This thesis focuses on enhancing the predictive accuracy of the ShorelineS one-dimensional (1D) coastline model, which is used to simulate coastal evolution. The research primarily addresses the limitation of ShorelineS, which excludes cross-shore sediment redistribution, impacting its ability to predict coastal changes, as demonstrated in the case of the Bacton Sandscaping project.

The Bacton Sandscaping project was designed to counter coastal erosion threatening the Bacton Gas Terminal, a crucial part of the UK's energy infrastructure. Instead of traditional hard engineering solutions, a soft approach, inspired by the Dutch Sand Engine, was chosen. This method involves depositing a large volume of sand along the coast, which is gradually redistributed by natural forces to offer long-term protection. Despite the project’s success, challenges were identified in modeling the coastline's evolution, particularly with ShorelineS, which only considers longshore sediment transport. This thesis explores how incorporating cross-shore redistribution into ShorelineS can improve its predictive capability, especially for large-scale nourishment projects like Bacton.

The research begins by evaluating ShorelineS in its current form, comparing modeled and observed coastline changes. The model tends to underestimate erosion near the gas terminal and overestimate sediment distribution to nearby villages, leading to inaccuracies. To address this, a redistribution factor (R-factor) is introduced, which adjusts the model based on observed cross-shore changes. The R-factor is applied to the terminal section, improving predictions slightly, though overall performance remains limited due to the model's sediment conservation assumptions.

The study concludes that cross-shore redistribution significantly affects coastline evolution, as seen in the Bacton case. Although the R-factor improves predictions somewhat, the limitations of ShorelineS, such as its sediment retention assumptions and the CERC2 transport equation, suggest that further model refinements are necessary. Future research should explore alternative approaches to cross-shore redistribution, more frequent coastline updates, and sensitivity analyses to enhance the model's accuracy in predicting the evolution of mega nourishment projects.

On large dams, spillways are used to evacuate excess inflow discharges from the upstream reservoir to the downstream tailwater. When passing over the spillway the high potential energy of the water is transformed into kinetic energy and must be dissipated, which generally happens in stilling basins or plunge pools. Failing to dissipate sufficient energy can lead to erosion or scour in these structures. If this process is left uncontrolled, the structural safety of the foundation might be endangered and therefore the stability of the whole dam. During construction of the Calderwood Dam in the USA, a scour hole of 15 meter occurred because the weir controlling the water level in the pool was still under construction. At the Kariba Dam, the rock in the plunge pool has eroded to a depth of 70 meters below the original riverbed. Various spillways with different dissipation structures exist, the focus of this thesis is on the free-falling nappe initiated on a sharp crested weir in combination with a man-made plunge pool. When not all energy is dissipated before reaching the pool bottom, the remaining nappe exerts dynamic pressure on it, potentially causing scour to develop. Being able to predict the characteristics of these pressures is crucial for designing structures that can withstand them. In practice this is often done by performing pressure measurements on scale models and extrapolating the results to prototype scale. This is done by using appropriate scale factors or by making the measurements dimensionless. However, due to
the inability of achieving full similitude between scale and prototype models, scale effects influence these measurements. The objective of this study was to quantify the influence of these scale effects on pressure measurements performed downstream of the free-falling nappe. To fulfil this, 2 scale models of the same prototype but of different scale were constructed in the Hydraulics Lab of the University of Liège. On both models pressure measurements were performed and their results compared. Due to scale effects the properties of the dimensionless pressures are different across the models. In absence of a water cushion, the mean in the centre is overestimated on the small model and the
fluctuations around this mean underestimated. Additionally, when comparing the empirical density histograms, on the large model two peaks are observed. One close to the fall height and one close to 0, while on the small scale model only the peak close to the fall height appears. Furthermore, the impact location of this centre is further downstream on the large model than on the small one. With increasing water cushion height in the plunge pool, two phases affecting impact pressures related to effective and non-effective cushions can be observed on the small model. For the non-effective cushion, the cushion does not reduce impact pressures compared to the absence of a cushion. In contrast, during the effective phase, a reduction in impact pressures occurs, and this reduction increases with increasing cushion height. This distinction is absent on the large model, where any cushion height
reduces impact pressures. This reduction continues as the cushion height increases.
To increase the understanding of these scale effects, future research should focus on several aspects. If results from other scale models are published, scaling relationships could be developed to better predict pressures across different model sizes. Additionally, conducting measurements on existing prototypes, where controlled test conditions can be replicated, could be an option. Further investigation is needed to understand the cause of the peak observed near zero in the density histograms of the large model. Since air concentration in the flow has been identified as a potential primary cause of these scale
effects, qualitative research is necessary.

