The global push to mitigate climate change has accelerated the transition to renewable energy, with offshore technologies emerging as a promising solution to meet rising energy demands while reducing land use. Among these, offshore solar, an innovative approach leveraging the ocean’s abundant solar radiation, offers significant potential. However, harsh marine conditions pose challenges, particularly in terms of material degradation and end-of-life management. This study evaluates the environmental impacts of offshore solar systems across their life cycles, focusing on degradation under prolonged marine exposure and the implications of various end-of-life strategies for key components such as photovoltaic panels, floating structures, and mooring systems.

Using a prospective cradle-to-grave Life Cycle Assessment, three degradation scenarios, low, medium, and high, were developed based on observed degradation mechanisms from offshore structures and terrestrial PV systems. Each scenario is linked to a distinct end-of-life strategy. Results show that environmental impacts are significantly influenced by material recovery rates rather than performance losses, with the reuse of PV modules in the low degradation scenario yielding the lowest environmental footprint. A backcasting analysis positions this low degradation scenario as a desirable future vision, emphasizing design for longevity, reuse, and circularity.

Key strategies identified include the use of advanced encapsulants, durable backsheets, anti-corrosion coatings, and marine-adapted cleaning technologies. This research underscores the importance of early-stage assessments to embed circular economy principles in offshore solar design, highlighting material innovation and sustainable end-of-life planning as critical to the long-term success of this emerging renewable technology.

This thesis presents two wave energy converters (WECs), an oscillating surge wave energy converter and a heaving point absorber wave energy converter and a reverse osmosis desalination system which are numerically modeled and compared. The primary objective was to assess and contrast their performance in terms of Freshwater Production and Specific Energy Consumption (SEC) over a variety of realistic sea states, which are specified by significant wave heights (1–5 meters) and energy periods (5–9 seconds) incorporating a particular wave spectrum for irregular waves.

An open source MATLAB based solver was used to integrate hydrodynamic data from frequency-domain Boundary Element Method (BEM) solver into time-domain simulations. Both devices harnessed mechanical energy, which was then sent to the reverse osmosis unit via a hydraulic piston configuration. Power matrices displaying SEC, water production and permeate concentration were used to present the results, offering a direct comparison.

Results showed that the two devices differed significantly. Only in high-energy wave circumstances did the heaving device operate effectively, exhibiting low SEC of 2-4 kWh/m³ and significant freshwater output in certain sea states. However, in moderate or lower-energy seas, its efficiency significantly decreased. With SEC normally ranging from 2 to 4.5 kWh/m³ and consistently higher freshwater output, even in milder sea conditions, the oscillating surge device, on the other hand, showed more stable performance. According to the study, the oscillating surge device can provide desalinated water with salt concentrations below the threshold of 600 ppm suggested by the World Health Organization in the majority of sea states, whereas the heaving device often crosses this limit, with the exception of energetic wave conditions. These findings are in good alignment with previous studies on wave-powered desalination.

Limitations include the exclusion of operational issues such as membrane fouling or long-term system degradation, the assumption of linear interpolation for calculating intermediate sea states, and possible errors resulting from simplified models.

The use of complex interpolation techniques to improve accuracy, more simulations over multiple sea states, and experimental validation of results are some suggestions for future research. Additionally, combining environmental and economic evaluations will help in determining if larger-scale deployment of these wave-powered desalination systems is feasible. This study highlights oscillating surge devices as a strong option for sustainable freshwater generation and offers insightful information for enhancing wave energy desalination.

The increasing presence of electric vehicles onshore has also sparked a growing interest in offshore electrification. Simultaneously, the past decade has seen a significant increase in offshore renewable energy sources, a trend projected to accelerate in the future. Based on this growth and improving battery technology, the market potential of offshore charging solutions is highlighted. To address this emerging opportunity, this report presents a technical feasibility study of the novel KONGSBERG floating offshore charging station (OCS). The primary focus of the system is the offshore wind sector, particularly the support of operations for crew transfer vessels (CTVs) and service operation vessels (SOVs). As the majority of offshore wind farms are currently located in shallow water, this is where the largest market potential is expected. However, shallow water presents greater design challenges, as wave non-linearity increases and wave height becomes more significant relative to the water depth.

In this report, it is studied how the water depth affects the technical feasibility of the KONGSBERG OCS in shallow water. To do so, the KONGSBERG OCS is modeled in OrcaFlex for water depths ranging from 60 to 30 meters, analyzing key system components such as the buoy, the mooring system and the dynamic power cable (DPC). A surface-based charging concept was found to be unfeasible due to excessive pitch motion, leading to a focus on submerged designs. The analysis shows that the OCS is technically feasible at 40 m and 60 m depths, fulfilling both ultimate and fatigue limit state requirements. At 30 m depth, the system remains technically possible, but it exhibits several limitations, including a significantly reduced cable fatigue life of about 7.5 years, occasional buoy emergence above the sea surface, and increased interference with the seabed and mooring lines. The dominant driver of fatigue was identified as cable motion and the most critical load cases were those with aligned wave and current directions. Polyester was confirmed to be the most suitable mooring material, maintaining acceptable cable curvature in all feasible configurations.

