Dissertations / Theses on the topic 'Wave breaking'

Thesis (M.S. in Applied Science (Physical Oceanography))--Naval Postgraduate School, June 2005.
Thesis Advisor(s): Timothy P. Stanton. Includes bibliographical references (p. 51). Also available online.

The research presented in this dissertation focuses on understanding the dynamics of waves and currents in the presence of wave breaking. The simplest approach, direct numerical simulation of the ocean dynamics, is computationally prohibitive--waves typically have periods of tens of seconds, while currents vary on times from hours to days. This work uses a multi-scale asymptotic theory for the waves and currents (Craik and Leibovich, 1976; McWilliams et al., 2004}, similar to Reynolds-averaged Navier-Stokes, in order to avoid resolving the wave field. The theory decomposes the total flow into the mean flow (current) and fluctuations (waves), then takes a moving time average of the total flow equations to determine the wave forcing on the current. The main challenge is extending this theory to include a physical model for dissipative wave effects, notably breaking, in terms of the wave age, wind speed, and bottom topography. Wave breaking is difficult to observe, model, and predict, because it is an unsteady, non-linear process that takes place over disparate scales in both space and time. In the open ocean, white-capping often covers less than 2% of the surface, yet still plays an important role in the flux of mass, momentum, heat, and chemicals between the atmosphere and ocean. The first part of this dissertation proposes a stochastic model for white-capping events, and examines the stability of the ensemble average of these events. Near the shore, the decreasing ocean depth causes waves to overturn and break. Over time, this drives currents that erode sediment from beaches and deposit it around coastal structures. These currents are often so strong that their effect on the wave field, and thus their own forcing, is significant. A detailed analysis of this phenomena makes up the second part of this dissertation.

Determining the largest breaking wave height which can occur in water of finite depth is a fundamental reference quantity for the design of coastal structures. Current design guidelines are based on investigations which predominantly used monochromatic waves, thereby neglecting group effects which are inherent to the free propagation of waves in deep water. The Coastal Engineering Manual (CEM) states that wave grouping and its consequences is of significant concern, with breakwater armour damage being generally attributed to higher waves associated with wave groups. However, the CEM also acknowledges that there is little guidance and few formulae for use in practical engineering. This thesis describes a laboratory-based investigation into the effect of wave groupiness on wave shoaling, breaking and surf zone processes. New optical-based techniques for data abstraction, developed within this study, have allowed examination of the interaction between deep water intra-wave group processes and shallow water shoaling processes. The applicability of existing methods for predicting breaking wave height and position is evaluated, along with the implications of groupiness on engineering design in the nearshore. The effect of wave groupiness on overtopping and hazard on emerged rock platforms is similarly assessed. Wave group testing has revealed that the spatial phasing of intra-group processes during shoaling can result in considerably different shoaling and breaking regimes. Under certain regimes, wave breaking occurred further shoreward and in a more plunging manner than under other regimes. Within the mid to inner surf zone, waves were also observed to propagate into shallower water before breaking than is predicted by existing design guidelines. This could result in under-prediction of wave height by up to 100%. Expressions are developed for the prediction of maximum wave heights and surface elevation on plane slopes. These expressions implicitly include non-linear group effects and group-induced water-level variations within the surf zone, and are found to provide conservative upper envelopes for the range of data observed within the current testing regimes. Predictive schemes are similarly developed for overtopping hazard on emerged rock platforms based on critical wave and water-level conditions. Variations in maximum overtopping flow values due to intra-wave group processes of up to +/-35% were found. These group effects were found to reduce by up to 30% the threshold wave conditions before the initiation of hazard.

The aim of this project is to visualize multiple failure of an inelastic rod, caused by wave propagating through the rod, as the result can be applied to a spaghetti where it commonly breaks into multiple pieces. By looking into the wave we will see that when the wave propagates, it will cause local increase of bending which causes a secondary break. Method which is used to solve this problem is primary solving a fourth order partial dierential equation (PDE) which is derived from calculus of variations. This PDE is then solved numerically and analytically. Other approach to this problem is also done, where the simulation is based on basic solid and rigid mechanics. The method used to perform these calculation and simulation is shown and how it is implemented in MATLAB. Results from the mechanics point of view can be questioned, but the result based on the PDE do show promise as it have a successful attempt in showing waves to exists and are related to the secondary breaks.
Rapportens mål är att använda olika metoder för att visualisera hur en spröd stav (där sträck och brottgränsen ligger vid samma punkt) kan brytas i 　era delar, på grund av vågor som fortplantar sig i materialet. Denna process kan exempelvis appliceras i vardagliga problemet, om varför en spaghetti oftast bryts i 　era delar. Det angrepps punkt som rapporten har på problem, är då att simulera dess rörelse, efter att man har släppt en stav från ett jämt böjt läge, där den fria punkten ska motsvara ett första brott. Det som kommer då visas att det bildas lokala ökningar av böjningar, vilket motsvarar lokala spänningar ökas jämfört med initialt läget. Två metoder kommer testas, en lösning med energi perspektiv kommer användas, som löses analytisk och numerisk. Den andra metoden, är en mekaniks synsätt, där grundläggande mekanik och hållfasthetslära används. Dess fysik och matematik, kommer att presenteras i rapporten och dess implementation i MATLAB. Resultatet från den mekaniska tillvägagångssätt kan diskuteras, då resultat inte nådde upp till förväntan. Resultatet från energiska perspektivet klarar av att visa att vågor propagerar, och hur dessa skapar lokala ökningar av spänningar, vilket kan ses som en lyckad simulering.

Thesis (M.S. in Physical Oceanography) Naval Postgraduate School, March 1996.
"March 1996." Thesis advisor(s): Edward B. Thornton, Thomas C. Lippmann. Bibliography: p. 47-48. Also Available online.

