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.

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.

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.

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.

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...

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.

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.

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.

The Haringvlietbrug, which was delivered in 1964 and connects the island of Goeree-Overflakkee to the Dutch mainland, approaches the end of its lifetime. Rijkswaterstaat and Witteveen+Bos investigate the potential use of vibration-based structural health monitoring (SHM) to track deterioration. In vibration-based SHM, a change in the structure’s eigenfrequencies indicates probable damage but most current approaches focus on fundamental modes of the structure which are not or hardly affected by small structural impairments. In this study, vibration-based SHM was employed on local modes of vibration of the Haringvlietbrug, with the hope of detecting small-scale damage. New obstacles arose as a result of this: the influence of environmental and operational variabilities (EOV) on the eigenfrequencies of the structure was often larger than the influence of small damage. As a result, the EOVs should be filtered out of the recorded acceleration data before damage sensitive features can be extracted.
To investigate this, 32 accelerometers and 16 temperature sensors were installed in two segments of the Haringvlietbrug. The sensors yield a large data set which was analysed extensively. This made it clear, among other things, that the dynamic response of the bridge deck showed large variability when comparing different vehicle passages.

The first research objective was to investigate the applicability of similarity filtering (SF) to filter out operational variabilities from the Haringvlietbrug acceleration signals to extract damage-sensitive features. SF amplified similarities and damped differences between samples of vehicle passages. This way, only consequently excited modes should remain in the signals which were subsequently used as damage-sensitive features for SHM.
This study found that using SF to filter the operational variabilities from the Haringvlietbrug data set was ineffective. Three reasons were identified for this. First, the method was not robust as a single deviating sample or a poorly chosen filter coefficient significantly influenced the results. Secondly, missing closely-spaced modes might have caused inconsistency of the results. Lastly, SF was not able to converge to consistent behaviour as the variability of response of the bridge deck might be too great for different passages. The latter reason was investigated further in the remaining of the research.

The second research objective was to improve the understanding of the effect of vehicles on local bridge vibrations of the Haringvlietbrug for the application of vibration-based SHM. First, the eigensystem realisation algorithm (ERA) was used to identify and compare consistent mode shapes in order to better understand bridge deck vibrations and find patterns in the eigenfrequencies. ERA is an operational modal analysis (OMA) and output-only system identification technique.
ERA was able to identify two consistent modes in the data but they had a large variance in both shape and eigenfrequency. The uncertainties of the results were too large to draw firm conclusions based on ERA because two of ERA’s key assumptions were not perfectly met and the input samples were not optimal.

Next, a semi-analytical model of a segment of the Haringvlietbrug was built to simulate the important sources of the variability as found in the acceleration recordings of the Haringvlietbrug. The goal of the model was to investigate the sensitivity of the response of the beam to variations of input parameters. The model was both used for time-history analyses and eigenfrequency analyses. Parametric studies showed that the response of the beam was highly sensitive to the time delay between moving masses (dependent on the axle configuration and vehicle velocity), the unevenness (describing any source of vibration of the interaction between vehicle and bridge deck) and the vehicle velocity. These parameters influenced both the amplitude and the shape of the acceleration response of the Haringvlietbrug bridge deck in the time and frequency domain.
The effect of the three dominant parameters was further investigated by simulating four characteristic cases from the Haringvlietbrug data set. Hypotheses on the source of the measurement variability were formed by qualitatively comparing the results of the model to the measured response of the bridge. The model parameters were able to describe a large part of the variability but it was concluded that it is likely that some factors that were not included in the model also play a role in the variability of the measurements.

The above findings led to the following recommendations for further research. Firstly, it is recommended to only select similar vehicle passages for SF because this would improve the ability to converge to consistent modal behaviour. Secondly, should someone want to further explore ERA, it is recommended to equip a section of the bridge with a high spatial density of accelerometers to improve the reliability of the results.
Next, some recommendations related to the model were made. The first step of follow-up research would be to verify the influence of the model parameters on the dynamic response of the Haringvlietbrug by experimenting with different test vehicles. Subsequently, depending on the importance of the parameters, possible extensions of the measurement set-up for a new campaign were proposed. Secondly, the current model could be improved by introducing more parameters, like acceleration of the moving mass or by implementing a more realistic vehicle model, to be better able to explain the dynamic variability. Thirdly, more parameters could be investigated by building a 3D finite element model. This would make it possible to investigate the influence of the presence of multiple vehicles on the bridge and 3D wave propagation.
Upcoming research into data-driven approaches of vibration-based SHM of bridge decks is recommended to focus on similar passages as not all samples contain the same information on the dynamic behaviour of the structure. Decreasing the variability of the input samples might improve the performance of the algorithms.

