it was assumed that the beams, columns, non-structural elements and the low-rise structure have a negligible influence on the stiffness of the structure. The underestimation in the natural frequencies, led to the conclusion that the stiffness of the structure is underestimated. A complete model of the NEMC was modelled using the SCIA Engineer software. All the structural systems were added to the model. Modal analyses, including different combinations of structural systems and parameter magnitudes, were performed. It was found that for the NEMC the assumption that the beams and columns have a negligible contribution to the natural frequency, was correct. The main contributors to the stiffness of the superstructure were the outer tube and the central cores. The partition walls were added to the model using low stiffness wall elements, by added the walls, the natural frequency was increased by 8.5\%. Assumptions were made to include the influence of the low-rise structure. The determined natural frequency was increased past the measured natural frequency, however, this result might not be realistic.
The final conclusion of the thesis is that the stiffness of the superstructure is underestimated. This leads to the conclusion that there are certain elements which provide the structure with extra stiffness, which is not yet taken into account. At the end of the thesis several recommendations are made as to determine where this extra stiffness comes from.","High-rise structures; Tall buildings; Free vibration; Natural frequency; FEM; Dynamic beam theory; wind; underestimation; parameter uncertainty","en","master thesis","","","","","","","","","","","","Civil Engineering | Structural Engineering | Structural Mechanics","",""
"uuid:fcba6da4-5d83-415d-a5b9-28fc054e7b15","http://resolver.tudelft.nl/uuid:fcba6da4-5d83-415d-a5b9-28fc054e7b15","Wave damping by large-scale offshore kelp farms - A numerical modelling framework using a porous medium approach","Ruesen, Joël (TU Delft Mechanical, Maritime and Materials Engineering)","Colomes, Oriol (mentor); Metrikine, A. (graduation committee); van Driel, Robert (graduation committee); Hoogeveen, Maas (graduation committee); Delft University of Technology (degree granting institution)","2022","Large-scale cultivation of seaweed presents opportunities for multiple global challenges currently at play. Cultivated seaweed can provide a sustainable source of protein for humans and cattle without competing for land, freshwater supply or the use of fertilisers. Kelp forests are known to be a solid basis for an elaborate biome that supports biodiversity in areas that have been damaged by over-fishing or rising sea temperatures. Additionally, kelp forests can lock-in large amounts of Blue Carbon, expanding the oceans’ buffering capacity to mitigate anthropogenic emissions. Furthermore, with their densely seeded lines, offshore kelp farms are found to attenuate wave amplitude, thus providing coastal protection and benefits like increased workability for offshore operations. Both academic publications and industry reviews underline the potential of this sector and significant growth in cultivation is expected in the near future.
Methods currently used for quantification of the damping effects of large-scale offshore kelp farms are diverse and entail varying degrees of accuracy and computational cost. Experimental observations that support the outcomes of these methods are limited to scaled experiments in wave flumes, with various methods used to mimic vegetation. No convergence is found in the most suitable methods for application to large-scale offshore kelp farms.
This research presents a novel modelling framework based upon the Finite Element method, implemented using Julia Programming Language. The effects of the vegetation on the wave climate are represented with a Darcy-Forchheimer term borrowed from porous medium flow theory, including a linear and a quadratic resistance term. The framework comprises a numerical wave tank, using the incompressible Navier Stokes equations. The single-phase model captures the free surface using the coupling of dynamic pressure with a virtual elevation variable through a linearized transpiration boundary condition. Wave energy dissipation is shown to increase significantly by moving the farm structure close to the water surface. Similarly, a decrease in relative water depth - compared to the vegetated height - increases damping potential. Wave period is found to be of strong influence on dissipation, where short waves are attenuated more. Scaling vegetation length with wave length, however, diminishes the reduction in damping of longer waves. Conversely, wave amplitude is shown to be of less influence on the transmission of amplitude through a vegetated patch.
The framework presents a method that is easily scalable, flexible in application on a wide range of flows and vegetation characteristics, and at reasonable computational cost. Introduction of both the linear and quadratic terms extends applicability compared to traditional methods. The approach is verified using convergence studies, application of the model is validated by comparison to existing experimental data. It is shown that experimental set-ups can be reproduced effectively, and simulation results coincide with experimental findings. Validation of outcomes on scales larger than common wave tanks was found unfeasible due to a lack of measurement data. A theoretical case study was performed to predict wave damping of a full-scale kelp farm, demonstrating promising potential with up to 40% wave energy reduction at the local peak wave period.
Further research into the establishment of the Darcy- and Forchheimer-coefficients is recommended. A preliminary range of values has been found, based upon calibration on existing experiments that represent realistic ranges of vegetation characteristics. Furthermore, the main conditions of the flow and vegetation that dictate damping potential are identified. On this basis, research into a physics-based determination of the coefficients is recommended. Additionally, full-scale measurements are advised to validate application on future kelp farm designs.
Through this novel approach, the range of application is increased compared to existing methods, while straightforward setup and usage are governed, and limited computational costs allow for simulation without the need for a dedicated computer setup. The framework is shown to be robust by generating consistent simulation results. In summary, the established framework shows to be a good alternative to existing approaches to investigate the wave damping potential of large-scale offshore kelp farms.","Numerical model; FEM; Julia Language; Porous medium; Kelp farming; Seaweed; Wave damping","en","master thesis","","","","","","","","","","","","Offshore and Dredging Engineering","",""
"uuid:8a841901-d443-4b14-8169-373beff44d03","http://resolver.tudelft.nl/uuid:8a841901-d443-4b14-8169-373beff44d03","Modelling alkaline silicon-air batteries: A finite element model","van Grootel, Raimon (TU Delft Electrical Engineering, Mathematics and Computer Science)","van Swaaij, R.A.C.M.M. (mentor); Vogt, M.R. (graduation committee); Delft University of Technology (degree granting institution)","2021","Renewable energy sources such as solar and wind energy rely on climate and weather conditions, like sun irradiation in the case of solar energy, and wind speed in the case of wind energy. These change throughout the day and with the seasons. There are periods of little wind, and during the night there is no sunlight. During periods of no sunlight and little to no wind, there is still a demand for energy. This leads to a shortage of energy. On the other hand, there are periods when the amount of available wind and solar energy will surpass the demand for energy, leading to an energy excess. To mitigate this mismatch between energy production and energy demand the excess energy can be stored to be used during periods of shortage. Many different solutions for this have been investigated in recent years. One of the storage technologies that is currently quite dominant is battery storage. Lithium-ion batteries are used quite widely, among others in battery electric vehicles. However, the use of batteries as a storage device to overcome energy mismatch is not yet implemented on a large scale, as most battery technologies are still quite novel, making them
uneconomical for this use compared to traditional hydrocarbon fired power plants. Furthermore, many battery technologies depend on scarce and expensive minerals. Recently, a battery utilizing silicon as its anode and oxygen from the air at the cathode has been proposed. This socalled silicon-air battery utilizes mainly silicon and oxygen, which are the two most common elements on earth. Furthermore, the theoretical energy density of this battery type was shown to be significantly higher than the energy density of lithium-ion batteries. Because of this, the silicon-air battery has been a growing area of research in the last years.
Battery models help to simulate batteries based on empirical data and electrochemical systems. These models are a powerful tool in the evaluation of the performance of batteries. Parameters of the battery can be altered quickly and specifically. This can provide a powerful analysis tool to determine weaknesses in a batteries. They can also help in further developing an understanding of the operating principles of the battery technology. A specific type of model is the finite element model. In this type of model the object that is modeled is divided into small pieces and for each piece a set of (partial) differential equations is evaluated. Different electrochemical, chemical, physical and mathematical models can be modelled and combined in this tool. For this thesis a finite element model of an alkaline silicon-air battery is developed in COMSOL. The model is based on an earlier model that was developed in 2020.
Besides the discharge mechanism, alkaline silicon-air batteries are subject to two secondary reactions that hinder the performance of the battery: corrosion and passivation. Corrosion consumes a large part of the silicon without contributing to the discharge. Passivation creates an oxide layer on the surface of the silicon electrode, stopping the discharge reaction. Both these reactions have been implemented in the model. Besides that, a metal contact on the silicon anode is implemented in the model. The parameters used in this model are supported by empirical values for these parameters. Finally, the model was compared to experimental results.
The simulation of the discharge of the alkaline siliconair battery was improved in several ways compared to the pre-existing model. The corrosion was shown in the simulations, although the mechanism is somewhat simplified because of the 1D nature of the model. The passivation reaction was shown in the simulations as well, and was improved on compared to the previous model by breaking it up into two steps. Using this model, experimentally observed trends could be simulated reasonably well. The simulated discharge potential was a close representation of the experimental data, although the open circuit potential was somewhat higher, and for higher current densities the potential was somewhat lower. For different electrolyte concentrations the model showed results similar to what was found in experiments.","FEM; Silicon-air; Battery; Renewable Energy; Energy Storage","en","master thesis","","","","","","","","","","","","","",""
"uuid:27e1ac12-5cdb-4154-abcd-3358d244fab4","http://resolver.tudelft.nl/uuid:27e1ac12-5cdb-4154-abcd-3358d244fab4","A hybrid approach to implement the Digital Twin concept into a damage evolution prediction for composite structures","Coenen, Robert (TU Delft Aerospace Engineering)","Zarouchas, D. (mentor); Delft University of Technology (degree granting institution)","2021","Improvement in the SHM of composite materials requires an enhanced understanding of the damage accumulation processes and helps in the way towards lighter, more optimized, and more sustainable aerospace structures. The Digital Twin concept has the potential to address this problem and may revolutionize the designing, certifying, maintaining, and operating of systems and their components in the long term. This thesis presents a first step to assess its fit in the prediction of damage accumulation within composite materials, specifically the accumulation of transverse matrix cracks within a carbon/epoxy cross-ply specimen under a quasi-static tensile load. To make use of a data-driven technique, a sufficiently large data set is essential. An existing dataset of experiments provides a solid basis but needs augmentation. To augment an existing dataset of tensile tests on cross-plies, a FEM model was constructed that models both transverse matrix cracks and delamination by making use of XFEM-CE. Material variability is implemented per element in the model to overcome the deterministic nature of FEM and generate various crack patterns. The crack patterns and mechanical behavior of the FEM simulations show to be in good agreement with the experimental data. The digital twin that provides real-time predictions is proposed as a LSTM-based neural network. The applied strain to the specimen was predicted with reasonable accuracy. The error of predicting the next crack decreased significantly between predicting the 2nd and 5th crack, after which the mean value of the error and standard deviation remain at similar values. These findings imply that from predicting the 5th crack onward, stochasticity’s role is minimized on the part of predicting the next crack strain. The stochasticity and underlying relationship between the locations of the cracks turned out to be too complex to model with the given approach. Two of the main reasons that are attributed to the latter phenomenon are the modest size of the data set, in spite of further augmentation of the data set after theaddition of the FEM crack patterns, and chosen approach in problem definition.","Digital Twin; composite structure; transverse matrix cracks; LSTM; RNN; damage prediction; XFEM-CE; FEM; deep learning","en","master thesis","","","","","","","","","","","","Aerospace Engineering","",""
"uuid:8682e3f1-3336-4d91-acba-25e9e04740c8","http://resolver.tudelft.nl/uuid:8682e3f1-3336-4d91-acba-25e9e04740c8","Assessment of macro-instability using SHANSEP in RFEM: The application of SHANSEP in combination with RFEM for safety assessment of dikes.","Ünal, Esat (TU Delft Civil Engineering & Geosciences)","Hicks, M.A. (mentor); van den Eijnden, A.P. (mentor); Lanzafame, R.C. (graduation committee); Delft University of Technology (degree granting institution)","2021","The Dutch Water board revised their guidelines for the safety assessment of dikes in 2017. A major change for the assessment of macro-stability is the use of the SHANSEP method to estimate the strength of impermeable cohesive layers. The failure probabilities are estimated with a deterministic analysis using limit equilibrium methods. The use of design values and safety factors to account for uncertainty is basic and proven to be conservative leading to over engineering.
In this thesis, it is investigated how the SHANSEP method can be incorporated to the more advanced Random Finite Element Method. It is found that three random fields for SHANSEP parameters S,m and POP are required. The random fields do not show particular trends in mean or standard deviation. A random field generator is coded in Python. a simple version of the in-house FEM is modified to read the generated random fields. This code is used to test various geotechnical assumptions.
A final version of the assumptions is coded into a more advanced version of the simulator to do the comparison. The output of the FEM code are the FOS and failure mechanism of a single evaluation with a combination of three random fields. A mean and standard deviation of the FOS results are calculated. The probability of failure is estimated by the area under the probability density function of a lognormal distribution for values below unity. The probability of failure of the deterministic case is estimated using the First Order Second Moment method.
The results show that the probability of failure is overestimated in a FOSM analysis by one order of magnitude compared to the most conservative RFEM simulation. It is expected that this difference is even higher for the more conservative deterministic approach the Dutch guidelines prescribe. The slip surfaces of RFEM were found to be similar to their deterministic counterpart. The RFEM slip surfaces went through local weak zones in random fields.