The design of rubble mound breakwaters usually focuses on the main armor layer. A review of the existing literature reveals that different equations are used to design rock armors in non-breaking wave conditions. However, most rubble mound breakwaters are constructed in the depth-induced breaking zone where they are attacked by waves breaking in the foreshore; in these conditions, existing design equations are not valid. Therefore, in this PhD thesis, the hydraulic stability of double-layer rock armors is analyzed through a series of small-scale tests conducted with a bottom slope m=1/50. Based on test results, a new potential relationship is given to design rock armors in depth-limited breaking wave conditions with armor slope cot¿=1.5, stability numbers within the range 0.98¿Hm0/(¿Dn50)¿2.5, and relative water depth at the toe 3.75¿hs/(¿Dn50)¿7.50. When concrete units are used for the armor layer, mound breakwaters are usually protected by a toe berm. This toe berm is placed on the seafloor or underlayer, providing support for the concrete armor units which are placed later on the structure slope. Toe berm design is commonly related to the armor design; in non-breaking wave conditions, the mass of toe berm rocks is one order of magnitude lower than the units of the layer. In breaking wave conditions, however, the highest waves start breaking on the bottom and impact directly on the toe berm. This is the common case of rocky sea bottoms with m=1/10 or higher slopes and thus, a correct design of the toe berm is crucial to guarantee the armor stability. The present PhD thesis examines the hydraulic stability of rock toe berms placed on a m=1/10 bottom slope and in very shallow waters (0.53Dn50): (1) the nominal toe berm or the most shoreward toe berm area which effectively supports the armor layer, and (2) the sacrificial toe berm or the most seaward toe berm area which serves to protect the nominal toe berm. Considering the nominal toe berm damage, a new method is developed to reduce the rock toe berm size (Dn50) by increasing the toe berm width (Bt) if the required rock size is not available at the quarries. Finally, cube armor damage is examined, and the influence of the placement technique on armor stability is also characterized from physical tests conducted with cubes randomly- and uniformly- placed on the armor in two layers.
El manto principal de los diques en talud suele estar formado por escollera natural o elementos prefabricados de hormigón; su función es resistir la acción del oleaje. Una revisión del estado del arte pone de manifiesto que son numerosas las fórmulas existentes para el diseño de mantos derivadas de ensayos físicos a escala reducida con oleaje sin rotura por fondo. Sin embargo, la mayoría de diques en talud se construyen en la zona de rompientes con oleaje limitado por fondo, donde las ecuaciones de diseño habituales no son del todo válidas. En esta tesis doctoral se analiza la estabilidad hidráulica de mantos bicapa de escollera, a partir de ensayos a escala reducida con pendiente de fondo m=1/50. En base a los resultados obtenidos de los ensayos físicos, se propone una nueva relación potencial para el diseño de mantos de escollera en condiciones de oleaje limitado por fondo, válida para taludes con cot¿=1.5, números de estabilidad 0.98¿Hm0/(¿Dn50)¿2.5, y profundidades relativas a pie de dique de 3.75¿hs/(¿Dn50)¿7.50. Cuando el manto principal está formado por elementos de hormigón, es habitual construir una berma de pie que proporciona apoyo a los elementos del manto y, en su caso, colabora en la protección de la zona inferior del dique contra la socavación. Dicha berma suele construirse con escollera natural y su peso está condicionado al de los elementos del manto en el caso de no haber rotura por fondo. El peso de los elementos de la berma de pie suele ser un orden de magnitud inferior al peso de las unidades del manto; sin embargo, si la pendiente de fondo es fuerte (p.e. m=1/10) y las aguas someras esta regla no se cumple ya que algunas olas rompen sobre el fondo impactando directamente sobre la berma de pie. En estos casos, el peso de la escollera de la berma puede sobrepasar el de las unidades del manto y su correcto diseño es crucial para garantizar la estabilidad del dique. Además de estudiar la estabilidad del manto principal de diques de escollera, la presente tesis doctoral analiza también la estabilidad hidráulica de bermas de pie de escollera ubicadas en fondos con pendiente m=1/10 y aguas someras (0.53Dn50): (1) berma nominal o zona de la berma de pie sobre la que realmente apoya el manto principal, y (2) berma de sacrificio o zona de la berma de pie que protege a la berma nominal. A partir del daño de la berma de pie nominal, se propone un nuevo método para reducir el tamaño de piedra (Dn50) incrementando el ancho de la berma (Bt) cuando no se disponga del tamaño requerido en cantera. Finalmente, se examina el daño del manto de cubos y se analiza la influencia del método de colocación sobre el mismo, a partir de ensayos realizados con mantos bicapa de cubos con colocación aleatoria y uniforme.
El mantell principal dels dics en talús sol estar format per roca o elements prefabricats de formigó, la seva funció és resistir l'acció de l'onatge. Una revisió de l'estat de l'art manifesta que són nombroses les equacions de disseny existents per a condicions d'onatge no trencat. No obstant això, la majoria de dics en talús es construeixen a la zona de rompents amb onatge limitat per fons, on les equacions de disseny existents no són del tot vàlides. En aquesta tesi doctoral s'analitza l'estabilitat hidràulica de mantells bicapa de roca, a partir d'assajos a escala reduïda realitzats amb pendent de fons m = 1/50. En base als resultats obtinguts dels assajos, es proposa una relació potencial per al disseny de mantells de roca en condicions d'onatge limitat per fons vàlida per a talussos amb cot¿ = 1.5, nombres d'estabilitat 0.98¿Hm0/(¿Dn50) ¿2.5, i profunditats relatives a peu de dic de 3.75¿hs/(¿Dn50)¿7.50. Quan mantell principal està format per elements de formigó , és habitual construir una berma de peu que proporciona suport als elements del mantell i, si escau, col¿labora en la protecció de la zona inferior del dic contra la soscavació. Aquesta berma sol construir amb roca i el seu pes està condicionat al dels elements del mantell en el cas de no haver trencament per fons. El pes dels elements de la berma de peu sol ser un ordre de magnitud inferior al pes de les unitats del mantell; però, si el pendent de fons és fort ( p.e. m = 1 /10) i les aigües someres aquesta regla no es compleix ja que algunes onades trenquen sobre el fons impactant directament sobre la berma de peu. En aquests casos, el pes de la roca de la berma pot sobrepassar el de les unitats del mantell, i el seu correcte disseny és crucial per garantir l'estabilitat del dic. A més d'estudiar l'estabilitat del mantell principal de dics de roca, la present tesi doctoral analitza també l'estabilitat hidràulica de bermes de roca ubicades en fons amb pendents m = 1/10 i aigües someres (0.5 3 Dn50): (1) berma nominal o zona de la berma de peu sobre la qual recolza el mantell principal, i (2) berma de sacrifici o zona de la berma de peu que protegeix la berma nominal. A partir del dany de la berma de peu nominal, es proposa un nou mètode per reduir el tamany de roca (Dn50) incrementant l'amplada de la berma (Bt) quan no es disposi de la mida requerit en pedrera. Finalment, s'examina el dany del mantell de cubs i s'analitza la influència del mètode de col¿locació sobre el mateix , a partir d'assajos realitzats amb mantells bicapa de cubs amb col¿locació aleatòria i uniforme.
Herrera Gamboa, MP. (2017). Mound Breakwater Design in Depth-Limited Breaking Wave Conditions [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/82553
TESIS

Thesis (M.S.Civil and Environmental Engineering and Construction Management)--Oregon State University, 2005.
"January 2005." Description based on title screen as viewed on June 1, 2010 DTIC Descriptor(s): Three Dimensional, Bathymetry, Tsunamis, Earthquakes, Coastal Regions, Ocean Waves, Inertia, Landslides, Gravitational Fields, Seafloor Spreading, Long Wavelengths, Models, Energy, Theses, Time Includes bibliographical references (p. 84-85). Also available in print.

In this thesis, mountain wave breaking triggered by directional wind shear is investigated using numerical simulations of idealized and semi-idealized orographic flows. Idealized simulations are used to produce a regime diagram to diagnose conditions for wave breaking in Richardson number-dimensionless mountain height parameter space. It is found that, in the presence of directional shear, wave breaking can occur over lower mountains than in a constant-wind case. Furthermore, the extent of regions within the simulation domain where Clear-Air Turbulence (CAT) is expected increases with terrain elevation and background wind shear intensity. Analysis of the model output, supported by theoretical arguments, suggest the existence of a link between wave breaking and the relative orientations of the incoming wind vector and the horizontal velocity perturbation vector. This condition provides a possible diagnostic for CAT forecast in directional shear flows. The stability of the flow to wave breaking in the transition from hydrostatic to nonhydrostatic mountain waves is also investigated. Wave breaking seems to be inhibited by non-hydrostatic effects for weak wind shear, but enhanced for stronger wind shear. In the second part of the thesis, a turbulence encounter observed over the Rocky Mountains (in Colorado, USA) is studied. The role of directional shear in causing wave breaking is isolated from other possible wave breaking mechanisms through various sensitivity tests. The existence of an asymptotic wake, as predicted by Shutts for directional shear flows, is hypothesized to be responsible for a significant downwind transport of unstable air detected in cross-sections of the flow. Finally, critical levels induced by directional shear are studied by spectral analysis of the horizontal velocity wave perturbations. This is done for a fully idealized flow and for the more realistic flow corresponding to the investigated turbulence encounter. In these 2D power spectra, a rotation of the most energetic wave modes with the background wind and their selective absorption can be found. Such behaviour is consistent with the mechanism leading to wave breaking in directional shear flows.

This dissertation investigates the energetics of the Indian Ocean Meridional Overturning Circulation (MOC) using hydrographic data (Part I), and the interaction between a broad band internal wave field and a mean flow using idealized numerical simulations (Part II). The main objective of this work is to quantify how much energy is needed to drive the Indian Ocean MOC and to compare this with the energy available in the internal wave field. The turbulent dissipation needed to sustain the MOC is estimated by assuming a `mixing efficiency' of 0.2 and an advective-diffusive balance in neutral density layers. The advective transport of mass into this box-model is based on published estimates of the flow field at 32�S and the Indonesian Through-flow. A comparison of the large scale dissipation rates with estimates of the input of energy by the tides and the wind shows that most published overturning solutions require more energy than is likely to be available. This result suggests that energy budgets may be useful as constraints in inverse models. Estimates of turbulent dissipation due to internal wave breaking are inferred from in-situ observations of shear and strain using a fine scale parameterization. The isoneutral mean of the inferred internal wave dissipation rates is about one order of magnitude smaller than dissipation rates inferred from the large scale flow fields. This result appears robust when considering potential sampling biases in the internal wave observations and leads to the main conclusion of this work: the Indian Ocean MOC cannot primarily be driven by internal wave breaking. A preliminary investigation into other processes capable of dissipating energy in the ocean interior shows that the MOC may be closed by hydraulic turbulence in the numerous Fracture Zones in the Indian Ocean.

