The increased consciousness of the negative impact of human-induced climate change has resulted in rapid developments within the offshore wind industry. With Wind Turbine Generators (WTGs) becoming increasingly larger and available shallow water sites becoming scarcer, new offshore wind solutions must be developed to accomplish the goals set by today’s policymakers. The new deep water sites available for offshore wind are not applicable for the current benchmark of monopiles and jack-up vessels. New state-of-the-art applications, such as Floating Offshore Wind (FOW), come into play in the global offshore wind market. To meet this demand, Heerema is developing installation methodologies for floating to floating installation applications. One of these methodologies is the RNA+ method (Rotor Nacelle Assembly + Tower), lifting a fully assembled WTG module in one lift from the vessel deck on top of its foundation to limit the number of critical lifts. Operability studies are required to examine whether such operation is feasible. As the FOW industry is the new kid on the block, little is known about FOW’s configuration and other influences. Therefore, this research aims to determine the effect of design parameters of the three key components of an offshore floating to floating installation on its operability. These key components are the WTG, floater, and installation vessel. For this research, the IEA 15 MW reference turbine with an altered tower, a Tension Leg Platform (TLP) provided by Intecsea, and Heerema’s Semi-Submersible Crane Vessel (SSCV) Sleipnir were used as WTG, floater, and installation vessel respectively. A numerical base case model containing these key parameters was built to address the influence of the design parameters. This base case models the free-hanging stage of a complete WTG module suspended in the SSCV’s crane 3 m above the TLP in a water depth of 150 m. The numerical model was analyzed in the Frequency Domain (FD), considering only first-order effects. With respect to this base case, all parameter variations were compared. A mean JONSWAP spectrum was used as wave spectrum. The results show that this installation method is sensitive to long wave periods ( > 8 s). The clearance between the nacelle and crane-boom is deemed the most governing limiting criterion. The relative vertical Z-tip motion between the tower bottom and TLP top and the side-lead angle of the crane hoist wire are the secondary governing limits. Design parameters that influence the static clearance between the nacelle and crane-boom have the most impact on the total operability. With the current design parameters world’s largest SSCV has a limited operability for installing the modified version of the IEA 15 MW reference turbine with a single crane lift. Alterations to increase its crane boom reach and clearance are needed to perform this single lift installation. The hub height and nacelle casing size of the WTG limit the operability significantly. Furthermore, due to its relatively small size, stability and stiffness in heave direction, the TLP hardly affected the operability.

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.

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.

Jumbo Maritime is a shipping company active in the heavy lifting market. Jumbo uses stabilisers to enlarge the stability of the ship during lifting. By using stabilisers Jumbo can perform heavy lifts with a relative small ship, this is one of the major advantages. Downside of using stabilisers is that the installation and de-installation is a time-consuming process. Besides that the usage also causes safety issues, more and more port authorities no longer approve the usage of stabilisers. Research is done in finding alternatives for the use of stabilisers, focusing on alternatives for new ships that need to be build. Looking at Jumbo’s position in the market shows the following unique selling points, for the J-type: • Limited draft compared to its competitors • Length < 150 meters On the one hand the usage of smart stabiliser to speed up the installation and de-installation of stabilisers is looked at. Because smart stabilisers are still stabilisers, also alternatives are analysed that do not require a stabiliser at all. By widening the ship, the ship can be stable enough to perform lifts without extra support from stabilisers. A model is created to be able to determine the required width for each concept. This model is generated based on the input and requirements set by literature, market analysis and Jumbo’s specifications. Some of these requirements are: limited dimensions, minimum required stability, anti heeling and deadweight. The four concepts that are created as input for the model are: • Base concept, concept 1..., Concept 2... Concept 3...Concept 4...: A case study is performed to be able to compare the concepts. Three cases are created, which are actual relevant cases for JumboMaritime: For each concept the costs are determined to sail the certain case. Because the heavy lift market consists of somany single jobs that differ a lot on weight, complexity and distance it is difficult to map the revenues. The costs are determined per job, to be able to compare the different concepts. Costs consists of the capital costs, fuel costs and operational related costs. Besides cost per job, also cost per ton/mile is calculated to determine the economical speed. For case 1 the economical speed is 14 knots, which is similar to the required design speed. This means that the ships sails most cost efficient at this speed. The time that is saved by eliminating the stabiliser is used to reduce the sailing speed. In this way the same amount of jobs can done in the same time. This research shows that the saved fuel consumption as a result of slower sailing can compensate the longer sailing time and increased resistance for a wider hull concept. Comparing the concepts in the different cases shows that concepts 3 and 4 are more beneficial in case the stabiliser usages goes up. It can be concluded that awider hull shape can operate at 2-5%lower costs. The fuel consumption of the V-shape decreases more significantly at lower drafts. It is an advantage at ballast sailing or during sailing light cargoes. Besides the lower costs, the increase of deck space for the wider concepts is added value in the heavy lift market. An other important advantage of the wider ship concepts is the elimination of safety issues because the usage of stabilisers is not needed any more to lift heavy cargoes safely.

