Dissertationen: „Coastal Ocean Waves“

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Trainor, Lincoln Thomas. „Field observations and SWAN model predictions of wave evolution in a muddy coastal environment“. Thesis, Monterey, Calif. : Naval Postgraduate School, 2009. http://edocs.nps.edu/npspubs/scholarly/theses/2009/Jun/09Jun%5FTrainor.pdf.

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Thesis (M.S. in Physical Oceanography)--Naval Postgraduate School, June 2009.
Thesis Advisor(s): Herbers, Thomas H. C. ; Janssen, Tim T. "June 2009." Description based on title screen as viewed on July 14, 2009. Author(s) subject terms: ocean waves, continental shelf, mud, littoral, SWAN. Includes bibliographical references (p. 69-71). Also available in print.

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Orszaghova, Jana. „Solitary waves and wave groups at the shore“. Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:5b168bdc-4956-4152-a303-b23a6067bf42.

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A significant proportion of the world's population and physical assets are located in low lying coastal zones. Accurate prediction of wave induced run-up and overtopping of sea defences are important in defining the extent and severity of wave action, and in assessing risk to people and property from severe storms and tsunamis. This thesis describes a one-dimensional numerical model based on the Boussinesq equations of Madsen and Sorensen (1992) and the non-linear shallow water equations. The model is suitable for simulating propagation of weakly non-linear and weakly dispersive waves from intermediate to zero depth, such that any inundation and/or overtopping caused by the incoming waves is also calculated as part of the simulation. Wave breaking is approximated by locally switching to the non-linear shallow water equations, which can model broken waves as bores. A piston paddle wavemaker is incorporated into the model for complete reproduction of laboratory experiments. A domain mapping technique is used in the vicinity of the paddle to transform a time-varying domain into a fixed domain, so that the governing equations can be more readily solved. First, various aspects of the numerical model are verified against known analytical and newly derived semi-analytical solutions. The complete model is then validated with laboratory measurements of run-up and overtopping involving solitary waves. NewWave focused wave groups, which give the expected shape of extreme wave events in a linear random sea, are used for further validation. Simulations of experiments of wave group run-up on a plane beach yield very good agreement with the measured run-up distances and free surface time series. Wave-by-wave overtopping induced by focused wave groups is also successfully simulated with the model, with satisfactory agreement between the experimental and the predicted overtopping volumes. Repeated simulations, now driven by second order paddle displacement signals, give insight into second order error waves spuriously generated by using paddle signals derived from linear theory. Separation of harmonics reveals that the long error wave is significantly affecting the wave group shape and leading to enhanced runu-up distances and overtopping volumes. An extensive parameter study is carried out using the numerical model investigating the influence on wave group run-up of linear wave amplitude at focus, linear focus location, and wave group phase at focus. For a given amplitude, both the phase and the focus location significantly affect the wave group run-up. It is also found that the peak optimised run-up increases with the wave amplitude, but wave breaking becomes an inhibiting factor for larger waves. This methodology is proposed for extreme storm wave induced run-up analysis.

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Siddorn, Philip David. „Efficient numerical modelling of wave-structure interaction“. Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:de36bd2f-cd23-4f11-b67f-9d8cd48ecd3c.

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Offshore structures are required to survive in extreme wave environments. Historically, the design of these offshore structures and vessels has relied on wave-tank experiments and linear theory. Today, with advances in computing power, it is becoming feasible to supplement these methods of analysis with fully nonlinear numerical simulation. This thesis is concerned with the development of an efficient method to perform this numerical modelling, in the context of potential flow theory. The interaction of a steep ocean wave with a floating body involves a moving free surface and a wide range of length scales. Attempts to reduce the size of the simulation domain cause problems with wave reflection from the domain edge and with the accurate creation of incident waves. A method of controlling the wave field around a structure is presented. The ability to effectively damp an outgoing wave in a very short distance is demonstrated. Steep incident waves are generated without the requirement for the wave to evolve over a large time or distance before interaction with the body. This enables a general wave-structure interaction problem to be modelled in a small tank, and behave as if it were surrounded by a large expanse of water. The suitability of the boundary element method for performing this modelling is analysed. Potential improvements are presented with respect to accuracy, robustness, and computational complexity. Evidence of third order diffraction is found for an FPSO model.

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Mohd, Haniffah Mohd Ridza. „Wave evolution on gentle slopes : statistical analysis and Green-Naghdi modelling“. Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:26270be8-c3ee-4749-a290-7bdb4a174a4a.

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An understanding of extreme waves is important in the design and analysis of offshore structures, such as oil and gas platforms. With the increase of interest in the shipping of LNG, the design of import and export terminals in coastal water of slowly varying intermediate depth requires accurate analysis of steep wave shoaling. In this thesis, data from laboratory experiments involving random wave simulations on very gentle slopes have been analysed in terms of a model of large wave events, and the results interpreted by observation of the shape and magnitude of the large wave events. The auto-correlation function of the free surface elevation time histories, called NewWave, has been calculated from the wave spectrum and shown to fit very well up to the point where waves start to break (when compared to the ‘linear’ surface elevation time history). It has been shown that NewWave is an appropriate model for the shape of the ‘linear’ part of large waves provided kd > 0.5. A Stokes-like expansion for NewWave analysis has been demonstrated to match the average shape of the largest waves, accounting for the dominant vertical asymmetry. Furthermore, an appropriate local wave period derived from NewWave has been inserted into a Miche-based limiting criterion, using the linear dispersion equation, to obtain estimates for the limiting wave height. Overall, the analysis confirms the Miche-type criterion applies to limiting wave height for waves passing over very mild bed slopes. A derivation of general Green-Naghdi (GN) theory, which incorporates non-linear terms in its formulation, is also presented. This approach satisfies the boundary conditions exactly and approximates the field equations. The derived 2-dimensional vertical GN Level 1 model, capable of simulating steep waves on varying water depth, is validated against solitary waves and their interactions, and solitary waves on varying water depth and gives good qualitative agreement against the KdV equation. The developed and validated numerical model is used to simulate focussed wave groups on both constant depth and gentle slope. In general, the behaviour of waves simulated by the numerical model is very similar to that observed in the experimental data. There is evidence of vertical asymmetry as the water depth is reduced, owing to the non-linearity. Although the main physics is still controlled by linear dispersion, the higher order harmonics become increasingly important for shoaling waves. The numerical results also show a slope-induced wave set-up that keeps on increasing in amplitude as the wave group travels on the gentle slope.

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Morim, Nascimento Joao M. „Projections of Global Multivariate Wave Climate for the End of The 21st Century: Robustness and Uncertainties“. Thesis, Griffith University, 2020. http://hdl.handle.net/10072/398879.

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Ocean wind-waves are dominant contributors to coastal sea-level and shoreline dynamics and can be primary disruptors of coastal populations, marine ecosystems and coastal and offshore infrastructures. Hence, understanding climate-driven changes in the multivariate global ocean wind-wave climate and its extremes is paramount to successful offshore and coastal climate adaptation planning. When projecting future ocean wave conditions under climate change, uncertainty is introduced from a wide range of different sources including future emission scenario, climate model-forcing, and wind-wave modelling methodology. However, the use of single-method wave downscaling ensembles and inherent variability arising from different methodologies has led to unquantified uncertainty amongst existing global wave climate projections. This thesis addresses this significant knowledge gap by investigating the current state of knowledge in projected ocean wind-wave climate. It then, for the first time, quantifies the relative significance of these major sources of uncertainty and establishes the robustness among existing global wave climate projections. This thesis addresses former limitations associated with independent studies by performing a unique analysis of a coordinated, multi-method ensemble of future global wave scenarios assembled from ten individual state-of-the-art studies to yield a 155-member ensemble. This thesis analyses significant wave height, mean wave period and mean wave direction and also explores the underlying large-scale drivers of projected future changes in storm ocean wave events which remain largely unknown. The results of a systematic literature review demonstrate qualitative consensus between existing global and regional-scale wave climate projection studies in terms of a projected increase in mean significant wave height within the Southern Ocean area, Baltic Sea, and tropical eastern Pacific, and a projected decrease in the North Atlantic and Mediterranean Sea. In contrast, current projections of mean ocean significant wave height lack scientific consensus across the remaining ocean regions, with existing projections of extreme wave climate lacking consensus almost everywhere. In addition, results demonstrate a notable lack of knowledge in terms of projected changes in wave period and/or wave direction which are of critical importance, particularly for the mitigation of coastal hazards/risks. Furthermore, the projection uncertainty surrounding wind-wave climate projections has been poorly sampled to date, therefore implying a need for a shift towards a systematic, community-based framework to foster concerted knowledge. Quantitative analysis of surface wind fields from CMIP5 models used to force dynamical and statistical wave models demonstrate that climate models are typically well capable of reliably reproducing large-scale spatial patterns of historical surface winds, albeit there is considerable uncertainty between models with strong latitudinal dependence. Inter-model uncertainty is ~2-4 times larger than uncertainty stemming from GCM internal variability. In addition, results show that CMIP5 climate models exhibit limitations in their ability to accurately represent inter-annual/seasonal variability particularly within tropical cyclone-affected areas. In further analysis, results that surface wind field bias from climate models are largely intrinsic to their atmospheric core components. Inconsistency between surface wind fields from atmospheric-only and coupled models are largely driven by sea surface temperature errors. To address the existing limitations surrounding future wave climate, a large 155-member ensemble has been collated from ten contributing organisations as part of the COWCLIP (herein Coordinated Ocean Wave Climate Project) community. The ensemble comprises general and extreme statistics of significant wave height, mean wave period, and mean wave direction computed over historical (1979-2004) and future (2081-2100) time slices. This ensemble comprises data originated from different wave downscaling approaches, multiple climate-model forcing and future emissions scenarios. Results of wave ensemble model skill against satellite-database measurements of ocean significant wave height and multivariate wave reanalysis for the present-day time-slice demonstrate that models are able to successfully represent annual and seasonal wave variable statistics. Quantitative results derived from this new coordinated multi-method ensemble show, that under a high-emissions scenario, widespread ocean areas exhibit robust changes in annual mean significant wave height and mean wave period of 5-15% and pattern shifts in mean wave direction of 5-15°. Results show that approximately 50% of the world’s coastline is at risk from wave climate change, with ~40% revealing projected robust changes across at least two wave climate variables. Furthermore, results demonstrate that uncertainty in current projections is dominated by climate model-driven uncertainty and also that single-method downscaling studies are unable to resolve up to ~50% of the total uncertainty. In further analysis, hemispheric-scale changes in extreme ocean wave events are analysed using a set of proposed indices that describe the frequency, magnitude and/or persistency of such events. The results demonstrate changes in high-frequency (sub-annual) extreme wave events of the order of 50 to 100% for global warming exceeding 2° C; thus, nearly doubling the projected future changes expected for global warming stabilizing below 2° C (when globally integrated). These changes exhibit strong inter-hemispheric asymmetry, with an increase over the tropics and high latitudes of the Southern Hemisphere, and a widespread decrease across most of the Northern Hemisphere. Lastly, statistical comparison between projected future changes and historical large-scale patterns of change demonstrate that projected changes in extreme wave events across the tropics, high latitudes of the Southern Hemisphere region and across most of the Northern Hemisphere are consistent with their historical response to the positive and negative phase modes of the Southern Annular Mode (SAM) and El Nino-Southern-Oscillation (ENSO), respectively. These results highlight that many nations with low-adaptive capacity located within the Southern Hemisphere region (e.g. West Africa, Australia, New Zealand) will likely face increasing exposure to much more frequent extreme wave events in the future. The results presented in this thesis, and the dataset developed, provide a new perspective on the knowledge on global wave climate projections, providing key insights and support for broad-scale coastal risk and vulnerability assessments and climate adaptation analysis around the world. Whilst the results presented in this thesis have far-reaching implications from many different perspectives, they only address meteorologically-driven changes in ocean wave characteristics. Concentrated community effort is urgently needed to quantify morphologically-driven wave climate change as a contributor to global coastal water level changes, as we look towards improved coastal vulnerability assessments from the climate community.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Eng & Built Env
Science, Environment, Engineering and Technology
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Raby, Alison Caroline. „Extreme waves, overtopping and flooding at sea defences“. Thesis, University of Oxford, 2003. http://ora.ox.ac.uk/objects/uuid:82fcc770-8838-4f9b-9abe-32eecdd05f9a.

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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.

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Grice, James Robert. „Prediction of extreme wave-structure interactions for multi-columned structures in deep water“. Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:dd7320c1-7121-4ea7-827f-527af9405e9a.

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With a continuing and rising demand for hydrocarbons, the energy companies are installing infrastructure ever further offshore, where such infrastructure is often exposed to extreme waves. This thesis explores some aspects of wave-structure interaction, particularly the maximum water surface elevation increase in severe storms due to these local interactions. The effects on wave-structure interactions of column cross-sectional shape are investigated using linear and second-order wave diffraction theory. For multi-column structures, the excitation of locally resonant wave modes (near-trapping) is studied for several column cross-sectional shapes, and a simple method for estimating the surface elevation mode shape is given. The structure of the quadratic transfer functions for second-order sum wave elevation is investigated and an approximation assuming these QTFs are flat perpendicular to the leading diagonal is shown to be adequate for the first few lowest frequency modes. NewWave-type focused wave groups can be used as a more realistic model of extreme ocean waves. A Net Amplification Factor based on the NewWave model is given as an efficient tool for finding the incident frequencies most likely to cause a violent wave-structure interaction and where these violent responses are likely to occur. Statistics are collected from Monte Carlo type simulations of random waves to verify the use of the Net Amplification Factor. Going beyond linear calculations, surface elevation statistics are collected to second-order and a `designer' wave is found to model the most extreme surface elevation responses. A `designer' wave can be identified at required levels of return period to help to understand the relative size of harmonic components in extreme waves. The methods developed with a fixed body are then applied to an identical hull which is freely floating, and the responses between the fixed and moving cases are compared. The vertical heave motion of a semi-submersible in-phase with the incident wave crests is shown to lead to a much lower probability of water-deck impact for the same hull shape restrained vertically. The signal processing methods developed are also applied to a single column to allow comparison with experimental results. Individual harmonic components of the hydrodynamic force are identified up to at least the fifth harmonic. Stokes scaling is shown to hold even for the most violent interactions. It is also shown that the higher harmonic components of the hydrodynamic force can be reconstructed from just the fundamental force time history, and a transfer function in the form of a single phase and an amplitude for each harmonic. The force is also reconstructed well to second-order from the surface elevation time history using diffraction transfer functions. Finally, possible causes of damage to a platform high above mean water level in the North Sea are investigated.

