<p>Kraftindustrin arbetar oavbrutet med att försöka höja och upprätthålla dammsäkerheten i Sverige. Erosionsskydd för fyllningsdammar skall dimensioneras och utformas så att de medverkar till en god dammsäkerhet. Vid dimensionering och projektering av erosionskydd måste vågberäkningar utföras för att bedöma angripande våglast. I Sverige genomförs dessa beräkningar utifrån kraftföretagens riktlinjer för dammsäkerhet, RIDAS. Uträkningarna och bedömningar av våglasterna är ur dammsäkerhetssynpunkt viktiga eftersom de ofta avgör erforderligt fribord. Vågberäkningarna är behäftade med stora osäkerheter, speciellt i fall då störningar i form av öar, uddar och uppgrundande partier finns framför dammkonstruktionen.</p><p>Syftet med examensarbetet har varit att utvärdera vågförhållanden och därmed våglasterna på Vojmsjöns regleringsdamm. Vågförhållandena har simulerats och analyserats med den numeriska modellen MIKE 21 Spectral Wave. Tillvägagångssättet är nytt och modellen har tidigare inte använts inom området. Således genomfördes en verifiering och orienterande kalibrering i magasin Sädvajaure. Utifrån de kunskaper och erfarenheter som erhölls vid utförandet i Sädvajaure användes modellen i fallstudie Vojmsjön. Ett mer övergripande syfte har varit att utreda om förfarandet är en ny möjlig metod för att utvärdera vågor i vattenkraftmagsin.</p><p>Undersökningen i Sädvajaure visade på en relativt god korrelation mellan uppmätta och simulerade våghöjder. Modellens noggrannhet är starkt beroende av tillförlitligheten hos indata. Mer exakt indata hade förmodligen resulterat i ännu bättre samband. Fallstudie Vojmsjön visade på signifikanta skillnader i resultat mellan vågberäkningarna enligt RIDAS och de av modellen simulerade. RIDAS beräkningsmetoder överskattar våghöjderna i området framför Vojmsjöns regleringsdamm, främst till följd av att beräkningarna genomförs med grova förenklingar av magasinets form och att vågorna antas propagera fritt utan inverkan av refraktion och uppgrundande partier.</p><p>Förfarandet med att använda en numerisk modell för att analysera vågor i vattenkraftmagasin anses vara tillämpbar. Metoden bedöms, utifrån denna studie, vara ett bra komplement för tillfällen när RIDAS beräkningsmetoder anses vara otillräckliga och särskilda utredningar är påkallade. Liknande mer grundliga utredningar, skulle kunna ge bra underlag för att fatta goda ekonomiska och dammsäkerhetsmässiga beslut.</p> / <p>The power industry is constantly trying to raise and maintain the safety of dams in Sweden. Erosion protection for embankment should be designed to contribute to a high level of dam safety. When designing an erosion protection, wave calculation must be carried out to assess the wave load. In Sweden, these calculations and assessments are based on the Power Companies Guidelines for Dam Safety, named RIDAS. The calculation of wave loads is important from a dam safety point of view, because they often determine the required freeboard. The wave calculations are subject to large uncertainties especially in cases when islands, capes and shoaling areas are located in front of the dam construction.</p><p>The aim of the thesis has been to assess the wave conditions and thereby the wave loads in reservoir Vojmsjön. The approach has been to simulate and analyse the wave conditions with a numerical model MIKE 21 Spectral Wave. The procedure is new and a verification and orientated calibration was conducted since the model has not previously been used in the field. The verification of the model was carried out in reservoir Sädvajaure. Based on the knowledge and experience obtained during the investigation at Sädvajaure the model was used in the case study Vojmsjön. A more general aim has been to investigate whether the approach is a new possible method to evaluate waves in hydropower reservoirs.</p><p>The investigation in Sädvajaure showed a relatively good correlation between measured and simulated wave heights. The model precision is highly dependent on the accuracy of input data. More accurate input data had probably given even better results. Case study Vojmsjön showed significant differences in result between wave calculation based on RIDAS and the model simulated. RIDAS calculation methods overestimate the wave heights in the area in front of regulation dam Vojmsjön. Mainly because the calculations are based on simplifications of the reservoir structure, but also depending on the fact that the waves are assumed propagating freely without the influence of refraction and shoaling.</p><p>The approach of using a numerical model to evaluate the waves in hydropower reservoirs is believed to be applicable. The method is considered to be useful as a complement in investigations when RIDAS calculation methods are considered being insufficient and special investigations is necessary. Similar more extended investigations could provide good material to make good decisions, both from an economic and a dam safety point of view.</p>

