The need for a fast transition towards clean electricity generation pushed large investments in high-risk, high-impact technologies such as floating Airborne Wind Energy Systems (AWESs), which are expected to be highly cost efficient with respect to state-of-the-art offshore wind energy technology. Current research on the matter does not address the design challenge of a tailored floater, necessary to suit at most the unique features of such systems, and foster their industrial and commercial development. This study proposes a simulation-based design optimisation framework for the floating structure and associated mooring system tailored to offshore AWES deployment. By reviewing conventional floating wind energy solutions and analysing expected AWES loading conditions, a spar-like floater and taut mooring system are proposed as the baseline design for a numerical case study. A state-of-the-art first-order potential flow model is employed for the floater, coupled with a novel quasi-static model for the mooring system, to simulate system motions in the frequency domain. The design optimisation aims to minimise capital expenses and wave-induced motions, with constraints on the strength and fatigue lifetime of mooring ropes. A multi-objective genetic algorithm is used to explore the design space and approximate the Pareto front, with sensitivity analyses on the latter revealing the significant impact of mooring line materials on system performance. Verification of the optimisation results includes an assessment of aerodynamic loads using a decoupled AWES model and time-domain simulations in OrcaFlex for selected configurations under various wave conditions. Although the quasi-static mooring model showed coherence with dynamic simulations, optimal configurations deviated significantly from the initial spar-like design, indicating potential benefits from alternative baseline designs. The impact of AWES aerodynamic loads on deck motions highlights the need to integrate them into the design process. Despite these challenges, the proposed simulation-optimisation framework shows promise as a powerful tool for the preliminary design of floating AWESs, paving the way for future refinements.

Experimental testing of floating offshore wind turbines (FOWT) is essential for understanding the various engineering challenges posed by their dynamic motion. For example, the pitch and surge motion of the FOWT results in unsteady aerodynamic effects caused by wake interaction. In this project, two FOWT models (DTU10MW with TripleSpar and IEA15MW with VolturnUS) were developed for testing with a hybrid hardware-in-loop (HIL) setup. This setup integrates physical wind loading in a wind tunnel with numerically simulated hydrodynamic loading.

The HIL setup comprises a scaled wind turbine model, a hexapod that can actuate the floating motion, an instrumentation system with sensors to measure forces and accelerations, and a numerical model that simulates FOWT dynamics in real-time based on measured data. This work explores the methodology of developing a numerical model that can simulate the dynamics of the scaled FOWT model in real-time with the applied wind loading and numerically simulated hydrodynamic loading. Furthermore, a methodology for correcting the measured forces to obtain external aerodynamic forces is introduced and validated.

The process of developing the numerical model is thoroughly detailed, including its tuning and validation. The challenges encountered during the validation process are discussed in depth, with an emphasis on their underlying causes. Finally, the HIL numerical model was used to test the scaled DTU10MW wind turbine with a simulated TripleSpar floater at the Open Jet Facility (OJF) wind tunnel at TU Delft. This study also presents intriguing results regarding the HIL model's performance and the impact of wind on FOWT dynamics observed during the test campaign.

Rising global CO2 levels have created a growing need for renewable energy resources. Offshore wind energy is a promising solution, with monopile (MP) foundations preferred for their relatively low cost, provided the site conditions are suitable. Recently, wind turbines have significantly increased in size for greater cost efficiency, leading to the development of 3XL MPs with diameters of 12 meters or more. Depending on the site and marine contractor preferences, a jack-up vessel may be used to install a 3XL MP. Marine contractors typically employ dynamic models to determine suitable weather windows for each installation phase. Lowering the 3XL MP through the splash zone and gripper to just above the seabed is a critical phase. To optimize the dynamic models for this phase, understanding the 3XL MP’s behavior during splash zone lowering is essential. This thesis therefore investigates the dynamic behavior of a 3XL MP during lowering phase through the splash zone until just above the seabed using a jack-up vessel.
A 1-DOF model, considering only the rotational DOF of the MP, is established to examine this behavior. Results from this model show that the most probable maximum (MPM) of the MP rotational motion response, evaluated with a dynamic lowering simulation for irregular spread waves, is 75% lower compared to the conventional steady-state simulations at critical MP drafts. Additionally, the dynamic behavior of the MP is highest for increasing peak periods, as these coincide with the natural periods of the 1-DOF model at larger MP drafts where wave-excitation loads are greatest. Several physical phenomena which are not included in the model are examined to assess their impact. Ambient currents traveling in the same direction as irregular unidirectional waves during a dynamic lowering simulation, reduce the MP motion response by 25%. Vortex shedding frequencies do not coincide with natural periods and are thus neglected. The same goes for the 2nd order difference frequency wave drift forces. Both the dynamic amplification and the mean motion displacement due to these second order wave forces are negligibly small. Lastly, the influence of jack-up motion is negligibly small during peak periods of 8 and 9 seconds but reduces the MP rotational motion during a peak period of 7 seconds.

