Cutter suction dredgers (CSD) are highly vulnerable to large wave loading due to their stiff, spud-based mooring. Many mitigations targeted at reducing the resulting stresses on the spud and other critical operating components have been proposed in recent years, most notably by adding a level of flexibility to the connection between the pontoon and the spud for rotational motions. Investigating the merits of the implementation of a flexible spud keeper however are hindered by the lack of accurate, CSD-specific models that are able to simulate real waves in the working area, as well as the multibody system of a CSD and its complex interactions with the sea floor. In this thesis, an ANSYS AQWA model is developed to conduct an operability analysis of a CSD in operation in offshore, coastal conditions. Three modelling objectives were established to provide a complete analysis of the effect of increased flexibility in a spud keeper: adding non-linear wave effects, improvement of the soil boundary conditions, and building a dynamic multibody system of a CSD in ANSYS AQWA.

A wave model is developed that expands upon standard Linear Wave Theory (LWT) through the use of Stokes 2^nd Order Wave Theory (S2). S2 was found to be valid for a larger range of water depths and wave parameters than other wave theories, mainly in shallow, coastal conditions, which is the main operating area of a CSD. These non-linearities cannot be implemented into a frequency domain (FD) model, therefore a time domain (TD) model is required. A combination of S2 waves in a JONSWAP spectrum is used to simulate the motion and force response in TD, as well as second-order forces from the interaction of wave groups with the CSD. The model output is then used as a means of verification of these assumptions and to show the effect of the wave shapes on the spud bending stress.
An altered spud model is proposed for shallow, wide spuds, using a rotational spring system instead of the commonly used clamped model. For the use-case of a CSD it shows a spud's tendency for rigid motion below the mudline, while also providing an upper operational limit for soil failure around the spud. The model output showed this upper limit to likely not be a important operational limit, but it can be used to investigate spud rotation below the mudline. Mooring effects from the cutter are absent in older models, but are added in the form of spring elements to better approach reality.
Finally, a number of CSDs with different levels of flexibility are tested for four operational limits. The model shows a clear shift in motion resonance towards lower frequencies when the stiffness is decreased, while operability analysis in TD presents a significant increase in operability when a CSD is free to move in pitch. This completely flexible connection provides a major reduction in spud bending stress, but is governed by the acceleration limit of the pontoon. Other reduced stiffness designs are shown to only provide limited benefits to the operability.

After decades of exploitation of hydrocarbons, the offshore facilities constructed for this purpose are nearing the end of their design life and/or economic operation. According to international law, these offshore structures need to be completely removed. Decommissioning of the substructures often requires for soil to be removed in piles to facilitate pile cutting works below the seabed. One way of achieving this is by deploying a specialized tool, a so-called Soil Plug Removal Tool (SPRT), that operates using hydraulic excavation.

This research carried out under supervision of Royal Boskalis Westminster N.V. aims to get a more solid basis for comparison of different SPRT concepts that are available in the market. The tools are designed to handle a wide range of soil types. Removal of cohesive sediment is more challenging, mainly due to the very low water permeability present compared to granular soils. This study therefore focusses on the excavation of cohesive soil types only.
In order to verify the performance of several concepts an experimental test program is set up on model scale. The primary goal is to investigate the achievable excavation production in terms of tool progress rate. Therefore, a jetting tool is developed that covers the (complete) spectrum in terms of cohesive soils and performance of the available tools. Two basic SPRT concepts are incorporated in this single tool based on head movement: static or rotating.

Jet pressure, clay strength, rotational velocity and set down pressure of the tool are altered during testing on the condition that all other parameters are fixed. This requirement is met for the testing clay by merely varying the shear strength. The testing clay was therefore prepared both with an artificial and natural clay with shear strengths ranging from 20 kPa to 100 kPa.

It is found that next to jetting, soil failure can also be attributed to cutting and jet trench failure under influence of the jetting head that rests on top of the clay. For this reason, production values belonging to jetting could not be obtained directly and had to be calculated using jetting theory to distinguish between jetting and jet trench failure. Based on the power that is required to excavate a certain volume of soil (i.e. specific energy), insight is given in the contribution of each failure mechanisms to the production in terms of tool progress rate.

During static jetting, the current (nozzle) configuration did not remove enough soil from the jet cavities for the jetting tool to progress downwards. The opposite is true for the rotational tests which comprise the largest part of the test series. An analytical model is proposed to predict the cavity width and depth. This model is only valid for jets with small rotational velocities as encountered in this study.

The total production, which was measured, is found to be inversely proportional to shear strength and directly proportional to jet pressure and rotational velocity.

