In this thesis, the loading characteristics of a crown wall on a rubble mound breakwater are investigated using a 2D physical model. The study examines both overall stability (through sliding) and the temporal and spatial distributions of pressure along the face and base of the crown wall. A range of wave conditions is tested, with particular emphasis on the influence of foundation level on the loading characteristics. Additionally, a second breakwater core is used to assess the impact of permeability on the wave loading characteristics. The findings highlight the significance of both parameters and analyze the discrepancies between predicted and measured maximum horizontal and vertical forces after wave impact. Furthermore, a novel two-step method is proposed to improve existing design methods, enabling more accurate estimation of wave loads. ... Read more

Many regions around the world are prone to tsunami risk, and their populations are expected to increase. Moreover, past events like the 2011 Great Eastern Japan Earthquake and Tsunami resulted in numerous fatalities and the failure of many coastal protection structures. These events underscore the urgent need for further research in tsunami engineering and the mitigation of tsunami risk. In fact, the capability of coastal protection structures, such as breakwaters, to withstand tsunami loads is not yet fully understood. Additionally, these structures are typically designed to resist wind waves loads rather than the longer waves produced by tsunamis. This research provides further insight into the interaction between tsunamis and composite breakwaters by analyzing experimental results where a unique technique capable of accurately reproducing tsunamis as scaled N and E-waves was used. The experiments employed a 2-dimensional flume where waves were generated with a tsunami simulator and propagated until they impacted a composite breakwater model, inspired by the world-record breakwater in the Kamaishi bay in Japan. This research thoroughly analyzed the results of one of the experiments conducted at the HR Wallingford research center in the UK, with the objective of understanding the response of a composite breakwater when impacted by a tsunami, focusing particularly on the caisson on top of the structure and its stability. Another objective was the development of a numerical model based on the coupling of the two software OceanWave3D and OpenFOAM, aiming to reproduce physical experiments on tsunami-structure interaction and provide further insights beyond the capabilities of physical tests. The results of this research indicate that the pressures and forces induced by a tsunami on the caisson of a composite breakwater have a dominant hydrostatic contribution. The absence of wave breaking as the tsunami approaches the breakwater and shoals on its rubble mound prevents the generation of impulsive forces on the structure. The analysis also shows that, for the considered tsunami at prototype scale, the caisson would be unstable and fail due to sliding, primarily because of the water level and pressure differences on the two sides of the structure. The model developed in this research demonstrated a good accuracy in representing the physical experiment, as evidenced by elevation and pressure time series, with minor limitations on the lee side of the structure and on its rubble mound. With further validation using additional experimental results, this model can serve as a starting point for future studies on tsunami-structure interaction. It overcomes some limitations of physical testing, potentially provides more accurate results for caisson stability analysis, and offers a cost-effective alternative to physical experiments. ... Read more

Salt Marshes are a coastal ecosystem which have numerous benefits as coastal defense such as wave attenuation and can adapt to sea level rise. Wave flume tests, using a scale model of a cross-section of a salt marsh adjacent to a dike, were conducted in the Hydraulic Laboratory, to quantify the effectiveness of such a salt marsh system as flood defense (part of the Living Dikes research program).

This thesis focuses on the reduction in wave run-up due to salt marshes on the adjacent dike, with a focus on high water levels. The wave run-up was measured using video processing, using a newly created algorithm to track the water movement on the dike slope. The results show a significant reduction in wave run-up due to wave attenuation over the salt marsh, further dependent on the presence of vegetation and the water depth on top of the salt marsh. The measured wave run-up values show some differences with values acquired using the TAW/EurOtop wave run-up formula. There is a correlation found with the wave steepness, where waves with a lower wave steepness do match the equation, and show a larger deviation for increasingly higher wave steepnesses. ... Read more