During single-blade offshore wind turbine (OWT) installation, wind disturbance results in blade root motion. The sensitivity to this wind disturbance is more significant for larger blades, reducing the allowable installation weather limit. A potential solution is a Hook Mounted Compensator (HMC) between the crane and the load that can provide high-precision compensation across multiple degree of freedom (DOF), and compensate for the influence of wind on the OWT blade. Several Actuation Method (AM)s have been identified that can be used in a HMC. However, these AMs have not been modelled dynamically and their effectiveness for the desired application is unknown. The aim of this study is to analyse and assess the compensation effectiveness of these AMs in a HMC. For this purpose, the AMs are simulated and analysed in various levels of complexity and DOFs. Initially, the system is considered in a 1DOF. A linear representation is formulated, based on which a Proportional-Integral-Derivative (PID) controller for each AM is formulated. This enables simulation of the Single-Blade Installation System (SBIS) in the time domain. Assessment criteria are used to quantify the compensation effectiveness and actuation input of the AMs. To simulate the SBIS for each AM, 3DOF numerical models are developed that describe the operation of the AMs in their respective operational planes. Six actuation methods are included in the assessment. Based on the assessment results, three AMs are combined in a HMC concept. A XY table is used to control blade root position in the x- and y-directions, gyroscopes for the z-direction, and COG shifting with counterweight to prevent gyroscope saturation. The PID controllers based on the linear 1DOF representation are used, operating in parallel, to control the blade root position in all DOF. The blade root motion is reduced by 96% along the blade axis and 86% radially. The blade root motion is sensitive to the mean wind speed, turbulence intensity, and angle of the incoming wind. The HMC shows robustness to variations in tugger line angle and pretension. The static blade pitch angle affects the magnitude and distribution of the wind-induced moment on the blade. For a pitch angle of -180, the moment around the z-axis is minimal, providing optimal HMC performance. The HMC concept can not directly actuate the blade around the z-axis. Instead, the XY table translates the blade at the COG, resulting in increased cylinder stroke and high power consumption for other pitch angles. Two AMs were assessed to actuate the blade around the z-axis, both showing poor performance. Further exploration of AMS that can directly control the blade rotation around the z-axis could lead to improvement of the HMC concept. Additional improvement can be made in optimization of counterweight and gyroscopes sizes, potentially reducing weight and improving system performance. Further suggestions for future work include; exploring the compensating for the now neglected hub motion using the HMC, examining the stability of the HMC once the blade is mated to the hub, and the impact of sensor noise and delay on the HMC’s performance.

With the pressing matter of climate change, the importance of renewable energy sources is increasing day by day. A large portion of this renewable energy is to be generated with the use of wind turbines, which are commonly located onshore. In recent decades, great effort has been put in the development to place these turbines offshore, because of a higher yield in energy production, as a result of higher wind speeds, greater consistency and less interference from human-made objects. These offshore turbines can be placed on floating or bottom-founded structures. Only 20% of all possible wind farm locations are suitable for the application of a bottom-founded wind turbine, due to its depth restriction. Therefore, a great deal of development is focused on the application of floating wind turbines. In essence, there exist three different types of floating structures: semi-submersible, Single Point Anchor Reservoir (SPAR) and Tension Leg Platform (TLP).

In this thesis, the TLP is considered for a floating foundation because to its superior motion characteristics compared to the other structures. The TLP obtains its stability from its mooring system due to excessive buoyancy, which causes the mooring lines to be under tension. This in turn causes the TLP to have compliant and constrained Degrees of Freedom (DOFs). These constrained DOFs cause the eigenfrequencies of the system to be out of reach of first-order wave loading. However, from the oil & gas industry it is known that this type of structure does have a high-frequency response. This is known as springing and ringing, where this thesis is devoted solely to springing. Springing is identified as the resonance of the constrained DOFs of the TLP caused by the subsequent wave loading on the floater.

From initial evaluations of the motion characteristics of the case model TLP, it is seen that there are eigenfrequencies of the system that coincide with both the high frequency tail of the first-order wave load spectrum and the second-order wave load spectrum. Therefore, first- and second-order wave loads are considered. These forces are evaluated with the use of potential theory and calculated with OrcaWave and Hydrostar, which are commercially available diffraction programmes. Springing is subsequently evaluated using time-domain analysis with OrcaFlex, which is a commercially available software capable of performing time-domain analyses with aero-hydro-servo-elastic coupled models.

From initial simulations, it is seen that springing events are indeed present in the system and are mainly affecting the fatigue life of the tendons. Additionally, slack tendon events are present to a larger degree and are correlated to the whipping of the tower and RNA. This mainly causes the exceedance of structural limits. As springing is a resonance problem, only adjustments to the mooring system are considered that influence the location of the eigenfrequency. In this thesis, adjustment of the axial stiffness and inclination of the tendon are considered. Adjusting the axial stiffness did not produce the desired effect, because the range of common values in the mooring industry is rather limited to invoke any considerable change in the motion characteristics of the TLP. Furthermore, the TLP showed a large number of slack tendon events. that are correlated with the whipping of the tower and consequently caused the exceedance of structural limits. Adjusting the axial stiffness is not able to prevent these events. Adjusting the tendon angle did show promising results. For the case study, an optimum angle of 16° is found, which on average halves the tendon tensions. A reason for this is that with the introduction of a tendon angle, the TLP rotates around a certain focal point. At 16°, this focal point is located at the Rotor Nacelle Assembly (RNA). Thus, the TLP tends to rotate around the RNA instead of the other way around. This change of motion behaviour also prevents the occurrence of slack tendon events. Although not preventing the occurrence of springing events, the optimal tendon angle does reduce the effect and rate of occurrence of springing to a satisfactory level.