It is recommended to Dutch policy makers to investigate the use the random finite element method. Although conservatism is preferable in safety assessments, an conservatism of this significance compared to the RFEM approach is unnecessarily costly.","SHANSEP; SHANSEP NGI-ADP; macro stability; RFEM; FEM","en","master thesis","","","","","","","","","","","","","",""
"uuid:74882c32-bfef-4dc8-8586-ebf732f6aad8","http://resolver.tudelft.nl/uuid:74882c32-bfef-4dc8-8586-ebf732f6aad8","The effects of local fibre organization on the elastic and rupture behaviour of tissue engineered fibrous cap models","Swaab, Maarten (TU Delft Mechanical, Maritime and Materials Engineering)","Akyildiz, A.C. (mentor); Gijsen, F.J.H. (graduation committee); Veeger, H.E.J. (graduation committee); Delft University of Technology (degree granting institution)","2021","Atherosclerosis is a cardiovascular disease in the arteries and a primary cause of death in the industrialized world. Most deaths due to atherosclerosis occur when the fibrous cap covering the necrotic core ruptures, leading to a blood clot. To determine whether an atherosclerotic plaque will rupture requires the development of accurate computational models. One of the key aspects for these models is the material model, in which collagen fibres play a major role. This study aims to contribute to the making of a numerical model which accurately represents atherosclerotic plaque by comparing the elastic and rupture behaviour of engineered collagenous micro tissues and their respective finite element models in ABAQUS. The Holzapfel-Gasser-Ogden material model of these computational models is based on a combination of global material parameters and local material parameters based on the local fibre organisation. A framework developed to measure the local fibre organisation using provided imagery of a nuclear stained tissue engineered sample shows the collagen fibres align along the loading direction and the edges of the geometry. The fibers are less dispersed along the edges of the geometry and on the left and right of a formed soft inclusion. A uniaxial tensile test was performed on four tissue engineered samples. The elastic and rupture behaviour of the samples during the uniaxial tensile tests is replicated in ABAQUS using both isotropic and homogeneous material parameters, and anisotropic heterogenous material parameters. The stresses measured in the simulations are highly dependent on both the material parameters and the geometry of the model. The strains are mostly dependent on the geometry, but are affected by the material model. Due to the higher stiffness at the edges of the geometry of the anisotropic samples, the stresses increased greatly, and the strains decreased slightly. The rupture behaviour of the cultured samples is replicated in the FEM simulations using extended finite element method (XFEM). The damage in the samples with isotropic material parameters initiates both from the soft inclusion as the left and right edges of the geometry. The damage in the samples with anisotropic material parameters initiates, similarly to the cultured samples, only from the sides of the soft inclusion. The damage in both the cultured and simulated samples propagate mostly horizontal and from the soft inclusion outward. In three out of four isotropic samples however, damage propagates to varying degrees from the edge of the geometry inward. Based on these findings it is concluded that implementing the local fibre organisation in the material model can improve the accuracy of finite element simulations of collagenous soft tissues, which includes atherosclerotic plaque, as the rupture behaviour of the simulations with anisotropic material parameters more accurately represents the rupture behaviour of the engineered fibrous tissues in comparison with simulations with isotropic material parameters.","atherosclerosis; FEM; XFEM; Biomechanics; plaque rupture; Finite Element Modeling; artery; collagen","en","master thesis","","","","","","","","","","","","Mechanical Engineering | BioMechanical Design","",""
"uuid:74eb3038-2de4-44b9-bac7-07d94becd48e","http://resolver.tudelft.nl/uuid:74eb3038-2de4-44b9-bac7-07d94becd48e","Mars Surface Stress Modelling: Investigation on the crustal structure of Mars with Finite Element Method","Qin, WeiLun (TU Delft Aerospace Engineering)","Root, B.C. (mentor); Delft University of Technology (degree granting institution)","2021","Mars has been a target for space exploration for decades. Exploring the interior of the red planet could reveal information about its formation and evolution. In this thesis, the crustal structure of Mars is investigated by a power spectra analysis of both topographic and gravitational data. With models of flexural isostasy, the best-fitting lithospheric (crust + uppermost mantle) thickness is found to be between 136 km and 158 km globally. Possible values for the thickness of the lithosphere range from 120 km to 580 km. In addition, a 3D flat Finite Element Method (FEM) model is created for Mars. The FEM Mars model incorporates the above-mentioned crustal profiles and calculates the surface stresses in the regions of interest. The calculated stresses are compared to observed faults in Tharsis, Hellas, and Utopia to reveal information about the evolution of these regions.","Mars; FEM; Stress Analysis; Isostasy","en","master thesis","","","","","","","","","","","","Aerospace Engineering","",""
"uuid:6652a9ee-61a6-4c4a-9b28-ef4fda1010f9","http://resolver.tudelft.nl/uuid:6652a9ee-61a6-4c4a-9b28-ef4fda1010f9","Hydroelastic wave deformation of Very Flexible Floating Structures: A performance study of a monolithic finite element model","van Hoof, Sjoerd (TU Delft Civil Engineering and Geosciences)","Antonini, A. (mentor); Schreier, S. (graduation committee); Colomes, Oriol (graduation committee); Morshuis, Sander (mentor); Hoogeveen, Maas (graduation committee); Delft University of Technology (degree granting institution)","2021","At the moment, the world is at the verge of an energy transition. One of the most promising green resources is solar energy, which is a rapidly growing market. However, to fully use its potential of economy of scale, the application of offshore floating solar should be explored. A promising option is the use of a flexible type of Very Large Floating Structures (VLFSs), which are called Very Flexible Floating Structures (VFFSs). They are characterised by their large length to height ratio compared to rigid bodies and depending on their material properties have a hydroelastic response to the incident wave. In the late 1990s, a lot of research has been done on VLFSs by Tsubogo and Okada (1998) who derived an analytical dispersion relation assuming a zerodraught structure. However, only recently, Schreier and Jacobi (2020b) did experimental research on VFFSs in a towing tank at the Delft University of Technology, as little is still known about flexible structures. This report focuses on a numerical alter native that covers both VLFSs as well as VFFSs using a Finite Element Method (FEM) Fluid Structure Interaction (FSI) model which has been built based on potential flow to model the fluid and a dynamic EulerBernoulli beam that represents the floating structure using the Julia package Gridap. One of the main advantages is that the zerodraught assumption is not necessary and, therefore, structures with larger draughts can also be modelled. Next to this, the numerical model is able to cope with irregular shapes, for which no analytical method yet exists. The model is built such that it can handle 2D as well as 3D domains. A 2D analysis has been made to understand the influence of hydroelastic wave deformation of the incident wave, in terms of wavelength dispersion as well as amplitude dispersion on floating structures. To verify the model, the numerical results were compared to the analytical solution and experimental research in a towing tank, which showed accurate results. Test runs were set up that mimicked the towing tank setup and a fullscale solar park. Furthermore, a sensitivity study was executed that shows the limits of the flexible domain and to see in which cases significant (>1%) hydroelastic wave deformation would occur using governing mean and extreme ocean waves, as well as a typical lake wave. Finally, the influence of the draught of the structure was examined. This report provides a good overview of when wave deformation should be accounted for in terms of bending rigidity and density. Confirming existing theory, it was found that the stiffness of the VFFS causes wave stretching and the draught of the structure influences the extent of wave shortening. It was also found that significant wave deformation will not occur for ocean waves as the required stiff ness is beyond existing materials. For extreme ocean waves, there is even no dispersion at all. As the wave frequency increases, the hydroelastic interaction gets stronger. The typical lake wave showed to be well within the flexible regime and also showed significant dispersion with realistic material parame ters. The numerical model is able to cope with large draught scenarios which lead to wave shortening, which in its turn leads to wave focusing. Ultimately, the numerical model showed to be a good alternative to existing methods to investigate the behaviour of VLFSs outside the floating solar domain, where one could think of ice floes, floating islands or floating airports.","Very Large Floating Structures; Fluid Structure Interaction; Very Flexible Floating Structures; FEM; potential flow; Floating Solar","en","master thesis","","","","","","https://oriolcg.github.io/GridapOffshore.jl/FSI/VFFS/ Tutorial of numerical model","","","","","","Civil Engineering | Hydraulic Engineering | Coastal Engineering","",""
"uuid:9918d2fd-8f98-4cc1-a420-187bfd14d4c5","http://resolver.tudelft.nl/uuid:9918d2fd-8f98-4cc1-a420-187bfd14d4c5","Reliability Assessment of Steel Structural Elements in Wind Excited Buildings","van Hulst, Jeffrey (TU Delft Civil Engineering & Geosciences)","Veljkovic, M. (mentor); Kavoura, Dr. Florentia (graduation committee); Hendriks, M.A.N. (graduation committee); Steenbergen, R.D.J.M. (graduation committee); la Gasse, L.C. (mentor); Delft University of Technology (degree granting institution)","2021","One of the basic principles of the design of structures is that they must be sufficiently safe and meet the required reliability requirements. In Eurocode NEN-EN 1990 specific minimum reliability index values are defined, which depend on a certain reference period and reliability class. To ensure that the structures meet the reliability requirements, partial factors are applied in the Eurocode. The aim is to steer the design to the minimum reliability requirements in a relatively simple way without a complete reliability assessment. Since such a reliability assessment is much more complex and requires more time and knowledge of the engineer. This research investigates how the reliability of a steel main bearing structure in a wind excited building can be determined, taking into account all uncertainties on both the resistance and load side. A new method is developed in which wind tunnel measurements, wind speed models and a finite element model of the building can be directly linked. This is an improvement on recent studies. With this method it is possible to determine the load effects of the wind in specific elements of the building. This can then be used to determine the reliability of the steel main bearing structure in a wind excited building.
First of all, all probabilistic models concerning the resistance side of the reliability assessment are identified by means of an extensive literature study. In this way all material properties and uncertainties are included in the reliability assessment. In addition, wind speed models, boundary layer wind tunnel pressure measurements and a FEM of the case study building are used. A wind load effect model quantifies the forces that occur in the structure due to the given wind load (based on the wind tunnel research) on the structure. This wind load effect model consists of several deterministic and stochastic parameters as input. All these data and models are linked to each other to determine the peak load effects and associated sampling uncertainties in various elements of the case study building. To further use the wind load effects in the reliability assessment, extreme value theory must be applied to determine the extreme value distributions of these peak load effects. It should be taken into account that the extremes extracted from the data are independent and identically distributed.
To demonstrate that the method works, it is applied to a case study building. This case study building is initially designed in a deterministic Eurocode manner. Next, the reliability of a number of elements of the steel main bearing structure is extensively determined. For this particular case study building, it is evident that the design can be further optimised compared to the Eurocode design. In conclusion, this method shows that the possibilities in the field of a reliability-based design are certainly worthwhile for the further optimisation of a structure. And the use of this new method in which all data and models can be linked makes the application of a reliability-based design a lot more efficient, more accurate and therefore more interesting.
explore how quantum computing can be used to aid in solving structural optimization problems. Two methods are developed with which simple 2-dimensional truss systems can be optimized using the D-Wave quantum annealer. The methods aim to find the most lightweight choices for the truss cross-sectional areas while complying with material limit stress constraints. The first method directly casts such an optimization problem into a QUBO format. However, due to difficulties with formulating the stress constraint, this method was found to produce a trivial optimization problem. The second method attempts to symbolically solve a truss finite-element problem, using the resulting symbolic expressions to set up an optimization objective function. Although these objective functions are confirmed to work via classical brute-force analysis, the quantum annealer is shown to have difficulty finding the global optimum solution for truss systems with three or more elements. These results indicate that it is not currently beneficial to use quantum annealing for these structural optimization problems. Nevertheless, some improvements to the method for setting up the objective functions are suggested. The next generation of quantum annealers is expected to perform better for these practical applications, potentially becoming a useful tool in the engineering toolbox.","Quantum Computing; Quantum Annealing; Structural Optimization; QUBO; Truss; FEM; Python","en","master thesis","","","","","","","","","","","","Aerospace Engineering","",""
"uuid:1b827ff8-7b5f-4d6f-9c4f-b24f71203c98","http://resolver.tudelft.nl/uuid:1b827ff8-7b5f-4d6f-9c4f-b24f71203c98","Optimising the functionality of smart quay walls using measurement data obtained during the construction process: A case study in the port of Rotterdam: HHTT-quay","Schouten, Onno (TU Delft Civil Engineering and Geosciences)","Korff, M. (mentor); Gavin, K.G. (mentor); Voorendt, M.Z. (mentor); Roubos, A.A. (mentor); Post, M. (graduation committee); Delft University of Technology (degree granting institution)","2020","Quay walls are often designed with Finite Element models (FE models) to take into account the complex soil-structure interaction and highly non-linear soil behaviour. These are complex models that rely on many input parameters that have uncertainties. Nowadays, new quay walls are often equipped with sensors that collect information about the behaviour of the quay wall. These quay walls are known as \textbf{smart} quay walls. The measurement data of smart quay walls could be used to validate FE models and reduce parameter uncertainties. This could lead to an optimisation of the functionality of the quay walls. By means of a case study this thesis determines if measurement data obtained during the construction process has the potential to optimise the functionality of smart quay walls. The case used is the HES Hartel Tank Terminal (HHTT-quay), which is a smart quay wall in the port of Rotterdam. The HHTT-quay consists of sections with and without a relieving platform, both are considered in this thesis. In this thesis the functionality of a quay wall refers to the retaining or bearing functionality. Therefore, an optimisation of the functionality could consist of an optimisation in the retaining height or the surface loads. The case study used in this thesis shows that measurement data obtained during the construction process already provides important information that can be used to optimise the functionality of the quay wall. This indicates that for smart quay walls the construction process can act as a load test and this could reduce the necessity to perform a load test during the service life.","Quay walls; Measurement data; FEM; Updating; functionality","en","master thesis","","","","","","","","","","","","Geo-Engineering","",""
"uuid:7179b5c2-d9f0-45a3-8608-58af84ae9dcf","http://resolver.tudelft.nl/uuid:7179b5c2-d9f0-45a3-8608-58af84ae9dcf","Predicting the failure behavior of off-axis composite laminates subjected to dynamic compression loads","Kota, S.K. (TU Delft Civil Engineering and Geosciences)","van der Meer, F.P. (mentor); Weerheijm, J. (graduation committee); Pavlovic, M. (graduation committee); Delft University of Technology (degree granting institution)","2020","In recent times, composite materials are widely applied in the construction industry because of their superior properties compared to traditional materials like steel and concrete. The use of composite materials in defense and infrastructure protective applications to resist high rate dynamic loading conditions has been gaining the interest of a lot of researchers over the previous decade. The limitations involved in studying the behavior of composites when subjected to high rate dynamic loads experimentally generated a need for numerical models that could simulate such complex material behavior. These numerical models are also highly useful in situations where it is difficult to perform direct measurements in experiments. The idea of this thesis originated from an aim to study the behavior of a TNO developed composite laminate with alternate 0-degree and 90-degree ply layup when subjected to out of plane blast loads. Considering the complexities involved in such a loading situation, a simplified test setup that can approximately replicate stress conditions in the composite laminate due to out of plane blast load has been proposed to be designed. This simplified test setup is prepared by performing an angled cut from the composite laminate, thus making the plies off-axis with respect to the global coordinate system of its cross-section. The motivation behind choosing such a test setup is that the interface/s can be loaded by a combination of compressive and shear stresses with axial loading on the specimen. The behavior of the simplified test setup with off-axis angles 30-degree, 45-degree, and 60-degree, when subjected to dynamic compression loads with different rates ranging from quasi-static to high is analyzed in this thesis using the finite element method. The initial parts of the study focus on analyzing the quasi-static failure behavior of the off-axis angled composite specimens with a single critical interface at the center modelled using the rate-independent cohesive law coupled with friction. The later parts of the study focus on analyzing the dynamic failure behavior of the composite specimens. The rate-independent cohesive law with friction is improved by adding a rate-dependency feature based on a Johnson-Cook law. Finally, the dynamic behavior of different off-axis angled composite specimens with critical interface/s modelled using the rate-independent and the rate-dependent cohesive laws with friction when subjected to compression loads with different rates is analyzed. The results obtained from the quasi-static analyses indicate that an increase in the mode-II cohesive strength, mode-II cohesive fracture energy, and interface friction coefficient lead to an increase in the peak load carried by the laminates. An increase in the thickness of the plies of an off-axis angled composite specimen results in a decrease in its peak load and changes its governing failure mechanism. There will be a dominant contribution of local inertia and wave propagation effects in dictating the failure behaviors of the specimens when subjected to compression loads with higher rates. The rate-dependent cohesive law with friction developed in this thesis seemingly captured the rate effects in the off-axis angled composite specimens when loaded in compression at different rates. Finally, it is suggested to design the simplified test setup by performing a 45-degree cut from the original composite laminate to simulate delamination due to compression loads of different rates effectively. But all three simplified setups have to be tested to derive the unique set of interface parameters that dictate the failure behaviors of the specimens.","Off-axis laminates; Failure behaviour; Dynamics; Compression; FEM; Cohesive Zone Modeling","en","master thesis","","","","","","","","","","","","","",""
