Auswahl der wissenschaftlichen Literatur zum Thema „Overtopping volume“

In the past decades, the crest height of the seawall was determined by the allowable average wave overtopping rate q. Franco (1994) concluded that individual wave overtopping，particularly the maximum individual volume, provided a better design method than q, considering the stability of the seawall and the safety of vehicles and people along the coastal area protected by the coastal defense structures. Shanghai, located on the west bank of the Pacific Ocean, is quite sensitive to the risk of storm surges and violent wave overtopping. The crown-wall serves as an engineering measure to reduce the wave overtopping effectively.

Wave overtopping discharges at coastal structures are well described in the EurOtop Manual (2007), including the distribution of overtopping wave volumes. Each volume that overtops a dike or levee will have a certain flow velocity and depth record in time, often given by the maximum velocity and flow depth. This paper describes some further development of the theory on flow depth and velocities on the crest, but will also show an inconsistency with respect to the mass balance. The second part of the paper gives an analysis of measured values on real dikes, simulated by the Wave Overtopping Simulator. It gives also the method of "cumulative hydraulic load" to compare overtopping discharges for different wave conditions. A large wave height with less overtopping waves, but larger overtopping wave volumes, is more damaging than a small wave height with more, but smaller overtopping volumes, even if the overtopping discharge is similar. The reasons to develop the cumulative hydraulic load have been compared with the recently in the US developed method of erosional equivalence.

Design criteria for coastal defenses exposed to wave overtopping are usually restricted to the assessment of mean discharges and maximum individual overtopping volumes, however it is not possible to give unambiguous or precise limits to tolerable overtopping for all kind of layouts (EurOtop, 2018). A few studies (e.g. Endoh and Takahashi, 1994) analyzed the relationship between wave overtopping flows and hazard levels for people at the crest of sea dikes. Sandoval (2016) confirmed that one single value of admissible mean discharge or individual overtopping volume is not a sufficient indicator of the hazard, but detailed characterization of flow velocities and depths is required. This work presents the results of an experimental campaign aiming at characterizing the flow characteristics associated to maximum individual overtopping volumes for an urbanized stretch of a town along the Catalan coast, where a bike path and a railway run along the coastline, exposed to significant overtopping events every stormy season.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/DwVl9wFJoq0

Design criteria for coastal defenses exposed to wave overtopping are usually assessed by mean overtopping discharges and maximum individual overtopping volumes. However, it is often difficult to give clear and precise limits of tolerable overtopping for all kinds of layouts. A few studies analyzed the relationship between wave overtopping flows and hazard levels for people on sea dikes, confirming that one single value of admissible mean discharge or individual overtopping volume is not a sufficient indicator of the hazard, but detailed characterization of flow velocities and depths is required. This work presents the results of an experimental campaign aiming at analyzing the validity of the safety limits and design criteria for overtopping discharge applied to an urbanized stretch of the Catalan coast, exposed to significant overtopping events every stormy season. The work compares different safety criteria for pedestrians. The results prove that the safety of pedestrians on a sea dike can be still guaranteed, even for overtopping volumes larger than 1,000 L/m. Sea storms characterized by deep-water wave height between 3.6 and 4.5 m lead to overtopping flow depth values larger than 1 m and flow velocities up to 20 m/s. However, pedestrian hazard is proved to be linked to the combination of overtopping flow velocity and flow depth rather than to single maximum values of one of these parameters. The use of stability curves to assess people’s stability under overtopping waves is therefore advised.

Landslide-generated impulse waves in dammed reservoirs run up the reservoir banks as well as the upstream dam slope. If large enough, the waves may overtop and even breach the dam and cause flooding of the downstream area with hazardous consequences. Hence, for reservoirs in landslide-prone areas, it is important to provide a means to estimate the potential size of an event triggered by landslides along the reservoir banks. This research deals with landslide-generated waves and the overtopping process over the dam crest in a three-dimensional (3D) physical model test, presenting a case study. The model set-up describes the landslide impacting the reservoir in a perpendicular manner, which is often the case in natural settings. Based on the experimental results, dimensionless empirical relations are derived between the overtopping volume and the governing parameters, namely the slide volume, slide release height, slide impact velocity, still-water depth, and upstream dam face slope. Predictive relations for the overtopping volume are presented as applicable for cases relating to the specific model set-up. Measured overtopping volumes are further compared to a two-dimensional (2D) case reported in the literature. An important feature regarding the overtopping process for the 3D case is the variation in time and space, resulting in an uneven distribution of the volume of water overtopping the dam crest. This observation is made possible by the 3D model set-up, and is of value for dam safety considerations as well as for foundation-related issues, including erosion and scouring.