Kraftindustrin arbetar oavbrutet med att försöka höja och upprätthålla dammsäkerheten i Sverige. Erosionsskydd för fyllningsdammar skall dimensioneras och utformas så att de medverkar till en god dammsäkerhet. Vid dimensionering och projektering av erosionskydd måste vågberäkningar utföras för att bedöma angripande våglast. I Sverige genomförs dessa beräkningar utifrån kraftföretagens riktlinjer för dammsäkerhet, RIDAS. Uträkningarna och bedömningar av våglasterna är ur dammsäkerhetssynpunkt viktiga eftersom de ofta avgör erforderligt fribord. Vågberäkningarna är behäftade med stora osäkerheter, speciellt i fall då störningar i form av öar, uddar och uppgrundande partier finns framför dammkonstruktionen. Syftet med examensarbetet har varit att utvärdera vågförhållanden och därmed våglasterna på Vojmsjöns regleringsdamm. Vågförhållandena har simulerats och analyserats med den numeriska modellen MIKE 21 Spectral Wave. Tillvägagångssättet är nytt och modellen har tidigare inte använts inom området. Således genomfördes en verifiering och orienterande kalibrering i magasin Sädvajaure. Utifrån de kunskaper och erfarenheter som erhölls vid utförandet i Sädvajaure användes modellen i fallstudie Vojmsjön. Ett mer övergripande syfte har varit att utreda om förfarandet är en ny möjlig metod för att utvärdera vågor i vattenkraftmagsin. Undersökningen i Sädvajaure visade på en relativt god korrelation mellan uppmätta och simulerade våghöjder. Modellens noggrannhet är starkt beroende av tillförlitligheten hos indata. Mer exakt indata hade förmodligen resulterat i ännu bättre samband. Fallstudie Vojmsjön visade på signifikanta skillnader i resultat mellan vågberäkningarna enligt RIDAS och de av modellen simulerade. RIDAS beräkningsmetoder överskattar våghöjderna i området framför Vojmsjöns regleringsdamm, främst till följd av att beräkningarna genomförs med grova förenklingar av magasinets form och att vågorna antas propagera fritt utan inverkan av refraktion och uppgrundande partier. Förfarandet med att använda en numerisk modell för att analysera vågor i vattenkraftmagasin anses vara tillämpbar. Metoden bedöms, utifrån denna studie, vara ett bra komplement för tillfällen när RIDAS beräkningsmetoder anses vara otillräckliga och särskilda utredningar är påkallade. Liknande mer grundliga utredningar, skulle kunna ge bra underlag för att fatta goda ekonomiska och dammsäkerhetsmässiga beslut. / The power industry is constantly trying to raise and maintain the safety of dams in Sweden. Erosion protection for embankment should be designed to contribute to a high level of dam safety. When designing an erosion protection, wave calculation must be carried out to assess the wave load. In Sweden, these calculations and assessments are based on the Power Companies Guidelines for Dam Safety, named RIDAS. The calculation of wave loads is important from a dam safety point of view, because they often determine the required freeboard. The wave calculations are subject to large uncertainties especially in cases when islands, capes and shoaling areas are located in front of the dam construction. The aim of the thesis has been to assess the wave conditions and thereby the wave loads in reservoir Vojmsjön. The approach has been to simulate and analyse the wave conditions with a numerical model MIKE 21 Spectral Wave. The procedure is new and a verification and orientated calibration was conducted since the model has not previously been used in the field. The verification of the model was carried out in reservoir Sädvajaure. Based on the knowledge and experience obtained during the investigation at Sädvajaure the model was used in the case study Vojmsjön. A more general aim has been to investigate whether the approach is a new possible method to evaluate waves in hydropower reservoirs. The investigation in Sädvajaure showed a relatively good correlation between measured and simulated wave heights. The model precision is highly dependent on the accuracy of input data. More accurate input data had probably given even better results. Case study Vojmsjön showed significant differences in result between wave calculation based on RIDAS and the model simulated. RIDAS calculation methods overestimate the wave heights in the area in front of regulation dam Vojmsjön. Mainly because the calculations are based on simplifications of the reservoir structure, but also depending on the fact that the waves are assumed propagating freely without the influence of refraction and shoaling. The approach of using a numerical model to evaluate the waves in hydropower reservoirs is believed to be applicable. The method is considered to be useful as a complement in investigations when RIDAS calculation methods are considered being insufficient and special investigations is necessary. Similar more extended investigations could provide good material to make good decisions, both from an economic and a dam safety point of view.