Sea dikes have long been one of the main coastal defense infrastructures in the Netherlands, protecting against flooding and storm surges. As climate change intensifies severe phenomena and sea level rises, dikes must be heightened to protect the coast efficiently against future threats. Meanwhile, nature-based solutions are emerging as viable alternatives. One of these solutions is the use of salt marshes as coastal protection in front of dikes instead of heightening the dike, which could potentially lead to a more cost-effective solution. A salt marsh vegetated foreshore not only dampens the incoming waves but also adapts to the advancing waters of the sea level rise by trapping sediment.
This study’s main objective is to assess the efficacy of salt marshes in mitigating wave run-up and overtopping on a real-scale sea dike with a vegetated foreshore.
To carry out these large-scale experiments were carried out at the Deltares Delta Flume. Experiments were carried out for low (0.75 m), medium (1.5m) and high (2.5m) water depths above the foreshore, designed to simulate the extreme storm scenarios experienced by the Friesland dikes in the northern Netherlands. In addition to these conditions, the tests were performed for three different qualities of vegetation, good damaged, and mowed vegetation. First, the experiments ran for a fully vegetated foreshore, then after several runs the vegetation was assumed damaged as an important part of the biomass had eroded. Finally, the vegetation is mowed to leave a bare foreshore which is the baseline scenario.
The acquired run-up results are compared with empirical equations from literature. In addition, the results were compared with those of similar research on salt marshes. Finally, the other important objective of this study is to quantify the reduction in wave loads according to vegetation conditions by introducing certain damping ratio parameters.
To measure the important parameters for the completion of this study, three wave gauges offshore and three wave gauges close to the toe of the dike were used for the measurement of the wave characteristics. For the wave run-up a camera was placed above the dike slope to capture the run-up events over time, and at the same time a LIDAR laser scanner recorded the same slope to collect data on run-up and overtopping.
From the wave analysis, the spectral parameters offshore and at the toe of the dike were calculated. From this, it was possible to have a first estimate of the wave attenuation by comparing the incident significant wave height at these two locations. The results reveal a 14 to 30 % decrease in wave height for low conditions. For medium and high storm conditions the attenuation was decreased to a range between 5 to 15% and 4 to 19% respectively.
The video process run-up measurements were in good agreement with the literature with RMSE = 0.18 - 0.19 m. An additional method was used to validate the results of the run-up. The detection of the run-up was completed visually, by tracking the waves that exceed the markers on the slope, for part of three experiments to compare their signal with the signal derived from the video process. The bias between the signals ranged from 0.017 to 0.022 m, indicating a strong agreement between the methods. One of the most important findings from this study is that the reduction in run-up is not directly attributed to the presence of vegetation itself, but rather to the role played by the significant wave height at the toe of the dike. The run-up was reduced between 2 and 16% for low storm conditions and a reduction between 4 and 24% for medium storm conditions, with an average value of 10.3%. At the same time, the reduction of run-up from damaged vegetation to fully vegetated foreshore is up to 9% with an average of 7.7%. The laser scanner was also used to measured the wave run-up. The signal obtained from the laser is compared with the signal of the visual detection method and reveals a bias between 0.032 and 0.037 m. The run-up 2% results were also compared with the same results from the video camera, revealing a 0.14 m (7%) deviation which may be due to the accuracy of the laser.
The laser scanner also obtained the overtopping results using the virtual overtopping method. From this method, the virtual volume and the virtual overtopping discharge can be calculated and then compared with the equations from the literature. The comparison reveals a strong agreement between the calculated and predicted values, which proves that the equations predict accurately the overtopping discharges for the case of a living dike. For low storm conditions, a decrease of 2 to 50 % of the maximum virtual overtopping volumes is possible, while for medium conditions a maximum volume decrease of 5 to 54% according to the crest height. For the highest storm conditions, this volume decrease is calculated to be between 20 to 28%.
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In the field of offshore engineering, subsea rock installation has emerged as a pivotal technique. As offshore operations extend to greater water depths, the deployment of a versatile fallpipe has become a cornerstone for precise rock particle placement. A comprehensive determination of the overall rock material volume required for installation entails accounting for geometric factors, operational losses, and seabed displacements. To ensure effective project management and cost estimation, a precise grasp of volume loss during installation proves indispensable. Against this backdrop, the current thesis delves into the intricate domain of volume loss stemming from rock penetration within sand substrates.

The core endeavor of this research is the development of a model that quantifies volume loss due to rock penetration within sandy seafloors. The investigation combines theoretical modeling with empirical validation through lab testing. Through analysis, it is revealed that the complex behavior of granular media necessitates an in-depth understanding of the theory, together with assumptions and simplifications to create an effective penetration depth model. The literature study outlines the various forces exerted on a rock as it impacts the seafloor and commences its penetration into the sand. Within the summation of forces, one component to consider is the bearing force exerted by the sand. This force can be calculated using two distinct approaches: the Terzaghi formula for shallow foundations and the Brinch Hansen formula, also applicable to shallow foundations. In this thesis, both formulas are employed to assess their applicability to the dynamic penetration of spherical particles in a sandy seafloor. Once these forces have been aggregated within the equation, two distinct methods to resolve the equation and determine the penetration depth of a spherical rock in sand are employed. The first method is rooted in the principle of a work-energy balance, stating that the cumulative work done by the sum of forces matches the change in the rock's kinetic energy. In contrast, the second method is based on the impulse-momentum balance, underlining the concept that the summation of forces multiplied by a specific duration in time, is equivalent to the change in the rock's momentum during that defined time interval. The work-energy method is preferred over the impulse-momentum method because of the specific objective of the single stone model, which centers on determining penetration depth, a distance measurement. The work-energy method inherently incorporates the distance variable within its formula, aligning directly with the desired outcome. In contrast, the impulse-momentum method necessitates calculating penetration depth by multiplying time with velocity for each discrete time step, introducing a less efficient computational process. \\
Following a comparison between the results derived from laboratory tests and the computed penetration depths using both the Terzaghi and Brinch Hansen-based models, it becomes evident that the Terzaghi formula offers a closer approximation to the behavior of the bearing force.

Further insights are drawn from multi-stone penetration testing, wherein assumptions and simplifications are strategically employed. The intersection of the multi-stone model with a three-dimensional normal distribution delineates the positions of rocks post-fallpipe discharge, bridging theoretical modeling with practical subsea rock installation scenarios. Although a somewhat unrealistic scenario of centric rock-rock collisions and perfect stacking of rocks on top of each other is assumed, the model provides a valuable worst-case scenario in terms of volume loss.

