With the climate goals of the Paris Agreement and the European Green Deal, countries need to reduce their carbon footprint and increase their renewable energy production. For countries with high population density, land-based photovoltaics (solar) takes up valuable space. Therefore, solar application at sea is considered. One of the proposed designs is by the Joint Industry Project (JIP) Solar@Sea II. The JIP structure is flexible, inflatable, and considerably smaller than Very Large Floating Structures (VLFS). The goal is to mitigate the installation and transportation disadvantages associated with VLFS. Combining multiple of these singular structures in an array allows for the same operational solar footprint as would be the case for a single VLFS. To keep the structure at the intended location, a mooring system needs to be designed. For the mooring line analysis, the motions of the attachment points of the mooring lines to the floating structure must be deter-mined. These motions are dependent on the interaction between the fluid, structure, and mooring line system. The development of a numerical method that is able to determine the flexible motions of the structure is required. This method should be suitable for the initial design stages of the structure and mooring system. A numerical method for the deep-water regime in frequency domain was developed. The structural deformations are determined by means of the Finite Element Method (FEM) in ANSYS. The fluid interactions with the structure are determined by means of a lower order Boundary Element Method (BEM). The combined effect of both structural motions and fluid behavior is captured in an equation of motion. The motions of the flexible structure can then be determined by solving the equation of motion. The method is written in Python and the interaction with ANSYS is achieved by means of an ANSYS APDL interface. The numerical method was successfully verified by comparison of results with analytical solutions. The nu-merical method is validated by comparing the numerical result with experimentally determined responses of a 1:1 scale JIP structure to incident regular deep-water waves as measured by MARIN. Suitable deep-water test cases were determined from the MARIN data. The undisturbed numerical wave was compared with the undisturbed deep wave measured by MARIN. Finally, three test cases were selected for the validation of the interaction of the structure and the wave. These consisted of a wave longer than the structure, a waveslightly shorter than the structure, and a significantly shorter wave than the structure. The numerical method was able to accurately predict the structure motions for waves longer than the structure. For waves shorter than the structure, the error between the numerical method and the experimental data increased as the wavelength decreased. The errors found can likely be attributed to the nonlinear interaction of the ballast bags, which are not considered in the current numerical method. This cannot be confirmed based on the available experimental data. The presented work is part of a larger intended method, which is not yet finished. Satisfactory results were found for the components considered in the verification. The validation provided points for improvement for the current numerical method. The response to waves longer than the structure can be determined accurately. The method is less accurate for waves shorter than the structure. The recommendation is therefore to research the effect of the ballast bags on the structure response in shorter waves. This could result in a better approximation for structural responses in shorter waves.

The growth in the offshore wind industry sees an increased demand for offshore service vessels (OSVs). These vessels often operate in harsh conditions, and their performance is heavily dependent on their seakeeping characteristics. Conventional ship design processes fail to effectively consider seakeeping early in the design process, leading to sub-optimal vessel design. A design framework has been developed in the software 'NAPA' to efficiently design high-performing OSV concept designs. The developed framework is able to optimize a hull shape -specifically the main particulars and length of different hull sections- to maximize performance in certain objectives. These objectives are seakeeping, ship resistance, lightship weight, and station keeping power requirements. Regarding seakeeping, the attainable percentage operability is calculated for each iteration, although the Operability Robustness Index (ORI) is optimized. The ORI is a more robust seakeeping key performance indicator (KPI) than percentage operability, which is advantageous when facing concept design uncertainty. The framework maximizes ORI, thereby seakeeping performance, for a particular loading condition, motion sensitive criteria, and operational area. The ORI is evaluated based on the area of operation's scatter diagram and wave spectrum, governing motion limits, and iteration-specific RAOs. Designs are required to satisfy an initial stability constraint, to ensure feasibility. The framework's output is a Pareto-frontier showing the trade-offs between different KPIs, and the corresponding variable combinations. Thereby, the naval architect can evaluate what design offers the best overall performance. A 'feeder' OSV, designed to transport wind turbine components to wind installation vessels has been optimized to validate the framework. This OSV is currently being developed as a concept by C-Job naval architects. The ship has been optimized for maximum operability of an Ampelmann motion compensated platform. A single optimization run took three and a half hours to complete 300 iterations, thereby finding the Pareto-frontier. Comparing the Pareto-optimal solutions with the base vessel, the ORI can be increased up to 3.6%, the lightship weight decreased by 21.1% and the ship resistance decreased by 13.0%. The framework showed that smaller vessels can still attain good seakeeping performance, leading to a substantial reduction in lightship weight. The increase in seakeeping performance allows for the use of less expensive motion compensated equipment while maintaining high operability. The framework showed that there is a trade-off to be made with regard to seakeeping, and lightship weight, and ship resistance. The framework presents what variables and ship attributes cause these trade-offs. This information allows naval architects to determine the optimal design direction during concept design. Clients and naval architects can decide what trade-off in performance provides the ideal combination to achieve the ship's mission. Consequently, besides producing high-performance designs, the framework substantially increases early design knowledge. Thereby, the overall design process becomes more efficient. The framework showed to be a valuable tool for OSV concept design. By the extensive incorporation of seakeeping early in the design process, naval architects can design high-performance OSVs efficiently. The produced designs maximize performance in any of the KPIs, ensuring vessels have a high operability, but do not weigh more, or have higher fuel costs than is needed.