Modelling of Floating Offshore Wind Turbines (FOWTs) is challenging due to the strong coupling between the aerodynamics of the turbine and the hydrodynamics of the floating structure, which makes the dynamic response of the whole system highly complex. A variety of numerical approaches can be used to predict this response.

The frequency-domain method (FD) is chosen for further development. These methods are considered as efficient tools for analyzing first design iterations. Given the ongoing development of new concepts for FOWTs, the industry could benefit from such a tool. Currently, only one such open-sourced method is developed (RAFT), but the method still has room for improvements.

After enhancing RAFT's control modeling, the frequency-dependent aerodynamic added mass and damping coefficients are determined following RAFT's methodology. These coefficients are then implemented in a wave diffraction program to predict the surge, pitch, and mooring line tension response of FOWTs for four different design load cases (DLCs). These results are compared against time-domain (TD) simulations.

The method proved capable of predicting the surge and pitch motions well, but the mooring line tension prediction still needs improvements.

The demand for renewable energies is rising due to climate goals and high oil prices. Not only the established renewable sources like wind and solar are interesting to exploit. There is a vast amount of energy stored in the world’s oceans. To harvest this energy, one needs a Wave Energy Converter (WEC). There
are already some prototype WECs tested around the world but there is no leading design that proves to be a cost-effective way to convert this energy to electricity.

A company from the Netherlands, Dutch Wave Power, also tries to build a cost-effective device to harvest the ocean’s energy. Their design consists of a floating tube or cylinder that converts the heave and sway motion into a pitch motion. This pitch motion drives a generator which generates electrical power. The generator is connected to the outer wall of the float and rotates as the float pitches. Inside the generator is a shaft that is kept in place by an inside pendulum. Dutch Wave Power validated their concept with experimental tests in a wave flume. The next step in the development is a numerical model. This model
gives insight into the effects that influence the dynamics and power production of the WEC. Secondly, a numerical model eliminates the need for new experimental tests each time a design parameter is changed.

The numerical model estimates the dynamics of the WEC. The BEM software NEMOH is used to estimate the diffraction and radiation forces coefficients. A state-space approximation of the Cummins equation is used to capture the memory effect of the radiation forces. The Froude-Krylov forces are fully non-linear and are evaluated for each time step. Lastly, some friction and drag forces are included. The PTO system is described as a linear damper. The numerical model is validated with experimental tests executed by Dutch Wave Power.

Next, the numerical model is adapted to also estimate the hydrodynamics in irregular waves. The irregular waves used in this thesis are based on a JONSWAP spectrum. Using the parameters of the JONSWAP spectrum, a sea-state with the desired significant wave height and peak period can be generated. The
Froude-Krylov and the diffraction forces are estimated based on the principle of superposition. With this irregular wave model, a power matrix is constructed for a WEC with twice the size that was used in the experimental tests. This power matrix gives an indication of the ideal operational wave conditions, where the efficiency of the WEC is the highest, and it makes it enables the possibility to compare the performance of the WEC at different sea-states.

In recent years, the demand for renewable energy has increased significantly because of its lower environmental impact than conventional energy technologies. As a result, wind power is one of the most important renewable energy sources. As land-based turbines have reached their maximum potential, recent market trends are moving into deeper waters with higher capacity turbines. The design of a floating offshore wind turbine (FOWT) foundation poses technical challenges. Mooring design, installation operations and the fact that it is a new engineering field, to name a few. Moreover, as mooring design for FOWT is still at an early stage of development, cost-effective installation remains one of the critical issues. After the FOWT is towed to the site, the mooring lines are hooked up, and one line is usually shortened. This can be performed in three ways: By seabed tensioning, inline tensioning or tensioning at the fairlead. In this investigation, details about mooring installation processes are collected from interviews, academic papers, manuals and videos to investigate differences between mooring system installations and ultimately figure out how pre-tensioning of these systems can be carried out most effectively. This work presents a comparison between these three existing methods for the final phase of mooring installation. To perform a quantitative study, the Umaine VolturnUS-S 15MW floater is considered. Current modelling techniques are expanded to allow for the static simulation of the rotations or sliding at the tensioning device. The model framework is used to find the static equilibrium and tensions at different phases in the installation operations. Additionally, an alternative mooring configuration is proposed with synthetic inserts to verify whether the tension is dependent on the mooring configuration. Finally, the dynamics between the anchor handling vessel(AHV), the FOWT and the mooring chains are modelled as a linear mass-spring system. Vessel responses and work wire tensions are compared against each other for identical environmental conditions and equipment specifications. Based on simulation results, it is found that the seabed tensioner causes little dynamic relation between the AHV and the floater and was not further investigated. Inline tensioning showed to be the method that requires the lowest tensions in the AHV work wire. Fairlead tensioning was found to be discouraged since the high required bollard pull forces. This issue is mitigated by a proposed new concept of fairlead tensioning. When the chain is hauled in from above the fairlead by a vessel crane or A-frame, it is possible to tension effectively without fuel-intense bollard pull.