Though the model's validation is confined to sandy seafloors, its implications extend beyond. The study underscores the need for real-world data integration to refine the model. ... Read more

Wave overtopping of coastal structures is generally expressed in terms of average discharge and maximum overtopping volume. While substantial research can be found on the relationship of such variables with incident spectral characteristics and other geometrical dimensions, limited research has been done to identify the conditions for which severe individual overtopping events occur. The objective of the present work is to further investigate the statistical dependencies between individual overtopping volumes and incident wave characteristics and to identify the conditions which result in maximum overtopping events. To this aim, we statistically analyse timeseries of waves and overtopping events for the case of a vertical wall breakwater on a horizontal bed under non-breaking wave conditions. The timeseries are generated using a validated numerical model for 6 sets of boundary conditions. The analysis of the data shows that, among the examined variables, the incident wave crest level at the toe of the structure has the highest rank correlation with the individual overtopping volumes. Conversely, the incident wave heights show a lower rank correlation while the wave periods show no correlation at all. Additionally, by leveraging the tool of copulas we find that the incident wave crest levels have strong upper tail dependence with the individual overtopping volumes while the wave heights show no tail dependence. Subsequently, we examine possible dependencies with the wave group periods and wave group energy. We find that a moderate correlation exists between wave group periods and overtopping volumes but no upper tail dependence. Moreover, our results show that the fraction between the wave group energy and the group period has a high correlation and upper tail dependence with the overtopping volumes. Finally, we discuss possible practical applications of our findings as well as points for future research. ... Read more

Following significant physical and economic damage associated with large tsunami disasters, this research assessed the efficacy of both nature-based and man-made tsunami mitigation measures. With an expected increase of the population living in tsunami-prone areas, it is critical to develop a better understanding of tsunami engineering.

To achieve this, a series of large-scale tsunami modelling experiments was carried out at HR Wallingford. The experiments utilized the Tsunami Simulator and involved generating a set of 20 trough- and crest-led waves with periods ranging from 20 to 240 seconds in a divided flume with a length of 100 meters.

The effectiveness of nature-based mitigation techniques was assessed through the implementation of land cover roughness onto a sloping bathymetry. The man-made measures included the in-situ construction of a scaled-down offshore breakwater similar to the Kamaishi breakwater. The study involved a comprehensive assessment of multiple factors, including run-up height, delay of inundation, pressures exerted on the breakwater, and a stability analysis of the breakwater.

In addition to determining the effect of roughness on tsunami-like wave run-up, the results were compared to available predictor equations. The empirical relation defined by McGovern et al. (2018) is found to be suitable for the prediction of waves with a period of 50 seconds or less. On the other hand, the predictive equation proposed by Wronna et al. (2021) displayed a similar trend but significantly overestimated the dimensionless run-up parameter.

The results demonstrate that nature-based run-up mitigation strategies are most effective for waves with laboratory periods less than 60 seconds. However, nature-based mitigation measures provide more promising results in terms of inundation delay. The offshore breakwater was found to be the most effective measure against tsunami run-up, significantly reducing the dimensionless run-up parameter.

Man-made mitigation measures are found to be the most effective solution for tsunami mitigation. However, not all coastal communities possess the financial resources to construct an offshore breakwater. In such cases, a combination of nature-based and man-made measures with robust early warning systems and evacuation strategies should be considered. This balanced approach maximizes coastal resilience given financial constraints and geographical circumstances. ... Read more

Crownwalls are often placed on top of vertical composite breakwaters to reduce overtopping. Adding a seawards facing overhang at the top of crownwalls has successfully reduced overtopping even further without increasing the freeboard of the crownwall. Crownwalls with a fully curved (FC) face are most often used in seawalls where they are subjected to wave load by breaking waves. However, it has recently become of interest to explore the possibility of using the fully curved shape for vertical breakwater crownwalls instead of a crownwall with a recurve (R). This thesis aimed to investigate further the wave loading by non-breaking waves and the dynamic response of a FC crownwall on a vertical breakwater through an offline one-way coupling of a CFD-generated pressure-time series and a FEM model in Diana FEA. The results were then compared to those of other studies on the wave load and dynamic response of a R crownwall. Pressure-time series from CFD numerical simulations of three wave states (W5, W6 and W7) were analysed to determine how the structure was loaded. The analysis of the pressure-time series showed that for the smallest wave state, W5, the pressure distribution at the moment of maximum total force was trapezoidal. However, for the larger wave states, W6 and W7, there was a pressure peak at the top of the curve of the crownwall due to the C-CI phenomenon. Waves with impulsive pressure and force impacts were found in all wave states, and the pressure and force impulses were much less variable than the maximum pressure and force values. Dynamic nonlinear analysis showed the fully curved crownwall cracks under wave load by wave states 6 and 7. Cracking occurs at the centre of the curve, where the largest tensile stresses are located. Comparing the results to those of the recurved crownwall, it was concluded that the fully curved crownwall was less favourable than the recurved crownwall. For the same wave states, the FC crownwall was subjected to larger wave forces than the R crownwall, which led to a larger bending moment exerted on the structure. The FC crownwall is also larger than the R crownwall, with the same freeboard, and therefore requires more use of concrete. Due to the shape of the FC crownwall, the maximum tensile stresses are 2.5-3 times higher than those in the R crownwall. More use of steel reinforcement bars is therefore also needed. It would, however, be interesting to investigate further FC crownwalls on vertical breakwaters with different geometries, e.g. radius of the curve, to see if their design can be improved. The applicability of the extended Goda method for calculating static wave load on recurved crownwalls was also investigated for the FC crownwall. It was found that for waves with wave steepness less than 6% and vertical wave velocity less than 2.4 m/s, the calculation method could be used for a preliminary design. However, the dynamic response of the structure must be addressed in the final design, e.g. with a dynamic analysis or the DAF method. ... Read more

During ‘float-out’ installation of export cables, the cable is pulled to shore while floating, supported by inflatable floaters. Understanding the hydrodynamic behaviour of these cable-floater-systems (CFS’s) is important, to be able to relate the hydraulic environment to the cable stresses and determine the maximum allowed hydraulic conditions for these procedures. The software package OrcaFlex has appeared to be insufficient and gives untrustworthy results, namely really high peak axial tension and compression forces in the cable. In this research, the CFS is studied with three methods to explain these extreme forces and improve the CFS design.