To facilitate the process of setting up small scale environmental models in coastal and offshore areas a wave model and a 2D current model for the Baltic Sea have been set up with MIKE 21. The ambition is that the Baltic Sea model can serve as a source of boundary conditions for local models. The main focus in the project has been to determine which input data to use to get the best results and then to calibrate and validate the model with the best data sets available. The wave model has been tested with three different sources of wind forcing and the results with the different sources are evaluated. The wave model has been calibrated and validated against five wave buoys and the current model against three current observation stations. The comparison shows that the wave model gives good estimations of wave height, period and direction. The output of the current model coincides with observations where distinct current patterns exist. The wave model is considered a good source to extract wave statistics from for the entire Baltic Sea. The current model can be used for scenarios or areas that do not suffer from the limitations of a 2D model.

Rogue waves are unexpected, individual ocean surface waves that are disproportionately large compared to the background sea state. They present considerable risk to mariners and offshore structures when encountered in large seas. Rogue waves have gone from seafarer’s folktales to an actively researched and debated phenomenon. In this work an easily derived spectral parameter, as an indicator of rogue wave risk, is presented, and further evidence for the generation mechanism responsible for these abnormal waves is provided. With the additional goal of providing a practical rogue wave forecast, the ability of a standard wave model to predict the rogue wave probability is assessed. Current forecasts, like those at the European Centre for Medium-Range Weather Forecasts (ECMWF), rely on the Benjamin Feir Index (BFI) as a rogue wave predictor, which reflects the nonlinear process of modulation instability as the generation mechanism for rogue waves. However, this analysis finds BFI has little predictive power in the real ocean. From the analysis of long term sea surface elevation records in nearshore areas and hourly bulk statistics from open ocean and coastal buoys in the Northeast Pacific, crest-trough correlation shows the highest correlation with rogue wave probability. These results provide evidence in support of a probabilistic prediction of rogue waves based on random linear superposition and should replace forecasts based on modulation instability. Crest-trough correlation was then forecast by a regional WAVEWATCH III ® wave model with moderate accuracy compared with the high performance of forecasting significant wave height. Results from a case study of a large fall storm October 21-22, 2021, are presented to show that the regional wave model produces accurate forecasts of significant wave height at high seas and presents a potential rogue wave probability forecast. / Graduate

In this study, a two-dimensional depth-averaged beach evolution numerical model is developed to study the medium and long term nearshore sea bottom evolution due to non-cohesive sediment transport under the action of wind waves only over the arbitrary land and sea topographies around existing coastal structures and formations. The developed beach evolution numerical model is composed of four sub-models: a nearshore spectral wave transformation model based on energy balance equation including random wave breaking and diffraction terms to compute the nearshore wave characteristics, a nearshore wave-induced circulation model based on the non-linear shallow water equations to compute the nearshore depth averaged wave-induced current velocities and mean water level changes, a sediment transport model to compute the local total sediment transport rates occurring under the action of wind waves and a bottom evolution model to compute the bed level changes in time due to gradients of sediment transport rates in cross-shore and longshore directions. The governing partial differential equations are solved utilizing finite difference schemes. The developed models are applied successfully to several theoretical and conceptual benchmark cases and an extensive data set of laboratory and field measurements. As an alternative approach to be used in beach evolution problems, a distributed total sediment load formula is proposed based on the assumption that the local total sediment transport rates across the surf zone are proportional to the product of the rate of dissipation of wave energies due to wave breaking and wave-induced current velocities. The proposed distribute load approach is validated with the available laboratory and field measurements.

