Offshore wind is expected to become the largest energy source in the Netherlands. However, its economic viability has come under increasing pressure. Integrating energy storage with wind generation offers a potential solution by enhancing system flexibility and enabling additional revenues through multi-market participation. Hybrid Power Plants (HPPs) combine generation and storage technologies within a single system. This study investigates how the integration of short- and long-duration energy storage affects the profitability of wind-based HPPs operating across multiple electricity markets.
Short-duration lithium-ion (Li-ion) battery storage was compared with long-duration Liquid Piston Compressed Air Energy Storage (LPCAES). Lithium-ion batteries were evaluated while explicitly accounting for degradation, whereas LPCAES represents an emerging near-isothermal CAES technology with improved compression efficiency. Both technologies are evaluated across different energy capacities and charge/discharge rates within a multi-market framework, including participation in the day-ahead and automatic Frequency Restoration Reserve (aFRR) markets. Profitability is assessed using operational revenues and a Net Present Value analysis.
Results show that economic performance strongly depends on market conditions, storage sizing, degradation effects, and investment assumptions. Without degradation, Li-ion batteries generally outperform LPCAES in terms of profit due to higher efficiency and power capability. When degradation is considered, outcomes become year-dependent: LPCAES can achieve higher profitability under moderate price conditions and larger storage sizes, whereas Li-ion remains superior in high-price years. Overall, no single technology is universally optimal; the economically preferred option depends on the specific market environment and system configuration.

The increasing deployment of floating offshore wind turbines has driven the development of novel installation concepts, for which the dynamic behaviour during critical load-transfer and release operations must be well understood to ensure safe and reliable offshore execution. This study examines the safe release of a fully pre-tensioned Tension-Leg Platform (TLP) with an installed wind turbine from a submerged installation deck (ID) within Allseas Engineering’s Windchanger installation concept. In this approach, a Heavy Transport Vessel (HTV) transports the assembled TLP wind turbine offshore, submerges the ID, tensions the tendons, and eventually releases the TLP from the deck. The release is a critical operation as hydrodynamic forcing and the mechanical interactions within the coupled HTV–ID–TLP system can generate abrupt changes in motion and load if not properly controlled.

This release sequence in this thesis is divided into three phases. In the pre-release phase, the ID remains coupled to the HTV, and different stiffness–damping configurations are tested to assess how possible passive softening can reduce the vessel motion transmitted to the TLP. At the release, the physical connection between the ID and the TLP is removed, causing the remaining support to shift to the tendon system. This moment produces a transient response that is strongly dependent on the wave phase at the instant of release. In the post-release phase, the ID is lowered to establish a positive clearance gap that prevents the deck from re-contacting the TLP under continued vessel motion.

To investigate these dynamics, a hybrid modelling approach is used. First, a linear 9-degree-of-freedom model is developed using the Euler–Lagrange formulation, capturing heave, pitch, and roll motions of the three bodies. It includes tendon stiffness, hydrostatic restoring, radiation damping, and an adjustable HTV–ID interface. This model is used to study modal properties, frequency-response behaviour, and sensitivity to interface softening. Second, a nonlinear time-domain model is implemented in OrcaFlex to simulate realistic hydrodynamic loading, tendon behaviour, and the complete release sequence under both regular and irregular waves.

The results demonstrate that applying softening reduces the transfer of HTV motion to the TLP in the pre-release phase, particularly in heave motion, and can therefore improve operability. The linear 9-DOF model identifies the dominant coupled heave–pitch and roll modes of the three-body system and demonstrates how softening influences its natural period and amplitude, explaining the trends observed during the release. The frequency-response analysis further shows that motion transfer at the release-relevant frequencies is strongly affected by the HTV–ID interface settings. In regular waves, the release response depends strongly on the wave phase. In irregular-wave simulations for moderate sea states, the tendon loads remain smooth at the release instant with no snap effects, and the turbine top shows only a brief acceleration peak immediately after release due to the sudden change in support. These responses remain within acceptable limits, and the results show that tendon loading is driven mainly by the pre-release motions rather than by the release itself. After the release, lowering the installation deck provides the required clearance, with beam-sea conditions being the most critical due to larger roll motions.

Overall, the results show that submerged release within the Windchanger concept is technically feasible in mild sea states, provided that the release moment is selected at a favourable timing and vessel motions are effectively controlled. Interface softening is not strictly necessary, but it improves operability by reducing pre-release motion transmission. The hybrid model approach forms a basis for defining operational limits and supporting procedural planning. Future work should refine hydrodynamic modelling, explore the practical implementation of softening methods, and develop operational guidance for offshore execution.