With the first method, the CFS is modelled as an Euler Bernoulli Beam (EBB) on a continuous elastic foundation. In this analytical model, straight, accessible formulas showed that the CFS is a really stiff dynamic system, dominated by the buoyancy stiffness of the floaters. As a consequence, the natural frequencies are relatively high and in the same range as the wave frequency spectrum. This lead to this research’ hypothesis that the extreme, internal stresses in the cable-floater-system are caused by resonance taking place between the external wave forcing and the CFS itself.

With the second method, the CFS is modelled with the finite-element-method. In the vertical direction, the natural frequencies are again in the range of wave frequencies and are barely increasing for higher modes. The explanation for both of these observations is given by the local oscillations in the modal shapes occurring in between floaters. A parametric study on floater spacing shows that the length of these oscillations is determined by the floater spacing. Since the original floater spacing is small, it causes small wave lengths and high frequencies.

With the third method, dynamic analyses are done in OrcaFlex with cases varying in wave frequency and presence/absence of a current in order to test the hypothesis of resonance. It can be concluded that the CFS is really sensitive to Stokes drift when an other current is absent. This causes a different positioning of the CFS and a mean axial tension in the cable decreasing in wave direction. Consequently, the hydrodynamic behaviour of the CFS is changing throughout its length. Near the cable end most closest from where waves originate, the Stokes drift induced axial tension causes the CFS to be unable to move vertically in waves. Consequently, no interaction between wave and CFS, necessary for resonance, is taking place. Near the other cable end, the mean axial tension is close to zero and the most extreme axial forces occur for resonance conditions with wave frequency equal to natural frequency.

The results do not fully confirm the hypothesis, but do give answer to the first part of the research question. Regarding the second part on the optimisation of a CFS design, one could focus on eliminating the chance on the occurrence of resonance, by increasing the floater spacing or decreasing the floater dimensions, or focus on decreasing the impact of resonance by increasing the floater’s drag area in vertical direction. ... Read more

The Falsterbo Peninsula is a low-lying area that provides a home to 7,000 residents, as well as various bird and vegetation species. To protect this densely populated area, the municipality was granted a permit to build flood protections. As part of the strategy, the dune system in the study area will be used as natural barriers against storm surges. Despite being part of the protection strategy, the strength of the dune system in safeguarding the hinterland has not been assessed. This had led to the objective of this thesis, which aims to evaluate the strength of the current dune system. To achieve this objective, the following research question were formulated:

To what extent does the dune system on the Falsterbo Peninsula contribute to safeguarding the hinterland against the impact of historical storm conditions?

To seek answers to this question, the research was didvided into three parts. The first part of the methodology involves collecting the environmental data such as the wind, water level and wave data. Additionally, the data on the dune's morphology was collected during the field work. The second step of the methodology involves identification of extreme conditions within the time series spanning from 1959 to 2022. Considering the complex interaction between the waves and water levels, the extreme conditions were identified based on the combined effect of the two variables, which was represented in the total water level (TWL). The sampling method was based on the peak over threshold method applied to the time series of TWL. The choice of the threshold value was based on the scenarios of potential coastal flooding in the study area. The largest storm surge, the 1872 storm, was included in the analysis to evaluate its impact on the present dune system.

The dune erosion due to the selected extreme conditions was determined in the last part of the methodology. Two morphological models, the XBeach model and the storm impact model were employed to estimate the dune erosion in four transects withing the dune system.

The obtained dune erosion was expressed as a fraction of the available dune volume. The maximum dune erosion was found in the transect situated at the far-right end of the dune system when facing north. The maximum dune erosion under extreme conditions in the period 1959 to 2022, estimated by the XBeach and the storm impact model are 7.67% and 32.89%, respectively. Based on these results, it can be concluded that the present dune system is strong enough to provide protection to the hinterland against the impact of extreme condtions.

For the 1872 storm, the XBeach model estimated erosion percentage of 67.89%, whereas the storm impact model estimated more than 100%. This indicates that in the event of recurrence of the 1872 storm, a dune breach could be expected. While the 1872 storm may not be the design storm condition for the dune system, the storm impact model result highlights the need of reevaluation of the formulation of potential plans to reinforce the dune system.