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Stuart, Duncan Charles Alistair. „Characterizing long wave agitation in the port of Ngqura using a Boussinesq wave model“. Thesis, Stellenbosch : Stellenbosch University, 2013. http://hdl.handle.net/10019.1/85567.

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Thesis (MScEng)-- Stellenbosch University, 2013.
ENGLISH ABSTRACT: The port of Ngqura is situated on the east coast of South Africa. Since its first operational winter excessive vessel motions have interrupted container shipping operations and lead to mooring line failure. A major component contributing to the excessive motions is the presence of seiching in the port, resonating long waves. This study investigates the long wave generation, penetration into the port and subsequent resonance in the vicinity of the problem berths. An extensive literature review identified two predominant types of long waves along the coast of South Africa. Long waves with periods over 12 min generated by resonant air-water coupling and then shorter long waves between 30 s and 6 min attributed to bound long wave energy and broadly speaking, surf beat. A review of the state of the art long wave modelling techniques was included and contributed to the methodology in this study. Analysis of simultaneous measurements from the outside and inside of the port confirmed the generating mechanism of the long waves to be storm systems also responsible for generating short waves. Long waves outside the port were found to be on average 8% of the height of the short waves. On average 90% of the long wave height outside the port penetrated the port. The measurements further identified distinct resonating periods of the long wave energy inside the port. Calibrated Boussinesq wave models allowed for identification of how long waves penetrated the port and subsequently resonated. Both surface elevation measurements and white noise spectra were used as inputs. The penetration mechanisms were attributed to direct diffraction around the main breakwater as well as reflection off the beach south of the port leading to refraction and reflection off the lee side of the main breakwater. Tests with both free and bound long waves proved that at least for some period intervals the long wave energy was indeed bound to short waves. The excessive vessel motions are attributed to berths positioned in line with nodes created by the resonating long waves; nodes are characterized by strong horizontal currents which can induce surge motions in vessels. Various long waves between the period intervals of 45 s to 125 s resonate in the port to generate nodes at the berths of interest. In conclusion, the port of Ngqura is susceptible to a range of long wave periods resulting in significant basin oscillations which present nodes at mooring places. As a result of the analyses in this study the mechanisms of interaction between the port, port basins and the long waves penetrating into the port directly, or via the surf zone as surf beats, have been modelled, documented and better understood. This provides the potential for better prediction of severe long wave events and for the investigation of feasible mitigation measures to prevent damage to moored ships in the port.
AFRIKAANSE OPSOMMING: Die Ngqura hawe is aan die ooskus van Suid-Afrika geleë. Sedert die hawe se eerste operasionele winterseisoen, het oormatige skeepsbewegings operasies van behoueringskepe onderbreek en gelei tot faling van vasmeertoue. Die teenwoordigheid van langgolf resonansie is ‘n groot bydraende faktor tot die oormatige skeepsbewegings. Hierdie studie ondersoek die opwekking, penetrasie en gevolglike resonansie van langgolwe in die areas aangrensend tot die problematiese kaaie. ‘n Uitgebreide literatuurstudie het twee tipes langgolwe aan die Suid-Afrikaanse kus geïdentifiseer, naamlik langgolwe met periodes langer as 12 minute wat deur resonante lug-water koppeling opgewek word en korter langgolwe met periodes tussen 30 s en 6 min wat aan gebonde langgolfenergie of, meer algemeen, surf beat toegeskryf word. Verder is ‘n studie rakende die jongste langgolfmodelleringstegnieke ook uitgevoer waaruit die metodiek van hierdie studie bepaal is. ‘n Analise van gelyktydige opmetings binne en buite die hawe het bevestig dat kortgolwe wat deur stormsisteme gegenereer word, die opwekkingsmeganisme van lang golwe is. Daar is bevind dat langgolwe buite die hawe gemiddeld 8% so hoog soos kort golwe is. ‘n Gemiddeld van 90% van die langgolfhoogte het die hawe penetreer. Die opmetings het ook verder duidelike resonansieperiodes van langgolfenergie binne die hawe aangedui. Gekalibreerde Boussinsq-golfmodelle is gebruik om te indentifiseer hoe langgolwe die hawe binnedring en gevolglik resoneer. Beide oppervlakmetings en wit geraas spektra is as invoerwaardes vir die model gebruik. Die penetrasiemeganismes is toegeskryf aan diffraksie rondom die hoof hawemuur asook refleksie vanaf die strand, suid van die hawe, wat lei tot refraksie en refleksie teen die lykant van die hoof hawemuur. Toetse met vry langgolwe het bewys dat die langgolfenergie, vir ten minste sommige periode intervalle, aan die kort golwe vebonde is. Die oormatige skeepsbewegings is toegeskryf aan die kaaie wat in lyn met nodes van die langgolfresonansie geposisioneer is. Nodes word gekarakteriseer deur sterk horisontale strome wat surge bewegings in skepe kan veroorsaak. Verskeie langgolwe met periode intervalle tussen 45 s tot 125 s resoneer in die hawe en vorm nodes by die kaaie van belang. Ten slotte, die Ngqura hawe is vatbaar vir ‘n reeks langgolfperiodes wat ossilasies in die bekkens van die hawe veroorsaak en nodes naby kaaie vorm. As gevolg van die analises in hierdie studie is die meganismes van interaksie tussen die hawe, sy bekkens en langgolwe wat die hawe direk of via die brandersone binnedring gemodelleer, gedokumenteer en beter verstaan. Hierdeur is die potensiaal vir beter voorspelling van ernstige langgolftoestande verhoog en is dit moontlik gemaak om lewensvatbare oplossings vir skade aan vasgemeerde skepe te ondersoek.

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Kühn, Yannik. „Machine Learning Methods for the Analysis of Coastal Sea States“. Electronic Thesis or Diss., Pau, 2024. http://www.theses.fr/2024PAUU3029.

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Des prévisions de vagues précises sont essentielles pour de nombreuses communautés côtières, car elles contribuent à assurer la sécurité des opérations maritimes, la prévention des risques côtiers, ou encore les activités nautiques de loisir. Bien que des prévisions fiables existent aux échelles globales à régionales, les prévisions locales à haute résolution font souvent défaut en raison de leur coût de calcul élevés. Cependant, les récentes avancées en apprentissage automatique ont permis de développer plusieurs approches prometteuses permettant de réduire considérablement le temps de calcul des prévisions.Cette thèse étudie l'une de ces approches d'apprentissage automatique, nommée super-résolution, qui a déjà été employée avec succès pour accélérer les calculs dans le domaine de la mécanique des fluides.Le concept consiste à utiliser un modèle numérique sur un maillage de basse résolution, puis à convertir les résultats en une résolution plus élevée à l'aide d'un modèle d'apprentissage automatique entraîné, évitant ainsi de lourds calculs numériques en haute résolution. Ce travail analyse la faisabilité d'une approche de super-résolution appliquée aux prévisions de vagues en zone côtière. La première partie de cette thèse présente une étude conceptuelle de la méthode de super-résolution appliquée aux résultats d'un modèle spectral de vagues avec maillage structuré. Cette étude démontre qu'une telle approche peut accélérer les prévisions jusqu'à 50 fois par rapport à un calcul direct à haute résolution, avec une erreur négligeable devant celles habituellement observées pour le modèle. La deuxième partie de cette thèse étend la méthode aux maillages non structurés, analysant l'influence des conditions bathymétriques et des régimes énergétiques différents fournis par une simulation rétrospective des états de mer au large de la côte basque. Il est constaté que les réseaux de neurones en graphes et les régressions polynomiales sont deux approches prometteuses, la première étant plus adaptée à des champs de vagues très variables et la seconde à des contextes où le critère de rapidité est essentiel. Une troisième partie de la thèse est consacrée à l'application de la méthode aux spectres de vagues. Bien qu'il soit complexe d'évaluer le meilleur des quatre modèles testés, les résultats suggèrent que la super-résolution est capable de fournir des prédictions précises et rapides des spectres simulés à haute résolution en différents point distribués à travers la zone d'étude
Precise wave forecasts are essential for many coastal communities as they help ensuring safe maritime operations, mitigation of coastal hazards, and the enjoyment of marine recreation. While a reliable global forecast coverage does exist, local, high-resolution forecasts are often not available in many areas due to a significant computational demand. However, recent advances in machine learning have produced several promising approaches to drastically reduce forecast computation time.This thesis investigates one such machine learning approach called super-resolution, that was already successfully employed to speed up computations in fluid mechanics.The concept involves using a numerical model over a mesh with coarse resolution and then converting the results to a higher resolution using a trained machine learning model, thereby avoiding heavy computations in high resolution. This thesis examines the feasibility of the super-resolution approach for coastal wave forecasts. The first part of the thesis presents a proof-of-concept study on data-driven super-resolution using results from a spectral wave model over a structured grid. It demonstrates that this approach can accelerate forecasts by up to 50 times compared to a direct high-resolution computation, with a negligible loss in accuracy. The second part extends this method to unstructured meshes, analyzing the influence of bathymetry and wave energy conditions through a hindcast along the Basque coast. It is found that graph neural networks and polynomial regressions are promising approaches, where the former is suited for highly variable wave fields and the latter for scenarios where speed is paramount. A third part extends the application of super-resolution to wave spectra directly. Despite challenges in evaluating the best model among four tested options, the results suggest that data-driven super-resolution can provide accurate and fast predictions of spatially distributed wave spectra with an accuracy comparable to high-resolution wave model computations

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Wust, Isak. „A feasible design concept for the deep water breakwater of the proposed new Durban Dig-Out Port“. Thesis, Stellenbosch : Stellenbosch University, 2014. http://hdl.handle.net/10019.1/95969.