An important trend exhibited by the offshore wind market is the increase in the size of wind turbines, leading to longer and stiffer monopiles with larger diameter-to-thickness ratios. Current transport analysis is focused on loads resulting from hydrodynamic accelerations, without taking loads into account resulting from differences in bending deflection between the vessel and cargo. This thesis covers a study carried out on the structural response of a monopile and sea-fastening system subjected to displacement-based loads. The loadcase follows from a vessel excited using a regular wave leading to bending deflections and rigid body accelerations. The saddles used to support the monopile are modeled as unilateral springs, emphasizing the need to use a non-linear solution method to obtain structural responses. The harmonic nature of hydrodynamic-based loads led to the selection of the harmonic balance method (HBM) used as solution method in the structural model. A novel understanding how cargo properties, seafastening properties and seafastening arrangements influence the structural response of the coupled cargo-seafastening system. Various parametric studies are performed to identify behaviors related to the total structural response. Based on this study, the conclusion can be drawn that a large number of saddles in combination with a low stiffness is desired to minimize the structural response of the cargo and sea-fastening system. Furthermore, the influence of lashing stiffness and pretension is limited with respect to the total response. At last, a parametric analysis on the properties of the cargo showed that certain sea-fastening arrangements can be identified which comply with design criteria.

The offshore wind energy market is expanding and the number of offshore wind turbines being installed in the near future is rising. Offshore wind turbines are being installed further offshore and in deeper waters. Besides, to lower the cost of wind energy offshore wind turbines are increasing in size and power output. Both wind turbines and their support structures are expected to keep increasing in size and weight in the coming years. After fabrication, wind turbine components and support structures have to be transported to onshore storage depots or to their offshore location. To enable safe transports, wind turbine components and support structures are constraint to heavy transport vessels or transport barges by sea fastening structures. As a result of wind turbine components and support structures increasing in size and weight, the reaction loads for which sea fastening structures need to be designed are increasing as well. Since increasing reaction loads have various negative consequences which are expected to become more critical for future transports, there is a need for an optimized reaction load calculation. The current method of calculating the reaction loads which is widely used in the industry is often referred to as being a conservative method. The aim of this thesis was to enhance the existing calculation method of the reaction loads by shifting from a conservative approach towards a method of calculating reaction loads based on an acceptable probability of occurrence during transports. By calculating the reaction loads for an acceptable probability of occurrence it is avoided that sea fastening structures are designed for overly conservative reaction loads while the structural reliability of these structures will still be ensured. In this thesis an existing sea fastening design project from the industry was used to perform a case study. Data and information from this project were used as input to perform motion analyses of a vessel which is transporting a jacket support structure. The obtained linear wave-induced accelerations of the jacket CoG were used as the main input for calculating the reaction loads. It was first investigated how these 6-DoF accelerations of the CoG are used in the current method of calculating the reaction loads. This was followed by introducing statistical extreme value theory with the purpose of using the accelerations of the jacket CoG as input for a probabilistic method of calculating the reaction loads. The findings of this research show that optimized reaction loads can be obtained by replacing the current calculation method by a long-term probabilistic method. It was found that this long-term probabilistic method could be derived by combining 3-hour extreme value density functions of reaction loads with the probabilities of encountering the various sea states at the location on the route for which the most severe environmental conditions are expected. The long-term probabilistic method was used to perform a probabilistic investigation of the reaction loads calculated with the current calculation method. It was found that the return periods of the reaction loads calculated with the current method were significantly different for the individual jacket legs. Moreover, it was found that the sea fastening design for at least one of the jacket legs was expected to be over-conservative. By presenting the long-term probabilistic calculation method, a methodology was introduced which determines reaction loads based on acceptable return periods while avoiding over-conservative sea fastening designs. This research has provided a new insight into the method of designing sea fastening structures. The long-term probabilistic calculation method can be applied in practice to determine optimized reaction loads incorporated in sea fastening designs. This research therefore makes a valuable contribution to preparing the reaction load calculation method for future transports which are expected to become more critical due to wind turbine components and their support structures growing in size and weight.

