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.

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.

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.

For the development of Arctic offshore structures, design ice loads are required. These design loads represent the ice loads a structure may be exposed to for specified requirements. The design ice loads depend on magnitude of the ice loads and on the probability of exposure to the ice loads. Both are impacted by local sea ice conditions.

Climate change affects the sea ice conditions causing change in the ice loads Arctic offshore structures are expected to experience. To obtain accurate design loads, the effect of climate change should be considered in defining those.

Conventional methods to determine design ice loads are based on historical data and assume this data can be used to represent the loads during the lifetime of the structure. However, historical data cannot represent future ice conditions if climate change is considered as sea ice conditions will change. This means that the effect of climate change is not incorporated in the design ice loads when these are based on conventional methods. To include the effect of climate change a new method needs to be developed.

In this thesis, such a new method is proposed that enables to include the effect of climate change into the design ice loads. Instead of historical data, the new method considers the future ice conditions. The method allows to base the design ice loads on sea ice conditions that change over time.
To determine design ice loads, extremal distributions are used. Extremal distributions describe the probability of seasonal maximum ice loads. Commonly, the extremal distribution is based on data covering multiple seasons and cannot properly include inter-seasonal change in sea ice conditions. The new method allows to determine the design ice loads based upon changing extremal distributions. The extremal distributions are determined for seasons separately based on sea ice conditions of one season only.

For the proposed method, a concept referred to as an 'ice state' is introduced. Ice states describe a period of time in which the sea ice conditions are assumed to be constant. When sea ice conditions are constant, the corresponding short-term ice load distributions and the ice load frequency can be determined. Both are required to be able to determine the extremal distribution for one season.

According to the new method, the increase of drift speeds causes increase of design ice loads whereas the decrease of ice concentration, thickness and compressive strength causes decrease of the design ice loads. Based upon expected future climate change scenarios, the new method indicates that design ice loads are lower when compared to the design ice loads according to the conventional method.

The modeling method for the performance of positive displacement pumps of hydraulic pumps is based on collecting operational data of the pump for its operational envelope and using equations with empirical fitting parameters and fit these equations to the data. This way values for the fitting parameters are obtained, with which the equations can be used as model for the operating performance of this specific pump. By implementing this modelling method no information about the contribution of each component present in the pump to the performance losses is obtained. A model which analyzes each coponent and estimates its contribution to the total power losses would be beneficial in the design of pumps. Therefore the answers to the following research questions are sought after in this work:

- What are the components critical to performance within hydraulic pumps?
- To what accuracy can a component-wise, analytical model for pump performance be created?
- How sensitive to certain parameters used in the equations is the model?
- What are the possibilities of implementing this model into pump design?

After the pump system was analyzed and the internal interactions found, the components which effect pump performance the most were identified. These include bearings, rollers, seals, springs, valves and leakage flow which is dependent on gap size, piston movement and viscosity of the hydraulic fluid. For these components analytical equations are presented which are incorporated in the model.

The accuracy of the model is tested by comparing its results to test data of an experimental camring driven radial piston pump. The model predicts leakage flow to an average difference of 3% relative to the data, but outliers up to 49% for high pressures and -35% for low pressures are observed. Input torque is predicted to an average difference of -19% relative to the data. This difference is mainly caused by the inaccuracy of the predictions below 30 bar operating condition, where outliers up to -61% are observed. These results are compared to an empiric modelling method and are found to be more accurate for leakage flow for the entire operational envelope, yet on average less accurate for input torque.
The sensitivity of the model to certain parameters is tested. The parameters investigated are the rolling resistance coefficient of rollers and bearings, bearing lubricant viscosity, hydraulic fluid temperature, piston-cylinder alignment and the corresponding forces resisting piston motion and the assumption of laminar leakage flow.

To show the possibilities of the model in pump design the rollers and appurtenant bearings present in the pump are replaced with hydrostatic bearings. The design is discussed and a hydrostatic bearing with an orifice restrictor is designed of which implementation will approximate the total efficiency of the pump with rollers. The Reynolds number of the flow necessary is found to be too high for capillary restrictors. To approximate the same total efficiency for each operating condition the average bearing flow is found to be 0.0016 L/s, which corresponds to an average fluid film height of 12 μm. The orifice restrictor diameter which allows this flow is found to equal 0.24 mm.