Armoured slopes are commonly used in coastal structures to dissipate wave energy and protect adjacent infrastructure. To limit the height of these slopes in an efficient manner, regularly a concrete crest wall is placed at the upper part of the slope. Understanding the loads on these crest walls is essential for the design of coastal protection works. Conducting scaled physical model tests is a well established approach to confirm and optimise the design of coastal structures, albeit time consuming, scattered, and costly. This study aims to investigate the use of compact, focused wave signals in comparison to the common practice of using wave signals typically comprising a thousand waves in physical model tests. The physical model tests conducted in this study revealed that a compact wave signal was able to reproduce the extreme hydraulic response recorded during the simulation of a thousand irregular waves. This was observed in terms of sliding failure and extreme pressures exerted at the front vertical wall of the model crest wall. Results showed that the shape of the pressure signals, pressure distributions and integrated forces are reasonably well reproduced during focused waves. This suggests that this approach is promising for reproducing extreme responses at crest walls using focused waves; thus, resulting in reduced testing times. However, findings so far cannot support the use of this approach as a standalone tool for this application.

With a setback storm wall impact wave loads can occur which cause much higher loads than with a straight vertical wall. Empirical formulas for a first estimation exist, but they do not consider the geometry of the structure (height storm wall, length quay) or are not applicable for negative freeboard, or both. Due to this limitation, the main research question of this research is “What is the influence of the geometry of a retreated storm wall on top of a quay wall on the wave forcing exerted on the storm wall?”. The main method used for this research is numerical modelling using DualSPHysics (Smoothed Particle Hydrodynamics). This model is validated using a laboratory experiment. The result of the thesis is are formulae for rough first approximations of the horizontal force for the conceptual design.

Coastal cities and communities are threatened by Sea Level Rise (SLR). Designing adaptations to protect against the rising sea requires a novel approach. With changing conditions, a broader approach considering multiple climate scenarios is required. A city facing an increasing threat from sea levels is Venice, one of the UNESCO world heritage sites. To protect the historic Italian city against floods, the MOSE barrier was constructed by the Italian government.
In 2020, the MOSE barrier was used for the first time. The mobile barrier closes when high water levels are foreseen in the city, preventing floods. Due to SLR, it is anticipated that the barrier will have to close more in the future, leading to questions about the functionality of the barrier when water levels rise. This might require adaptations or alternatives for the MOSE barrier.

The main objective of this thesis is to explore the potential of the framework proposed by Rosner et al. (2014) to evaluate the economic feasibility of an adaptation strategy against sea level rise in the city of Venice.
This framework assesses the potential regrets (monetary losses) on the decision to invest in an adaptation strategy accounting for errors in the evaluation of the level of sea level in the future. The framework incorporates trends based on historical sea level observations, including the uncertainties around these trends.

First, different methods of calculating design values under varying conditions are compared. This comparison is focused on different non-stationary Extreme Value Analysis (EVA) distributions. Due to SLR, a stationary and thus constant situation is not valid for Venice. This leads to the choice of the Rosner framework since it evaluates the feasibility of adaptations under varying conditions.

The regret of adapting or not adapting to a trend or SLR scenario is calculated from the damages associated with that scenario and the costs of the adaptation. The damages are computed by calculating the number of MOSE barrier closures for the different scenarios and multiplying this number by the costs that are related to a closure event. The adaptation that was chosen for evaluation is raising the entire city by 30 cm. This is accomplished by injecting seawater into a deep soil layer underneath the city.

The analyses resulted in smaller expected regrets when the choice is made to adapt. This was the case for all SLR scenarios, the difference between the adapt and not adapt regrets is larger for higher levels of SLR. This includes a higher SLR scenario due to a trend with large uncertainty. This is under the assumption that the adaptation, lifting the city, will work, the technical feasibility of this method was not investigated in this thesis.
A more precise calculation of the number of closures is advised. However, it is evident that adaptations are required to keep the MOSE barrier functional and the city of Venice safe from high waters. Raising the city will allow more time to evaluate which alternative to the MOSE barrier is best suited for the future.

In 2008, a new concept to extract tidal energy was introduced called Dynamic Tidal Power (DTP). In this concept, the natural tidal wave propagating along a coastline is blocked using a long dam, inducing a water level difference between both sides of the dam. This water level difference, called the hydraulic head, can be exploited by placing turbines inside the dam. This is a promising concept, but the feasibility and suitable locations for DTP are largely unknown yet.

This study aimed to identify locations that have the highest potential to implement the DTP concept. By investigating the feasibility criteria and their influence and translating these criteria to spatial analysis, geographic regions with high potential were identified. Additionally, linkage opportunities were assessed and identified to possibly improve the feasibility of DTP.