There is a good deal of uncertainty and sensitivity in the results for wave impact. In a practical situation, many parameters such as the wave climate will not be known with any accuracy especially the frequency and severity of wave breaking. Even if the wave spectrum is known, this is usually recorded offshore, requiring same sort of (linear) transfer function to estimate the wave climate at the seawall. What is more, the higher spectral moments will generally be unknown. Wave breaking, according to linear wave theory, is known to depend on the wave spectrum, see Srokosz (1986) and Greenhow (1989). Not only is the wave climate unknown, but the aeration of the water will also be subject to uncertainty. This affects rather dramatically the speed of sound in the water/bubble mixture and hence the value of the acoustic pressure that acts as a maximum cutoff for pressure calculated by any incompressible model. The results are also highly sensitive to the angle of alignment of the wave front and seawall. Here we consider the worst case scenario of perfect alignment. Given the above, it seems sensible to exploit the simple pressure impulse model used in this thesis. Thus Cooker (1990) proposed using the pressure impulse P(x, y) that is the time integral of the pressure over the duration of the impact. This results in a simplified, but much more stable, model of wave impact on the coastal structures, and forms the basis of this thesis, as follows: Chapter 1 is an overview about this topic, a brief summary of the work which will follow and a summary of the contribution of this thesis. Chapter 2 gives a literature review of wave impact, theoretically and experimentally. The topics covered include total impulse, moment impulse and overtopping. A summary of the present state of the theory and Cooker’s model is also presented in Chapter 2. In Chapter 3 and Chapter 4, we extend the work of Greenhow (2006). He studied the berm and ditch problems, see Chapter 3, and the missing block problem in Chapter 4, and solved the problems by using a basis function method. I solve these problems in nondimensionlised variables by using a hybrid collocation method in Chapter 3 and by using the same method as Greenhow (2006) in Chapter 4. The works are extended by calculating the total impulse and moment impulse, and the maximum pressure arising from the wave impact for each problem. These quantities will be very helpful from a practical point of view for engineers and designers of seawalls. The mathematical equations governing the fluid motion and its boundary conditions are presented. The deck problem together with the mathematical formulation and boundary conditions for the problem is presented in Chapters 5 and 6 by using a hybrid collocation method. For this case, the basis function method fails due to hyperbolic terms in these formulations growing exponentially. The formulations also include a secular term, not present in Cooker’s formulation. For Chapter 5, the wave hits the wall in a horizontal direction and for Chapter 6, the wave hits beneath the deck in a vertical direction. These problems are important for offshore structures where providing adequate freeboard for decks contributes very significantly to the cost of the structure. Chapter 7 looks at what happens when we have a vertical baffle. The mathematical formulation and the boundary conditions for four cases of baffles which have different positions are presented in this chapter. We use a basis function method to solve the mathematical formulation, and total impulse and moment impulse are investigated for each problem. These problems are not, perhaps, very relevant to coastal structures. However, they are pertinent to wave impacts in sloshing tanks where baffles are used to detune the natural tank frequencies away from environmental driving frequencies (e.g ship roll due to wave action) and to damp the oscillations by shedding vortices. They also provide useful information for the design of oscillating water column wave energy devices. Finally, conclusions from the research and recommendations for future work are presented in Chapter 8.

In 1989 the Schiehallion FPSO suffered bow damage from a steep fronted wave slap and the uncertainty in how to design for this type of loading became a concern to the oil industry and the regulators. The aim of this study is to research the insight of breaking wave impact on the bow of ship-type offshore structures experimentally and develop a methodology on how to design this type of loading. Steep wave impact pressures and the structural dynamic response on FPSO (shipshaped Floating oil Production Storage and Offloading vessel) bows are studied using 1180 scale instrumented models and time domain simulation with the funding from HSE and BP, a grant from EPSRC, associated in-kind industrial contributions, a University/Departmental Scholarship and an IMarEST Scholarship. This work has increased the understanding of the nature of the breaking waves that can cause large slap forces that are important for the design of offshore floating structures (and should also be relevant to ship design). Methods of generating model scale wave groups that should produce approximately the 1 in 3 hour maximum loads, when large waves break in unidirectional sea states prescribed by Hs and Tz, have been developed. These methods have been extended to spread seas and also to a 'partial' breaking wave in less steep seas, but no testing has taken place in spread seas or the longer period seas. In addition an empirical relationship has been determined that represents the steepening of a wave front based on the underlying linear wave. The forces and pressures from these waves have been measured on 1180 scale models of the Schiehallion FPSO and Loch Rannoch shuttle tanker. A time history simulation method of bow loading in random seas has been developed. It uses the wave front steepening relationship derived from the tests and a relatively simple slap force prediction based on velocity times rate of change of added mass. Incident wave pressure effects (with a non-linear correction) and added mass times acceleration forces are also included. Simple slam coefficient type formula has also been derived for easy application. The formula accounts for the effect of the size of the loaded area on the average pressure and the rise and decay times of the average pressure and, hence, the dynamic amplification of the response at the bow. The above experimental and theoretical work has considerably advanced the quantitative understanding of bow slap. Quantitatively we have some confidence in the most probable maximum slap force predictions in: long-crested seas with sea state steepnesses around 1114 - 1115 and when no air is trapped.