Climate change is a recurring topic in the news and goes side by side with the energy transition. The energy transition focuses on using clean energy generated by resources like wind and water. Due to the increasing demand for technology that focuses on generating and storing clean energy, the demand for metals grows. These metals are currently extracted from landbased locations but are also found on the bottom of the ocean. Three types of resources are found on the
ocean floor: hydrothermal vents, cobalt crusts, and polymetallic nodules. To extract these resources from the ocean floor, a project called ”Blue Nodules was launched in 2020. This project addresses the challenge of creating a viable and sustainable value chain to retrieve the polymetallic nodules from the ocean floor. Royal IHC is one of the partners on this project and designed the seafloor nodule collector. The total mining system consists of a surface vessel, a vertical transport system, a flexible hose (jumper hose) and a seafloor nodule collector. In combination with a hose developing company, IHC designed the flexible hose. This design was projected on a prior design of the seafloor module collector. Since then, the seafloor module collector design has advanced, but the flexible hose design did not. Therefore the main objective of this master thesis is to design and analyse the flexible hose with its main focus on the dynamic behaviour.
The methodology for this thesis is addressed in the following manner. The old design of the flexible hose was investigated, and all relevant parameters were addressed. A static model was built to verify the parameters that modelled the hose with these parameters. The parameters of interest were: the length of the hose, the distance between crawler and vertical transport system in height and width, number of buoyancy modules, number of buoyancy modules per hose section, starting position of buoyancy nodules. This static model was used to perform a parameter study, resulting in an optimal set of parameters tested against design criteria.
The next stage was implementing the static design in a dynamic software packet called ”OrcaFlex”. Orcaflex is a software program for static and dynamic analysis of offshore systems. The static model is implemented end tested with this software. This resulted in a failure of the set of parameters and adjustment to the static model. After a redo of the parameter study, a new set of parameters was
extracted. This set is tested for an inline motion of the crawler compared to the vertical transport system and for a perpendicular motion. These motions expand in size until the flexible hose reaches its critical values. These tests resulted in a range around the VTS where the crawler could move in.
Results show that the crawler can move in this range for a selected set of parameters. Throughout the research, it is shown that the parameter set needs further development to complete the flexible connection design. It is recommended that some disregarded motions, parameters and environmental forces are further investigated and that the failure criteria that test the hose need to be expanded.

The Hyperloop is a high-speed means of transport, consisting of a bullet-shape vehicle travelling in a quasi-vacuum tube, electrically powered and moving through an electromagnetic levitating system. This allows the reduction of air resistance and wheel-rail contact friction, which translates in higher speeds for smaller power inputs. In the Netherlands, the Dutch company Hardt Hyperloop, has developed a new design concept of such technology, by means of electromagnetic suspension systems, unlike the most commonly applied levitating techniques.

The main aim of this project is to investigate the stability of the electromagnetic suspension levitation system, study the effect that the implementation of an error-based closed-loop control system has on the system dynamics and investigate the vehicle-structure interaction once a control system has been applied to the system.

Along these lines, the overall infrastructure-vehicle system is modelled through an equivalent two degrees of freedom system. In this manner, the inherent instability of the electromagnetic system is confirmed and the initial vehicle dynamics are highlighted. Afterwards, an error-based closed-loop PD-control system that applies to the system definition and reacts on the uncontrolled system dynamics is implemented and the effect of the control parameters on the dynamics and the stability of the system is studied. A certain stability region in the parametric space is derived, which ensures the stability of the system for significant perturbations of the vehicle from its equilibrium point. Besides, the existence of a subcritical bifurcation with respect to the parameter combination is demonstrated. The safety margin in the time delay of the controller response is studied, so as to define a slack time that accounts for not only processing and sampling delays, but also unforeseen events. Finally, the vehicle-infrastructure interaction is studied and its stability is ensured, by means of the previously defined control scheme.