Floating offshore wind energy is a technology that has gained significant interest over the past few years due to its potential to unlock vast, high-quality wind resources far from shore and in deeper waters, areas that fixed-bottom turbines cannot reach. However, harnessing this resource presents unique challenges, among them are maximising annual energy production (AEP) while minimising blade fatigue damage. These objectives inherently conflict. Aggressive control settings that boost energy capture tend to increase loads, accelerating material fatigue. Crucially, both AEP and fatigue life depend on the turbine controller. By systematically varying a set of key features of a proportional–integral (PI) controller, this thesis sets up a workflow to investigate how controller parameters shape the trade-off between AEP and blade fatigue. To navigate this multi-objective landscape, Pareto optimisation is employed, generating a front of controller configurations that balance energy yield against blade durability. Economic viability is assessed through levelised cost of energy (LCOE) calculations, linking extended fatigue life to deferred maintenance costs and potential improved lifetime. Within the existing literature, where past studies have treated AEP, fatigue, and control in isolation, this work offers a unified framework, demonstrating how slight adjustments in controller settings can unlock significant performance gains. The core contribution of this thesis lies in the framework itself. An end-to-end roadmap is presented, combining metocean data analysis from Utsira Nord, aero-servo-hydrodynamic simulations using SIMA, AEP analysis and fatigue life estimation, Pareto front construction, and LCOE impact assessment. Key results show that blade life can be extended by over 15% with less than a 1% drop in AEP, translating to a meaningful reduction in LCOE of at least 3% under typical economic assumptions. These findings highlight the opportunity to explore the controller parameter space further with this system, paving the way for more finely tuned strategies that optimise the balance between the two objectives.

Offshore Floating Wind Energy (OFWE) presents a promising yet underdeveloped sector due to its higher costs and engineering complexities compared to fixed-bottom systems. Unlike fixed-bottom systems, OFWE isn't restricted by water depth, offering over four times more ocean area for deployment. This flexibility allows for positioning wind farms further offshore where wind speeds are higher and more consistent, maximizing energy generation potential. However, the current viability of OFWE heavily depends on governmental subsidies to remain competitive.
Integrated Systems (IS) have emerged as a promising solution to address the need for affordable, scalable, and transportable renewable energy storage. IS combines offshore wind farms with hydrogen production systems, aiming to enhance the Techno-Economic Performance (TEP) of OFWE and potentially render it economically feasible.
A case study focusing on Japan's Goto City Wind Farm illustrates the challenges and opportunities associated with OFWE and IS integration. Japan, with its ambitious wind energy goals and limited suitable areas for fixed-bottom wind energy, serves as an ideal location for such a study. Additionally, Japan's interest in integrating hydrogen into its energy mix further underscores the relevance of this research.
The initial analysis of the Goto City Wind Farm without IS integration revealed its lack of economic viability over its operational lifetime. However, by integrating additional components for hydrogen production, such as desalination, electrolysis, and hydrogen carrier configuration units, the project's Techno-Economic Performance was significantly enhanced.
One key advantage of the IS approach lies in its flexibility in power allocation between grid supply and hydrogen production. By dynamically adjusting power allocation based on prevailing market conditions and a predetermined switch price, the IS can optimize revenue generation and adapt to fluctuating energy markets.
Further analyses, including examinations of different hydrogen carrier configurations, capacity assessments, scenario analyses, and sensitivity analyses, were conducted to comprehensively evaluate the TEP of the system.
Results indicated that hydrogen production during periods of low power prices substantially improved the TEP of the Goto City Wind Farm, making it economically feasible by the end of its operational lifespan. Moreover, the ability to switch between hydrogen production and grid supply mitigated risks associated with future uncertainties in hydrogen and power prices.
In conclusion, integrating hydrogen production with OFWE through Integrated Systems offers a promising pathway to enhance TEP and improve the economic viability of offshore wind energy projects, contributing to a more sustainable energy future.

This research evaluates the economic feasibility of adding offshore solar farms (OSFs) to planned offshore wind farms (OWFs) in Europe, identifying feasible ranges of OSF and subsidy levels to reach economic feasible projects. Ultimately, this leads to conditions to reach economically feasible projects for adding OSFs to OWFs. Using shared infrastructure, such as the power export infrastructure (PEI), it reduces the need for offshore grid expansion and lowers initial OSF investment costs. This study addresses a gap by examining the economic feasibility of this integration, specifically through an economic added value (EAV) analysis, combined with various OSF cost scenarios through a net present value (NPV) assessment.