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Thesis (MEng)–Stellenbosch University, 2014.
ENGLISH ABSTRACT: The Port of Durban is forecasted to reach its capacity in terms of container handling soon, which necessitates the investigation of an alternative port in the vicinity. The old Durban Airport site has been identified as a potential location to develop a new deep water container harbour. This is driven by a demand for deep water berth capacity as a result of shipping liners preferring the benefits of scale in their operations, leading to the use of larger ships with deeper drafts. To protect the new port from wave energy penetrating inside the basin as well as from sedimentation from the adjacent beaches, the design and construction of breakwaters are required. The proposed main breakwater for this dig-out port is expected to extend 1 200m into the sea, up to depths of 30m at the seaward roundhead. The deeper parts of the breakwater face wave onslaught in a different manner than a conventional breakwater in shallower waters. At these larger depths, the breakwater has to dissipate the energy of non-breaking waves. In this thesis, the wave climate nearshore, adjacent to the proposed breakwater is studied and extreme wave events are simulated with a SWAN numerical model. The results for a range of wave conditions, corresponding to selected events up to a return period of one in 100 years, are presented. A study of deep water breakwaters was undertaken to investigate other examples of similar structures. This indicated a clear distinction between vertical wall type breakwaters and the more traditional rubble-mound type breakwaters. For this thesis, a rubble-mound breakwater was chosen as the breakwater type for testing under conditions of the Durban Dig-Out Port (DDOP). Focussing on a deep water trunk section of the proposed main breakwater, a concept cross-section was designed using deterministic design methods. The formulae incorporated in this method did however not take into account the packing density of the armour layer and only assumed the recommended values. The hypothesis is thus put forward that the breakwater will still be hydraulically stable for packing densities below the recommended values. This would decrease material consumption and save on cost over the entire breakwater. A physical model was designed to experiment with different armour layer configurations of single- and double layer Cubipod arrangements. The unit was chosen for its massive shape and structural integrity even during impact. A physical model study was performed at the facilities of the CSIR in Stellenbosch. It entailed setting up a fixed-bed two-dimensional physical model in a glass wave flume. Measuring wave heights, wave reflection, overtopping, wave transmission and armour damage, the hydraulic stability and operational performance were analysed for several tests. Based on the results of the first few test series, alterations were made to the breakwater geometry and armouring. The results confirmed the hypothesis that lower packing densities were still hydraulically stable under 1 in 100 year return period wave conditions without inhibiting operational performance. A final cross-section is presented as concept design for the deep section of the proposed DDOP main breakwater.
AFRIKAANSE OPSOMMING: Volgens vooruitsigte gaan Durban hawe binnekort sy kapasiteit bereik wat die hantering van skeepshouers betref. Hierdie verwikkeling noodsaak die ondersoek na ‘n alternatiewe hawe in die nabye omgewing. Die voormalige Durban lughawe is intussen geïdentifiseer as ‘n potensiële perseel waar ‘n diep water houervrag hawe ontwikkel kan word. Dit word gedryf deur die aanvraag na diep water kaai kapasiteit as gevolg van skip operateurs wat skaalvoordele verkies, sodat groter skepe met diep rompe meer populêr word. Die ontwerp en konstruksie van breekwaters word dus benodig, om te verhoed dat beide golwe, sowel as sediment van aangrensende strande, die hawe binnedring. Die voorgestelde hoof breekwater vir hierdie hawe sal na verwagting tot 1200m in die see in strek, waar dit tot 30m diep is naby die seewaartse hoof van dié breekwater. Die dieper gedeeltes van só ‘n breekwater sal blootgestel word aan ‘n ander soort golf aanslag as ‘n soortgelyke konvensionele breekwater in vlakker water. In hierdie waterdiepte is die breekwater verantwoordelik vir die energie verbreking van ongebreekte golwe. In hierdie tesis word die golfklimaat langs die kus, naby aan die voorgestelde breekwater bestudeer. Die uiterste golf gebeurtenisse word gesimuleer met ‘n SWAN numeriese model. Die resultate van ‘n reeks golf kondisies, ooreenstemmend met bepaalde gebeurtenissemet herhaal periodes van tot 100 jaar, word aangebied. ‘n Studie van diep water breekwaters is onderneem om voorbeelde van soortgelyke strukture te ondersoek. Die studie toon ‘n definitiewe onderskeid tussen vertikale muur breekwaters en die meer tradisionele “rubble-mound” breekwater tipes. Vir hierdie tesis is die “rubble-mound” breekwater tipe gekies vir toetsing, onderhewig aan die kondisies van die “Durban Dig-Out Port” (DDOP). ‘n Konsep deursnit is ontwerp vir ‘n diep water romp gedeelte van die voorgestelde hoof breekwater, deur van deterministiese metodes gebruik te maak. Die formules soos vervat in hierdie proses maak egter nie voorsiening vir die pakdigtheid van die bewapeningslaag nie, maar aanvaar slegs die voorgestelde waardes. Die hipotese word dus aangevoer dat die breekwater steeds hidrolies stabiel sal wees vir pakdigthede wat laer as die voorgestelde waardes is. Dit sal die verbruik van materiale verlaag en lei tot koste besparings vir die breekwater. ‘n Fisiese model is ontwerp om te eksperimenteer met verskillende opstellings van die bewapeningslaag. Dit sluit enkel- en dubbel laag bewapening met Cubipod eenhede in. Hierdie eenheid is gekies vir sy massiewe vorm en strukturele integriteit, selfs tydens impak. ‘n Fisiese model studie is uitgevoer by die fasiliteite van die WNNR in Stellenbosch. Dit het die opstel van ‘n vaste-bodem, twee-dimensionele fisiese model in ‘n glas golftenk (“wave flume”) behels. Hidroliese stabiliteit en operasionele werksverrigting is geanaliseer deur golf hoogtes, -weerkaatsing, -oorslag, -deurlating, en skade aan die bewapening te meet vir verskeie toetse. Gebasseer op die resultate van die eerste paar toetsreekse, is veranderinge gemaak aan die breekwater se geometrie en bewapening. Die resultate het die hipotese bevestig dat laer pakdigthede steeds hidrolies stabiel is tydens golf kondisies met ‘n 1 in 100 jaar herhaal periode, sonder om die werksverrigting van die breekwater te belemmer. ‘n Finale deursnit word voorgestel as ‘n konsepontwerp vir die diep water deursnit van die DDOP se hoof breekwater.

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Schoonees, Talia. „Impermeable recurve seawalls to reduce wave overtopping“. Thesis, Stellenbosch : Stellenbosch University, 2014. http://hdl.handle.net/10019.1/86369.

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Thesis (MScEng)--Stellenbosch University, 2014.
ENGLISH ABSTRACT: Sea-level rise due to climate change results in deeper water next to existing coastal structures, which in turn enables higher waves to reach these structures. Wave overtopping occurs when wave action discharges water over the crest of a coastal structure. Therefore, the higher waves reaching existing structures will cause higher wave overtopping rates. One possible solution to address increasing overtopping, is to raise the crest level of existing coastal structures. However, raising the crest level of a seawall at the back of a beach, will possibly obstruct the view to the ocean from inland. Alternatively, recurves can be incorporated into the design of both existing and new seawalls. The recurve wall reduces overtopping by deflecting uprushing water seawards as waves impact with the wall. The main advantage of seawalls with recurves is that their crest height can be lower, but still allow for the same wave overtopping rate as vertical seawalls without recurves. This project investigates the use of recurve seawalls at the back of a beach to reduce overtopping and thereby reducing the required wall height. The objectives of the project are twofold, namely: (1) to compare overtopping rates of a vertical seawall without a recurve and seawalls with recurves; and (2) to determine the influence that the length of the recurve overhang has on the overtopping rates. To achieve these objectives, physical model tests were performed in a glass flume equipped with a piston type wave paddle that is capable of active wave absorption. These tests were performed on three different seawall profiles: the vertical wall and a recurve section with a short and a long seaward overhang, denoted as Recurve 1 and Recurve 2 respectively. Tests were performed with 5 different water-levels, while the wall height, wave height and period, and seabed slope remained constant. Both breaking and non-breaking waves were simulated. A comparison of test results proves that the two recurve seawalls are more effective in reducing overtopping than the vertical seawall. The reduction of overtopping can be as high as 100%, depending on the freeboard and wave conditions. Recurve 2 proves to be the most efficient in reducing overtopping. However, in the case of a high freeboard (low water-level at the toe of the structure), the reduction in overtopping for Recurve 1 and Recurve 2 was almost equally effective. This is because all water from the breaking waves is reflected. Even for the simulated lower relative freeboard cases, the recurve walls offer a significant reduction in overtopping compared with the vertical wall. A graph is presented which shows that the length of the seaward overhang influences the overtopping performance of the seawall. As the seaward overhang length increases, the wave overtopping rate decreases. However, for high freeboard cases the length of the seaward overhang becomes less important. The graph gives designers an indication of how recurves can be designed to reduce seawall height while retaining low overtopping. It is recommended that further model tests be performed for additional overhang lengths. Incorporation of recurves into seawall design represents an adaptation to problems of sea-level rise due to global warming
AFRIKAANSE OPSOMMING: Stygende seevlak as gevolg van klimaatverandering, veroorsaak dat dieper water langs bestaande kusstrukture voorkom. Gevolglik kan hoër golwe hierdie strukture bereik. Golfoorslag vind plaas wanneer water oor die kruin van ‘n kusstruktuur, hoofsaaklik deur golfaksie, spat of vloei. Dus sal hoër golfhoogtes tot verhoogde golfoorslag lei. Een moontlike oplossing vir hierdie verhoogde golfoorslag is om die kruinhoogte van bestaande kusstrukture te verhoog. In die geval van ‘n seemuur aan die agterkant van ‘n strand, kan hoër strukture egter die see-uitsig na die see vanaf die land belemmer. Om hierdie probleem te vermy, kan terugkaatsmure in die ontwerp van bestaande en nuwe seemure ingesluit word. Terugkaatsmure verminder golfoorslag deurdat opspattende water, afkomstig van invallende golwe terug, na die see gekaats word. Die grootste voordeel van ‘n terugkaatsmuur is dat hierdie tipe muur ‘n laer kruinhoogte as die vertikale seemuur sonder ‘n terugkaatsbalk, vir dieselfde golfoorslagtempo kan hê. Hierdie projek ondersoek dus die gebruik van terugkaatsmure aan die agterkant van ‘n strand met die doel om golfoorslag te verminder en sodoende die vereiste muurhoogte te verminder. Die doelwit vir die projek is tweeledig: (1) om die golfoorslagtempo van terugkaatsmure te vergelyk met dié van ‘n vertikale muur sonder ‘n terugkaatsbalk; en (2) om die invloed van die terugkaatsmuur se oorhanglengte op die golfoorslagtempo te bepaal. Om bogenoemde doelwitte te bereik, is fisiese modeltoetse in ‘n golfkanaal, wat met ‘n suiertipe golfopwekker toegerus is en wat aktiewe golfabsorbering toepas, uitgevoer. Hierdie toetse is op drie verskillende seemuurprofiele, naamlik ‘n vertikale muur en ‘n terugkaatsmuur met ‘n kort en lang oorhang, genaamd “Recurve 1” en “Recurve 2” onderskeidelik, uitgevoer. Die muurhoogte, die seebodemhelling asook die golfhoogte en –periode is tydens al die toetse konstant gehou. Vir elke profiel is toetse by 5 verskillende watervlakke vir beide brekende en ongebreekte golwe uitgevoer. Uit die toetsresultate is dit duidelik dat terugkaatsmure meer effektief as vertikale mure is om golfoorslag te beperk. Die vermindering van golfoorslag kan tot 100% wees, afhangende van die vryboord en golftoestande. Daar is bevind dat “Recurve 2” golfoorslag die effektiefste verminder. In die geval van hoë vryboord (lae watervlak by die toon van die struktuur) is daar egter gevind dat “Recurve 1” en “Recurve 2” die golfoorslag feitlik ewe goed beperk. Dit is die geval aangesien alle water van die brekende golwe weerkaats word. In die geval van ‘n lae vryboord, word die voordeel van die terugkaatsmuur teengewerk deurdat daar ‘n kleiner verskil in golfoorslagtempo’s tussen die drie profiele is. ‘n Grafiek is voorgelê wat wys dat die lengte van die terugkaatsmuur se oorhang golfoorslag beperk. ‘n Groter oorhanglengte van die terugslagmuur veroorsaak ‘n groter vermindering in golfoorslag. Vir gevalle met ‘n hoë vryboord, is daar egter gevind dat die oorhanglengte van die terugslagmuur minder belangrik is. Hierdie grafiek gee ontwerpers ‘n aanduiding van hoe terugslagmure ontwerp kan word met ‘n lae hoogte terwyl ‘n lae oorslagtempo behou word. Die gebruik van terugslagmure bied ‘n aanpassing vir die probleme van seevlakstyging, as gevolg van klimaatverandering.

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Velissariou, Panagiotis. „Development of a Coastal Prediction System That Incorporates Full 3D Wave-Current Interactions on the Mean Flow and the Scalar Transport With Initial Application to the Lake Michigan Turbidity Plume“. The Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=osu1229959016.

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Trinh, Philippe H. „Exponential asymptotics and free-surface flows“. Thesis, University of Oxford, 2010. http://ora.ox.ac.uk/objects/uuid:e87b1f22-2569-4c0f-86a2-5bde76f34953.

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When traditional linearised theory is used to study free-surface flows past a surface-piercing object or over an obstruction in a stream, the geometry of the object is usually lost, having been assumed small in one or several of its dimensions. In order to preserve the nonlinear nature of the geometry, asymptotic expansions in the low-Froude or low-Bond limits can be derived, but here, the solution invariably predicts a waveless free-surface at every order. This is because the waves are in fact, exponentially small, and thus beyond-all-orders of regular asymptotics; their formation is a consequence of the divergence of the asymptotic series and the associated Stokes Phenomenon. In this thesis, we will apply exponential asymptotics to the study of two new problems involving nonlinear geometries. In the first, we examine the case of free-surface flow over a step including the effects of both gravity and surface tension. Here, we shall see that the availability of multiple singularities in the geometry, coupled with the interplay of gravitational and cohesive effects, leads to the discovery of a remarkable new set of solutions. In the second problem, we study the waves produced by bluff-bodied ships in low-Froude flows. We will derive the analytical form of the exponentially small waves for a wide range of hull geometries, including single-cornered and multi-cornered ships, and then provide comparisons with numerical computations. A particularly significant result is our confirmation of the thirty-year old conjecture by Vanden-Broeck & Tuck (1977) regarding the impossibility of waveless single-cornered ships.

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Coutts-Smith, Aaron J. „The significance of mega-rips along an embayed coast“. Phd thesis, School of Geosciences, 2004. http://hdl.handle.net/2123/6082.

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Hudier, Eric. „Dynamique sedimentaire dans le deferlement (longue pointe de mingan-golfe du saint-laurent)“. Nantes, 1987. http://www.theses.fr/1987NANT2064.

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Ce travail decrit les mecanismes de transport sedimentaire regissant l'equilibre de la premiere barre cotiere ou barre de deferlement. On etudie en particulier les echanges sedimentaires d'axe terre-mer par dessus la premiere barre. L'utilisation de diverses formules de vitesse critique de debut d'entrainement, de calcul du courant littoral et d'estimation du transport sedimentaire permet de faire une etude comparative critique par rapport aux mesures in-situ. On met en evidence deux modes d'evolution differents entre les periodes de temps calme et les periodes de tempetes correspondant a deux modes de transports distincts

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Van, der Westhuysen A. J. „The application of the numerical wind wave model SWAN to a selected field case on the South African coast“. Thesis, Link to the online version, 2002. http://hdl.handle.net/10019.1/3632.

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17

Joubert, J. R. „An investigation of the wave energy resource on the South African Coast, focusing on the spatial distribution of the South West coast“. Thesis, Link to the Internet, 2008. http://hdl.handle.net/10019.1/351.

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18

Williams, Sally Jayne. „Wave-seabed interaction in a stratified coastal environment“. Thesis, The University of Sydney, 2010. https://hdl.handle.net/2123/28910.