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.

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.

This thesis presents the potential of solar energy to answer the increasing demand for sustainable energy. Multiple floating solar parks are installed on inland water bodies. This trend is a result of the lack of surface for PV systems and a result of legislation on national and international governmental levels, for the reduction of greenhouse gasses. This inland technology is currently well established. Still, in densely populated areas such as the Netherlands supplementary surface could be beneficial to unlock the full potential of solar energy. Ocean and sea surfaces are a possible, but challenging solution to this problem. These offshore water surfaces could be used for electricity or synthetic fuel production. Offshore locations are attractive because of the abundant availability of surface. Still, an OFPV-system needs to overcome multiple technical and non-technical challenges and requirements. This challenge demands technical solution within the constraints of a suitable business case. Furthermore, the impact on people and ecology also needs to stay within ethical borders. An OFPV can be subdivided into three physical subsystems: an energy converting system, a position monitoring or mooring system and a floating support structure. Multiple concepts were proposed in literature or by the industry. All proposed concepts are variations of support systems that provide a surface for conventional PV-technology. It also was concluded that none of the proposed concepts is fully developed. Currently, only one system is in the testing phase. The current state of the technology, and the high potential of an OFPV are the drivers behind the search for a new concept design. In this thesis, the requirements for an OFPV support structure were formulated, and a brainstorm resulted in the buoy and beam concept for further research. The buoy and beam structure is a system in which submerged beams form a triangle grid are held together by floating buoys. The buoys support triangle platforms, by carrying the corners of the platforms. All connections between the buoys, beams and platforms are fully hinged. Because of the hinges, the structure can move with the waves and therefore mitigates the loads it experiences. In the second part of this thesis, the feasibility of the buoy and beam structure was assessed. It was concluded that the heave response is the most critical response to the feasibility of the concept. When the platform would heave too much, the waves will slam into the platforms and the solar panels, leading to damage and excessive loads on the structure. Consequently, the heave response and the relative wave height seen from the moving triangle platform are researches and modelled. The structure was identified as a hydrodynamic transparent structure. Consequently, the relevant hydrodynamic loads are obtained with the Morison equation and Airy wave theory. All damping terms are linearised. A differential equation incorporated the constrains for both, the construction and the hydromechanic loads. The mechanical equations can be linearised by assuming small angular displacements of the beams. This differential equation is implemented in a calculation tool in MATLAB. The code is verified over multiple steps. The tool made it possible to obtain the response based on the topology and the main dimensions of the buoys and the beams. With this calculation tool relations between the dimensions of the buoys and beams on one side and the frequency response, on the other hand, are identified by simulating different variations of a simplified starting design. The following conclusions were made on the eigenfrequencies. Firstly, it was noted that the eigenfrequencies of the system are in proximity to each other. Secondly, it was shown that the first and second eigenfrequency could be calculated in a simplified manner. Thirdly, it was seen that the buoy diameter to mass ratio has a positive linear correlation with respect to the eigenfrequency, i.e. the stiffness to mass ratio of the system severely influences the eigenfrequency. Furthermore, it was seen that an increasing beam length has a slight linear correlation with the eigenfrequency. Also, it was concluded that a large hexagon system (for example, nineteen buoys) could be beneficial because a hexagon structure creates a large surface with respect to the number of buoys. Moreover, in reality, the response should be lower than the model prediction, as a result of the high number of beams that cause damping. Additionally, a hexagon system should have a minimal change in response for different incoming wave angle. To obtain a feasible system, the response peaks of the structure should not overlap with the wave spectrum. Based on the additional simulation, it was concluded that it should be possible to design a system with a low eigenfrequency resulting in a system that will only slightly move with the waves. Additional relations between the dimensions of the buoys and beams and the response peaks were found. The requirements to obtain a low eigenfrequency and a modest response match, which positively influences the feasibility. Some further steps on the research of the heave response and the relative wave height are needed. The calculation tool can still be improved. A preciser estimation of the response peaks is of significant importance. Some further iterations must be executed to determine the full potential and feasibility of the concept design. Furthermore, in a scientific point of view, it will be highly interesting to validate the model on a model scale. In the development of the buoy and beam structure, additional critical responses need to be researched. The forces in the hinges and the response in horizontal direction need to be known for further assessment of the feasibility. Next to the technical aspects, the human, ecological and economic implications of the buoy and beam structure need to be researched.