In an era where global energy consumption has been rising steadily, the demand and supply of renewable energy sources have become increasingly important. Offshore wind is a promising renewable energy source, which has been actively developed in the last decades in the form of bottom-founded offshore wind, bound to shallow water. Floating Offshore Wind Turbines (FOWT) offer a solution for countries without shallow coastal waters with an abundance of wind potential. In a competitive market with different solutions, Bluewater Energy Services (Bluewater) has developed a tension leg platform (TLP) type substructure to support a 15MW turbine. These FOWT installations are subject to the random nature of environmental loading which is highly stochastic in terms of amplitude, frequency and phase angle and is hence considered multiaxial non-proportional (random) variable amplitude loading. Multiaxial loading does not, however, guarantee a multiaxial stress response. One of the considerations for offshore structures subject to repetitive loading is fatigue lifetime estimation, which is predominantly done using uniaxial assessment methods. This is not an issue if the stress response is dominantly uniaxial, however, literature has demonstrated that evaluating a specimen subject mode-{I,III} multiaxial stress response using uniaxial (mode-{I}) assessment methods can lead to a significant overestimation of the fatigue lifetime. To investigate the (multiaxial) stress response of fatigue-critical weld seams in TLP-type FOWT substructures, a new simulation methodology needed to be developed, which allowed for the structure's rigid body motions and elastic deformations to be captured. This methodology was built on an existing hybrid rigid-flexible modelling approach. It was improved upon by considering local (panel-based) hydrodynamic pressure and kinematic structural boundary conditions in order to conduct coupled (aerodynamic-hydrodynamic-mooring) analysis with integrated structural analysis. This approach allowed for the system motion and structural response to a dynamic metocean environment to be simulated using a range of commonly occurring seastates. The integrated coupled analysis was completely conducted within the Ansys environment. Next, time-varying mode-{I,III} stress signals were reconstructed from the structural analysis model using a traction-based structural stress assessment method. In order to assess the extent to which fatigue-critical weld seams are subject to multiaxial stress response, a damage accumulation calculation should be conducted. However, given the added computational expense of such a calculation, a screening method was first considered in order to better understand the characteristics of stress response behaviour. The screening method considered was based on a Minimum-Circumscribed Ellipse method. From this screening method, it was found that stress response behaviour is predictable and can be related to specific loading & response frequencies. Furthermore, it was found that parts of the considered structure were subject to significant levels of multiaxial non-proportional stress response and that applying uniaxial fatigue assessment criteria risks overestimating lifetime estimation and misplacing the governing fatigue hotspot. Finally, it was concluded that fatigue-critical weld seams in a FOWT TLP-type substructure are subject to multiaxial stress to the extent that multiaxial damage accumulation models should be considered. If this is not possible, a multiaxial stress response screening should be conducted to identify fatigue governing locations in the welds, as well as locations subject to multiaxial stress.

