Currently, the accurate prediction of the impact of an extreme wave on infrastructure located near shore is difficult to assess. There is a lack of established methods to accurately quantify these impacts. Extreme waves, such as tsunamis generate, through breaking, extremely powerful hydraulic bores that impact and significantly damage coastal structures and buildings located close to the shoreline. The damage induced by such hydraulic bores is often due to structural failure. Examples of devastating coastal disasters are the 2004 Indian Ocean Tsunami, 2005 Hurricane Katrina and most recently, the 2011 Tohoku Japan Tsunami. As a result, more advanced research is needed to estimate the magnitude of forces exerted on structures by such bores. This research presents results of a numerical model based on the Smoothed Particle Hydrodynamics (SPH) method which is used to simulate the impact of extreme hydrodynamic forces on shore protection walls. Typically, fluids are modeled numerically based on a Lagrangian approach, an Eulerian approach or a combination of the two. Many of the common problems that arise from using more traditional techniques can be avoided through the use of SPH-based models. Such challenges include the model computational efficiency in terms of complexity of implementation. The SPH method allows water particles to be individually modeled, each with their own characteristics, which then accurately depicts the behavior and properties of the flow field. An open source code, known as SPHysics, was used to run the simulations presented in this thesis. Several cases analysed consist of hydraulic bores impacting a flat vertical wall as well as a sloping seawall. The analysis includes comparisons of the numerical results with published experimental data. The model is shown to accurately reproduce the formation of solitary waves as well as their propagation and breaking. The impacting bore profiles as well as the resulting pressures are also efficiently simulated using the model.

Currently, the accurate prediction of the impact of an extreme wave on infrastructure located near shore is difficult to assess. There is a lack of established methods to accurately quantify these impacts. Extreme waves, such as tsunamis generate, through breaking, extremely powerful hydraulic bores that impact and significantly damage coastal structures and buildings located close to the shoreline. The damage induced by such hydraulic bores is often due to structural failure. Examples of devastating coastal disasters are the 2004 Indian Ocean Tsunami, 2005 Hurricane Katrina and most recently, the 2011 Tohoku Japan Tsunami. As a result, more advanced research is needed to estimate the magnitude of forces exerted on structures by such bores. This research presents results of a numerical model based on the Smoothed Particle Hydrodynamics (SPH) method which is used to simulate the impact of extreme hydrodynamic forces on shore protection walls. Typically, fluids are modeled numerically based on a Lagrangian approach, an Eulerian approach or a combination of the two. Many of the common problems that arise from using more traditional techniques can be avoided through the use of SPH-based models. Such challenges include the model computational efficiency in terms of complexity of implementation. The SPH method allows water particles to be individually modeled, each with their own characteristics, which then accurately depicts the behavior and properties of the flow field. An open source code, known as SPHysics, was used to run the simulations presented in this thesis. Several cases analysed consist of hydraulic bores impacting a flat vertical wall as well as a sloping seawall. The analysis includes comparisons of the numerical results with published experimental data. The model is shown to accurately reproduce the formation of solitary waves as well as their propagation and breaking. The impacting bore profiles as well as the resulting pressures are also efficiently simulated using the model.

Surface gravity waves carry enormous amounts of energy over our oceans, and if their energy could be harvested to generate electricity, it could make a significant contribution to the worlds power demand. But the survivability of wave energy devices in harsh operating conditions has proven challenging, and for wave energy to be a possibility, peak forces during storms and extreme waves must be studied and the devices behaviour understood. Although the wave power industry has benefited from research and development in traditional offshore industries, there are important differences. Traditional offshore structures are designed to minimize power absorption and to have small motion response, while wave power devices are designed to maximize power absorption and to have a high motion response. This increase the difficulty of the already challenging survivability issue. Further, nonlinear effects such as turbulence and overtopping can not be neglected in harsh operating conditions. In contrast to traditional offshore structures, it is also important to correctly account for the power take off system in a wave energy converter (WEC), as it is strongly coupled to the devices behaviour. The focus in this thesis is the wave loads and the peak forces that occur when a WEC with a limited stroke length is operated in waves higher than the maximum stroke length. The studied WEC is developed at Uppsala University, Sweden, and consists of a linear generator at the seabed that is directly driven by a surface buoy. A fully nonlinear CFD model is developed in the finite volume software OpenFOAM, and validated with physical wave tank experiments. It is then used to study the motion and the forces on the WEC in extreme waves; high regular waves and during tsunami events, and how the WECs behaviour is influenced by different generator parameters, such as generator damping, friction and the length of the connection line. Further, physical experiments are performed on full scale linear generators, measuring the total speed dependent damping force that can be expected for different loads. The OpenFOAM model is used to study how the measured generator behaviour affects the force in the connection line.