To further improve the system and expand its applicability, several areas of future research are proposed. These include: evaluating the system’s behavior during charging mode with vessel interaction; developing a plug retrieval mechanism for emergency release scenarios; conducting fatigue enhancement studies for operation in shallower depths; incorporating rotational flow and vortex shedding effects using CFD to improve added mass and damping accuracy; and performing an economic assessment comparing the submerged system to a monopile-mounted alternative in very shallow waters. These directions aim to refine the design and expand its deployment potential within the growing offshore wind and electrification landscape.

Floating photovoltaic (FPV) systems offer a way to expand solar power offshore and can potentially be integrated with existing wind farms to diversify energy mix. A key challenge is the design of the dynamic power cable (DPC) that transports electricity from floating units to the seabed while subjected to waves, currents, and wind. This thesis evaluates the structural behaviour and installation feasibility of DPCs for a lightweight FPV concept (Solar@Sea III developed by Bluewater Energy Services) in shallow North Sea conditions at 20 m and 35 m water depth.

In this study, time-domain finite-element simulations in OrcaFlex are used under Ultimate Limit State (ULS) conditions. Two configurations, catenary and lazy-wave, are compared. A parametric study varies hang-off point (HOP) angle, bend-stiffener dimensions, and buoyancy-section characteristics. Decoupled and coupled analyses then assess three integration points within the FPV system: the floater, a corner buoy, and the transverse line. Performance is measured by peak curvature, tension, and seabed clearance.

Curvature is the governing design constraint; tensions remain well below strength limits across cases. Standard bend stiffeners reduce end-region curvature but are not sufficient alone. Combined HOP-angle adjustments and stiffer or longer bend stiffeners are most effective in 20 m water depth. At 35 m, curvature hotspots move away from the ends, and benefits from local end-point adjustments decrease. Lazy-wave configurations increasingly help at 35 m by lowering curvature, distributing it along the cable’s length, and stabilising tensions. At 20 m, however, they provide limited seabed clearance (often <2 m), which is operationally risky without accurate buoyancy calibration and regular inspection.

System integration strongly influences performance. Among the tested connection points, the corner buoy offers the best balance of mechanical response and practicality, acting as an accessible hub that reduces motions at the HOP and eases installation and maintenance. For 20 m depth, a catenary cable connected at the corner buoy is the most reliable and feasible option. At 35 m, the lazy-wave configuration becomes more attractive due to improved curvature and tension margins, though with higher installation complexity.

Overall, reliable DPC design for offshore FPV requires an integrated approach that couples lay-out configuration, connection strategy, installation, and operations from the outset. This initial analysis indicates that a catenary DPC configuration is feasible for lightweight FPV systems in the North Sea, but an increase in cable bending stiffness is preferred to improve curvature control and design margins.

The offshore wind industry is rapidly advancing, expected to play a crucial role in renewable energy production, with a growing emphasis on addressing associated environmental concerns, particularly the impact of underwater noise generated during the installation of wind turbines. In response, bubble curtain technology (BCT) has emerged as a potential solution. While the BCT operational concept has been demonstrated in practice, a detailed investigation related to fluid dynamics, geometric characteristics, and operational parameters has yet to be conducted. It's important to note that this need for investigation is specifically applicable to large BCT systems. This research aims to enhance the understanding of unsteady compressible flow inside BCT hoses and examine the impact of operational parameters on the pneumatic aspects of the bubble curtain system along the hose length.

This thesis systematically defined its fundamental objectives, beginning with the development of a 1D unsteady model for compressible flow in pipeline systems. This model, which served as the basis for subsequent studies, was verified against the existing literature, revealing a 2-4% difference in flow rates and pressure responses. Subsequently, the scope was broadened to include nozzle configurations, which were gradually included in the pipeline model. The model evolved through configurations with one, three, and five nozzles, where larger diameters increased dampening on transient pressure fluctuations. As the research progressed, the final model, incorporating five nozzles, was used as the basis for the scaled Bubble Curtain Technology (BCT) model.