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The attenuation of non—breaking waves in shallow waters can be dominated by soft seabed effects as opposed to water viscosity. Due to the complexity of natural systems, rheological approaches can provide useful parameter constraints on natural behaviours. In part I of this thesis a layered rheological model of the seabed is adopted. The upper part of the seabed is considered to be in a state of dynamic liquefaction, whilst the lower portion of the bed is more consolidated. It is demonstrated that in the absence of wave-induced turbulence the magnitude of the surface wave damping due to the presence of the porous bed is greater than that due to shear at the interface between the two fluids. For the case of a shallow layer of fluidised bed material, it is shown that the maximum damping effect of the porous elastic bed coincides with the maximum damping rates due to boundary layer shear effects, thus accentuating wave damping when the dimensionless lower layer depth is approximately 30—50% greater than the non—dimensionalised boundary—layer thickness. In part II of this thesis a model for the interaction between interfacial waves with the seabed is considered. A new wave dispersion equation is derived for waves on a two-layer stratification above a porous seabed including free surface effects. Numerical results indicate that the wavelength and wave amplitude are attenuated faster by a coarse seabed material as opposed to a fine sandy bed. It is shown that the profile of an interfacial wave exhibits properties similar to that of an interfacial wave propagating above a rigid bed and agrees qualitatively with observations of interfacial waves in littoral waters. The effect of a porous elastic bed is to increase the wave steepness, causing a narrower crest and a Wider trough. Comparison of the numerical results with experimental results on the different mechanisms for interfacial wave decay show that, in water of intermediate depth, the energy attenuation caused by a coarse—grained sandy seabed is greater than that due to bottom boundary layer damping, interfacial wave shear or interior Viscous damping.

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Khan, Muhammad Ahsan. „CFD Applications for Wave Energy Conversion Devices (MoonWEC) and Turbulent Fountains for Environmental Fluid Mechanics“. Master's thesis, Alma Mater Studiorum - Università di Bologna, 2020.

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This thesis is based on two studies that are related to floating wave energy conversion (WEC) devices and turbulent fountains. The ability of the open-source CFD software OpenFOAM® has been studied to simulate these phenomena. The CFD model has been compared with the physical experimental results. The first study presents a model of a WEC device, called MoonWEC, which is patented by the University of Bologna. The CFD model of the MoonWEC under the action of waves has been simulated using OpenFOAM and the results are promising. The reliability of the CFD model is confirmed by the laboratory experiments, conducted at the University of Bologna, for which a small-scale prototype of the MoonWEC was made from wood and brass. The second part of the thesis is related to the turbulent fountains which are formed when a heavier source fluid is injected upward into a lighter ambient fluid, or else a lighter source fluid is injected downward into a heavier ambient fluid. For this study, the first case is considered for laboratory experiments and the corresponding CFD model. The vertical releases of the source fluids into a quiescent, uniform ambient fluid, from a circular source, were studied with different densities in the laboratory experiments, conducted at the University of Parma. The CFD model has been set up for these experiments. Favourable results have been observed from the OpenFOAM simulations for the turbulent fountains as well, indicating that it can be a reliable tool for the simulation of such phenomena.

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Adcock, Thomas A. A. „Aspects of wave dynamics and statistics on the open ocean“. Thesis, University of Oxford, 2009. http://ora.ox.ac.uk/objects/uuid:e5631aa8-b6c8-4d85-b8a2-c6df2a30beab.

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Water waves are an important design consideration for engineers wishing to design structures in the offshore environment. Designers need to know the size and shape of the waves which any structure is likely to encounter. Engineers have developed approaches to predict these, based on a combination of field and laboratory measurements, as well theoretical analysis. However some aspects of this are still poorly understood; in particular there is growing evidence that there are rare "freak" waves which do not fit with our current understanding of wave physics or statistics. In the first part of this thesis a new approach is developed for measuring the directional spreading of a sea-state, when the free surface time-history at a single point is the only available information. We use the magnitude of the second order "bound" waves to infer this information. This is validated using fully non-linear simulations, for random waves in a wave-basin, and for field data recorded in the North Sea. We also apply this to the famous Draupner wave, which our analysis suggests was caused by two wave systems, propagating at approximate 120 degrees to each other. The second part of the thesis looks at the non-linear evolution of Gaussian wave-groups. Whilst much work has previously been done to investigate these numerically, we instead derive an approximate analytical model for describing the non-linear changes to the group, based on the conserved quantities of the non-linear Schrodinger equation. These are validated using a numerical model. There is excellent agreement for uni-directional waves. The analytical model is generally good for predicting change in shape of directionally spread groups, but less good for predicting peak elevation. Nevertheless, it is still useful for typical sea-state parameters. Finally we consider the effect of wind on the local modeling of extreme waves. We insert a negative damping term into the non-linear Schrodinger equation, and consider the evolution of "NewWave" type wave-groups. We find that energy input accentuates the non-linear dynamics of wave-group evolution which suggests it may be important in the formation of "freak" waves.

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Duman, Cagatay. „Evaluation And Comparison Of The Wave Energy Potential In Selected Coastal Regions In Turkey“. Master's thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/12612626/index.pdf.

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In order to meet energy needs in world, studies on wave energy, alternative energy, are becoming more and more important with each passing day. The purpose of this study is to identify the wave energy potential along the coastline of Turkey. For this purpose, the data of wind speed and direction, swell and wind wave height, period and direction for certain duration with the six hours time intervals are obtained from ECMWF for the wind and wave climate computations. In order to compute the wind and wave climate at any selected coastal location, software is developed by Serhan Aldogan in his MSc thesis. By the help of the specifically developed software, for every location, by utilizing existing wind data, depending on geographical location of station, in the direction of energy thought to produce, by using calculated average wind speed of storm which is above the selected wind speed u0, characteristics (Hs
Tm) of the waves of this storm and power (P, W/m) per unit length will be calculated. The duration curves for power, Hs and T, can be obtained. The duration curve represents the occurrence of the parameter (wave height, wave period, wave energy or wave power). It can also be called occurrence curve or availability curve. From these curves, for various percentages of the total storm duration, P, Hs and T&rsquo
s values can be determined. Also, in the analysis, the shapes of these curves can provide important information about the available wave energy for the selected coasts.

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Fleming, Conor F. „Tidal turbine performance in the offshore environment“. Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:f51fd313-1589-4e9c-98cc-ae6e64c1184b.

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A three dimensional computational model of a full scale axial flow tidal turbine has been used to investigate the effects of a range of realistic environmental conditions on turbine performance. The model, which is based on the Reynolds averaged Navier-Stokes equations, has been developed using the commercial flow solver ANSYS Fluent. A 1:30 scale tidal turbine is simulated in an open channel for comparison to existing experimental data. The rotor blades are directly resolved using a body-fitted, unstructured computational grid. Rotor motion is enabled through a sliding mesh interface between the rotor and the channel boundaries. Reasonably good agreement in thrust and power is observed. The computed performance curves are offset from the measured performance curves by a small increment in rotor speed. Subsequently, a full scale axial flow turbine is modelled in a variety of conditions representative of tidal channel flows. A parametric study is carried out to investigate the effects of flow shear, confinement and alignment on turbine performance, structural loading, and wake recovery. Mean power and thrust are found to be higher in sheared flow, relative to uniform flow of equivalent volumetric flow rate. Large fluctuations in blade thrust and torque occur in sheared flow as the blade passes through the high velocity freestream flow in the upper portion of the profile and the lower velocity flow near the channel bed. A stronger shear layer is formed around the upper portion of the wake in sheared flow, leading to enhanced wake mixing. Mean power and thrust are reduced when the turbine is simulated at a lower position in a sheared velocity profile. However, fluctuations in blade loading are increased due to the higher velocity gradient. The opposite effects are observed when the turbine operates at greater heights in sheared flow. Flow misalignment has a negative impact on mean rotor thrust and power, as well as on unsteady blade loading. Although the range of unsteady loading is not increased significantly, additional perturbations are introduced due to interactions between the blade and the nacelle. A deforming surface is introduced using the volume-of-fluid method. Linear wave theory is combined with the existing free surface model to develop an unsteady inflow boundary condition prescribing combined sheared flow and free surface waves. The relative effects of the sheared profile and wave-induced velocities on turbine loading are identified through frequency analysis. Rotor and blade load fluctuations are found to increase with wave height and wave length. In a separate study, the performance of bi-directional ducted tidal turbines is investigated through a parametric study of a range of duct profiles. A two dimensional axi-symmetric computational model is developed to compare the ducted geometries with an unducted device under consistent blockage conditions. The best-performing ducted device achieves a peak power coefficient of approximately 45% of that of the unducted device. Comparisons of streamtube area, velocity and pressure for the flow through the ducted device shows that the duct limits the pressure drop across the rotor and the mass flow through the rotor, resulting in lower device power.

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23

Smith, Albert William S. „The function and behaviour of natural beaches“. Thesis, Queensland University of Technology, 1986. https://eprints.qut.edu.au/36454/1/36454_Smith_1986_Vol-1.pdf.

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This study may well be considered to represent a rather simplistic contribution, towards the science of coastal engineering. This is in fact, perhaps as it should be, because the mathematics involved, are of the most basic kind, and no profound theories have been expounded. This work has nothing to do with the development of existing theories or existing dogma, within the current realms of the particular discipline. That must remain for others. This writer is not a scientist within any stretch of the classification, he remains a simple engineer, who has spent most of his life, in the role of being that of a basic observer. This status is often regarded as being that of a semi-professional technician, and perhaps that is rightly so. On the other hand, the common observer, in recording his observations, might still well contribute something of value. He might for example, document his prototype experiences particularly where he finds that classical theory does not fit the "facts" as he sees them. He might also well ponder why these theories appear to predict natural process phenomenon, that cannot be seen on the prototype, or where the real prototype can be readily seen to be doing something different. These things are what this study is made from. In dealing with coastal process observations, the writer's first introduction to the subject occurred late in 1938, on the Paekakariki coast of New Zealand. At that time, very profound changes were affecting the entire fabric of this coastal area, after many decades of relatively prior stability. At that time, a coastal recession of 50m in one year was obvious, as was the degradation of a previous completely sandy beach, into a residual boulder remnant within three years. These things exerted an immense impact on this writer as a juvenile - he could appreciate the dramatic effect of Nature even then - guided no doubt by his engineer father, a Marine Engineer of vast experience. At least the writer's family, always expounded the thesis, that an ounce of observation was often worth a pound of theory, and perhaps sometimes, even a ton. In very many ways, it may well be reasonable to conclude that this very primitive concept, may still hold some reasonable value. This work therefore, is an attempt to record the results of a lifetime's observations of natural coastal processes, together with a rather hesitant approach towards postulating the mechanisms, that are the central essence of these processes. If much of this work is orientated towards interpretating, the subtle interactions of Nature, in addressing coastal engineering actions and responses, then this has been deliberate. This in many ways, is only a crude representation of how Nature really works. Nature, it might be noted, appears quite benign for most of the time, such that when an extreme event hits us, we often consider this an extraordinary event, in fact often as an "Act of God". This is not Nature's way at all. In everything that Nature does, she displays a very single minded, pragmatic, quite re~entless and ruthless approach to every natural reaction. Every natural resource is treated for the maximum of economy of resources - nothing is ever wasted. If any action cannot be counterbalanced by the available reaction resources, then these current resources are instantly discarded (to be used later for other purposes) and another line of defence mechanisms are immediately called into action. The more one may consider these natural processes, then the more obvious the fantastic inter-relationship~ that are called into action - may become obvious. Mankind, in its engineering arro5c:illce, often chooses to ignore Nature's action, and response mechanisms. Coastal engineers are particularly prone to fall into this error. They only so often conclude that their small scale hydraulic flumes, may completely eliminate the total fury of Nature, on the prototype, as a hazard. In this, they have to date, proven to be sadly in error. The dramatic failures at Keelung, Sines, Bilbao, San Ciprian (and others) all attest to this miss-placed, self appointed, over-confidence in engineering interpretations, of Nature's real and often unexpectedly "raw" behaviour. It seems that the design of major coastal structures, is commonly accepted as being capable of conclusion within offices and laboratories, far remote from the site. It is tendered here, that this isolationist approach, must be an open invitation to the unexpected, and thus to total failure. Such, only happens so often, in real coastal engineering practice. This work therefore, is entirely related towards an attempt to interpret and explain Nature's processes, and all based upon observations on the prototype. For certain, many of the interpretations made, may later be shown to be in error. However, one must start somewhere, and this is at least an attem:pt to do so. Many of the things said herein, may appear to the more orthodox, to be irrational, unprecedented or even nonsense. As such, the conventional orthodox are welcome to their own opinions. What is set-out herein, is entirely the writer's opinions, and he will stand by them. These opinions however, are not the resultants of reading only other people's publications nor interpreting only other people's data. What is recorded here is the results of sim:ple site observation on dozens of prototypes, over a period of forty years or more. Whether these observations are of any value, must in the end, be up to the reader. Only time will tell.

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Holt, Robert D. „Rip current spacing in relation to wave energetics and directional spreading“. Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2003. http://library.nps.navy.mil/uhtbin/hyperion-image/03Jun%5FHolt.pdf.

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Thesis (M.S. in Physical Oceanography)--Naval Postgraduate School, June 2003.
Thesis advisor(s): Edward B. Thornton, Timothy Stanton. Includes bibliographical references (p. 59-62). Also available online.

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MACHADO, GUILHERME AMADO. „OCEAN WAVE ENERGY IN URBAN COASTAL AREAS: A CASE STUDY IN THE LEME DISTRICT, RIO DE JANEIRO“. PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2016. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=29319@1.