[ES] El cambio climático y la conciencia social sobre el impacto de las infraestructuras en el medio está llevando a la necesidad de diseñar diques en talud con cotas de coronación reducidas frente a eventos de rebase más extremos. Además, la mayoría de estos diques se construyen en zonas de profundidades reducidas, donde el oleaje rompe a causa de la limitación por fondo. Estudios recientes apuntan a la necesidad de considerar no sólo la caudal medio de rebase (q) sino también el máximo volumen individual de rebase (Vmax), el espesor de lámina de agua (OLT) y la velocidad del flujo de rebase (OFV) en el diseño de la cota de coronación de un dique en talud según criterios de rebase. No obstante, existen pocos estudios en la literatura científica centrados en Vmax en estructuras costeras sometidas a oleaje limitado por fondo. Además, estos estudios proporcionan resultados contradictorios en relación a la influencia de la limitación por fondo del oleaje sobre Vmax. En cuanto a OLT y OFV, no se han encontrado estudios en la literatura científica que permitan su predicción en diques en talud. En esta tesis doctoral, se han realizado ensayos físicos 2D en diques en talud rebasables (0.3≤Rc/Hm0≤2.5) sin espaldón y con tres mantos principales (Cubípodo®-1L, cubo-2L y escollera-2L) sobre dos pendientes de fondo suaves (m=2% and 4%) en condiciones de oleaje limitado por fondo (0.2≤Hm0/h≤0.9). Vmax junto con q son las variables más recomendadas en la literatura científica para diseñar la cota de coronación de diques en talud según criterios de rebase. En el presente estudio, los mejores resultados en la estimación de Vmax*=Vmax/(gHm0T012) se han obtenido empleando la función de distribución Weibull de dos parámetros con un coeficiente de determinación R2=0.833. Durante la fase de diseño de un dique en talud, es necesario predecir q para calcular Vmax cuando se emplean los métodos dados en la literatura científica. Por tanto, se debe estimar q con fines de diseño si no se dispone de observaciones directas. En caso de emplear la red neuronal CLASH NN para estimar q (R2=0.636), la bondad de ajuste de la función de distribución Weibull de dos parámetros propuesta en esta tesis para predecir Vmax* es R2=0.617. Así, el ratio entre Vmax* medido y estimado cae dentro del rango de 1/2 a 2 (banda de confianza del 90%) cuando se emplea q estimado con CLASH NN. Los nuevos estimadores desarrollados en la presente disertación proporcionan resultados satisfactorios en la predicción de Vmax* con un método más simple que aquellos propuestos en la literatura científica. No se ha encontrado una influencia significativa de la pendiente de fondo ni de la limitación por fondo del oleaje sobre Vmax* en este estudio. OLT y OFV están directamente relacionados con la estabilidad hidráulica de la coronación del dique y la seguridad peatonal frente a rebase. Por tanto, se requiere estimar OLT y OFV en la coronación del dique para diseñar apropiadamente su cota de coronación empleando criterios de rebase. En este estudio, se han empleado redes neuronales para desarrollar nuevos estimadores explícitos que permiten predecir OLT y OFV superados por el 2% del oleaje incidente con un alto coeficiente de determinación (0.866≤R2≤0.867). El número de cifras significativas apropiado para los coeficientes experimentales de dichos estimadores se ha determinado en base a su variabilidad. El punto óptimo en el que las características del oleaje deben ser estimadas para predecir OLT y OFV se ha identificado a una distancia de 3h desde el pie de la estructura (siendo h la profundidad a pie de dique). La pendiente de fondo tiene influencia sobre OLT y OFV. Los valores más extremos de OLT y OFV se han descrito empleando las distribuciones Exponencial de un parámetro y Rayleigh, respectivamente, con resultados satisfactorios (0.803≤R2≤0.812).
[CA] El canvi climàtic i la consciència social sobre l'impacte de les infraestructures al medi està portant a la necessitat de dissenyar dics en talús amb cotes de coronació reduïdes front a esdeveniments d'ultrapassament més extrems. A més, la majoria dels dics es construeixen en zones amb profunditats reduïdes on l'onatge es trenca a causa de la limitació per fons. Estudis recents apunten a la necessitat de considerar no solament el cabal mitjà de sobrepasse (q) sinó també el màxim volum individual de sobrepasse (Vmax), l'espessor de la làmina d'aigua (OLT) i la velocitat del flux de sobrepasse (OFV) pel disseny de la cota de coronació d'un dic en talús segons criteris de sobrepasse. No obstant, existeixen pocs estudis a la literatura científica centrats en Vmax en estructures costeres sotmeses a onatge limitat per fons. Addicionalment, aquests estudis proporcionen resultats contradictoris en relació a la influència de la limitació per fons de l'onatge sobre Vmax. Quant a OLT i OFV, no s'han trobat estudis a la literatura científica que permeten la seua predicció a dics en talús. En aquesta tesi doctoral, s'han realitzat assajos físics 2D amb dics en talús amb sobrepassos rellevants (0.3≤Rc/Hm0≤2.5) sense espatlló i amb tres elements al mantell principal (Cubípode-1L, cubs-2L i esculleres-2L) ubicats sobre pendents de fons suaus (m=2% i 4%) en condicions d'onatge limitat pel fons (0.2≤Hm0/h≤0.9). Vmax conjuntament amb q són les variables més recomanades a la literatura científica per dissenyar la cota de coronació en dics en talús segons criteris d'ultrapassament. Al present estudi, els millors resultats en l'estimació de Vmax*=Vmax/(gHm0T012) s'han obtingut utilitzant la funció de distribució Weibull de dos paràmetres amb un elevat coeficient de determinació R2=0.833. Durant la fase de disseny d'un dic en talús, és necessari predir q per calcular Vmax quan s'utilitzen els mètodes donats a la literatura científica. Per tant, es deu estimar q amb fins de disseny si no es disposa d'observacions directes. Si s'aplica la xarxa neuronal de CLASH NN per estimar q (R2=0.636), la bondat d'ajust de la funció de distribució Weibull de dos paràmetres proposada a aquesta tesi per predir Vmax* és R2=0.617. Així doncs, el ràtio entre el Vmax* mesurat i estimat es troba dins del rang de 1/2 a 2 (banda de confiança del 90%) quan s'usa q predit amb CLASH NN. Els nous estimadors desenvolupats a aquesta dissertació proporcionen resultats satisfactoris en la predicció de Vmax* amb un mètode més senzill que aquells proposats a la literatura científica. No s'ha trobat una influència significativa de la pendent de fons ni de la limitació de l'onatge per fons sobre Vmax* a aquest estudi. OLT i OFV estan directament relacionats amb l'estabilitat hidràulica de la coronació de dics i la seguretat de vianants front a ultrapassaments. Per tant, es requereix estimar OLT i OFV en la coronació de dics per dissenyar apropiadament la seua cota de coronació utilitzant criteris de sobrepasse. En aquest estudi, s'han usat xarxes neuronals per desenvolupar nous estimadors explícits que permeten predir OLT i OFV superats pel 2% de l'onatge incident amb un elevat coeficient de determinació (0.866≤R2≤0.867). El nombre de xifres significatives apropiat per als coeficients experimentals dels mencionats estimadors s'ha determinat basant-se en la seua variabilitat. El punt òptim on determinar les característiques de l'onatge deuen ser estimades per predir OLT i OFV s'ha identificat a una distància de 3h des del peu de l'estructura (on h és la profunditat a peu de dic). La pendent de fons té influència sobre OLT i OFV. Els valors més extrems de OLT i OFV s'han descrit amb les distribucions Exponencial d'un paràmetre i Rayleigh, respectivament, amb resultats satisfactoris (0.803≤R2≤0.812).
[EN] Climate change and the social concern about the impact of infrastructures is leading to mound breakwaters with reduced crest freeboards facing higher extreme overtopping events. In addition, most mound breakwaters are built in the surf zone where depth-limited wave breaking takes place. Recent studies point out the need of considering not only the mean wave overtopping discharge (q) but also the maximum individual wave overtopping volume (Vmax), the overtopping layer thickness (OLT) and the overtopping flow velocity (OFV) when designing mound breakwater crest elevation using overtopping criteria. However, few studies in the literature are focused on Vmax on coastal structures under depth-limited breaking wave conditions. In addition, those few studies report contradictory conclusions regarding the significance of depth-limited breaking waves on Vmax. With respect to OLT and OFV, no studies are found in the literature for their prediction on mound breakwaters. In this PhD thesis, 2D physical model tests were conducted on overtopped mound breakwaters (0.3≤Rc/Hm0≤2.5) without a crown wall armored with three armor layers (Cubipod®-1L, cube-2L and rock-2L) on two gentle bottom slopes (m=2% and 4%) in depth-limited breaking wave conditions (0.2≤Hm0/h≤0.9). Vmax together with q are the most recommended variables in the literature to design mound breakwater crest elevation based on overtopping criteria. In the present study, the 2-parameter Weibull distribution provides the best results when estimating Vmax*=Vmax/(gHm0T012) with coefficient of determination R2=0.833. During the design phase of a mound breakwater, q is needed to predict Vmax using methods given in the literature. Thus, q must be estimated for design purposes when direct observations are not available. If CLASH NN is used to estimate q (R2=0.636), the goodness-of-fit of the 2-parameter Weibull distribution proposed in this thesis to predict Vmax* is R2=0.617. Hence, the ratio between the estimated and measured Vmax* falls within the range 1/2 to 2 (90% error band) when q is predicted using CLASH NN. The new estimators derived in this study provide satisfactory estimations of Vmax* with a method simpler than those found in the literature. Neither the bottom slope nor the depth-induced wave breaking seem to significantly influence the dimensionless Vmax* in this study. OLT and OFV are directly related to the hydraulic stability of the armored crest and the pedestrian safety. Thus, OLT and OFV are required to properly design crest elevation using overtopping criteria. Neural Networks (NNs) are used in this study to develop new explicit unbiased estimators for the OLT and OFV exceeded by 2% of the incoming waves with a high coefficient of determination (0.866≤R2≤0.867). The appropriate number of significant figures of the empirical coefficients of such estimators is selected according to their variability. The optimum point where wave characteristics are determined to predict OLT and OFV was identified at a distance of 3h from the toe of the structure (where h is the water depth at the toe of the structure). The bottom slope does influence both OLT and OFV. The most extreme values of OLT and OFV are described with the 1-parameter Exponential and Rayleigh distribution functions, respectively, with satisfactory results (0.803≤R2≤0.812).
Al Ministerio de Educación, Cultura y Deporte, por la financiación brindada con el programa de Formación de Profesorado Universitario (FPU16/05081). Al Ministerio de Economía y Competitividad, por la financiación de los proyectos ESBECO (EStabilidad hidráulica del manto, BErmas y COronación de diques en talud con rebase y rotura por fondo, BIA2015-70436-R) y HOLOBREAK (Estabilidad Hidráulica y Transmisión de Diques Rompeolas Homogéneos de Baja Cota Diseñados a Rotura por Fondo, RTI2018-101073-B-I00-AR).
Mares Nasarre, P. (2021). Overtopping flow on mound breakwaters under depth-limited breaking wave conditions [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/163154
TESIS