Subsea rock installation is a process in offshore engineering where rocks are placed on the seabed or subsea structures using a fallpipe. An example of a subsea structure could be a cable or pipeline that must be protected. In this research, the main scope is rock installation for scour protection of the foundation of offshore wind turbines. As the US government is planning to build 30 gigawatts of offshore wind capacity by 2030, many rock installation projects are planned. This is where GLDD wants to contribute by being part of a more sustainable future by building a subsea rock installation vessel. This vessel with a 20.000 ton rock capacity is placing rocks using a solid fallpipe. Accurate knowledge of how rocks are placed using a fallpipe is necessary to plan, manage and estimate the costs of a project. The main focus of this thesis project is to establish an optimal computer model for an inclined fallpipe for subsea rock installation. This model can be used to calculate rock velocity during operating the inclined fall pipe (IFP). Additionally, the particle concentration and the distribution of particles over the pipe’s cross-sectional area can be determined. The velocity of particles is essential for future models calculating where the rocks settle down after leaving the fallpipe. Based on the literature two models were made: Vertical fallpipe model 1 (VFM1) and Sliding bed model 1 (SBM1), these models are improved based on data and observations from lab research. These improvements lead to Vertical fallpipe model 2 (VFM2) and Sliding bed model 2 (SBM2). In the lab research, a scale model of a fallpipe is made. This is done by placing a transparent fallpipe in a 5x2.5x2 meter tank of water. This fallpipe is attached to a conveyor belt, making it possible to precisely control the amount of rocks per second placed in the fallpipe

Ocean wave energy has a huge potential to make a contribution to global energy transition. However, the high Levelized Cost of Energy (LCOE) is currently a big hurdle to the development of wave energy converters (WECs). This thesis is motivated to improve the techno-economic competitiveness of WECs. It focuses on the effects of systematic sizing of WECs. "Systematic sizing" is reflected in this thesis by considering the effects of sizing on the two main components of WECs, namely the buoy and PTO system. The main body of this thesis starts with a literature review. First, it is intended to provide an overview of current wave energy technologies and the application of power take-off (PTO) systems. Secondly, the studies relevant to sizing of WECs are reviewed, and sizing methods used in the context are discussed and compared. It indicates that the existing studies mainly focus on the effects of buoy sizing and there is a lack of consideration of PTO sizing. In addition, the sizing methods based on the Budal diagram and Froude scaling can only be used to conduct sizing of buoy but the influence of PTO sizing cannot be covered. Numerical simulation can be applied to take into account both effects of buoy sizing and PTO sizing, but it is usually associated with low computational-efficiency. As sizing can be regarded as a kind of optimization which normally requires a number of iterations, an efficient method is beneficial for accelerating the design process of WECs. Followed up by the literature review, Chapter 3 to Chapter 7 of this thesis are dedicated to accomplishing two main research objectives...

The deployability, regarding mobility, of Boskalis trenchers, is currently determined by practical knowledge. The lack of theoretical knowledge means that risk assessments in the tender phase are less accurate. This reduced accuracy has two negative consequences. First, the trencher may fail. Secondly, the safety margins can be too large. Both consequences result in additional duration and costs. This research considers two ways of failure. The first one is slipping; as a result of this, the track does not have enough traction, which causes the tracks to turn while the trencher does not move forward. The slipping can happen in two ways. The first way is due to soil failure with the grousers fully penetrated. This results in the trencher digging itself in. The other way is that the grousers are not penetrated and the trenchers slips due to the tracksoil interaction. In order to prevent the trencher from slipping, horizontal stability between the soil and tracks should be obtained. The second way of failure is that the trencher sinks into the soil. Vertical stability between the applied pressure and the bearing capacity should be achieved to prevent this kind of failure. In this research a model has been developed that can approximate the operating range of different trenchers. With the help of these operating ranges, the model can make risk assessments in an early phase of the project. There will be little knowledge about the soilspecific parameters and the exact external conditions in this phase. Should there be a risk in the area of mobility along with the project, the model is also able to provide a more indepth analysis. In addition, the model aims to apply to different types and sizes of trenchers. The research answers the following question: ”Which different operational environments and soil conditions have a critical influence on the deployability of a subsea tracked trencher regarding the vertical stability and horizontal stability of the soil¬track interaction system? The model considers the trencher’s mobility in terms of vertical and horizontal stability, where the axes rotate with the slope. Meyerhof’s effective area method approximates the vertical stability. This method is used to take into account the eccentric loads. A traction calculation model approaches horizontal stability. Based on the penetration depth of the individual elements of a track, a shear mode is determined. The available traction force per element can be calculated using these shear modes using the Mohrcoulomb shearing theory. With a case study for the CBT2400, the research question is answered. In this case study, we first look at the different external processes that influence mobility. In addition, the various soil parameters and trencher dimensions are examined. Finally, the results of this study will be compared with two reallife projects. The results show that the mobility of the trencher is better in granular soils than in cohesive soils. In cohesive soils, the trencher’s mobility depends on the external factors that change in the driving direction, like pitch slopes and currents that have a frontal impact. In cohesive soils, the sensitivity is a vital soil parameter besides the undrained shear strength. Since the sensitivity is not included in the soil research, it is recommended to do it in future projects. In granular soils, external factors from all angles must be taken into account, like pitch and roll angles and currents from all directions. With granular soils, especially the relative density and internal friction angle are essential; in addition, the grain size must be taken into account. The grain size influences the permeability of the soil. The permeability, together with the relative density, determine if contractancy and dilatancy will take place in the soil. It could be interesting to change the grouser and track dimensions to improve the trencher’s mobility. However, this depends on the circumstances in which the trencher would have to operate. The model was validated using two cases involving the Borssele and Moray East projects. An important conclusion is that the model can be used to estimate the potential risk areas reasonably. However, it is recommended to test the model in predefined circumstances and soil parameters.