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O crescimento da população urbana e o incremento na demanda por energia elétrica para residências brasileiras, especialmente em zonas costeiras, indicam a relevância do aproveitamento da energia oceânica para o Brasil. Neste cenário, o trabalho investiga o potencial de energia de ondas na orla da cidade do Rio de Janeiro e suas possíveis relações com o planejamento sustentável da engenharia urbana costeira. O estudo sobre a microbacia do Bairro do Leme, localizado na orla oceânica da zona sul da cidade do Rio de Janeiro, estima um potencial de energia oceânica por aproveitamento energético das ondas do mar capaz de suprir a demanda de energia elétrica para toda a população do Bairro em torno de 14.000 pessoas. O potencial energético das ondas foi estimado a partir da análise estatística de um prognóstico anual do clima de ondas para essa orla, elaborado através da modelagem computacional de propagação de ondas. Sendo utilizados onze anos dados de onda extraídos do modelo global ERA/INTERIM. Em um modelo físico-reduzido (escala 1:40) do perfil tipo da orla do Leme, construído em canal de ondas irregulares, foi avaliada a vulnerabilidade da orla ao risco de galgamento de ondas durante extremos de marés de ressaca. Nos ensaios de modelagem física também foram testadas soluções de engenharia com vistas ao aproveitamento e controle do potencial energético de ondas. Com os resultados obtidos das modelagens, discute-se um plano conceitual para resiliência urbano-costeira da orla oceânica baseado na reengenharia do perfil de praia elaborado no projeto de obra estabelecido em 1970.
The growth of urban population and the increasing demand for electricity to Brazilian consumers, especially in coastal areas, indicate the importance of the use of ocean energy for Brazil. In this scenario, this thesis investigates the wave energy potential on the south area of the city of Rio de Janeiro and its possible relation to sustainable planning of the coastal urban engineering. About 3.9 billion people (54 per cent of world population) live in urban areas. It is estimated that the growth of cities should result in an urban population of over 6.4 billion people by 2050, especially in the less developed areas, with poor urban planning and vulnerable to environmental risks (UN-Habitat, 2016). The urbanization of coastal areas in developing countries demands greater attention due to infrastructure needs and the necessary management to mitigate pressures of increasing human activities on the environment (Cicin-Sain and Knecht, 1998). This framework is particularly important for Brazil that has a high degree of urbanization with marked concentration of population in its coastline (IBGE, 2015) with urban interventions on ocean beaches through works poorly integrated into the city, neglecting nature s ability to claim the balance taken away from her. According to the report Act Now or Pay Later, made by the organization Christian Aid, the rapid growth of urban populations along the coastlines of the world and the growing threat of climate change display evidences that more than one billion people will be vulnerable to coastal flooding in 2060 (Doig and Ware, 2016), in cities exposed to rising sea level, which should increase for the next century in global average between 0.18 and 0.70 meters above the current level (IPCC, 2014).

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Tong, Judith Anne. „Development of a finite element model for the modelling of topography induced internal wave behaviour in the coastal ocean“. Thesis, The University of Sydney, 2016. http://hdl.handle.net/2123/14356.

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It is universally accepted that the world’s oceans act as a large heat engine and play a critical role in shaping the earth’s climate. Understanding ocean circulation and the transport of heat throughout the global ocean is thus a necessary and challenging journey for the climate scientist. The physical oceanography community, in trying to construct better ocean models, are calling for improved representation of mesoscale processes and associated mixing. Processes specifically targeted are those occurring about the thermocline such as wave and vortical modes. Tidal currents over deep ocean and shallow coastal topographies are a strong source of internal waves and mixing. Today, ocean general circulation models are primarily based on the Reynolds averaged Navier-Stokes (RANS) equations with the hydrostatic pressure approximation and a finite difference numerical formulation. Mesoscale processes and mixing are represented through sub-grid scale parameterisations, sometimes by rather elementary forms of vertical diffusivity. Recently, an exciting shift has become apparent, with momentum towards ‘next generation’ ocean models with non-hydrostatic physics and finite element numerics. These models are still in their infancy for global application and hence the need remains for smaller higher resolution diagnostic models to examine mesoscale and small scale mixing processes in more detail and assist with their customised parameterisation. This was the impetus for pursuing the present research. This thesis describes the development of a hydrodynamic code for buoyancy influenced topographic flow. To represent bathymetry and density variation, a two-dimensional (x-z) modelling domain was chosen. The model is based on the steady state RANS equations, is non-hydrostatic, has a k-ε turbulence closure and employs the finite element method. A non-hydrostatic formulation is necessary in order to capture internal wave behaviour and wave-current interactions. The k-ε model calculates turbulence quantities with turbulence dissipation rate both a practical parameter and with potential to link with established spectral laws. A pressure split combined with a supporting spline routine for calculation of horizontal hydrostatic pressure gradients and an implicit implementation of a discontinuous Galerkin method flux in the element coefficient matrices for density transport are two novel approaches attempted in this study. Both theories were introduced with the aim to help overcome computational difficulties associated with buoyancy influenced flows. A number of model simulations have been performed for simple geometry problems at laboratory scale, including simulations of the widely used benchmark problem of the backward facing step. Model results are compared to two backward facing step experimental data sets and the model is shown to perform well, with good agreement in the key flow characteristic of reattachment point, demonstrating verification and validation of the code. Simulations are also conducted using scaled down topography of two coastal sills, to apply the model to a more natural topography. The flow field and density contours from the steady state simulations do not resemble sill field observations at the time of maximum sill flow and it is concluded that a transient model is required for the gradual build up of complex flow conditions that eventually lead to the observed flow features at maximum tidal flow.

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Rouse, Sally. „Quantifying benthic secondary productivity on artificial structures : maximising the benefit of marine renewable energy devices“. Thesis, University of Aberdeen, 2016. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=231790.

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Marine renewable energy developments (MRED) will result in large quantities of infrastructure being deployed in coastal habitats, and the localised exclusion of fishing. The ecological consequences of this scale of deployment are largely unknown, particularly for benthic species. Infrastructure has the capacity to act as artificial reefs (ARs), providing novel habitat, and this may viewed as a benefit of MRED, or a means to mitigate the exclusion of fishing. At present, the functioning of AR ecosystems remains poorly understood. As a measure of ecosystem function, secondary productivity can be used to assess the implications of MRED. The lack of suitable methodology, deployable at relevant scales within time and/or cost constraints, has limited benthic secondary productivity (BSP) quantifications on ARs. Techniques to measure potential BSP and particle flux were developed and applied to the Loch Linnhe Artificial Reef (functionally similar to scour protection material). Variations in BSP and mobile epifaunal densities on, and between, structures in different environments were quantified. Reefs exposed to intermediate current had the highest potential productivity. The BSP on internal areas of structures contributed to the total productive output, but the relative contribution varied according to reef location and design. BSP was primarily determined by particle supply, but the response was not consistent among locations. Mobile epifaunal densities related to reef location, but not reef design, and were highest on reefs in the deepest water and exposed to the fastest currents. The evidence presented in this thesis highlights the need to account for the receiving environment when predicting the ecological consequences of MRED, or when modelling the productive capacity of structures. Such information can be used to suggest modifications to proposed or existing structures in order to maximise their benefit to coastal ecosystems.

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Coutis, Peter F. School of Mathematics UNSW. „Currents, coasts and cays : a study of tidal upwelling and island wakes“. Awarded by:University of New South Wales. School of Mathematics, 2000. http://handle.unsw.edu.au/1959.4/18207.

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In this thesis, the phenomenon of flow-topography interaction is considered in the context of two dynamically distinct case studies. In the first study, tidally-driven upwelling is investigated usingfield data collected in Hydrographers Passage (20????S), a narrow, navigable channel in the dense outer reef matrix of the southern Great Barrier Reef, Australia. In the second study, island wake formations at Cato Island (155????32????E, 23????15????S) in the deep, Western Coral Sea are examined using a combination of field data and numerical experiments. The result of the Hydrographers Passage study are of considerable scientific interest since they apply to numerous smaller non-navigable reef-edge passages dotted throughout the southern Great Barrier Reef. Strong, semi-diurnal flood tides flowing through a gap in a distal patch reef system at the shelf break generate strong upwelling, providing a pulsed, semi-diurnal input of nutrients to the reefs offshore of the passage. If stable in the long term, this mechanism could have profound evolutionary implications for large reefal areas in the southern Great Barrier Reef. In the second study, two sets of field observations at Cato Island coincided with conditions of strong (~0.7m s-1), vertically sheared incident currents and weaker (~0.3m s-1), more variable incident flows. The combination of dynamically distinct flow regimes and a tall, steep-sided island penetrating oligotrophic surface waters provides a unique opportunity to investigate the impact of island wakes on hydrographic structure and biological enhancement. Field data indicate that flow disturbances downstream of Cato Island are likely to generate biological enhancement during conditions of eddy shedding and non-shedding wakes. A primitive equation numerical model configured on the basis of field observations faithfully reproduces the key features of both data sets; mechanisms responsible for producing these key features are proposed. Previous numerical studies of island wakes have concentrated primarily on eddy shedding flows. In this thesis, the sub-critical (non-shedding) flow scenario is also considered. It is demonstrated that particle retention in island wakes has a ????hair trigger???? characteristic controlled by incident flow speed. This observation leads to a new proposal to explain the long-standing recruitment problem of biological oceanography.

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Defne, Zafer. „Multi-criteria assessment of wave and tidal power along the Atlantic coast of the southeastern USA“. Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/33864.

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The increasing demand for energy and the increased depletion rate of nonrenewable energy resources call for research on renewable alternatives. Mapping the availability of these resources is an important step for development of energy conversion projects. For this purpose, the wave power potential along the Atlantic coast of the southeastern USA, and the tidal stream power along the coast of Georgia are investigated in this study. Wave power potential is studied in an area bounded by latitudes 27 N and 38 N and longitudes 82 W and 72 W (i.e. North Carolina, South Carolina, Georgia, and northern Florida). The available data from National Data Buoy Center wave stations in the given area are examined. Power calculated from hourly significant wave heights and average wave periods is compared to power calculated using spectral wave energy density. The mean power within 50 km of the shore is determined to be low, whereas higher power is available further offshore beyond the 3500 m contour line. The tidal stream power potential along the coast of the state of Georgia is evaluated based on the NOAA tidal predictions for maximum tidal currents and three dimensional numerical modeling of the currents with Regional Ocean Modeling System (ROMS). The modeling results are validated against the available measurements. This region has low to moderate average tidal currents along most of the coast, but with the possibility of very strong local currents within its complex network of tidal rivers and inlets between barrier islands. Tidal stream power extraction is simulated with a momentum sink in the numerical models at the estuary scale to investigate effect of power extraction on the estuarine hydrodynamics. It is found that different power extraction schemes might have counterintuitive effects on the estuarial hydrodynamics and the extraction efficiency. A multi-criteria method that accounts for the physical, environmental and socioeconomic constraints for tidal power conversion schemes is proposed to select favorable locations and to rank them according to their suitability. For this purpose, the model results are incorporated into a Geographical Information System (GIS) database together with other geospatial datasets relevant to the site selection methodology. The methodology is applied to the Georgia coast and the candidate areas with potential are marked.

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Chahboun, Abderrahim. „Les formations sableuses fluviatiles, littorales et eoliennes aux embouchures des oueds tensift, ksob et souss (atlas-atlantique, maroc)“. Paris 6, 1988. http://www.theses.fr/1988PA066131.

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L'etude des formations sableuses aux embouchures des oueds tensift, ksob et souss de l'atlas-atlantique (maroc) permet de mettre en evidence les processus de leur mise en place, ainsi que l'origine de leur materiel. Les oueds apportent jusqu'a l'ocean des elements terrigenes (quartz, feldspaths et mineraux lourds). Ces elements sont remanies et melanges aux depots marins. Le stock sedimentaire est redistribue par les actions marines, et principalement une forte derive littorale nord-sud. Ainsi, dans le systeme du tensift, le materiel dunaire evolue sous l'influence des alizes et des vents d'ouest, mais l'activite de ces derniers se revele plus efficace. Dans le systeme de ksob, le materiel dunaire evolue sous l'action principale des alizes. Dans le systeme du souss, la dynamique eolienne se fait sous l'action conjuguee des alizes et des vents d'ouest. Ces evolutions sedimentaires se traduisent par une amelioration du tri, une diminution progressive du grain moyen et des teneurs en carbonates et mineraux lourds, ainsi que par une eolisation croissante des grains quartz.

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Barthélémy, Eric. „Etude des ondes longues internes et de leur dynamique dans les zones côtières“. Grenoble 1, 1989. http://www.theses.fr/1989GRE10002.

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La theorie des ondes longues en eau peu profonde est utilisee pour calculer plusieurs equations decrivant les ondes internes en fluide stratifie. On reformule l'equation de kdv et on calcule l'equation des ondes longues d'interface a fortes courbures. Une revue de synthese des etudes sur la generation des ondes internes par le passage de la maree sur le talus continental introduit notre etude theorique: les methodes de l'eau peu profonde generalisee nous permettent le calcul des ondes baroclines et barotropes, reflechies ou transmises lors de l'interaction de la maree avec le talus vertical. Nous etudions ensuite les ondes longues internes de grandes amplitudes. On etablit le role des conditions dites critiques sur l'existence d'ondes solitaires. Enfin on montre qu'en presence de courants moyens les caracteristiques (longueur d'onde, celerite,. . . ) des ondes longues d'interface sont qualitativement modifiees

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Schoonees, Jacobus Stefanus. „Longshore sediment transport : applied wave power approach, field data analysis and evaluation of formulae“. Thesis, Stellenbosch : Stellenbosch University, 2001. http://hdl.handle.net/10019.1/52327.