A sensitivity analysis for this study was carried out utilizing parameters from existing research. The sensitivity study specifically emphasized the influence of geometric (hose and nozzle diameters, hose length, nozzle spacing) and operational factors (discharge coefficient, water depth, air flow rate) on the flow dynamic of Bubble Curtain Technology (BCT). The main findings from this research included reducing backflow with smaller diameters and lowering reverse flow with greater discharge coefficients and airflow rates. Changing the hose length and nozzle spacing proved effective for adjusting the required flow rates. The investigation also found that nozzle diameter and discharge coefficient had a considerable impact on nozzle flow rates, with a 2-3% increase over reference values at the maximum value range. Other geometric and operational parameters in the tested ranges had a relatively lower influence on the nozzle flow rates or generated pressure variations.

The scaled BCT unsteady compressible flow dynamics model presented in this thesis is still in its early stages of development, but it can serve as a basis for the development of full-scale pneumatic models that can enhance BCT and lessen the environmental impact of offshore wind farm operations.

An increased interest in the use of renewable energy, mainly accelerated by the growing awareness of the problem of global warming, has been observed over the last decades. For the installation of the popular monopile and other support structure types, high-energy pile driving is used in around 90% of the cases. The noise emitted by the pile driving forms a serious threat for marine mammals. To mitigate the underwater noise, air-bubble curtain systems are used in the offshore industry. A better understanding is required of the working principle of air-bubble curtain systems in practice to gain more insights into the air transport through the hose-nozzles (perforated pipes).
For this study a physical medium scale pneumatic model of the air-bubble curtain system was designed based on data available from the offshore industry. Tests were performed both in dry and wet conditions which approximate those that are seen in the industrial practice. The role of several geometrical and operational parameters of the pneumatic system, like the inlet pressure, inlet flow rate, internal hose diameter, nozzle diameter, nozzle spacing, static water pressure, on the operational conditions along the hose-nozzle is explored. The influence of the volumetric flow rate along the hose-nozzle on the pressure development along the hose-nozzle is examined. The examined correlation between air flow temperature and air flow rate at the inlet of the compressed air supply and the pressure development over the hose-nozzle forms valuable input for a future numerical model that includes the temperature of the inlet flow rate. The test setup with configurations of reduced lengths in dry conditions is used to experimentally determine the discharge coefficients of a range of different nozzles. Here, the limitations of the test setup are carefully considered and a comparison with numerical results provided by compressible flow theory is followed.

The increasing demand for renewable energy and the need to achieve global decarbonization goals have led the energy sector to explore remote areas where Floating Offshore Wind Turbines (FOWTs) are expected to play a significant role. These far from shore located turbines harness strong and consistent winds, but their deployment in deeper waters poses challenges. In addition, the intermittent nature of wind energy, grid congestion, and transmission losses further complicate meeting the energy demands. Combining FOWTs with offshore hydrogen production offers a promising solution by reducing reliance on electrical infrastructure. Green hydrogen, produced from renewable sources, provides a versatile and proven option for decarbonizing hard-to-abate sectors. The integration of hydrogen production directly from a FOWT presents a compelling alternative, but the transportation of hydrogen from Hang-Off Point (HOP) at the FOWT to the Termination Point (TP) at the seabed through flexible pipes requires ensuring the structural integrity under static and environmental loading.
This research evaluates the impact of various parameters in lazy wave configurations on the tension and curvature behavior of flexible pipes used for hydrogen transport in offshore wind-to-hydrogen systems, utilizing simulations performed in OrcaFlex (OF). The research shows that failure modes, tension, overbending, and compression, are only exceeded in non-optimal wave configurations, with the Minimum Bend Radius (MBR) being a more critical constraint than the Minimum Breaking Load (MBL). However, both limits are breached when compression, looping at the Touch Down Point (TDP), or collapse has already occurred, suggesting that the pipe may be overdesigned or that the lazy wave configuration represents a conservative design approach. Furthermore, research also finds that environmental factors have minimal impact on tension and curvature, with static effects contributing for 86\% of total tension and 78\% of total curvature. This indicates that static analysis can provide an initial configuration without the need for computationally demanding dynamic simulations, as the design limits of MBL and MBR are exceeded in similar static and dynamic scenarios. Lastly, the design of a lazy wave configuration can be simplified to three configurational parameters: a buoyant section parameter (the outer diameter of the Buoyancy Modules (BM), pitch between BMs, or the buoyant section length), the first section catenary length, and a total configuration parameter (total length or horizontal distance between the HOP and TP), since the parameters within each group exhibit similar behavior in terms of tension and curvature responses when varied individually.