In an era where global energy consumption has been rising steadily, the demand and supply of renewable energy sources have become increasingly important. Offshore wind is a promising renewable energy source, which has been actively developed in the last decades in the form of bottom-founded offshore wind, bound to shallow water. Floating Offshore Wind Turbines (FOWT) offer a solution for countries without shallow coastal waters with an abundance of wind potential. In a competitive market with different solutions, Bluewater Energy Services (Bluewater) has developed a tension leg platform (TLP) type substructure to support a 15MW turbine. These FOWT installations are subject to the random nature of environmental loading which is highly stochastic in terms of amplitude, frequency and phase angle and is hence considered multiaxial non-proportional (random) variable amplitude loading. Multiaxial loading does not, however, guarantee a multiaxial stress response. One of the considerations for offshore structures subject to repetitive loading is fatigue lifetime estimation, which is predominantly done using uniaxial assessment methods. This is not an issue if the stress response is dominantly uniaxial, however, literature has demonstrated that evaluating a specimen subject mode-{I,III} multiaxial stress response using uniaxial (mode-{I}) assessment methods can lead to a significant overestimation of the fatigue lifetime. To investigate the (multiaxial) stress response of fatigue-critical weld seams in TLP-type FOWT substructures, a new simulation methodology needed to be developed, which allowed for the structure's rigid body motions and elastic deformations to be captured. This methodology was built on an existing hybrid rigid-flexible modelling approach. It was improved upon by considering local (panel-based) hydrodynamic pressure and kinematic structural boundary conditions in order to conduct coupled (aerodynamic-hydrodynamic-mooring) analysis with integrated structural analysis. This approach allowed for the system motion and structural response to a dynamic metocean environment to be simulated using a range of commonly occurring seastates. The integrated coupled analysis was completely conducted within the Ansys environment. Next, time-varying mode-{I,III} stress signals were reconstructed from the structural analysis model using a traction-based structural stress assessment method. In order to assess the extent to which fatigue-critical weld seams are subject to multiaxial stress response, a damage accumulation calculation should be conducted. However, given the added computational expense of such a calculation, a screening method was first considered in order to better understand the characteristics of stress response behaviour. The screening method considered was based on a Minimum-Circumscribed Ellipse method. From this screening method, it was found that stress response behaviour is predictable and can be related to specific loading & response frequencies. Furthermore, it was found that parts of the considered structure were subject to significant levels of multiaxial non-proportional stress response and that applying uniaxial fatigue assessment criteria risks overestimating lifetime estimation and misplacing the governing fatigue hotspot. Finally, it was concluded that fatigue-critical weld seams in a FOWT TLP-type substructure are subject to multiaxial stress to the extent that multiaxial damage accumulation models should be considered. If this is not possible, a multiaxial stress response screening should be conducted to identify fatigue governing locations in the welds, as well as locations subject to multiaxial stress.

Traditionally, the control point (CP) of a dynamically positioned vessel is located around its center of gravity (CoG). However, during offshore operations, other locations, such as the crane tip or gripper position, become more critical due to the load being located there. This thesis proposes shifting the control point from the CoG to an alternative location, specifically the gripper position, to minimize the DP footprint at this location. Minimizing the DP footprint at the gripper location could lead to smaller motion deviations at this critical point. Consequently, this could potentially improve the workability of the vessel, which in turn could lead to higher operational yields. Additionally, the risk of potential damage and unsafe situations offshore is mitigated. The conventional DP system contains a Kalman Filter, to filter out the first-order motions, a P(I)D controller that calculates the demanded forces to keep the vessel in place, and a thruster allocation algorithm that distributes the demanded forces to all the thrusters in an optimized way. A new design for a DP system with the control point at the gripper position for the Deepwater Construction Vessel (DCV) Aegir is presented and evaluated. Time domain simulations were performed with the Aegir containing its conventional DP system and with the Aegir containing the newly