In this thesis I will show the realisation of a multiline anchor system using a suction pile anchor (SPA). From the literature research it can be concluded that the SPA is a suitable anchor for a multiline anchor system and that the most probable mooring configurations will be either the original single-line, the 3-line or the 6-line system. Furthermore it could be concluded that when using a catenary mooring solution for the 3-line system, that the anchor perceives a lower horizontal net force due to anchor lines coming from different directions and cancelling parts of each other. This would, in theory, make the SPA for the 3-line multiline system smaller and also there would be 67% less anchors needed in a wind farm array. Furthermore the 6-line anchor does seem to have a bigger horizontal net force which requires the SPAs to be bigger but 83% less anchors are needed in an array of wind turbines. The looked at FOWT-system was the University of Maine VolturnUS-S reference floating offshore wind turbine semi-submersible, which supports the IEA-15-240-RWT turbine with a turbine rating of 15MW. With the original mooring configuration being a catenary one, a comparison has been made with a taut system and its implementation into a multiline anchor system has been researched. Lastly three different soil profiles have been chosen: normally consolidated clay, slightly consolidated clay and loose sand. In Chapter 4 Suction anchor concept design, the forces on the anchor are set up using the data set-up by NREL and the University of Maine and the C. Fontana papers. A SPA has more bearing capacity when the mooring-anchor connection point is below the mudline. Because of this feature the mooring line attaches to the SPA at an angle and in this thesis a range of angles of approach are chosen to be investigated: 25 and 35 degrees for the chain and 45 degrees for the taut line. Because of the angle there is a vertical force introduced to the anchor which need to be added together for each line. Because of this the total net force on the anchor is increased for the 3-line and 6-line anchors compared to the single-line anchor. With the mean and maximum forces the calculations for the holding capacity/pull-out capacity can be set up by looking at the Ultimate Limit State (ULS) or maximum forces in the system. These calculations are taken from the DNV guidelines which are the industry standard. To set-up the first parameters estimation a embedment (h/D-ratio) starting value has to be chosen and from literature and in discussion with SPT offshore the starting values were set at 5 for the clay profile and 1.5 for the sand profile. The weight of the SPA must be defined which was done as the mean vertical force applied to the anchors as such they will not be pulled out over time. The installation and removal calculations are an important step in the design and are also set up. Here the under pressures required to fully install the SPAs are calculated. Furthermore, structural failure due to buckling is checked for and different soil failures are analysed. Lastly the removal pressure of each concept is checked which allows for complete removal of the suction anchor. By lowering the embedment ratios of the different concepts the pressures inside the anchors can be minimised and problems can be averted. In the detailed design the full design of a in use SPA is shown and each part is defined. Furthermore, the one-line-broken criterium is discussed and it can be concluded that in case this happens the 6-line multiline system is very dangerous because a chain reaction can be started which can take out large parts of a wind farm array. Also a weight estimation of each SPA is made from which the extra needed ballast is calculated. Subsequently a cost estimation of each anchor concept can be made by calculating the cost of each system from the structural weight, the ballast and the mooring line lengths. At a depth of 200m, at which this study is situated, the taut multiline system cannot be set-up but the single-line taut system can be compared to the catenary single line system. Lastly a parametric analysis is done where changes in different parameters are compared to each other. What can be concluded from this thesis research is that a multiline system is technically feasible for a 15MW floating offshore wind turbines using SPAs. The 3-line and 6-line systems both have larger anchors than the single-line system although they need less anchors in a system. When including the mooring line costs together with these anchor costs it can be concluded that the 3-line anchor is more economically viable but the 6-line anchor is not. What can also be concluded from these mooring line costs and what is discussed in the parametric analysis is that the system works better if the wind turbines are closer together because the lines will be shorter. This distance is dictated by the wake recovery and an optimisation study is recommended for the 15MW wind turbine but it is also recommended that smaller turbines and deeper depths are looked at.

In offshore operations a trend is forming where vessels are more often required to do multiple short operations within a small-time frame. Traditional mooring systems require execution time far beyond the operation time. Dynamic positioning systems offer great advantages for short time span operations such as crew transfer or lift operations.

Currently operations are planned based on DP capability plots and experience of captain and DPO. DP capability plots have little operational value as this is a static calculation and only provide information for average station keeping capability. During operations, the displacements made by the vessel around the DP set-point, also referred to as DP offset, are of great importance to determine the operability of an operation. Currently, the only way of calculating the DP offset is by conducting extensive time domain simulations, which are hard to integrate in the operational workflow of a DP vessel involved in walk-to-work operations. Therefore, a new approach is developed which predicts the vessel’s DP offset in the frequency domain, which enables a quick and robust calculation of the DP offset which is suited to merge into the on-board workflow. A frequency domain model is per definition a linear model. This leads to the main challenge of this research. A vessel operating on DP is non-linear. Currently there is no insight in what the effect is of non-linear components present in a DP system, on the linear approximation of a frequency domain model.

To investigate the effect of non-linear components onto the DP frequency domain model, a time domain model is developed that is capable of systematically enabling/disabling different non-linear components. The time domain model will serve as the ’truth’ in this research as no actual vessel data is available. Furthermore, this helps identify the effects more easily, as the input for both models are identical. From the time domain model transfer functions can be derived that serve as the basis for the frequency domain model. The transfer function is a linear relation between two variables. In this case, between second order wave drift forces and displacement of the vessel in surge, sway and yaw direction. The following non-linear components are investigated in this research: Thruster ramp up, thruster turning rate, forbidden zones, saturation and thruster allocation. Thruster allocation is present in each model that will be tested, as this is an essential part of a DP system.