The stability analysis of electromagnetic suspension system applied to Hyperloop in simplified two degrees of freedom system has been studied deeply where the track-beam is regarded as a point mass and the effects of velocity and beam are neglected. However, there is little reference on the study of the interaction between electromagnetic suspension system and wave effects.

The main aim of this thesis is to investigate the dynamic behavior of the EMS vehicle-beam coupled system using the one-dimensional model, and illustrate the combined effects of the EMS and guideway on the vehicle instability at different horizontal velocity by comparing with results of EMS system in simplified model and mechanical system in one-dimensional model.

Along these lines, the tube is modelled as an infinite long Euler-Bernoulli beam resting on a homogenous viscoelastic foundation and the vehicle is modelled as a point mass. The response of the system is obtained both numerically and analytically. The values of control gains are determined based on the equivalent simplified two degrees of freedom EMS system. A representative mechanical system is designed to show the anomalous Doppler waves effects. It is found that for inappropriate values of control gains which will cause instability of vehicle at static state, the one-dimensional guideway has positive effects which can stabilize the vehicle at certain range of subcritical velocity, whereas for appropriate values of control gains the EMS system can counteract the wave-induced instability and keeps the vehicle stable at even supercritical velocity. Finally, a method to linearize the system is presented which allows eigenvalue analysis.

All over the world, many offshore structures have been built in the last decades, both by the oil and gas industry and by the renewable industry. When these structures reach their end of life, they have to be removed. The removal is done in decommissioning projects. Many of those offshore structures are bottom founded. Of that amount, a big part has steel space frame substructures called jackets. Jackets are often removed with a heavy lift vessel. The crane hook of such a vessel is connected to the structure to be lifted by means of lift points. These lift points are the connection point of the rigging with the structure. The structures removed in decommissioning projects are often more than 30 years old. Because of that, there are a lot of uncertainties encountered by the industry in decommissioning projects that can lead to issues, such as loss of information or unknown material strength. The result is that all aspects of a decommissioning project have to be reconsidered each time. This makes the preparation phase costly and time-consuming. An aspect of the preparation is the selection of the lift point type, while it is unclear how and whether an optimum solution is chosen. Therefore the question arises, if the decision making process can be optimized by improving the selection of the lift point type in the preparation phase. One way to optimize such a decision-making process is by means of artificial intelligence. AI is able to compare data where humans see no connection, it can analyze large pieces of data in a much shorter time than humans can, it makes unbiased decisions and it can significantly reduce errors and increase accuracy and precision. This thesis will therefore focus on the optimization of the decision-making process of the lift point design of jackets by means of artificial intelligence. To answer the overall research question, first an analysis is made of various decommissioning projects of the past years. These projects were carried out by Boskalis. In this analysis, an attempt is made to visualize which steps are taken in the lift point selection process. By means of these steps it can be investigated whether there is a repetition or trend in the selection process of the lift points. In addition, the analysis aims to find the criteria the decisions are based on. Secondly, the analysis shows that certain steps are taken by Boskalis in the decision-making process of the lift point design in decommissioning projects. A trend was clearly visible in the way the lift points were selected. The relatively simple options are examined first, after which the more difficult options are investigated if the others prove impossible. In addition, the analysis found clear criteria that are used in the selection of the lift points. These criteria were reflected in the selection process of the execution strategy and in the selection process of the lift points. In addition to the total costs, among others ease of installation and the total duration also play a major role in the decision-making process. For example, an option was chosen that was more expensive than its alternative, but had a much shorter duration. This information made it possible to determine whether AI could be used in decommissioning projects in the future, to accelerate the preparation phase. Thirdly, it is investigated whether AI can improve the decision-making process of the lift point design. Therefore, three AI applications are examined and compared with the previous findings. The AI applications are: machine learning, genetic algorithms and single variable optimization. All three turned out not to be a good solution to the problem. For machine learning there is too little data available. Genetic algorithms do not seem to give the desired output with the given inputs. And single variable optimization is too limited in its solution. The final conclusion is therefore that the three investigated AI applications in this way will not improve the decision-making process of the lift point design. If the data set were to be expanded, machine learning could eventually be applied in the future. In addition, it could be investigated in future research whether genetic algorithms can be used if the input is changed. This thesis only briefly discusses what GA entails and whether the method has the desired output with the data found. Also, only a limited number of AI applications have been investigated in this thesis. But there are many today. For example, multi variable optimization could be a starting point for further research. Because there, the optimization function can have two variables, so that, for example, time and cost can be entered in different units.

