This thesis develops a numerical Rhino-OrcaWave-OrcaFlex model of the 15 MW Elevator floating wind concept near Curaçao and uses it to compare quasi-static (QS) and dynamic (DYN) mooring-line models. The site is characterised by deep water, with depths of about 800 m close to shore, making the mooring system an important part of the floating wind design problem.

The comparison focuses on selected first-order, wave-only irregular-wave cases. The QS and DYN simulations use the same floater representation, hydrodynamic database, mooring geometry, target pretension, unstretched line length, environmental input, wave seed, simulation settings, and post-processing method. The main response quantities are maximum horizontal platform offset and governing fairlead effective tension.

For the selected cases, the two mooring-line models give almost identical predictions. The largest horizontal offset is approximately 1.15 m, and the largest governing-line maximum effective tension is approximately 963.5 kN. The case-specific offset dynamic amplification factors range from 0.997 to 1.002, while the tension-range ratios remain below unity. The small differences are explained by the limited fairlead excitation in the selected first-order wave-only cases and by the separation between the dominant wave periods and the main moored-system response periods.

The results indicate that the QS mooring-line model is suitable for predicting maximum horizontal platform offset and governing fairlead effective tension within the selected comparison setup. This conclusion should not be generalised to wind-wave-current design cases, second-order wave-drift loading, current-induced line vibration, vortex-induced vibration, turbine-control effects, fatigue, or certification-level mooring design. ... Read more

Going-on-Location (GoL) is a critical phase in jack-up vessel operations, during which the unit transitions from a free-floating condition to seabed support. During touchdown, the spudcans may experience short-duration, high-magnitude impact forces due to the coupled effects of wave-induced vessel motions, nonlinear soil-spudcan contact, and leg deformation. Current GoL workability assessments rely on detailed time-domain simulations to determine impact forces, structural unity checks, and allowable sea states. Although these methods provide a physics-based basis for operational decision-making, they are computationally demanding and mainly describe simulation outcomes rather than the underlying relation between vessel motion and touchdown severity.

This thesis investigates whether the global mechanical energy response of a jack-up vessel can be used as a physically interpretable indicator for touchdown severity and GoL workability assessment. An energy formulation is developed within an existing time-domain GoL simulation framework and verified using energy and power balance relations. The method is applied to transient impact simulations with seabed contact enabled and to free-floating steady-state
simulations in which seabed contact is disabled.

The results show that global mechanical energy provides useful physical interpretation, but does not directly predict impact severity. Critical wave realisations do not exhibit a consistent pre-impact energy level, energy build-up, or common energy peak. Instead, elevated periods in the free-floating global mechanical energy response are most relevant when they occur within the
same time window as the touchdown interval identified in the corresponding impact simulation. Three-hour free-floating simulations can characterise the timing, magnitude, and persistence of these elevated energy periods, but do not provide a consistent threshold between allowable and non-allowable GoL cases.

It is concluded that global mechanical energy should not be used as a standalone workability criterion. Its main value lies in identifying potentially critical response periods and interpreting touchdown behaviour relative to seabed contact. Future work should focus on near-touchdown and initial-contact simulations to relate energy transfer more directly to impact magnitude, while RAO-based reconstruction of the free-floating energy response could be investigated as an efficient screening method. ... Read more

Operability assessment of multibody offshore operations is commonly performed using large numbers of high-fidelity time-domain simulations. When environmental conditions are discretised across realistic ranges of wave, wind, and current parameters, simulation campaigns can involve up to 10⁵ individual three-hour runs, resulting in substantial computational cost. This challenge is shared across a broad class of coupled floating-body operations, including offshore hydrocarbon offloading, CO₂ ship-to-ship transfer, and floating wind installation.

This thesis investigates the use of data-driven prediction models to support simulation-driven operability assessment while retaining response-based decision criteria, using an FLNG–LNGC side-by-side offloading configuration as a case study. The study is based on a simulation dataset produced by the Maritime Research Institute Netherlands (MARIN) for Shell, consisting of time-domain simulations of a spread-moored FLNG with an LNG carrier in side-by-side configuration. From this dataset, a sea-wave subset of 8317 simulations is used for model development and evaluation. Each simulation includes summary response extrema as well as full time-series records of wave elevation, vessel motions, mooring line tensions, and fender loads.

Two complementary machine learning (ML) approaches are considered. The first is a summary-statistics-based learning (SSBL) approach, which predicts operability-limiting response extrema directly from static environmental descriptors using feed-forward regression models. The second is a time-series-based learning (TSBL) approach operating on full response time series. Within this framework, a segment-based forecasting model based on long short-term memory (LSTM) networks and a full time-series model based on transformer architectures with cross-attention heads are employed. For time-series modelling, response signals are decomposed into wave-frequency and low-frequency components to distinguish first-order wave-induced behaviour from second-order drift-dominated dynamics.

At a training fraction of approximately 70%, wave-frequency models achieve mean coefficients of determination R² between 0.6 and 0.8, while low-frequency LSTM models attain mean R² values of approximately 0.8. To reduce training requirements while preserving operability-critical behaviour, a compact training dataset of 1500 simulations is derived using a two-stage selection strategy combining stratified sampling over key sea-state parameters with K-means clustering in response space.