Floating structures have developed significantly in recent years. As land is becoming scarce, the use the water surface will contribute to ease this scarcity. Therefore in recent years, floating structures covering large areas have been developed, also called flexible floating structures. In this project the focus is set on the mooring system very flexible floating structures (VFFS). At the TU Delft, two towing tanks can be used to investigate the mooring system of VFFS, however first a reliable measuring system is required that is able to examine a specific part of the mooring system. Conventional setups that measure the mooring forces consist of large instruments, as these instruments only have a small effect on their investigated structure (vessels). The response of VFFS is dominated by elastic deformations and differs from conventional rigid structures. For VFFS, these type of instruments will have a large effect on the structure motions and thus these conventional setups cannot be used. Therefore, a new measuring system is required to conduct small scale experiments with VFFS, and the following objective is formulated: Develop an instrumented mooring system for VFFS at model scale for the towing tank at the TU Delft and determine its accuracy. A new concept is developed in this project. This concept resulted from an extensive concept development where all functions of the system were analyzed. With the use of a Morphological Chart and a Multi Criteria Analysis the best concept was selected. For this concept, it was determined that the focus should be on the sensor configuration and calibration procedure. First, the optimal sensor configuration of the concept was specified by analysing the working principle of the concept. Second, the calibration procedure was further analyzed. From this analysis, three calibration procedures were developed: the single sensor calibration matrix, the full fixed calibration matrix and the full rotated calibration matrix. From literature and theory, it was not possible to determine in advance what calibration procedure should be selected, and therefore the performance of the procedures were verified with experiments. All calibration procedures were executed, whereafter the performance of the different procedures were compared. The two main considerations for the comparison were the accuracy and the usability of the procedures. After performing the comparison, the main conclusion was that the full upright calibration procedure is the optimal procedure. To verify the concept under realistic conditions, an example application was performed in the towing tank No.1 at the TU Delft. By doing this, the concept has proven to be suitable to measure the mooring force and transform them into usable data. In this project a new concept was developed into a working system. This system forms an excellent base for extensive research into the mooring system of VFFS, and is a good addition to the measurement instruments for the towing tank at the TU Delft. It is concluded that the system is able to measure the mooring forces and the direction. The accuracy of the system still has to be improved, and with additional research the working concept can be further developed.