"uuid:995fba9f-a727-4384-99cc-eaebb73c8136","http://resolver.tudelft.nl/uuid:995fba9f-a727-4384-99cc-eaebb73c8136","Sacral anchoring of the LUMiC prosthesis: Development of a protocol to in vitro evaluate newly designed 3D printed patient specific prosthesis for the sacrum after tumour resection","van Rijn, Lisa (TU Delft Mechanical, Maritime and Materials Engineering)","Zadpoor, A.A. (mentor); Janbaz, S. (graduation committee); Dijkstra, Sander (graduation committee); Kaptein, Bart (graduation committee); Delft University of Technology (degree granting institution)","2020","After en bloc resection of primary pelvic bone tumours, orthopaedic oncologists usually try to perform reconstruction in order to achieve limb salvage. Reconstruction after these types of resections is challenging. Especially when the total ilium and parts of the sacrum needs to be removed. One of the reconstructive options is endoprosthetic fixation to sacral bone with the LUMiC prosthesis, but using the LUMiC prosthesis in the sacrum resulted in poor clinical results. Emerging new production techniques such as 3D printing provide for customised prostheses that could be an adequate reconstructive option in these cases and could complement the LUMiC prosthesis to enable sacral anchoring of the LUMiC prosthesis. One of the challenges of customised prostheses is that they are not ‘off the shelf’ and therefore are all different in terms of geometry and, thus, performance. Therefore, these implants cannot be subjected to stringent regulations and registrations used in conventional arthroplasty. In order to ensure maximal safety of these implants we must perform biomechanical testing before implantation. Unfortunately, the bone models for biomechanical testing currently available are not validated on implant fixation and thus unreliable for prosthesis testing. Therefore, in this thesis a new prosthesis that enables sacral anchoring of the cup of the LUMiC prosthesis is designed and two strategies are developed in order to mechanically evaluate this newly designed prosthesis for the sacral anchoring of the LUMiC cup. First strategy is using Finite element modelling to develop a model of the sacrum with implanted prosthesis. Second strategy is the development of 3D bone models of the sacrum using 3D printing together with performing experiments to mechanically evaluate the newly designed prosthesis. Four different mechanical bone models with different shell thickness and infill density were developed and compared to the FE model. Results showed that the new prosthesis design performed better in terms of micromotions between implant and bone compared to the use of the old LUMiC stem in the FE model. Furthermore, a 3D printed mechanical bone model with shell thickness of 1mm and infill structure of 20% showed most comparable results in terms of micromotions between implant and bone compared to the developed FE model. There could be concluded that the FE model and the development of 3D printed mechanical bone models together with the experiments are good starting points in the development of a protocol to in vitro evaluate newly designed 3D printed patient specific prosthesis for the sacrum after tumour resection. The mechanical bone model with shell thickness 1mm and infill structure 20% is the best option in terms of mimicking real bone. Furthermore, the newly designed prosthesis for sacral anchoring of the LUMiC cup showed promising results and could be considered as a improved alternative for the old LUMiC prosthesis stem. In future research cadaver tests should be performed to further validate the found results.","Prosthesis design; Bone models; FEM; sacrum","en","master thesis","","","","","","","","","","","","","",""
"uuid:b1d66af3-0acb-475e-a4d4-06bf948aea17","http://resolver.tudelft.nl/uuid:b1d66af3-0acb-475e-a4d4-06bf948aea17","Timber Creep of Historic Urban Quay Walls: The influence of timber creep on the assessment of inner-city quay walls","Spannenburg, Trevor (TU Delft Civil Engineering and Geosciences)","Korff, M. (mentor); Peters, D.J. (graduation committee); Gard, W.F. (graduation committee); van de Kuilen, J.W.G. (graduation committee); op de Kelder, M. (graduation committee); Delft University of Technology (degree granting institution)","2020","Amsterdam and many other cities consist of a network of old quay walls, which sometimes have been constructed over a century ago. A large uncertainty exists concerning the current safety of these quay walls and their remaining service lifetime. In the current framework for the assessment of old urban quay walls, the influence of timber creep in the structure is being omitted. It had been expected that a part of the excessive deformations occurred are part of this timber creep as opposed to progressive failure. Hence, this research studied the influence of wood creep on the structural behaviour of old urban quay walls, using a case study based on the Herengracht. For the modelling of the quay walls, use has been made of the Embedded Beam Row (EBR) elements in Plaxis 2D. As this element type has no material model which takes into account creep,
use has been made of pseudo-elasticity. The behaviour over time had been modelled by reducing the elastic stiffness of the EBR elements with increasing creep factors. To force Plaxis to perform calculations, this stiffness reduction has been introduced as a reduced strength in the form of a custom moment-curvature diagram. At the time of writing, the Embedded Beam Row had not yet been validated for cohesive soils. Hence, a verification has been executed of the EBR using a full-scale load test performed on a pile group in Salt Lake City. In
this case, a 3x5 pile group driven in multi-layered cohesive and non-cohesive soils had been laterally loaded. The results included deformations, total horizontal load and bending moment distributions over depth. It
has been found that the EBR provides reasonable results when modelling laterally loaded pile groups. The force-displacement curve from the field test was only slightly stiffer compared to those obtained using Plaxis 2D. Maximum bending moments obtained using the EBR had been found to be 20 to 30% compared to the experimental data. The group efficiency of the pile group was initially lower for small displacements, which was likely caused by the lack of installation effects of driven piles in the Plaxis model. It has been observed
that the Interface Stiffness Factors (ISF) that are used to calibrate the EBR behaviour have a limited range. Increasing the ISF values beyond a certain limit will no longer affect results, as the interface connecting the EBR to the soil will have become practically rigid at this point. Nevertheless, it has been concluded the EBR can be used in this case to model laterally loaded pile groups. The influence of the timber creep on the structural behaviour of quay walls has been studied using a model based on the Herengracht in Amsterdam. A maximum creep factor has been applied of Φ=1.6. Two methods have been used to apply the final creep factor. With the ""Direct"" method, the maximum creep factor was
applied in the same phase as the load. With the ""Indirect"" method, the creep factor has been applied incrementally in steps of 0.1. It has been observed that the results from these methods deviate significantly. With the Indirect method, larger creep displacements have been calculated, as well as lower maximum compressive stresses in the piles. The creep behaviour has been studied in more depth using the Indirect method. In this case study, creep displacements of 2.22 times the initial displacement have been calculated. When plotted against the increasing creep factors, it has been observed a power function could be fitted to the data. In addition, a stress reduction of 0.590 times the initial maximum compressive stress has been observed in the front two pile rows. This stress reduction was achieved at φ=0.4. In the most landinwards pile row, stresses
continued to decrease, with a reduced rate beyond φ=0.4. A sensitivity analysis has been performed to study which parameters have significant influence on the creep behaviour. Conclusions were drawn based on the relative change in horizontal displacement and maximum compressive stress in the front pile row. It has been concluded that the shear strength parameters of the top layer, the elastic modulus of the timber, surface load and the geometry have the largest influence on the creep behaviour. Furthermore, it has been discovered
that the size of the creep factor steps influences the final stress and displacement. With decreasing stepsize, convergence occurred in the results. From the results it has been concluded that the structural behaviour of
old urban quay walls is significantly influenced by timber creep. The inclusion of timber creep resulted in large displacement increases, but also in stress reduction. The results suggest that excessive deformations of quay walls does not mean that an ultimate limit state has been reached. It is recommended to include the timber creep in the modelling and assessment of existing quay walls.","Quay structures; Quay walls; creep; timber creep; timber; urban quay walls; historic quay walls; old quay walls; wood; wood creep; timber quay walls; plaxis 2d; EBR; Embedded Beam Row; Laterally loaded pile; pile group; horizontally loaded piles; Laterally loaded pile group; ISF; Interface Stiffness Factor; Herengracht; Amsterdam; FEM; soil; modelling; pseudo-elasticity; creep factor","en","master thesis","","","","","","","","","","","","","",""
"uuid:7408e962-afb8-4c83-9f46-302db0b3bddf","http://resolver.tudelft.nl/uuid:7408e962-afb8-4c83-9f46-302db0b3bddf","A stiffness independent Interfacial Thick Level Set method: A modified approach for crack analysis","Sluijs, J. (TU Delft Civil Engineering and Geosciences)","van der Meer, F.P. (mentor); Dekker, R. (mentor); Pavlovic, M. (graduation committee); Delft University of Technology (degree granting institution)","2020","Crack growth is an important failure mechanism in many engineering materials. Numerical models for crack growth have been developed within the framework of damage mechanics. All these models aim for the same goal, obtaining accurate results for crack growth under various loading conditions. Many damage models are based upon the cohesive crack approach. However, level set based models provide advantages compared to the cohesive crack models with regard to fatigue analysis. An alternative method to the existing thick level set (TLS) method was proposed, the interfacial thick level set (ITLS) model. The use of interface elements made the model more suitable to simulate several failure processes. In this thesis it is demonstrated that this method suffers from a dependency on the initial interfacial stiffness for the global response of a system by conducting a parameter study under quasi-static loading conditions. This parameter study proves that for a varying value of the initial interfacial stiffness parameter K the global response varies as well. This gives motivation to conduct further research on the removal of the initial interfacial stiffness from the current ITLS model. Two methods are developed to overcome the initial interfacial stiffness dependency. The first method assumes that the initial interfacial stiffness dependency is caused by the current formulation of the constitutive
law of the interface. A new expression for the interfacial stiffness is adapted after which all constitutive relations are updated. The new method shows a
perfect agreement with the current ITLS model, which validates the method as an accurate alternative. Compared to the current ITLS model, method 1 allows for the control of the initial stiffness of the undamaged part of the interface by changing the lower bound damage without affecting the global response. However, when executing simulations for a varying initial interfacial stiffness K the same problem as for the current ITLS is observed. It can be concluded that in a way this method removes the dependency on the initial interfacial stiffness but the initial interfacial stiffness parameter K should then remain constant. Furthermore, the calibration process is not simplified compared to the current ITLS model. For this reason method 1 is rejected as the final solution to the problem and a second method is proposed. The second method assumes a direct relation between the damage parameter c1 and the initial interfacial stiffness parameter K. This damage parameter is responsible for the steepness of the damage profile. The results from the parameter study showed that an increase of one of these parameters results in opposite behaviour for the initial stiffness of the global response. The leading hypothesis becomes that an increase in the stiffness parameter K can be neutralized by an increase in the damage parameter c1. Proportionality between both parameters is assumed. By trial and error the proportionality is found to be one to one. When using this proportionality condition, simulations with different values for the initial interfacial stiffness showed a perfect agreement for the load-displacement and the crack growth responses. Moreover, the proportionality condition is accurate for both a linear elastic (LE) material and an elastic-plastic (EP) material. The proportionality condition is proven by elaborating the interfacial stiffness over the damaged zone. This elaboration is done both numerically and analytically and proves that there is a one to one proportionality between c1 and K, which validates the replacement of c1 by a constant c multiplied with K. Lastly, the method should be compared to a response obtained through a different type of analysis. The method is compared with the solution of an analytical analysis resulting in a very good agreement for both a LE and an EP material. Therefore, method 2 can be approved as a solution to the initial interfacial stiffness dependency problem.","FEM; Damage mechanics; ITLS model; Fatigue; Crack growth; Fracture mechanics","en","master thesis","","","","","","","","","","","","Civil Engineering | Structural Engineering","",""
"uuid:3e51ef1b-1d7c-454d-82b1-220b9cb14054","http://resolver.tudelft.nl/uuid:3e51ef1b-1d7c-454d-82b1-220b9cb14054","Bored Tunnel Lining Behaviour in Discontinuous Rock: Railway Tunnel in Middle-East","Dobrovinski, Daniel (TU Delft Civil Engineering and Geosciences)","Broere, Wout (mentor); Ngan-Tillard, Dominique (graduation committee); Reinders, Kristina (graduation committee); Lantinga, Carolina (mentor); Colard, Gilles (mentor); Jovanovic, Predrag (graduation committee); Delft University of Technology (degree granting institution)","2020","In a bored railway tunnel project in the Middle-East, difficulties in terms of ovalization, water leakages and settlement of several lining rings located in a fault zone were observed at the end of the construction stage. The present research attempted to find the cause for this lining behaviour. The determination of critical loading conditions, the application of the longitudinal beam model and the analytical and numerical modelling (in Plaxis) of a monolith tunnel lining in abrupt ground property transition were analyzed. Thereby, the global lining stiffness reduction due to joints was also considered. The literature review led to the following expected factors that caused difficulties in the Middle-East case: the squeezing and submerged ground conditions, the rock mass disturbance and the improper backfilling of the rings. Additionally, the ring stiffness reduction due to joints was an essential factor for lining behaviour. The geotechnical conditions, the lining design and the observed difficulties in the case were defined in the next section. Critical missing information, such as geotechnical properties of the fault zone material and limited monitoring data, led to essential assumptions. The settlements were expected to be caused by rock mass disturbance and improper backfilling. These altered the water flow during and after the boring operations and led to lowering of the groundwater level and increase of effective stresses. The water leakages were caused by ring ovalization in the soft fault zone, leading to opening of joints. The analysis for this research was divided in 2D transversal, 2D longitudinal and 3D modelling of the lining in and around the fault zone. The 3D model was seen as the integral model, which took into account the transversal and longitudinal behaviour of the lining. However, most of the behaviour of the lining was analyzed by carrying out parametric analysis for both directions in 2D. Moreover, the 2D models were used to validate the results of the 3D model to identify the influence of the third dimension. The assessment of the results from these analyses led to the following conclusions. The behaviour of the tunnel lining in small width fault zones was governed by the transversal action. The ovalization was mainly influenced by the ground stiffness, the vertical to horizontal stress ratio, the backfilling stiffness and the ring stiffness. Using Erdmann's analytical solution, the approximate lining forces can be determined. However, this overestimated the ground pressures acting on the lining, especially in cases where vertical to horizontal stress ratios were not equal to 0.5. This was because the 2D transversal behaviour did not take into account the longitudinal arching effect, which depended mostly on the stiffness ratio between ground types. The final conclusion was that the global reduction of lining stiffness due to the joints led to a discrepancy with regard to the distribution of the longitudinal displacements. A complementary analysis using a numerical model taking into account the joint structure and discontinuous behaviour between rings would probably allow a better prediction of longitudinal displacements.","Bored tunnel; TBM; Lining; Discontinuous rock; Hoek Brown; Fault zone; Plaxis; FEM","en","master thesis","","","","","","","","","","","","Geotechnical Engineering","",""