Large-scale cultivation of seaweed presents opportunities for multiple global challenges currently at play. Cultivated seaweed can provide a sustainable source of protein for humans and cattle without competing for land, freshwater supply or the use of fertilisers. Kelp forests are known to be a solid basis for an elaborate biome that supports biodiversity in areas that have been damaged by over-fishing or rising sea temperatures. Additionally, kelp forests can lock-in large amounts of Blue Carbon, expanding the oceans’ buffering capacity to mitigate anthropogenic emissions. Furthermore, with their densely seeded lines, offshore kelp farms are found to attenuate wave amplitude, thus providing coastal protection and benefits like increased workability for offshore operations. Both academic publications and industry reviews underline the potential of this sector and significant growth in cultivation is expected in the near future.

Methods currently used for quantification of the damping effects of large-scale offshore kelp farms are diverse and entail varying degrees of accuracy and computational cost. Experimental observations that support the outcomes of these methods are limited to scaled experiments in wave flumes, with various methods used to mimic vegetation. No convergence is found in the most suitable methods for application to large-scale offshore kelp farms.
This research presents a novel modelling framework based upon the Finite Element method, implemented using Julia Programming Language. The effects of the vegetation on the wave climate are represented with a Darcy-Forchheimer term borrowed from porous medium flow theory, including a linear and a quadratic resistance term. The framework comprises a numerical wave tank, using the incompressible Navier Stokes equations. The single-phase model captures the free surface using the coupling of dynamic pressure with a virtual elevation variable through a linearized transpiration boundary condition. Wave energy dissipation is shown to increase significantly by moving the farm structure close to the water surface. Similarly, a decrease in relative water depth - compared to the vegetated height - increases damping potential. Wave period is found to be of strong influence on dissipation, where short waves are attenuated more. Scaling vegetation length with wave length, however, diminishes the reduction in damping of longer waves. Conversely, wave amplitude is shown to be of less influence on the transmission of amplitude through a vegetated patch.
The framework presents a method that is easily scalable, flexible in application on a wide range of flows and vegetation characteristics, and at reasonable computational cost. Introduction of both the linear and quadratic terms extends applicability compared to traditional methods. The approach is verified using convergence studies, application of the model is validated by comparison to existing experimental data. It is shown that experimental set-ups can be reproduced effectively, and simulation results coincide with experimental findings. Validation of outcomes on scales larger than common wave tanks was found unfeasible due to a lack of measurement data. A theoretical case study was performed to predict wave damping of a full-scale kelp farm, demonstrating promising potential with up to 40% wave energy reduction at the local peak wave period.

Further research into the establishment of the Darcy- and Forchheimer-coefficients is recommended. A preliminary range of values has been found, based upon calibration on existing experiments that represent realistic ranges of vegetation characteristics. Furthermore, the main conditions of the flow and vegetation that dictate damping potential are identified. On this basis, research into a physics-based determination of the coefficients is recommended. Additionally, full-scale measurements are advised to validate application on future kelp farm designs.
Through this novel approach, the range of application is increased compared to existing methods, while straightforward setup and usage are governed, and limited computational costs allow for simulation without the need for a dedicated computer setup. The framework is shown to be robust by generating consistent simulation results. In summary, the established framework shows to be a good alternative to existing approaches to investigate the wave damping potential of large-scale offshore kelp farms.