For operability classification based on response extrema across the full sea-wave dataset, a multilayer perceptron trained on the reduced dataset achieves an overall accuracy of 98.22% for 6816 unseen sea states. Time-series-based models achieve an overall classification accuracy of 86.7% and enable reconstruction of complete multibody response histories when the training data sufficiently represent dominant physical regimes, including head-sea, beam, and near-beam wave conditions.

From a computational perspective, the original MARIN sea-only time-domain simulations require approximately 1428 core-hours to evaluate 8317 sea states. In contrast, transformer-based time-series models require approximately 18.9 GPU-hours for one-time training on 1500 sea states and 2.85 GPU-hours for prediction over the remaining sea states, while extrema-based model prediction is effectively instantaneous. These results demonstrate that data-driven models can substantially reduce the computational burden of simulation-driven operability assessment for coupled floating-body systems more broadly. ... Read more

Offshore wind energy is often considered the Formula One of renewable energies. It is a proven technology that provides millions of people with clean and affordable power. However, the available locations for bottom-fixed turbines are being depleted quickly, while the potential of wind energy in deeper waters is immense. Installing power cables for these large floating electricity generators is more complex than for fixed wind turbines. In November 2025, DEME will install the first dynamic cable for an offshore floating wind farm. During the preparation phase, DEME encountered several challenges related to the attachment of ancillaries and low operability. This thesis focuses on the limitations associated with dynamic cable installation.

This research is structured into three main phases. The first phase consists of an extensive literature study conducted to gain insight into the equipment required for the installation process and the ancillaries that must be attached to the cable to keep it properly in place. The second phase involves developing a new vessel layout to enhance the workability of this installation setup. Once a new configuration is established, the third phase consists of building a model of the setup using the time-domain software OrcaFlex. This model was then used to simulate various environmental scenarios, and the results were analysed to compare different methods based on operability.

Key findings from the literature study highlight the complexities of the cable installation process. These complexities include operational weather windows, onboard logistics, ancillary handling, installation speed, and the limitations of the cable, ancillaries, and equipment. One of the main considerations is the importance of risk-mitigating measures to ensure the safe deployment of the cable and its ancillaries.

Multiple concepts were explored and developed with the goal of improving onboard processes and the overall operability of the system. A multi-criteria analysis resulted in the selection of a stinger frame as an alternative to the current cable installation setup.

Cable modelling was performed to obtain the required insights into cable behaviour. The output from the model identifies the limiting factors during installation, such as curvature, sidewall pressure, and cable tension. The simulations include scenarios with various combinations of environmental conditions, such as wave height, wave direction, and wave period.

The simulations showed that a rigid stinger does not improve operability. Due to increased motions at the stinger tip, tensions rise, which further limits operations. However, the risk of minimum bend radius (MBR) breach for the buoyancy modules (BMUs) in the splash zone was reduced significantly by decreasing the time they spend in high-risk positions. Sidewall pressure (SWP) did not prove to be a critical parameter. These findings suggest that a more advanced stinger design could help increase operability.

This thesis provides valuable insights and recommendations for future research, supporting the offshore wind industry’s transition towards floating solutions to access deeper waters with higher energy yields. This development will further strengthen the global supply of sustainable renewable energy. ... Read more

As offshore wind turbines grow in size, the installation of monopile foundations faces increasing technical, operational, and environmental challenges. A key concern is underwater noise pollution generated during pile driving, which poses risks to marine life and must comply with increasingly strict environmental regulations. While conventional impact piling is still the most commonly used technique, it often requires extensive mitigation measures to reduce noise levels. As turbine dimensions, and consequently the required driving energy, continue to increase, these mitigation measures may no longer be sufficient to ensure compliance with noise limits. This has led to growing interest in alternative installation techniques, such as vibropiling and vibrojetting, which are expected to operate more quietly but introduce technical uncertainties, particularly regarding drivability.

This thesis presents a comparative evaluation framework to support early-phase decision-making for low-noise monopile installation and related mitigation strategies. The framework quantifies trade-offs between underwater noise emissions, technical feasibility (drivability risk), operational duration, and total cost across a wide range of installation-mitigation combinations. It is implemented as a modular Python model with Excel-based inputs, in which the user can specify the relevant project parameters. This setup enables flexible and transparent comparison of fundamentally different technological strategies.

The framework was developed through an iterative process of four main steps. First, the current state of installation methods and mitigation technologies was assessed, including recent innovations. Second, internal Van Oord data was analysed to identify key parameters, complemented by expert interviews to validate assumptions and fill data gaps. Third, a dynamic model was implemented and verified through logic testing. Lastly, the framework was applied to case studies to evaluate performance trends, with sensitivity analyses to assess robustness under varying assumptions.

The results demonstrate how the framework enables systematic comparison of installation strategies and the trade-offs between noise, technical feasibility, and cost. This integrative approach is made possible by linking expertise from different specialisation fields within Van Oord. Information that was previously considered in isolation is now combined, creating a holistic overview. While still in its early stages, the framework shows strong potential to provide valuable insights for decision-making, particularly as it is further expanded and refined with additional data.

The case studies indicate that, under current conditions, impact piling remains the most cost-efficient option, primarily due to uncertainties in the drivability of alternative methods. For Van Oord, meeting noise regulations is essential, but achieving the required penetration depth is equally critical, and this is still most reliably achieved with impact piling. According to the model, compliance with noise limits can be reached using an impact hammer with full mitigation, although this relies on idealised assumptions and leaves very little margin, as the hammer operates close to the noise threshold. In practice, site-specific conditions may still lead to exceedances. Moreover, this framework is based on a 15~MW turbine, and as turbine sizes are expected to increase towards 20~MW or beyond, the likelihood that impact piling can meet noise regulations will further diminish. This underlines the importance of advancing alternative installation methods...