"uuid:22aece3a-86e0-431e-a3c6-4f3d17440cbe","http://resolver.tudelft.nl/uuid:22aece3a-86e0-431e-a3c6-4f3d17440cbe","Towards high-order discontinuity-enriched finite element method","Song, Yi (TU Delft Mechanical, Maritime and Materials Engineering)","Aragon, A.M. (mentor); Langelaar, M. (graduation committee); van Ostayen, R.A.J. (graduation committee); Delft University of Technology (degree granting institution)","2020","The computational study of discontinuous problems becomes increasingly important due to industrial needs, such as the application of natural or artificial composites and the understanding of damage and fracture processes of materials. The discontinuity-enriched finite element method (DE-FEM) and interface-enriched generalized finite element method (IGFEM) are promising computational approaches developed in recent years for solving problems containing discontinuities, which are capable of decoupling the mesh morphology from the geometry of discontinuities. Nonetheless, these formulations have only been developed for linear or quadratic polynomial interpolants. We introduce high-order discontinuity formulations aiming at improving the accuracy of the approximation by fixing the mesh size while increasing the polynomial degree of the interpolant, namely the p-version of DE-FEM/IGFEM (p-DE-FEM/p-IGFEM). In the proposed methods, hierarchical shape functions of the p-version of FEM (p-FEM) are employed, and high-order enrichment functions constructed with different polynomial bases are applied in elements intersected by discontinuities. Through convergence tests, we show that p-DE-FEM solves one-dimensional elasticity problems with exponential rates of convergence, and p-IGFEM solves two-dimensional static heat conduction problems with the same exponential rates of convergence as those of p-FEM with meshes that align to discontinuities. When the mesh is refined and the polynomial degree is fixed, p-IGFEM obtains optimal rates of O(p), with p denoting the polynomial degree used. We also show that high-order enrichment functions constructed with orthogonal polynomial bases lead to better-conditioned stiffness matrices.","discontinuities; FEM; DE-FEM; IGFEM; p-version of FEM; high-order FEM; enriched FEM","en","master thesis","","","","","","","","2022-02-24","","","","","",""
"uuid:f9c953a8-8d7f-4881-8c76-800cb24ca1c3","http://resolver.tudelft.nl/uuid:f9c953a8-8d7f-4881-8c76-800cb24ca1c3","Dynamical electromechanical analysis of pole-piece rotors in pseudo direct-drive machines: Taking the next step towards tomorrow’s wind turbines","Desmedt, Michiel (TU Delft Electrical Engineering, Mathematics and Computer Science)","Dong, Jianning (mentor); Nilssen, Robert (graduation committee); Delft University of Technology (degree granting institution)","2019","Wind energy has shown to be a great renewable energy source, with a possible penetration of 20 % by 2040. In order to increase its competitiveness with fossil fuels, the LCOE should decrease further than it already has. Increasing the power rating of wind turbines has proven to be an effective way to achieve this. However, this results in impractical large nacelles which are hard to install offshore. Reducing the size can be done with a gearbox, but due to the gearbox being a high-risk component of offshore wind turbines, wind turbine manufacturers have moved to direct-drive topologies. The pseudo direct-drive topology, where a magnetic gear and direct-drive machine are combined, has shown great potential reducing the size of the generator while keeping the reliability of a direct-drive machine. However, due to the introduction of an extra rotor for the magnetic gearing, the mechanical complexity increases. Focusing on a particular 10 MW design, large deflections in this extra rotor of up to five times the air gap length have been observed during nominal operation. Simple modifications have been investigated, resulting in deflections of less than 1 mm. Each modification was then compared to identify the most promising one.","Wind Energy; FEM; Machine Modelling; Numerical Modelling; Permanent Magnet Machine,; Pseudo Direct Drive","en","master thesis","","","","","","","","2019-12-06","","","","European Wind Energy Masters (EWEM)","",""
"uuid:4dc92753-159c-4322-a8b9-ca634fa37e47","http://resolver.tudelft.nl/uuid:4dc92753-159c-4322-a8b9-ca634fa37e47","Connection between concrete columns and continuous floors with integrated steel beams","Dolganov, Mikhail (TU Delft Civil Engineering and Geosciences)","Yang, Yuguang (mentor); Hoogenboom, Pierre (graduation committee); Houben, Lambert (graduation committee); Delft University of Technology (degree granting institution)","2019","This research studies a simplified connection between one storey high concrete columns and the continuous floors with an integrated steel beam, of the THQ type, carrying hollow core slabs and covered by a reinforced structural screed. The final goal is to determine the strength of the connection. This is done with a calculation method, which may be used outside of this research by designers for an estimation of the design strength of their connection. A simplified design for the connection is set up as a reference design. It is loaded by two load combinations of the use stage of the building, a symmetric and an asymmetric load combination. A behaviour prediction is set up for the reference design under these load combinations. Based on that prediction, additions to the design are studied, which should improve the connection strength. Two adjusted designs are chosen to analyse alongside the reference design: a design with the integrated steel beam supported by additional steel webs at the connection and a design with the integrated steel beam being filled with mortar at the connection. The three designs are numerically modelled and analysed with the Finite Element Analysis (FEA) in DIANA FEA. With the results of the numerical analysis, the design strength of the connection is calculated. The numerical results show that the structural screed and the bottom column are the governing connection parts. The structural screed in the reference model is influenced most by the steel webs of the beam underneath and a limited load transfer area, which leads to higher stresses in the concrete. In the adjusted models this situation is improved, with the model with a mortar filling being the best adjustment, as it provides the maximum load transfer area. The bottom column is most affected by the bending of the steel beam flanges due to the load of the floor, causing a large load to be transferred over a small area at the column edges. The adjusted models do not show a strong improvement here, as the adjustments are limited in the stiffening of the beam flanges. The calculation of the design strength of the connection shows the adjustment of the mortar filling to be the best solution. However, the final design strength is low compared to the design strength of the concrete in the structural screed or the columns. This is the result of the horizontal tension in the structural screed, which reduces the concrete strength. A better result may be obtained by the removal of the structural screed at the connection and the placement of the concrete column directly on top of the steel beam. This adjustment needs a further research.
The conclusion is that the researched design in its current form is not effective enough to be applied in practice, but its drawbacks can be solved with a few adjustments to the design, making it an effective design solution.","THQ; FEM; Connection","en","master thesis","","","","","","","","","","","","Civil Engineering | Structural Engineering","",""
"uuid:bce1eb39-0d87-4edc-9ffc-3b60c1fe45c4","http://resolver.tudelft.nl/uuid:bce1eb39-0d87-4edc-9ffc-3b60c1fe45c4","Concrete slab beneath ballast bed - An Abatement Measure For Railway Induced Vibration","Kunicka, Ewa (TU Delft Civil Engineering and Geosciences)","van Dalen, K.N. (mentor); Metrikine, A. (graduation committee); de Oliveira Barbosa, J.M. (graduation committee); Lagendijk, P. (graduation committee); Houben, L.J.M. (graduation committee); Hosseinzadeh, Saeed (graduation committee); Delft University of Technology (degree granting institution)","2019","In this research project, an assessment of an abatement measure for mitigating railway induced vibrations is carried out. Ground-borne vibrations, which are primarily generated due to wheel-rail interaction, may also result in ground-borne noise in the buildings located in vicinity of railway tracks. An example of adverse environmental impact caused by ground-borne vibration and noise is the annoyance to people living those buildings. Assessing ground-borne vibration and noise is of crucial importance, especially in soft soils in which Rayleigh wave velocity is low and amplification of vibrations is more likely to occur. For mitigating the ground-borne vibration and noise exceeding the threshold values defined by technical standards in each country, abatement measures are applied. The main objective of this research is assessing the effectiveness of ‘concrete slab beneath ballast bed’ used as the abatement measure for reducing vibrations. For this purpose, Plaxis 3D based on Finite Element Analysis method is employed. Numerical model is created and validated through measurement data available from field tests conducted in the Netherlands. After having numerical model validated, several simulations are performed in order to study the factors influencing ground-borne vibrations.
From the results of this study, one can conclude that ‘concrete slab beneath ballast bed’ is effective in reducing vibration strength at all distances when train speed is considerably lower than Rayleigh wave velocity of the uppermost soil layer. It is notable, however, that the application of this measure may bring about amplification of the vibration strength in the vicinity of the track for trains running at higher speeds. Nevertheless, regardless of the train speed, there is always a reduction in the vibration strength at further distances from the railway track. From practical standpoints, this aspect is of interest for the buildings located in the far field. From the results of a sensitivity analysis on changes to the width and thickness of the concrete slab, it can be concluded that an optimal solution of concrete slab dimensions can be found. It is observed that by changing concrete slab dimensions, the maximum vibration strength is mostly affected in close proximity to the railway track. In addition, the dispersion lines and oscillatory moving load in the Wavenumber-Frequency plane are analyzed. Their intersection indicates that the moving oscillatory load excites a wave of frequency and wavenumber given by the intersection point. If these frequencies are harmful for the environment then concrete slab application can diminish their content from response. Sleeper passing frequency content increases when the concrete slab is applied. The obtained results and recommendations from this study can be used for further studying the other factors influencing the effectiveness of the measure. Examples of these factors include, among others, various ground conditions (e.g., soft soils of different stratification, local changes in soil proper-ties, etc.), and optimization of concrete slab dimensions, material parameters, as well as, cracked and uncracked concrete stage. The numerical model developed during this research study can be further employed to analyze different aspects of railway induced ground-borne vibrations.","FEM; Railway induced vibration; vibration; abatement measure; concrete slab; Numerical Analysis; Train; Dynamic Analysis; Plaxis 3D","en","master thesis","","","","","","","","2021-11-14","","","","","",""
"uuid:85e8f4ac-4e3c-485c-9b5d-f320e08fc5a7","http://resolver.tudelft.nl/uuid:85e8f4ac-4e3c-485c-9b5d-f320e08fc5a7","Identification of mine blast interaction pressure on excited plates: Using transient adjoint optimization for solving the inverse problems","van den Brink, Robbert-Jan (TU Delft Aerospace Engineering)","Turteltaub, S.R. (mentor); Chen, B. Y. (graduation committee); Alderliesten, R.C. (graduation committee); de Jong, Bart (graduation committee); Delft University of Technology (degree granting institution)","2019","Mines and improvised explosive devices are the cause of many mortalities of vehicle occupants. Both experimental and numerical research in this field aims to improve the safety of military vehicles. TNO has advanced Finite Element (FE) models to simulate such events. The numerical research is done to better understand mine blasts. Another aim is to reduce experimental costs for Defence Material Organization (DMO). For full vehicle simulations the empirical Westine model is the basis of the in-house TNO mine blast model. The model consists of a triangular pressure pulse consistent with the Westine impulse which is calibrated using the a test rig developed by TNO and DMO. Experiments are compared with numerical results using the TNO mine blast model and the jump height, representative for total impulse transferred, shows scattered results for different vehicle tests. A possible cause can be accuracy of the current mine blast model. This research will study a new technique to validate mine blast models. When this new technique results in improvements in validation of mine blast models it can be used to study and improve the current TNO model. The aim of the new validation method is to calculate the interaction pressure of an plate excited by a mine blast loading. The obtained pressure can be compared with existing mine blast models for validation of the mine blast model. The methodology is based on solving the inverse problem which requires transient Digital Image Correlation (DIC) measurements of the deforming plate for the duration of the mine blast loading. Such measurements are done with the state of the art test setup from TNO and DMO. Several methods to solve the inverse problem will be studied. The proposed best way to solve the problem at hand is by solving the corresponding optimization problem using an iterative gradient of descent algorithm. The main difficulty in this approach will be the calculation of the gradient of the objective function. To do this the corresponding transient adjoint problem has to be solved. First an algorithm to solve the inverse problem is implemented for a linear Kirchhoff Love plate model to study the behaviour of the inverse problem for a relatively simple test case. For this algorithm the transient adjoint problem is derived. The forward and adjoint problem are numerically solved. The implementation is verified using the method of manufactured solutions and a convergence study. The algorithm is verified using three different bench mark test pressures. It was found that without any exception the displacement of the algorithm converged with great accuracy to the applied displacement. The corresponding pressure converged good for smooth pressure distributions. Non smooth pressure distributions representative for mine blast interaction pressure did not converge. This shows the non-uniqueness of the solution of the inverse problem. It was realized after these tests that the forward problem acts as a low pass filter for time and spatial oscillations of the pressure distribution. This implies that the inverse problem in non-unique and that noise in the displacement data will be amplified in the obtained pressure from the inverse solution. The total force and radial position as function of time, obtained after integration over the spatial domain, for a localized load are accurately captured back. These parameters could be useful to validate a mine blast model such that research was continued for a continuum model. A non-linear elastic material model is proposed to model the deforming plate assuming monotonically increas- ing strain. This model is used and calibrated against the Johnson-Cook plasticity model. One plate simulation excited by the TNO mine blast model verifies that the non-linear elastic and Johnson-Cook material model result in almost the same displacement. The adjoint problem for a general continuum with elastic material model is derived. The same optimization algorithm is implemented for the continuum model using the calibrated non-linear elastic material model. The forward and adjoint problem are solved using the author’s transient FEM implementation which is verified using commercial software. From the benchmark tests it was verified that the displacement converged quite well however less compared to the linear problem studied earlier. The corresponding pressures behaved similar. It was concluded that the total force and centroid position of a localized load are not always in agreement for the benchmark and solved pressure. This research shows that the limitations of the inverse problem shed light on the limitations in the validation methods employed by many researchers in the field.","Mine blast; Inverse problem; Inverse analysis; Adjoint optimization; Adjoint problem; Transient Analyses; FEM; Kirchhoff Love plate; Non-linear; Non-linear FEM; Explicit","en","master thesis","","","","","","","","","","","","Aerospace Engineering","",""
"uuid:350f908e-0ad5-4c2d-961f-af4cc10d7d4e","http://resolver.tudelft.nl/uuid:350f908e-0ad5-4c2d-961f-af4cc10d7d4e","A 3D Glacial Isostatic Adjustment model for Northwestern Europe","van Casteren, Rosalie (TU Delft Aerospace Engineering)","van der Wal, W. (mentor); Delft University of Technology (degree granting institution)","2019","The Earth is subjected to 100,000 year cycles of glaciation and deglaciation. The deformations induced by glacial and oceanic loading and the continuous attempt at recovery of the isostatic equilibrium within the solid Earth, are referred to as Glacial Isostatic Adjustment (GIA). This process is ongoing still and yields a large contribution to present day surface deformation and sea level change in formerly glaciated areas. In order to accurately model GIA, the lateral viscosity variations within the interior of the Earth are accounted for (Kaufmann et al., 2000; Steffen et al., 2006; Wu and van der Wal, 2003). Additionally, an increased level of accuracy is obtained by adopting a combination of linear and non-linear viscoelasticity as demonstrated by Barnhoorn et al. (2011); Forno and Gasperini (2007); van der Wal et al. (2013);Wu and Wang (2008).
During the Last Glacial Maximum, the British-Irish and Fennoscandian Ice Sheets covered large parts of Northwestern Europe. The interior of the Earth in this area is known to consist of material of very heterogeneous tectonic origin (Artemieva et al., 2006). Additionally, research in this area is promoted by the availability of the independent regional ice model Bradley2018 (Bradley, personal communication), an RSL observation database for the Rhine-Meuse Delta (Hijma and Cohen, 2019), and a collection of GPS derived uplift rates throughout Europe (Teferle, personal communication).
At the Astrodynamics and Space Missions research group of Delft University of Technology, a 3D GIA FEM model has been developed to model GIA in Antarctica (Blank et al., 2017). This model follows the work by Wu (2004) and van der Wal et al. (2013), and is complemented with an iterative algorithm to solve the sea level equation in accordance with Kendall et al. (2005). This research aims to provide a single GIA model best suited for the prediction of GIA induced vertical surface deformation in Northwestern Europe, by adapting the existing model. In doing so, a better understanding of the interior of the Earth in Northwestern Europe can be achieved.
The response of the Earth is dictated by the composite rheology creep flow laws for olivine (Hirth and Kohlstedt, 2003). By varying the grain size as well as the water content of the mantle material, and by implementing a global temperature model of the Earth’s interior, four 3D composite rheology Earth models are obtained. The fifth Earth model considered is the radially symmetric VM5a viscosity profile developed by Peltier et al. (2015) in conjunction with the global ice model ICE-6G_C. The performance of all five Earth model configurations in combination with both the ICE-6G_C model and the Bradley2018 model is analysed in terms of relative sea level and uplift rates.