First, a literature review explores the economic and technical benefits, focusing on shared OWF infrastructure and identifying relevant stakeholders, when adding an OSF. A techno-economic model is developed to calculate the economic added value based on increased OSF revenues and the added value subsidy (AVS), which reflects cost savings from using shared infrastructure. Subsequently, the model is applied to two OWF case studies, a wind farm site in the Netherlands and wind farm site in Italy, where economic feasibility is evaluated.

This study concludes that the addition of an OSF to an OWF at the Italian site is economically feasible, when an optimistic OSF cost scenario is used. With less optimistic OSF cost scenarios, the the addition of an OSF to an OWF would require higher AVS from increasing shared infrastructure costs to become feasible. The integration of OSFs shows greater economic potential in southern Europe, particularly in regions such as Italy, where abundant solar resources and a lower wind potential contribute to a higher EAV per unit of OSF capacity because of substantial growth of the PEI capacity factor. Locations with lower initial OWF capacity factors, greater increases in additional OSF capacity factors, and high shared infrastructure costs lead to faster NPV improvement and reduced dependence on subsidies, representing economically favourable conditions for adding OSFs to OWFs.

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

The Jones Act, limited US port facilities, and absence of Jones Act-compliant installation vessels pose significant challenges for offshore wind farm installations. These factors force contractors to explore new installation strategies, such as feedering. Feedering is an installation strategy where the wind turbine installation vessel remains stationed at the offshore wind farm, while a feeder vessel transports all wind turbine components from the marshaling port to the installation site. With the rise of U.S. wind farm developments on the East Coast, it becomes apparent that alternative vessel designs and strategies will play a vital role in the near future. Therefore it is crucial to gain an understanding of Jones Act complaint vessel designs and strategies.

In this thesis, a new method for optimizing feeder vessel design concurrently with a wind turbine installation strategy is introduced. The approach combines multi-agent discrete-event simulation and design space exploration to define the optimum within the design space. The proposed method facilitates the evaluation and comparison of the operational performance of design configurations using historical environmental data, operating limits, and operational characteristics. Importantly, the proposed approach accommodates for the interdependency of operations making it suitable for the design and evaluation of repetitive multi-tasked operations. This method provides an improvement over the commonly used workability percentage and thereby allows for improved and fit-for-purpose designs.

A case study is performed based on Vineyard Wind WTG installation works that shows the potential of the proposed approach and the impact of vessel size, installation strategy and equipment characteristics on operational performance. This research offers new insights into the optimization of offshore wind farm installation processes and vessel designs paving the way for more efficient and effective installations in the rapidly growing U.S. wind energy sector.

Offshore wind is a rapidly maturing renewable energy technology and is expected to play a central role in future energy systems. It has the potential to generate more than 420,000 TWh per year worldwide, an amount approximately equal to eighteen times the global electricity demand today. While many of the most abundantly resourceful sites are at water depths too extreme for fixed-base solutions, current floating turbine technologies suffer with high-costs and inefficiencies. Seawind Ocean Technology B.V., a Netherlands based company, is a manufacturer of fully integrated floating wind turbine systems. They have designed an innovative set of low-cost, low-weight, upwind two-bladed wind turbines, with teetering hinge and yawed power control. This teetering hinge decouples the shaft from rotor, by adding an extra degree of motion, and protects the turbine from harmful aerodynamic and gyroscopic loads, as well as the rotor from hydrodynamic loads. The innovative active yaw control eliminates the need for complex pitching systems to regulate power output, in turn reducing turbine head weight and turbine costs.