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The need for more sustainable and cost-effective energy generation has increased the interest in offshore wind development in deep-water regions. Floating wind turbines offer a promising solution at water depths where bottom-fixed structures are not feasible. Currently, the implementation of floating wind turbines remains limited due to high costs and complex system dynamics. There is a need for efficient, automated optimisation tools that can efficiently identify cost-effective design spaces early in the development process. While optimisation studies have been conducted for semi-submersible and spar-type platforms, limited optimisation related research exists on tension leg platforms (TLPs). This study addresses that gap by developing an optimisation framework for TLPs supporting 15MW wind turbines, allowing for efficient, accurate and cost-effective design iterations while considering platform specific dynamics,.

To achieve this, a frequency-domain model was developed by extending the open source RAFT software. The extensions incorporate features particularly relevant to TLP modelling, including tower flexibility, a sum-frequency force approximation and an analytical tension leg mooring module. The resulting frequency-domain model achieves an error margin within $\pm16\%$ of non-linear time-domain simulations for TLPs with (near) vertical tendons, while reducing computational time by 98.5\%. This makes the model suitable for dynamic analysis within optimisation studies, while enabling TLP-specific response characteristics to be captured at a fraction of the computational cost.

The developed model was integrated into a multi-step genetic algorithm-based optimisation framework to explore the design space, with the objective to reduce the levelised cost of energy (LCOE). The framework, built around a single-column TLP design with four pontoons with tendons at their ends, took into account six design variables to describe the essential system properties. The resulting six dimensional complex design space considers the main column diameter and draft, pontoon diameter and length, tendon angle and tendon pretension. To enable complete design performance evaluations and potentially provide early-stage insights that support certification preparation, each concept was assessed against an extensive set of load cases according to standards, covering both ultimate and fatigue loads in operational and extreme conditions.

The results of the optimisation study identified draft, tendon pretension, tendon angle and pontoon length as the most influential parameters for dynamic performance due to their strong influence on platform stability and mooring stiffness. The column and pontoon diameter had the most significant influence on platform mass and therefore platform cost, while pretension dominated mooring system cost. Despite the identification of these most influential variables, the highly coupled nature of TLPs requires to take all identified design variables into account.

A detailed cost model was implemented, enabling comparison of design concepts within the study, and comparison with floating wind platform designs in other research. To achieve this, the model combines variable platform and mooring costs with fixed lifecycle costs. Multiple optimisation runs revealed several distinct, cost-efficient design spaces, with convergence toward lower LCOE values with increasing iterations of the optimisation. The most cost-effective designs achieved LCOE values around 65 €/MWh, making them competitive with other floating wind concepts across different studies.

Altogether, this work provides an efficient optimisation framework for TLPs in the context of floating offshore wind. It enables accurate and cost-effective design iterations that account for TLP-specific dynamics while significantly reducing computational time. By considering a wide range of load cases and maintaining a balance between speed, adaptability and physical accuracy within a limited degree of uncertainty, the framework offers a holistic approach. This makes it well suited to support early-stage design decisions and concept selection for future deep-sea wind farms using TLPs. ... Read more

As urbanization intensifies and rail and road traffic increase, infrastructure and buildings face growing challenges from ground-borne vibrations, particularly at low frequencies. Traditional mitigation methods, such as heavy masses or stiff trenches, are often ineffective due to the large wavelengths involved. This research investigates metamaterials—mass–spring systems with viscous damping—as a novel solution capable of attenuating low-frequency vibrations through local resonance. Three metawedge configurations—uniform, wave conversion, and rainbow trapping—were evaluated at a target frequency of 10 Hz, typical of soil vibrations induced by trains and traffic. The wave conversion metawedge proved most effective at mitigating surface vibrations, while the rainbow trapping metawedge minimized impact on the surrounding environment by dissipating rather than redirecting energy. Based on these findings, design criteria were developed, including the relative resonator bandwidth (RRBN), optimal mass range, and resonator spacing considerations. Additionally, the potential of impact-based resonators to enhance energy dissipation by exciting higher frequencies was explored. While promising results were observed in a simplified two-degree-of-freedom system, numerical simulations on a soil domain revealed unexpected amplification, highlighting the need for further investigation. This work establishes a foundation for the practical design of metawedges and identifies directions for future research into nonlinear and impact-based vibration mitigation strategies.

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The increasing size and mass of offshore wind monopiles (MPs) present significant challenges for the conventional installation methods, primarily due to limited crane capacities. Vessels with sufficient crane capacity to install future generation XXL MPs, exceeding 3000 t, are scarce and expensive. This creates a need for alternative installation methods that allow the use of existing equipment.

Buoyancy-Assisted Installation (BAI) offers a promising solution to this challenge. Buoyancy has the potential to generate additional lift during the upending and lowering phases of monopile installation, thereby reducing the effective load on the crane. That could enable existing vessels to install larger monopiles without exceeding their crane limits, or requiring costly vessel upgrades.