Early establishment of competing vegetation often presents an obstacle to the success of planted white spruce (Picea glauca (Moench) Voss) seedlings. We followed growth and development of white spruce and associated vegetation for up to 17 years in Alaska’s boreal forests to quantify roles of overtopping plant cover in suppressing conifers. The three study areas represented a range of site conditions of varying productivity and species of competing cover, different site preparation and release treatments, and different bare-root and container white spruce stock types. Herbaceous overtopping peaked early after planting and decreased as white spruce were able to outgrow competitors. Overtopping by shrubs and hardwoods, especially aspen (Populus tremuloides Michx.) and resin birch (Betula neoalaskana Sarg.) peaked somewhat later than herbaceous overtopping and decreased over time for most sites and treatments. In a model that combined all sites, vegetation management treatments, and years, overtopping and previous year’s volume explained approximately 85% of the variation in volume growth. Increasing the size of planting stock helped reduce overtopping, hence suppression, even in treatments dominated by hardwood species. Results suggested that control of overtopping was essential for maximum growth and long-term or increasing levels of overtopping severely suppressed white spruce seedling growth.

Run-up on a truncated impermeable beach is analysed theoretically and experimentally to find the volume of fluid, associated with a single wave event, that flows over the end of the beach. The theoretical calculations investigate the motion using the shallow-water equations and the fluid is allowed to flow freely over the end of the beach. Two models of wave events are considered: dam-break initial conditions, in which fluid collapses from rest to run-up and overtop the beach, and a waveform that models swash associated with the collapse of a long solitary bore. The calculations are made using quasi-analytical techniques, following the hodograph transformation of the governing equations. They yield predictions for the volume of fluid per unit width that overtops the beach, primarily as a function of the dimensionless length of the beach. These predictions are often far in excess of previous theoretical calculations. New experimental results are also reported in which the overtopping volumes due to flows initiated from dam-break conditions are studied for a range of reservoir lengths and heights and for a range of lengths and inclinations of the beach. Without the need for any empirically fitted parameters, good agreement is found between the experimental measurements and the theoretical predictions in regimes for which the effects of drag are negligible.

Impulse waves generated by landslides falling into reservoirs may lead to overtopping of a dam and, in turn, to flooding of the downstream area. In the case of an embankment dam, the overtopping may lead to erosion of the downstream slope, ultimately resulting in breaching and complete failure with consequent further hazardous release of water to the downstream area. This research deals with the overtopping process of a dam due to landslide generated waves in a three-dimensional (3D) physical scale model setup. Experiments have been conducted with varying the slide, reservoir, and dam parameters. The primary focus is on investigating the feasibility of employing the steady state weir equation in order to predict the overtopping discharge over a dam crest due to landslide generated waves. Calibration and validation of the coefficient of discharge values for the different dam section are conducted for the specified model setup. Accordingly, a two-step calculation procedure is presented for predicting the overtopping discharge based on the maximum overtopping depth values. Hence, for the fixed setup, which includes a constant slope angle of the landslide surface, a predictive equation for maximum overtopping depth is proposed, based on slide volume, slide release height, still water depth, upstream dam slope angle, and dam height. The relative slide volume and relative still water depth both seem to have a significant effect on the relative overtopping depth.

The overtopping of solitary waves and bores present major hazards during the initial phase of tsunami inundation and storm surges. This paper presents new laboratory data on overtopping events by both solitary waves and solitary bores. Existing empirical overtopping scaling laws are found to be deficient for these wave forms. Two distinct scaling regimes are instead identified. For solitary waves, the overtopping rates scale linearly with the deficit in run-up freeboard. The volume flux in the incident solitary wave is also an important parameter, and a weak dependence on the nonlinearity of the waves ( H / d ) is observed. For solitary bores, the overtopping cannot be scaled uniquely, because the fluid momentum behind the incident bore front is independent of the bore height, but it is in close agreement with recent solutions of the nonlinear shallow water equations. The maximum overtopping rate for the solitary waves is shown to be the lower bound of the overtopping rate for the solitary bores with the same deficit in freeboard. Thus, for a given run-up, the solitary bores induce greater overtopping rates than the solitary waves when the relative freeboard is small.