The dynamic behavior of structural components can largely change in the presence of damages. Understanding this behavior is of particular importance for critical engineering systems, and in particular bridges. Damage identification methods forms a key objective in structural health monitoring of bridges so many researches have been conducted in this area. In this thesis, damage identification techniques on beam bridges under moving vehicle loads will be presented in order to produce useful conclusions about the assessment of existing bridges by investigating various numerical applications of different scenarios.
The first objective of this thesis is to derive the analytical expressions needed to be able to predict the dynamic response of many different cases of bridges so that as many real scenarios as possible can be treated. This means that these expressions would be used to investigate damaged beam bridges that can be modelled as an assembly of beams with any number of different material properties, any type of interface or boundary conditions and any number of cracks. For this reason an approach to analyze the bridge as an assembly of n piecewise homogeneous damaged Euler-Bernoulli beams jointed at their edges, will be presented, using the generalized functions to obtain a single expression of the solution which depends on the 4 integration constants associated with the boundary conditions. The closed-form expressions of these 4 constants will be provided. Furthermore, in the presence of internal or externals springs, translational or rotational, additional constants representing the discontinuities have to be taken into account and are computed by considering one additional condition for each discontinuity. The feasibility of this approach and the corresponding analytical formulations is shown with two numerical applications that include all the different capabilities mentioned. Moreover, the implementation of these expressions in a deterministic approach for damage localization is presented, mainly as another example of the many possibilities of the use of analytical formulations instead of other approaches and as an introduction of the so called Inverse Problem with deterministic and probabilistic methods.
The second objective concerns the optimization of damage identification on bridges by comparing different quantities that are evaluated while measuring the response of the bridge (direct monitoring) and the response of the moving vehicle when it passes along the bridge (indirect monitoring). First, the governing equations for the dynamic response of these models are derived, considering the crack(s) as a rotational spring, the bridge as an Euler-Bernoulli beam (or multiple with different properties) and the moving vehicle as a spring-mass system. In this manner, the dynamic response of the bridge is calculated (modal characteristics and displacement) as well as the one of the moving oscillator (displacement and acceleration) and the reaction force acting on the surface of the beam from the moving vehicles. Numerical applications with different beam properties and different number of cracks are performed, using MATLAB for the analytical expressions and SAP2000 for the finite element model, to derive the optimal quantity to be used for damage identification. Lastly, the results are validated by considering and comparing an alternative way of modelling crack, namely as a zone with reduced rigidity, for the same numerical examples, leading to the same conclusions about the crack(s) identification.
Last but not least, the third objective of this thesis is to be able deal not only with the widely used time-invariant damages, namely the always-open crack model, but also with time-variant damages and in this case with the switching crack model. To achieve this, the analytical expressions for the closed-form solutions of the mode shapes derived for the always-open crack are modified to be able to tackle the switching crack model by introducing a Boolean switching crack array which identifies open cracks, modelled as rotational springs. These new expressions would still be able to be used for any number of Euler-Bernoulli beams, any type of interface or boundary conditions and any number of switching cracks. Then, the governing equations for the dynamic response of this model are derived, considering the moving vehicles as moving masses in order to validate the approach with numerical examples existing in the literature and then by introducing its new capabilities. Further, as the computational strategy has been validated, a comparison between time-variant and time-invariant damages is performed concerning crack identification, so that the reader would recognize the importance of understanding the dynamic behavior of different ways of modelling damage in complicate engineering systems like bridges.

The instability of a moving mass / oscillator due to surpassing the velocity of the minimum group wave velocity (in a continuous homogeneous structure) has been studied extensively and is well understood. In contrary to that, Parametric Instability of a moving mass / oscillator on a continuous periodic structure has been studied less extensive and therefore the mechanism behind the instability is unknown. Literature that is avaiable on this topic mainly focuses on continuous periodic inhomogeneous structures, namely where the foundation is modeled as a continuous periodic inhomogeneous structure. Even less well studied are models where instead of a continuous periodic inhomogeneous foundation discrete periodic supports have been used. So far as known to the author there has also been no studies where the discrete supports are coupled through a medium. In order to solve the transition curves discerning the stable and unstable domains concerning the parametric instability of a moving mass / oscillator the analogy with the Mathieu equation is used, which tells us that the solution on those transition curves will be periodic with once or twice the period of the parametric excitation. In this thesis we have focussed on studying the use of the analogy on continuous structures founded upon periodic supports.