For future studies, it is strongly recommended to establish a long-term monitoring program for the dune system on the Falsterbo Peninsula. The obtained dune erosion data can be used to calibrate the morphological models to enhance its accuracy in the predictions. Additionally, dune recovery data can aid in the understanding of the dune system as a whole. ... Read more

Understanding the factors that drive extreme water levels is key to an accurate assessment of flood hazard. The city of Venice has always been affected by flooding due to extreme water levels. In this study, we examine the factors driving and influencing extreme water levels in the Venice lagoon, aiming at deriving accurate extreme water level estimates in the Venice lagoon.
Due to the shallowness of the Venice lagoon, extreme water levels are influenced by both atmospheric forcing (surge) and water level of the lagoon (tide and bottom level) and interactions between these two. Furthermore, these extreme water levels have been changing over time due to variations in the bottom level. These variations are reportedly due to local (anthropogenic and natural) subsidence and sea level rise. In this study we resort to the available long-term water level observations of the Punta della Salute tide-gauge. Given the effects of subsidence and sea level rise in these data, we start by homogenizing the data by removing these trends and jumps from the time-series. Using the homogenized time-series, we study the influence of the dependence between tide and surge components on the extreme water level estimates. Finally, we quantify the effect in the estimates of modelling this dependence in the extreme value models.
To homogenize the data and better understand the underlying trends, a time-series analysis was performed on the time-series of water level observations. Mann-Kendall tests for monotonic trend were performed, followed by an analysis using changepoint detection methods. Changepoint detection was performed using the RHtest and BEAST methods on the Punta della Salute time-series as well as time-series from neighbouring tide-gauge stations. Ultimately trend decomposition using the BEAST method was used to detrend and homogenize the Punta della Salute time-series.
After detrending, the tide and surge components were separated using tidal harmonic analysis and reconstruction. The relationship of these now separated components was quantified during extreme water levels using the Pearson r correlation and the Kendall τ rank correlation. This relationship between tide and surge was described using copulas to estimate extreme water levels. Different copula variants were evaluated and extreme water level estimates derived using copulas that describe dependence were compared to extreme water level estimates using a copula that describes tide and surge as independent components. Lastly, these were compared to those derived from univariate extreme value analysis to assess the influence of separation of tide and surge components combined with copulas as opposed to a more traditional univariate extreme value analysis.
The main conclusions of this study are as follows.
• The water level observations of the Punta della Salute tide-gauge are indeed affected by jumps and trends due to subsidence and sea level rise. These can be successfully removed using the applied techniques.
• There is a clear dependence between tide and surge in the Venice lagoon, with lower tide levels leading to higher surge levels. The non-inclusion of this dependence (by assuming independence) in the combined analysis of tide and surge signals to drive total extreme water levels leads to an overestimation of the total water level extremes.
• Extreme water level estimates from the combined analysis of the tidal and surge signal are higher, but compatible with those from the analysis of the total water level signal (without separation of tidal and surge signal). This gives confidence in the combined analysis accounting for the dependence between the signals and allowing for a further application of the models to account for projected climate changes.
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Breakwaters used to protect harbours and coastal areas worldwide are one of the most common coastal structures. The complexity of the physical processes associated with the design has led to the development of many empirical formulas while a standardized method for the selection of breakwaters’ design parameters in the EU does not yet exist. The most common approach to design such a structure nowadays entails using information and recommendations from design manuals and guidelines such as PIANC and the Eurotop Manual. A new Eurocode 1 which includes specific considerations for coastal structures such as breakwaters is in the development process. This study aims to compare the PIANC method with the method to derive actions/loads included in the Eurocode proposal prEN1991-1-8. To do so the following research question has been formulated:
“What differences between the PIANC method and the method proposed by the new EUROCODE in the design of a vertical wall breakwater can be identified, using the new breakwater at the Port of Genoa as a case study?“
As mentioned in the question, a case study is used. The Port of Genoa, one of the biggest ports in Italy plans to construct a new vertical wall breakwater. An initial design is openly available along with wave and water level data. This design is assessed using both methods and is further optimized. The aim is to gain insights into the differences between the PIANC and the new method.
At first, the failure mechanisms of such a structure are defined along with the safety factors and parameters. The data required to perform such an assessment is also an important aspect of the exercise. Most of the data are openly available during the consulting phase for the new breakwater in Genoa. In cases where extra data were necessary, they were based on the literature or on reasonable assumptions.
Based on the failure mechanisms and the retrieved data, the initial breakwater cross-section was assessed. The assessment both with the PIANC method and the new Eurocode proved that this design is sufficient and can be further optimized to decrease its costs. A high-level optimization is also conducted as part of this study in order to better understand the differences between the two methods. It can be concluded that the differences lay more in the method than in the actual result. For example, the proposed Eurocode creates a stable theoretical framework of how to choose a return period. The actual number may be very similar to the one that one would have used either way, but the choice can be argued in a better way.
On the other hand, the use of the new Eurocode revealed some problems and inconsistencies in the document which is confusing in certain parts. In addition, the new Eurocode which among others aims at standardizing the design process. However, parts like the combination of wave and water level actions and the choice of return period for the two main limit state functions are relatively clearer providing a solid base.
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The purpose of this report is to design a wave energy converter, in particular a U-oscillating water column (U-OWC), to maximize energy conversion in the low wave energy environment of Gwadar, Pakistan. At present Pakistan’s 1000km coastline is largely undeveloped and the county is devoid of any wave energy harnessing devices or studies. However, recent years have seen an influx of Chinese investment being made under the China-Pakistan economic corridor agreement, which is stimulus for the near future construction of a large rubble mound breakwater to shelter an assistance vessel basin in the city of Gwadar.