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Thesis (PhD)--University of Stellenbosch, 2001.
ENGLISH ABSTRACT: The process of sand being moved parallel to the coast by wave and current action is called longshore (sediment) transport. Knowledge oflongshore transport is essential for the design of breakwaters at harbour entrances, for navigation channels and for calculating the amount of dredging they require, for beach improvement schemes and for the determination of the stability of inlets and estuaries. Different aspects oflongshore transport have been investigated, namely, (1) analysis offield data, (2) evaluation oflongshore transport formulae and (3) the development of the wave power approach as an alternative method to calculate longshore transport. In the development of a better understanding oflongshore sediment transport, the following has been done for the first time: (1) a comprehensive data set has been compiled covering almost a full range of conditions occurring on natural beaches; and (2) virtually all longshore transport formulae have been evaluated against this extensive data set. A new improved method, the applied wave power approach, has been developed and extensively calibrated against the same data set. Based on this evaluation, guidelines are now available for design engineers as to which are the best bulk and detailed predictors oflongshore sediment transport. These are respectively, the recalibrated Kamphuis formula and the applied wave power approach. Another useful first, is the derivation of confidence intervals for a longshore transport formula, showing what accuracy can be obtained and that accurate predictions are now possible. In addition, it has now been determined what the minimum required measurement period should be and what the most cost-effective way is for obtaining the true long-term mean net longshore transport rate at a particular site.
AFRIKAANSE OPSOMMING: Die proses waarvolgens sand ewewydig aan die kus deur golf- en stroomwerking vervoer word, word langsstrandse (sediment-) vervoer oflangsvervoer genoem. Kennis van langsvervoer is noodsaaklik vir die ontwerp van golfbrekers by hawe-ingange, navigasiekanale en vir die berekening van die hoeveelheid baggerwerk daarvoor benodig, strandverbeteringskemas en vir die bepaling van die stabiliteit van inlate en getyriviere. Verskillende aspekte van langsvervoer is ondersoek, naarnlik, (1) die ontleding van velddata, (2) die beoordeling van langsvervoerformules en (3) die ontwikkeling van die golfdrywingsbenadering as 'n altematiewe metode om langsvervoer mee te bereken .. Tydens die ontwikkeling van 'n beter begrip van langsstrandse sedimentvervoer is die volgende vir die eerste keer gedoen: (1) 'n omvattende datastel is versamel wat bykans aIle toestande wat aan natuurlike strande voorkom, dek; en (2) feitlik aile langsvervoerformules is teen hierdie uitgebreide datastel beoordeel. 'n Nuwe verbeterde metode, die aangewende golfdrywingsbenadering, is ontwikkel en omvattend teen dieselfde datastel geyk. Gebaseer op hierdie beoordeling, is riglyne nou vir ontwerp-ingenieurs beskikbaar rakende watter totaal- en detail-iangsvervoervoorspellers die beste is. Dit is onderskeidelik die hergeykte Kamphuisformule en die aangewende golfdrywingsbenadering. Nog 'n nuttige eerste is die afleiding van betroubaarheidsgrense vir 'n langsvervoerformule, wat wys watter akkuraatheid nou haalbaar is en dat noukeurige voorspellings nou moontlik is. Verder is dit nou vasgestel wat die vereiste meettydperk behoort te wees en wat die mees koste-effektiewe manier is waarop die ware langtermyn-gemiddelde netto langsvervoertempo by 'n spesifieke terrein verkry kan word.

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Enckevort, Irene M. J. van. „Daily to yearly nearshore bar behaviour /“. Utrecht : Koninklijk Nederlands Aardrijkskundig Genootschap : Faculteit Ruimtelijke Wetenschappen, Universiteit Utrecht, 2001. http://bvbr.bib-bvb.de:8991/F?func=service&doc_library=BVB01&doc_number=009772437&line_number=0001&func_code=DB_RECORDS&service_type=MEDIA.

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Aldogan, Serhan. „Wind And Wind Wave Climate For Turkish Coast And Application To Aegean And Mediterrenean Sea“. Master's thesis, METU, 2008. http://etd.lib.metu.edu.tr/upload/12609627/index.pdf.

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The wind waves have significant effects on small craft and fisheries. Therefore, wind wave climate has an important role in the design and operation of fishing harbors and harbors for small craft. The purpose of this study is to identify the wind wave climate along the eastern part of the Mediterranean Sea coastline of Tü
rkiye. For this purpose, wind wave data for a certain period is obtained from ECMWF for the analysis. Moreover, the data will be analyzed for locations selected along the Turkish coast using a special software developed for this thesis study. For every location, the wind wave roses, significant wind wave height versus mean period of primary wind relations, extreme probability distribution, and log-linear cumulative probability distributions will be presented. By the help of software developed, it will be possible to analyse any coordinate using ECMWF data.

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Guibourg, Sandrine. „MModélisations numérique et expérimentale des houles bidimensionnelles en zone cotière“. Université Joseph Fourier (Grenoble), 1994. http://www.theses.fr/1994GRE10160.

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Une analyse theorique detaillee des equations de boussinesq et de serre a ete realisee. Les domaines de validite de chaque equation ont ete determines theoriquement. Ces equations d'ondes longues sont discretisees selon un schema aux differences finies pour des ondes de surface libre sur fond plat et fond variable. Par le biais d'une comparaison numerique avec des essais experimentaux d'ondes longues sur fond plat, les modeles numeriques ont ete etendus a la description des ondes courtes. Un terme dispersif correctif a ete introduit pour ameliorer les capacites dispersives des modeles. Des essais numeriques de propagation d'ondes longues sur un talus ont egalement ete compares aux experiences. Une etude de l'interaction d'une houle courte de haute frequence avec une onde solitaire nous a conduit a mesurer le dephasage que subit l'onde courte apres le passage du soliton. Nous nous sommes consacres a la validation experimentale d'une comparaison entre les modeles de boussinesq et de serre sur des plages peu inclinees, ainsi qu'a l'evolution du nombre d'ursell le long de la plage. L'etude experimentale a ensuite ete etendue aux phenomenes de run up, de run down et aux calculs des coefficients de reflexion des plages etudiees. Pour calculer numeriquement les run up, nous avons ameliore le modele de serre par des conditions de trait de cote variable

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Filho, André Palóczy. „Intrusions of South Atlantic Central Water on the Espírito Santo Basin shelf (18ºS-22ºS, Brazil)“. Universidade de São Paulo, 2015. http://www.teses.usp.br/teses/disponiveis/21/21135/tde-28082015-141105/.

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The intrusion pathways and physical mechanisms associated with intrusions of cold, nutrient-rich South Atlantic Central Water (SACW) onto the continental shelf of the Espírito Santo Basin (ESB), off southeast Brazil (18°S-22°S), are investigated. The approach consists of analyses of a set of simplified, process-oriented, primitive-equation numerical models supported by the analyses of an independent, more realistic numerical model and available observations. The cross-isobath circulation is found to be strongly dominated by wind-driving, consistent with previous findings. In the model experiments, SACW enters the ESB shelf through two preferential pathways along the Tubarão Bight area (TB, 19.5°S-22°S). These pathways are found to be locations where an equatorward along-isobath pressure gradient force (PGFy∗) of ∼2 x 10-6 m s-2 develops in response to steady wind forcing. This equatorward PGFy∗ is essentially in geostrophic balance, and therefore induces onshore flow across the shelf edge and most of the shelf proper. The Brazil Current (BC) imparts an additional equatorward PGFy∗ on the shelf. The momentum budget reveals that the ageostrophic residue of the PGFy∗ is compensated mostly by momentum advection and bottom friction. Buoyancy arrest might be important under more intense SACW intrusion events, as suggested by the maximum observed values of the slope Burger number (0.32-0.92). Among the deep ocean forcing mechanisms considered, the intrinsic pycnocline uplifting effect of the BC seems to be responsible for ∼1.4°C colder upwelled water under steady, upwelling-favorable wind forcing, relative to a flat stratification scenario. The BC also seems to induce local intrusions by inertially overshooting the shelf edge, consistent with Rossby numbers of ∼0.3-0.5, as estimated for the area along the TB shelf edge. Finally, the planetary β-effect is also related to a background equatorward PGFy∗. In addition, the steady response of the continental shelf to a periodic (in the along-shelf direction) pressure forcing at the shelf edge is compared with the BC-forced primitive-equation numerical solutions. A simple Arrested Topographic Wave (ATW) analytical model is found to be successful in representing the general features of the numerical solutions. The cross-shelf e-folding scales of the cross-shelf velocity estimated from the numerical solutions agree in order of magnitude with the cross-shelf penetration scale q-1 = [-2r/(lfs)]½ = 10 km predicted by the ATW, where r is a linear bottom resistance parameter, l is the along-shelf wavenumber of the forcing at the shelf edge, f is the Coriolis parameter and s is the bottom slope. Furthermore, the use of quadratic bottom stress accounts for some of the relative increase in the numerical onshore penetration scales, which are predicted to be qquadratic-1 = [-2CD/(lfs)]½ [Ubot]½, where CD is a quadratic bottom friction parameter and Ubot is the near-bottom velocity magnitude. The kind of steady response to periodic deep ocean forcing examined here may provide insight into other continental shelves under the influence of western boundary currents.
Os caminhos e os mecanismos físicos associados ao fenômeno de intrusão da Água Central do Atlântico Sul (ACAS) na plataforma continental da Bacia do Espírito Santo (BES) ao largo da costa sudeste (18°S-22°S) são investigados nesta dissertação. A abordagem consiste da análise de experimentos numéricos de equações primitivas simplificados, combinados com a análise de um modelo numérico mais completo, e com análise de observações disponíveis. Conclui-se que a circulação na direção perpendicular às isóbatas é fortemente dominada pelo vento, de acordo com resultados pretéritos. Nos experimentos numéricos, a ACAS ingressa na plataforma da BES através de dois caminhos preferenciais de intrusão no Embaiamento de Tubarão (ET, 19,5°S-22°S). Estes caminhos de intrusão coincidem com áreas em que uma Força do Gradiente de Pressão na direção paralela às isóbatas (PGFy∗), com magnitude de ∼2 x 10-6 m s-2, se forma em resposta ao vento. A PGFy∗ se encontra essencialmente em balanço geostrófico, e impulsiona um escoamento na direção da costa. A Corrente do Brasil (CB) induz uma PGFy∗ adicional favorável à intrusão. O balanço de momentum revela que o resíduo ageostrófico da PGFy∗ é balanceado principalmente pela advecção de momentum e pelo atrito de fundo. O mecanismo de desligamento da camada de Ekman de fundo por empuxo (tradução livre de buoyancy arrest) pode ser importante em eventos mais intensos de intrusão de ACAS, em razão das estimativas do número de Burger de inclinação (tradução livre de slope Burger number) observado (0,32-0,92). O efeito de soerguimento da termoclina ligado à CB aparenta diminuir em ∼1,4 °C a temperatura da água que aflora em eventos de ressurgência costeira. A CB também parece produzir intrusões locais na borda da plataforma por efeitos inerciais, de acordo com as estimativas de ∼0,3-0,5 para o número de Rossby ao longo da borda da plataforma. Por fim, o efeito β planetário também é associado a uma PGFy∗ básica na direção do equador. Adicionalmente, a resposta estacionária da plataforma continental a um campo de pressão periódico ao longo da borda da plataforma é comparada com as soluções numéricas. Um simples modelo analítico do tipo Onda Topográfica Aprisionada (OTA, tradução livre de Arrested Topographic Wave) representa as características gerais das soluções numéricas. As escalas de decaimento Neperiano (e) na direção perpendicular à plataforma estimadas a partir das soluções numéricas são comparáveis à escala de penetração q-1 = [-2r/(lfs)]½ = 10 km prevista pela OTA, onde r é um coeficiente linear de atrito de fundo, l é o número de onda da forçante, f é o parâmetro de Coriolis e s é a inclinação do fundo. O uso de uma parametrização quadrática para o atrito de fundo prevê parte da diminuição da e. A escala de penetração quadrática é qquadratic-1 = [-2CD/(lfs)]½[Ubot]½, onde CD é um coeficiente quadrático de atrito de fundo e Ubot é a magnitude da velocidade próxima ao fundo. Este tipo de resposta estacionária da plataforma a uma forçante periódica ligada ao oceano profundo pode ajudar a elucidar processos físicos em outras plataformas continentais que se encontram sob a influência de correntes de limite oeste.

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Chapalain, Georges. „Étude hydrodynamique et sédimentaire des environnements littoraux dominés par la houle“. Université Joseph Fourier (Grenoble ; 1971-2015), 1988. http://www.theses.fr/1988GRE10121.

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La propagation des houles longues est étudiée expérimentalement, théoriquement et numériquement. La validité du modèle harmonique quasi-résonnant de lau et barcilon (1972) est confirmée. Les processus hydro-sédimentaires se développant dans la couche limite turbulente de fond générée par la houle sont analysés à l'aide d'un modèle uni-dimensionnel avec fermeture turbulente au second ordre. Un modèle simplifie avec fermeture turbulente au premier ordre est envisagé dans la perspective d'une modélisation des interactions des trains de houle avec un fond sableux. La modélisation hydro-morphologique ainsi élaborée explique la formation des barres sableuses d'avant-cote. Elle est confrontée avec succès à des mesures effectuées dans le lac Huron et dans le golfe du Saint-Laurent. L'extension de la modélisation a des substrats de granulométrie étendue est réalisée en vue de la simulation du tri granulométrique observe sur les systèmes de barres littorales. Enfin, un essai d'intégration des pertes d'énergie par les déferlements multiples survenant sur les séquences de barres est entrepris.

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Ould, Ahmed Khalifa Mohamed Abderahmane. „Calcul automatique des deformations de la houle, refraction, diffraction, friction : application a l'etude d'un chenal d'acces portuaire“. Nantes, 1987. http://www.theses.fr/1987NANT2055.