Based on a sustainable feasibility study framework, the key aspects can be categorized into three main categories; technical, economic and social-ecological feasibility. These aspects were translated into criteria, whose influence was investigated using a hydraulic model. Considering the technical criteria, the tidal flow velocity proved to be more influential on the feasibility than the depth, finding weighting factors of 0.87 and 0.13, respectively. In order to define a threshold of the feasibility of DTP, the technical and economic criteria were combined by assessing the upper threshold of the Levelized Costs Of Energy (LCOE) of 0.1 €/kWh to find a minimum required average flow speed of 0.63 m/s. This threshold was used in the spatial model. The island linkage opportunity proved to be highly valuable. Connecting an island increases the effective blockage length, resulting in a hydraulic head and power output increase with approximately the same dam construction costs. This lowers the mean tidal current speed required for feasibility to 0.39 - 0.57 m/s.

The spatial analysis used a Multi-Criteria Weighted Overlay Analysis (MCWOA) approach, combining datasets and weighting factors for each criterion to find a total Potential Index (PI) score. In total 41 potentially feasible locations for DTP were identified. The geographic regions with the highest potential to implement DTP are the Yellow Sea, the seas in Southeast Asia, and the seas of Oceania. This is due to a combination of high tidal current velocities, relatively modest water depths and a good combination of secondary criteria (energy usage, population size & low shipping disruption). A high share of the island linkage opportunity was found in the locations with the highest potential (44%). It is recommended to investigate whether additional island linkage opportunities can be identified, by lowering the tidal current velocity threshold in the spatial model. Additionally, 233 locations were discarded, mostly due to their remote location. However, since these locations are technically feasible, it is recommended to investigate the possibility of transmitting the energy over long distances using Ultra High Voltage Direct Current transmission lines and study the total feasibility of DTP at these remote locations.

This study assessed the feasibility of DTP and identified that the Yellow Sea, the seas in Southeast Asia, and the seas of Oceania have the highest potential for a DTP project. Additionally, it provided new insights regarding the influence and thresholds of certain influential criteria, and it presents a hydraulic model and GIS tool that can be adjusted based on the preference of the user. These findings could be useful in future research on the DTP concept.

Coral reefs are considered to be a crucial ecosystem and form of natural coastal protection. They owe their effectiveness to their high structural complexity. This complexity, which positively influences aspects like species richness, coral recovery, live coral cover, and coastal protection, is often quantified using parameters such as porosity and rugosity as has been done in this thesis. However, coral reefs are currently facing decline due to both natural processes and human activities. To address this issue, artificial reefs (ARs) have been proposed as a potential solution. Coastruction, a start-up specializing in 3D printing, has developed a 3D printer capable of creating artificial reefs in any shape. In this thesis, biomimicry-inspired complex ARs were designed and printed to examine the impact of structural complexity on wave attenuation.

Data was collected through physical model tests in a wave flume at Deltares, using Froude scaling with a length scale of nL=4. The experiments involved 1 to 2-meter-long reefs composed of three distinct structures with different geometrical complexity levels: design 1 (medium complexity), design 2 (maximum complexity), and cubes (low complexity). These structures were tested under similar, primarily non-breaking wave conditions. The aim was to determine if the dissipation observed resulted from friction rather than wave breaking.

The results of the conducted experiments showed that structural complexity does not significantly affect wave transmission. Overall, high transmission coefficient were observed across the different structures, ranging from 0.96-0.99. Additionally, no significant differences in dissipation were found among the three structure types, with dissipation ranging from 5.5% to 13.5% of the incoming wave energy. However, increased reef coverage positively impacts transmission reduction and spectral wave dissipation, exhibiting a linear decrease in transmission coefficients and a simultaneous increase in dissipation.

In summary, the various artificial reefs examined in this study demonstrated minimal effectiveness in wave attenuation, with negligible differences among reefs featuring different degrees of structural complexity. Despite the similar wave attenuation effects, the environmental benefits of a highly structurally complex reef suggest that it should be considered a viable solution.

In this study loading characteristics of rubble mound breakwater crown walls are investigated. This is done using a 2D physical model, testing for overall stability (through sliding) and temporal & spatial distributions of pressure along the face and base of the crown wall. A variety of wave conditions and geometries is used, with special attention for the influence of foundation level on the loading characteristics. This study shows the importance of this parameter and its link to the time lag between the maximum horizontal force and maximum vertical force in a wave impact. Using a new analysis method based on the factor of safety, this time lag is quantified and a reduction factor for the vertical forces is introduced.