Typically, a WEC is not feasible in low incident wave energy environments because the economic return from minimal energy generation cannot offset the capital cost of the structure. However, the opportunity in Gwadar is unique in the sense that a substantial investment is already envisaged for the creation of a breakwater. Therefore, it is worth investigating if re-designing this structure with vertical caissons embedded with U-OWC chambers is feasible. In this way, the structure can fulfill the dual role of sheltering the assistance vessel basin against wave attack, and produce renewable energy over its design life.

To assist with this task, existing data and methods available in literature along with numerical codes have been utilized. A 10 year SWAN hindcast has been performed, the result of which have been condensed into 60 representative design sea-states on the basis of which the U-OWC chamber geometry
and turbine configuration have been optimized. This was achieved by employing a random sampling technique to determine which combinations produce the most power and by identifying the ideal turbine
operating revolutions for each sea-state.

Next, the approximate cost of the caisson breakwater integrated with U-OWC chambers is calculated and compared against the currently proposed rubble mound design. It is expected that despite an attempt to maximize the energy generation by the device, its levelized cost of energy will be high, given
the low wave energy in the region. Nevertheless, if the design proves cheaper than its rubble mound counterpart, it goes to show that wave energy converter can be deployed in low energy environments provided an opportunity exists where they can be integrated into proposed marine structures. This will
be an important finding, considering that the majority of the global coastline is subjected to moderate to low incident wave energy, and neglected from WEC deployment considerations. ... Read more

The authorities of the Port of Genoa have requested the construction of a new vertical breakwater for the Sampierdarena canal, as well as the subsequent demolition of part of the existing breakwater. The reason for this project is the need to expand the size of the canal, to allow larger vessels to safely use it. A choice is made for a vertical-type breakwater, i.e., a concrete caisson placed on top of a rubble mound foundation. The main goal of this thesis is to provide a preliminary probabilistic design of a cross-section of the new breakwater at the port of Genoa by applying a vine-copula model for the wave climate in a Monte-Carlo simulation.

All possible regular vines were obtained by permuting the six equivalence classes for 5 nodes. 13 different copula types and all 480 possible 5-node regular vines were fitted on extreme wave data. The best vine-copula was selected based on the lowest AIC value. The performance of the vine-copula model was compared to that of an independent model.

Offshore waves were transformed to onshore waves by applying SWAN. A MATLAB loop-function was made to automate this process. Prof. Goda's method was used for determining the wave-induced loads on the vertical breakwater. 10 failure modes were considered in total. A Monte-Carlo simulation was built in MATLAB. Using the Monte-Carlo simulation, several dozen designs were tested in an iterative matter to find an optimized design. The proposed preliminary cross-sectional design fulfilled all design criteria.
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Wave overtopping, in which a wave washes over the crest of a dike and damages its inner slope, is one of the many mechanisms that is found to be responsible for dike failures. As these dikes are generally covered with grass, insight into the erosion resistance of these grass covers against wave overtopping is desired. To assess the performance of dikes against wave overtopping, various concepts exist, such as the widely used cumulative overload method. However, these concepts lack a thorough understanding of the physical mechanisms at play during grass cover failure as a result of wave overtopping. Furthermore, the methods are generally not time-efficient and are labor intensive, leading to high costs. Therefore, a time-efficient and predictive method is desired that is based on the physical mechanisms of grass cover failure.

The grass pull device, which is used extensively in this thesis, may serve as an alternative for the existing assessment methods. The device, which is reminiscent of a tensile test used in mechanical sciences, is able to exert various load mechanisms on the grass cover. In this thesis, the grass pull device is used to study various aspects of grass cover failure. Special attention is given to the influence of cyclic loading on the grass cover. Additionally, material properties have been derived that may serve as input for numerical grass erosion models. Furthermore, the influence of grass roots, subsoil type and pore saturation on the failure mode of grass covers was investigated.

The results of this study showed a continuous growth of deformation and a decrease in stiffness when the grass cover is loaded cyclically. The behavior of grass during cyclic loading was found to be comparable to other composite materials, such as fiber-reinforced plastics. The material properties Young's and shear modulus were derived. The Young's moduli were found to be slightly overestimated, while the shear moduli were found to be comparable to what may be expected from literature. Differences in grass cover properties on different subsoils were identified, showing that grass covers on clay are generally better at resisting deformation, while having a brittle failure mode. For grass covers on sand, a large spread was observed and the material was found to deform easily, while still providing resistance at large deformations.