Continuous development in the wind turbine industry leads to increasing size of wind turbines. Allseas investigates the possibility to enter the offshore wind turbine installation industry with Pioneering Spirit.
For Allseas’ preliminary wind turbine installation design, wind turbines are assembled offshore, requiring wind turbine components to be brought from shore to Pioneering Spirit by means of a cargo barge. This operation requires a proper mooring procedure of which the mooring system is an essential part. The mooring system secures the barge alongside Pioneering Spirit where it has to stay for multiple days.

In this research a pre-defined vessel orientation is analysed where the barge stern is extended 40m in longitudinal direction from Pioneering Spirit stern, to increase the barge area reachable by the unloading crane.
This barge position is challenging due to limited shielding from Pioneering Spirit, leading to excessive environmental loads acting on the barge. Due to the barge extension, also properly connecting the mooring system to Pioneering Spirit is a challenge.
The above leads to the main objective of this thesis: improve the mooring system to secure a barge alongside Pioneering Spirit in offshore conditions, including an evaluation of the dynamic mooring loads.

The main mooring system design requirements are that the system Safe Working Load and motion limits are not exceeded.
Evaluation of the mooring systems starts with a multi-body diffraction analysis with hydrodynamic matrices and other hydrodynamic properties as output. This data is imported in a time domain model which enables capturing non-linearities, e.g. the mooring system and wind and current loads. Validation and verification steps are required to assure realistic outcome and understanding limitations of the numerical models.

Before new mooring systems are introduced, a base case mooring system is defined and modelled in the time domain.
Finding the limiting sea state for which the Safe Working Load limit is reached enables to compute the workability for the reference location defined. Two reference locations are considered: a wind sea area and swell sea area. Wind and current speed is assumed to be constant over time and independent of elevation. Workability is defined as the percentage of time the mooring system is able to operate.

Evaluating the base case mooring system shows performance of 67% workability for wind sea areas and 16% for swell areas. Next to the base case, four mooring improvement concepts are evaluated from which the Cavotec Moormaster® system shows most promising results. This system consists of three main components: ‘fixed structure - hydraulic cylinder - vacuum pad’ (Figure 2) that connects the barge to Pioneering Spirit. This system is modelled as a link with constant stiffness and damping properties within its operational limitations.

The Moormaster system, shows perspective to improve the workability for both wind and swell seas. Besides workability, the Moormaster system improves the entire mooring procedure by quick connection and safe disconnection upon exceeding operational limits.

The energy transition, is one of the most important topics nowadays. Renewable energy sources contribution in the energy mix is growing rapidly. However, due to their intermittent power output, they cannot ensure system security and stability, and therefore, energy storage technologies are needed. In this direction, hydrogen is an energy carrier with great potential. When produced from water electrolysis based on electricity from renewable energy sources (green hydrogen), it represents a sustainable fuel. Due to that, industry’s interest is turn on green hydrogen production, with several large scale projects announced on a daily basis. In many countries, especially in Europe, there is not enough empty land for large scale renewable energy projects, turning the interest to offshore areas. This research aims to design and analyse the economic feasibility of an offshore hydrogen production system, intending for 2030, based on offshore solar energy,
located in Greece, for the production of a million tons of hydrogen per year. The
produced hydrogen will be injected into the European hydrogen network. Considering the main components of an offshore solar to hydrogen system, four possible system configurations are proposed based on two parameters for comparison. The first parameter for examination is the electrolyzer type, which can be either alkaline or PEM. The second parameter is the involvement of batteries into the system. The sizing and cost details about the different systems were selected and all the configurations were modelled using Matlab and Simulink software. From the model results, the levelized cost of hydrogen
for all the systems was calculated to evaluate the project. The most cost-effective
configuration was the one based on alkaline electrolyzer and without the involvement of batteries. The levelized cost of hydrogen for the selected
onfiguration was calculated to be 1.5 €/kg of hydrogen, making it comparable with blue hydrogen costs and with green hydrogen costs of relevant announced projects. A sensitivity analysis showed that the most influencing factor in the cost calculation is the capital expenditure of the floating photovoltaic system. More specifically, by decreasing the floating photovoltaic costs by 30%, the levelized cost of hydrogen can be reduced by 19%. Finally, in an optimistic scenario,
where all influencing factors are improved by 20%, hydrogen can be produced at
a cost slightly higher than 1 €/kg. Overall, it is concluded that an offshore hydrogen production system based on offshore floating solar energy, located in Greece, northern to Crete, can produce hydrogen at a competitive cost.

Climate change is triggering among others a larger demand for offshore wind energy. This leads to new developments of which larger next-generation Wind Turbine Generators is the most relevant. These next-generation WTGs create problems for the carrying capacity of current-day installation jack-up vessels that work according to the conventional installation method (shuttling). These installation vessels can carry less or even nil of these WTGs per trip compared to the current-day WTGs. Fewer turbines per trip would allow the larger current-day installation vessels to maintain their work. However, they have more sailing time since more trips are required. This could also be more inefficient since the Offshore Wind Farms are moving further offshore. The other option within the conventional method is to build larger installation vessels that would carry more WTGs per trip.