It is found that the Bradley2018 model is the preferred ice model for GIA modelling in Northwestern Europe. The ICE-6G_C model outperforms the Bradley2018 model at far-field RSL sites, which is attributed to its superior representation of global eustatic sea level rise. The 3D composite rheologies lead to improved fits to RSL observations for the majority of the investigated measurement sites compared to the 1D scenario. The dry 4 mm grain size rheology yields the best overall performance out of all rheological configurations considered. A preference towards wet rheology exists in regions of Sveco-Norwegian tectonic origin. The strongest rheology is preferred in the mid-west of Scotland. No definitive connection is found between the local tectonic origin and preferred rheology fromRSL simulations. It is believed that this analysis may benefit from the inclusion of laterally varying grain sizes and water content inferred from geophysical observations, as well as the extension of the variable space for the water content.
For both ice models, an improved fit to observed uplift rates can be obtained through the application of a 3D composite rheology. The GPS derived uplift rates can be reproduced best using the dry 10 mm grain size rheology in combination with the Bradley2018 ice history. This model is deemed to be best suited for simulation of GIA induced uplift rates in Northwestern Europe. The second-best performance in terms of uplift rate is found using the 1D Earth model. In Scandinavia the 4 mm dry rheology yields uplift rates equal to roughly half the observed uplift rates, while the uplift rates for the 10 mm and 4 mm wet rheologies are near-zero. In the far-field, where other surface deformation mechanisms may infer a larger deformation rate than GIA (Fokker et al., 2018), no model could reproduce the observed uplift rates.
The presence of a high viscosity anomaly beneath Eastern Fennoscandia is captured by the 3D rheologies and results in a shift of the centre of positive and negative uplift rates. As the spatial distribution of minima and maxima in both uplift rates and RSL change rates is sensitive to the inclusion of a 3D rheology, this should be accounted for in future regional sea level change and surface deformation projections.
could result in lower back pain. Goal: To create a finite element model of a spinal unit for investigating mechanical influences of the disc onto its adjacent vertebrae. Assessment was performed by examining bone adaptation as a result from simulated disc generation. Methods: A MATLAB script was written to assemble an input file of a parametric model to be used for finite element analyses in Abaqus/CAE. The model was validated with experimental data from literature. A bone adaptation algorithm was used to assess a change in bone material properties before and after simulating disc degeneration by adjusting disc material properties. Results: Finite element analyses showed how a load was transferred by the disc and how bone consequently adapted in response to simulated disc degeneration. The overall trabecular structure was observed to become softer, especially in the vertebral core, while the structure inferior to the anulus became relatively stiffer. Conclusions: Visualisation of bone adaptation after simulating disc degeneration supports the hypothesis that disrupted disc biomechanics indeed affect bone configuration in the adjacent vertebrae.","FEM; intervertebral disc; biomechanics; spine; vertebrae; bone adaptation","en","master thesis","","","","","","","","","","","","Mechanical Engineering","",""
"uuid:51e618ca-b570-4983-a732-844a34ea98be","http://resolver.tudelft.nl/uuid:51e618ca-b570-4983-a732-844a34ea98be","Damage to Masonry Houses due to a Riverine Dyke Breach: A hydraulic and structural approach","Teeuwen, Max (TU Delft Civil Engineering and Geosciences)","Jonkman, Bas (graduation committee); Molenaar, Wilfred (mentor); Hoogenboom, Pierre (mentor); Delft University of Technology (degree granting institution)","2019","The Netherlands has always been in close proximity to water, whether its rivers or the sea. This proximity to water and the need for land to settle and farm, led to vast amounts of land reclamation by constructing dykes along the water features to prevent flooding of the new earned land. This newly reclaimed land started to subside over the years, increasing the difference between the high water in the rivers and the low-lying land even more. With an expanding population, rising water levels and increasingly severe storms, the consequences of a future flood due to a riverine dyke breach are ever rising.
The aim of this thesis follows from these increasing consequences and is to determine the potential structural damage to a masonry house due to a dyke breach leading to a riverine flood.","masonry; dyke; bore; breach; DIANA; FEM; flood wave","en","master thesis","","","","","","","","","","","","Civil Engineering | Hydraulic Engineering","",""
"uuid:615f2151-bcae-4e78-a2cb-3f1891a28275","http://resolver.tudelft.nl/uuid:615f2151-bcae-4e78-a2cb-3f1891a28275","An Integrated Machine Learning and Finite Element Analysis Framework, Applied to Composite Substructures including Damage","Gulikers, Tom (TU Delft Aerospace Engineering)","Chen, B. Y. (mentor); Delft University of Technology (degree granting institution)","2018","Engineering fields such as aerospace rely heavily on the Finite Element Method (FEM) as a modelling tool. In combination with the scale and complexity of the structures typically involved here, computational cost remains a traditional issue. To perform FEM analyses of such structures efficiently nonetheless, engineers rely on techniques such as substructure homogenisation. Essentially, the advantages to using homogenised models are an easier division of labour, less model preparation time and a reduced computational time. Unfortunately, the classical approach to substructuring is either limited to linear elasticity as in the case of static condensation, or is still computationally expensive as non-linear FEA of detailed substructure models need to be performed each time a different loading is applied to the full structure. To improve the efficiency and/or accuracy of homogenised substructures, it would therefore be of interest to develop a methodology which allows to capture a complex structural response without constantly resorting to non-linear FEA. An emerging technology that may assist in improving the efficiency and accuracy of how homogenised substructures are modelled, is machine learning. While the fundamental principles of this field were developed in the 1940's, the ever-increasing accessibility and magnitude of computational power have resulted in a leap of popularity since the 1990's. Especially the (deep) Artificial Neural Network (ANN), a versatile machine learning framework, has proven to be a promising tool that can perform tasks ranging from image recognition to the failure analysis of composites. In the current master's thesis, a framework is developed that integrates ANN and FEM techniques as to establish a highly flexible approach to substructure homogenisation. More specifically, this framework allows to establish a homogenised representation of a substructure regardless of its structural complexity (e.g. inclusions or cut-outs) and material complexity (e.g. damage progression and failure). To achieve this, traditional techniques to approximate homogenised behaviour are replaced by a constitutive model that is captured in an ANN. The developed framework consists of three parts. Firstly, the data generator module creates, runs and post-processes a series of FEM simulations of a chosen substructure, based on a predetermined Design of Experiments. In this DoE, all independent parameters (e.g. applied loads) that influence the response to be modelled should be sufficiently varied. The second module trains an ANN based on the generated data. In doing so, it learns to predict the homogenised mechanical behaviour of the chosen substructure as a function of the independent parameters. The third module then integrates this trained ANN in the FEM software package Abaqus as a user material subroutine (UMAT). The substructure of choice is now homogenised and represented by a single element, which can be readily used together with traditional elements in a global model.
The described methodology was applied to two FEM models of increasing complexity. The first model was a biaxially loaded, 2D elasto-plastic high strength steel material without additional complexities. An initial ANN design was made based on this model and it turned out that a network with 2 Hidden Layers (HL) and 10 nodes per HL was ideal to capture the response. Furthermore, it was determined that the ANN converged after training for 1,500 epochs with the 'Nadam' scheme. The second model was a composite plate with an elliptical cut-out and Hashin damage, thus adding both structural and material complexities. This model was loaded in biaxial tension and in-plane shear. A 2-HL network was found to be the most suitable architecture with 60 and 40 nodes in each HL respectively. A training time of 10,000 epochs was required to reach convergence using the Nadam optimiser, which led to an excellent fit of the mechanical response. Moreover, several input and output vectors for the ANN were investigated. It was concluded that the best results are obtained if the input vector contains the previous and current stress and strain state as well as the strain increment, whereas the output is the predicted stress increment.","Composites; Homogenisation; Homogenization; Substructuring; Machine Learning; Neural Networks; Artificial Neural Networks; Structural Analysis; Structural Modelling; Finite Element Method; FEM; Finite Element Analysis; FEA; Damage","en","master thesis","","","","","","","","2018-12-20","","","","Aerospace Engineering","",""
"uuid:293a5061-ec16-44bb-80dc-d0d7adb3ff9c","http://resolver.tudelft.nl/uuid:293a5061-ec16-44bb-80dc-d0d7adb3ff9c","Behaviour of Suction Caisson subjected to Cyclic Loading in Tension","Sudhakaran, Kamaleshwar (TU Delft Civil Engineering and Geosciences)","Askarinejad, A. (mentor); Gavin, Kenneth (graduation committee); Lanzafame, R.C. (graduation committee); Galavi, Vahid (graduation committee); Delft University of Technology (degree granting institution)","2018","As countries around the world are in a race for clean energy, various renewable energy sources are harvested to meet the energy needs. In Western Europe, wind energy is the primary source of renewable energy. To meet the energy demand, higher capacity wind turbines are being installed in deeper waters. In deep waters, monopile foundations are ineffective due to its inability to withstand large overturning moments. Thus, multi-caisson foundations are preferred in deeper waters. Typically jacket or tripod foundations are preferred as multi-caisson foundation and these foundations are supported by either piles or suction caissons. Suction caissons are preferred due to the ease of installation and removal.Based on the literature, it was understood that various kinds of research are being undertaken throughout the world to better understand the performance of suction caisson foundations. Two main components of suction caisson are researched widely, first being the installation behaviour, and second being the behaviour of caisson during repeated cyclic loading. This thesis seeks to gain further insight on the installation behaviour of the suction caisson. For this purpose, a suction installation apparatus was designed to be used in centrifuge. Various installation characteristics such as flow rate, soil profile has been studied in this thesis and detailed analysis is provided. Extraction tests of caisson were also done at a slow rate to determine the drained tensile capacity, which was used for determining tensile amplitudes in cyclic loading tests.Tripod structures withstand load by ’push-pull’ system, where the windward caisson is pulled out of the soil due to the cyclic environmental loads. This movement is compensated by the push behaviour of the other two caissons. Thus, the tensile capacity ofcaissons plays an important role in the design of caissons in a tripod structure. Windward caisson of a tripod foundation was modelled in this thesis to study the behaviour of the caisson under cyclic loading in tension. Cyclic loading tests were done at 100g using the geo-centrifuge at Delft University of Technology. A series of tests was done for various cyclic loading characteristics such as the average load, frequency and soil profile. Settlement and stiffness response of the suction caisson were obtained for each scenario. A brief discussion of the results is made in this thesis report. Very high settlement was observed when one-way compressive load was applied on the caisson installed in layered sand. A test was also done to study the response of caisson to storm loading where very high tensile amplitudes were used. The results obtained from these tests show the complexity of the response under tensile loads. When the tensile amplitude was more than 50% of the tensile capacity of the caisson, significant uplift of the caisson was witnessed along with a significant reduction in the stiffness of the soil.Finally, Finite Element Modelling (FEM) was done using the geotechnical finite element software - Plaxis 2D to compare the cyclic loading results obtained from centrifuge modelling with FEM. It was observed that the initial settlement behaviour was captured well in plaxis. But after few cycles, no more accumulation of strain was witnessed in the centrifuge tests. However, plaxis failed to capture this behaviour and thus higher settlements were observed in FEM analysis.This thesis can be used as a basis for the design of tripod foundations for OWT using suction caissons. The results obtained from this thesis reinforces previous studies and adds confidence in understanding the tensile behaviour of suction caissons.","Suction caisson; Offshore Wind Energy; Sand layer; Cyclic loading; FEM","en","master thesis","","","","","","","","2020-12-31","","","","Geo-Engineering","",""
"uuid:213ce335-202a-4f74-88f2-737c853c42a0","http://resolver.tudelft.nl/uuid:213ce335-202a-4f74-88f2-737c853c42a0","Analysis of Single and Group Micropile Behavior: The Bearing Capacity of Single Pile and Pile Groups under Axial Tensile Loading using FEM","Feiz, Marziyeh (TU Delft Civil Engineering and Geosciences; TU Delft Geo-engineering)","Broere, W. (mentor); Brinkgreve, R.B.J. (mentor); Gavin, Kenneth (mentor); Hendriks, M.A.N. (mentor); Haasnoot, JK (mentor); Delft University of Technology (degree granting institution)","2018","This thesis investigates the behavior of single and group micro piles under axial tensile loading. Micro piles are small diameter piles consist of grout and steel rebar and they are capable of absorbing tensile loads. By constructing a group of piles the bearing capacity of each pile within a group is less compared to the single pile. The reason is due to the existence of group effect in the pile group which influences the bearing capacity. During the production of the piles for Amsterdam car parking project, load tests are performed to check whether the piles behave according as expected which can be considered as acceptance tests. However in this test, only individual piles are tested and not a pile group. CUR 236 design procedure states that the bearing capacity of a pile in a pile group is less than the bearing capacity of that pile when it is loaded not in a group. To take this effect into account for the acceptance test, an additional load is added to the test load. It turned out at the Amsterdam car parking project that piles failed the acceptance tests due to this additional load which is required to apply according to CUR 236 design guide. However this procedure is questionable because the pile is loaded into a much higher level than it will actually experience during its lifetime. Therefore an evaluation of the standards and the influence of group effects on micro pile behavior is needed. The initial plan of approach was to investigate the standards of other countries and compare them to Dutch standards to find the eventual existing gap and propose an improvement method which did not succeed. The reason was that the standards of other countries were all written in their national language and therefore it was not possible to study them. Seeking for the research on tension pile group behavior did not help so much because many researchers believe that including a realistic group effect in the design is not an easy task and there was no clear conclusion on micro pile group influence. The direction of approach is then changed towards the numerical modelling and based on it the influence of group effects on micro pile behavior is presented. First a single micro pile is modelled with Finite Element Method in Plaxis. The single pile is finally modelled in plane strain by using Embedded Beam Row element. Model parameters and properties are defined based on Amsterdam case study. The load-displacement behavior of the single pile model was comparable with the one from Amsterdam field failure test and is therefore validated based on field failure test data. After development of single pile model, the model for pile groups is made. This group model is made to represent the practical situation in a building pit for Amsterdam case study. Three models for the pile group have been made which differ in pile spacing and the impact of this parameter on the capacity per micro pile is investigated. The different used pile spacings are 5D, 10D and 15D which are equal to 1 meter, 2 meters and 3 meters. Also for each pile spacing, the dominant failure mechanism is determined. According to the results it was concluded that for 5D and 10D pile spacing, the failure mechanism is based on soil plug pull-out while for 15D, it is according to slip failure. By validation of the pile group model, an improvement for the space between the piles within a pile group can be proposed as 10D where the soil plug pull-out is dominant failure mechanism. It is recommended to validate the pile group model based on full-scale failure test on pile groups or by small-scale test using Geo-centrifuge models. Also by monitoring, a real data base of the group behavior can be obtained. Comparing the monitoring data to the design values based on CUR 236 could give an idea how well the design guide is formulated.","Micropile; Plaxis; FEM; Analysis; bearing capacity; Single pile; Pile group; Axial tensile loading","en","master thesis","","","","","","","","","","","","Geo-Engineering","",""
"uuid:0314e592-ffa2-4f1d-bc31-5da7011805b7","http://resolver.tudelft.nl/uuid:0314e592-ffa2-4f1d-bc31-5da7011805b7","Implementation of a Fluid-Structure Interaction Solver for a Spinnaker Sail","Ramolini, Anna (TU Delft Aerospace Engineering)","van Zuijlen, Alexander (mentor); van Oudheusden, Bas (graduation committee); Schmehl, Roland (graduation committee); Folkersma, Mikko (graduation committee); Delft University of Technology (degree granting institution)","2018","The design of sails has always been done experimentally, and only recently simulations are starting to be used in the design process. This thesis is a first attempt in creating a solver that couples CFD and FEM in order to compute the deformed sail shape (flying shape) and the thrust it can provide. Such solvers already exist but are not available to the public, or if they are they come with a very high license price. The complexity of the problem is both in the flow, which is fully turbulent and detached, and in the structure, which is deformable and free to move in all directions. Moreover, the coupling of the solvers has to be performed in a way that minimizes loss of information and accuracy.