While current BAI methods mainly explore the use of end caps to seal the MP and generate buoyancy, these caps introduce operational risks. Failure of caps can lead to the monopile sinking, costly delays, and safety hazards such as equipment damage or risk to nearby personnel. Therefore, this thesis specifically investigates the feasibility of using inflatable buoyancy bags for BAI. The use of buoyancy bags is attractive due to their light weight, their adjustable buoyancy through inflation or deflation, and their safety provided by redundancy when using multiple bags.

The research follows an engineering design process. It includes a hydrostatic MP stability study and the development of four buoyancy bag concepts. These concepts were evaluated through a Multi-Criteria Decision Analysis (MCDA), leading to the selection of the most promising configuration. This concept was further investigated through numerical simulations using OrcaFlex and OrcaWave, assessing hydrodynamic performance across various wave conditions and MP upend angles.

Results show that the proposed buoyancy bag configuration can reduce crane loads significantly. The study concludes that buoyancy-assisted upending with external bags could provide a feasible solution for installing monopiles whose weight exceeds the available crane capacity. ... Read more

Electromagnetic actuators are an interesting option for inducing vibrations in structures. However, their performance when attached to a flexible structure is relatively unknown. Therefore, this thesis aims to investigate the coupled dynamic behaviour of an electromagnetic actuator and a flexible structure. The goal is to see if the actuator can induce large displacements in the structure, in a controllable manner, and using a small input power.
Physical experiments were performed with an actuator placed on top of a flexible beam. In addition, a computer model was made that could simulate the system and predict its response. In the experiments, multiple input settings for the actuator were tested using frequency sweeps. Two different control settings were compared: the open-loop setting, which controls the current that is sent through the actuator, and the closed-loop setting, which controls the motion of the moving cylinder in the actuator. For both settings, an input signal is sent to the system. Respectively the current or the cylinder motion, relative to the tip of the beam, has to follow that input signal. The amplitude and frequency of the signal can be adjusted.
The experiments showed that there is no perfect input setting. Each setting has its advantages and disadvantages. Therefore, the best input setting to use depends on the situation. Using the open-loop setting at the resonance frequency of the system resulted in large beam tip displacements, a high effectiveness. However, this coincided with a low predictability of the displacements. On the other hand, the closed-loop setting gave a high predictability with a low effectiveness.
Looking at the efficiency of the system, the beam tip displacements normalised by the electrical input power, also did not give an ideal input setting. This was a result of the dynamic behaviour of the beam and the actuator counteracting each other a little. The beam vibrated most efficiently at its resonance frequency. However, this coincided with large relative displacements of the moving cylinder in the actuator. This generated a large Back EMF, causing the actuator to use significantly more electrical power. Thereby, the Back EMF cancels out the efficiency of the resonance.
In the closed-loop setting, the relative displacement is being controlled, and therefore it cannot increase to large values. This kills the resonance in the system, preventing the beam tip displacement from increasing.
The computer model was reasonably capable of predicting the response of the system. Due to a few inaccuracies in the model, it often slightly overestimated the displacements of the beam. However, the model showed patterns comparable to the results of the experiments, with resonance peaks at the same frequencies.
The model was also used to simulate the system response to closed-loop settings where either the beam tip displacement or the absolute motion of the cylinder was controlled, instead of the relative motion. These control settings were not possible in the physical experiments, due to limitations in the test setup. However, the model results were promising. Both of these settings could give large beam tip displacements, a high effectiveness, in combination with a high predictability. More research with physical experiments on these settings is recommended.
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This thesis is dedicated to applications of high-throughput sequencing data analysis in immunology. Initially, the project included the part focusing on the T cell biology in the context of cancer, supervised by Dr. Pia Kvistborg, and the part focusing on the translational analysis of the breast cancer clinical trials, supervised by Dr. Marleen Kok, both under the general supervision of Dr. Lodewyk Wessels. Because of the COVID19 pandemic, Part 1 of this work focused instead on the T cell functionality in the context of COVID-19. As Dr. Kvistborg resigned in 2022, the larger part of the thesis, Part 2, was completed under the supervision of Dr. Kok and Dr. Wessels, the copromotor and promotor of this work. Thus, this thesis describes bioinformatics approaches to the translational studies in immunology in the context of COVID-19 disease and breast cancer. We demonstrate that the use of genomic and transcriptomic data, including whole-exome and shallow whole-genome DNA sequencing and single-cell and bulk RNA sequencing, allows us to make conclusions about the underlying biology of the disease and identify biomarkers related to disease outcomes and response to treatment. Fatigue damage has been observed in offshore pre-piling templates, yet current design checks do not fully account for it. This thesis examines one potential mechanism: the interaction between the pile, the surrounding water confined in the sleeve annulus, and the template during installation. To capture this behaviour, a high-order cylindrical shell model with soil impedances is combined with a confined-water added-mass representation. The dynamic response under hammer impacts is then solved using modal superposition. Parametric studies are carried out on industry-scale geometries to assess the effects of pile embedment depth, sleeve length, and annular gap size. Transient annular pressures are then converted into fatigue metrics using rainflow counting. A key finding of this study is that confinement is the decisive factor. By increasing the effective hydrodynamic inertia, confinement lowers the natural frequencies of the system. As a result, radially dominated modes are shifted into the frequency range excited by the hammer. This causes originally separate resonances to merge into a dense modal cluster, which amplifies the pressure response. The mode shapes in this cluster are less effective at mobilising soil damping because they contain many local oscillations. As a result, the motions are damped less efficiently, leading to oscillations that are both stronger and more persistent. Compared with unconfined water, where annular pressures are small and cycles are not fatigue-critical, confined cases generate MPa-level pressures and raise the Miner’s sum by up to four orders of magnitude. Severity increases with smaller gaps and longer sleeves. It diminishes with greater embedment due to added stiffness and damping, although this comes with an increase in the number of cycles. While viscosity, compressibility and full soil nonlinearity are idealised, the framework isolates the confinement-driven inertial mechanism and identifies clear design levers. This study clarifies governing parameters and coupling pathways, offering a baseline for future measurements and high-fidelity modelling, but it is not intended as a predictive design tool. ... Read more