Using two methods of determining transfer functions the model and the effects of all non-linear components are tested. The model is subjected to a variety sea-state, with different wave directions. Both methods offer similar results even though different approaches to determine the transfer functions are used. The selected method is capable of accurately predicting vessel offsets, although some extreme offsets are not captured.

It is concluded that the presence of non-linear components have little to no effect on the DP offset as calculated by the time domain model. Because natural frequencies characteristic to these non-linear components are expected to exist at much higher frequencies that naturally present in second order wave drift forces. Thus, making a linear frequency domain model suitable for DP offset forecasting. It is advised to investigate the effect of including 2D input spectra as this is expected to improve the current model.

Offshore contractors use special cable laying vessels (CLV’s) in order to install subsea power cables, which transport offshore generated energy. Workability studies are performed to evaluate whether operations can be performed or not. These workability studies are subsequently a combination between operability assessments (performed in OrcaFlex months prior to operation) and forecasted weather windows. During the operability assessment, eventually limiting sea states are defined which are expressed in significant wave height (Hs), wave peak period (Tp) and incident wave angle relative to the vessel heading (a). If the forecasted weather windows exceed the predefined limiting sea states, operations cannot be executed. These current workability assessments are based on 1D JONSWAP spectra. This thesis contains an exploratory study of implementing a motion-based forecasting (MBF) method into workability studies, based on 2D wave spectra. This is done by focusing on the motions at the chute of the CLV, as this is where the subsea power cable leaves the CLV. Before MBF can be implemented, however, at first a specific limiting motion predictor needs to be identified that covers the cables integrity limits. Furthermore, this limiting motion needs to be quantified as well in order to compare this essentially composed new cable limit with MBF predicted chute motions. Subsequently, all cable integrity criteria need to be converted into this limiting motion to preserve the subsea power cables integrity. For normal cable lay operations, eventually all mechanical properties and cable limits are covered by three main cable integrity criteria. These are minimum bending radius (MBR), minimum bottom tension (BT) and maximum top tension (TT). By means of modelling a lot of various environmental loading conditions, the research described in this thesis shows that the chute z velocity is eventually indicated as a proper limiting motion predictor. Out of all investigated chute motions, chute z velocity (which represents the vertical velocity of the chute) shows the best correlations with the aforementioned cable integrity criteria. To determine workability by implementing motion based forecasting, this limiting chute z velocity needs to be quantified. The chute z velocity needs to account for all three main cable integrity limits, hence these limits are essentially converted into one single chute z velocity limit (which is essentially a new introduced cable limit). To quantify this limiting chute z velocity not the entire relation is of interest, but only the range close to breaching the cable integrity limits. Therefore, a percentile line method is introduced which is constructed on the 90th-percentile values per bin. Based on this research, it was found that binwidths must not exceed values of 0.5m/s to obtain robust results. However, no minimum amount of data points per bin was established as this varied for all assessed subsea power cables. Finally, workability studies of the current 1D JONSWAP (based on a single Hs −Tp sea state) method was compared to a 2D superimposed JONSWAP accounting for both swell and wind wave contributions. This comparison indicates that when determining workability based on more detailed 2D spectra, the workability study provides more smoothed results. This means, the higher chute z velocity peaks from the 1D total sea state are downscaled when simulating a 2D spectrum, whereas the lower chute z velocity peaks from the 1D total sea state are upscaled when implementing a 2D spectrum. The obtained motion-based chute z velocity forecasts indicate that optimization is possible by splitting the total sea states into both swell and sea waves contributions and accounting for wave spreading.

Irmão is a beach restaurant located in the region of Lisbon in Portugal and has been taken over by the new owners one year ago. Since the takeover, the owners of Irmão have been trying to work in a sustainable way, but there is always room for improvement. In addition, Irmão may have to move 100 metres inland due to a possible change in local regulations. Because of the uncertainty in the course of events, this report is written as guideline in order to make the current restaurant more sustainable and as a guideline during the design of the new beach restaurant, should the restaurant have to be relocated.

The aim of the report is therefore to provide beach restaurant Irmão with a consult on how to establish and operate a more sustainable beach restaurant, in present or future times. The study, executed at Irmão, focused on three main themes; the water system, waste management and the energy system. The level of sustainability in these areas is quantified in three ways, namely: the use of resources such as fossil fuels and groundwater; the emission of greenhouse gases CO2, NOx and CH4; the pollution of the direct environment, for example waste that ends up in nature or polluted waste water that flows into the soil. The present and future times refer to the two different scenarios used to implement sustainable solutions. If the restaurant is allowed to stay at its current location, it is referred to as the Improved Irmão Scenario. If the location has to be changed, it is referred to as the Future Irmão Scenario. For the Improved Irmão Scenario, the boundaries and limits of the current restaurant are taken into account and the design is carried out within these limits. For the Future Irmão Scenario on the other hand, these limits are loosened and the design is carried out from scratch.

To provide Irmão with a consult how to establish and operate a more sustainable beach restaurant, three steps were taken. First, the current situation of the three subjects is analysed to get a clear understanding of the current situation. This is done to have a baseline against which the final improvements can be compared. Secondly, different solutions to make Irmão more sustainable, within the three main topics, are compared using a multi¬criteria analysis to determine the most promising solutions. Thirdly, the final solutions are elaborated for the Improved Irmão Scenario and for the Future Irmão Scenario.