Floating offshore wind turbines offer opportunities to harvest wind energy at deep-water locations, where the construction of fixed-base turbines is infeasible. The dynamic power cables, which interconnect turbines and transport the generated electricity, are under large dynamic stresses due to the environmental loads and the motion of the floating platform. Limited knowledge about the structural behaviour of these cables is available, which is why there is need for new analysis and design methods. This MSc thesis presents a method for the preliminary design optimization of the dynamic power cable configuration. A parametric model of a dynamic power cable is built in the commercial software package OrcaFlex, from which motions, loads and fatigue on the cable can be calculated. Following that, a radial basis function model-based optimization algorithm is applied to find the optimal cable configuration for an arbitrary environmental scenario. The key performance indicator here is fatigue damage on the copper conductor, which is expected to be critical due to the cyclic loading on the cable and the poor mechanical properties of copper. Experiments are carried out to test the optimization model’s validity in terms of convergence, robustness and efficiency. The final method is capable of consistently finding a near-optimal dynamic power cable configuration design within reasonable time. Additionally, findings are presented about the fatigue behaviour of the DPC, what causes the fatigue damage and how to mitigate the effects.

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.

The development of renewable energy applications has become increasingly important in the past couple of years due to a growing global energy demand and increasing consciousness of global warming. A recent development in renewable energy is the application of offshore floating solar systems. A prototype design for this application, as developed by the company ’Oceans of Energy’, consists of multiple floating platforms (floaters), moored to the sea bed. One of the challenges for offshore floating solar systems is the continuous wave induced force acting on the floater that can become significant in severe weather conditions. Numerical simulations are often used to analyse and predict these forces. Combined frequency-time domain solvers are the most promising tool for this design to obtain reliable results within reasonable computational time. However, it is unknown what the capabilities of this solver is for the novel offshore floating solar system. The goal of this study is therefore to determine to what extend the frequency-time domain solver is able to accurately simulate the behavior of the multi-body, offshore floating solar system. A numerical model was developed in the simulation tool ’aNySIM’. Experiments conducted in the offshore basin at MARIN were used for the model structure development and validation. Additionally, viscous damping effects were implemented from empirical data based on the experiments. Decay tests were used for damping determination. This resulted in inaccurately determined forces and motion amplitudes for regular and irregular wave tests. A new damping determination method was introduced, using regular wave results as input. The accuracy of the model improved with 4% using this method. Nonetheless, inaccuracies in mooring line forces, oscillating behaviour and motion amplitudes are present. These inaccuracies have been addressed with an uncertainty analysis and sensitivity studies. Trends within the accuracy of the simulation model were linked to physical phenomena that occurred during the experiments. Analysis showed that several effects, related to the novel design characteristics, influence the model accuracy. Multi-body (e.g. shielding of floaters) and mooring system aspects (e.g. hydrodynamic loads on mooring lines) have been identified, influencing the viscous damping of the system. Additionally, nonlinear effects due to, amongst others, breaking waves have been identified. For regular wave tests and lower irregular wave tests, the simulation model gives reliable results with errors in the mooring line forces below 10%. These errors are mainly ascribed to viscous damping effects. For higher sea states the simulation behaviour shows discrepancies and errors in the mooring line forces increase. In these tests, nonlinear effects due to breaking waves become more relevant. For future work, different uncertainty causes must be further isolated in the simulation model. This can be done by obtaining more experimental data. To quantify the effects, studies in other numerical tools can be performed (e.g. CFD calculations) and more extended sensitivity studies must be executed in aNySIM. We present a structured

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.