Limiting global warming to 1.5°C is urgent, as highlighted by IPCC and IEA reports aiming for net zero emissions by 2050. Wind energy, particularly offshore, offers significant potential for renewable energy capacity expansion. Although offshore installations are limited to shallow waters using monopiles, deeper waters with higher wind speeds require larger turbines. This transition to deeper waters and larger turbines is challenging and requires continuous development and innovation. Floating wind turbines show promise for overcoming these challenges, but further improvements are needed to scale up floating wind farms and reduce installation costs for profitability. Bluewater Energy Services is a company actively exploring solutions to improve the installation method of floating wind turbines with the Transport and Installation Frame. In addition to the market gap for the installation of floating wind turbines, there are also opportunities in the development of bottom-fixed wind for larger wind turbines and greater water depths. Therefore, the goal of Bluewater is to design a frame for the transport and installation of both bottom-fixed and floating wind to increase profitability.

The aim of this research project is to assess the feasibility of the Transport and Installation Frame for bottom-fixed wind. The research question has been answered using a systematic design methodology. Initially, information was collected, research questions were formulated and starting points were established through a literature study. The first phase, system analysis, outlined the transport and installation methodology and defined the design criteria. Subsequently, the design of the bottom-fixed structure, which could be installed using the frame was explored. Finally, the limitations of the transport and installation methodology were examined, particularly focusing on the maximum angle of heel, natural period, and the weather window.

Towards the conclusion of the thesis, an evaluation is presented regarding the feasibility of the frame for bottom-fixed wind. This includes an initial design for the bottom-fixed structure and the transport and installation methodology, based on the integrated installation method for a 15 MW wind turbine. The transport and installation methodology in this thesis focuses on the compression principle. In which the Transport and Installation Frame remains at the waterline and the bottom-fixed structure is lowered to the seabed at 80 meters by pushing it with spud piles down. This study identifies critical stages and associated issues related to static stability, maximum heeling angles, deck or edge immersion, spud pile strength, seabed placement, and the natural periods in heave and pitch.

The results of the design research indicate that, within the identified limitations, there are no significant unresolved issues affecting the feasibility of the transport and installation frame for bottom-fixed wind. This conclusion is based on analyses focused on static and strength analysis. To assess the technical feasibility, it is recommended that the specifications of the weather window be refined, static optimisation be performed, and critical issues related to dynamic behavior be addressed, specifically during seabed placement and dynamic responses to external forces. To further develop this project and explore the profitability, it is recommended to obtain an overview of the specific location, costs, and installation time. ... Read more

In recent decades, the global push for sustainable energy has grown, with offshore wind turbines emerging as a successful solution. This has led to the rapid growth of the offshore wind farm industry. As more wind farms are built, the demand for offshore installation vessels has increased significantly. It’s crucial for contractors to complete wind turbine installations safely, reliably, and fast. As turbines continue to increase in size, they require higher lifts of larger blades, complicating the installation process due to component movement.

One of the most critical stages in turbine installation is aligning the rotor blade with the hub. Blades can be attached to the hub from various sides. The most used method involves horizontal blade installation, but also diagonal and vertical installation has been done. To achieve alignment with the hub, the blades are lifted using yokes and their position is controlled using taglines. Taglines connected to the crane boom, slewing platform, or both are used. Taglines can operate in constant tension or speed-dependent tension modes. The question arises, how do different blade installation methodologies perform and compare.

The objective of this research was to model and quantitatively compare the performance of various blade installation configurations. Performance is measured by how well the blade root stays within a 0.2 meter envelope under different wind conditions to allow the final mating of blade and hub. The first step was to study the parameters affecting turbine blade alignment simulation, focusing on wind as the main environmental factor causing blade movement. This led to a detailed examination of the essential parameters to accurately model turbine blades.
A 6 degrees-of-freedom dynamic simulation model of a 15 MW wind turbine blade suspended from an installation crane was developed, focusing on the blade’s dynamic behavior during alignment with the hub. The model simulates the aerodynamic forces on the blade and its motions under different scenarios, considering environmental factors like wind velocity and turbulence intensity, but excluding movement of the jack-up vessel, vessel crane, and hub. The model allows for simulating many combinations of blade position, tagline configuration, and tagline operation mode, comparing the performance of different installation techniques during various wind conditions.

From the results, it is most likely that the way of attacking the hub by the turbine blade (side or bottom) is of high importance. From the results it appears that horizontal installation is most reliable. The model indicates that a tagline system that adjusts the pull force based on the speed of the blade’s movement as the most effective and the tagline configuration was of less importance. The results demonstrated that a higher steepness of the slope (ratio between tagline force and pay- out speed) of the damping tugger improves the damping of the blade and is most favourable for offshore turbine blade installation. The model indicated that the horizontal-horizontal installation method was the most effective. The results showed that it was most feasible to install the blades at wind speeds up to 8 m/s. For higher wind speeds, installations could still proceed if there was lower turbulence intensity.