Regarding the Water system, the analysis showed that the water consumed at Irmão partly originates from the water grid and partly from the borehole in the dunes. The water use is estimated to cause an emission of 182 kg CO2 annually, leaving little room for improvement in emission reduction as this is a relative low amount. However, the water system is currently not water-efficient because it does not contain any water circularity and the water system does not contain any water saving equipment. Improvements regarding water usage are therefore possible. Regarding waste management, the analysis showed that currently, only residual waste is not recycled. Therefore, the section on waste management focused on making residual waste more sustainable. Regarding the energy system of Irmão, it became clear from the analysis that Irmão currently consumes propane gas and electricity from the local electricity grid. Both the consumption of propane gas and electricity from the local grid contribute to an emission of 26.8 tonnes of CO2 annually. From all processes carried out during the operation of Irmão, only the consumption of propane gas leads to an emission of NOx, namely 382 kg NOx annually…

A 3D dynamic numerical model is established for modelling the excavation process for dredging purposes. The interaction between the solid and fluid phases is realized by a specially designed DEM-FVM coupling mechanism, where the fluid-particle interaction forces, the volume fraction information and the particle information are constantly updated and exchanged. Dry and underwater sand cutting simulations are conducted and validated against experimental results. Simulation results of cutting of cohesive soil in atmospheric condition match with the experimental data within acceptable error margin, while the underwater cutting simulations of cohesive soil have not been validated due to the lack of experimental data. Besides, the general applicability of using Discrete Element Modelling (DEM) to create rock samples, and the calibration of DEM rock samples have been investigated, which are essential for conducting atmospheric and underwater rock cutting simulations in the future.

To realize sustainable development, offshore wind energy has been a highly valuable solution to meet the demand for renewable energy. Accompanied with the construction of the offshore wind turbines, cable casting and the following cable trenching process in the underwater condition are necessarily required. The research on the underwater sand cutting process so far has been limited to some extent. (Miedema, 2014) has suggested the analytical solution and performed the experiments of underwater sand cutting. But all the work until then was in 2D and the description of the water influence was in the scope of statics. Thus, it is necessary to carry out the numerical simulation to describe the cutting process and the effect of the fluid by means of DEM-CFD coupling. (Chen et al., 2015) suggested a framework of modelling the underwater excavation process. The method is to describe the particle phase by Discrete Element Modeling (DEM) and the flow phase by Finite Volume Method (FVM). Starting from this method, the software package CFDEM coupling, LIGGGHTS for DEM calculation and OpenFOAM for CFD calculation, is applied. In the coupled simulation, DEM transfers the particle information to CFD. CFD solves the governing equations and updates the pressure field and velocity field. Then the fluid-solid interaction forces are calculated in CFD and transferred back to DEM. Sand particle is not spherical in reality. To describe the sand particles more accurately, a constant directional torque is added to each spherical particle to restrict its angular movement. And the sphericity of the particles is adjusted to make the sand sample in the simulation have reasonable permeability. Two sets of the numerical simulations of underwater sand cutting are conducted in this research, the simulations of 2D effect and 3D effect. The results from the simulations of 2D effect are validated with the analytical and experimental results, while the ones of 3D effect are mainly analyzed to investigate the fluid flow field and the fluid-solid interaction force. Many factors are analyzed to find out their effects on the cutting process, such as the blade geometry, the cutting layer thickness, the hydrostatic pressure, the cutting speed and the particle size. Many conclusions are found from the simulation. It turns out that the stress on the blade increases with the blade angle, the cutting layer thickness and the cutting speed. The relation between the stress and cutting layer thickness is approximately linear. And the stress has nothing to do with the hydrostatic pressure and the particle size. The features of the fluid flow field show some differences according to low, medium and high cutting speeds. The dilatation happening in the shear zone can be observed from the distribution of the fluid pressure. With a higher cutting speed, the pressure gradient in the shear zone is larger. For the fluid-solid interaction force, the effect of the cutting speed is very obvious. Besides, the dimensionless cutting forces from the simulation matches good with those from the experiments by (Miedema, 2014). From the simulation with large blade angles, a wedge between the blade and the layer cut is observed both from the velocity distinction of the particles and the stress on the blade. With the good matching in the validation work, this research confirms the reliability of DEM-CFD coupling to describe the underwater sand cutting process. Although the analysis is into depth in many aspects, further research is still needed. Using spherical particles with a constant counter torque to describe sand particles gives reasonable results. Non-spherical particle is another possible solution that is worthy to try. And the analysis about the cavitation is necessary to be performed.

This study is focused on the decommissioning of a jacket with a heavy lift vessel. During the transport the crane suspended jacket hanging in air can start swinging due to swell waves. This can result in undesired risks such as a collision between the jacket and the vessel. To prevent this undesired risks from occurring a solution must be sought. A possible contingency scenario to prevent this risks from occurring is to (partly) submerge the jacket. The aim of this study is to investigate in which way the jacket motion response changes if it would be in the water. A research methodology will be derived to investigate this. This will be done by investigating the a jacket transport with the Thialf. As a starting point, and for later comparison, the behaviour of the a jacket in air, while it is free hanging from the cranes of the Thialf, will be investigated in a frequency domain solver Liftdyn. The resulting modes and response between the model and measurements indicate a good starting point. Thereafter the jacket will be lowered in to the water and the resulting forces will be determined. The forces on the jacket will be determined using the linearised Morison equation. For the damping two approaches are investigated, i.e. the absolute velocity approach and the relative velocity approach. Subsequently different submerged depths are investigated and the effect of adding tugger winches is investigated. The operability for the different scenarios is derived and compared. It is observed that by submerging the jacket the pitch mode is limiting the operability for wind waves. This mode can be damped by adding tugger winches. By submerging the jacket deeper the operability improves. For swell waves the operability is improved when the jacket is submerged. It is concluded that submerging the jacket can be used as a contingency scenario for a swell train, but it is crucial to know the behaviour of the jacket. Because submerging it at the wrong depth could lead to large resonant responses. And by understanding the behaviour of the jacket tugger winches can be used to damp out a specific modes.