Based on the findings of this study, recommendations were made to improve the grass pull device. It was found that the grass pull device was successful in providing insight into various physical processes. Whether the grass pull device will be able to capture all relevant erosion mechanisms remains questionable, but it has proven to be a successful addition to existing assessment methods.
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The design of hydraulic structures like breakwaters and crest walls is often based on empirical formulations, physical models test, numerical models and a fair amount of expert judgement. Each technique has its own pros and cons. The main limitation of the empirical formulas is that often they have to be applied outside their range of validity. Physical modelling also has its own shortcomings. When breaking waves hit the structure, the location of the maximum pressures is still not well known due to the high spatial variability. By using an array with low spatial resolution, the forces estimated in the physical ume will usually underestimate to some extent the actual forces experienced by the wall (Ramachandran et al., 2013). In the last decades, numerical modelling has become an attractive alternative in simulating wave-structure interactions. Nevertheless, estimating loads on crest walls in the numerical ume is still at its early stages. On that account, the present work validates the prediction of wave induced forces on the front face of crest walls on top of rubble mound breakwaters in CoastalFOAM. A scale model of the Holyhead breakwater, located in Wales, is used. The key validation topics are the reproduction of wave-structure interaction when heavily breaking waves reached the wall, the evaluation of the ventilated boundary condition implemented by Jacobsen et al. (2018), the porous ow inside the armour layer formed by Tetrapods units and whether the simplication of not using a turbulence model, as done by Jensen et al. (2014) and Jacobsen et al. (2018), is also valid under heavily breaking waves. Four validation cases were used to test the capabilities of the numerical ume. The results conrm that it is possible to accurately reproduce the wave conditions and the wave induced forces from a physical modelling campaign. Overall, the CoastalFOAM model is able to capture the shape and the order of magnitude of the force events. A calibrated model predicts the highest wave induced forces (forces with an exceedance probability of 0.4% and 0.1%) with errors lower than 20%. Moreover, the results indicate that for practical applications it is not essential to include a turbulence model in the numerical ume to obtain reliable forces on the front face of crest walls for dierent wave conditions. Another outcome of this study is that the implementation of the ventilated boundary condition is required in the interface between water surface and structural elements to mimic accordingly the air-water mixture when the structure is subjected to a heavy wave attack. Nonetheless, there is still room for improvement in this area, where a better understanding of this boundary condition and of the air entrapment during wave-structure interaction needs further research. Despite the large computational time required by the numerical ume when large wave trains must be simulated, a CFD model during design stages of breakwaters and crest walls provides higher spatial and temporal resolution of the wave induced pressures exerted on the wall than a physical test. Therefore, a better picture of the forces and pressure distribution in the front face can be obtained. ... Read more

Flooding has been a serious risk to the old-town of Venice, its residents and cultural heritage and continues to be a challenge in future. Despite this existence-defining condition, limited scientific knowledge on flood hazard and flood damage modelling of the old-town of Venice is available to support decisions to mitigate existing and future flood risk. Therefore, this study proposes a risk assessment framework to provide a methodical and flexible instrument for decision-making for flood risk management in Venice. It uses a state-of-the-art hydrodynamic urban model to identify the hazard characteristics inside the city of Venice. Exposure, vulnerability and corresponding damages are modelled by the multi-parametric, micro-scale damage model INSYDE transferred and adapted to the specific context of Venice with its dense urban structure and high risk awareness. A set of individual protection scenarios is implemented to account for possible variability of flood preparedness of the residents. The developed risk assessment framework was tested for the flood event of 12 November 2019. It was able to reproduce flood characteristics and resulting damages well. A scenario analysis based on the meteorological event like 12 November 2019 was conducted to derive flood damage estimates for the year 2060 for a set of sea level rise scenarios in combination with a (partially) functioning storm surge barrier MOSE. The analysis suggests that a functioning MOSE barrier could prevent flood damages for the considered storm event and all sea level scenarios almost entirely. It could reduce the damages by up to 34 % for optimistic sea level rise prognosis. Contrary, damages could be 1.08 to 5.92 times higher in 2060 compared to 2019 for a partial closure of the storm surge barrier depending on different levels of individual protection. ... Read more

At the moment, the world is at the verge of an energy transition. One of the most promising green resources is solar energy, which is a rapidly growing market. However, to fully use its potential of economy of scale, the application of offshore floating solar should be explored. A promising option is the use of a flexible type of Very Large Floating Structures (VLFSs), which are called Very Flexible Floating Structures (VFFSs). They are characterised by their large length to height ratio compared to rigid bodies and depending on their material properties have a hydroelastic response to the incident wave. In the late 1990s, a lot of research has been done on VLFSs by Tsubogo and Okada (1998) who derived an analytical dispersion relation assuming a zero­draught structure. However, only recently, Schreier and Jacobi (2020b) did experimental research on VFFSs in a towing tank at the Delft University of Technology, as little is still known about flexible structures. This report focuses on a numerical alter­ native that covers both VLFSs as well as VFFSs using a Finite Element Method (FEM) Fluid Structure Interaction (FSI) model which has been built based on potential flow to model the fluid and a dynamic Euler­Bernoulli beam that represents the floating structure using the Julia package Gridap. One of the main advantages is that the zero­draught assumption is not necessary and, therefore, structures with larger draughts can also be modelled. Next to this, the numerical model is able to cope with irregular shapes, for which no analytical method yet exists. The model is built such that it can handle 2D as well as 3D domains. A 2D analysis has been made to understand the influence of hydroelastic wave deformation of the incident wave, in terms of wavelength dispersion as well as amplitude dispersion on floating structures. To verify the model, the numerical results were compared to the analytical solution and experimental research in a towing tank, which showed accurate results. Test runs were set up that mimicked the towing tank set­up and a full­scale solar park. Furthermore, a sensitivity study was executed that shows the limits of the flexible domain and to see in which cases significant (>1%) hydroelastic wave deformation would occur using governing mean and extreme ocean waves, as well as a typical lake wave. Finally, the influence of the draught of the structure was examined. This report provides a good overview of when wave deformation should be accounted for in terms of bending rigidity and density. Confirming existing theory, it was found that the stiffness of the VFFS causes wave stretching and the draught of the structure influences the extent of wave shortening. It was also found that significant wave deformation will not occur for ocean waves as the required stiff­ ness is beyond existing materials. For extreme ocean waves, there is even no dispersion at all. As the wave frequency increases, the hydroelastic interaction gets stronger. The typical lake wave showed to be well within the flexible regime and also showed significant dispersion with realistic material parame­ ters. The numerical model is able to cope with large draught scenarios which lead to wave shortening, which in its turn leads to wave focusing. Ultimately, the numerical model showed to be a good alternative to existing methods to investigate the behaviour of VLFSs outside the floating solar domain, where one could think of ice floes, floating islands or floating airports. ... Read more