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Pour amenager un site cotier quelconque, l'ingenieur de genie civil a besoin de connaitre les differents facteurs physiques susceptibles de le solliciter. Dans cette recherche, nous nous limitons a l'etude des deformations de la houle car elle est le principal facteur de ces sollicitations. Dans ce cadre, nous avons developpe un code de calcul, resol, base sur la modelisation de l'agitation de la houle, quand elle se propage sur des fonds variables. Cet outil permet d'etablir des plans de houle donnant les deformations des cretes dans l'espace. Cependant, quand les fonds deviennent tourmentes, les plans de houle qu'il fournit presentent des croisements d'orthogonales ou theoriquement les hauteurs de houle y sont infinies. C'est pour cette raison que nous avons concu un code de calcul complementaire, red, base sur un modele mathematique combinant la refraction a la diffraction (modele de radder). Afin d'avoir des resultats realistes, il est indispensable de tenir compte des phenomenes dissipatifs qui se produisent a l'interface eau-sol. Dans ce but, une ebauche d'analyse de l'influence de la friction est integree a resol, en supposant que les fonds restent fixes. Les differents modeles, issus d'etudes bibliographiques, sont d'abord traites avant d'en presenter les analyses algorithmiques. Diverses applications a des configurations theoriques simples ont ete le support d'une validation theorique systematique des codes. L'une des principales originalites de ce travail demeure, d'une part l'analyse de l'agitation de la houle dans des sites concrets (baie de saint brieuc et estuaire de la loire) grace a ces deux codes et, d'autre part la validation experimentale du modele de refraction diffraction par une serie de mesures en nature

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Kounta, Diop Lala. „Le rôle de la dynamique océanique et atmosphérique en Atlantique Nord sur le fonctionnement de l'upwelling ouest-africain“. Electronic Thesis or Diss., Sorbonne université, 2019. https://accesdistant.sorbonne-universite.fr/login?url=https://theses-intra.sorbonne-universite.fr/2019SORUS649.pdf.

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Cette thèse avait pour objectif de mieux comprendre le rôle de la dynamique océanique et atmosphérique régionale sur le fonctionnement de l’upwelling ouest africain. La première partie est consacrée à l’étude du cycle saisonnier, de la dynamique et de l’origine des masses d’eau du courant de bord qui alimente l’upwelling ouest africain. Ce courant est situé sur la pente continentale et est dénommé WABC (pour West African poleward Boundary Current en anglais). Son lien avec la circulation à l’échelle de l’Atlantique Tropical Nord Est (ATNE) est aussi étudié. Les résultats obtenus sont principalement basés sur des sorties de simulations numériques avec une configuration régionale du modèle NEMO (TROP025). Le WABC est constitué d’un sous courant dirigé vers le pôle (communément appelé Poleward Under Current (PUC) en anglais) et d’un courant de surface également dirigé vers le pôle et fréquemment appelé courant de Mauritanie (Mauritania Current en anglais ; MC). Le WABC est présent quasiment toute l’année. Il est visible en surface (en l’absence du jet d’upwelling côtier) et s’étend jusqu’à ~ 250 m de profondeur ou en gamme de densité. Son transport méridien vers le nord est la conséquence des gradients de pression baroclines mis en place par le vent et aussi d’un rotationnel de vent positif le long des côtes ouest africaines. L’étude du cycle saisonnier a permis de montrer que le WABC présente deux pics de transport dans l’année : un premier en Avril-Mai et un second en Octobre- Novembre. Ce cycle semi-annuel du WABC résulte de l’activité des ondes côtières générées par les fluctuations du forçage par le vent. Le premier pic est causé par une relaxation des vents locaux (dans la zone côtière ouest africaine). Pour le second pic automnal la zone de forçage est distante et principalement située dans le golfe de Guinée. La quantité d’eau transportée par le WABC est estimée à 1 Sv en moyenne annuelle. Du fait de la variation du paramètre de Coriolis avec la latitude (effet β), les ondes côtières associées à la variation du WABC donnent naissance à des ondes de Rossby se propageant vers l’ouest. Les caractéristiques de ces ondes qui changent suivant la latitude, sont mises en évidence dans la thèse. L’étude de l’origine des masses d’eau du WABC a permis de clarifier le lien entre le WABC et la circulation dans l’ATNE. En effet, les masses d’eau transportées par le WABC sont amenées par le sous courant nord équatorial et sont principalement situées dans la thermocline (100-240 m). Elles subissent de fortes recirculations et une advection moyenne faible (~1 cm/s) dans la "shadow zone" avant d’être amenées par le WABC. Cette étude nous a aussi permis de montrer que la circulation au nord du dôme de Guinée (notamment la recirculation vers l’ouest associée à la présence du dôme de Guinée) tend à être surestimée lorsque les vitesses sont calculées à partir de l’équation du vent thermique avec des niveaux de références peu profonds. En effet, la prise en compte des gradients thermohalins profonds est importante et tend à renforcer l’advection vers le nord-est dans l’ATNE. La dernière partie de la thèse a concerné l’étude des modes de variabilité atmosphérique grandes échelles qui modulent, aux échelles de temps synoptiques, l’intensité des vents d’upwelling le long des côtes sénégalaises. Les analyses menées sur des données de réanalyses (Era-Interim) montrent que les fluctuations du vent, à ces échelles de temps et dans cette zone, sont principalement liées à l’intensité et la position de l’anticyclone des Açores, de l’anticyclone Saharo-Libyen et de la dépression Saharo-sahélienne. La variabilité du régime de vent à Dakar en lien avec ENSO s’explique notamment par la manière dont ces centres d’action sont affectés par ce mode de variabilité climatique
The southern end of the Canary current system comprises of an original upwelling center that has so far received little attention. This Ph.D. Thesis focuses on the dynamical functioning of the Southern Senegal-Gambia Upwelling Center (SSUC). We are interested in the upwelling circulation and thermohaline structure on the shelf between the coastline and 100-200 km offshore. Our focus is on the upwelling period (November to May). The main originality of the SSUC compared to other upwelling centers stems from its conti-nental shelf that is broad and shallow (20–30 m over tens of kilometers). The normal state of the system comprises the classical upwelling front but also a well-defined inner-shelf front that separates cold upwelled waters from nearshore warmer waters. We investigate its dynamical functioning using analysed satellite images, in situ data and state-of-the- art 3D numerical simulations. Through a fine-scale analysis of the physical conditions of the SSUC, this work poses the basis of an integrated approach to the Senegalese marine environment functioning. A first part of results is based on the careful examinations and analysis of over 1500 satellite images of sea surface temperature scenes contextualized with respect to wind conditions. Analysis confirm the regularity and stability of the SSUC dynamical functioning (as manifested by the recurrence and persistence of particular SST patterns). The analyses also reveal subtle aspects of its upwelling structure : shelf break cooling of surface waters consistent with internal tide breaking/mixing ; complex interplay between local upwelling and the Mauritanian current off the Cape Verde headland ; complexity of the inner-shelf/mid shelf frontal transition. The amplitude of the diurnal cycle suggests that large uncertainties exist in the SSUC heat budget. The studies limitations underscore the need for continuous in situ measurement in the SSUC, particularly of winds. The dynamical functioning of SSUC is also investigated by means of numerical simulations, using the hydrodynamical Regional Ocean Modeling System ROMS (∆x ≈ 2 km). Different simulations have been carried with varying forcings (climatological or synoptic wind ; fine-scale adjustments of heat flux in coastal area ; presence or absence of tides). Numerical solutions show a good agreement with available satellite and in situ observations. These solutions clarify the dynamical functioning of the system especially in terms of circulation, location of cold water upwelling but also fate of upwelled water through a Lagrangian analysis. We show in particular that the northern part of the SSUC is the main upwelling area. Waters that upwelled in this area predominantly come from the southern of the SSUC, through advection by the Mauritanian current. Lagrangian analysis also revealed the dynamics associated with the coastal area of nursery and nuance the conceptual retention scheme previously admitted. The sensitivity of the dynamics of SSUC to atmospheric forcings is modest with nevertheless some modulations of the cross-shore exchanges that may be important to the ecosystem

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Katzev, David H. „Simulation of coastal processes in a circular wave basin“. Thesis, 1992. http://hdl.handle.net/1957/36579.

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The circular wave basin provides a means of physically modeling the nearshore without the typical problems associated with end walls. Three different coastal processes were examined to demonstrate the use of a spiral wavemaker in a circular wave basin. These were longshore currents, shear waves, and groin circulation. A beach was designed and constructed to concentrate breaking in a narrow region and minimize wave reflection. Currents in the longshore direction were generated by both the motion of the wavemaker and oblique wave approach. Two methods for measuring nearshore currents were employed. First, a 3-D acoustic current meter was positioned at various locations in the cross shore and the local radial and tangential velocities were recorded. Second, a video camera was placed approximately 8 meters above the wave basin to record the motion of a ball in the nearshore. The video tape was digitized by an image processor and the motion of the ball was determined. Measurements of nearshore circulation in the circular wave basin were used to investigate longshore currents, shear waves, and groin circulation. Average measured longshore current profiles in the cross shore were compared with numerical model predictions. An analysis of the existence of shear waves in the circular wave basin was performed by calculating longshore and cross shore current spectra. Particular attention was focused on the low frequency end of the spectra where shear waves are most energetic. Model groins were placed in the circular wave basin and measured currents were compared to predicted circulation patterns. All three applications indicated that the circular wave basin is a useful device for simulating coastal processes in a laboratory environment.
Graduation date: 1992

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McGehee, David D. „Three applications of wave measurements in coastal engineering“. Thesis, 1997. http://hdl.handle.net/1957/28070.

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Yan, Ching-Jung, und 顏靖容. „Application of Visual Performance to Ocean Waves and Evaluating Coastal Landscape“. Thesis, 2002. http://ndltd.ncl.edu.tw/handle/75855883914449978947.

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碩士
國立交通大學
土木工程系
90
ABSTRACT Scientific visualization is an effective way to display data and information. In this study, an integrated visualization environment is developed and applied to assessment of coastal landscape and visualization of wave deformation. The system mainly includes database and Internet technologies to provide with image demonstration, questionnaires, and basic statistical analysis. Both images and panoramas for Kong-Nan coastal landscape were used as two kinds of media to survey preference evaluation by semantic differential (SD) method in the association with questionnaires in this system. The results indicate that significant disparity on preference evaluation was distinguished form different visualization and personal background. It implies that different visualization has an effect on coastal landscape assessment. In the visualization of wave deformation, the surface elevation resulting from shoaling, refraction, and wave breaking was calculated by linear wave theory from offshore to near shore regions. It is easily to see the wave deformation from this system and to know what the wave deformation is. The present system can provides with good complement media for wave mechanics.

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Ruggiero, Peter. „Wave runup on high energy dissipative beaches and the prediction of coastal erosion“. Thesis, 1997. http://hdl.handle.net/1957/34397.

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Gill, Eric William. „An algorithm for the extraction of ocean wave parameters from wide beam HF radar (CODAR) backscatter /“. 1990. http://collections.mun.ca/u?/theses,29292.

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Davis, Joseph P. „A spectral approach to the transient analysis of wave-formed sediment ripples“. Thesis, 2005. http://hdl.handle.net/2440/37718.

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Wave-formed rippled sediment beds are extremely important to the processes that act on or across the sediment-water interface. Ripples increase the exchange of materials between the sediment and the water column, enhance sediment transport rates, and act to increase the dissipation of waves by increasing the hydraulic roughness of the seafloor. Previous research has, however, failed to take into account the substantial spatial and temporal variation rippled beds display when formed under real sea conditions. Based on a set of laboratory experiments a spectral method to predict and model rippled beds has been developed. Through the use of the rippled surface's spectral density function the spatial and temporal variability of the rippled surface can be taken into account with greater efficiency. A prediction method for the equilibrium ripple spectrum was developed based on a nondimensional spectral form, which utilised the peak orbital excursion diameter and the 50th percentile grain size diameter of the sediment bed. The method provided an effective technique to predict ripple parameters with the same degree of accuracy achievable at small scale as more accepted ripple prediction methods. A new method was derived to model the changes a rippled bed undergoes as it actively evolves between two given equilibrium states due to a change in surface wave conditions. The evolution of a rippled bed can be described mathematically in exactly the same way as a rippled bed growing from a flat bed condition. The method allows any bed to be modelled through time if the flow conditions and sediment properties are known. There is little advantage in using the spectral method to predict rippled beds when they are in equilibrium with the flow conditions. The main benefit of the spectral method comes when attempting to model rippled beds evolving under changed flow conditions. In the same way as the parameterisation of surface waves in terms of their spectral density function has increased the ability to model wind generated wave fields, studies of rippled beds would benefit from the increased detail and ease the spectral method brings.
Thesis (Ph.D.)--School of Civil and Environmental Engineering, 2005.

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46

Davis, Joseph P. „A spectral approach to the transient analysis of wave-formed sediment ripples“. 2005. http://hdl.handle.net/2440/37718.