The Mathieu equation describes the motion of a parametric oscillator, for example a pendulum with a length that periodically varies over time. The theory that predicts the solution to the Mathieu equation is called Floquet theory and ascociated with the solution are the Floquet exponents, these exponents dictate whether the solution will be periodic and bounded or unbounded. By solving for the Floquet exponents of the Mathieu one sees that for an increase of the amplitude of the parametric excitation the system will experience a greater exponential growth. For a greater mistuning between the parametric excitation and the natural frequency of the equivalent non-parametrically forced equation we see that the system will experience a smaller exponential growth. Outside the instability domains the solutions will be bounded and periodic and contain a wide variety of frequencies. When damping is introduced, the value of the damping coefficient (if written in the canonical form of a viscously damped single degree of freedom equation) will be subtracted from the value of the undamped Floquet exponents and by that result in an upward shift and narrowing of the transition curves. Furthermore, outside the instability domains we will see two regions: the first lies close the the transition curves and is asymptotically stable with a period equal to that of the transition curve, the second covers the remaining stable region and is asymptotically stable and periodic with a wide variety of frequencies.

Regarding the Parametric Instability of a moving mass / oscillator we have studied three different models: a continuous Euler-Bernoulli beam on periodic spring supports, a continuous Euler-Bernoulli beam on periodic supports that are complex (i.e. modeled as an oscillator between two springs), and a continuous Euler-Bernoulli beam on periodic supports that are founded upon a 2-dimensional lattice. Of these models we have conducted a parametric study as to study what the effects are of the various parameters. We have seen that whenever the ratio between the stiffness of the supports and that of the beam is increased, the instability domains will shift to higher velocities and become wider. For certain combinations also 'islands' of instability may appear, where these 'islands' indicate stable areas between regions of instability. If damping is introduced into the system, this will generally narrow the instability domains and shift them to higher values of the mass and lower values of the velocity. However, for certain parameter combinations adding damping will lead to a widening of the instability domain. In the case of a moving oscillator the instability domains will narrow and be shifted to lower values. If the support is modeled with a mass it will affect the general trend of the transition curves through its own resonance, hence for a complex structure it is advised to model the supports with the correct dynamic equations. Last but not least, if the supports are coupled through a medium (a 2-dimensional lattice in this case) one will generally see a similar effect as adding damping has.

In this thesis we have also studied three real world cases: a regular railway track, a high-speed railway slab-track, and the Hyperloop. In the first case we have seen that Parametric Instability will most likely have no influence. For the slab-track, being much more stiff, Parametric Instability will be important. However, a more extensive study with several cases must confirm this. In the last case, namely the Hyperloop, we have seen that for a moving mass the instability domains are relatively large as compared with the other cases. We have also studied the Parametric Instability of a test-pod, which showed that its instability domains that are negligible. Of course, this was merely a test-pod not capable of transporting people, hence when a larger pod is studied it may be expected that the instability domains may not be neglected.