Les énergies marines renouvelables (EMR) sont soumises aux vagues générées par le vent. Une caractérisation précise de ces vagues est nécessaire dans les zones côtières et littorales où les vagues interagissent fortement avec le fond, générant de la réfraction et du déferlement parmi d’autres processus.Une étude approfondie sur l’initiation du déferlement est développée. La validité du critère de déferlement conventionnel uc/c (rapport entre la vitesse orbitale horizontale à la crête et la vitesse de phase) est examinée numériquement. Cette étude nous mène à définir un nouveau critère cinématique basé sur le rapport entre la vitesse orbitale maximale ||um|| et c. Ce nouveau critère améliore la détection de l’initiation du déferlement, car la position d’où s’initie l’instabilité conduisant au déferlement est mieux capturée à partir de ||um||. La variabilité spatiale du champ de vagues en zone côtière est majoritairement étudiée à partir de modèles spectraux. La capacité d’un modèle à phase-résolue (type Boussinesq BT) à fournir des informations complémentaires pour les EMR est étudiée. Les modèles spectraux et BT produisent des résultats très différents en termes de hauteur de vagues et de puissance en présence d’une forte réfraction causée par la variabilité de la bathymétrie. On définit une méthode innovante pour extraire des informations liées aux vagues à partir d’images satellites, issues d’un radar à synthèse d’ouverture (SAR), et les comparer aux sorties des modèles. Nos résultats montrent des similitudes encourageantes entre le modèle BT et les données SAR
Since Marine Renewable Energy (MRE) systems are submitted to wind generated waves. Accurate wave characterization is required in the coastal and nearshore environment where the waves are strongly modified by their interaction with the sea bottom, inducing refraction and wave breaking among other processes.A comprehensive study regarding the wave breaking initiation process is developed. The conventional kinematic criterion uc/c (ratio between the horizontal orbital velocity at the crest and the phase velocity) validity is numerically investigated. Our study leads us to a new kinematic wave breaking criterion based on the ratio between the maximum fluid velocity ||um|| near the wave crest and c. This new criterion improves the detection of the breaking initiation, since ||um|| accurately captures the location of the fluid instability leading to breaking.The wave field spatial variability in coastal areas is mostly studied with spectral wave models. We explore the ability of a phase-resolving model (Boussinesq-type, BT) to provide additional wave information for MRE applications.Spectral and BT models lead to significantly different spatial wave height and power patterns in the presence of strong bottom-induced refraction. We define an innovative methodology to extract wave information from satellite Synthetic Aperture Radar (SAR) images for comparison with models’ outputs. Our results highlight encouraging similarities between the BT model and SAR data

Many different astrophysical events related to pulsars are taught to be due to starquakes, that could be caused by various possible loadings acting on the crust. However, at the present time, there is still a lack of theoretical well based modelling for most of these loadings and, therefore, we have only a very rough knowledge of the physics of neutron stars’ crust response. This PhD work wants to be a first development of a quite realistic calculation of the effects of chosen loadings, being that the forces due to uniform rotation, differential rotation or pinning, on the crust of pulsars. A Newtonian model, already used in Geophysics, has been adapted to the very different physical conditions of neutron stars’ physics and used to describe self-gravitating neutron stars, both in the incompressible and compressible scenario, subjected to different kinds of loadings. In particular, the deformations due to uniform rotation, differential rotation and slack pinning are studied. It is found that the response of the star is very sensitive to the adiabatic index value, while it is weakly influenced by the stellar mass. In all the cases, the strain developed between two glitches is found to be insufficient to break the crust, a result that challenges the standard picture of pulsar glitches based on crustquakes. Finally, attention is focused on accreting neutron stars in low-mass X-ray binaries and millisecond pulsars. The scenario is the following: the star spins up due to the accretion of matter thus building up stress; the mass quadrupole moment associated with crustal failures leads to the emission of gravitational waves which, in turn, spins down the star until equilibrium. The equilibrium frequency calculated is found compatible with observations. It is also argued that these gravitational waves could be potentially detected by the LIGO-Virgo interferometers in the near future.

Spirals are common in Nature: the snail's shell and the ordering of seeds in the sunflower are amongst the most widely-known occurrences. While these are static, dynamic spirals can also be observed in excitable systems such as heart tissue, retina, certain chemical reactions, slime mold aggregates, flame fronts, etc. The images associated with these spirals are often breathtaking, but spirals have also been linked to cardiac arrhythmias, a potentially fatal heart ailment. In the literature, very specific models depending on the excitable system of interest are used to explain the observed behaviour of spirals (such as anchoring or drifting). Barkley [5] first noticed that the Euclidean symmetry of these models, and not the model itself, is responsible for the observed behaviour. But in experiments, the physical domain is never Euclidean. The heart, for instance, is finite, anisotropic and littered with inhomogeneities. To capture this loss of symmetry, LeBlanc and Wulff [48,51] introduced forced Euclidean symmetry-breaking (FESB) in the analysis. To accurately model the physical situation, two basic types of symmetry-breaking perturbations are used: translational symmetry-breaking (TSB) and rotational symmetry-breaking (RSB) terms. LeBlanc and Wulff, [51] and LeBlanc [48] have studied the effects of these individual perturbations, and they have shown that phenomena such as anchoring and quasi-periodic meandering can be explained by FESB. However, these specific perturbations only tell part of the story. In this thesis, the effects of multiple TSB perturbations, as well as those of combined TSB-RSB perturbations are studied and provide a more complete explanation for two aspects of spiral dynamics: anchoring and boundary drifting. Higher co-dimension phenomena are also considered.

The Southern Ocean is governed by strong wind forcing, energetic eddies and probably intense internal wave fields, which are considered to be generated in part by interaction of the eddy field with bottom topography. While wind and eddy forcing have been recognized in the dynamical balance of the Southern Ocean Meridional Overturning Circulation (MOC), the role of internal waves remains uncertain. The present study aims to investigate the extent to which the interaction of an energetic eddy field with realistic bottom topography, leading to diabatic forcing of the interior stratification through internal wave breaking, can sustain a deep overturning circulation and provide an additional leading order term in the Southern Ocean MOC that is unaccounted for by current theories and numerical models. A hierarchy of experiments to test this hypothesis is conducted in this thesis. The MIT General Circulation Model (MITgcm) is configured to simulate a circumpolar current in two individual versions of a zonal channel, namely a coarse-resolution setup with Gent-McWilliams eddy parameterisation and a mesoscale eddy-resolving setup. The energy input that arises from internal wave breaking and forces the buoyancy budget of the MOC is parameterised in the model via a vertical diffusivity profile. Initially forced to follow a simple constant shape, this diffusivity profile is subsequently estimated online via the internal lee wave energy generation rate, which is calculated from the model stratification, velocities and from prescribed sub-grid-scale topography, following nonlinear internal lee wave theory. Results from the individual experiments are discussed in view of the extent and mechanisms by which internal waves generated by eddy-topography interaction force the cross-channel MOC. The main results of this thesis show that the internal lee wave energy generation rate enhances the diapycnal diffusivity near the bottom, which results in a substantial increase in the strength of the residual MOC of the lower limb and a warming of the deep interior of the channel.

Since the first discovery of an extrasolar planet around a solar-type star, observers have detected over 500 planets outside the solar system. Many of these planets have Jovian masses and orbit their host stars in orbits of only a few days, the so-called 'Hot Jupiters'. At such close proximity to their parent stars, strong tidal interactions between the two bodies are expected to cause significant secular spin-orbit evolution. This thesis tackles two problems regarding the tidal evolution of short-period extrasolar planets. In the first part, we adopt a simple model of the orbit-averaged effects of tidal friction, to study the tidal evolution of planets on inclined orbits. We also analyse the effects of stellar magnetic braking. We then discuss the implications of our results for the importance of Rossiter-Mclaughlin effect observations. In the second part, we study the mechanisms of tidal dissipation in solar-type stars. In particular, internal gravity waves are launched at the interface of the convection and radiation zones of such a star, by the tidal forcing of a short-period planet. The fate of these waves as they approach the centre of the star is studied, primarily using numerical simulations, in both two and three dimensions. We find that the waves undergo instability and break above a critical amplitude. A model for the tidal dissipation that results from this process is presented, and its validity is verified by numerical integrations of the linear tidal response, in an extensive set of stellar models. The dissipation is efficient, and varies by less than an order of magnitude between all solar-type stars, throughout their main-sequence lifetimes, for a given planetary orbit. The implications of this mechanism for the survival of short-period extrasolar planets is discussed, and we propose a possible explanation for the survival of all of the extrasolar planets currently observed in short-period orbits around F, G and K stars. We then perform a stability analysis of a standing internal gravity wave near the centre of a solar-type star, to understand the early stages of the wave breaking process in more detail, and to determine whether the waves are subject to weaker parametric instabilities, below the critical amplitude required for wave breaking. We discuss the relevance of our results to our explanation for the survival of short-period planets presented in the second part of this thesis. Finally, we propose an alternative mechanism of tidal dissipation, involving the gradual radiative damping of the waves. Based on a simple estimate, it appears that this occurs even for low mass planets. However, it is in conflict with current observations since it would threaten the survival of all planets in orbits shorter than 2 days. We discuss some hydrodynamic instabilities and magnetic stresses which may prevent this process.