This work shows the possibilities of such a model, yet there is plenty room for improvement of the accuracy of the predictions made. Recommendations to this end are given in the conclusion and recommendations of the report.

After the construction of the Grevelingendam (1965) and Brouwersdam (1971), the tidal movement in Lake Grevelingen disappeared. This caused a deterioration of ecological parameters influencing the surrounding flora and fauna and consequently a decline of the water quality set in. Amongst others, Rijkswaterstaat and the provinces of Zeeland and South-Holland aim to reconnect Lake Grevelingen with the North Sea to infuse oxygen enriched water into the lake and reintroduce an attenuated tide in the lake, thereby improving the quality of the local ecology. To reach the desired water quality, culverts will be installed in the Brouwersdam, thereby restoring the connection between the two water bodies. As part of an integrated approach, Rijkswaterstaat intends to implement turbines into the culverts to not only generate power, but also perform water management. The conclusion from the literature study is that implementation of constrained flow devices, wherein the entire mass flow is guided through the turbine, is preferred as these turbines are able to modulate discharge through the tidal barrage. Moreover, constrained flow devices have a higher theoretical power output than the other considered hydropower methods applicable in a tidal barrage. In order to broaden the insight into the behaviour of the water level in Lake Grevelingen, due to the construction of the tidal barrage, three hydraulic configurations are evaluated wherein input water level data from the North Sea is used to model the tidal variation in the lake while simultaneously estimating the energy output of the system. Considering a culvert array of 18 culverts, measuring 8 m by 8 m, the first considered case takes into account 11 of the culverts equipped with unidirectional turbines, while the remaining culverts are unequipped. The second case involves all 18 culverts with unidirectional turbines, while the third case is set up with 18 bidirectional devices. Additionally, to provide a larger view on the possibilities, a multivariable analysis of the three cases is carried out wherein power generation and water management requirements are considered. Herein varying the cross-sectional area of the culverts and their numbers, though, for the configuration consisting of equipped and unequipped culverts, also the number of empty culverts is varied. From these analyses, one can conclude that installing unequipped culverts and unidirectional turbines in the array will diminish the controllability, whereas bidirectional turbines increase the controllability of the flow which is desirable. Furthermore, full time turbine modulation, wherein the turbines are not generating the optimal amount of power over the full scope of the tidal range for the purpose of water management is preferred over intermittent turbine modulation, wherein turbine modulation only occurs when the water level surpass certain water levels, because the turbines can be altered continuously, which increases the controllability of the discharge. Nevertheless, for the culvert arrays with bidirectional turbines applies that the required values of the monthly averaged and maximum tidal ranges are insufficient. Even though, the water level in Lake Grevelingen does not exceed the overshoot/undershoot boundaries, established by Rijkswaterstaat, the entire vision of water management is only partially fulfilled due to the lack of amplitude in the tidal range.

The study concludes with the selection of the following culvert array existing of 24 culverts measuring 9 m by 9 m executed with bidirectional turbines. From an economic feasibility study, wherein, amongst other involved parameters, an installed capacity of 36 MW, a market price of electricity of € 0.13 per kilowatt hour for the first 15 years and € 0.049 per kilowatt hour for the second 15 years and a loan period of 15 years, follows a payback period of 15 years and a levelised cost of energy value of € 0.058 per kilowatt hour.

In the simulation of floating wind turbines, a traditional rigid floater assumption becomes less valid while pursuing large size floating wind turbines with steel-efficient floaters. Up to date, hull flexibility still cannot be efficiently incorporated into aero-servo-elastic-hydro simulation tools, and the possible influence of hull flexibility has not yet been well-understood. Consequently, it is necessary to identify the significance of hull flexibility and the possible effect of it.

Recent researches have been investigating the influence of hull flexibility on substructural internal load, global responses and dynamics of the system. However, little has been done from a tower design perspective. Moreover, tower design for a floating foundation has also been seldom documented. To fill the knowledge gap, two research questions are defined: What is the difference in tower design with a floating foundation? and What is the effect of hull flexibility on tower design?