First the CFD simulations have been run and validated with two softwares, OpenFOAM and FINE/Open. The results were very satisfying for FINE/Open, while quite poor for OpenFOAM. Consequently, the FEM solver has been successfully validated for some cases of which the analytical solution is known, due to lack of reference data for this specific case.
Finally, the interpolation techniques have been implemented in Matlab and the fluid structure interaction solver has been run. The solver has been validated on a given testcase with satisfying results; however there is still room for improvement in terms of run times and automatization of the solver. From the results it can be argued that the design and flying shape of the sail are quite different and provide different thrusts. That is an indication of the significance of this type of analysis in the sail design process.","Fluid Structure Interaction; CFD; FEM; Sailing; Spinnaker","en","master thesis","","","","","","","","","","","","Aerospace Engineering","",""
"uuid:dca3dbc8-2b74-4904-ba89-084cdb97ff64","http://resolver.tudelft.nl/uuid:dca3dbc8-2b74-4904-ba89-084cdb97ff64","Glass Flood Defences: A theoretical and practical assessment of the impact resistance of Glass Flood Defences to floating debris","van der Meer, Roos (TU Delft Civil Engineering and Geosciences)","Nijsse, R. (mentor); Veer, F.A. (mentor); Molenaar, W.F. (mentor); Staphorsius, John (mentor); Lenting, Fred (mentor); Delft University of Technology (degree granting institution)","2018","In the far south of the Netherlands, the erratic river Meuse flows through the landscape. It recently flooded twice in the 1990s, causing much economical damage. Emergency measures, such as a demountable flood wall, were taken to prevent future flooding. And while this solution was to the liking of the inhabitants, the update in the flood safety standard called for a more permanent structure. In the search for an alternative and permanent solution, a glass flood wall was suggested.
Nowadays there are not many examples of glass used in a flood defence in Dutch practice, and certainly not as part of a primary flood defence. It can be classified as an innovation, from which little is known from a structural safety perspective. Glass is used globally to retain water in numerous applications such as aquaria, under water glazing, glass bottom boats, etc; therefore water pressure is not seen as a high risk to the glass. What happens when floating debris hits the glass structure? Impact on glass can result in immediate failure, where the water retaining function could be lost. This thesis aims to answer this question, by theory and later on by impact experiments in a dry setting.
A literature study was performed to gain insight into the areas of interest that needed to be studied. This theory in combination with a review of the structures led to the critical cross sections of the respective structures. These cross sections were then modelled with conventional design methods (Blum and D-Sheet Piling). The Blum method determined the individual contributions of several aspects (loads, water, soil) to the horizontal stress distribution along the combined sheet pile wall and calculated the reaction forces using a set of boundary conditions. Within D-Sheet Piling the relieving platform was modelled by removing it, the loads that acted on it, and the soil that rested on it. The last method that was applied was a FEM software (Plaxis 2D). The FEM models were validated in three steps: First, by comparing their results to that of the conventional methods, it was found that the results of the conventional methods were within ca. 30% of the FEM results. Second, by comparing the results to actual field data, here the results showed both deviation and similarities, these deviations could however be explained. Lastly, by critically assessing the models to ensure that certain aspects were incorporated into the models correctly, this resulted in uncertainty about drained or undrained soil conditions for the thicker clay layers. The main function of both quay structures was the storage of certain goods, for that reason the only aspect that was not constant in the test loading set up was the magnitude of the primary surcharge. Both geotechnical and structural failure were taken into consideration for the quay structures.
The results of the FEM models showed that neither of the structures had failed at their design loading conditions. For the Amazonehaven it was found that the magnitude of the primary surcharge at the first failure of the model was relatively close to that of the design loading conditions, it was incited by the exceedance of the geotechnical bearing capacity of the M.V.-piles. The first failure of the SIF model occurred at a surcharge that was more than 4 times the magnitude of the design loading conditions, it was incited by the exceedance of the normal stress capacity of the M.V.-piles.","FEM; combined sheet pile wall; quay structures; relieving platform; M.V.-piles; Blum; D-Sheet Piling; Finite Element Method; Plaxis 2D; load capacity; Maasvlakte","en","master thesis","","","","","","","","","","","","Civil Engineering | Hydraulic Structures","","51.9595317, 3.985464"
"uuid:277f7b38-3eb2-455d-9d4f-c5afdf349b06","http://resolver.tudelft.nl/uuid:277f7b38-3eb2-455d-9d4f-c5afdf349b06","An investigation of finite element model updating of the Pioneering Spirit","Schout, Arthur (TU Delft Mechanical, Maritime and Materials Engineering)","Kaminski, M.L. (mentor); Bos, R.W. (mentor); van Woerkom, P.T.L.M. (mentor); van der Horst, Tim (mentor); Rodenburg, Freek (mentor); Delft University of Technology (degree granting institution)","2018","Correctly predicting the structural behavior of the Pioneering Spirit is vital for ensuring the structural integrity of the ship and the cargo. A detailed finite element model is used to predict the structural behavior of the Pioneering Spirit. The finite element method is based on fundamental principles in solid mechanics. However, when using finite element models considerable differences between the predicted and observed behavior of a structure can occur, even when best industry practices are used to create such models. Because of these
differences there is a need to validate the detailed finite element model of the Pioneering
Spirit.
Finite element model updating is a method that can validate finite element models. In this method the discrepancy between the measured behavior and the observed behavior is minimized by modifying model assumptions and parameters. Currently a number of sensors is installed on the Pioneering Spirit, which can be used to find the measured behavior. Whether or not the measured behavior is detailed enough to be used in the validation of the finite element model is the subject of this research. To investigate this a simplified finite element model of the Pioneering Spirit was created using beam elements, this model provides the predicted behavior. Then sensitivity-based finite element model updating was implemented and applied to the beam model.
Simulated
measurements were used to show that the beam model can be updated using the current sensor setup. When actual measurements were used to update the beam model it was found that the beam model does not correlate with the measured behavior, making it impossible to update the beam model in a meaningful way.
The detailed model does correlate with measured behavior. By assuming that the method will work similarly for the detailed model as it did for the beam model, it can be concluded that the detailed model can be validated using the current sensor setup for a static case. For a dynamic case this is not possible.","FEMU; Finite element model updating; FEM","en","master thesis","","","","","","","","2023-08-27","","","","","",""
"uuid:f72a6568-d033-4803-8477-3c4727c82de0","http://resolver.tudelft.nl/uuid:f72a6568-d033-4803-8477-3c4727c82de0","Structural Wave Propagation in Unconsolidated Granulates","Evans, Louis (TU Delft Civil Engineering & Geosciences)","Van Damme, Bart (mentor); Manen, Dirk Jan Van (mentor); Drijkoningen, G.G. (graduation committee); Delft University of Technology (degree granting institution); ETH Zürich (degree granting institution); Rheinisch-Westfälische Technische Hochschule (degree granting institution)","2018","Unconsolidated granulates exhibit complex, nonlinear behaviour when subjected to dynamic forces. The presence of granular contacts gives this type of material a relatively low stiffness and provides hysteretic energy losses. These features make unconsolidated granulates suitable for railway ballast as it provides dissipation of vibrational energy from passing trains which is important to minimise vibrational disturbance. However, simulating the response of the railway superstructure under dynamic loads becomes difficult due to then onlinearity of the ballast. In order to develop better prediction tools, the elastic behaviour of unconsolidated rocks is first investigated experimentally by quasi-static and dynamic stress-strain experiments yielding the Young's modulus, nonlinear resonance shift and analysis of harmonic generation. In addition, the transmission of structural waves through granulates is investigated by assessing the transfer function for different thicknesses of granulates, different
particle sizes and different materials with varying viscous damping. Three granulates are used, small-scale ballast, a gravel, and two sizes of uniform steel spheres. All three materials exhibit a combination of classical and hysteretic nonlinearity where the strain depends on the stress amplitude and history.
A completely new finite element approach is taken to model the hysteretic nonlinearity, based on an existing phenomenological static model. Multiple spring-slider elements with gaps are used, as opposed to implementing a homogenised material model. It is shown that only 50 elements can reproduce the hysteretic nature of the material, which is a significant advantage to a traditional material model requiring the discretisation of the entire ballast volume. Each spring-slider element is parameterised by two springs constants, a yield force and an initial gap. A distribution of these parameters across the 50 elements is found that reproduces the quasi-static stress cycles acquired experimentally. In addition, a parametric study of the model parameters during dynamic excitation reveals that key indicators of nonlinearity can be simulated. The finite element simulations prove that using a set of spring-slider elements
to model the behaviour of unconsolidated granulates is viable method. With experimental tests performed on true ballast and further work on the finite element model to understand optimal parameter distributions, a more accurate and efficient railway superstructure model can be produced.","geophysics; FEM; granulates","en","master thesis","","","","","","","","","","","","Applied Geophysics | IDEA League","",""
"uuid:86d469f3-0c44-4f45-9396-ec296d87031f","http://resolver.tudelft.nl/uuid:86d469f3-0c44-4f45-9396-ec296d87031f","A Multiphysics Numerical Framework for Epoxy Resins: Investigating Hygrothermal Ageing in Laminated Composites","van Leeuwen, Robbie (TU Delft Civil Engineering and Geosciences)","van der Meer, F.P. (mentor); Rocha, I.B.C.M. (mentor); Sluys, Lambertus J. (mentor); Bessa, M.A. (mentor); Delft University of Technology (degree granting institution)","2018","Epoxy resins are increasingly used in critical structural components with widespread applications in the transportation, construction and energy industries. The wind energy sector is one of the fastest growing commercial markets for epoxy resins, meaning that the structural behaviour of epoxy resins is becoming a key area of research, especially regarding its application to wind turbines. Wind turbines, particularly those in off-shore installations, are subject to a wide range of environmental conditions, most notably large variations in humidity and temperature. Both moisture and increased temperatures have been observed to have a significant impact on the stiffness and strength of epoxy resins. These environment effects, coupled with complex time dependent mechanical behaviour, means that the accurate prediction of the structural performance of epoxy resins has not yet been fully described.
This thesis presents a multiphysics framework for the simulation of hygrothermal ageing in epoxy resins. The constitutive model formulated in this thesis consists of a non-linear viscoelastic and viscoplastic mechanical model, physically coupled with a Fourier heat conduction model and a Fickian diffusion model. Degradation based on a glass transition surface is implemented to describe the multi-state behaviour of epoxy resins. To justify the model assumptions, DMA and creep tests are performed on epoxy resin specimens and their temperature dependent mechanical behaviour is established. A number of numerical benchmark tests and case studies are performed using a finite element implementation of the numerical framework. It is shown that the multiphysics framework can capture the characteristic mechanical and hygrothermal ageing behaviour exhibited by epoxy resins. Recommendations are provided for further development of the numerical model and calibration of the material properties. In a secondary study, a mesh sensitivity analysis is performed on an existing viscoelasitc-viscoplastic-damage model and recommendations for an improved formulation are provided.","Multiphysics; Viscoelasticity; Viscoplasticity; Epoxy Resin; FEM; Hygrothermal Ageing; Continuum Damage; Glass Transition","en","master thesis","","","","","","","","","","","","Civil Engineering | Structural Engineering","",""
"uuid:903db796-7f25-4ce3-b5ce-c92fd207c883","http://resolver.tudelft.nl/uuid:903db796-7f25-4ce3-b5ce-c92fd207c883","Development of a Reliable and Efficient 3D Calculation Model of a High-Rise Building Under Seismic Loading","Mussche, Henk (TU Delft Civil Engineering and Geosciences)","Rots, Jan (graduation committee); Hendriks, Max (graduation committee); Terwel, Karel (graduation committee); Delft University of Technology (degree granting institution)","2018","This thesis research focusses on the development of a reliable and efficient 3D calculation model of an existing high-rise, reinforced concrete building in the Groningen area, in order to analyse the dynamic behaviour of the existing and subsequently retrofitted main bearing structure of this high-rise building. The assessment of the existing building is performed through a Non-Linear Time History analysis in Simulia Abaqus, in which cracking of concrete and yielding of reinforcement is taken into account. Multiple NLTH analyses are performed for optimisation of the 3D model in order to obtain correct results with a minimum amount of calculation costs. This optimisation process results in a clear understanding of the dynamic behaviour of the building and the main sensitivities of the model.
The 3D model is verified by means of a simplified 1D beam type model, developed and analysed with the software package Matlab. This 1D model consists of three elements, corresponding to the three main structural parts of the building. Next to this, a ‘modal response spectrum analysis’ is performed for verification of the 3D model results.
The seismic assessment of the building is performed according to the Near Collapse criterion of the NPR. The results show that the building meets this criterion, based on one record of the NPR. Since at least seven various records should be applied, it is possible that the building does not meet the Near Collapse criterion for one of these records. Also from a structural point of view, it is interesting to develop and analyse strengthening possibilities for this specific building. therefore, three strengthening proposals are developed and initially analysed with the 1D model in Matlab.","Seismic; Abaqus; 3D Model; Reliable; Efficient; 1D Model; Simulia; Matlab; Groningen; Response; Response Spectrum; Accelerogram; NPR; Near Collapse; Seismic loading; Modal Response Spectrum Analysis; Verification; Base Shear; Existing; High-Rise; Reinforced Concrete; Earthquake; Earthquake analysis; Human induced; Gas extraction; dynamic behaviour; strengthening; strengthening measures; Zonneveld ingenieurs; TU Delft; Harm Hoorn; Jan Rots; Max Hendriks; NPR9998; Eurocode 8; Concrete Damaged Plasticity; NLTH; NLTH Analysis; Euler Bernoulli; Plastic analysis; Non-linear; Awesome; Optimisation; Finite Element Method; FEM; Analysis; Henk Mussche","en","master thesis","","","","","","","","","","","","Civil Engineering","",""
"uuid:4614239a-961c-4cee-bbbf-87431119e2ca","http://resolver.tudelft.nl/uuid:4614239a-961c-4cee-bbbf-87431119e2ca","An improved 3D embedded beam element with explicit interaction surface: A study into the improvement of a numerical modelling technique that enables simplified modelling of pile foundations","Smulders, Carla (TU Delft Civil Engineering and Geosciences; TU Delft Materials- Mechanics- Management & Design)","Sluijs, Bert (mentor); Brinkgreve, Ronald (graduation committee); Houben, Lambert (graduation committee); Hosseini, S (graduation committee); Delft University of Technology (degree granting institution)","2018","Numerical modelling of pile foundations can be done in several ways. In commercial finite element packages two main options are available; using volume elements with interface elements between the pile and soil domains and the embedded beam approach. The embedded beam element was first proposed by Sadek and Shahrour (2004) and considers a beam element that can cross a solid element at any arbitrary location with any arbitrary inclination. This has several advantages to the volume pile method, such as the need for fewer elements and the mesh uncoupling of the pile and soil, which make this method much more efficient and leads to a significant reduction in calculation time. However, the embedded beam element also deals with a number of limitations and drawbacks. This research focuses on overcoming the mesh sensitivity, which is caused by the stress singularity that is introduced in the soil by the beam element. Also, the inability to take into account the pile surface will be resolved, aiming to improve the lateral pile-soil interaction.