Aiming to comply with the Paris Agreement, the reduction of Europe’s GHG emissions in the energy sector is a must. Due to the intermittency of renewable sources, energy storage technologies are essential to this plan. Offshore Low Head Pumped Hydro Storage (LH PHS) is presented as an alternative to partly solve this problem. Considering that its infrastructure entails a reservoir of a 5km diameter ring in the middle of the sea and needs millions of tonnes of concrete, sand, granite and steel among other materials for its construction; environmental concerns arouse, which this report aims to address.
Information from the Alpheus project about the engineering requirements for an offshore LH PHS plant is used, following ISO 14044 Life Cycle Assessment (LCA) methodology. In this study, the construction, maintenance and operation of an offshore LH PHS plant are assessed, focusing on Global Warming Potential (GWP), Water Use Depletion Potential (WUDP) and Abiotic Depletion Potential for Elements (ADP-E). This is studied with and without the input of electricity, sourcing it from wind or from the Dutch grid mix. Moreover, these results are compared with Lithium iron phosphate (LFP) Batteries and for Wind-Green Hydrogen.
For the construction, operation and maintenance of the LH PHS plant, it is estimated that the emissions would reach 2.8Mt of CO2-eq, 601 million m3 of water and 140.2t of Sb-eq. These emissions are mainly shared between civil and electromechanical infrastructure, the former has more relevance for GWP with almost 56% of the emissions whereas the latter reaches 69% for WUDP and 98% for ADP-E. When electricity is incorporated into the equation and these emissions are translated per kWh, emissions from the generation of electricity exceed 2.4, 5.6 and 1.8 times those emissions from the infrastructure for GWP, WUDP and ADP-E. When comparing LH PHS with other technologies using wind as the only source of electricity production, LFP Batteries outperform LH PHS most of the time for GWP and WUDP, whereas LFP are consistently the worst performer for ADP-E. LH PHS always performs better than Green Hydrogen in all three impact categories.
If emissions reductions are to be achieved in the LH PHS case, the focus should be put on the electricity side: improving the efficiency of the plant, storing only clean energy and improving the performance of renewables. Finally, there are other considerations to LH PHS implementation that should be taken into account that are not assessed in this report. The use of materials and their circularity must be considered, as well as the social ramifications of projects like PHS and mining materials for Li-ion Batteries. Furthermore, impacts on biodiversity must be addressed and its damages should not only be minimized but restored or even improved.

The rapid increase in global population and rising demands have resulted in a shortage of clean water, depleting several of the Earth's reservoirs, especially those that reserve fresh water. Just 0.007% of the water on Earth is used to hydrate and feed billions of people, as determined by the water balance of the planet. Water-stressed nations are now desalinating salty ocean water to produce fresh water for use in their homes, industries, and fields. Among the processes used to produce freshwater, reverse osmosis (RO) is the most reliable technique for seawater desalination due to the high energy efficiency of the membranes and low desalination-associated costs. The major disadvantage of this technology is its high energy consumption, which is mostly derived from conventional sources like fossil fuels. Therefore, with a view to a sustainable future, renewable energy sources must be integrated to power the reverse osmosis systems.

All conventional wind systems convert mechanical energy into electricity, which is used to power the desalination units. Delft Offshore Turbine (DOT) aims to replace the conventional drivetrain with a hydraulic transmission system that uses seawater as a hydraulic transfer medium. The examined DOT500 PRO system consists of a wind turbine connected to a hydraulic positive displacement pump, which induces seawater flow under high pressure. A reverse osmosis unit can be used to desalinate saltwater using this high-pressure flow and a Pelton turbine generator can be used to produce electricity. The long-term objective of the DOT project is to lower complexity, mass, maintenance, and capital expense to make offshore wind a competitive source of electricity. To further reinforce the concept's techno-economic components, the future strategy calls for the centralized production of electricity.

This study aims to develop an operating strategy for the DOT500 PRO system for freshwater production at an offshore location. The viability of using such a system in a place with offshore wind conditions and predetermined freshwater demand was investigated using a constant operating scheme of a single spear valve. A numerical model is developed in Python to deliver the appropriate desalination unit size under offshore wind conditions in order to cover the water requirements of a given location. The model is applied to a case study of Agios Efstratios in Greece and can be used as a tool to investigate possible applications using the associated datasets. This research has yielded the following results:
1. A simple and robust system operating strategy for maximum water production that will ensure stable turbine function, while active control is used to maintain the system at constant operation when its limits are reached.
2. The direct influence of the spear valve position and reverse osmosis unit size on the system’s rated conditions and a reduced rated wind speed by 21.3% from the one utilized conventionally on the reference wind turbine.
3. The minimum required number of RO pressure vessels and membranes according to site-specific offshore wind profile and freshwater demand, as well as options for reducing the RO unit size.

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.

The world is currently in a global energy transition. To reach the global energy goals requires massive deployment of clean and efficient energy technologies. The use of solar photovoltaic (PV) therefore has to be scaled up. Offshore deployment of floating PV would be a suitable solution. There are currently different concepts in development for offshore floating PV. One solution is to design the offshore floating solar structures using interconnected rectangular floaters on which the solar panels are mounted. Multiple design choices have to be considered, such as the size of the structure and the design of the connections between the floaters. The main aspect to consider are the forces that arise in the connections due to the motions and loading of the offshore floating solar structure in the waves.