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

This study reports on a new formulation of the spectral dissipation source term Sds for wind-wave modelling applications. This new form of Sds features a nonlinear dependence on the local wave spectrum, expressed in terms of the azimuthally integrated saturation parameter B(k)=k^4 F(k). The basic form of this saturation-dependent Sds is based on a new framework for the onset of deep-water wave breaking due to the nonlinear modulation of wave groups. The new form of Sds is succesfully validated through numerical experiments that include exact nonlinear computations of fetch-limited wind-wave evolution and hindcasts of two-dimensional wave fields made with an operational wind-wave model. The newly-proposed form of Sds generates integral spectral parameters that agree more closely with observations when compared to other dissipation source terms used in state-of-the-art wind-wave models. It also provides more flexibility in controlling properties of the wave spectrum within the high wavenumber range. Tests using a variety of wind speeds, three commonly-used wind input source functions and two alternative full-development evolution limits further demonstrate the robustness and flexibility of the new saturation-dependent dissipation source term. Finally, improved wave hindcasts obtained with an implementation of the new form of Sds in a version of the WAM model demonstrate its potential usefulness in operational wind-wave forecasting applications.

In terms of future power generation in UK and Germany, offshore wind is the next big player with 40GW and 32GW capacity planned for installation in both countries respectively by 2030. The latest Round 3 of sites owned by the Crown Estate explore deeper water depths of up to 78m in the Irish Sea. Foundations for offshore wind structures consume around 25% of the total project cost therefore the design of support structures is the subject of this thesis. The current state-of-the-art support structure options available for offshore wind turbines have been outlined in this thesis with an evaluation of the preliminary design of monopile and jacket solutions. This assessment resulted in further studies into the loading acting on a monopile foundation along with research into the fatigue design of multiplanar tubular joints for jacket structures. Mathematical modelling of linear and nonlinear waves combined with the Morison equation was completed to check the effects of breaking waves on a monopile foundation. Results indicated that measured forces were up to a factor of 2.5 times greater than calculated values, which suggests that loads could be under predicted if the effects of breaking are not considered. The theoretical maximum wave height before breaking was then linked to wind speed and a comparison of overturning moments from the two loads was made. Wave loads dominated at water depths of around 30m for lower wind speeds but this depth decreased to around 12m as wind speeds approached cut-out of 25m/s. For deeper water depths and larger capacity turbines, jackets are the preferred design solution. Joint design in FLS is the critical aspect of jacket design with castings often required to provide adequate capacity. A review of stress concentration factors (SCF) for tubular joints indicated that the coded approach, which uses SCF equations for uniplanar joints, could be missing the multiplanar effects. Finite element (FE) modelling of multiplanar tubular joints was completed using ANSYS Workbench to examine the effects of loading in out-of plane braces. Carry-over of stress from the loaded brace of the joint to unloaded neighbouring braces was observed which implies the importance of modelling joints as multiplanar geometries. A parameter study in ANSYS Workbench covering 1806 different geometrical configurations and loads was carried out with a regression of the data to give new sets of SCF equations for multiplanar tubular joints. SCFs from these equations were improved compared to Efthymiou but difficulties were encountered when superimposing the output (including Efthymiou). Further work on the superposition of individual load cases was therefore recommended for future work.

Coastal flooding from wave overtopping causes considerable damage. Presently, to model wave overtopping one can either make use of physical model tests or empirical tools such as those described in the EurOtop manual. Both these methods have limitations; therefore, a quick and reliable numerical model for wave overtopping would be a very useful tool for a coastal engineer.This research aims to test and develop a numerical model (in one horizontal dimension) for nearshore waves, runup and overtopping. The Shallow Water And Boussinesq (SWAB) model solves the Boussinesq-type equations of Madsen and Sorensen (1992) for non breaking waves and the nonlinear shallow water equations for breaking waves. Through testing against a range of physical model data using regular and random waves, the SWAB model's transfer from non-breaking to breaking waves was optimised. It was found that a wave height to water depth ratio worked consistently well as a breaking criterion.A set of physical model tests were carried out, based on previous field testing of wave overtopping that had previously taken place at Anchorsholme, Blackpool. The SWAB model was used to simulate some of these physical model tests, giving good results for mean overtopping rates. SWAB models the force imposed by steep walls and recurve walls on the incident flow; this force was found to have a significant effect on overtopping rates. A comparison was made between mean overtopping rates from the SWAB model, the physical model tests, empirically-based software (PC-Overtopping) and the field data. The physical model and SWAB results compared well with the field data, though the empirical software gave large overestimates.The SWAB model was applied to the analysis of overtopping at Walcott, Norfolk. It was found that beach levels affected overtopping rates, but not as much as different randomly phased wave trains. A simulation of a recent storm event was performed, with overtopping rates being slightly lower than those reported by local residents. A joint probability analysis showed that the predicted frequency of such an event was in line with these reports.An alternative modelling technique was also tested, where a spectral energy model was coupled with a nonlinear shallow water solver. Results for wave runup parameters were very accurate, when the coupling location is at the seaward edge of the surf zone. Extension of this modelling technique into two horizontal dimensions would be more straightforward than with the SWAB model.

Simulations of the circulation in the middle atmosphere during northern winter performed with a nonlinear, mechanistic, global circulation model show that the upper mesospheric jet is greatly overestimated and also the position with respect to latitude and height does not correspond to observations. Apart from that also the winter wind reversal in the mesopause region, evoked by breaking gravity waves (GWs), is located too low around 80km, but is observed to be usually around 100 km. These discrepancies are planned to be eliminated by modifying the distribution of GW amplitudes driving the GW parameterization. This distribution is currently based on potential GW energy data derived from GPS radio occultation measurements and has to be replaced by a distribution based on momentum flux estimates applying midfrequency approximation. The results show a weaker mesospheric jet more realistically tilted towards lower latitudes with height. Also the meridional circulation extending from the summer to the winter pole decelerates and less GWs are propagating into the mesosphere. By additionally varying the GW amplitudes in magnitude and time, the wind reversal is shifted upwards and the mesospheric jet is slowed down.
Simulationen der Zirkulation der mittleren Atmosphäre während des nordhemisphärischen Winters unter Verwendung eines nicht-linearen mechanistischen globalen Zirkulationsmodells ergaben beim Vergleich mit Messungen, dass der simulierte, mesosphärische Jet stark überschätzt wird und dessen Position von den Beobachtungen abweicht. Die in der Mesopausenregion einsetzende Windumkehr, hervorgerufen durch brechende Schwerewellen, befindet sich in etwa 80 km anstatt in 100 km. Diese Diskrepanzen sollen eliminiert werden. Hierfür wird die Verteilung der Schwerewellenamplituden, die die Schwerewellenparametrisierung innerhalb des Modells antreibt, am oberen Rand der Troposphäre modifiziert. Diese basiert derzeit auf global beobachteten, zonal gemittelten Daten der potentiellen Energie von Schwerewellen abgeleitet aus GPS Radiookkultationsmessungen und soll durch eine auf Impulsflüssen basierende Verteilung ersetzt werden. Das Modellexperiment zeigt, dass der mesosphärische Jet mit der Höhe in Richtung niedriger Breiten geneigt ist und abgebremst wird. Zudem schwächt die Meridionalzirkulation vom Sommer- zum Winterpol leicht ab und weniger Schwerewellen dringen bis in die Mesosphäre vor. Zusätzlich wird durch zeitliche und unterschiedlich starke Variation der Schwerewellenamplitude die Windumkehr verlagert und der mesosphärische Jet abgebremst.

This dissertation was a formative evaluation of the Waves for Change Surf Therapy Programme, and included both a process evaluation and an outcome evaluation. Waves for Change used surfing as a means of engaging children and adolescents thought to be at risk of long-term social exclusion. This engagement was necessary in order to deliver a psychosocial curriculum. Waves for Change aimed to use this curriculum to enhance psychosocial wellbeing and reduce antisocial behaviour, and association with antisocial peers. Five evaluation questions were generated using programme documents and a rapid evidence assessment. These were concerned with whether the programme was capable of enhancing psychosocial wellbeing, and reducing antisocial behaviour and association with antisocial peers. Further, the evaluation wished to determine whether the programme was correctly targeted, and delivered with fidelity. An intention to treat analysis was conducted within a randomised control trial, using 115 primary school students from Masiphumelele, Khayelitsha, and Lavender Hill. Further 88 interviews were conducted with programme beneficiaries, and 15 coaches were submitted to performance review. The programme was found to be suitably targeted, but delivery of the programme was not achieved with fidelity to the programme design. There were a number of reasons for this, including inadequate completion of programme tasks by coaches, and inadequate attendance by children and adolescents. The result was that children and adolescents received less than half of the psychosocial curriculum, and did not show a change on the outcomes of interest. However, this evaluation suggested that the programme is feasible, pending improvements.