The idea of Turello et al. (2016) of an embedded beam element with explicit interaction surface is extended and generalised leading to a new embedded beam formulation. In the proposed model the beam displacements at the interaction surface are obtained by a mapping scheme that takes into account Timoshenko beam theory and which is generalised to model inclined piles as well. A constitutive equation that describes the relation between the interface stresses and relative displacements between the pile and soil is defined along the shaft and at the foot of the pile. Along the shaft of the pile a shear stress limit is defined based on the Mohr-Coulomb failure criterion in order to incorporate plasticity in lateral direction. Furthermore, a more practical and efficient assembly procedure is proposed.
Validation of the proposed method proofs that the proposed model leads to a significant mesh sensitivity reduction in case of axially loaded models compared to the existing implementation. The overall response of laterally loaded piles is improved considerably as well. However, the proposed method is still unable to capture lateral interface behaviour in order to model soil slippage around the pile. Furthermore, it is recommended to formulate a generally applicable foot interface stiffness and to optimise the code in order to reduce the computation time. The description of the interaction surface opens up many new possibilities for future research, such as modelling the true cross-section shape.
Increasing the thickness can bring more defects, like voids.
This master thesis focuses on the multi-scale voids prediction and their mechanical effect simulation of thick composite laminates manufacturing by \ac{RTM}.
It could be potentially used in safe design of thick composite components.
The main objective of the thesis work is to analyze the effect of multi-scale voids caused by the filling process on mechanical properties of thick composite laminates.
First is using PAM-RTM to simulate the locations of voids and their percentage.
Then, the material properties of each \ac{MVE} with different micro and macro voids are evaluated by Digimat at micro and meso scales.
After that, the macro-scale material properties of the thick laminates are simulated in ABAQUS.
%This simulation process is reliable after verifying with the results of a literature.
The simulation processes are verified by using the parameters from the literature and then comparing with the published results.
The simulation from PAM-RTM indicates the average void percentage of the whole laminate reduces with the increasing injection pressure or permeabilities.
The total void volume increases with an increasing laminate thickness but the average void volume does not change with the changing thickness.
The result of this thesis suggests that the effect of multi-scale voids on material properties (i.e., Young's modulus, Poisson's ratio, and Shear modulus) does not change due to an increasing thickness.
The writing presents the actions taken in order to achieve the objective of the research successfully.","Thick compoiste; RTM; voids; FEM","en","master thesis","","","","","","","","","","","","Aerospace Engineering","",""
"uuid:d1b77685-5b95-4991-bd41-7ce4cdd01605","http://resolver.tudelft.nl/uuid:d1b77685-5b95-4991-bd41-7ce4cdd01605","Parametric reduced order modeling of structural models by manifold interpolation techniques: Application on a jacket foundation of an offshore wind turbine","Speet, Jeroen (TU Delft Mechanical, Maritime and Materials Engineering; TU Delft Precision and Microsystems Engineering)","Langelaar, Matthijs (mentor); Delft University of Technology (degree granting institution)","2017","An important aspect of structural design is to obtain adequate knowledge and prediction of the structure’s dynamic behavior. Wind Turbine Manufacturers (WTMs) design their wind turbines for a lifetime of typically 25 years during which the structure has to withstand a large variety of loads, induced by wind- and wave conditions. To obtain a suitable design, numerous load calculations have to be performed for each design. A versatile approach is to use Reduced Order Models (ROMs) to restrict the computational effort that comes with
these numerical techniques, which are also used in other industries (automotive, aerospace, etc. ). However, during the design process, structural changes are often applied. Since ROMs lack robustness with respect to these variations, this approach calls for a reconstruction of the ROM each time the initial model is changed, and the intensive calculation procedure has to be repeated afterwards.
With the motivation to improve the limitations of ROMs and how they are used in engineering practice, a literature survey was performed on relevant Parametric Reduced Order Model (PROM) methodologies. Based on appropriate criteria in the context of a WTM’s design cycle, a methodology was selected that interpolates between the precalculated ROMs and their corresponding Reduced Order Basis (ROB). To preserve the properties these matrices typically have (i.e. symmetric-positive definiteness, orthogonality, etc.), the interpolation is
performed on a matrix tangent manifold. For the three most commonly used reduction techniques, being Modal Truncation (MT), Guyan Reduction (GR) and Craig-Bampton (CB), the method is applied on an offshore jacket foundation, designed to support a 5 MW wind turbine, and subjected to realistic design
changes in a local section of the structure. In the presented configuration, the interpolation approach is suitable to update the GR basis with high accuracy. The technique also shows good performance while updating the MT and CB basis, but challenges are found when the structure preserves symmetry properties because of close and multiple eigenvalues of the modes. Furthermore, promising results were shown while updating the ROM matrices, but influence of off-diagonal elements has been observed.","ROM; PROM; reduction; reduced; parametric; FEM; structural; dynamics; eigenmode","en","master thesis","","","","","","","","","","","","Mechanical Engineering | Precision and Microsystems Engineering","",""
"uuid:29f2aaca-239b-47c5-8323-4d1ed22fd11c","http://resolver.tudelft.nl/uuid:29f2aaca-239b-47c5-8323-4d1ed22fd11c","Constraining Glacial Isostatic Adjustment with Horizontal GPS Velocities in Antarctica","Hermans, Tim (TU Delft Aerospace Engineering; TU Delft Space Engineering)","van der Wal, W. (mentor); Delft University of Technology (degree granting institution)","2017","Glacial isostatic adjustment is the viscoelastic response of the Earth to ice and ocean loads. In forward models of glacial isostatic adjustment, mantle viscosity is often assumed to be laterally homogeneous. However, a lateral transition in shear wave velocities suggests a sharp transition in viscosity between West and East Antarctica. Along this transition, horizontal GPS velocities of
ANET/POLENETWest of the Ross Sea Embayment point towards the ice load rather than away from it. It is unclear why, as the dependency of horizontal velocities on viscosity is not well understood. In this thesis, this dependency is clarified, and it is investigated with a 3D finite-element model if the horizontal GPS velocities can be used to constrain the viscosity transition.
It was found that horizontal velocities point away from the ice load for viscosities of 1020 Pa s and lower, whereas for 1021 Pa s and higher their direction is reversed. The results in this thesis show that the GPS measurements at the Ross Sea Embayment likely require a lateral viscosity transition.
Preferred viscosities in the upper mantle are found to lay between 1018 and 1019 Pa s at the West Antarctic side of the transition, and between 1021 and 1022 Pa s at the East Antarctic side. The results demonstrate that horizontal GPS velocities can be used to constrain lateral variations in rheology. As more studies will start to use 3DEarth models, horizontal GPS velocities should be used as one of the
primary constraints of glacial isostatic adjustment, since their direction can be reversed depending on mantle viscosity.","Glacial Isostatic Adjustment; GPS; Horizontal; Antarctica; FEM; 3D; Viscosity; Ross Sea Embayment","en","master thesis","","","","","","","","2018-12-31","","","","Aerospace Engineering | Astrodynamics & Space Missions","",""
"uuid:2a4f3015-0fb5-4342-96c8-eb6fd1d92646","http://resolver.tudelft.nl/uuid:2a4f3015-0fb5-4342-96c8-eb6fd1d92646","A NURBS-enhanced Discontinuity-Enriched Finite Element Method","De Lazzari, Elena (TU Delft Mechanical, Maritime and Materials Engineering)","Aragon, A.M. (mentor); van Keulen, A. (graduation committee); van der Meer, F.P. (graduation committee); Turteltaub, S.R. (graduation committee); Delft University of Technology (degree granting institution)","2017","Generalized finite element methods have proved a great potential in the mesh-independent modeling of both weak and strong discontinuities, such as the ones encountered when treating materials with inclusions or cracks. By removing the constraint of a conforming mesh, more freedom is offered to modeling exact geometries by means of splines. However, very few studies have been published which combine Non-Uniform Rational B-Splines (NURBS) to interface-enriched methods, addressing uniquely weak discontinuities. Therefore, the aim of this thesis is to propose a NURBS-based enhancement to the Discontinuity-Enriched Finite Element Method (DE-FEM) in two dimensions and to discuss the potential of its application. The main advantage of this method is the possibility to study problems that present discontinuities with arbitrary smooth shapes, while maintaining exact geometries throughout the analysis: in this way, the equivalence between design and computational geometry is preserved. To this purpose, a suitable NURBS-based analysis technique is selected and implemented within the framework offered by the group's finite element library, Hybrida.
The capabilities of the NURBS-enhanced DE-FEM to solve several weakly discontinuous problems are assessed for composites of different complexities. Furthermore, a novel study is presented which extends this technique to the treatment of strong discontinuities, in the context of fracture mechanics. The accuracy, convergence properties and numerical efficiency of the proposed method are investigated, in particular in comparison with the standard DE-FEM. Based on these observations, further insights are provided into the convenience and the limitations of adopting NURBS enhancements within the DE-FEM formulation. Lastly, some recommendations about possible directions of improvement are provided.","FEM; NURBS; structural mechanics; discontinuities; composites; fracture mechanics","en","master thesis","","","","","","","","","","","","Mechanical Engineering","",""
"uuid:31539dc5-f695-4bba-b277-037a800df3a6","http://resolver.tudelft.nl/uuid:31539dc5-f695-4bba-b277-037a800df3a6","Evaluation of the Fatigue Resistance of Offshore Jacket Joints by Numerical Approaches","Mendoza Espinosa, Jorge (TU Delft Mechanical, Maritime and Materials Engineering)","Metrikine, A. (mentor); Muskulus, Michael (mentor); Vossbeck, Marc (mentor); Lourens, E. (mentor); Delft University of Technology (degree granting institution); Norwegian University of Science and Technology (NTNU) (degree granting institution)","2017","Jacket support structures are a preferred solution for offshore wind turbines in deeper waters. Extensive knowledge exists in relation to its construction technique as well as its crucial components, but due to considerable cost pressure, continued optimization is essential for the future competitiveness of the concept in the offshore wind business. Their joints along with their complex welds are of special interest in terms of cost reduction. The design of tubular joints is generally driven by fatigue resistance. Due to the size, complexity and cost of these joints, this is assessed by using detailed FE models.
Several aspects that have an impact on the results of the models are found to require further research and are investigated within this project: (1) influence of using solid versus shell elements in the modelling of the joint members; (2) degree of accuracy of the Efthymiou equations; (3) influence of the carry-over effect in multiplanar KK-joints; (4) differences in the fatigue life predictions between the hot-spot and the effective notch stress methods.
Guidelines recommend the use of both solid and shell theories for the definition of the FE models used in the hot-spot fatigue assessment. Both options are compared in terms of accuracy of the results and computational time. Generally speaking, significant differences are found between both models. The background of the differences is studied.
The employment of the Efthymiou formulae is common in practice. These equations provide the SCF at the locations around the weld where they are found to be maximum. The output of this approach is compared with the results of numerical models. The validity of its use is quantified.
Offshore wind jacket joints are mainly multiplanar KK-joints. Loading in the braces of one face of the jacket may yield significant carry-over effects on the out-of-plane braces connected to the same joint. A parametric comparison is carried out to study the accuracy of modelling the joint as a planar K-joint. In general, it is found that the carry-over effect cannot be neglected and the assumption is not accurate.
The fatigue assessment of tubular joints by means of the hot-spot method is subjected to several assumptions that limit the optimization of the members. The notch concept is a more realistic method that is presented as an alternative. However, this method is not widely used in engineering practice due to the difficulties in building the numerical model and the high computational requisites. An algorithm to carry out the effective notch stress assessment, based on the sub-modelling technique, is proposed. A comparison of the fatigue life prediction, between the hot-spot and the effective notch methods, is presented. The latter method is found to predict a higher fatigue life for many of the situations tested. Furthermore, since this method allows for a more detailed modelling, the weld profile can also be designed in order to optimize the fatigue resistance. The weld slope is found to have a significant impact on the results.","Offshore; Wind energy; Jacket; Fatigue; FEM; Hot-spot; Notch","en","master thesis","","","","","","","","","","","","European Wind Energy Masters (EWEM)","",""
"uuid:c54afaaf-1bb2-49d8-bcab-a01fd061c5b8","http://resolver.tudelft.nl/uuid:c54afaaf-1bb2-49d8-bcab-a01fd061c5b8","Analysis of a reinforcement detail in a bar reinforced soil-mix wall: An experimental and numerical approach","Dik, Inge (TU Delft Civil Engineering and Geosciences; TU Delft Engineering Structures)","Hordijk, D.A. (mentor); Braam, C.R. (mentor); Hoogenboom, P.C.J. (mentor); Meijdam, Jeroen (mentor); Van Bezooijen, Joost (mentor); Delft University of Technology (degree granting institution)","2017","Soil-mix walls are subsoil walls, which are constructed by in situ mixing of soil
with cement and water. The technique was initially used as a ground improvement
technique and is now being developed as construction method for walls
with a structural purpose. Currently these walls are reinforced with large steel
profiles, which requires a large quantity of steel. Replacing the profiles with
bar reinforcement might lead to a decrease in required material quantity and
thus a reduction of material costs.
There are multiple aspects which influence the possibilities and limitations
of bar reinforced soil-mix walls. These include predictability of the material
quality, durability and cooperation between soil-mix and the reinforcement.
The aim of this project was to contribute to this research by analysing one
of the influential aspects. The specific goal of this research project was to
analyse the capacity of a reinforcement detail within a soil-mix wall and define
the governing failure mechanism. The research combined an experimental and
numerical approach to the subject.
The critical detail was chosen based on the Huybrechts et al. (2016), Ganne
et al. (2010), Dörendahl et al. (2004) and contact with soil-mix experts. To
model this detail in a finite element model, in 2D and 3D, material parameters
were derived from Denies et al. (2012a), Denies et al. (2014), Denies et al.
(2015a) and performed physical tests. The 2D models represented the most
critical sections of the detail based on the theoretical stress distribution. The
geometrical parameters of the reinforcement design were varified in the models
to provide insight in the influence of the design on the capacity.
The model results were used to define an preliminary set of design guidelines
for the reinforcement cage, related to the depth of the wall. Since only
the capacity of the detail is considered, these guidelines are not suficient for
a complete design of a bar reinforced soil-mix wall and can only serve as an
initial indication.