It is recommended to extend the model to include vessel, crane, and hub motions. Another recommendation is to validate the simplified blade model with detailed (confidential) blade data. Finally, using a more detailed model to explore tools and control strategies to minimize blade root motions is recommended to improve workability. ... Read more

Founded in 1910, Boskalis, a leader in offshore operations, contends with limitations in ABB's Ability Marine Advisory System 'OCTOPUS' in predicting maximum vessel motions for heavy-transport vessels (HTVs). Accurate prediction of these motions, especially roll and pitch, is vital for transporting large, heavy structures, as exceeding predefined limits can jeopardize both vessel and cargo integrity. OCTOPUS's challenges, stemming not only from its reliance on linear theory but also potentially from the quality of its environmental data, underline the need for exploring alternatives, such as Machine Learning (ML) approaches, adept at handling complex, nonlinear phenomena, to ensure operational safety and efficiency.

This thesis presents the development and comparison of three new approaches to predict maximum roll and pitch motions. The approaches are compared and evaluated against OCTOPUS. Two validation strategies are used to test their performance under known and unknown loading conditions (LCs). Known LCs in this context refer to the evaluation of data that incorporate LCs that are included in the training dataset for ML-based approaches. On the other hand, unknown LCs refer to the evaluation of data that incorporate LCs that are not included in the training dataset for ML-based approaches. The approaches are trained and validated using sensor data, LC data, and environmental data from 24 different voyages for a specific HTV. They differ in their design and the type of environmental data they use.

The superior performance of ML-based approaches over OCTOPUS in known LCs is mainly due to two factors. First, ML approaches inherently incorporate nonlinear phenomena, which is particularly effective in accurately predicting maximum roll motion. Second, they are better equipped to handle flaws in environmental data. Although these advantages contribute to a significantly lower mean absolute percentage error (MAPE) compared to OCTOPUS, ML-based approaches face challenges in unknown LCs and extreme motion response scenarios. However, it is noteworthy that ML approaches quickly adapt to unknown LCs when small portions of these LCs are included in the training dataset.

ML shows potential in vessel motion prediction, and this thesis underscores the importance of diverse training data to enhance its reliability in unknown LCs and extreme motion response scenarios. For Boskalis, addressing these challenges with strategies such as adjusting the custom loss function, data augmentation, and implementing ensemble methods could improve the accuracy of these approaches. This progress is significant for Boskalis and the wider maritime industry, paving the way for adaptive and efficient prediction systems. Collaborative efforts between industry and academia, using rich data and expertise, are essential to drive these innovations. ... Read more

The maintenance and repairs of transition zones pose significant challenges in the railways industry due to their accelerated degradation rates in comparison to free tracks. These zones, characterized by track property variations, amplify their response when a source travels along the tracks. The resulting amplifications in stress and strain fields lead to differential settlements, affecting both track's stability and passenger comfort. This study investigates the influence of incorporating active control forces and moments at the interface of transition zones to mitigate the excessive degradation of soft domains.

Three 1-dimensional models are developed, which include active control forces and moments as a novel method to minimize the amplification of the response in the soft domain of transition zones, as well as, the derivation of these forces. The purpose of these three models is to give the reader an inside view of the method to derive these active control forces with models that increase in complexity.

The first model involves an Euler-Bernoulli beam resting on a piece-wise inhomogeneous Winkler foundation. The second model extends this by including a shear beam and a second layer of foundation, with the first layer being homogeneous and the second layer piece-wise inhomogeneous (Kerr foundation). The third model is a hybrid model between the first two, on which the soft domain is represented by the description of the second model, and the rigid domain by the description of the first model. Numerical solutions in the time-domain were applied to these models, and the study focused on a transition zone subjected to a constant amplitude moving load with constant velocity, traveling from a soft to stiff domain. The purpose of the first model is to give the reader a general idea on the derivation of a very simplistic model. The second model's purpose is to better represent the different elements of a railway structure, on which the shear beam and the lower layer of springs represent the mobilised soil under the tracks, while the top layer of springs and the Euler-Bernoulli beam represent the ballast, the sleepers and the rail. Finally, the third model was made to represent a transition zones, on which the soil is discontinued due to a man-made structure, e.g. a concrete bridge, which leads the structure under the ballast, in the rigid domain, to be consider infinitely stiff and to be represented just by an Euler-Bernoulli beam on a Winkler foundation.

Findings reveal that the active control forces and moments are capable of fully mitigating the dynamic amplification in soft domains of transition zones, however, they increase the dynamic amplifications in the stiff domain. Moreover, the shape that these forces take over time is dictated by the interaction between both domains of the transition zone, when the interface of the transition zone has continuous elements, the forces take a similar shape to the eigenfield of the system, while when there is discontinuous elements over the interface, the forces take a 'flipping' shape. Furthermore, of the two parameters studied (velocity of the moving load and vertical stiffness), the dominating parameter in the response of the system depends upon the regime that the system is being subjected to. For relatively low and extremely high velocities of the moving load, the system is dominated by the vertical stiffness ratio, while for medium velocities of the moving load, the system is dominated by the velocity of the moving load. Finally, transition zones with discontinuous elements require significantly more energy to be absorbed and added into the system by the active control forces to mitigate the dynamic amplifications in the soft domain of the system.