designed DP system. These time domain simulations were performed using Orcaflex, which contains a model of the Aegir. This model of the vessel is connected to an external Python code, that contains the DP system, including a thruster allocation. As the new DP system at the gripper location has to cope with coupled equations of motion, it is equipped with a new Multiple-Input-Multiple-Output (MIMO) PD controller, that consists of a decoupling module and separate PD controllers for each DOF. To obtain state estimates for the second-order motions at the gripper location, the state estimates calculated by the Kalman Filter are translated to the gripper location. The effects on DP performance were assessed by evaluating and comparing the motion responses in the horizontal plane and DP footprint at the gripper location of both models. Also, the thruster behavior and energy consumption of both models are compared. This was done for an incoming wave direction of 135 degrees, a peak period (Tp) of 8 seconds, and significant wave heights (Hs) from 1.0 m to 2.0 m with increments of 0.5 m. The wave spectrum used is a JONSWAP spectrum. As recommended by the classification society, three-hour simulations are performed for the so-called 'base case' sea state with Hs = 1.5m. However, due to the extensive simulation time only one-hour simulations were performed for the cases with Hs = 1.0m and 2.0m. When comparing the motion responses, one of the most remarkable results is an improved yaw response for the gripper control point model in all sea states that are considered in this study. Further on, the motion responses for sway appeared to be bigger for the gripper control point compared to the center control point in Hs = 1.5m and Hs = 1.0 m. However, the differences in sway are observed to be marginal for Hs = 2.0m. The results show that the DP footprint has slightly improved in the x-direction for the gripper control point model compared to the center control point model for the base case. The same observation is done for Hs = 2.0m, but the differences found between the models in Hs = 1.0m are marginal. Also, the DP footprint was observed to be slightly larger in the y-direction for Hs = 1.0m and Hs = 1.5m for the gripper control point. The total thrust outputs as delivered by the DP system during the simulations were converted to power, by using the propeller diagrams (for DP-speed state) for the specific types of thrusters the Aegir is equipped with. From these results, it became clear that the gripper point control model consumes less energy in all tested sea states compared center control point model. From the results presented in this study, it is concluded that the system itself has potential, but no hard conclusions can be drawn for the system in its current form. Problems were observed with the current thruster allocation algorithm from HES, which need to be explored in more detail and resolved. It is recommended to look into developing a stable working thruster allocation algorithm for both control point models, such that more accurate dynamic simulations can be performed and the system can be assessed under more sea states.

A two-dimensional (2D) panel method is developed to find the first and second order wave forces acting on a semi-submerged cylinder in regular waves. The panel method is based on potential flow and the waves are modeled for both finite and infinite water depth. The motion is limited to heave, but allows for extensions to other modes as well. It uses boundary conditions for floating body dynamics with Neumann and mixed type boundaries on the surfaces. The waves are generated and the reflection of the waves is suppressed by generating absorbing boundary conditions (GABC) on the radiation surfaces. The model is used to investigate the hydrodynamics of an oscillating buoy wave energy converter (point energy converter). For this, an analytical solution of the optimal damping is used. The method uses panels along all boundaries to solve the boundary conditions. The model can be used for any time-harmonic free surface flow problem. A second order wave running through the domain is successfully modeled, without the interference of a body. Challenges of a second order model with body are explained. The boundary element method has innate challenges finding the correct solution to tangential flows on the panels and spatial derivatives of the velocity, which are required for the second order solutions.

A mathematical model has been developed to determine the timing of the tasks that can be performed on a variety of units to produce a variety of end states and to monitor the flow of the material through the network. The mathematical model is based on the work of Kondili et al. (1993) and is extended with the ability to monitor and restrict the shelf-life of a state, the ability to implement a mandatory storage action with shared storage and the ability to implement batch-size dependent processing times for batch-sizes that can only take a certain value.