Another installation method in the literature called feedering is a potential substitute for the conventional method. Very limited research has been done for feedering as well the practical implementation whereas the conventional method has extensive research and is mostly used in practice. The models in the literature compared two different feeder methods, called, the base port feeder and feeder-ship method, to the conventional method. The models are generic and lack different strategies to find the best feeder solution. The feeder-ship method has the most potential to solve the aforementioned problems and is therefore further investigated to find the best installation strategy, being either the conventional or feeder method.

First of all, the feeder-ship method is evaluated based on practical knowledge and adapted so a base port is used to temporarily store all components that come from the production port. The feeder sails back and forth between the base port and the installation site to supply the installation vessel with WTG components. The installation vessel will stay at the installation site to be as efficient as possible (the least amount of sailing time). This research only looks at the feeder and installation side and leaves the port elements out of the problem. Feeder strategies (within this method) differ in the number of feeder vessels/types and transfer options using either barges or Platform Support Vessels and being indirect (transfer components onto the installation vessel) or direct (install components from the feeder). The installation vessel for feedering is also looked into as being either a current-day or a special feeder purpose installation vessel. Different carrying capacities of the installation vessels are used to create different strategies for the conventional method.

A stochastic Discrete Event Simulation model is created and used in this research to evaluate the strategies. The output of the DES simulation is the project duration per sailing distance and strategy. The costs for this duration is calculated in a costs model from the perspective of the contractor as well as the developer. Besides duration and costs (based on the European market), the strategies are also evaluated on emissions (fuel consumption) since this is an increasingly important element in the industry. A sensitivity analysis has been performed to get a better understanding of which critical parameters the feeder strategies are most sensitive to. The analysis is also used to find the best next-generation WTG installation strategy in Europe which is the main focus of this thesis.

At the moment, the world is at the verge of an energy transition. One of the most promising green resources is solar energy, which is a rapidly growing market. However, to fully use its potential of economy of scale, the application of offshore floating solar should be explored. A promising option is the use of a flexible type of Very Large Floating Structures (VLFSs), which are called Very Flexible Floating Structures (VFFSs). They are characterised by their large length to height ratio compared to rigid bodies and depending on their material properties have a hydroelastic response to the incident wave. In the late 1990s, a lot of research has been done on VLFSs by Tsubogo and Okada (1998) who derived an analytical dispersion relation assuming a zero­draught structure. However, only recently, Schreier and Jacobi (2020b) did experimental research on VFFSs in a towing tank at the Delft University of Technology, as little is still known about flexible structures. This report focuses on a numerical alter­ native that covers both VLFSs as well as VFFSs using a Finite Element Method (FEM) Fluid Structure Interaction (FSI) model which has been built based on potential flow to model the fluid and a dynamic Euler­Bernoulli beam that represents the floating structure using the Julia package Gridap. One of the main advantages is that the zero­draught assumption is not necessary and, therefore, structures with larger draughts can also be modelled. Next to this, the numerical model is able to cope with irregular shapes, for which no analytical method yet exists. The model is built such that it can handle 2D as well as 3D domains. A 2D analysis has been made to understand the influence of hydroelastic wave deformation of the incident wave, in terms of wavelength dispersion as well as amplitude dispersion on floating structures. To verify the model, the numerical results were compared to the analytical solution and experimental research in a towing tank, which showed accurate results. Test runs were set up that mimicked the towing tank set­up and a full­scale solar park. Furthermore, a sensitivity study was executed that shows the limits of the flexible domain and to see in which cases significant (>1%) hydroelastic wave deformation would occur using governing mean and extreme ocean waves, as well as a typical lake wave. Finally, the influence of the draught of the structure was examined. This report provides a good overview of when wave deformation should be accounted for in terms of bending rigidity and density. Confirming existing theory, it was found that the stiffness of the VFFS causes wave stretching and the draught of the structure influences the extent of wave shortening. It was also found that significant wave deformation will not occur for ocean waves as the required stiff­ ness is beyond existing materials. For extreme ocean waves, there is even no dispersion at all. As the wave frequency increases, the hydroelastic interaction gets stronger. The typical lake wave showed to be well within the flexible regime and also showed significant dispersion with realistic material parame­ ters. The numerical model is able to cope with large draught scenarios which lead to wave shortening, which in its turn leads to wave focusing. Ultimately, the numerical model showed to be a good alternative to existing methods to investigate the behaviour of VLFSs outside the floating solar domain, where one could think of ice floes, floating islands or floating airports.