On a global scale, the present-day demand of coastal protections, port expansions and construction of artificial islands, rises. To be able to accommodate for all these environmental changes, complex dredging operations have to be performed. Depending on the type of soil and in-situ conditions, a suitable excavation and transportation method has to be chosen. From an economic point of view it is desired to make this process as efficient as possible. The only way in doing this, is to understand the physics of the rock cutting process and be able to predict the behavior of the rock formation during cutting.

This research focusses on the physics that come paired with the excavation of rock deposits under atmospheric conditions. The removal of rock results from the interaction between the cutting tool and intact rock, destructing the internal structure of the rock formation. A rock may either fail in a brittle tensile, brittle shear or ductile manner. Over the past decades various calculation models have been developed to predict the cutting forces in rock cutting. Most known prediction models assume one failure mechanism to be dominant, using a specific cutting tool geometry. For the sake of this research a sharp pickpoint is used. The elaborated, existing calculation models within this research using a sharp pickpoint as a cutting tool, all consider the rock cutting process to be a two-dimensional problem. To investigate if this hypothesis about the rock cutting process is correct, experimental research is conducted. A distinction is made between two different rock types, both varying in strength (e.g. sandstone and artificial rock).

Experimental research revealed that the measured forces greatly underestimate the results of the existing prediction models. The author states that this inaccuracy partially arises from the fact that, in practice, the excavation of rock is actually a three-dimensional problem, since visual observations clearly showed that chips broke out sideways. Based on the experimental measurements, two new calculation models were set up, incorporating this three-dimensional effect. The first model implemented fracture mechanics theory, focussing on the required local crack tip stresses to initiate a tensile crack. Due to several unknown empirical parameters, the tensile-dominated fracture model gave unsatisfactory results, underestimating the measured cutting forces. The second model was set up by focussing on the actual physics that were observed during cutting. Based on visual observations and individual chip investigation, three different failure mechanisms can be substantiated that occur during cutting: crushing, major shear failure and tensile failure.

By elaborating on the developed prediction model, it appears that the forces due to crushing dominate the total force spectrum. For a crushed zone to develop, penetration into the material is required. The author discovered that rock's resistance to obtain a certain penetration, needs to be accounted for when calculating the stresses within the crushed zone. By achieving the desired penetration, a large vertical force arises, indicating that frictional effects also need to be considered. This means that forces due to crushing are dependent on the hardness of the rock and frictional resistance between the cutting tool and rock's top interface. Based on production measurements and cutting groove analysis, the crushed zone dimensions were able to be determined, whereupon an expression for the pickpoint's indentation area was found. A surprising discovery was made during the analyzing phase of the force data. Regardless of the pre-set cutting configuration, a basic force level was observed during cutting, which is quite well-approximated by the crush force component, including frictional effects. Despite the formation of a crushed zone, chips failed in a cataclysmic manner. Individual chip investigation revealed that a certain fraction of shear and tensile failure is present along the failure plane. It appeared that the contribution due to tensile failure becomes more significant as the penetration depth of the pickpoint increases. This can be explained by the fact that a tensile crack has the ability to grow and propagate to the rock's top interface. The results of this research show that predictability of the forces increased significantly, compared to the existing two-dimensional calculation models.

Contractors can be stimulated to offer sustainable product innovations through tenders in the GWW sector. But despite the sustainability ambitions of clients to achieve a 100% circular economy by 2050 and sustainably generated energy in the Netherlands, contractors are hindered from being able to offer sustainable product innovations by clients. To make recommendations to clients to optimize the preparation phase of public procurement. In order to contribute to this, it is made clear how contractors can be stimulated by investigating the influential (external) factors of the tender phase that can stimulate contractors to offer sustainable product innovations with a TRL level 7-9 during the tender phase.