The use of renewable energy sources like solar and wind energy for the generation of electricity are expected to increase in the coming decades. However, these sources are intermittent. Therefore Electrical Energy Storage (EES) systems are needed in the near future to assure a reliable electricity supply. These systems should also be able to deliver power in longer periods of time with low generation from wind and solar energy sources. An example of such an EES system is the GreenBattery, developed by AquaBattery. This is a flow battery that stores the electricity by splitting salt water in an acid and a base. Because the main component of the GreenBattery is salt water, this battery is safe in use, as it cannot catch fire or explode. Furthermore, this makes the battery environmentally benign and cost competitive with other EES systems. The main focus of this thesis is to make a concept design of a GreenBattery that can be placed on a water like a lake. This concept is evaluated in a case study regarding the energy storage lake of the Delta21 project. This battery could provide a reliable backup electricity source for e.g. the Port of Rotterdam or stabilise the electricity output of renewable sources. Therefore, the main research question of this thesis is: ‘How can AquaBattery’s GreenBattery be realised on the energy storage lake of the Delta21 project, providing long term storage?’ To answer this question, first the design basis is explored. Based on this, concepts are generated using a morphological chart method and the most feasible concept is chosen using a multi-criteria analysis. This chosen concept is worked out in more detail, after which its technical and economic feasibility is investigated. The most feasible concept turned out to be a floating concept. This concept uses floating rigid tanks to store the different liquids present in the GreenBattery. The power unit, where the electricity conversion takes place, is placed on top of these tanks. Furthermore, the feasibility of integrating a solar photovoltaic system on the floating tanks is investigated, because of the large area available for multiuse on such an island. The resulting dimensions of the floating tanks is 98 by 98 by 3 m (length, width, draft). Four of these tanks can be coupled together to form one floating island. Such an island can store about 560 - 800 MWh of energy, depending on the required storage duration and about 3.2 MWp of solar panels can be placed on top of the tanks. In total, about 300 of such islands can be placed on the energy storage lake of the Delta21 project. Such an island is technically feasible, because the natural periods are larger than the expected wave periods. Therefore, the motions and forces of the island will be minimal. Furthermore, in terms of costs, the floating GreenBattery is cost competitive with other EES systems and therefore will be economically feasible as well.

The research effort on autonomous ships has increased over the last years. The realisation of these ships will have as a consequence that the crew can be reduced significantly or even be removed entirely, resulting in unmanned ships. Although there is a strong belief that unmanned ships would lead to more economic efficiency, only limited research has been performed in order to demonstrate what the overall effect of the change to unmanned shipping would have on transport costs. Nonetheless, more reductions in cost or improvement of transport performance for unmanned ships would make them more attractive and economically viable. The design of a ship is subjected to regulations and requirements that limit the design freedom, but it increases safety. Removing the crew from the ship reduces the risk of shipping, under the assumption that the probability that an incident occurs does not change, since the lives of the crew are no longer at risk. If the risk is lower, the requirements to the design of unmanned ships might become less strict, while maintaining equivalent safety. In this way more design freedom can be realised for unmanned ships, as well as more economic efficiency. Within this report the required subdivision index will be evaluated, for it is expected that reducing this requirement can create more design freedom. Therefore, this research will focus on what reduction in the requirement concerning damage stability for unmanned ships can be allowed, if they are subjected to an equivalent level of risk as manned ships of the same size and type. It has been found that the required subdivision index can be lowered for unmanned ships, based on equivalent safety. The contribution of the risk of losing lives to the overall level of risk is larger for smaller ships. This is reasonable, since for larger ships, the size of the crew increases with a lower rate compared to the amount of cargo, installed power or capital costs. Therefore, the allowable reduction in the required subdivision index is largest for smaller ships. However, the size of the reduction depends strongly on missing accident statistics concerning the loss of life. The missing data results in the following uncertainties, for which further research is recommended. Firstly, for different ship types differences in the accident statistics are present. There are significantly less fatalities related to bulk carriers and container ships compared to general cargo ships. It is expected that these differences are related to the individual ship size and crew size, for which both the correlation with the probability of losing life is unknown. Secondly, there is a discrepancy between the theoretical probability of survival of a ship, namely the attained subdivision index, and the probability of survival that the accident data suggests. The attained subdivision index suggests that at least 30% of all accidents should lead to a total ship loss. The accident data reveals that for general cargo ships around 10% leads to a total ship loss.