Global warming has caused an increasing demand for renewable energy. Currently, 50% of the renewable energy is provided by wind and solar combined. However, these renewable energy sources are highly volatile. Wave energy converters can provide a stable renewable energy source. Previous research has contributed to understanding various combined effects of length, aspect ratio, hydro-elasticity and PTO damping on the optimisation of peak power absorption for regular waves. However, research on optimising the combined effects on annual energy production and especially power stability is missing. This thesis aims to better understand these effects by answering the following research question: "How can the combined effects of total length, aspect ratio, raft stiffness and PTO damping influence yearly energy conversion and energy stability of a pitching raftWEC"

To do this, a novel formulation for a monolithic finite element model containing Timoshenko beam theory and Linear potential flow is developed. This FEM consists of a two-dimensional domain, where the water is excited by linear irregular waves. The wave energy converter is modelled as two floating Timoshenko beams connected by a damped joint. The model is verified by proving that the solution converges according to the polynomial order +1 for decreasingmesh size. Additionally, it is proven that energy is conserved which shows that there is no wave reflection resulting from the domain boundaries. Finally, the model is validated by comparing the results of the structure with and without joint to previous research.

Two experiments are developed to understand the combined effects. Initially, an eigenmode analysis of the undamped structure is performed. This gives insight into the influence of individual parameters on the eigenfrequencies and shapes. Moreover, the real eigenmodes are used to decompose the real part of the complex resonance shapes of the relative rotation response amplitude operator (RAO). This provides a coupling between the performance according to the relative rotation RAO and the eigenmodes and frequencies. A limitation of this method is that phase differences cannot be considered.
The second experiment maximises the annual energy conversion and energy stability of thewave energy converter with three sets of variable parameters: (total length, aspect ratio, damping parameter), (total length, symmetrical raft stiffness, damping parameter) and (stiffness fore-aft, stiffness aft-raft, damping parameter). This is done in three steps. First, the RAO for the relative rotation at the joint is constructed. This is converted to a power spectrum. Secondly, the power spectrum is scaled by the JONSWAP energy density spectra. These
spectra are constructed using the annual wave conditions, significant wave heights and peak periods from a wave scatter diagram. Subsequently, the results per spectrum are scaled by the number of occurrences of the wave conditions to obtain the annual energy conversion. Third, The optimum damping parameter per configuration is determined by calculating the annual energy conversion for a set of damping parameters. These results are interpolated to select the damping parameter that maximises annual energy conversion.
Finally, the performance of each configuration with their respective optimum damping parameter is assessed on annual energy conversion and capture width per peak wave period to give insight into the energy conversion and stability. The optimisation results are clarified with the results of the eigenmode analysis.
It was found that the optimal total length, considering raft stiffness, aspect ratio and PTO damping can be determined by matching the dimensionless wavelength corresponding to the third mode, and the annual significant wavelength.

Furthermore, It is proven that an aspect ratio of 0.2 to 0.3 increases the performance in high-frequency waves without compromising on low-frequency waves. The capture width is more evenly distributed over peak wave periods, indicating a higher energy stability. This results in an increase of annual energy conversion of 31% with respect to an aspect ratio of 0.5. Besides the aspect ratio, it was found that an asymmetrical raft stiffness, with a moderately flexible fore raft and a rigid aft-raft increase energy stability without compromising annual energy conversion.

Two-bladed offshore wind turbines regained interest in finding the most profitable way of generating wind energy. Wind industry companies demand the safe operation of two-bladed offshore wind turbines. To guarantee safe operation, the companies perform operational modal analyses to investigate modal properties variation which might be allocated to damage. However, the operational modal analysis of an operative two-bladed offshore wind turbine faces multiple challenges. (1) Fundamental operational modal analysis assumptions about the applied loads are violated by environmental and operational loads. (2) The closely spaced modes of an offshore wind turbine are hard to identify. (3) An operative two-bladed offshore wind turbine is a linear time-variant system. This paper introduces an enhanced operational modal analysis procedure to overcome some of the mentioned challenges. The enhanced procedure incorporates a post-processing technique in a transmissibility-based approach. A developed representative model of an operative two-bladed offshore wind turbine is used to compare the enhanced procedure with the frequency domain decomposition method. Based on the comparison, this paper proposes a new operational modal analysis method that combines a transmissibility-based approach, the post-processing technique, and the frequency domain decomposition method. This paper proves that this proposed combined method is a promising new operational modal analysis technique that outperforms the enhanced procedure and the frequency domain decomposition method in identifying the modal properties of a two-bladed offshore wind turbine.

This study investigates the capacity of an open inverted filter to stabilize the interface between the sand fill and core fill in a rubble mound breakwater. The strength of this filter relies on the arching mechanism of the base material, which is directly influenced by factors such as stability ratio and effective stresses. These forces arise from porous flow, and its quantification involves both parallel and perpendicular hydraulic gradients.
A full-scale physical model, with a 760 mm open inverted filter, is employed to determine the critical hydraulic gradients required to initiate erosion. The model consists of three compartments, with the central compartment containing the open inverted filter. The two side compartments are filled with water, with one of them featuring a plunger mechanism to induce flow. Pressure sensors and water level gauges are used to measure the hydraulic gradients. In addition to the physical model, a numerical model is developed to gain insights into the flow dynamics within the system.
The tests reveal that an increase in effective stress results in higher critical parallel and perpendicular gradients. Furthermore, the addition of fines at 5% or 10% seems to enhance the critical parallel and perpendicular gradients. A negative correlation was found between SR and 𝑖⊥,𝑐𝑟𝑖𝑡, the results were fitted to a hyperbolic function. The findings further indicate that, even after erosion occurs, a stable interface can be reestablished. Therefore, designing solely for the single largest wave is not imperative.