L'analyse de la climatologie des aléas océano-météorologiques tels que les états de mer est fondamentale pour comprendre l'évolution et la dynamique des zones côtières, estimer les risques naturels survenant lors d'événements de tempête majeurs, définir les moyens optimaux de protection des ports et infrastructures onshore et offshore, caractériser la ressource houlomotrice pour des projets de récupération d'énergie des vagues, comprendre les processus d'érosion et accrétion des plages, etc. Pour répondre à ces problématiques dans un contexte de questionnement croissant sur les conséquences potentielles associées au changement climatique, le travail de thèse s'inscrit dans une démarche double : (i) approfondissement de la connaissance du climat de vagues actuel le long des côtes Atlantique, Manche et Mer du Nord en France d'une part, et (ii) estimation des évolutions futures potentielles de cette climatologie des vagues pour différents scénarios d'évolution climatique. L'estimation de l'impact du changement climatique sur le climat de vague se compose de trois éléments principaux : (i) une connaissance détaillée de la variabilité climatique actuelle des états de mer, (ii) l'utilisation de scénarios de changement climatique à l'horizon 2100 et (iii) la définition d'une méthodologie de descente d'échelle adaptée. Pour appréhender ces sujets, l'Atlas Numérique d'Etats de Mer Océanique et Côtier ANEMOC-2 a été construit à l'aide du modèle spectral de 3ème génération TOMAWAC (Benoit et al., 1996) sur la période 1979-2009 et le climat de vagues futur a été simulé à l'horizon 2100 par des méthodes de descente d'échelle dynamique et statistique en considérant les scénarios de changement climatique du quatrième rapport du GIEC (IPCC, 2007).En particulier, un travail original de comparaison de projections d'états de mer par approche dynamique et par approche statistique des types de temps a été réalisé sur la période 2061-2100 pour les scénarios B1, A1B et A2 simulés par le modèle ARPEGE-CLIMAT de Météo-France (Salas-Mélia, et al. 2005). Les résultats des deux approches (à savoir hauteur significative, période moyenne, direction moyenne et flux d'énergie des vagues) ont été comparés en termes de valeurs moyennes, écarts-types, distributions jointes et variabilités saisonnière et interannuelle. Ce travail a abouti à une estimation de l'impact du changement climatique sur la climatologie des états de mer le long des côtes Atlantique, Manche et Mer du Nord françaises sur la période 2061-2100 en tenant compte des incertitudes intrinsèques aux méthodes de descente d'échelle et aux scénarios de changement climatique. En hiver par exemple, nous observons une augmentation des valeurs moyennes et de la variabilité des paramètres de hauteur significative, période moyenne et flux d'énergie des vagues, notamment en Mer du Nord (pour les scénarios B1, A1B et A2) et dans le Golfe de Gascogne pour le scénario B1. En complément, ces paramètres d'états de mer ont tendance à diminuer dans le Golfe de Gascogne pour les saisons printemps, été et automne. Enfin, les paramètres d'états de mer associés aux hauteurs de vagues du quantile 95 tendent à augmenter sur une large emprise de l'Atlantique nord-est / Wave climate analysis is of utmost importance to understand the evolution and dynamics of coastal zones, to estimate the occurrence of extreme events, to design protections for ports, onshore and offshore infrastructure, to characterize wave resources for wave energy conversion, to quantify sediment erosion and accretion processes, et cetera. Thus, this thesis project aims to improve knowledge of wave climatology in the growing context of climate change prediction with a two-step approach: (i) enhancement of the understanding of the present wave climate along the French coastline facing the Atlantic Ocean, English Channel and North Sea and (ii) estimation of possible future wave climate evolution. For this purpose, the estimation of climate change impacts on the wave climate requires three key parameters: (i) detailed knowledge of current wave climate variability, (ii) the application of climate change scenarios from Global Climate Models and (iii) the definition of an appropriate downscaling method. To answer these questions, ANEMOC-2, a hindcast sea-state data base has been built based on the third-generation spectral wave model TOMAWAC (Benoit et al., 1996) over the period 1979-2009, and