The penetration of the renewable energy sources in the global market has been constantly growing over the last years. This trend is expected to accelerate even more in the future due to the improving technologies, the economies of scale, the competitive supply chains and the improving developer experience. The main challenge for a faster and wider implementation of these resources is their intermittent character and the limitations that this implies. A concept that successfully deals with this variable energy output is the Hybrid Power Plant (HPP). HPPs combine at least two different sources of energy with the goal of delivering stable power with reduced fluctuations throughout the year. In addition, HPPs present various other synergies such as in operational costs or in the developing processes, that could lead to a reduced Levelized Cost of Energy (LCOE). The goal of this thesis is to assess the potential synergy of a combined wind and solar park for the case of the Energy Storage Lake (ESL) of the project Delta21. The Delta21 project has a twofold character: firstly, the usage of the ESL as a large battery integrated with green energy production and secondly the protection of the inland against floods due to high sea level or superfluous river discharge. The main challenge for this specific case is the large water level fluctuations within the lake in a daily basis due to the operation of the lake. The feasibility of a hybrid wind and solar park can be examined by various different perspectives and disciplines. Among these relevant components, the most frequently studied ones are the optimization of the energy resources, the use of common electrical infrastructure and the effect of the intermittent wind turbine shadows on the solar panels. Due to the special conditions, with the large water level fluctuations met at the lake, two more components become critical. These are the type of foundation of the wind turbines and the mooring configuration for the floating solar units. This project is evaluating a new potential synergy that regards the use of the wind turbine towers as anchor- ing points for the floating solar units. Therefore, the research is focused on the estimation of the forces acting on a floating solar unit. These forces are a combination of wind loads acting on the solar panels and the freeboard of the floaters, and wave forces acting on the submerged part of the floaters. In particular, the technology of the floating solar boat as introduced by GroenLeven and the small-scale wind turbines as designed by Dutch Wind are adopted for this project. Analytical formulations are used for the calculation of the wind loads. As for the wave forces, the linear potential theory is used and the calculations of the hydrodynamic coefficients and wave exciting forces are performed through the Boundary Element Method (BEM) software NEMOH. After the computation of first order wave forces and the corresponding responses of the floaters, the far-field approach is used for the estimation of the Quadratic Transfer Function (QTF) of the drift force. The methodology developed in this project and the accuracy of the model are validated with the use of reference data that regard the interaction of connected floating units placed in a close proximity and the corresponding second order wave forces as predicted by the far-field approach.

Structural health monitoring of maritime and offshore structures can contribute to the reduction of the amount of uncertainty in assessment of the operational loads and the structural integrity. Such a survey can also reduce the large safety margins during the design and optimize the conservative inspection and maintenance schedules. One of the emerging variants of structural health monitoring are the so-called digital twin systems that not only allow the monitoring of the structures, but can also simulate the past or the future state of the structural integrity. In the context of this thesis, the feasibility of a digital twin system for the structural health assessment of marine structures based on machine learning algorithms and utilization of big data is examined. The main research question is if the digital twin technology can be enhanced with machine learning to accurately monitor the structural health of marine structures in terms of loading and fatigue damage accumulation. In order to answer this question four modules have been developed and tested. The first module uses artificial neural networks trained on operational data to predict the fatigue damage accumulation and the frequency that corresponds to the maximum stress power density. The error of the developed networks turned out to be negligible in the investigated cases, with standard deviation of less than 4% in the predictions. The peak frequency of the stress power density is predicted using a random forest regression algorithm. The optimized version of the algorithm has led to an accuracy of 93% with standard deviation of less than 1% in the predictions. The second module is used to recalibrate the design response amplitude operators of the structure using the predictions of the first module or the operational data, if available. The design response amplitude operators are scaled and shifted in order to minimize the deviation between the spectral fatigue calculations and the predicted (or measured) data.The third module is a static/quasi-static load-reconstruction module. Using on-board strain measurements it is able to calibrate the loading of the structure based on a reformulation of the conventional finite element problem for static and quasi-static loading. A sensitivity analysis of the algorithm effectiveness have been performed using multiple load cases in which the reconstruction error turned out negligible. The fourth and final module relates to structural reliability analysis. This module is based on the estimation of the Hansofer-Lind reliability index as a minimization problem. The employed optimization engine is a variation of the particle swarm optimization algorithm using chaotic system behaviour to iteratively calculate the user-defined parameters. The limit state equation is formulated in a way that it takes the uncertainties related to the fatigue damage accumulation prediction model and Miner's Rule into consideration. Uncertainties related to the material and the fabrication process are not taken into account. The developed modules have been tested on structural details of a vessel monitored in the scope of Monitas Joint Industry Project (JIP). About a year's worth of data has been used to train the machine learning algorithms.