To answer the first research question, a FEM model with rigid hull is built based on four floating concepts designed for DTU 10MW wind turbine. The tower fore-aft bending natural frequencies are compared between fixed foundation and floating foundation. The second research question is answered by developing a FEM model with flexible hull based on a spar-buoy concept. The rigid hull model and the flexible hull model are compared by implementing structural analysis and fatigue damage estimation under waves load.

The result shows that the 1st tower bending natural frequency increases significantly(except for TLP) from a fixed foundation to a floating foundation, making it difficult to achieve a soft-stiff tower design. Furthermore, it is indicated that hull flexibility can decrease the 1st tower bending natural frequency, and the magnitude varies with different tower designs. A stiff-stiff tower decreases more while a soft-stiff decreases less. Lastly, the fatigue damage estimation implies that a soft-stiff design can be lack of fatigue strength to survive from waves load.

In conclusion, a soft-stiff tower design is difficult for large size floating wind turbine partly due to the increase in 1st tower bending natural frequency from fixed foundation to floating foundation, and partly because of strength requirement for fatigue load. As for a stiff-stiff tower design, without considering hull flexibility, there is a high uncertainty in the 1st tower bending natural frequency. As a result, for large size floating wind turbines, inclusion of hull flexibility is necessary for the tower design.

To respond to the growing offshore industry Jumbo Maritime has designed a new vessel to expand its offshore fleet: The Stella Synergy. The vessel will be able to install monopiles for the offshore wind and oil and gas industry. The main objective of this thesis is: Making a model that is able to predict the motions of the vessel as well as the forces induced by the monopile on the vessel during the monopile installation process. First the most suitable upending technique has been chosen for the Stella Synergy. The upending of a monopile can be seen in figure 1. The different techniques are analysed in a multi criteria analysis. Upending with the gripper turned out to be the best choice. The gripper design has been chosen the same way. The two rotating arm gripper and linear four arm gripper score highest but have almost the same score, therefor one of these two grippers is advised. The hydrodynamic parameters of the vessel are obtained using AQWA, then a model of the vessel is made in Matlab to decide on the best location for the gripper with the least severe motions. The calculated RAOs are compared with the measured RAOs by Marin and are almost similar. When the crane hoisting curve is taken into account only two possible upending locations remain: x = 42m and x = 70m. Both locations are on the starboard side of the vessel. At the location x = 70m the motions are far less severe, so the dynamic forces will be less high. A disadvantage of this location is that only monopiles up to 100 m can be placed into the gripper without coming to close to the secondary crane.
The forces on the crane and gripper during upending and the workability of upending have been examined using a model in Matlab, the upending process is split up in six phases. Because the monopile is partly under water during four of the six phases the wave forces, added mass and damping that act on the monopile are calculated using AQWA. The viscous damping is calculated using the drag coefficient of a cylinder. The dynamic forces are the biggest during phase 3, where the monopile is only submerged with a small part far away from the vessel. The static forces during phase 1 to 5 are really low, therefor the workability of upending in phase six is computed, the workability is 34.3%. The workability of the vessel while it is hoisting a monopile from a barge onto the gripper is investigated using a ten degree of freedom model. The natural frequencies of the model are calculated and compared with the RAO plots. The total workability for a hoisting cable length of 64m is 29.9% and for 80m is 27.9%. Increasing the offlead angle from one to two degrees will increase the workability to 44.0% for 80m and 36.7% for 64m. It is advised to look into increasing the maximum offlead angle of the crane.