Large parts of the Netherlands lay below mean sea level. An extensive network of flood protection measures is in place to prevent flooding. Periodic safety assessment and reinforcement are required to guarantee a resilient system. Currently, in the Netherlands, an extensive sea dike reinforcement program is underway to meet the safety standards mandated by the Dutch government. A dike reinforcement project encompasses several components, often interacting with each other. This study focuses on the outer dike revetment. Traditionally, the revetment design is optimised for financial costs. This study aims to optimise the dike revetment design for the lowest Environmental Cost Indicator (ECI). This quantifies the carbon dioxide equivalent emissions generated throughout the entire life cycle of a construction project or its constituent parts. This is pertinent in the current context as the Dutch Government harbors ambitions of achieving a fully circular economy by 2050, with an interim goal of a 50% circular economy by 2030. This ambition is to be implemented by companies within their organization. The revetment is optimised as a whole by assessing the entire outer revetment and applying different types of revetment based on their probability of failure. The primary objective of this study is to acquire knowledge on designing a dike revetment that fulfils technical requirements and has the lowest environmental cost indicator possible. The revetment types to study are loose rock, concrete elements (Basalton), interlocking elements (Verkalit), hydraulic asphalt concrete and grass. The following main research question is defined:

"What sea dike revetment design fulfils safety requirements and has the lowest environmental impact for the Lauwersmeerdijk-Vierhuizergat dike reinforcement project?"

To answer this question, a Python-based model was made. The model evaluates the probability of failure of each design option and calculates the corresponding ECI and financial costs. The LauwersmeerdijkVierhuizergat project, a Waddenzee dike reinforcement, is used as a case study. The required safety level for the Lauwersmeerdijk-Vierhuizergat outer revetment is 1/60.000 years. The model requires input for the design equations. The input consists of decision variables, control variables and hydraulic boundary conditions. The decision variables are the variables in the design equations that the designer can alter. The control
variables are the variables to which the designer has no influence. The hydraulic boundary conditions are determined for each water level discretised in steps of 0.2m. Next to the input for the probabilistic calculation, the input for the ECI and financial costs are required. The ECI data is obtained from the ’Milieudatabase’
(Schipper et al., 2022). The financial cost data is obtained from cost experts from Arcadis.

For loose rock, the probability of failure is calculated with the equations as defined by van der Meer (1988a). For the placed elements, the probability of failure is calculated with the equation defined by Klein Breteler and Mourik (2014). The asphalt revetment is designed with the uplift and wave impact equations as defined in TAW (2002). The grass revetment is designed with the use of the ’Gras erosie buitentalud’ (GEBU) tool. The equations for erosion according to Klein Breteler (2022a) are included in this tool. The design equations are evaluated using crude Monte Carlo analysis for each water level with corresponding hydraulic boundary conditions, decision parameters, and control parameters.

More than 2,000 designs, each meeting safety requirements, are made with varying transition heights. The optimal sea dike revetment design for environmental impact is the design with the lowest ECI score. When the
probabilistic approach is applied, this design has loose rock revetment at the lower section, Basalton for the middle section, and grass for the upper section. In general, it is concluded that loose rock contributes most to the ECI and should be limited as much as possible. The middle section is traditionally made of hydraulic asphalt concrete. However, when replacing this with placed elements, a lower ECI is achieved. The grass revetment often requires large volumes of high-quality clay from external locations, requiring long transport distances. This results in high ECI costs for thick clay layers. When comparing the revetment with the lowest ECI to the revetment design with the lowest financial costs, it is concluded that the design with the lowest financial costs has a large section with hydraulic asphalt concrete instead of placed elements. The study design costs €1890 per meter, with an ECI of €373 per meter. The financially most attractive design costs €1439 per meter, with an ECI of €458 per meter. The difference in financial costs is €451 per meter (24%) and €85 per meter ECI costs (23%). For the revetment design made by Arcadis, deterministic and semi-probabilistic
calculation methods are applied. The asphalt layer thickness is reduced by 50% when applying this method due to the large uncertainty in the probabilistic design. This results in a €12 per meter dike width lower ECI than the design with the lowest ECI made with the probabilistic approach.