This thesis discusses the development of a Numerical Wave Tank (NWT) capable of describing the coupled behaviour of Wave Energy Converters (WECs) and their moorings under extreme wave loading. The NWT utilises the open-source Computational Fluid Dynamics (CFD) software OpenFOAM(R) to solve the fully nonlinear, incompressible, Reynolds-Averaged Navier-Stokes (RANS) equations for air and water using the Finite Volume Method (FVM) and a Volume of Fluid (VOF) treatment of the interface. A method for numerically generating extreme waves is devised, based on the dispersively-focused NewWave theory and using the additional toolbox waves2Foam. A parametric study of the required mesh resolution shows that steeper waves require finer grids for mesh independence. Surface elevation results for wave-only cases closely match those from experiments, although an improved definition of the flow properties is required to generate very steep focused waves. Predictions of extreme wave run-up and pressure on the front of a fixed truncated cylinder compare well with physical measurements; the numerical solution successfully predicts the secondary loading cycle associated with the nonlinear ringing effect and shows a nonlinear relationship between incident crest height and horizontal load. With near perfect agreement during an extreme wave event, the reproduction of the six degree of freedom (6DOF) motion and load in the linearly-elastic mooring of a hemispherical-bottomed buoy significantly improves on similar studies from the literature. Uniquely, this study compares simulations of two existing WEC designs with scale-model tank tests. For the Wavestar machine, a point-absorber constrained to pitch motion only, results show good agreement with physical measurements of pressure, force and float motion in regular waves, although the solution in the wake region requires improvement. Adding bespoke functionality, a point-absorber designed by Seabased AB, consisting of a moored float and Power Take-Off (PTO) with limited stroke length, translator and endstop, is modelled in large regular waves. This represents a level of complexity not previously attempted in CFD and the 6DOF float motion and load in the mooring compare well with experiments. In conclusion, the computational tool developed here is capable of reliably predicting the behaviour of WEC systems during extreme wave events and, with some additional parameterisation, could be used to assess the survivability of WEC systems at full-scale before going to the expense of deployment at sea.

Currently, the accurate prediction of the impact of an extreme wave on infrastructure located near shore is difficult to assess. There is a lack of established methods to accurately quantify these impacts. Extreme waves, such as tsunamis generate, through breaking, extremely powerful hydraulic bores that impact and significantly damage coastal structures and buildings located close to the shoreline. The damage induced by such hydraulic bores is often due to structural failure. Examples of devastating coastal disasters are the 2004 Indian Ocean Tsunami, 2005 Hurricane Katrina and most recently, the 2011 Tohoku Japan Tsunami. As a result, more advanced research is needed to estimate the magnitude of forces exerted on structures by such bores. This research presents results of a numerical model based on the Smoothed Particle Hydrodynamics (SPH) method which is used to simulate the impact of extreme hydrodynamic forces on shore protection walls. Typically, fluids are modeled numerically based on a Lagrangian approach, an Eulerian approach or a combination of the two. Many of the common problems that arise from using more traditional techniques can be avoided through the use of SPH-based models. Such challenges include the model computational efficiency in terms of complexity of implementation. The SPH method allows water particles to be individually modeled, each with their own characteristics, which then accurately depicts the behavior and properties of the flow field. An open source code, known as SPHysics, was used to run the simulations presented in this thesis. Several cases analysed consist of hydraulic bores impacting a flat vertical wall as well as a sloping seawall. The analysis includes comparisons of the numerical results with published experimental data. The model is shown to accurately reproduce the formation of solitary waves as well as their propagation and breaking. The impacting bore profiles as well as the resulting pressures are also efficiently simulated using the model.