One of the main challenges is to quantify the effect of the different design choices regarding size and connection compliance on the forces within the connections between the floaters. The aim of this research is to give insight into the interaction between connection forces and different concept choices regarding the size of the floaters and the compliance of the connections between the floaters.

A numerical model of two floaters which are connected with two connections at each end of the structure is developed. The forces and motions of the floating structure are computed using numerical tools in the frequency domain. The hydrodynamic coefficients and wave excitation forces are obtained using the boundary element method software NEMOH. The connections between the floaters are modelled as a set of linear translational and rotational springs in each degree of freedom. The results are validated using earlier studies.

The influence of the design choices is investigated for application at the North sea for different wave directions. First, four different dimensions are varied, the length, the width and the draft of the floaters and the size of the gap between the floaters. The results are then analyzed and compared for each dimension. The comparison of the results shows the influence of each dimension on the force in the connections. Secondly, the connection stiffness is varied in four different directions, the axial, shear, bending and torsional stiffness. The comparison of the results show the interaction between connection stiffness and resulting forces in the connections.

The developed numerical frequency domain model shows the interaction between forces and moments in the connections and different design choices. The results can be used to give an insight into the occurring forces within the connections between two floater for application in the North sea.

The ever-increasing size of offshore wind turbine substructures and the development of wind farms at sites further offshore, with greater water depths and with extremer weather conditions, raise logistical challenges that have never been faced before. Additionally, the offshore wind industry has to deal with governments cutting subsidies, small profit margins and limited practice guidelines, while it is expected to lower the associated levelised cost of energy to a competitive level in the market. Scientific studies have identified room for optimisation in the substructure (the focus is laid on Monopiles (MPs) with Transition Pieces (TPs) and pre-piled jackets) transportation and installation phases. However, no studies that evaluate the performance of strategies for these phases are identified. Hence, the objective of this study is to “generate insights into the complex system of interdependent strategies for the installation of offshore wind turbine substructures, and to identify and quantify cost-reduction opportunities.” The considered strategies are formed by combinations of transportation and installation strategies, which differentiate based on the number and type of the deployed vessels and the sequence in which the operations are performed.

To quantitatively compare the strategies, and to consider stochastic processes (e.g., weather conditions), a discrete-event simulation modelling approach is adopted. To arrive at substantiated conclusions, a framework is followed, which provides a roadmap and rigour criteria for the design, implementation and evaluation phases. First, a conceptual model is developed and face validated. Next, a numerical “base model” is constructed, which describes the most basic strategy. This model is face validated by industry experts and evaluated by parameter variability, convergence and historical data validation tests. It is concluded that the base model is structured according to shared practical experiences, responds satisfactory to parameter changes, requires 35 simulation runs to converge, and has good predictive capabilities. Hence, it is deemed suitable to function as a “template” for the modelling of the other strategies.

The simulation results are evaluated for each of the considered substructures separately. (i) MP – TP installation. In general, assembly-line installation strategies, in which two Heavy Lift Vessels (HLVs) are deployed, are associated with the shortest installation time. The shuttling – assembly-line and the shuttling–alternating (in which MPs and TPs are installed alternatingly) strategies are associated with the lowest costs. Both involve a shuttling transportation strategy, in which the HLV(s) ensure(s) both the transportation and installation of the components. The mooring of barges alongside an HLV in feeder strategies (feeder vessels supply components to an HLV, which stays at the wind farm under development) and the installation of TPs by a relatively small HLV in assembly-line strategies are identified as the main bottlenecks. Reducing these by relatively simple solutions can result in significant performance increases. Lastly, the project start date is found to be a strong determinant of strategy performance. (ii) Jacket – foundation pile installation. The assembly-line strategies are found to result in the shortest jacket installation times as well. However, only the shuttling – assembly-line strategy is additionally associated with the lowest costs. Furthermore, it is found that a separate pile-dredging vessel can help to reduce the time and costs associated with separate phases installation strategies, in which jackets and their foundation piles are installed in different phases. Also for jackets, the barge mooring alongside the HLV is identified to be the largest bottleneck. Reducing this bottleneck can result in significant performance benefits. Lastly, a relationship is found between the performance of jacket installation strategies and the project start date, although weaker than for MP installation.

The developed decision support tool can provide a platform for further research into the logistics of offshore wind and other industries, whereas the obtained results are only valid within the set boundaries. To widen the applicability, it is recommended to perform follow-up studies in which a stochastic mechanical failure component is included, and the sensitivity to the wind farm size and port-to-farm distance is tested. Furthermore, it is advised to extend this study to investigate the potential of the industry adopting a more holistic process or market point of view.