Every year large quantities of plastic waste accumulate in Bali’s environment. This has a negative impact on Bali’s environment, local society and its tourist driven economy. With lacking waste management facilities and local awareness plastic waste enters Bali’s rivers, through which the waste ends up in the ocean. A concept small-scale recycling business, aiming to improve local waste management and awareness, is proposed to solve the problem at the source. The goal of this research is to investigate the technological, social and financial feasibility of the concept recycling business and to find a target location. The research first aims to choose three potential locations with different social-demographics through a literature study on Bali’s regional social-demographics and the results of previous ”Pantai” Project researches. Based on this three locations are chosen: Denpasar, Canggu and Pulukan. For better understanding of the areas of interest, the crucial steps for setting up a business on Bali and its local waste management are investigated. A detailed stakeholder analysis is therefore also conducted. This is researched through participatory observation, literature study and interviews with local inhabitants, local businesses and governmental institutions. Surveys are conducted in the areas of interest to analyze how to Balinese handles their plastic waste, their mentality towards the plastic problem and their willingness to participate in the concept recycling plan. The results of the survey show enthusiasm of the local people towards the concept recycling business in the target areas. However, not all stakeholders are represented in conducted surveys, thus care must be taken when concluding the social feasibility. To investigate the technological feasibility literature study is done on plastics and different techniques in all steps of the recycling chain. Through this, feasible techniques for all steps of the recycling chain are chosen, regarding the concept recycling business. Plastic waste is to be sorted by hand and processed by easy operable machinery based on the open-source designs of Precious Plastic. A conceptual model of the small-scale recycling business is introduced for better understanding of the plastic and money streams involved in the concept recycling facility. To investigate the financial feasibility, first the plastic stream is evaluated. In each location households separated and collected all their plastic from the rest of their waste for one week to estimate the composition and quantity of their weekly plastic waste production. From this result the plastic input per location is estimated through calculations. A model is presented to evaluate financial stability of the concept recycling business. Input values for the model are the results from own waste collection measurements and the values acquired from connected parties. Calculations show, although being a rough estimate, financial feasibility. However more in-depth market study has to be performed for more detailed results. Taking everything into account it can be concluded that it is indeed feasible to start a small-scaled recycle business on Bali in Pulukan or similar areas, which is determined by a multi criteria trade-off. However close consideration of local conditions should always be taken into account.

Context: The shift to green energy offers a need for offshore wind farms. The transition from a relatively cheap energy production from carbohydrates, to a young offshore wind energy industry needs innovations to lower the cost. Increasing the efficiency of wind turbines and lowering the installation cost of a wind farm, will eventually make wind energy cheaper then energy produced by coal. A part of the installation process is the burial of the submerged power cables. The fragile power cables have to be buried a couple meters below the seabed, to be protected from anchors, fallen objects, and fishing activity. Problem definition: To submerge the power cable into the seabed, a trench have to be made. The soil of the seabed can consist of sand, silt, clay, rock or any combination of them. This research focuses on the trenching though clay. Clay has a very low permeability compared to sand, and clay has cohesive strength. For trenching in clay, a narrow plough is mostly used. These ploughs have a small frontal area and are build to cope with the high ploughing forces. A prediction of ploughing forces and velocities are made by models in preparation of cable burial projects. With accurate predictions, the best equipment can be chosen and a planning of the trenching operation can be made. The prediction models take into account the geometry of the plough and the soil characteristics. A reduction in pulling force results in an increase in ploughing velocity and therefore lowering the time and cost of cable installation. Approach: A large part of the pulling force in clay is caused by the adhesive force on the sides of the plough sliding through the clay. The adhesive force is therefore the main focus of this research. There are two main goals: the first goal is to investigate the adhesion force in relation to the strength of the clay; the second goal is to investigate ways to reduce the force caused by the adhesion. The adhesion factor is a parameter that is included in the prediction models. In literature of construction and agricultural engineering, predictions of adhesion factors and ways to reduce the adhesive force can be found. However, the circumstances during subsea ploughing are vastly different then in the other fields of engineering. Therefore, the approach of this study is to use small scale ploughing experiments with different strengths of clay to investigate the two goals under subsea ploughing conditions. For the experiments, a test setup is used. In this setup, a block of clay of a meter long can be hold into place in a water tank and be submerged. On top of the water tank, an electric motor can pull a cart over rails. A small scale plough can be bolted underneath the cart. During an experiment, the plough is pulled through the clay and the velocity and pulling forces are measured with sensors. Results and conclusions: The adhesion factors of three types of clay are found. The softest clay with a undrained shear strength of 25 kPa has a adhesion factor of 0.43. Literature shows that the adhesion force is about 1.0 at 25 kPa. This low adhesion factor could be the result of the frontal cutting that disrupt the clay. The residual shear strength is lower then the undisturbed clay. For the medium (80 kPa) and hard (131 kPa) clay the adhesion factor is respectively 0.68 and 0.53. These values are on the higher side of what literature reports. This could have to do with the relative high velocity during ploughing. The downward trend of adhesion factor with increasing clay strength does correspond to literature. To research the possibility of reducing the adhesion force, three small scale ploughs with modified adhesion surfaces are tested. The Alpha plough, which uses vertical gaps, reduced the adhesion force by 52 percent in both soft and hard clay. The Bravo plough, which uses convex shapes, reduced the adhesion force 39, 72 and 54 percent in respectively soft, medium and hard clay. The Charlie plough, which uses water nozzles at the adhesion surface, reduced the adhesion force by 70 percent in soft clay and 63 percent in hard clay. This experimental study obtained valuable knowledge of the adhesion factor and possibilities to reduce the adhesion force.

Deep-sea mining is becoming more popular. The Atlantis II Deep is a deep sea mining field of metalliferous muds in the Red Sea. This field could be exploited by transporting the sediments through a pipeline laid from shore onto the sea bed to the field. From determined concentrations with their shear stress-shear rate relation, parameters for the power law and Bingham plastic model were determined, relayed to test data, so that in the end the Bingham Plastic model was used to calculate pwoer consumption for a variety of cases.