the future wave climate has been simulated over the period 2061-2100 by means of dynamical and statistical downscaling methods. In particular, an original approach comparing sea-state projections obtained from dynamical and statistical downscaling methods has been applied over the period 2061-2100 for B1, A1B and A2 scenarios (Forth Assessments Reports, IPCC, 2007), based on the ARPEGE-CLIMAT (Salas-Mélia et al., 2005) model simulations. The wave spectral parameters resulting from the projections (i.e. significant wave height, mean period, mean direction and wave energy flux) have been compared in term of mean, joint distribution and seasonal and interannual variability.The possible climate change impacts on the wave climate along the Atlantic, English Channel and North Sea French coastline have also been evaluated. The analysis provides estimations of the inherent uncertainties of climate change scenarios and downscaling methods. Wave climate evolution trends are presented in terms of the mean, joint distribution, and seasonal and interannual variability of significant wave height, mean period, mean direction and wave energy flux

No description available.

La physique de la couche limite atmosphérique en domaine océanique est principalement régie par les processus couplés liés au vent, à l’état de mer local, et à des effets de flottabilité. Leur compréhension reste néanmoins parcellaire et leurs descriptions théoriques et stochastiques sont pour le moins lacunaires, lorsqu’elles ne sont tout simplement pas mises à mal par les rares observations. Dans un contexte d’exploitation croissante de la ressource éolienne offshore, la mise en place de méthodes numériques visant à une description plus fine des propriétés turbulentes de cette couche limite sera une étape déterminante dans la réduction des coûts et l’optimisation des structures pour des rendements de récupération d’énergie améliorés. Ainsi, un outil numérique a été mis en place afin d’étudier le couplage entre un écoulement atmosphérique et l’état de mer. Un code Large-Eddy Simulation massivement parallèle pour la simulation des écoulements atmosphériques incompressibles développé par P. Sullivan au National Center for Atmospheric Research est couplé à un code spectral d’états de mer non-linéaires développé au Laboratoire de recherche en Hydrodynamique, Energétique et Environnement Atmosphérique. De nombreuses configurations de vents et d’états de mer sont modélisées. On montre que les lois semi empiriques souvent utilisées pour représenter la distribution verticale de la vitesse moyenne du vent sont une bonne approximation dans les situations où un petit état de mer est soumis à un fort vent. Néanmoins, dans le cas de houles très rapides se propageant dans des zones de faible vent, la création d’un jet de vent par la houle invalide ces lois semi-empiriques. / Modelling the dynamic coupling of ocean-atmosphere systems requires a fundamental and quantitative understanding of the mechanisms governing the windwave interactions: despite numerous studies, our current understanding remains quite incomplete and, in certain conditions, sparse field observations contradict the usual theoretical and stochastic models. Within the context of a growing exploitation of the offshore wind energy and the development of met ocean models, a fine description of this resource is a key issue. Field experiments and numerical modelling have revealed that atmospheric stability and wave effects, including the dynamic sea surface roughness, are two major factors affecting the wind field over oceans. A numerical tool has been implemented in order to study the coupling between an atmospheric flow and the seastate. A massively parallel large-eddy simulation developed by P. Sullivan at the National Center for Atmospheric Research is then coupled to a High-Order Spectral wave model developed at the Hydrodynamics,Energetics & Atmospheric Environment Laboratory in Ecole Centrale de Nantes. Numerous configurations of wind and sea states are investigated. It appears that, under strongly forced wind conditions above a small sea state, the semi-empirical laws referred to as standards in the international guidelines are a good approximation for the vertical profile of the mean wind speed. However, for light winds overlying fast-moving swell, the presence of a wave induced wind jet is observed, invalidating the use of such logarithmic laws.