Thus, when designing a sea dike revetment probabilistically, aiming to reduce the ECI as much as possible,
apply as little and the smallest possible loose rock grading, and replace the hydraulic asphalt concrete layer for placed elements.

The projected increase in sea level is expected to increase the intensity of coastal flooding threatening communities living along the coast. This, in combination with population growth and urban expansion, calls for a better understanding of Extreme Water Levels (EWLs), the mechanisms generating them, and their components, i.e., astronomical tide and storm surge, since they drive the maintenance and design of flood protection systems. Netherlands' flood defense is crucial in facing the risk of flooding given its particular geographical configuration, its large number of inhabitants, and its high value of assets. For this, a better understanding of EWLs and their components is essential to assessing the quality of current structures and developing new adaptation strategies since they drive design and risk assessment procedures. Hence, in this paper, we investigate EWLs in Hook of Holland which represents a strategic location due to the inlet of the port of Rotterdam and the Maeslant storm surge barrier. Here, we present a stepwise procedure that starts by defining EWLs, assessing drivers of storm surges on observed sea levels via spectral analysis and coherence, and ends in estimating the statistics of EWLs based on multiple approaches, i.e., univariate extreme value analysis, copula functions, and Joint Probability Method (JPM). The results show that storms in the Southwest Delta have a duration of about 4 days and that EWLs components, i.e., surge and astronomical tide, present negative dependence (the Kendall's tau $\tau = -0.50$). From the comparison between statistical approaches to model EWLs and infer design values, results show that copulas and JPM lead to an overestimation of EWL. However, EWLs modeled via copulas fit better low quantiles.

Climate change is triggering an ever-growing demand for renewable energy. The U.S. is still far behind Europe when it comes to offshore wind energy. They have made ambitious plans to reach 30 GW in offshore wind energy by 2030 while currently 42 MW is installed. One of the main challenges in the U.S. is the installation method since a legislation called the Jones act prevents the usage of European installation vessels for shuttling (the conventional method). Building a Jones act. compliant installation vessel is a large investment which comes with risks and long lead times. Feedering is an alternative strategy, but barely any research on it is available. Here, a feeder vessel sails back and forth from the storage port to the (non-Jones act. compliant) installation vessel to supply Wind Turbine Generator (WTG) components. These components need to be lifted from the floating feeder in order to be installed. In the literature, this step is deemed to be the riskiest. However, barely any technical research is available with regards to the lift-off.

In the first thesis of this double degree program, a lift/installation sequence called the direct installation method is deemed to be highly interesting with respect to the logistics and costs. However, this research misses a technical study in order to understand if it is technically reachable to directly install these components. In this offshore engineering thesis, a barge is used as a feeder vessel and tower segments of a 20 MW WTG are chosen as the to-be lifted components. This research focuses on the pre-tension phase before the lift-off. This contains the steps where the crane of the installation vessel is already attached to the tower, pre-tension is building up and the release of the sea-fastening. Here, pre-tension is a percentage of the load that is taken in the crane before the lift-off. This research aims to increase the understanding of whether a tower can be released safely on the floating barge and what can be done in order to realise the idea of a direct installation method.

Frequency, as well as time-domain simulations, are used to investigate the problem. The results show that snap loads occur for pre-tensions up to 10\%. From 30\% and higher, the tower will start toppling. Toppling is initiated due to the inertia of the large tower segment when it is released from its sea-fastening. Toppling the tower is not allowed since this could damage the tower itself, the sea-fastening and/or other components on deck of the feeder. Increasing the limiting wave height is a must in order to make the direct installation method more practicable. This can firstly be done by using more tower segments. Therefore, reducing the size of each segment. Another option is to implement a motion compensation tool that decouples the motions of the feeder and the tower. The third option is to design a seafastening system that reduces the moment after the release, a temporary counteracting toppling system. All in all, can be stated that safely releasing a 20 MW tower segment on a floating barge is highly challenging and more research is required to solve the issues that are found in this research. This is necessary to allow the direct feeder method to be used for future offshore wind installation projects in the U.S.

The water authority ”Hunze en Aa’s” initiated a demonstration project adjacent to the Dollard where non traditional dike reinforcement strategies could be developed. For this project Sweco designed a sea dike with an outer slope more gentle than traditional. This dike is called the ”Wide Green Dike” (WGD) and has an outer slope of 1:7. This dike is designed for 10 l/s/m overtopping with hydraulic boundary conditions provided by HYDRA-NL. This report examines whether 10 l/s/m of overtopping leads to failure of the WGD. In this context failure means erosion of the inner dike slope. Whether failure occurs is based upon the cumulative overload method (Steendam et al., 2015).

The WGD is rebuilt in a computational model called SWASH, which is a general-purpose numerical tool for simulating non-hydrostatic, free-surface, rotational flows and transport phenomena in one, two or three dimensions. The flow velocities on the rebuilt dike for the overtopping design condition are analysed. In this study SWASH is used to analyse 2D wave interactions from nearshore along a shallow foreshore towards and over a sea dike.