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Wave-formed rippled sediment beds are extremely important to the processes that act on or across the sediment-water interface. Ripples increase the exchange of materials between the sediment and the water column, enhance sediment transport rates, and act to increase the dissipation of waves by increasing the hydraulic roughness of the seafloor. Previous research has, however, failed to take into account the substantial spatial and temporal variation rippled beds display when formed under real sea conditions. Based on a set of laboratory experiments a spectral method to predict and model rippled beds has been developed. Through the use of the rippled surface's spectral density function the spatial and temporal variability of the rippled surface can be taken into account with greater efficiency. A prediction method for the equilibrium ripple spectrum was developed based on a nondimensional spectral form, which utilised the peak orbital excursion diameter and the 50th percentile grain size diameter of the sediment bed. The method provided an effective technique to predict ripple parameters with the same degree of accuracy achievable at small scale as more accepted ripple prediction methods. A new method was derived to model the changes a rippled bed undergoes as it actively evolves between two given equilibrium states due to a change in surface wave conditions. The evolution of a rippled bed can be described mathematically in exactly the same way as a rippled bed growing from a flat bed condition. The method allows any bed to be modelled through time if the flow conditions and sediment properties are known. There is little advantage in using the spectral method to predict rippled beds when they are in equilibrium with the flow conditions. The main benefit of the spectral method comes when attempting to model rippled beds evolving under changed flow conditions. In the same way as the parameterisation of surface waves in terms of their spectral density function has increased the ability to model wind generated wave fields, studies of rippled beds would benefit from the increased detail and ease the spectral method brings.
Thesis (Ph.D.)--School of Civil and Environmental Engineering, 2005.

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Yen-PinLin und 林演斌. „Development and applications of a GNSS buoy for monitoring tides and ocean waves in coastal areas“. Thesis, 2018. http://ndltd.ncl.edu.tw/handle/nz73jt.

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博士
國立成功大學
水利及海洋工程學系
106
Real-time tide data for estuaries are very important for simulations of river water levels to assess flood risks. To design coastal structures, wave data are important. Tide data in these regions are usually estimated by interpolating or extrapolating tide data from the neighboring tide stations. This method may be useful for normal conditions, but for extreme sea state conditions such as typhoon-induced storm surges or swells, this is not the case because the sea surface in the local area may vary significantly. However, a simple platform for measuring tide in estuaries and coastal areas is not available. Floating data buoys have been verified to be reliable platforms for ocean monitoring and they have been deployed worldwide to provide long-term and real-time meteorological and oceanographic data. Nevertheless, the previous studies did not measure real-time tides and waves simultaneously using a buoy in estuaries and coastal areas. This work was aimed toward developing a Global Navigation Satellite System (GNSS) buoy that observed water surface elevations and provided real-time tide and wave data in estuaries and coastal areas. In this work, a GNSS buoy that utilized a Virtual Base Station (VBS) combined with the Real-Time Kinematic (RTK) positioning technology was developed to monitor water surface elevations in estuaries and coastal areas. The GNSS buoy included a buoy hull, a RTK GNSS receiver, data-transmission devices, a data logger, and General Purpose Radio Service (GPRS) modems for transmitting data to the desired land locations. Laboratory and field tests were conducted to test the capability of the buoy and verify the accuracy of the monitored water surface elevations. For the field tests, the GNSS buoy was deployed in the waters of Suao (northeastern part of Taiwan), Wan-li, and Small liu-qiu (southwestern part of Taiwan). Tide data obtained from the GNSS buoy were consistent with those obtained from the neighboring tide station. The root-mean-square error (RMSE) of the tide data was within 10 cm. According to the correction of inclinations of the GNSS buoy, the reduction of RMSE was little. For Wan-li buoy, it was only 1.1 cm. The water surface elevations, significant wave heights, zero-crossing periods, one-dimensional wave spectra, directional wave spectra, and peak wave directions obtained from the GNSS buoy were generally consistent with those obtained from an accelerometer-tilt-compass (ATC) sensor. The significant wave heights observed by using GNSS and ATC were nearly identical, even when the height of a typhoon-caused swell was as high as approximately 7 m. Data were utilized to examine the performance of the GNSS buoy. The field tests demonstrated that the rate of effective data was 83% and 74% in measuring tides and waves, respectively. The data were considered to be effective data when their accuracies reach centimeter-level. For the field tests with the GNSS antenna installed at an elevation of 2.26 m, as the hourly averaged total inclination of the buoy hull was less than , the error in tide caused by the inclination was negligible. However, as the angle increased up to , the uncorrected GNSS tide underestimated the water level by 12 cm. Whenever the distance from the antenna to the still water surface was known, the relationship between the tide error and the instantaneous total inclination was a cosine-related function. The correction of the water level due to instantaneous total inclination did not cause a significant change in the values of significant wave height, mean wave period, or peak wave direction. Thus it is not necessary to incorporate inclinometers in the GNSS buoy for ocean wave observation. It is, however, necessary to incorporate inclinometers in the GNSS buoy for tide observation except when the distance from the antenna to the still water surface is equal to zero, or the error is acceptable. The field tests demonstrated that the developed GNSS buoy could be used to obtain accurate real-time tide and wave data in estuaries and coastal areas.

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Echevarria, AR. „Global to coastal modulation of wind-wave climates by ocean surface currents“. Thesis, 2021. https://eprints.utas.edu.au/39484/1/Echevarria_whole_thesis.pdf.

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This thesis examines the influence of the ocean surface circulation on the global wind-wave climate. Surface currents modulate wave properties through the Doppler shift effect, exchanges of energy mediated by the radiation stress, refraction, and through a modification of the relative wind. While the interaction between waves and currents has been thoroughly investigated in coastal locations with strong tidal flows, the impact of the global ocean circulation on the wave climate has received relatively little attention. In this study, spectral wind-wave simulations with and without current forcing were carried out using the WAVEWATCH III model. The current forcing data for the simulation with currents was taken from the Bluelink Reanalysis. Numerous wave observations taken from moored buoys, altimeter and Synthetic Aperture Radar (SAR) borne satellites were employed to carry out a comprehensive evaluation of both sets of wave simulations (with and without currents) to assess, describe and quantify the improvement in the representation of various wave parameters with the inclusion of currents. This dissertation examines and discusses the benefits of using directional wave spectra information for the description of the wave climate, as opposed to using integrated parameters. Drawbacks of the utilisation of bulk wave parameters are described, and circumstances where their usage leads to an imprecise description of the wave conditions are presented. First, a novel methodology is devised to investigate the seasonal variability of the global spectral wind-wave climate. By means of an empirical orthogonal function analysis, the main patterns of wave variability in the frequency/direction domain are extracted, together with their time evolution (Principal Component time series). This methodology that captures the spectral characteristics of the wave _eld provides a more comprehensive description of the wave climate variability in most areas of the world, with its largest influence found for low-latitude regions, especially in the Pacific Ocean, where various distinct wave systems (partitions) are present in the spectra. This approach also facilitates the quantification of changes in wave direction throughout the year. This analysis is also applied to evaluate the interannual variability of the global spectral wind-wave climate and to quantify how this variability is modulated by different large-scale climate modes. Importantly, we find that the Pacific South American modes (PSA-1 and PSA-2, the second and third modes of the Southern Hemisphere atmospheric circulation variability) have a remarkable impact on modelled wave heights and directions, especially across the South Pacific Ocean. The sensitivity of wind-wave modelling to the inclusion of surface current forcing is analysed by comparing results from simulations forced with and without currents. A significant improvement in significant wave height estimates in most areas of the world is attained in the current-forced simulation, especially in the Southern Ocean. Here, the positive bias in wave heights is lessened due to a reduced relative wind, a product of the Southern Hemisphere westerly winds and the Antarctic Circumpolar Current travelling in the same direction. The Equatorial currents and Counter-Current, as well as the western boundary currents around the world, induce broad and large changes in wave heights, periods and directions. The East Australian Current has a significant impact on the wave climate measured at the coast. Further, a comprehensive comparison with moored buoy observations around Australia and the United States shows statistically significant improvements in estimates of different wave parameters in the current-forced simulation. Finally, estimates of wind friction velocity, atmosphere-to-ocean energy and momentum fluxes, whitecap coverage, and Stokes drift speed and direction are substantially modified in Equatorial regions with the inclusion of currents into wave simulations. Numerous implications of these results on other wave processes are discussed. SAR borne satellites measure the directional wave spectra for long waves (swell). A thorough inter-comparison between Sentinel-1 SAR wave observations and modelled wave spectra from the Centre for Australian Weather and Climate Research (CAWCR) waves hindcast for the greater Australian region is presented. In particular, an exhaustive regional-scale evaluation of swell wave periods and directions is presented for the first time. SAR observations are divided by platform, incidence angles and orbit directions, which enables the identification of inherent errors in the model simulations and the observations. In addition, directional wave spectra from SAR are used to provide a detailed description of the seasonal variability of the spectral wave climate around Australia. Finally, the influence and importance of the ocean circulation on swell waves in the Australian region is assessed by comparing SAR observed directional wave spectra with wave simulations with and without surface current forcing. SAR measurements from Sentinel-1 satellites are co-located against a dense spectral output grid from the wave model. This comparison shows that swell significant wave height, mean period and peak direction estimates are generally improved in the current-forced simulation. Measurements of directional wave spectra from SAR are used to provide more clarity into the differences observed. In particular, swell wave periods are broadly improved, especially southwest of Australia. Overall, the results presented in this thesis demonstrate that surface currents are an essential consideration for the modelling of wind-waves in many areas of the world. Additionally, this work illustrates the benefits of describing the wind-wave climate using directional wave spectra data, which leads to a deeper understanding of the characteristics of the wind-wave fi_eld, and can enable further improvements in spectral wave models.

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Yuan, Ching-Feng, und 苑瀞丰. „On the Gravity Wave and Sea Surface Roughness Relationship in Coastal Ocean“. Thesis, 2011. http://ndltd.ncl.edu.tw/handle/80099879949877083446.

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碩士
國立中央大學
水文與海洋科學研究所
99
Physical surface roughness represents the actual elevation variations in various scales at the air-sea interface. It is affected by the gravity waves and the aerodynamic factors in the atmospheric boundary layer. It is one of the most crucial factors that determine the momentum, heat and water vapor exchange between the air and sea. Due to the shoaling of gravity waves in the coastal ocean, sea surface roughness features significant deviation compared with those observed in deep seas. The understanding of the characteristics of surface roughness in coastal ocean is of great importance since it has much influence on the climate change, water cycle, carbon cycle, wind driven current/storm surge predictions and the assessment and operation of offshore wind energy conversion. So far, parameters of Drag coefficient, Cd and Aerodynamic Roughness length Z0 are used to infer the sea surface roughness. However, they do not fully reflect the contribution of gravity waves to the surface roughness. In order to realize the characteristics of the sea surface roughness in the coastal ocean, the Mean Square Slope, MSS of surface elevation was adopted as the index to describe the sea surface roughness. In-situ observations were carried out at National Central University Coastal Observatory, TaiCOAST station located at the western coast of Taiwan. Synchronized observations of atmospheric boundary layer air-sea flux, gravity waves and current profiles, shore-based microwave radars were implemented during the period of northeast monsoon, i.e. from January 14, 2011 to January 31, 2011. The Drag coefficient is estimated using eddy-covariance method. The Roughness length is estimated by using the wind profile method and the spectral method. MSS is estimated from the surface elevation recorded by the three bottom-mounted Acoustic Doppler Current Profilers (ADCP). The surface tracking mode was implemented to obtain high resolution water elevation from the acoustic transducers. The wavenumber spectra were then calculated from the frequency spectra using the linear wave dispersion relationship. The slope spectrum can be derived and the MSS can be estimated by taking the integral of the slope spectrum. The magnitude of MSS is highly influenced by the spectral tail of full-range wavenumber spectrum. For non-saturated limited depth waves, it is not yet clear about the tail shape in high wavenumber range. In present study, six hypothetic spectral shapes were tested. Moreover, the criteria that distinguishes the spectral bands that governed by three wave interactions or quadruplet wave interactions, was determined. By using the criteria, the MSS that obtained from the lower-frequency slope spectra are associated with gravity waves; whereas those from high-frequency are associated with the turbulence. In present study, we use the absolute S-band radar backscatter intensity as reference to determine the tail property at the high wavenumber bands as well as the above-mentioned criteria. The result showed that the tail of full-range wavenumber spectrum is proportional to k-4. The best-fitted wavenumber cut-off wavenumber is about 42.3‧g/U102 . Futhermore, we discuss the dependency of the high-frequency MSS to the wind speed, and the low-frequency MSS to the wave age. The results show consistency with previous studies by Cox and Munk (1954). Moreover, when the wave age approximately equal to 0.8, the low-frequency MSS decreases. It is similar to the previous studies by Donelan(1990). Finally, an estimation of the contribution from the gravity waves to the surface roughness is about two-thirds at coastal oceans.

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Garcia, Medina Gabriel. „Nearshore wave predictions along the Oregon and southwest Washington coast“. Thesis, 2012. http://hdl.handle.net/1957/33936.

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This thesis contains a manuscript describing the implementation of a high resolution wave forecasting model for the coasts of Washington and Oregon. The purpose of this project was to advance the wave predictive capabilities of the states of Oregon and the southwest part of Washington by including the effects of local bathymetric features in the operational forecasts. A 30 arc-second resolution wave forecasting model was implemented making use of the WAVEWATCH III numerical code covering the coastal region from Klamath, CA to Taholah, WA. The wave forecasts extend to the continental shelf at this resolution. To assess the performance of the model, its output was compared against in situ data, with normalized root-mean-squared errors in significant wave height in the vicinity of 0.20 and linear correlation coefficients greater than 0.80. Making use of the resulting validated regional scale wave forecasting system, an evaluation of the model sensitivity to the inclusion of bottom friction and wind input at the shelf level was performed. Results suggest that neither dissipation due to bottom friction or wind generation are significant for long term forecasting/hindcasting in the region. Results from a series of hindcasts suggest that several significant offshore features may affect the nearshore wave field. To evaluate it, a shelf scale SWAN model was implemented and a series of numerical experiments performed. Results suggest that the Astoria and McArthur Canyons; the Stonewall, Perpetua, and Heceta Banks; and Cape Blanco are significant bathymetric features that are capable of producing significant alongshore variability in wave heights nearshore.
Graduation date: 2013

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