There are a number of aims and objectives for this thesis project. The first, and most fundamental, was to investigate two-bladed and floating offshore turbine technology and share these findings with the hope that they make their way into the hands of change-makers who can promote the technology and consequently accelerate the green transition. The second was to optimise the loading analysis models of the Seawind 6 turbine using DNV GL’s wind turbine design software, Bladed. This is a 6 MW two-bladed floating offshore turbine and is intended for commercialisation by 2024. Seawind have extensive operational data from the Gamma 60’s deployment (the world’s first variable speed, two-bladed, wind turbine with a teetering hinge) in the 1990s. The Gamma 60 was modelled and compared to this operational data, with the calibrations in turn applied to the Seawind 6 models to improve its accuracy. Once achieved, the third goal was to carry out a thorough ultimate and fatigue load analysis of the optimised Seawind 6 model for various design load cases at extreme water depths. This investigation proved that the various investigated turbine components have been adequately sized and that suitable construction materials have been selected considering the loads they are expected to withstand. Following this large body of work, the fourth objective was to verify the theory that teeter motion is aerodynamically damped when the blades of a two-bladed, teetered turbine, are vertically oriented due to differences in angles of attack of the oncoming and retreating blades when yawed out of the wind. The fifth and final goal of this thesis work was to pull everything together and compare the floating offshore two-bladed Seawind 6 to a conventional floating three-bladed state-of-the-art turbine competitor. This was in terms of ultimate and fatigue loads experienced, capital and operational expenses (CAPEX and OPEX), lifetime carbon abatement, levelised cost of energy (LCOE), ease of manufacture and deployment, and operational performance.

Renewable forms of energy, and especially wind energy, have become an integral part of the energy infrastructure around the globe. However, the constant increase of installed wind capacity has put a strain on the selection of potential onshore locations for wind turbine installation. As a result, the wind industry is focusing on offshore applications, mainly with the use of bottom-fixed sub-structures. Nevertheless, research community has started shifting their interest in floating wind turbine designs to harvest the abundant wind potential of far-offshore locations, sited in water depths where monopiles and jacket sub-structures are not economically feasible. Despite the progress on the design of such floating units, there is still no consensus upon their optimum installation and maintenance strategies, activities which comprise one third of the lifetime cost of a floating wind farm.

The aim of this research is to gain understanding on the optimum installation and maintenance strategies for semi-submersible and spar buoy floating units based on their cost and duration. Towards this direction, four different installation strategies are investigated: semi-submersible installation with wind turbine assembly at quayside, semi-submersible installation with wind turbine assembly at wind farm site, spar buoy installation with wind turbine assembly in a single lift with a heavy lift vessel (HLV) and spar buoy installation with wind turbine assembly with multiple lifts with a crane barge. Furthermore, based on the type of the required maintenance activities, the onsite minor and major repairs of wind turbines with the use of a crew transfer vessel (CTV) or a walk-to-work (W2W) vessel are examined, as well as the onsite or offsite replacement of major wind turbine components for wind turbines installed on both semi-submersible and spar buoy floating sub-structures. In the context of this thesis, a deterministic installation and O&M model was developed. This model relies on various input data, including weather time series for near-shore and far-offshore locations, vessels and facilities costs, personnel and components costs and an electricity price for the calculation of the lost revenue due to downtime.

The analysis of the installation and maintenance strategies is based both on a base case scenario and a sensitivity analysis of the main factors influencing the cost and duration of offshore activities: distance from shore/port and weather limits of activities. The results show that semi-submersible installation with wind turbine assembly at quayside is the most cost-effective and fastest of all implemented strategies, followed by the spar buoy installation with HLV. Furthermore, the use of a CTV for onsite repairs is more cost-effective, albeit slower, approach than the W2W one, for all examined distances and weather limits. Finally, the offsite major replacement strategy for semi-submersibles is the most cost-effective of the examined strategies. No definitive conclusion can be drawn on the best major component replacement strategy for spar buoys, as the cost difference between the onsite and offsite approach is small. When the cost difference of different installation and maintenance strategies is low, the final choice depends on the volatile vessel rates and the electricity market prices.

Offshore wind farms designed solely for hydrogen production are promising solutions for maximizing wind energy conversion, decarbonizing industries that cannot directly utilize electricity, and reducing the need for additional grid reinforcements. Furthermore, floating offshore wind turbines enable the capture of wind resources in deeper waters. This has created the possibility of locating wind farms far offshore. This study looks into the technological and economic feasibility of in-turbine hydrogen production, storage, and transport via vessels from far offshore floating wind farms. Transport of hydrogen via pipelines and transport of hydrogen via a large vessel connected to the entire wind farm are also studied for comparison and bench marking purposes. To investigate the performance of various transport methods, a wind farm model is built that includes the components required for hydrogen production at the wind turbine as well as the components required for hydrogen transport. The model simulates wind farm operation, vessel operations with regard to onsite storage, and vessel operations when connected to the entire wind farm. Based on the levelized cost of hydrogen(LCOH), the performance of the three different farms has been compared. The study was conducted over distances ranging from 100 to 700 km. Throughout the range of distances studied, on-site hydrogen storage and periodic removal via vessel proves to be the least cost effective solution. Weather conditions are seen to be a significant factor in the operation of the vessel fleet servicing the farm with on-site storage. When combined with a four-vessel fleet servicing the entire wind farm, the optimum storage size in the farm type with onsite storage is found to be equal to the wind turbine average weekly production. A key distinction is seen in the cost trends, a steady increase is seen in hydrogen transport via pipelines with increase in distance, while, the LCOH of hydrogen remains nearly identical for the transport of hydrogen via vessels over the range of distances studied. The farm produces the most hydrogen with pipeline transport of hydrogen followed by transport of hydrogen via a large vessel, and the least hydrogen with in platform hydrogen storage and periodic emptying of the storage by vessels. The study indicates that the pipeline transport of hydrogen is the most cost effective transport option.