A rapid increase in global energy demand and the international objective of increasing the contribution of renewable energy to satisfy this demand have spiked the interest in offshore wind energy. Depletion of suitable locations for bottom founded turbines has led to a new chapter in offshore wind development: floating wind farms. This relatively new business brings many uncertainties and no large-scale projects have been deployed yet. The performance impact of an increase in structural motions, in comparison with bottom founded offshore wind turbines, is not yet fully investigated with respect to power production of the system. This thesis seeks to quantify this impact on performance by performing an integrated system analysis of a 15-MW semi-submersible based offshore wind turbine for operational conditions at a site north of Scotland.
All considered elements in the fully integrated simulation model are broken down individually and assembled in a finite element analysis framework via OrcaWave and OrcaFlex. OrcaWave develops system RAOs and QTFs using linearised potential-flow hydrodynamic radiation and diffraction theory in the frequency domain, whereas OrcaFlex is a finite element analysis software tool with full non-linear capability in the time domain. The non-linear flow separation induced quadratic drag in a real system, which is not included in potential flow theory, is introduced via a damping matrix by addition of Morison elements to the structure. The overall system including tower, RNA, controller and mooring is analysed by OrcaFlex in time domain. This overall integrated model was first validated and verified against a well-documented open-source reference model, provided by NREL and the University of Maine, and then adapted to the semi-submersible substructure selected for this study. A case matrix is developed representing the site environmental loading scenarios under operating conditions to simulate the dynamic interactions between substructure, RNA and controller. The impact of wind-induced yaw misalignment mean offset angles on the mean power production is examined. For wind speeds below rated, an increase in yaw misalignment angle corresponds to a decrease in mean power production. For a functioning active yaw control system, misalignment angles of the rotor will be small and consequently the mean power reductions will be as well. For above-rated wind speeds, sufficient lift can be generated to compensate for the reduced rotor swept area caused by the yaw misalignment and therefore no reduction in mean power production occurs. Load case results show that with increasing sea state severity, the motions of the system increase. The impact of this increase in motions can be observed in the generator power and rotor thrust response through their fluctuations. Performing an FFT on these parameters shows that most energy in the fluctuations is situated at the incident-wave frequencies and correspondingly, the wind and wave unidirectional load cases present the largest spectral density values for generator power and rotor thrust fluctuations. Furthermore, the results present a connection between the severity of power output fluctuations and the mean power production for above-rated wind speeds. For increasing power production fluctuations, the mean power production experiences a reduction up to 0.39\%. A hypothesis is formed that links the mean power production reduction due to its fluctuations to the response time of the controller. In further research this hypothesis is to be tested and it should be further investigated whether a more detailed integrated analysis model produces similar results. The fluctuations in power production impose challenges on the ability to connect to the grid. Connection of a single floating wind turbine to the power grid is not recommended, but when considering a group of multiple turbines it is assumed that the peaks in power production are flattened out over the total power production of the group. Capacitor banks can then be implemented to create a stable power output to the grid. Quantification of this farm effect is recommended for further research. Finally, an indication of the rotor thrust impact on bending stresses at the tower-substructure interface is presented. A more detailed analysis is to be performed to find local stress concentrations and to address potential structural adjustments to fatigue-prone members.

Wind turbines are typically designed for an operational life of 20-25 years. The operation of the assets can be extended beyond their design life if structural components have sufficient reserves left. One approach is to monitor fatigue loads and compare these with design assumptions to determine the remaining useful lifetime of the assets. A major challenge is that sensors for measuring the stress history, such as strain gauges, only deliver local information. Monitoring of every hot spot is technically and financially not feasible due to cost and access restrictions. In addition, strain gauges only have a limited lifetime when compared to accelerometers. Several response estimation or extrapolation methods have been proposed in literature to tackle this problem. All of them are Kalman filter based methods, with the exception of the Modal Decomposition and Expansion Method. A new Kalman filter based method has been recently proposed in literature called Gaussian Process Latent Force Model. The aim of this work is to assess this new method with respect to existing ones both theoretically and numerically. Theoretically, the Kalman filter based methods always rely on white gaussian noise assumptions for the unknown loads, and the modal decomposition and expansion method disregard measurement imperfections. The new method improves upon these assumptions by providing a flexible stochastic definition for the unknown load, and by taking into account measurement imperfections. The numerical analysis is restricted to a comparison with respect to the modal decomposition and expansion method given the different theoretical backgrounds. The comparison is realised upon a simulation which illustrates and validates the methods, and upon a real-life onshore wind turbine equipped with accelerometers and strain gauges. Measured strains are compared with estimated strains. The accuracy of each method is quantified using the mean absolute error and by the correlation between measurement and estimation. The higher accuracy obtained shows that the new method is an improvement upon existing methods. This is further extended in the calculation of Damage Equivalent Loads. The result shows a relative error that, depending on operational conditions, ranges within 20-40[%] for the modal decomposition and expansion method and less than 10[%] for the new method. These results show that the novel Gaussian Process Latent Force Model method should be taken into account for response estimation when accuracy is relevant. Future works should aim on developing a mechanical model that better capture the real behaviour of the wind turbine, as the accuracy of the response estimation methods is mainly controlled by the validity of the underlying assumptions of the mechanical model. Furthermore, the strain estimations should be sought in the whole frequency range, this can be realised by including measurements that deliver this information: GPS sensors or inclinometers for example.