The offshore wind market is rapidly growing, resulting in increasing wind turbine sizes, increasing distances to port, and a shift to deeper waters. A literature study in this thesis shows that existing wind turbine installation vessels, vessels under construction, and innovative concepts will not be able to install next-generation turbines or that they would have installation bottlenecks, making them cost-inefficient. This goes against the goal of decreasing the Levelized Cost of Energy (LCOE) of wind energy, to ensure that offshore wind stays competitive with other energy sources, enabling the energy transition. There is thus a gap between future demand of offshore wind installation vessels and current and near-term solutions. The research proposes a new floating monohull vessel concept, called Moonshot, to fill this gap. Moonshot will thus be different than traditional jack-up or semi-submersible installation vessel options. In this research, various design strategies were analyzed. Based on the findings, a design strategy is developed to design and analyze Moonshot. A combination of Ulstein Design and Solution B.V.’s Controlled Innovation process and Blended Design were used and extended to develop this new concept. First, the important functions and design aspects of the design were established using Controlled Innovation. Blended Design was then used to create a design space of the design configurations and to explore multiple market scenarios to establish optimal ship parameters for further development. As part of the research, the existing design process and model were modularized and new features were developed to suit wind turbines, assess seakeeping behavior, and explore the design space of the future wind turbine installation vessel. The results of this research aim to elucidate optimal design parameters across certain market scenarios. Results show how optimizing the design for financial performance, seakeeping behavior, or a combination of the two, influences the optimal design point. With the optimal design ranges, the initial design parameters for the next stage in the design of Moonshot are established. Finally, Blended Design is used to benchmark Moonshot against existing wind turbine installation solutions to assess its performance. A version of Moonshot is developed as a direct competitor for the largest jack-up design available, the NG-20000X. Benchmarking with the jack-up, an SSCV, and Huisman’s WIV concept showed that Moonshot would be a more efficient solution, capable of installing a larger number of turbines per year at a considerably lower cost per megawatt compared to the other solutions. In summary, this research concludes Moonshot as an innovative concept to address the evolving challenges of offshore wind turbine installation. By combining innovative design strategies, extensive assessment, and optimization, Moonshot emerges as a promising contender in the quest for effective and cost-efficient installation solutions for offshore wind.

Catamarans are popular in the offshore sector as they combine good transverse stability and ample deck space with low wave resistance. However, their slender hull shape results in low restoring qualities in heave and pitch motions. The large motions in rough weather can often result in water impacting the underside of the deck connecting the two hulls, a phenomenon called cross-deck slamming. The impulse excitation from cross-deck slamming can then produce a transient hydroelastic response of the structure called whipping. Whipping excites mode shapes that would not normally be present in the response, as their natural frequencies are significantly higher than the wave encounter frequency. This results in detrimental contributions to fatigue life through high-amplitude cyclical bending moments. Both the calculation of slamming loads and the prediction of resulting structural responses have been a challenge for several decades. The highly nonlinear and three-dimensional character of the phenomenon, combined with the strongly coupled fluid-structure interaction means that it is unpredictable, and even the definition of slamming events has been a matter of disagreement among researchers.\ Experiments are still a vital part of these investigations, for validating ever-improving numerical techniques. An essential issue with experiments is the extent to which mode shapes and natural frequencies can be emulated in model scale. Traditional hydroelastic models are segmented and use either a flexible backbone or flexible joints to introduce stiffness. This often results in an excellent description of the 2-node bending mode, but an increasing error for higher modes leads to stress inaccuracies. In this investigation, a fully elastic model of a catamaran is designed and produced for hydroelastic experiments. The advantages and limitations of the concept are identified, and the verification against structural models is presented.