With a fast growing world population, the lack of fresh water is one of the world’s biggest future concerns. Water stress can lead to conflicts, holds back economic growth and has a major impact on human health. Nowadays, more and more countries that lack fresh water sources are using the saline water from the oceans and desalinate it to produce fresh water. The most common way to do this is by the means of Reverse Osmosis (RO). However, one of the biggest negative aspects of desalination is its high energy consumption, mostly provided by fossil fuels. Therefore, a more sustainable solution using renewable energy sources to power a RO system is necessary. Delft Offshore Turbine (DOT) is currently developing a hydraulic drive train wind turbine that converts the aerodynamic power captured from the wind into hydraulic power. With a positive displacement pump, a high pressure water stream is created for centralised electricity production using a spear valve and a Pelton wheel. Using this hydraulic turbine for the purpose of fresh water production with RO can be a well fitted combination. Using wind as an energy source for desalination purposes, however, creates some major challenges, one of which is dealing with the inconsistency of wind. For varying wind speeds, a hydraulic wind turbine is controlled by regulating system pressure hence the pump torque with the spear valve. With a Seawater Reverse Osmosis (SWRO) system with ERD, it is researched how to regulate the flows and pressures for a stable operation. In this thesis, the combination of the hydraulic wind turbine with a Reverse Osmosis system with an Pressure Exchanger Energy Recovery Device (ERD) is being analysed in more detail. For this, a numerical model is used to determine the systems' behaviour and an experimental test setup is designed and constructed to validate the model results. The aim of this thesis is to compare the desalination system performance with a stand-alone system without an ERD, to determine the influence of varying ERD settings on the systems' pressure for potential system pressure and torque controllability, and to investigate how the RO system with an ERD affects the wind turbines stability. The analysis shows a large positive influence on the amount of produced permeate when using an ERD in the RO system. In addition, the power consumption of the RO process can be reduced by up to 80%. A varying input provided by the high pressure pump, for example as a results of varying wind speeds, does not seem to (negatively) affect the efficiency of permeate production. By varying the ERDs' rotational speed, the feed pressure at the membranes inlet hence the pressure at the high pressure pump can be slightly influenced. However, this limited influence is not enough to effectively affect and control the high pressure pumps' torque. On top of that, for the wind turbine to operate in a stable operating region, it seems that the use of an ERD affects the system in such a way that water production can only be realised at fairly high wind speeds. To optimally make use of the hydraulic wind turbine and operate at the highest possible aerodynamic efficiency, a combination of electricity production at low wind speeds and water production with an ERD when wind speeds are sufficient, can be interesting. For this, future research is required.

Land scarcity is increasing and therefore one of the main challenges for renewable energy in the future is ‘physical space’. While renewables need a lot of space compared to conventional energy sources, and the competition for space is already increasing (food production, housing etc.), leading to higher land costs and opposition. Public resistance to new highly visible windfarms and onshore solar farms is hardening. Large land-based solar farms compete with agricultural use and can have negative effects on the ecosystem, by covering the soil from the solar light. A solution to the stated problems is by placing renewable energy production at sea, among which offshore floating solar energy.
One of the main challenges in offshore floating solar is the continuous wave-induced motion of floaters, and the forces that arise at the most critical points. Dynamically modelling multiple floaters in waves becomes very computationally and time intensive when the number of floaters increases. This research focused on creating and comparing a linear and a non-linear model that calculates motions of multiple floaters under first order wave forces. The aim is to perform these calculations with open-source software only.
The dynamic forces on the floaters are obtained by evaluating the radiation, diffraction and wave excitation potential in the open-source Boundary-Element-Method-Solver NEMOH and showed good resemblance with commercial software packages AQWA and DIFFRAC. The modelling of the motions is performed in time (linear and non-linear RK4-integration-scheme) and frequency domain (linear). The implementation of the dynamic forces in both cases showed to be the most critical for the behavior of the floaters. Especially the determination of the hydrodynamic coefficients: Infinite added mass and retardation function for the time domain simulation are key in getting the same result for the linear time domain and frequency domain. Suppressing non-realistic values of gap resonance between multiple floating bodies increases the efficiency of time-domain simulations. Small differences between the motions of the floaters can cause significant differences in the forcing, therefor it is rather advisable to perform the comparison between the linear and non-linear case in time domain.
A comparison of different wave directions and conditions showed that the results of the linear model are of the same order of magnitude as the non-linear model. For the determination of motions and forcing under first order wave forces this shows that both cases are similar. Nevertheless, other non-linear effects can be added in a follow-up study.