Adapting the size of upending cradles according to the ever-increasing dimensions of offshore wind turbine monopiles is costly and requires structural modifications to the associated Heavy Lift Vessels (HLVs). This study therefore investigates the potential of the Monopile Upending Smart Tool (MUST), which is a platform suspended in the HLV crane, on which a winch is installed. Two grommets of constant length connect the platform with two trunnions attached to the monopile, and the winch cable suspends the bottom of this structure. Unwinding the winch cable allows for in-crane upending of the monopile. This way, the dependency on the size of the available cradle is circumvented. The focus is laid on determining the workability of the application of the MUST in the crane of the Seaway Strashnov and identifying limitations in its design. Moreover, the potential of systems that increase the workability or reduce the limitations is investigated.

The installation of monopiles using the MUST comprises three phases: the barge mooring / lift-off, upending / slewing and lowering / driving phase. Based on the results from a qualitative critical event analysis, the lift-off phase is expected to be limiting. Hence, a hydrodynamic model is developed to quantitatively analyse this phase. Experimental simulations, which are performed in parallel with the model development, result in the preliminary conclusions that multiple pendulum effects influence the results to a limited extent, while viscous roll damping and hydrodynamic interaction effects can be strong determinants of the resulting responses.

The relative z-motion between the lifted monopile and the barge and the barge roll response are identified as governing parameters. To reduce the first limiting factor, a system that allows for instantaneously increasing the vertical clearance between the monopile and the barge is proposed. The effectiveness of this system is tested for two barge loadcases. For the first case, the average workability increase for the optimal heading at a typical location is calculated as 8.3%. For the second, the increase is marginal, as the barge responses are more limiting. Furthermore, is it found that a Passive Motion Compensator (PMC) can reduce the probability of the introduction of snap loads in the winch cable, and therefore allows for system optimisations. A PMC with 10% of critical damping can reduce the required winch capacity with a factor of 2.3 w.r.t. the uncompensated case.

It is recommended to perform follow-up studies into the system performance during upending / slewing and lowering / driving. Also, it is advised to evaluate the effect of a larger barge and a PMC on the workability. To balance the associated investments and workability increases, the logistical models developed in a parallel study can be used. Finally, for iterative calculations, it was found to be beneficial to make an estimate based on a fast simplified model and to subsequently feed the results back into a more detailed, but slower model.

To overcome the problem of wave-induced vessel motions on the crane tip, technologies have been developed to compensate for these motions. Most vessels nowadays, are equipped with dynamic positioning systems, these systems reduce the yaw, surge and sway movement of the vessel. This leaves, the motions roll, pitch and heave uncompensated. To reduce these motions, two main elements of motion compensation can be identified, consisting of heave compensation and anti load swing compensation. Existing technologies, like active and passive heave compensation tackle one of these elements. Other methods like the Stewart platform can compensate for both the heave motion and the load swing of the crane by stabilizing a platform on which the crane is mounted. In existing literature, not much work has been done to incorporate both the heave compensation and anti-swing control procedures in a combined control method. It would be much simpler if the crane could compensate the heave and payload swing by using only the crane's actuators.

This thesis, studies the mechanical feasibility of a motion compensated knuckle boom crane, compensating for the wave-induced vessel motions by controlling the available actuators in such a manner, that the crane tip stays stationary. A typical knuckle boom crane has three actuated degrees of freedom, consisting of the slewing, boom luffing and jib luffing angle. To study such a system, a numerical model is developed that combines the multi body dynamics of the knuckle boom crane with models for the hydraulic actuation of the crane and incorporates the full six degree of freedom vessel motions. The actuated degrees of freedom are controlled using three separate proportional integral controllers. The desired trajectories for the controllers are calculated using the geometric relations of the crane, based on the assumption that the desired crane tip coordinate in the global axis system is known.

Using the numerical model, insight is gained in the natural frequencies, forces/moments on the system, the necessary hydraulic properties and motion compensation performance. From the simulation results, it can be concluded that the cylinder forces and slewing torques increase when the motion compensation is turned on, compared to an uncompensated crane. Comparing the simulation results, to the Barge Master T40 crane, it can be concluded that cylinder forces, cylinder sizes, stroke velocities and power requirements are in line with requirements that can be achieved with existing technology. The main limitation, is expected to be the rated torque of the slewing motor, when the crane is positioned parallel to the vessel. In this position the main contributor to the motion compensation is the slewing motor. Using the proposed concept, motion compensation performance comparable to the existing Barge Master T40 is achieved. From the presented simulation scenarios, results indicate that the operational parameters and motion compensation performance of the system are feasible and competitive compared with existing technology.