A dynamic simulation of the response of an inflatable dam subjected to a flood was carried out to determine the survivability envelope of the dam where it can operate without rupture, or overflow. A fully nonlinear free-surface flow was applied in two dimensions using a mixed Eulerian-Lagrangian formulation.

An ABAQUS finite element model was used to determine the dynamic structural response of the dam. The problem was solved in the time domain which allows the prediction of a number of transient phenomena such as the generation of upstream advancing waves, and dynamic structural collapse. Stresses in the dam material were monitored to determine when rupture occurs. An iterative study was performed to find the service envelope of the dam in terms of the internal pressure and the flood Froude number for two flood depths. It was found that the driving parameter governing failure of the dam was the internal pressure. If this pressure is too low, the dam overflows; if this pressure is too high, the dam ruptures. The fully nonlinear free-surface flow over a semi-circular bottom obstruction was studied numerically in two dimensions using a similar solution formulation as that used in the previous study. A parametric study was performed for a range of values of the depth-based Froude number up to 2.5 and non-dimensional obstacle heights up to 0.9. When wave breaking does not occur, three distinct flow regimes were identified: subcritical, transcritical and supercritical. When breaking occurs it may be of any type: spilling, plunging or surging. In addition, for values of the Froude number close to 1, the upstream solitary waves break. A systematic study was undertaken, to define the boundaries of each type of breaking and non-breaking pattern, and to determine the drag and lift coefficients, free surface profile characteristics and transient behavior.
Master of Science

Thesis (MScEng (Civil Engineering))--University of Stellenbosch, 2009.
Multi purpose reefs are a relatively new concept that incorporate functionalities of beach stabilization, breakwater/seawall protection, biological enhancement and recreational amenity. Economic benefits increase their attractiveness. There is, however, some degree of uncertainty in design guidelines as to the predictability of each of these aspects. With regards to recreational amenity enhancement, one such uncertainty exists in the ability to predict the reef configuration required to give a certain degree of surfability of a reef, and more specifically, to predict the shape of a plunging wave. An extensive survey of the relevant literature has been conducted to provide a background on multi purpose reefs and the uncertainties in predicting the success of multi purpose reefs in achieving their design objectives. A study of wave breaking has been done, along with an analysis of existing breaker height and breaker depth formulae. The effects of bottom friction, refraction, shoaling, winds currents and varying water level on wave breaking has been addressed. Surfability aspects were reviewed including a definition of breaking intensity which is defined by the wave profile in terms of vortex shape parameters, and other surfability parameters that influence the surfability of a reef. Background on numerical modelling methods has been given, along with a description and some trial runs of a new and promising method, Smooth Particle Hydrodynamics. Numerical models were run using the open source SPHysics package in order to assess the applicability of the package in measuring vortex shape parameters. The SPHysics package is, however, still in a stage of development, and is not yet suitable for reef studies with very long domains and with high numbers of particles (required for sufficient resolution in the plunging vortex). A theoretical examination was done on the relevant literature in order to gain an insight into the dynamics affecting the development of the plunging vortex shape. A case study of a natural surf reef was carried out in order to give qualitative estimation of the wave dynamics and reef structure required to give good quality surfing waves and high breaking intensity. The West- Cowell surfing reef factor was used as a tool in predicting wave focusing effects of a naturally occurring reef. Extensive two dimensional physical model laboratory studies were conducted in order to quantify the effects of the reef configuration and wave parameters on breaking intensity. Design guidelines were developed in order to assist in the prediction of breaking intensity for reefs constructed with surfing amenity enhancement as one of their design objectives. The results show that large underwater topographic features can significantly affect the shape and size of incoming waves. Refraction, focusing and shoaling can transform ordinary waves into waves deemed suitable for surfing. The West-Cowell surfing reef factor gives reasonable results outside its applicable range. The 2D physical model laboratory tests show significant variations in vortex shape parameters due to interactions between broken and unbroken waves in a wave train and also to the reflections developed in the flume. Results show that the predicted trends agree with the observations. The results also show that the junction between the seaward reef slope and the horizontal crest may have an effect on the wave shape in the form of a secondary crest between the primary crests. Design guidelines based on the results are presented, and show that breaker height formulae for smooth planar slopes show good agreement with the values of breaker heights measured in the physical model tests, and that existing breaker depth formulae show average agreement. The design guidelines could assist with more effective design of artificial reefs for surfing purposes.

Une simple extension du modèle standard et de la relativité générale consiste à introduire une particule fondamentale de spin 3/2, car il s’agit de la seule pièce manquante entre les spin 0 et 2. En outre, nous ne connaissons qu’un seul candidat présentant un tel spin du point de vue de la théorie fondamentale, le gravitino, superpartenaire du graviton. Ainsi, l’existence d’un spin fondamental 3/2 pourrait également être une arme à feu de supersymétrie ainsi que la théorie des supercordes. L’axion est un autre candidat intéressant au-delà du modèle standard. Pour le problème du CP puissant, l’une des solutions les plus populaires consiste à introduire un axion. La théorie des cordes prédit des particules générales de type axion avec une gamme de masses plus étendue. Ils peuvent également être des candidats parfaits pour la matière noire. Dans cette thèse, nous discutons de leurs mécanismes de production et des signaux possibles pour la détection. Nous souhaitons également aborder certaines questions dans le cadre de la théorie des cordes, telles que la stabilisation des modules. Les travaux précédents utilisent largement les corrections non perturbatives pour générer le minimum pour les champs de modules, tandis que nous choisissons un chemin différent pour rechercher si le problème Dine-Seiberg peut avoir une solution simple. Nous espérons également répondre à la question: pourquoi notre univers observé est-il à quatre dimensions?
One simple extension of the Standard Model and general relativity is to introduce a fundamental particle with spin 3/2 since it’s the only missing piece between spin 0 and spin 2. Furthermore, we know only one candidate with such a spin from a fundamental theory point of view, the gravitino, superpartner of the graviton. Thus the existence of a fundamental spin 3/2 could also be a smoking gun of supersymmetry as well as Superstring theory. Another interesting beyond Standard Model candidate is the axion. For the strong CP problem, one of the most popular solution is to introduce an axion. General axion-like particles with a broader range of masses are predicted from String theory. They can be perfect cold dark matter candidates as well. In this thesis, we discuss their production mechanisms and possible signals for detection. We also want to address some questions in the framework of String theory like moduli stabilisation. Previous works widely use non-perturbative corrections to generate minimum for moduli fields while we choose a different path to investigate if the Dine-Seiberg problem can have a simple solution. We also hope to answer the question: why our observed universe is four-dimensional?

Two different air-water interfacial flows are studied including plunging wave breaking and flow past a vertical surface-piercing circular cylinder using complementary CFDShip-Iowa version 6 including Cartesian grid solver and orthogonal curvilinear grid solver. The plunging wave-breaking process for impulsive flow over a bump in a shallow water flume has been simulated using the exact experimental initial and boundary conditions. The overall plunging wave breaking process is described with major wave breaking events identified: jet plunge, oblique splash and vertical jet. These major events repeat up to four times before entering the chaotic breaking. The simulations show a similar time line as the experiments consisting of startup, steep wave formation, plunging wave, and chaotic wave breaking swept downstream time phases. Detailed wave breaking processes, including wave profile at maximum height, first plunge, entrapped air bubble trajectories and diameters, kinetic, potential, and total energy, and bottom pressures are discussed along with the experimental results. The simulations show differences and similarities with other experimental and computational studies for wave breaking in deep water and sloping beaches. The geometry and conditions in the present study are relevant to ship hydrodynamics since it includes effects of wave-body interactions and wave breaking direction is opposite to the mean flow. Large-eddy simulation with the Lagrangian dynamic subgrid-scale model has been performed to study the flow past a surface-piercing circular cylinder for Re and Fr effect. The flow features near the air-water interface show significant changes with different Reynolds numbers from sub-critical to critical regime. It is shown that the interface makes the separation point more delayed for all regime of Re. Remarkably reduced separated region below the interface is observed for critical Re regime and it is responsible for much reduced wake and recirculation region behind the cylinder and it recovers in the deep flow. At different Fr, significant changes are shown on the air-water interface structures. At lower Fr, relatively smaller bow waves are observed in front of the cylinder with Kelvin waves behind the cylinder and small amount of free-surface roughness and turbulence are also seen in the wake region. For higher Fr, the bow wave increases remarkably with the larger wake region and deeper depression and it breaks with similar features of plunging breakers. Much more small air-water interface structures including splashes and bubbles are observed behind the cylinder. It is hard to distinguish the Kelvin waves behind the cylinder due to much larger free-surface oscillations and turbulence. As Fr increases, the Kelvin wave angle decreases and deeper and narrower depression region behind the cylinder are observed. The flow features around the cylinder are significantly changed due to this cavity region behind the cylinder.