These thesis offer valuable insights for preliminary designs of active control forces aimed at diminishing the dynamic amplification of soft domains of transition zones railway. ... Read more

In recent years the global energy demand has rapidly increased and will continue to grow in the next decades. With the growing demand for energy and the international agreement to use more renewable energy, the offshore wind industry is developing rapidly. This causes offshore wind farms to be installed at locations with larger water depths and wind turbines becoming larger and heavier, leading to the use of support jackets. Due to this trend, pre-piling templates are used more often in the industry to decrease the installation time and increase the accuracy of offshore wind parks supported by jackets. Pre-piling templates are made to align and guide foundation piles during pile driving. Huisman built a pre-piling template to install two offshore wind farms off the coast of Taiwan. After installation, it turned out that the secondary steel on the template was severely damaged. In this thesis, research is done to identify the possible reasons for damage to the secondary steel of the pre-piling template during pile driving.

An investigation of currently available literature has identified possible causes of increasing loads on pre-piling templates. The difference between most of the pre-piling templates investigated in the literature and the template of Huisman is the use of friction pads instead of rollers to guide and align the foundation piles during installation. In addition to aligning and guiding the foundation piles, friction pads also clamp the pile. Based on a thorough literature review and the current design of the template, a hypothesis regarding the cause of the damage was formulated. The hypothesis states that the current design of the template causes an increase in normal force and friction force between the pile and the pads during pile driving, damaging the secondary steel of the pre-piling template.

To test the hypothesis, a model is developed to describe and analyze the dynamic interaction between the template and foundation pile during pile driving. The model exists of an external hammer force, a LuGre dynamic friction element to represent soil-pile interaction and a part representing the stick-slip interaction between the pile and the pre-piling template. The model has been implemented using Matlab to generate the system response in the time domain from the corresponding equations of motion. The different components of the model are validated and verified using field data and data from the literature. While the model has been fully verified, the model could not be quantitatively validated due to a lack of data, but the model has been qualitatively validated based on trends from literature.

The use of friction pads leads to energy transfer from the hammer blows into the template due to the existing friction forces between the pile and the pads. Additionally, results show an increase in normal force between the friction pads and the pile during a hammer blow due to the design of the centralizer. The rotation of the upper centralizer causes an increase in normal force between the pile and pad due to its orientation... ... Read more

The increase of demand for offshore wind energy resulted in an increase of larger wind turbines. These turbines are often placed on top of a monopile (MP) substructure. The conventional method for installing these MPs uses a jack-up vessel. However, due to the local bathymetry and soil conditions. This method has its drawbacks, such as unavailability due to soil conditions, impracticality in excessively deep waters, or high costs. Heerema Marine Contractors (HMC) aims for the novelty of installing these MPs by using semi-submersible crane vessels (SSCV). Installing the MPs with a floating vessel is an attractive alternative due to its accessibility and speed. To counteract the extra motions of the floating vessel a Motion Compensated Gripper Frame (MCGF) is utilized. This gripper frame uses eight rollerboxes (RBs) equipped with polyurethane (PU) rollers to keep the MP in position, being able to install MPs from 7 up to 12.5 meters in diameter.

During pile driving, vibrations will propagate through the MP, inducing vibrations within the RB. Existing pile driving models fall short in accurately describing the behavior of large diameter MPs. In large diameter MPs the effect of the so called ‘breathing’ of the MP is discarded as the radial coupling is neglected. In addition, the material properties of the PU rollers are undefined or uncertain.

This thesis investigates the coupling between the MP and RB vibrations by using a numerical model derived with the Finite Difference Method (FDM). Three models were proposed: (1) the MP model, (2) the RB model and (3) the coupled model. Where the latter is coupled by incorporating a spring-dashpot system to simulate the behavior of the linearized PU rollers. The MP is considered behave axisymmetrically, simplifying the 3D wave equations to a 2D system of equations. The resulting motions from these models are directly compared to the motions obtained from a Finite Element Method (FEM) simulation in Abaqus. The MP model, in particular, exhibits good agreement with the Abaqus model. The RB model and coupled model predict higher accelerations than their FEM counterparts, aligning with expectations as the FDM model is computed by the 1D Euler-Lagrange beam equation, directing all stresses and forces directly into bending of the beam.

Analysis of the dynamic stiffness in both the MP and RB reveals that the RB is vulnerable to excessive vibration when the roller stiffness aligns in such a way that the eigenfrequency of the RB intersects with the ring frequency of the MP. This susceptibility is particularly notable in the case of small-diameter MPs (7-7.7m), where the roller stiffness that causes excessive vibrations, is close to the assumed base value of 200 kN/mm. In the category of large diameter MPs, a roller stiffness exceeding 1650 kN/mm could produce a similar effect. As the roller stiffness is a critical parameter for the response of the RB, it is important to know its value during the design phase. To prevent or mitigate excessive vibrations, it is essential to choose a roller stiffness that avoids eigenfrequency intersections between the RB and the MP. This proactive step is vital for optimizing the performance and stability of the MCGF during pile driving operations.