To meet the targets set at the Paris climate convention, a rapid decrease in the emissions caused by the process of extraction of fossil fuels is required. Especially offshore, where a grid-connection is often non-existent, having power supplied by local renewable energy sources with a variable power generation can potentially lead to problems in the energy balance. To avoid the use of back-up diesel generators, Novgorodcev Jr. et al came up with the idea of implementing an energy storage unit based on the principles of potential energy, namely the SBGESS (Figure 1). The objective of this thesis was: To assess the dynamic behavior of the SBGESS system during installation and provide suggestions to increase workability by reducing the dynamic response. To this end, the SBGESS was preliminary dimensioned based on simulations of the energy balance and the lowering operation was modelled using these dimensions. A 10.32MWh SBGESS, with three power supply modes (including a power saving mode), is able to operate a 4.34MW water injection system with power being generated by two 12MW wind turbines. Simulations were run to assess the sensitivity of the system to the energy storage capacity and the ranges in which a certain mode was active. Based on historical wind data, this system is able to meet the empirical reliability and performance criteria for a water injection system. Using the energy storage capacity and power demand as input, the size and number of buoyancy- and gravity units were scaled to minimize overall dimensions as to reduce installation complexity. The vertical displacement of the SBGESS during the lowering phase was modelled using non-linear mass - dashpot - spring models (Figure 2). It was concluded that using polyester rope for the lowering cable leads to relatively low dynamic forces during the lowering and is able to meet the DNV criteria for an offshore operation in more sea states than other alternatives. Taking precautions such as heave compensation and a lower payout velocity are however necessary to avoid slack conditions and large dynamic forces during the beginning of the lowering operation, as this is where resonance predominantly may occur. A Sensitivity analysis showed that the hydrodynamic coefficients require extensive lab testing as their values have a large impact on the dynamic force. The added mass coefficient has a significant influence on the overall dynamic force and location of the resonance zone, while the drag coefficient mostly impacts the oscillation magnitudes in the early parts of the lowering operation.

For marine structures subjected to combined wind and wave loads, predicting the long-term extreme response corresponding to a certain return period is an important aspect during the design stage. Generally, a full long-term analysis (FLTA) is recognized as a highly accurate method to determine the long-term extreme responses. FLTA integrates all the short-term extreme responses with their corresponding occurrence probability of environmental conditions. Therefore, this approach is very time-consuming and inefficient, especially for complex marine structures. Therefore, the environmental contour method (ECM) is proposed as a more efficient alternative method for predicting the long-term extreme response of offshore structures. The traditional environmental contour is obtained using the joint distribution of mean wind speed, significant wave height, and spectral peak period. This method has been used extensively on marine structures subjected to wave loads with reasonable numerical accuracy. It decouples the response with the environmental variables and uses the largest most probable short-term response evaluated along with the environmental contour corresponding to a given return period or exceedance probability to represent the extreme response. However, for offshore wind turbines which are subjected to combined wind and wave loads, the ECM performs poorly on wind-induced responses (under wind only or combined wind and wave load conditions). This is due to the non-monotonic behavior of the wind-induced responses resulted from the control system of the wind turbine. The ECM will cause the deviation of the critical environmental conditions between the identified environmental contour and the realistic case. The modified environmental contour method (MECM) is proposed and developed to deal with such a system whose response changes discontinuously due to variations in the operating conditions with additional environmental contours taken into consideration. It is seen that environmental contour plays an important role in the application of both the ECM and the MECM. A set of environmental conditions are selected along the target contour to perform short-term response analysis for the determination of the long-term extreme response. Traditionally, the environmental contour is established based on the inverse first-order reliability method (IFORM) by Rosenblatt transformation with response excluded as a variable. Since this traditional method involves the transformation of the standard normal variables and original physical space which is related to the FORM-approximation closely, a possible over-or underestimation of failure probability may be induced. Another method to obtain environmental contour is the inverse second-order reliability method (ISORM). The ISORM approximates the failure surface by a quadratic function at the design point in standard normal space instead of a linear function in the IFORM. The result of contour based on the ISORM always being conservative, which cannot be ensured by the traditional IFORM method. The highest density region method (HDRM) is to define the environmental contour as the boundary, along which the joint probability density function (PDF) of the environmental variables is a constant. This method solves the contour in the original physical space and can be used in high-dimension conditions. Applying the environmental contour method and modified environmental contour method based on the IFORM, the ISORM, and the HDRM allows to predict the extreme response. The MECM results are much better than the results from the ECM according to safety requirements in the design stage. When applying the environmental contour method, the inverse second-order reliability method to obtain contour is recommended. The ISORM contour is more conservative than the traditional inverse first-order reliability method but the numerical analysis is more stable than the highest density region method in three dimensions, while when applying the modified environmental contour method, the traditional inverse first-order reliability is preferred because of its simplicity and time-efficiency in the calculation.