Large water motion inside the moonpool of vessels operating in waves can be excited by pressure fluctuations produced by external waves and vessel motion. Extreme consequences of this effect may include injuries for crew members, and damages to deck equipment resulting in downtime for the vessel. The accepted method to predict this non-linear phenomenon is a combination of model tests and potential solver. Nevertheless, model tests are generally conducted at the end of the design phase leading to serious problems if the moonpool performance is not sufficient. CFD solvers proved their capability of modelling complex flow phenomena and their use as a design tool for the moonpool is growing. However, a complete verification & validation is still missing. In the present work the water motion inside a moonpool and the forces on the hull, for a vessel in head waves without forward speed, are estimated using the MARIN software ReFRESCO. In doing so, the goal is to define the accuracy of the code for a rectangular moonpool with sharp edges without additional damping devices. For a deeper comprehension of the physics involved, a stepwise approach was followed. The work starts with an empty domain in which only regular waves were generated to assess the propagation and absorption of waves in ReFRESCO. Secondly, fixed vessel simulations were performed to study the influence of grid dimension, mesh refinement and boundary conditions. Then forced heave oscillations were simulated to estimate the damping and added mass. Verification studies were carried out for all the presented to this point. Finally, results from free-floating simulations were validated against experimental results.

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.

Long distance ocean towing is a commonly used transportation method in the oil & gas and renewable energy industries. Barges with cargo, vessels and various offshore structures are towed from and to location. Boskalis participates in this industry through its subsidiaries Smit and Fairmount Marine. From experience with these transports, it was found that the preliminary calculations do not match with the experiences offshore and that the impact of wave drift on these calculations is most promising for further research. To investigate this impact, the problem is split into three parts: wave drift estimation for a stationary vessel, wave drift estimation for a sailing vessel and the analysis of the towing stability.From the literature, eleven methods are identified for the wave drift estimation of a stationary vessel. These are compared for the surge, sway and yaw force components. The different methods are computed using the diffraction program Delfrac, the strip theory solver ShipMo and own implementations in Matlab. With vessel velocities included, ten wave drift estimation methods for the sailing vessel are compared. Specific attention is paid to the wave drift damping, which relates the stationary wave drift to vessel velocities. It is implemented using Aranha's formulations and the panel pressure output of Delfrac. The most applicable methods with respect to the sailing tow resistance are the far field and near field methods in combination with the wave drift damping. With respect to the total tow resistance, the wave drift contribution is found to make up roughly 25% of the total resistance, irrespective of forward velocity. The dynamic behaviour of the tow operation is examined for two barges: one course stable and one course unstable barge. Their towing stability properties are assessed without waves present and for head waves conditions. It is found that the head waves do not affect the stability of the course stable barge assuming the towing tug has sufficient available towing force. For the course unstable barge, the main stabilising effect is identified as the extra resistance due to the head waves and not the direct wave drift moment. The relative contribution of the waves with respect to the wind and current shows that the head waves have a significant stabilising contribution to the towing stability although the specific relative contributions are highly dependent on the environmental conditions. Head waves either reduce the path width of the fishtailing motion or dampen these oscillations into a stable towing position. This was verified by simulations in the time domain. Irregular waves also promote the stability: they stabilise the unstable barge in the entire range of physically relevant wave periods, irrespective of towline length.Overall, the contribution of the wave drift to the tow resistance is significant, especially while sailing. Head waves are beneficial for the towing stability of a course unstable barge, both in regular and irregular sea states. This increased insight reduces the uncertainty in the tow resistance prediction and contributes to the understanding of the towing stability properties of unstable barges.

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.

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.