Within this thesis an attempt is made to improve the seakeeping of a Service Operation Vessel (SOV) by means of an active anti-roll tank (ART). It is researched if the addition of a wave prediction system can improve the ART’s performance. As the seakeeping of the SOV is most important for the installed motion compensated gangway, the workability is assessed for different control methods based on the design criteria of the gangway. The computations have been made in frequency domain. A one directional model is used with two degrees of freedom: the ship roll angle and the tank’s fluid angle. Due to the presence of a wave prediction system, a feed forward loop can be introduced in the control system. It is found that if the pump moment leads the wave excitation moment, the tank’s fluid will oscillate in a less power demanding way. This is caused by the better interaction of the action and reaction forces that are caused by the pump. The action force on the ship’s structure will always oppose the wave moment, but the force acting on the tank’s fluid will only stabilise the vessel at certain frequencies. To obtain a robust model, the feed forward loop is combined with a feedback controlled model. The stability of the models’ feedback loop is assessed using Nyquist plots and sensitivity plots. It is found that for the damping factor belonging to the ART of the SOV, the feedback loop is unconditionally stable. On topic of the powers related to the active ART the dissipated and actual power are analysed. Based on the dissipated powers it is found that for the same amount of dissipated power by the pump, the feed forward controlled model causes a lower root mean square value of the ship’s roll in comparison with the feedback controlled model. This is explained by the better interaction of the forces generated by the pump. Based on the obtained RAO for the roll motion, the workability of the SOV is assessed for a significant wave height of 3m. It is found that even though the seakeeping of the vessel increases because the roll response decreases, the gangway motions aren’t significantly affected by the active control of the ART. The reduction in roll response is not proportional to the reduction of the gangway motions since other vessel motions such as heave and sway also effect the gangway’s motions. All in all, it is concluded that adding a feed forward loop to a feedback controlled model improves the seakeeping of the SOV. However, to improve the workability of the SOV it is recommended to include a passive ART in the design, instead of an active ART. This is because the active control has little impact on the gangway’s motions compared to the passive ART.

Moored vessels in harbours around the world are affected by waves penetrating into the port basin. Hydraulic conditions can lead to severe vessel motions that influence the (un)loading efficiency and can even lead to the failure of fenders and mooring lines, creating unsafe situations for operating staff and
A DMA is a chain of numerical models that computes motions of moored vessels due to wind, currents or waves. It is used to model the behaviour of moored ships to evaluate operational conditions and assess the effect of structural or operational measures. The most computational costly model in the DMA chain is the wave penetration model, which computes local wave field, speeding up this part of model chain can reduce time and costs of such DMA's.
In this research, the complex wave model is replaced by a computationally efficient alternative and the main research question reads:
How can a mild-slope wave model be used for the ship motion calculation on ships moored in ports and what are the benefits and limitations?
The research is split up into two parts: 1) Development of the coupling method and evaluating its application based on academic test cases and 2) Applying the coupling to the case study of La Coruña and assessing its suitability.
A practical and efficient method to extract wave components from the wave penetration model is the r-DPRA tool developed by Deltares. The developed method is applied to the case study of the port of La Coruña. Two separate moments in time of the same bulk carrier are modelled: one with moderate offshore wave conditions and one with more severe conditions.
In the measured time series of the surge and sway motions, a clear low frequency can be found. Similarly, in the simulated time series of the surge and sway motions; both in moderate and heavy cases no low frequency wave patterns can be found. A schematic approach is used to include the long waves in the wave model and ship motion model and this approach caused a low frequency wave pattern to arise and leads to more accurate significant motions.
The comparison between the measured motions and modelled motions demonstrated the complexity of modelling real life events. As the surge and sway motions are caused by second order effects that are not included in the applied linear wave model, it is recommended to apply the developed workaround to schematically include this low wave forcing. The result of this research demonstrates the potential for the development method.
Before directly applying the method, it is recommended to test the suitability of the method on a more fundamental case, this reduces uncertainties related to real life measurements and stronger conclusions about the performance of the coupling can be drawn. Moreover, the coupling should be tested for a case where the 2nd order low frequency wave forcing is negligible. As it is confirmed in this research that the developed method is not suitable for modelling non-linear 2nd order low frequency waves.

Offshore solar power installations can be increased in size and efficiency compared to land based installations due to the availability of space and the cooling effect of water. To increase survivability in large waves, very large floating solar platforms can be made flexible. However, a flexible structure is susceptible to wrinkling due to combinations of mooring loads, wave dynamics and the flexibility of the platform. Wrinkling is a limit state which is not commonly researched in maritime engineering, since generally structures are designed to be as stiff as possible. Wrinkling can lead to the global collapse of a very large flexible solar platform and should therefore be minimised. Very large floating platforms have an impact on the environment due to the shadow underneath. This problem can be diminished by adding holes to the platform. Furthermore, holes can be functional as manholes for maintenance of the bottom of the platform. Scientific research on the wrinkling behaviour of membranes has pointed out that wrinkling behaviour depends on the geometry of the membrane, which can for example be changed by adding holes to the membrane. The aim of this thesis is to set up a design and analysis framework for wrinkled membranes with permeability. In order to define this framework, (i) reliable computational indicators are developed; (ii) the influence of permeability on membrane wrinkling is investigated and; (iii) the framework is verified on a fictive case of an integrated stiff solar panel on a membrane. The first objective in this thesis is to find reliable computational indicators to assess the wrinkling behaviour of a membrane. Current concepts of offshore solar platforms are flexible membranes including mooring systems based on concentrated tension loads. To study the wrinkling behaviour of a (subregion) of such a flexible floating solar platform, in this study, it is modelled as a rectangular membrane subjected to uniaxial tension; following the available literature on the wrinkling problem. Numerical analysis of the wrinkling behaviour is first done by non-linear post-buckling calculations. However, it appeared that the results of this calculation are highly dependent on the initial deformation which is used. An alternative method which does not depend on user defined input was found in studying the second principal stress field: when negative second principal stress is present in the membrane, wrinkling can occur. When no negative second principal stress is present in the membrane, wrinkling will not occur. Furthermore, the distribution and the area of the negative second principal stresses region are indicators for the wrinkle distribution and amplitude. For a robust assessment of the susceptibility of a membrane to wrinkling, a study of the negative second principal stress field should thus be preferred over a post-buckling analysis. The second goal of this thesis is to research the influence of permeability on membrane wrinkling. The effect of holes on the wrinkling behaviour is researched by studying their influence on the second principal stress field. The aim is to find wrinkle free configurations and study the mechanisms which minimise wrinkling behaviour. Therefore, the size, location and shape of holes are varied systematically in membranes of different sizes. It was found that holes should be chosen so that when the membrane is strained, they deform in a way so that they bring tension in the regions of the membrane which are subjected to negative second principal stress in the non-permeable configuration. Furthermore, holes should be chosen such that the loadpaths in the membrane are not interrupted. The framework to research and design wrinkle free very large flexible solar platforms by adding permeability is verified and has proven to be effective by applying it on the configuration consisting of a stiff solarpanel mounted on a flexible membrane. In this configuration, the framework has led to holes by which the wrinkling region is localised. From the three parts of this thesis, it is concluded that a research framework for wrinkling of membranes with permeability was found in the analysis of the second principal stresses and the driving mechanisms were investigated and verified. To further develop this framework, research on the effect of stiffening the membrane and minimising wrinkling under load conditions other than tension are recommended.