Reducing the levelised cost of energy is crucial to accelerating the energy transition. To develop offshore wind solutions in greater water depths, a floating solution is required. The time-domain simulations of these Floating Offshore Wind Turbines (FOWTs) under wind-wave misalignment used in research and industry projects are computationally intensive and limits researchers and industry in their developments. To better understand the sensitivities of the fatigue loads of FOWTs to different parameters and environmental conditions, a computationally efficient method is needed. The aim of this research is to develop a frequency-domain method to quantify the effects of misaligned wind and waves on the response of a semi-submersible floating offshore wind turbine. Therefore, the following research question is defined: What is the effect of misaligned wind, windsea waves, and swells on the loads at the tower base of a semi-submersible type floating offshore wind turbine? Several sensitivity studies are conducted to quantify the contribution of yaw-roll coupling effects and aerodynamic damping to the responses and loads. From these studies, it appears that the yaw-roll coupling can increase the response when excited at wind/wave directions in which the structure is asymmetric. The magnitude of this effect is related to the wave peak period (and the resulting wavelength), the angle of misalignment with respect to the structure, and the apparent length of the structure. Also, the lack of aerodynamic damping in the direction of the rotor plane (side-side direction) leads to a noticeable increase in the response, directly or through coupling effects. Finally, the frequency-domain method is compared with the time-domain simulations (BHawC-OrcaFlex) carried out by Siemens Gamesa. Although reasonable agreement is found for the load driving rigid body modes, significant differences in the tower bottom loads are found for the lowest and highest production wind speeds. These results show that misaligned wind and waves can increase the response for headings where the structure is asymmetric due to coupling effects. Wind-wave misalignment leads to an increased response in the direction of the rotor plane due to the lack of aerodynamic damping. In general, the wind-wave misalignment can also have a mitigating effect on the maximum equivalent moment at the tower base, as the aerodynamic damping also reduces the response in the wave frequency range. Furthermore, the comparison shows the need to extend the frequency-domain method with the first tower bending modes and improvement of aerodynamic/mooring property estimation. Based on the findings and the conclusions, the recommendation is to investigate the floater specific sensitivities at an early stage of the design. Future research should focus on: the implementation of tower flexibility, improvement of the quasi-static estimation of mooring stiffness, frequency dependent aerodynamic properties, and implementation of second-order wave forcing.

During offshore construction with a Semi-Submersible Crane Vessel (SSCV) the vessel is station keeping by means of Dynamic Positioning (DP). DP enables a vessel to keep position and heading by utilizing its own propulsion, while being exposed to the environmental forces caused by waves, wind and current. In a comparison study between offshore measurements and time-domain simulations, an increased vessel/thruster response for the offshore measurement was observed. The results revealed, that in operational environmental conditions, the measured vessel response shows increased oscillations in Surge, Sway & Yaw, with periods of approx. 3-5 min. The goal of this thesis was to determine the causes for such an increased dynamic vessel response, which are not captured in time-domain simulations. At present, numerical methods and time-domain simulations that assess the DP performance of a vessel (e.g. aNySIM) assume a quasi-static current of which the variation is only caused by the tides. One thesis is, that time-varying currents on a scale of 1 to 5 minutes can cause an increased vessel response. Furthermore, the DP System as it is used onboard is not captured in aNySIM simulations. This means that the characteristics of the DP System onboard are but not represented in full detail in time-domain simulations. Vortex Induced Motion (VIM) has previously been observed to affect multi column floaters. However, the influence on a SSCV during DP-operations has not yet been studied. In this thesis it was investigated whether the unexpected increased motions originate from time-varying currents, VIM or the DP System itself. A significant challenge was posed to find current measurement data with a small enough time step to confirm the presence of such time-varying currents. One 45 min current measurement with a sampling rate of 1Hz became available. This measurement shows that time-varying currents on a scale of 1 to 5 minutes exist and cannot be assumed to be quasi-static. More research is required to confirm their presence. However, with this limited available data it was shown that time-varying currents can cause an unexpected motion response of a SSCV during DP-operations.In order to obtain the DP System characteristics, a DP Response Amplitude Operator (RAO) assessment was conducted wherein the spring and damping terms were derived as demanded by the controller and as experienced by the vessel. This assessment showed that between 20% to 67% of the demanded critical damping is lost over the control loop of the DP System. These damping losses cause the vessel to overshoot and the damped natural period to decrease. To determine the effects of VIM, current load tests carried out on the hull of an SSCV have been investigated. It was determined that strong currents on column type floaters can cause fluctuating forces and moments that originate from vortex shedding. Further, with real-time simulations it was demonstrated, that also VIM causes an increased, previously unknown, motion response of a SSCV. Lastly, a method was developed to extrapolate the current load test results to velocities below 2kn. Subsequently, in time-domain simulations it was shown that for current velocities above 0.5kn, the vessel experienced forces and moments that caused it to fluctuate around its setpoint.