The simulation using the locally generated waves results in no overtopping. The overtopping criterion is normative for the crest height and no overtopping indicates that it is likely that the design of the dike can be optimized. But before any decisive conclusion can be made more research into the wave cli-mate in the Dollard is needed.

As the scenario using the locally generated waves resulted in no overtopping, a new scenario is created. This scenario has other wave boundary conditions, such that there is overtopping. This simulation results in 57 l/s/m overtopping but without any initiation of damage on the lee side according to the cumulative overload method. This result would indicate that exceeding an average overtopping of 10 l/s/m might not necessary lead to failure for a dike with a more gentle, compared to standard, outer slope. The same simulation shows that the current relation for the flow on the lee side is likely not sufficient to describe the full flow pattern. According to literature the flow velocity on the lee side of a dike increases and stabilizes. However, SWASH simulation results show after the initial increase also a decrease in flow velocity. The current relations for the flow velocity on the lee side only include the first initial increase but do not include the observed decrease in flow velocity. The kinematic shock theory equation, shows good agreement with the decrease in velocity. The results show that the tipping point (change from flow velocity increase to decrease) is located at 97% of the predicted final flow velocity (Van Gent equation). It seems that a combination of the Van Gent equation and kinematic shock equation can represent the flow velocity along the lee side of a dike.

Coastal and offshore infrastructure must be designed to withstand extreme wave-induced loading conditions. Extreme Value Analysis (EVA) is often employed to infer probabilistic distributions that provide information about extreme design conditions. In traditional practices, EVA is performed under the assumption of stationarity. This means that the probability of extreme events is constant in time. However, hydraulic loading conditions are expected to exhibit temporal variability in severity and frequency as a result of climate change. Therefore, the assumption of stationarity becomes questionable. Nonstationary extreme value analysis (NEVA) for inferring extreme hydraulic loads have become more attractive in recent years. However, the applicability of NEVA models is debatable ansd differs on a case-by-case basis. Large scale oceanic bodies can be characterized by spatially and temporally varying extreme wave characteristics. Clustering analyses have proven to be successful to identify regions exhibiting similar extreme wave characteristics. Creating clusters based on similar extreme wave characteristics can potentially improve extreme value modelling because intra-cluster information can be pooled to derive more accurate extreme value models.

This research presents a practical assessment of the applicability of clustering analysis and non-stationary extreme value modeling of extreme wave statistics at cluster level in the North Sea. The primary objectives of this research are: (1) Study the temporal variability extreme significant wave height (Hm0) and extreme wind speeds (U10) in the North Sea domain, (2) Investigate how hierarchical clustering analysis (HAC) can be employed to cluster grid points that exhibit similar extreme wave characteristics, (3) How the obtained clusters and temporal variability can be employed to derive extreme value models describing extreme Hm0 statistics at cluster level and (4) assess whether NEVA models at cluster level form a practical alternative compared to conventional stationary analysis in the design and risk assessment of hydraulic infrastructure in light of climate change.

Temporal trend analysis of Hm0 in the North Sea showed that the period between 1990 and 2020 can be characterized by a decreasing trend. Between 1950 and 2020, a decrease in Hm0 intensity is observed in the Western regions and an increase is observed in the East. This is reason to believe that the variability in extreme wave climate is cyclical rather than monotonic. There is reason to believe that temporal variations of extreme U10 are responsible for the temporal variability of extreme Hm0. Initial clustering results partition the North Sea domain into 50 clusters based on characteristic values for the significant wave height (Hm0), peak period (Tp), and dominant wave directions (θ1 and θ2). After splitting clusters based on geo-location and merging clusters based on the intra-cluster statistical properties of the wave parameters, 63 clusters are obtained. The identified clusters and temporal variability are used to define NEVA models describing extreme Hm0 statistics at cluster level. Intra-cluster Hm0 observations are detrended before fitting the GEV parameters by means of Bayesian Inference. Informative priors are constructed by pooling the GEV parameter information from the intra-cluster grid points. Potential non-stationarity is accounted for by adding the Theil-Sen parameters (b and b0) to the location parameter (μ∗), making the location parameter a linear function of time. The model parameters subsequently read: Hm0 ∼ GEV (μ∗ + (b · t + b0) , σ∗, ξ∗). Using the extreme Hm0 data from the clustering centroid yields the most promising results for describing extreme Hm0 statistics at cluster level under the condition that the intra-cluster exhibits homogeneous values for b and b0.