This thesis investigates wave loading on bodies in the free surface using smoothed particle hydrodynamics (SPH). This includes wave loading on fixed bodies, waves generated by heaving bodies in still water and the heave response of a body in waves, representing a wave energy device. SPH is a flexible Lagrangian technique for CFD simulations, which in principle applies to steep and breaking waves without special treatment allowing us to simulate highly nonlinear and potentially violent flows encountered in a real sea. However few detailed tests have been undertaken even with small amplitude waves.This research uses the open-source SPH code SPHysics. First two forms of SPH formulation, standard SPH with artificial viscosity and SPH-Arbitrary Lagrange Euler (ALE) with a Riemann solver, are used to simulate progressive waves in a 2-D tank. The SPH-ALE formulation with a symplectic time integration scheme and cubic spline kernel is found to model progressive waves with negligible dissipation whereas with the standard SPH formulation waves decay markedly along the tank. We then consider two well-defined test cases in two dimensions: progressive waves interacting with a fixed cylinder and waves generated by a heaving semi-immersed cylinder. To reduce computer time in a simple manner a variable particle mass distribution is tested with fine resolution near the body and coarse resolution further away, while maintaining a uniform kernel size. A mass ratio of 1:4 proved effective but increasing to 1:16 caused particle clumping and instability. For wave loading on a half-submerged cylinder the agreement with the experimental data of Dixon et al. (1979) for the root mean square force is within 2%. For more submerged cases, the results show some discrepancy, but this was also found with other modelling approaches. For the heaving cylinder, SPH results for the far field wave amplitude and vertical force on the cylinder show good agreement with the data of Yu and Ursell (1961). The variable mass distribution leads to a computer run time speedup of nearly 200% in these cases on a single CPU. The results of the vertical force and wave amplitude are shown to be quite sensitive to the value of the slope limiter in the Riemann solver for the 2-D heaving cylinder problem. A heaving 2-D wedge or 3-D cone whose oscillatory vertical motion is prescribed as the elevation of a focused wave group is a precise test case for numerical free-surface schemes. We consider two forms of repulsive boundary condition (Monaghan & Kos, 1999, and Rogers et al., 2008) and particle boundary force (Kajtar and Monaghan, 2009) for the 2-D wedge case, comparing the result with the experimental data of Drake et al. (2009). The repulsive boundary condition was more effective than the particle boundary force method. Variable particle mass with different kernel sizes was then tested for 2-D problems for mass ratios of 1:4, 1:16 and 1:4:16 with satisfactory results without particle clumping and instability. For the 3-D cone case, SPH reproduces the experimental results very closely for the lower frequency tested where there is no separation from the bottom surface of the body but for the higher frequencies the magnitudes of force minima were underestimated. The mass ratios of 1:8 and 1:8:27 in two and three nested regions are tested for the 3-D cone problem where a computer run time speedup of nearly 500% is achieved on 16 processors for the mass ratio of 1:8.Finally, the floating body of a heaving wave energy device known as the Manchester Bobber is modelled in extreme waves without power take-off. The results for a single float are in approximate agreement with the experiment.