It is crucial to acknowledge that this thesis employs a simplified hammer input force for a 12.5m diameter MP, showcasing predominantly low frequencies. In reality, higher frequencies occur, which could result in more energy density, a significant consideration given that smaller diameter MPs result in higher ring frequencies. For future analyses, determining specific hammer forces corresponding to different diameters is therefore recommended.

Furthermore, the comparison between the industry practice for calculating resulting stresses in the RB and those derived from the numerical model indicates higher stresses in the industry approach. However, it is noteworthy that the predominant contribution to maximum stresses originates from the prestress on the MP, constituting 93% of the total stress. As a consequence, the additional stresses attributed to accelerations are relatively negligible in comparison. ... Read more

Jack-ups are used for offshore wind turbine installation (OWTI). To assess whether a jack-up can safely operate in a desired geographic location with known seismic activity, an earthquake response analysis is required for structural verification. This analysis is generally carried out according to the codes of the International Organization for Standardization (ISO). The prescribed procedure is called extreme level earthquake (ELE) screening and is performed using response spectrum analysis (RSA). This method is intended to be conservative and should produce higher utilization results than more detailed assessments. With offshore wind farm development moving into regions with greater seismic activity, more detailed assessments are required to demonstrate safe operation in those geographic locations.

The aim of this research was to improve the accuracy of earthquake screening of OWTI jack-ups in order to increase their geographic operability. A new ELE-screening procedure was proposed that uses time-history analysis (THA) and spectrum matched acceleration time history records (THR). For the development and benchmarking of the new method, an earthquake analysis was performed using both the new ELE-screening procedure with THA and the existing ELE-screening procedure with RSA. The analysis was performed for an OWTI jack-up based on the GJ-3750C located in a region offshore Japan. The RSA simulations were performed using Minifem; a new tool was developed in OpenSees for the THA simulations. To assess the effect of various parameters, simulations were run with different soil-structure connections, levels of damping, and design response spectra. The performance is evaluated using the global maximum action effects; limited to the forces and moments at the lower guide and footing. A soil-structure interaction analysis was performed on an equivalent single degree of freedom system to validate the soil-structure interface model, and the use of free field ground motions. A procedure and accompanying tools were developed for acceleration time history record selection and modification. The resulting spectrum matched THR are used for seismic excitation in the THA simulations.

The simulation results showed a reduction in the magnitude of calculated action effects when using the new ELE-screening procedure. A reduction of 10 to 20 percent in the global maximum shear force and moment was observed in the simulations best describing the jack-up and site-specific soil conditions. A small reduction of the global maximum normal force was also observed. The new ELE-screening procedure with THA can be used to demonstrate compliance with earthquake performance requirements when a jack-up does not satisfy the ELE-screening assessment criteria using RSA. Since safe operation can be demonstrated for more areas, the geographic operability of OWTI jack-ups is increased.
... Read more

Pile driving is a widely used technique for the construction of buildings and infrastructure. A popular technique is to vibrate the pile into the sediment. However, since building sites are increasingly being located in metropolitan areas, there is a growing concern about the environmental impact that vibrations may cause during driving. Therefore, pile driving assessment and prediction have become important for several reasons, including reducing the risk of damage to nearby structures and limiting disturbance to adjacent properties. In particular, pile driveability (i.e., the penetration rate) assessment is immensely useful prior to installation as it increases the construction performance and subsequently reduces costs and environmental impact.

The important factors influencing the penetration rate include vibrator characteristics, pile properties, and soil conditions. However, due to assumptions and the lack of methods that accurately represent the complex phenomena at play during vibratory driving, a disparity is obtained between the predictions of modern pile behavior programs and the observed penetration rate.

Recently, the registration of pile driving data has increased significantly. This extended amount of measurement data can potentially be leveraged for an improvement of the prediction of the penetration rate in future projects. Literature review on the application of machine learning (ML) within pile driving, geotechnical engineering and drilling revealed that the artificial neural network (ANN) is a promising alternative method for the prediction of the driveability of vibratory driven piles (i.e., vibro-driveability).

In this work, machine learning methods and the traditional model were utilized to predict vibro-driveability. Promising ML techniques include the multilayer perceptron neural network (MLPNN) and radial basis function neural network (RBFNN). These neural networks were trained with the particle swarm optimization (PSO) algorithm. The backpropagation (BP) algorithm was also incorporated to train the MLPNN and RBFNN models as a conventional method. Based on results obtained with the aforementioned methods, we propose a new model, the Vibratory Driveability (VD) model, that combines the fruitful characteristics of the MLPNN and RBFNN.

The performance of the five different models was compared with the performance of contemporary vibro-driveability prediction software for three test sets. This was done using different performance indices including the mean squared error (MSE), mean absolute error (MAE) and the weighted average percentage error (WAPE). Additionally, the desired characteristics of the predictions based on the geo-engineer's input were examined and compared with the obtained predictions. It was demonstrated that the ANN-based methods achieved drastic improvements in prediction performance and consequently outperformed the traditional model, making ANN-based methods the preferred alternative for the prediction of vibro-driveability. Among the ANN models, the VD model produced the highest performance, as it reflected the desired prediction behavior for all three test cases and showed competitive prediction performance in terms of the performance metrics.

This work leads to the first-ever published research on the application of artificial neural networks for the prediction of vibro-driveability. As such, it could form the foundation for the development of new (vibratory) pile driving behavior assessment and prediction software. The development of these commercial applications could lead to a considerable reduction in costs and environmental impact. ... Read more