The applied HAC analysis presented in this research is not the optimal strategy. The identified clusters exhibit heterogeneous values for b and b0 Because non-stationarity ofHm0 was not accounted for during the HAC analysis. This hinders the performance of the NEVA models at cluster level. Also, whether the derived methodology can be applied for the long-term projection of future extreme wave events in the North Sea is debatable. The non-stationary of extreme Hm0 is best described by a cyclic pattern. Without a thorough understanding of the underlying causes of the non-stationary in Hm0 and without future projections of the extreme wave climate, the applicability of NEVA for deriving extreme Hm0 design conditions in light of climate change cannot be guaranteed.

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.

This study investigates the use of an open filter in a land reclamation structure. The possibility of replacing the geotextile that secures the core-backfill interface with a granular filter has been investigated. This is easier to install and therefore a potential cost-saving. Experiments have been done to determine the influence of various parameters on the interface stability of a geometrically open inverted granular filter. Relationships have been found which can assist in designing such a filter.

This thesis concerns a hydroelastic analysis of a multi-module very large floating structure (VLFS), analysed in the frequency domain. To this end, the fluid-structure interaction is described by a 2D model, where the VLFS is represented by four floating beams interconnected with rotational springs. The fluid is modelled as an ideal fluid, and the floating beams are modelled by the Euler-Bernoulli beam theory. The finite element method is applied to solve the governing equations of the fluid motion and the motion of the beams, where the model is built using the FE-library Gridap, written in the Julia programming language.
The aim of the study is to investigate the influence of various module and connection stiffness on the behaviour of the system, with the view to obtain more insight in the complex relation between the hydroelastic response and internal loads, when the system is subject to regular waves.

Rubble mound structures are often constructed to prevent severe wave damage to ships. By constructing the crest at a certain level, the waves are reduced such that safety is ensured. However, a large increase in sea level rise is expected in the next century due to climate change. Because of this, multiple adaptations might be necessary to meet the required lifetime of a rubble mound structure. In current guidelines, the influence of these adaptations is already included. However, for a combination of solutions the empirical equations are not always accurate enough (van Gent, 2019). Accurate guidelines are necessary to correctly predict the overtopping rates for a combination of solutions. In this research, the accuracy of current guidelines is investigated.

The research performed in this thesis is divided into two parts. First, multiple solutions are derived to adapt a breakwater and ensure safety for a rising sea level based on existing empirical equations. Safety is ensured if the mean overtopping rate remains less than 50 l/s/m. Beyond this point, the ships behind the structure might become prone to large wave attacks. Secondly, the accuracy of current guidelines (i.e. the empirical overtopping equations) is tested in an OpenFOAM model. OpenFOAM is a so-called open-source Computational Fluid Dynamics (CFD) software that can solve complex fluid flows.

Several solutions are possible to ensure safety against severe wave overtopping. The four solutions applied in this thesis are the addition of a berm, the addition of a crest wall, an increased foreshore and the implementation of a low-crested structure. By combining these solutions, the overtopping rate remains below the maximum of 50 l/s/m. The combination of solutions forms a path, all paths together form a pathway. The adaptation pathways are a guideline for the moment in time at which a certain solution should be implemented. Therefore, a structure is not unnecessarily expensive and can be managed easily. The paths are rated based on the implementation costs of the combination of solutions.

In total two empirical equations are applied to derive an adaptation pathway. The first pathway is based on the overtopping equation proposed by the TAW (2002). The TAW is a Dutch advisory committee on flood defences. Based on the applied theory, the economically most attractive solution consists of a low-crested structure, a foreshore and a berm. As this equation does not account for the influence of a berm in non-breaking waves, an adapted TAW equation is applied as well. The adapted equation was proposed by Krom (2012) and includes the influence of a berm. Based on the adapted equation, the economically most attractive solution consists of a foreshore, a crest wall and a berm. Once the economically most attractive solution is derived, the accuracy of current guidelines is reviewed in a phase-resolving model. It is found that, there is a large discrepancy between the results calculated with the empirical equations and the results from the model. As no physical data is applied in this research it is hard to interpret and analyze the exact numbers. Therefore, the relative effect of an adaptation is compared. It is found that in contrast to the TAW overtopping equation for non-breaking waves, a berm decreases the overtopping rate by at least 30% for the case study applied. Furthermore, the current method to account for a crest wall proposed by the TAW overestimates the reduction (73% compared to 40% in OpenFOAM). Finally, it is concluded that the addition of a low-crested structure decreases the overtopping rate by a larger value than based on the applied guidelines (74% in OpenFOAM compared to 35% in theory).

Based on the performed research a realistic combination of the adaptation measures consists of a combination of a berm, a crest wall and a shallow foreshore. Therefore, it is advised to focus further research on the combination of these measures. It is necessary to improve the guidelines for combinations of these adaptation measures since the existing ones seem to be either incorrect (TAW, 2002) or require a better validation (Krom, 2012).