Ventilation events are the result of masses of air being transported from the water surface along the hull, through the propeller plane. Previous research in literature has shown that ventilation induces large and sudden variations of the load on the propeller. The response of the propulsion system had not been documented before. This is a problem with practical and theoretical relevance as both operators and designers of ships and propulsion systems cannot predict the response of these systems to these significant and sudden variations of the propeller-load. The problem can manifest itself in different ways. A first example lies in a possible loss of propulsion and the damages that could incur. A second example lies in the possible installation of too much engine power to respond to unpredictable load-variations such as those incurred by ventilation events. Increased understanding of the relation between wave properties, -height and -frequency, and the response of a marine Diesel engine, -speed and -torque, subjected to wave-induced ventilation, is the goal of this thesis and leads to the main research question: How does a marine Diesel engine respond to off-design loads, and in particular to frequently varying loads resulting from propeller ventilation? It focuses on the response of the prime-mover to variations of the propeller-load imposed by ventilation events. The scope of this thesis covers a monohull coaster with a medium-speed marine Diesel engine moving forward in head seas. A model is proposed based on the description of immersion by Journée and Massie (2001) [19]. It consists of three sub-models that describe vessel-motion, the propeller and the prime-mover. The vessel-motion is described with a combination of potential-flow based methods and viscous theory. A quasi-static approach is proposed to describe the influence of ventilation on propeller-functioning. The prime-mover is modelled with a closed-cylinder process and an idealised first-order turbo-charger model that applies the exhaust-flow temperature of the closed-cylinder process to describe the charge-pressure. Three limits to this model lie in the application of vessel-motion data in a limited, positive domain, the application of 1st quadrant propeller data and the propeller envelope. This model uses input consisting of waves and the engine speed setpoint. The output consists of the rotational speed and produced torque of the prime-mover subjected to ventilation. Verification showed responses comparable to, and in the range and time frame of experimental results by Koushan (2007) [21]. Validation efforts lie beyond the scope of this thesis. Experiments by means of simulations have been performed for two engine speed setpoints and different wave-types describing head seas: Regular waves characterised by low frequencies, -characterised by high frequencies and -characterised by different wave amplitudes. A final experiment subjected the model to an adverse long-crested wave-spectrum for ocean waves. The research at hand found that the propeller immersion-ratio couples imposed waves and vessel-motions, to the inception of ventilation events. The quasi-static approach to model the influence of ventilation on propeller-functioning provided a reasonable estimate in verification, although further validation efforts are still required. The main research question led to the answer that: Frequently varying loads resulting from propeller ventilation can induce a significant shift in the operational point in the propellers open-water diagram and engines PV diagram and increase of the variations of engine speed and -torque. The final chapter also provides a number of pointers for a further validation effort, possible improvements to the proposed method and advice regarding further research.