In recent years wind turbines have become increasingly large to increase energy yield and cost-effectiveness. This has led to taller turbine towers, subjected to larger loads. As a result, Lagerwey turbines experience lateral tower vibrations at different resonance frequencies. These vibrations result in rotor speed measurement disturbances due to tower top roll motion. Such disturbances affect controller performance and induce undesired generator torque variations. Generator torque excites the tower, thus, a closed-loop interaction between the tower and the torque controller exists. A tower model including two resonance frequencies has been obtained through model identification in a simulation environment, which includes tower top rotational velocity as an output. A Kalman filter based on this model is able to provide an accurate estimate of tower signals using the tower top acceleration measurement and the generator torque set point. The tower top rotational velocity estimate is used to filter the rotor speed measurement. In high-fidelity simulation, it is found that in above-rated conditions (where tower vibrations are most severe) tower loads are reduced by 5.85%. In order to obtain a further load reduction, a state-feedback tower damping controller has been developed. Vibration modes are damped individually with user-defined damping ratios. For the designed controller, an average load reduction of 32.5% is achieved at the cost of a 0.8% increase in standard deviation of electric power.

Using a floating vessel operating on its DP-system and using a motion-compensated pile gripper to install monopiles could be the installation method of the future. Therefore, this thesis focuses on this method. The main objective of this thesis project is to build a model that accurately describes the motions of the Stella Synergy, the monopile, and the motion-compensated gripper, depending on the environmental conditions.
This model is built in Anysim, which is a time-domain simulation software program of MARIN based on the RK2 numerical method. The model considers the early pile driving phase because this phase is governing in terms of risk. The monopile acts as an inverted pendulum in this phase, and the motion-compensated pile gripper must guarantee the stability of the monopile. The vessel uses its DP-system for station keeping. The DP-system contains a position reference system, a filter, a control system, and a thruster allocation algorithm.
The vessel describes the wind, current and wave forces on the monopile and vessel. The environmental conditions are assumed to be collinear, and wave spreading is added to the model for some simulations. The wave forces on the vessel are determined with diffraction calculations in Ansys AQWA. The diffraction calculation for the vessel is verified with a diffraction calculation of MARIN, and the diffraction calculation for the monopile considers the shielding effect and is verified with a calculation with the Morison equation.
A motion-compensated pile gripper with two PD-controllers is built in Python. The gripper considers static and dynamic friction forces and a maximum delta force per numeric timestep to model the pressure build-up time of the hydraulic cylinders.
Multiple 3-hour simulations are run to generate results. These simulations, which considers each a different sea condition, are tested by the six limitations of the model. First, the preferable incoming angle of environmental conditions is determined. The workability of the Stella Synergy is calculated operating at the North Sea using this preferable incoming angle of attack. Then, two adaptations to the model are tested to increase the workability. Using fast-rotating thrusters or changing the DP-gains result in the workability of 96.4%. The governing limitation is the pitch motion of the vessel.
It is tested if using mooring lines in combination with the DP-system results in a footprint reduction. It is concluded that adding mooring lines could result in a footprint reduction, but it is crucial to gain insight into the optimal axial stiffness of the mooring lines. The monopile's influence on the vessel's motion is also tested. It is concluded that the vessel's surge, sway, roll and yaw motion increases significantly due to the environmental forces on the monopile, which are passed through the gripper to the vessel. Finally, the workability of the vessel during the worst-case single failure is determined. After improving the DP-gains for particular sea conditions, the workability for the worst-case single failure was 96.0%. The failure results thus in a minor difference in the workability.