Statistical trend analyses of National Centers for Environmental Prediction (NCEP) gradient zonal winds for the months of February and March demonstrate that the zonal mean meridional wind shear for these months in the midlatitude lower stratosphere has tended to become more anticyclonic with time over the period from 1979 to 1998. Such a tendency favors the increased occurrence at these latitudes of anticyclonic, poleward, Rossby wave breaking events that transport low potential vorticity (PV), ozone-poor air from the subtropical upper troposphere to the midlatitude lower stratosphere while favoring the decreased occurrence of equatorward breaking, cyclonic events. Composite mean differencing and statistical trend analyses of NCEP-derived PV on the 330 K isentropic surface show that zonal mean PV values at midlatitudes in February and March have decreased with time, consistent with the expected trends in Rossby wave breaking behavior. Similar analyses of Total Ozone Mapping Spectrometer (TOMS) total ozone for the same 2 months show that total ozone trends correlate geographically with PV trends. Regression relationships between 330 K PV and total ozone deviations derived from monthly mean measurements on the Northern Hemisphere are applied to estimate that as much as 40% of the zonal mean total ozone decline at midlatitudes in February during the analysis period may be attributed to long-term trends in Rossby wave breaking behavior. As much as 25% of the midlatitude ozone trend in March may be attributed to such trends in wave-breaking behavior. At specific longitudes the contribution to ozone trends from this source (as well as long-term changes in quasi-stationary wave amplitudes and phases) can be well over 50%.

Because little was known about how the masonry lighthouses constructed during the 19th century at exposed locations around the British Isles were responding to wave action, the dynamic response of the Eddystone lighthouse under wave impacts was investigated. Like other so called 'rock lighthouses', the Eddystone lighthouse was built on top of a steep reef at a site that is fully submerged at most states of the tide. Consequently, the structure is exposed to loading by unbroken, breaking and broken waves. When the breaking occurs, wave loading leads to complex phenomena that cannot be described theoretically due to the unknown mixture of air and water involved during the wave-structure interaction. In addition, breaking waves are generally distinguished from unbroken and broken wave due to the fact that they cause impulsive loads. As a consequence, the load effects on the structural response require a dynamic analysis. In this investigation the dynamic response of the Eddystone lighthouse is investigated both in the field and by means of a small-scale model mounted in a laboratory wave channel. In particular, field data obtained by the use of geophones, cameras and a wave buoy are presented together with wave loading information obtained during the laboratory tests under controlled conditions. More than 3000 structural events were recorded during the exceptional sequence of winter storms that hit the South-West of England in 2013/2014. The geophone signals, which provide the structural response in terms of velocity data, are differentiated and integrated in order to obtain accelerations and displacements respectively. Dynamic responses show different behaviours and higher structural frequencies, which are related to more impulsive loads, tend to exhibit a predominant sharp peak in velocity time histories. As a consequence, the structural responses have been classified into four types depending on differences of ratio peaks in the time histories and spectra. Field video images indicate that higher structural frequencies are usually associated with loads caused by plunging waves that break on or just in front of the structure. However, higher structural velocities and accelerations do not necessarily lead to the largest displacements of around a tenth of mm. Thus, while the impulsive nature of the structural response depends on the type of wave impact, the magnitude of the structural deflections is strongly affected by both elevation of the wave force on the structure and impact duration, as suggested by structural numerical simulations and laboratory tests respectively. The latter demonstrate how the limited water depth strongly affects the wave loading. In particular, only small plunging waves are able to break on or near the structure and larger waves that break further away can impose a greater overall impulse due to the longer duration of the load. As a consequence of the depth limited conditions, broken waves can generate significant deflections in the case of the Eddystone lighthouse. However, maximum accelerations of about 0.1g are related to larger plunging waves that are still able to hit the lighthouse with a plunging jet. When compared to the Iribarren number, the dimensionless irregular momentum flux proposed by Hughes is found to be a better indicator concerning the occurrence of the structural response types. This is explained by the fact that the Iribarren number does not to take into account the effects of the wide tidal range at the Eddystone reef, which has a strong influence on the location of the breaking point with respect to the lighthouse. Finally, maximum run up were not able to rise up to the top of the lighthouse model during the laboratory tests, despite this having been observed in the field. As a consequence, the particular configuration of the Eddystone reef and the wind could have a considerable bearing and exceptional values of the run up, greater than 40 m, cannot be excluded in the field.

Video based remote sensing techniques are well suited to collect spatially resolved wave images in the surf zone with breaking waves and dynamic bathymetric changes. An advanced video-based depth inversion method is developed to remotely survey bathymetry in the surf zone. The present method involves image processing of original wave image sequences, wave property estimation based on linear feature extraction from the processed image sequences, and is combined with a nonlinear depth inversion model. The original wave image sequences are processed through video image frame differencing and directional low-pass filtering schemes to remove wave-breaking-induced foam noise having high frequencies in the surf zone. The features of individual crest trajectories are extracted from the processed and rectified image sequences, i.e. processed image cross-shore timestacks, by tracking pixels of high intensity within an interrogation window of a Radon-transform-based line-detection algorithm. The wave celerity is computed using space-time information of the extracted trajectories of individual wave crests in the cross-shore timestack domain. The presented retrieval of nearshore bathymetry from video image sequences is based on a nonlinear depth inversion using the nonlinear shallow water wave theory. The nonlinear wave amplitude dispersion effects at the breaker points are determined by combining the nonlinear shallow water celerity equation with a wave breaker criterion, thereby computing water depths iteratively from the celerity measured from the video data. The water depths estimated at the breaker points present initial bathymetric anchor points. Bathymetric profiles in the surf zone are inverted by calculating wave heights dissipated after wave breaking with a wave dissipation model and wave heights shoaled before wave breaking with a wave shoaling model. The continuous wave amplitude dispersion effects are subtracted from the measured celerity profiles, resulting in nearshore bathymetric profiles. The nonlinear depth inversion derived bathymetric estimates from nearshore imagery match the measured values with a biased mean depth error of about +0.06m in the depth range of 0.1 to 3m. In addition, the wave height estimates by the depth inversion model are comparable to the in-situ measured wave heights with a biased mean wave height error of about +0.14m. The present depth inversion method based on optical remote-sensing supports coastal management, navigation, and amphibious operations.

Laboratory experiments were performed to study and improve longshore sediment transport rate predictions. Measured total longshore transport in the laboratory was approximately three times greater for plunging breakers than spilling breakers. Three distinct zones of longshore transport were observed across the surf zone: the incipient breaker zone, inner surf zone, and swash zone. Transport at incipient breaking was influenced by breaker type; inner surf zone transport was dominated by wave height, independent of wave period; and swash zone transport was dependent on wave period. Selected predictive formulas to compute total load and distributed load transport were compared to laboratory and field data. Equations by Kamphuis (1991) and Madsen et al. (2003) gave consistent total sediment transport estimates for both laboratory and field data. Additionally, the CERC formula predicted measurements well if calibrated and applied to similar breaker types. Each of the distributed load models had shortcomings. The energetics model of Bodge and Dean (1987) was sensitive to fluctuations in energy dissipation and often predicted transport peaks that were not present in the data. The Watanabe (1992) equation, based on time-averaged bottom stress, predicted no transport at most laboratory locations. The Van Rijn (1993) model was comprehensive and required hydrodynamic, bedform, and sediment data. The model estimated the laboratory cross-shore distribution well, but greatly overestimated field transport. Seven models were developed in this study based on the principle that transported sediment is mobilized by the total shear stress acting on the bottom and transported by the current at that location. Shear stress, including the turbulent component, was calculated from the wave orbital velocity. Models 1 through 3 gave good estimates of the transport distribution, but underpredicted the transport peak near the plunging wave breakpoint. A suspension term was included in Models 4 through 7, which improved estimates near breaking for plunging breakers. Models 4, 5 and 7 also compared well to the field measurements. It was concluded that breaker type is an important variable in determining the amount of transport that occurs at a location. Lastly, inclusion of the turbulent component of the orbital velocity is vital in predictive sediment transport equations.

Kyoto University (京都大学)
0048
新制・課程博士
博士(工学)
甲第14147号
工博第2981号
新制||工||1442(附属図書館)
26453
UT51-2008-N464
京都大学大学院工学研究科都市環境工学専攻
(主査)教授 後藤 仁志, 教授 細田 尚, 准教授 牛島 省
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