Offshore and coastal infrastructure must be designed to withstand loading conditions that among others arise from extreme environmental conditions. Physical processes such as storm surges, tides, currents, and waves play an important role in the design of these structures. Several variables characterize the relevant physical processes (e.g. significant wave height, mean wave period, water level, wind speed) and a thorough analysis of these variables is required when dealing with offshore and coastal dynamics, durability, and reliability assessment.

Traditionally, a critical loading condition is defined by characteristic values of environmental variables that are determined based on the highest loads previously experienced. Modern design methods seek to derive loads that correspond to specified reliability by considering the frequency of a specific loading magnitude.Traditional design approaches do not take into account the interrelations and dependencies among the variables of interest. Hence, wrong representations of the physical processes and unnecessary conservative representations of the design loads might occur. This may severely limit their effectiveness and can lead to expensive and inappropriate decisions. Multivariate frequency analysis approaches currently receive much attention within the academic community, however, advanced statistical concepts such as regular vine copula are slow in being taken up by engineering practice.
This thesis presents a practical assessment and further development of a vine-based methodology, used for the derivation of design values, in continuation of the work performed by Sell´es Valls (2019). Regular vine copulae are advanced statistical models for high dimensional distributions using (conditional) bivariate copulae as building blocks. This study contributes to bridging the gap between the academic community and engineering practice on one hand, and on the other hand, contributes to a better understanding of the potential added value of incorporating dependence information in the design process of coastal and offshore infrastructure. It has a conceptual point of view where the concept of using dependence information by applying advanced statistical techniques is explored and the required adaptations throughout the entire design process are evaluated.
In this research, it is found that the multivariate vine-based methodology can be successfully incorporated in the design process of a breakwater structure, and on average results in minimal required dimensions of elements of the cross-sectional design that turn out to be smaller and the corresponding costs up to 25% lower compared to the univariate traditional approach. This is realized by adapting the framework enabling an offshore-nearshore transformation of the wave conditions using SWAN software. Furthermore, the theoretical framework is extended by introducing Kendall’s measure providing a suitable definition of the critical region from which the critical loading conditions can be obtained. It is concluded that the vine-based approach could act as a tool providing extra information about the behavior of the system and insights on the degree of conservatism of the traditional approach. The considered role of the vine-based methodology in the design process of a breakwater structure (or coastal infrastructure in general) is to provide the practitioner with additional insights supporting the traditional design approach and possibly optimizing the design.
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Lighthouses have guided seafarers for centuries and still play an essential role in navigating marine vessels and bringing them to safe harbours. With climate change, the already harsh ocean environment may become more severe. It is expected that future wave conditions can compromise the structural integrity of the lighthouses with their violent impact. The hydrodynamic processes of wave transition before, at, and after the point of impact are complex, highly non-linear, and turbulent. There is no exact description of these processes. Therefore, there is a need to further study them in order to better understand the broken wave load and its effect on the structural integrity of lighthouses. From the very beginning, wave breaking processes are complex. For instance, prior to impact with shoal-mounted cylindrical structures, waves undergo a rapid transition from deep to shallow water. During this transition the waves shoal, start to break, and once broken they hit the cylindrical structure of the lighthouse. It is therefore necessary to approximate the hydrodynamics. Since, it is difficult to measure the processes using only physical models. Consequently, this research focuses on broken wave load analysis using a process-based numerical model. An approach widely used for analysing wave forces on slender cylindrical structures is calibrated for breaking wave loads. Critical factors for determining these loads are the curling factor and slamming coefficient. However, there is still no scientific consensus regarding the exact values for these parameters. Further research, like this study, can help in determining these values. The main goal of this thesis is to assess the pressure distribution on the structure and quantify the values for the curling factor and slamming coefficient for a shoal-mounted slender cylindrical structure. The STORMLAMP (STructural behaviour Of Rock Mounted Lighthouses At the Mercy of imPulsive waves) project's experimental data of Dassanayake et al. (2019) is used as a benchmark case to validate the proposed computational framework. In addition, the performance of two different Volume of Fluid methods, isoAdvector and MULES, are assessed. This study demonstrates that the curling factor and slamming coefficient are significantly different for the broken wave load compared to the breaking wave load. The curling factor is found to be twice as large in the case of a broken wave load. On the other hand, the peak slamming coefficient is five times smaller. Moreover, the isoAdvector solver in comparison to the MULES solver produces results that better resemble the benchmark case results. Although the two solvers do not produce the same peak impact forces, they do both produce similar values for the aforementioned critical parameters. Also, it was found that the isoAdvector solver is faster and more efficient than the MULES solver in the case of a 3D simulation. From the results it can be concluded that the chosen numerical framework represents the benchmark case well, and that the methodology used for breaking wave loads can be applied for broken wave loads with adjustment of the curling factor and slamming coefficient. ... Read more