At the moment, offshore wind is an indispensable source of energy. Compared to onshore wind, wind speeds offshore are considerably higher and more constant. Furthermore, offshore wind turbines reduce noise and visual impacts. In contrast to fixed bottom foundations, floating wind can be economically feasible in global offshore waters that exceed a depth of 60 meters. However, floating wind has its challenges. Research has shown that the interaction between floater motions and wind turbine controller can be significant, especially above rated wind speed. The interaction between the hydrodynamics and aerodynamics above rated wind speed is the main reason why fully coupled aero-hydro-servo-elastic simulations are needed to determine the motions and mooring loads of the system. The downside of fully coupled simulations is, next to the need of comprehensive technical background, the high computational time which makes these simulations unsuitable for concept design studies. The purpose of the research is to developed a fast and simplified model that can be used for design iterations in concept design stages of Floating Offshore Wind Turbines (FOWTs). The simplified model must be able to predict the general motions and mooring loads with acceptable accuracy. Moreover, the simplified model should be based upon available wind turbine input data in an early design phase. A sensitivity analysis is carried out to determine the contribution of various physical phenomena, present in fully coupled aero-hydro-servo-elastic simulations, on the motions and mooring loads of the GustoMSC Tri-Floater with a 5MW NREL wind turbine located at its center. The fully coupled simulations are performed with aNySIM-Phatas. By this analysis, the main physical contributors to the motions and mooring loads of the GustoMSC Tri-Floater are selected to include in the simplified model. It is confirmed that the interaction between the aerodynamics and hydrodynamics is significant, especially for platform pitch motions in the above rated conditions. Furthermore, the (controlled) aerodynamic thrust calculated from Blade Element Momentum (BEM) theory, as well as the wind drag loads are found to be the main driving forces on the system. The simplified model is constructed by coupling an external Python code to the multi-body time-domain software aNySIM. Whereas aNySIM is responsible for the hydrodynamic and mooring calculations, Python is used for the simplified aerodynamic calculations. The effect of the wind turbine controller on the aerodynamic thrust is included by the use of the steady state thrust curve, aerodynamic damping ratios and filter on the incoming turbulent wind. The simplified model is compared with fully coupled aNySIM-Phatas simulations. Compared to fully coupled simulations, obtained results suggest that in a free floating condition the differences in the mean are found to be within 5% and 10% for platform surge and platform pitch, respectively. The mean and maximum differences in the forward fairlead tension were found to be within 2% and 5%, respectively. Moreover, the results show that the simplified model is 5 times faster and much easier to construct compared to the fully coupled simulations. The results of this research are encouraging as the simplified model can serve as a tool to predict the general motions and mooring loads with acceptable accuracy. Also, as Python is not coupled to aNySIM before to the best of the authors knowledge, this coupling opens doors to other simplified modelling strategies.

This thesis investigated the possibility of alternative ways to loading and offloading flexlay vessels and provides a concept design. This was investigated because currently, the vessels designed by IHC, have to sail back to port to restock on pipes. During this time the expensive pipelayer is not laying pipes and thus not making money for its operator. Some operators have already moved to designs which use cranes to load pipes at sea. However, lifting heavy objects results in limited operability and wide vessels. The problem owner (IHC) wants to avoid this. The goal was to find a way to transship pipes offshore, which improves on the current performance of the reference vessel without resorting to cranes to transfer the pipes.

The research was mainly focused on the modelling of the logistical process of getting pipes from the port to the location. The results of this were used for the conceptual design of a flexlay vessel capable of being supplied at sea. The reference vessel built by the problem owner turned out to be a suitable candidate for adaptation for this purpose. To reach this conclusion, a logistical model was made, which was used as a basis for parametric studies. As input to that studies, a seastate timeseries is generated together with different transshipment methods. Two sets of simulations were used to evaluate the effect of the transshipment method in relation to a range of operational limits, and the effect of the distance on the operation.

The resulting pipelayer is fitted with two mailbox type docks in the side, this elongates the vessel and decreases its initial draught. These docks are closed and drained afterwards in order to secure the barge. The main conclusion is that it is possible to redesign the original pipelayer to accommodate the transshipment of pipes offshore.

The goal of this thesis has been to develop a concept exploration tool for zero-emission double ended ferries, that determines the feasibility of different energy systems, creates corresponding design parameters and helps decide between zero-emission energy types.

The research goal was achieved in three steps. Firstly, knowledge was gained on double ended ferry design, double ended ferry operations, zero-emission energy systems and the early design stage. Research into zero-emission energy systems resulted in lithium-ion battery energy systems, hydrogen fuel cells energy systems and supercapacitor energy systems being identified as likely feasible energy systems for double ended ferries. In the second step, the knowledge was used to create the concept exploration model. This model consists of a set of algorithms that determines technical and economical parameters of double ended ferry concepts for each of the identified zero-emission energy types, for a provided transportation need. The model also does this for a diesel-electric energy system, that serves as a benchmark. Equal economical comparison of the concepts is aided by providing the net present value of the investment in the energy system, for each concept. In the third step, the model is transformed into the concept exploration tool, through implementation in the Python programming language. This step also includes obtaining results from the concept exploration tool.

One use of the concept exploration tool is by shipyards, in their early design process. The tool can provide naval architects with insights into which zero-emission energy systems are possible for a provided transportation need, as well as the characteristics of the corresponding concept designs.

A second use for the concept exploration tool is the analysis of large amounts of input. This can provide insights into how design input parameters influence the concept designs and the preferences for certain energy system types. This was done by performing a parameter variation study. The results of analysing the obtained data are expressed through 24 conclusions. These are divided into four sets, per party for which the conclusions are expected to be of the highest interest. These are Energy System Suppliers, Governments, Ferry Operators and Shipyards.

The most important conclusion of this thesis is that zero-emission energy systems are technically feasible and can be cost competitive with diesel-electric energy systems. This to such an extent, that they should be seriously considered for every double ended ferry. Based on the net present value of the energy systems over the vessel lifetime, battery energy systems are most frequently cost-competitive with diesel-electric systems. Hydrogen energy systems are only competitive in highly specific cases and mostly too expensive to be cost competitive with diesel systems. Supercapacitor energy systems are cost competitive when upward of 30 daily trips are sailed, over short distances.