Offshore wind electricity generation will play a key role in the transition to a sustainable energy sector. In 2020, the European Commission presented their Offshore Renewable Energy Strategy which includes 300 GW of offshore wind capacity by 2050 (European Commission, 2020). This research focusses on the steel mass development of OWT structural support components like the tower, substructure and foundation considering a trend of higher power turbines and exploitation at increasing water depth. The research follows an initial design approach, to estimate initial dimensions of monopile and jacket support structures for 5 reference offshore wind turbines. For simplicity, initial dimensions are based on design rules-of-thumb hence no ultimate, serviceable or fatigue limit states are considered. Reference turbines of 5, 8, 10, 15 and 20 MW rated power are included in the model, as these can be expected to be commercially available up to 2050. A water depth range of 20-80 meters is taken into account. Considering available development zones and environmental conditions, the study focusses on the North Sea region. For monopiles, the location of the natural frequency is used as a design driver to determine the tower and monopile diameter and plate thickness. For jacket structures, member slenderness and constant bay geometry are used as design drivers to determine member length, diameter and plate thickness. Overall, jacket structures show to be less steel intensive than monopile support structures considering their upfront steel requirements and have a higher steel recovery potential at end-of-life. Considering the climate change potential of OWT support structures, GHG emissions that emerge during steelmaking and recycling are taken into account. A GHG emission indicator of 1.22 tCO2-eq/t steel is derived with the aim to reflect European steel production processes. GHG emissions that emerge during transport, manufacturing and assembly or during the making of other materials than steel are not assessed in this research. A GHG emission payback time indicator is developed to provide insight into how the GHG emissions invested in support structure steelmaking compare to the GHG emissions avoided through the generation of renewable electricity. It is found that, depending on the combination of turbine rated power and water depth, for monopiles the emission payback time lies in a range of 4-9 months. For jackets this is 2-10 months.
In order to reduce the emission intensity of the offshore wind industry, this research recommends commissioners and designers to favour jacket over monopile support structures due to (i) reduced steel intensity for initial support structure manufacturing, and (ii) a higher recovery potential of support structure steel and its rare alloying elements at end-of-life. For 5 MW OWTs it is found that the application of jacket structures reduces an OWT’s total climate change potential with 15-20% compared to monopile structures. This research provides insight into to the contribution of bottom-founded support structures to the climate change potential of OWTs and shows that the combination of turbine rated power, water depth and support structure typology significantly influence the steel and GHG emission intensity of an offshore wind turbine.

The Ampelmann A-type hexapod platform is a motion compensating gangway system designed to transfer offshore personnel between a crew transfer ship and an offshore bottom founded structure. During operation, the platform is moved to compensate wave induced ship motion and create a still standing platform from which crew can safely transfer to the fixed structure. The hexapod platform is actuated by six high power linear actuators each capable of delivering 150 kW of power. To reduce the platform mass and reduce the operational energy requirements of the A-type, new actuator technologies are considered to replace the current conventional hydraulic actuators. Especially electro-hydrostatic and electro-mechanical actuation are promising alternatives to reduce mass and increase efficiency. Currently, properties of these technologies are only described up to power levels of 45 kW. Relative advantages of one over the other technology are not readily available in literature for higher power requirements.
To be able to compare both actuator technologies for use in the Ampelmann A-type, a preliminary design tool is made using existing and newly developed actuator mass and power loss models. General mass and loss properties of both actuators are determined and compared to develop a better insight in the optimal high power linear actuator technology for a specific application. Insights are applied but not limited to the Ampelmann application.

The Meuse river has been made navigable for ships by the construction of a cascade of seven weirs. At only two weirs hydropower facilities exist. This implies the full hydropower potential of the Meuse cascade is not utilized. Rijkswaterstaat only provides additional permits when fish friendly turbines are used. By using pump-turbines the river sections upstream the weirs might be usable as energy storage reservoirs.
The objective of this thesis is to study if the full hydropower- and energy storage potential of the Meuse cascade can be utilized by the use of pump-turbines within Dutch environmental regulations. In order to meet the objective a conceptual design of a pumped-storage hydropower plant has been compiled. By using this design, an assessment of utilizing the full hydropower- and energy storage potential of the cascade has been carried out. For the assessment a numerical model has been constructed and applied.
The cumulative installed turbine capacity for the cascade is 81 MW. The annual energy yield on hydropower is 225 GWh. The annual energy yield on pumped-stored power is 77 GWh. Up to 75.000 households can be powered with hydropower and pumped-stored power. When the Juliana canal is included in the assessment up to 131.000 households can be powered using an installed capacity of 134 MW.