The amount of energy enclosed in ocean waves has been classified as one of the most promising renewable energy sources. Nowadays, different wave energy conversion (WEC) systems are being investigated, but only a few concepts have been operated in a sea environment. One of the largest challenges is to guarantee the offshore survivability of the devices in extreme wave conditions. However, there are large uncertainties related to the prediction of extreme wave loads on WECs.  Highfidelity computational fluid dynamics (CFD) simulations can resolve nonlinear hydrodynamic effects associated with wave-structure interaction (WSI). This thesis explores the point-absorbing WEC developed by Uppsala University in extreme wave conditions. The dynamic response and the forces on key components (mooring line, buoy, generator's end-stop spring) of the device are studied and compared. The high nonlinear phenomena accompany the steep and high waves, i.e., breaking behavior, slamming loads can be well-captured by the highfidelity CFD simulations. A commonly used methodology for extreme waves selection, recommended by technical specifications and guidelines, is the environmental contour approach. The 100-year contour in Hamboldt Bay site in California and the 50-year contour in the Dowsing site, outside the UK, are utilized to extract the extreme waves examined in the present thesis. Popular methodologies and data from different sources (observational and hindcast data) are examined for the environmental contour generation providing useful insights. Moreover, two popular approaches for the numerical representation of the extreme sea states, either as focused wave or as equivalent regular wave, were examined and compared. A midfidelity model of the WEC is successfully verified, as the utilization of lower fidelity tools in the design stage would reduce the computational cost. Last but not least, in CFD simulations the computational grid is sensitive in large motions, something often occurs during extreme-WSI. The solution of this issue for the open source CFD software OpenFOAM is provided here.

Les blocs supratidaux de tempête que l’on trouve au sommet des falaises vont à l’encontre du schéma classique qui décrit l’érosion des falaises. Généralement, le recul des escarpements rocheux se fait au rythme des écroulements gravitaires dont les éléments s’accumulent en pied de falaise, la mer intervenant surtout dans le déblaiement des matériaux accumulés à la base des versants. Dans le cadre de cette thèse, nous étudions les processus d’érosion qui se traduisent par l’accumulation de dépôts grossiers en sommet de falaise. Nous montrons qu’au cours des événements météo-océaniques extrêmes, les effets combinés d’un niveau d’eau à la côte particulièrement élevé et du déferlement de vagues de haute énergie peuvent se manifester localement par l’arrachement et le transport de blocs littoraux supratidaux. Leur masse peut dépasser plusieurs dizaines de tonnes, et leur remaniement peut se faire à plusieurs mètres au-dessus du niveau des hautes mers. De même, leur déplacement peut atteindre plusieurs dizaines à centaines de mètres à l’intérieur des terres. A l’heure où l’on s’interroge sur une possible intensification et/ou augmentation de la fréquence des événements météoocéaniques extrêmes, la dynamique morphosédimentaire de ces blocs littoraux apparait comme un indicateur géomorphologique pertinent pour l’évaluation de ces changements. Un suivi topo-morphologique, sédimentaire et hydrodynamique pluriannuel a été réalisé sur plusieurs sites bretons (Finistère) et islandais (presqu’île de Reykjanes). Les résultats de ce suivi ont montré des schémas de circulation hydro-sédimentaire bien distincts suivant le contexte morphodynamique. Si dans certains cas, les processus transversaux prédominent dans l’édification et le remaniement de ces accumulations, dans d’autres cas, la composante longitudinale contrôle une partie des transferts à la côte. Les processus d’arrachement et de transport de blocs sont concomitants, et peuvent se produire à plusieurs reprises au cours d’un même événement et/ou hiver, y compris pendant les tempêtes d’intensité modérée. L’étude rétrospective des conditions météo-océaniques favorables au déclenchement de ces processus sur les 70 dernières années montre une forte variabilité interannuelle, sans périodicité ni tendance particulière. Cette variabilité est commandée par la dynamique atmosphérique WEPA aux latitudes tempérées de la Bretagne, et par l’ONA aux latitudes sub-polaires de l’Islande. / Cliff-top storm deposits (CTSDs) corresponding to boulder accumulations are locally identified along the North–Atlantic coasts (Iceland, Scotland, Ireland, France), where they are defined as one of the most remarkable morphosedimentary storm signature. Their study aims to understand the effects of high energy storm waves on these specific rocky cliffed coasts facing deep–water and exposed to energetic wave–climates. Recent works demonstrated the role of high energy storm waves (instead of tsunami waves) in transporting and supplying in boulders these deposits. In the context of climate change, and the possible intensification and/or increase in frequency of extreme meteo-oceanic events, CTSDs appears as a potential geomorphological indicator for the monitoring of these changes on high-energy rocky coasts. This thesis propose an analysis of their morphosedimentary dynamics based on field observations realized at high (64°N) and medium (48°N) latitude of the Northeast Atlantic basin. In the present work, their morphosedimentary dynamics have been annually surveyed using low altitude aerial photographs. Results shows two different hydrosedimentary circulation patterns of CTSDs. The first one concerns inland boulder transport, corresponding the directions of the incident waves. This pattern confirms the contemporary edification of ridges. The second one concerns longshore or seaward boulder transport, describing a longitudinal drift of this sedimentary material.The processes of quarrying and transport of CTSDs are concomitant and can repeatedly occur during one single event and/or winter, including during regular storms. The retrospective analysis of sea weather forecast favorable to these processes during the last 70 years showed an infraannual frequency with no particular periodicity nor tendency.