Ocean wave energy has a huge potential to make a contribution to global energy transition. However, the high Levelized Cost of Energy (LCOE) is currently a big hurdle to the development of wave energy converters (WECs). This thesis is motivated to improve the techno-economic competitiveness of WECs. It focuses on the effects of systematic sizing of WECs. "Systematic sizing" is reflected in this thesis by considering the effects of sizing on the two main components of WECs, namely the buoy and PTO system. The main body of this thesis starts with a literature review. First, it is intended to provide an overview of current wave energy technologies and the application of power take-off (PTO) systems. Secondly, the studies relevant to sizing of WECs are reviewed, and sizing methods used in the context are discussed and compared. It indicates that the existing studies mainly focus on the effects of buoy sizing and there is a lack of consideration of PTO sizing. In addition, the sizing methods based on the Budal diagram and Froude scaling can only be used to conduct sizing of buoy but the influence of PTO sizing cannot be covered. Numerical simulation can be applied to take into account both effects of buoy sizing and PTO sizing, but it is usually associated with low computational-efficiency. As sizing can be regarded as a kind of optimization which normally requires a number of iterations, an efficient method is beneficial for accelerating the design process of WECs. Followed up by the literature review, Chapter 3 to Chapter 7 of this thesis are dedicated to accomplishing two main research objectives...

Hydrokinetic energy is an environmentally friendly source of electricity and it has the advantage to be more predictable compared to other renewables. According to IRENA (2020), the capacity of converting hydrokinetic energy into electricity is expected to increase in the coming decades as many concepts are in the pipeline. One of these hydrokinetic energy concepts is the patented Van Rompay Turbine. The Van Rompay Turbine consists of a duct, an air chamber and a paddlewheel. The duct, which is based on a Venturi working principle, consists of a converging inlet, a throat and a diverging outlet. Above the throat, an air chamber is present to provide an air environment to reduce resistance for the paddlewheel. The goal of this research was to experimentally and numerically test a prototype (L:4.05m x W:1.17m x H:1.17m) of the ducted system.Three inclination angles: 21°, 26° & 31°, for the converging inflow and diverging outflow segment were tested, referred to as the small, medium and large ramp size, respectively, to determine which size represents the lowest energy losses in the system. The small in -and outflow ramp represents the lowest energy losses compared to the medium and large ramp. Subsequently, on the small inflow ramp, five designs were tested, referred to as the straight, curved and the high, mid & low frequency waved designs; to again determine which design represents the lowest energy losses. Roughed waved wall designs are streamwise wavy walls with each a different wavelength and amplitude. The small ramp with a high, mid & low frequency waved design results in the lowest energy losses in comparison to the straight and curved designs for inlet velocities between 0 m/s and 0.4 m/s. For inlet velocities between 0.4 m/s and 0.5 m/s, the small ramp with a curved design represents the lowest energy losses in comparison to the straight and high, mid & low frequency waved designs.The data points acquired during the experiments were scattered due to external factors increasing the uncertainty of the measurements. Besides this, the experimental investigations were tested over an inlet velocity between 0 m/s and 0.5 m/s, limiting the data analysis. For this reason, several CFD simulations were carried out to acquire data with no influence of external factors and to investigate the system for higher velocities. The CFD simulations were executed for the five different inflow ramp designs with an in -and outflow inclination angle of 21°. The CFD model solves the Reynolds-averaged Navier–Stokes (RANS) equations with a k-epsilon turbulence closure model. Based on these CFD simulations, the best performing design for the inflow ramp in terms of the lowest energy losses for an inlet flow velocity between 0 m/s and 0.75 m/s is the high frequency waved design. Regarding velocities between 0.75 m/s and 3 m/s, the curved design represents thelowest energy losses compared to the straight and high, mid & low frequency waved designs. After scaling up the ducted system in CFD simulations with a factor 2 and 10, the flow velocity reduces as there are more energy losses in the system. However, as larger systems have a marginal lower specific surface of contact between the water and the duct, an increase in available flow power could be found. The extent to which the ducted system can be scaled up depends on the space restrictions at the specific location. Besides, the minimal required inflow area of the free water flow should be met. It can therefore be concluded that the potentially available energy for generation also depends the location where the Van Rompay will be deployed.Experiments need to be performed to study the hydrodynamic impact and the hydrodynamic efficiency of the paddlewheel to determine the power performance output and thus its potential value for the hydrokinetic energy market. It is recommended for future research to test the prototype at higher velocities and to test the prototype in a laboratory facility as these offer the benefits of controlled testing.