In conclusion, the reinforcement detail is most sensitive to failure due to vertical
splitting and has suficient capacity for acceptable wall depths. As stated
before there are multiple aspects relevant to the feasibility of bar reinforced
soil-mix walls. The predictability of the material quality, the bond with the
reinforcement and the durability of the soil-mix strongly influence the final
capacity and behaviour of the wall. Therefore it is important to perform further
research on these, and other, aspects to conclude on the total structural
integrity of an entire bar reinforced soil-mix wall.","Soil-mix; Reinforcement; FEM","en","master thesis","","","","","","","","","","","","Civil Engineering | Structural Engineering | Concrete Structures","",""
"uuid:5ebdd5b3-7217-41c3-9152-e433e8108a6f","http://resolver.tudelft.nl/uuid:5ebdd5b3-7217-41c3-9152-e433e8108a6f","Determination of planar crack front geometry based on near-crack surface displacement field obtained from simulated digital image correlation measurements","Slagmolen, Mark (TU Delft Mechanical, Maritime and Materials Engineering)","Kaminski, Mirek (mentor); den Besten, Henk (mentor); Janssen, Michael (graduation committee); Synetos, Georgios (mentor); Delft University of Technology (degree granting institution)","2017","Digital image correlation (DIC) is a surface measurement technique that can be applied whilst performing experimental tests. At Delft University of Technology, a fatigue test is to be conducted and DIC will be used to measure surface displacements around the developing crack. These surface displacements are directly related to the crack geometry parameters. These crack geometry parameters can be found numerically via a minimisation algorithm where the difference between the surface displacements measured via DIC and surface displacement found via finite element analysis is minimised. Aim of present study is to perform a preliminary analysis before the experiment is performed in order to assess what is to be expected. It is looked into whether the out-of-plane surface displacement information that has to be taken into account since this influences the DIC hardware to be used during the experiment. Secondly, it has been looked into the noise as consequence of using DIC, and the influence of the noise on the minimisation to be performed. Finally it has been looked at the influence of the DIC noise on the accuracy of the minimisation. Since present study describes a preliminary analysis, simulated DIC surface measurements have been used. A finite element (FE) model of the specimen to be tested has been used in order to perform the study for uniaxial tension only. An algorithm using the FE model to perform the minimisation has been build and tested for simple 2D cases and a simpler 3D first before performing the 3D analysis with geometry considered. The simulated DIC noise taken is 0%, 1%, 2%, 5% and 10% of the mean measured displacement field in order investigate the influence of the noise on the minimisation. Present study showed that neglecting the out-of-plane displacement information introduces an error of around 2x10^-2 millimetres for 1000 MPa uniaxial tension applied. It is assumed that the algorithm used finds the same crack geometry parameters as have been used to construct the simulated DIC surface displacement field in case no noise is applied. It is found that this is not the case in present study. Reason is the algorithm converging to local minima located very close to the global minimum. Present study showed the location of the global minimum becoming less defined when noise applied is increased, i.e. the area in which the global minimum is located becomes larger. Present study shows that the algorithm can convergence towards the target crack geometry parameters. Accuracy of the algorithm as function of the noise has been checked for the full displacement field and the displacement field where out-of-plane information is neglected. Confidence intervals increase for increasing DIC noise, as can be expected. Due to the local minima the algorithm might converge to, it is not possible to draw conclusions on whether the full displacement field should be taken into account in order to have the accuracy required. Therefore, it is strongly recommended to change the algorithm to take extra information into account to make the algorithm converge to the global minimum. Furthermore, it is recommended to improve the numerical model, in order to improve the speed of the algorithm.","simulated DIC; FEM; Minimisation","en","master thesis","","","","","","","","","","","","","",""
"uuid:1cea9ad4-36c7-46ec-812a-0dd63b79b159","http://resolver.tudelft.nl/uuid:1cea9ad4-36c7-46ec-812a-0dd63b79b159","Analysis of Electromagnetic Behavior of Permanent Magnetized Electrical Machines in Fault Modes","Hassan, USMAN (TU Delft Electrical Engineering, Mathematics and Computer Science)","Polinder, Henk (mentor); Nilssen, Robert (mentor); Røkke, Astrid (mentor); Delft University of Technology (degree granting institution); Norwegian University of Science and Technology (NTNU) (degree granting institution)","2017","Over the years, the use of PM machines has been increasing in the offshore wind industry and marine industry. The industries thrive on efficient function of the PM machines. These machines are prone to electro-mechanical faults due to environmental conditions and maintenance. Out of all these faults, stator internal faults are concerning as they can lead to insulation failures which may take around 30 seconds to expand and lead to a fire on ships, or on wind turbines. These type of faults develop gradually, which gives the opportunity to control the fault currents before they reach dangerous levels. Rolls Royce Marine AS is also working to tackle this problem for their hybrid propulsion shaft generator. DNVGL requires the generator to be made electrically dead during such event and the long-term propulsion should not be affected. During such conditions, WTs are either turned off or field weakening is used to develop a fault tolerant control (FTC) by the help of power electronics for the WT. FTC helps the machine not to be turned off completely, but less power is generated during fault conditions. An alternative efficient field weakening method using a Dual Rotor PMSM was suggested for both the applications. The DR-PMSM has two rotors instead of one, with identical surface mounted magnets on both rotors. One of these rotors has the capacity to rotate with respect to the other, in order to reduce the flux or completely short the flux path by misalignment of rotors. The machine stator is exactly like the conventional PMSM. The machine is capable of reducing the induced emf to zero by field weakening.
In this thesis a transient 3D finite element model is presented to test the credibility of the machine. A 2D FEM of a conventional PMSM was also built to check the validity of the machine. It is seen that torque is a function of the active length of the machine, and if a gap is introduced between the rotors then the total length of the machine must be increased. Also, axial flux component which induces eddy currents in the stator teeth was studied. By modeling anisotropy in the stator iron, certain hot spots could be seen in the middle part of the stator. The forces that were in the shifting mechanism were studied and it was concluded that machine cogging can be reduced to reduce the effect of these forces. A machine prototype was also built which confirms the field weakening capability of the machine.
The DR-PMSM works like a conventional PMSM but with flux weakening capabilities and can be implemented on marine and wind turbine applications for these type of fault conditions.","FEM; FEM analysis; PMSM; stator faults; field weakening; COMSOL Multiphysics","en","master thesis","","","","","","","","","","","","","",""
"uuid:2fbfb0a9-ce2c-4b8b-997e-0c7df7216031","http://resolver.tudelft.nl/uuid:2fbfb0a9-ce2c-4b8b-997e-0c7df7216031","Modelling construction phases of bored tunnels with respect to internal lining forces: A comparison of Finite Element Programs","kunst, David (TU Delft Civil Engineering and Geosciences; TU Delft Geoscience and Engineering)","Broere, Wout (mentor); Safari, Bahram (mentor); Vardon, Phil (graduation committee); Blom, Kees (graduation committee); Delft University of Technology (degree granting institution)","2017","Areas are getting more and more populated causing new infrastructure lines to be constructed below the surface. A bored tunnel is one of the possibilities to create this subsurface infrastructure, but the construction process of a bored tunnel is a complicated one. Many loads and aspects are present in this construction process that can be divided into six phases. In each of these phases, different loads and aspects are acting on the tunnel lining or the surrounding soil which can cause the lining to deform.
The increasing complexity and demands of problems have led to the use of the finite element method. A computer based method which allows one to model the problem.
For finite element modelling, numerous programs are available of which several claim to be able to model bored tunnels. However, it is not yet clear what the exact differences between the different programs are. With many aspects to be modelled, many differences between programs occur, either in the soil, the tunnel lining or a combination of both.
This research has focussed on the possibilities of modelling the different construction phases of bored tunnels in two widely used programs: DIANA and Plaxis. Simple two dimensional (2D) models were created to which the different construction phases were added before continuing with three dimensional (3D) modelling. This approach has led to a good assessment of the possibilities and limitations within these two programs.
DIANA is not yet suitable for modelling the construction process of bored tunnels completely. The construction phases are modelled undrained to account for the relative short time they are acting. A consolidation phase in which the pore pressure can dissipate cannot be modelled in DIANA, which is essential for modelling the construction phases.
Plaxis, on the contrary, is not able to model joints in the segmental lining appropriate for 3D. In 3D, Plaxis only allows to model a joints as ""fixed"" or ""free"". In DIANA different theories can be applied to the joints, including Janssens. For 2D, both programs have a rotational springs besides the free and fixed connection for modelling the joints.
For the model in which the material models were changed, the difference with the main impact between the two programs occurred, especially for the bending moment. This means the Modified Mohr-Colomb material model in DIANA is different than the Hardening Soil model in Plaxis.
Including the construction phases leads to more favourable internal lining forces for tunnels, something of which clients should be convinced. However, not until the models have been benchmarked with measured data from a tunnel project.
While 3D models have been investigated in this research, they should be extended in order have a better understanding of the different 3D phenomena that are present in the construction of bored tunnels. This will both assess the possibilities of modelling this process and more potential differences between programs can be investigated.
Besides extending the 3D models, other programs should be investigated on their capabilities too. In order to come to a proper assessment of the possibilities, program experience is strongly recommended. These programs should also be compared with measured data for benchmark purposes.","Tunnelling; FEM; Lining Forces; Modelling","en","master thesis","","","","","","","","","","","","Geo-Engineering","",""
"uuid:3cf25e8e-397c-4aa5-a728-e07ea881bd3c","http://resolver.tudelft.nl/uuid:3cf25e8e-397c-4aa5-a728-e07ea881bd3c","The influence of the Transition Zone on the structural behavior of pin connected areas in local metal reinforced composites","Puzio, Tomek (TU Delft Aerospace Engineering)","Petersen, Enno (mentor); van Campen, J.M.J.F. (mentor); Delft University of Technology (degree granting institution)","2017","Fibre Metal Laminates (FML) are hybrid composites, with the attempt to combine the advantages of metals and fibre reinforced plastics. Their promising properties are used locally in joining areas to reduce the structural weight. As the metal foils density, in this case a steel alloy, is much higher than the density of carbon plies, its amount should be kept minimal. Hence, the replacement of the laminas is done gradually creating a so called Transition Zone (TZ).
In this research, the focus is given to the influence of the TZ on the structural behavior in pin connected FMLs. In the investigation two different designs of TZ and two different starting positions of TZ (closer and further from the pin) are considered. First their effect on the laminates behavior is investigated with static bearing tests accompanied by Digital image Correlation (DIC) measurement, followed by a Finite Element Analysis for an in-depth look at the laminas behavior. Later includes the implementation of the Cuntze failure criterion for damage prediction. The studies revealed that the distance between load introduction and start of the TZ can be very short without affecting the load carrying capacity.","FEM; FML; Fibre Metal Laminates; Transition Zone; Digital Image Correlation; Pin Bearing","en","master thesis","","","","","","","","2020-07-07","","","","Aerospace Engineering","",""
"uuid:2446d8cf-bdc1-4ae8-9a9a-398bb1bc6636","http://resolver.tudelft.nl/uuid:2446d8cf-bdc1-4ae8-9a9a-398bb1bc6636","Fatigue assessment in finite element analysis: A post-processor to FEA output for hot spot stress calculation","Swierstra, E.P.","Frissen, C.M. (mentor); Hendriks, M.A.N. (mentor); Veljkovic, M.V. (mentor); Pavlovic, M. (mentor)","2017","For the fatigue assessment of welded structures, several design methods are described by the design codes of IIW, Eurocode3 and DNV. The relation between the stress range and cycles to failures were derived from experiments: the SN curves. With the increased accessibility of finite element software to engineers, a more flexible approach emerged: the so-called hot spot stress method. Particularly suitable for welded structures, it assesses the influence of the geometric discontinuity on the stress distribution. A stress extrapolation procedure is required to overcome the high stresses computed by FEA at the notch. Normal stresses at the surface, perpendicular to the weld, are to be used. For curved welds and surfaces, e.g. in case of tubular joints, these stresses are complex to determine from FEA output. A method that automates the hot spot stress calculation as a post processor to FEA output would facilitate the process. Such an automated subroutine would further enable a study on the finite element modelling aspects, including the use of shell and solid elements and the inclusion of the weld profile, in relation to conducted fatigue experiments. This report describes the development of a subroutine as post-processor for FEA output to calculate the hot spot stresses. Read out points for stress extrapolation are located independently of the finite element mesh. In addition, for each weld node the local coordinate system is to be determined and subsequently the corresponding stress transformation is to be performed. Equivalent stresses at the read out points are determined by means of interpolation from a triangle-shaped plane formed by three element nodes. Cut-out specimens of an orthotropic bridge deck were tested against fatigue and strain gauges were used to measure the strains. This report shows that FEA stresses corresponded well with the measurements. Inclusion of the weld profile is important; ignoring the weld underestimates the stress levels by 10%. Use of shell elements resulted in 4% lower nominal stresses than solid elements, however in the weld region only the solid element model accurately reproduced the stress distribution. An alternative method for the fatigue classification described in EC3 is proposed, which represents better the observed stress levels for the crack initiation point at the weld root. Finally, this report considers stress concentration factors of tubular joints as recommended by CIDECT design guide. The FEA results are compared to the SCFs from parametric formulae. Good correspondence was found between the FEA and CIDECT results. A validation analysis of the boundary and loading conditions was performed, from comparing the joint model with the entire truss structure for shell elements. A correction function is derived to cover the small observed differences. Additionally, strain gauge measurements from experiments on large scale tubular joints in a marine environment are compared to the FEA results. Good correspondence was found between the measured and numerically computed strains. For solid element models, the weld leg size is found to be important for the hot spot stresses; each millimetre shift of the weld toe affected the stress levels by 3%. A characteristic SN curve was derived from the experiments. Fatigue assessment by means of the FEA hot spot stress in combination with the corresponding DNV SN-curve was found to be more conservative.","fatigue; FEA; FEM; hot spot stress; finite element analysis","en","master thesis","","","","","","","","","Civil Engineering and Geosciences","Structural Engineering","","","",""
"uuid:010174b9-fb1d-4956-9656-97767b54ca68","http://resolver.tudelft.nl/uuid:010174b9-fb1d-4956-9656-97767b54ca68","Calculation Methods for Steel Joints: Comparative Study of European Design Regulations and Partial Finite Element Analyses","van Egeraat, Hugo (TU Delft Civil Engineering & Geosciences; TU Delft Engineering Structures)","Veljkovic, M. (mentor); de Vries, P.A. (mentor); Pasterkamp, S. (mentor); Hendriks, M.A.N. (mentor); Houben, L.J.M. (mentor); van Lammeren, T. (mentor); Delft University of Technology (degree granting institution)","2017","style=""margin: 0cm 0cm 0pt; line-height: normal; mso-layout-grid-align: none;"">Traditionally, steel joints are calculated by the calculation rules described in the Eurocode 3: NEN-EN 1993-1-8. Effective lengths are important parameters to determine the different resistances of the components in the steel joint. Finite Element Analyses (FEA) are becoming increasingly important in engineering, including in construction industry. Specialised software is developed to determine the stresses and corresponding strains in the plate elements of the joints by the Finite Element Method (FEM). This thesis reports on a comparative study of the traditional calculation method and a method which is using partial FEA for determining the resistance of joints. The approach, assumptions and principles used for these calculations are explained in this report. It will be investigated whether the same components of a joint are decisive for each method and if there are differences in joint resistances. If so, the magnitude of the difference will be determined as well. This is done for different simple shear joints (SSJ) and moment resisting joints (MRJ). For the last group, two joint configurations (Flush End Plate Joint and Extended End Plate Joint) are calculated manually, partially modelled with the FEM, and compared with the results of executed experiments.