This thesis describes experiments that were carried out using focused wave groups in the UK Coastal Research Facility (UKCRF). Considerable effort was put into calibrating the UKCRF to determine the relationship between the input signals sent to the paddles and the waves generated in the facility. Focused wave groups of various sizes and phases, based on NewWave theory were generated, and measurements were made of the resulting surface elevation data, water particle kinematics, wave runup and overtopping volumes. NewWave theory models the profile of extreme waves in a Gaussian (random) sea. The thesis describes the first time this model has been applied in the context of coastal wave transformation. A method for the separation of the underlying harmonic structure of a focused wave group is described and results presented. This technique has been used in relatively deep water but is shown to work successfully in the coastal zone until wave overturning. A method has been devised to provide a theoretical Stokes-like expansion of the free and bound waves to model the surface elevation and water particle kinematics of the focused wave groups. Satisfactory agreement is achieved between the theoretical predictions of UKCRF measurements. Suggestions are made for an improved model. The underlying harmonic structure of the focused wave groups is presented as stacked time histories that give insight into the wave transformation process from deep to shallow water. Particular attention is paid to the low frequency wave generated as the wave group interacts with the beach. This is compared to the low frequency wave that is generated by a solitary wave in the UKCRF. Runup and overtopping measurements are in reasonable agreement with predictions based on certain empirical formulae, but not others. These comparisons are useful in identifying those formulae able to predict runup and overtopping of extreme waves in the coastal zone.

The main objective of wave energy converters (WECs) is to ensure reliable electricity production at a competitive cost. Two challenges to achieving this are ensuring an efficient energy conversion and offshore survivability.         This thesis work is structured in three different sections: Control and maximum power optimization, forces and dynamics analysis in extreme wave conditions, and statistical modeling of extreme loads in reliability analysis.        The need for prediction and future knowledge of waves and wave forces is essential due to the non-causality of the optimal velocity relation for wave energy converters. Using generic concepts and modes of motion, the sensitivity of the prediction horizon to various parameters encountered in a real system is elaborated. The results show that through a realistic assumption of the dissipative losses, only a few seconds to about half a wave cycle is sufficient to predict the required future knowledge for the aim of maximizing the power absorption.          The results of a 1:30 scaled wave tank experiment are used to assess the line force and dynamic behaviour of a WEC during extreme wave events. Within the comparison of different wave type representations, i.e. irregular, regular and focused waves, of the same sea state, the results show that not all the wave types deliver the same maximum line forces. As a strategy of mitigating the line forces during extreme wave events, changing the power take-off (PTO) damping may be employed. With consideration of the whole PTO range, the results indicate an optimum damping value for each sea state in which the smallest maximum line force is obtained. Although wave breaking slamming and end-stop spring compression lead to high peak line forces, it is possible that they level out due to the overtopping effect. Waves with a long wavelength result in large surge motion and consequently higher and more damaging forces.         On the investigation of reliability assessment of the wave energy converter systems, computing the return period of the extreme forces is crucial. Using force measurement force data gathered at the west coast of Sweden, the extreme forces are statistically modelled with the peak-over-threshold method. Then, the return level of the extreme forces over 20 years for the calm season of the year is computed.