CSD spillage is defined as “any soil that is dislodged above the lowest cutter tip trajectory of a single swing, but is not sucked into the suction pipe”. In addition to higher energy consumption and material wear for delivering the targeted depth, spillage can lead to a variety of environmental issues. As of yet, no analytical model exists in literature that can estimate spillage rates for a given set of cutting parameters. This thesis presents the Sand-Rock Cutting Spillage Model (SRCSM), an engineering model that is particle size-agnostic and makes use of cutting parameters that are all available to the dredge operator.
Prediction accuracy of 5 percentage point is achieved with a two-disc potential flow model complemented with empirical closing relationships. A triad of forces governs flow in the cutter head for typical cutting conditions: a centrifugal, suction and gravitational force are considered. For the centrifugal pump effect, and centrifugal pump effect only, the flow inside the cutter is considered steady, non-gravitational, inviscid and non-axial. This allows for the derivation of a pressure-discharge affinity law from the Navier-Stokes. The axial pump effect is governed by the mixture velocity at the suction mouth. It is hypothesized that the pressure difference over the discs drives an inflow at the disc closest to the nose. Centrifugal advection and rapid redeposition spillage are considered the two most significant spillage types out of the six classified. Centrifugal advection can be determined by identifying the onset of radial outflow at the disc near the cutter ring. The magnitude of rapid redeposition flow and its concentration depend on mixing effects that are proportional to the ratio particle settling velocity and the mixture velocity squared. The model is calibrated with three coefficients. User input parameters are the cutter geometry, cut-type factor f_d,type (-1 for under-cut), bank slope angle ξ, cutter inclination angle λ, bank height h, step size l_step, rotational velocity ω, settling velocity v_ts, swing velocity v_s, mixture velocity v_m and material densities.
Spillage=f(D_ring,D_nose,D_pipe,b,f_d,type,ξ,γ,h,l_step,ω,v_ts,v_s,v_m,ρ_q,ρ_b,ρ_w )
For calibration, an inverse flow number θ^-1 is used that is proportional to the ratio of centrifugal flow over mixture flow. Spillage rates from SRCSM are in high agreement with reference data for sand (Miltenburg, 1983) and rock (Den Burger, 2003) in an under-cut swing. A sensitivity analysis suggests that most cutter head dynamics are adequately incorporated. The model is less reliable for (non-typical) inverse flow numbers of  θ^-1= 6 [-] and higher due to a mixture velocity that drops below zero. In addition, the model is calibrated for a relatively high cutter inclination angle of 45 [deg] and bank angle of 45 [deg]. Caution should be observed with the results. It is also suggested that mixing effects related to the swing velocity are incorporated more explicitly in the model. For typical sand cutting conditions, the highest spillage reduction (-4.6%) is achieved by a 1 [%] smaller step size. For rock, the highest spillage reduction (-0.63%) is achieved for a 1 [%] decrease in swing velocity. Spillage appears to follow the theorem of Ellington (1934): it don’t mean a thing if it ain’t got that swing.

Several calculation models have been developed to predict the cutting forces in the linear rock cutting process. Rock failure can occur in different manners: brittle tensile, brittle shear and ductile. Each failure mechanism has a corresponding calculation model with specific cutting geometries and assumptions to predict the cutting forces as accurate as possible. However, several researches conducted in the past show that the predicted forces can differ considerably from the forces measured in the experiments. In this research the author proposes expansions to the existingmodels to increase the accuracy of the force predictions and thereby contribute to a more (cost) efficient cutting process. The calculation models considered in this research are based on two main assumptions: the cutting process is 3D and the tip of the cutting tool is sharp. In a 2D cutting process the width of the cut is equal to the width of the pick point and stays constant throughout the cut. During experiments the sideways outbreaking of rock pieces is observed which can increase the width of the cut tremendously and therefore increase the actual cutting forces. This sideways outbreaking makes the rock cutting process in fact a 3D problem. The assumption of a sharp cutting tool results in another inaccuracy in the force predictions. A sharp cutting tool will penetrate the rock more easily and create a clean cut. If the sharpness of the cutting tool decreases, for example due to wear and tear during the cutting process, a crushed zone will appear in front of the cutting tool, while a wear flat arise at the tip of the cutting tool. These phenomena result in extra forces that has to be overcome by the cutting force. For large cutting depths these effects might be negligible, but for small cutting depths these forces need to be considered. In some applications in the offshore environment only small cutting depths are encountered, such as the vertical drilling for monopile installation or the scraping techniques used in the oil and gas industry. An expansion to include these phenomena in the force prediction models would therefore be a widely applicable concept. After conducting experiments on sandstone samples the magnitudes of the 2D force prediction models, the forces due to the 3D effects and the indentation forces are established. Afterwards the empirical relations of these terms are composed based on the rock characteristics and cutting geometry. The results of this research show that the proposed expansions increase the accuracy of the cutting force predictions tremendously. It also shows that for cutting at a very small depth the forces predicted by the 2D models are negligible compared to the 3D expansion and the indentation expansion, but the 2D models are necessary to calculate the angle and length of the shear plane. However, if the cutting depth increases the indentation force converges to a constant value and the influence of the 3D expansion decreases as well, while the forces in the 2D models increase. The author therefore suggests to keep the 2D effects into the equation to keep the total formula broadly applicable.

In this Thesis the conceptual design of a hull cleaning support vessel in the ARAG will be described. The design will optimize the cleaning operation and benefit safety and efficiency.