A changing climate means that the combination of storm surge and river flood waves is becoming increasingly likely. The turbinepumping station of the Delta21 concept, is designed just for that. The energy storage lake and the pumps capable of up to 10,000 m3/s mean that even the highest river discharges can be sluiced to the North Sea in the event of closure of the storm surge barrier. When the pumps are not being operated to combat flood waves, the pumpturbines can be used for the purpose of storage of intermittent renewable energies. The required capacity of the pumping station means that the total width of the structure is in the order of kilometers. Past studies into the conceptual design have shown that if the pumping station and flood barrier are integral then this results in a massive structure. AnsorenaRuiz (2020) showed that such a massive structure performs very poorly in a life cycle analysis. For this reason, the goal of the thesis research is to develop an improved design for the turbinepumping station in which the structure can be separated into two parts resulting in a less monolithic form. The design is separated into two main parts: the hydraulic design and the structural design. The hydraulic design ensures that the turbinepumping station can operate at the required functionality. A pump characteristic as well as a turbine characteristic was received from equipment manufacturer Pentair and was adjusted to the requirements of the Delta21 turbinepumping station. A simulation showed that the total efficiency of the turbinepumping system is around 67%. Using timeseries of storm surges and predicted flood waves with various return periods, a simulation was also done of the response of the energy storage lake and pumping station. It showed that for flood waves of very low annual exceedance probability the required capacity of the turbinepumping station should be larger than 10,000 m3/s, but however the storage function of the energy storage lake does contribute to the sluicing of the superfluous discharge. Various alternatives for the hydraulic design were conceived, and it was concluded that the draft tube shape of the intake is the optimal solution. For the structural design the elements of the turbinepumping installation were integrated into a sea dike. The dike acts as a flood defense, keeping the North Sea out of the energy storage lake, while the elements of the pumping station ensure control of the water level inside the lake. This separation of functions allows for a less imposing structure to be achieved, without compromising on the performance. In this study, sea level rise and energy transition go hand in hand. On the one hand, pumping technology is used to protect delta areas from flooding, while on the other hand the technology of hydropumped storage is used to increase the productivity of renewable energies to offset further climate change. On top of this, the gridbalancing capabilities of the system make it financially attractive for potential investors. Hydropumped storage is already an upcoming technology in mountainous areas, but its potential in deltas and coastal regions is even bigger.

Renewable energy sources, such as wind energy, are gaining a lot of traction across the world. India intends to improve the amount of wind energy integration into the national electricity system. Wind/solar energy's major drawback is its inherent changeability and source unpredictability, making it a challenging resource to dispatch.

A proposed PHS system known as Subsea Pumped Hydro Storage (SPHS) has been assessed from a techno-economic standpoint. As intermittent renewable energy sources become increasingly widespread in the electrical system, the demand for power regulation grows. Implementing energy storage in the system is one approach to balance the demand for power with the supply. This thesis looked at an idea that is a sea-based variant of the existing pumped hydro storage technique. A SPHS unit is made up of a hollow structure on the seabed that may be emptied of water using a pump during periods of low demand and high energy generation in the system, and the unit is charged at that moment. When the system requires more energy, water is permitted to flow into the tank through a turbine, creating power.

In India, a locality study of prospective areas where the PHS may be placed and operated effectively is carried out. Muppandal (Tamil Nadu) is used as a case study. When the PHES is used, a positive influence on the power system's behavior may be seen, with the degree of wind integration being raised and dispatched on demand. The generation of peak demand by inefficient and costly units is reduced, lowering the total generating cost.

The main goal of this work is to determine the Technical feasibility of a proposed SPHSP system and to evaluate Levelised cost of storage. The study will be conducted to reach out to the suitable selection of turbines and pumps and to design the concrete storage tank in such a deep-sea environment. It is observed that the maximum depth upto which the storage tank can be built is 1200m depth for 5m high wall and 1000m depth for 7m high wall. The appropriate turbine is selected based on specific speed and it comes out that Francis turbine is suitable for depth 200m to 1200m. The levelised cost of storage (LCOS) is also calculated, and it works out to be $4.53 per kilowatt hour for 1200m depth. There are different methods suggested to increase the bearing capacity of the soil and compaction grouting seems to be the most appropriate improvement method.

Under real sea conditions, floating vertical-axis tidal turbines experience motions in six degrees of freedom which influence the relative velocity perceived at the turbine's blades, with a direct effect on the loading and performance of the rotor. Understanding the fluid-structure interaction of a vertical-axis tidal turbine under the floating carrier’s motions provides insights about critical aspects for the design of floating hydrokinetic systems.
In this project, the TU Delft in-house U2DiVA code is indicated as a conservative and time-effective tool to assess the hydrodynamic response of a vertical-axis tidal turbine under surge, sway and yaw motions compared to the computational fluid dynamics approach commonly used in the scientific literature. The effect of surge motion on the fluid-structure interaction of two existing vertical-axis tidal turbines is investigated using U2DiVA. The analysis focuses on the details of the time evolution of the flow field perceived at the blades and on the modified cyclic loading and power extraction when given surging conditions are imposed.