This research strives to contribute to the solution of the Amsterdam waste problem by improving the location determination of the various container types within the Centrum area. One of the modalities is an autonomous surface vehicle (ASV), and in this case, a Roboat. Since it is not possible to assign all demand to one modality, also trucks and small electric vehicles are taken into account. This waste collection problem is represented through a facility location problem with different facility types in order to maximize the coverage with a minimum number of containers. Case studies are designed in Amsterdam Centrum, and different calculation strategies are executed to compare different methods.

A significant percentage of the offshore wind resource is located in waters deeper than 60m. Therefore, several floating offshore wind turbines (FOWT) have been conceived in recent years. In deep waters, it seems logical to also harvest wave energy. One of the options to harness both resources is to use a floating offshore hybrid wind-wave energy converter (FOHWWEC), which physically combines a FOWT with a wave energy converter (WEC). Different studies have addressed the functionality, feasibility, optimization, control and survivability of FOHWWEC concepts. The majority considers a proven FOWT substructure to fit a certain type of WEC. Dynamic analyses in both, frequency and time domains, and laboratory experiments with models have been done. Nevertheless, the investigated studies have not considered the FOHWWEC concept as part of an extensive design space. In other words, they have not attempted to explore and compare the myriad design configurations that are possible in that space. Besides this, few studies have been able to deliver a comprehensive understanding on how certain parameters, intrinsic and extrinsic to the FOHWWEC system, influence its performance. The present study is the start of that space exploration and understanding. Three FOHWWEC design configurations (DC), based on the substructure stability principle, are proposed. Vertical cylinders are used as substructure and two spherical point absorbers are connected through a PTO without mechanical spring to the cylinder supporting the WT. The objective is to compare their performances, based on two variables: the annual average absorption width and the maximum standard deviation of the horizontal nacelle acceleration. Besides this, three draft levels are considered and their impact in the performance is also analyzed. The hydrodynamic analysis of the FOHWWEC with parked WT is performed in the frequency domain. Hydrodynamic coefficients and wave-excitation forces are obtained from the BEM solver NEMOH. The software FOHWWEC Analysis program, developed by the author, solves the EoMs and calculates the performance variables. The North Sea is the selected region and a JONSWAP spectrum has been applied. The results indicate that the design configuration 3 (DC3) FOHWWECs have a wave power absorption mechanism based on the heave resonance of both, substructure and WECs. This mechanism is more efficient than DC1 and DC2's mechanisms. This allows to maximize the absorption width. Besides this, DC3 FOHWWECs can also minimize the nacelle accelerations (DC3-D2 case). The effect of the draft on both performance variables differs depending on the DC. Wide-ranging deductions from the results can be summarized as follows. It is reasonable to design a FOHWWEC as a whole system, considering both, wind and wave power generation from the beginning. Using an existing substructure means to lose performance improvement opportunities. It is also reasonable to select a buoyancy-stabilized substructure for the design. This allows to reach the most efficient wave power absorption mechanism, while providing the required flexibility to thoroughly explore and find the balance between design parameters such as WPA, displacement, draft, size and position of the WECs, mooring, among others.

A dam including a tidal power station with pumping capacity is a new type of flood defence. The negative ecological impact normally associated with closure dams is partially mitigated by including a tidal power station in the structure. Water can move through the tidal power station resulting in a reduced tidal stroke at the created lake. This tidal stroke plays an important role in maintaining the desired water- and nature quality within the lake. By including pumping capacity in the tidal power station the tidal stroke can be maintained as sea level rises with respect to the mean water level in the artificial lake. The aim of the study is to assess the feasibility of a dam including a tidal power station with pumping capacity given the uncertainty of sea level rise. To this end a few locations worldwide with high flood risk were selected for further analysis. A hydro energetic cost model was developed to simulate a tidal power station with pumping capacity. An optimization model was developed to generate optimal designs for power stations at all locations under evaluation. The economic feasibility of the dam with tidal power station including pumping capacity was assessed through a series of business cases, using the results from the two models. The solution was compared to the business case of other flood protection measures. The analysis showed that the concept has potential mainly as a long term solution, when a strong reduction of the tide at the created lake is allowed, and when a large amount of sea level rise is expected during the lifetime of the structure.