[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

O princípio operacional do dispositivo de galgamento consiste de uma estrutura que utiliza uma rampa para direcionar as ondas incidentes para o reservatório. A água armazenada retorna para o oceano após a passagem por uma turbina que está acoplada a um gerador de energia elétrica. O presente trabalho propõe dois estudos numéricos a respeito de um conversor de energia das ondas do mar do tipo galgamento. Para ambos os casos, o objetivo do estudo é a aplicação do método Design Construtal na definição da melhor forma para a rampa de modo a maximizar a massa de água que entra no reservatório, conduzindo a uma maior geração de energia elétrica. O grau de liberdade b/B, isto é, a razão entre a base superior e a base inferior da rampa trapezoidal, foi otimizado, mantendo-se fixos a área total do tanque de ondas, a área da rampa e as características da onda. Para a análise numérica do princípio de funcionamento deste dispositivo foi empregado um domínio computacional tridimensional (3D), gerado através do software GAMBIT, onde o conversor é acoplado a um tanque de ondas regulares. A solução das equações de conservação e a equação do transporte da fração volumétrica foi realizada com o código comercial de Dinâmica dos Fluidos Computacional FLUENT, que é baseado no Método de Volumes Finitos (MVF). Aplica-se o modelo multifásico Volume of Fluid (VOF) no tratamento da interação água-ar. Para o primeiro estudo, as características da onda regular empregada estavam em escala de laboratório. Os resultados mostraram que houve uma razão ótima (b/B)o = 0.43, que maximiza a quantidade de água que entra no reservatório para o caso estudado. Para ambos os casos, a razão ótima foi encontrada para o extremo inferior do grau de liberdade, além dos resultados apontarem um aumento significativo na massa admitida no reservatório e, por consequente, um maior aproveitamento das ondas incidentes.
The operational principle of an overtopping device consists of a structure which utilizes a ramp to direct incident waves to the reservoir. The stored water returns to the ocean after passing through a turbine that is coupled to an electric generator. This work proposes two numerical studies of a WEC of sea waves of the type overtopping. In both cases, the objective of the study is the application of Constructal Design method to define the best geometry of the ramp which maximizes the mass of water entering the reservoir, leading to increase the generation of electricity. The degree of freedom b/B, that is, the ratio between the upper base and the lower base of the trapezoidal ramp, has been optimized, keeping fixed the total area of the wave tank, the area of the ramp and the wave characteristics. For the numerical analysis of the working principle of this device it was used a three-dimensional computational domain (3D) generated by GAMBIT software where the device is inserted to a tank of regular waves. The solution of conservation equations and equation of transport of the volumetric fraction was carried out with the Commercial Code of Computational Fluid Dynamics FLUENT, which is based on Finite Volume Method (FVM). It was applied the multiphase model Volume of Fluid (VOF) in the treatment of the interaction water-air. For the first study, the characteristics of the employed regular wave were on a laboratory scale. The results showed that there were an optimal ratio (b/B)o = 0.43, which maximizes the amount of water entering the reservoir for the case study. For the second study, the characteristics of the regular wave were employed at actual scale and the results showed that there was an optimum ratio (b/B)o = 0.38, which maximizes the amount of water entering the reservoir for the case study. In both cases, the optimum ratio is found for the extreme lower of freedom of degree and the results showed a significant increase in the mass allowed in the reservoir and, consequently, larger use of the incident waves.

Wave run-up and overtopping of coastal structures are simulated using Lagrangian Blocks on Eulerian Mesh (LBEM). In the LBEM simulations, the blocks carry the mass and momentum. The movement of the blocks is calculated in a Lagrangian reference frame. The water depth defined by the volume blocks is non-negative. The wave fronts across the wet-and-dry interface are simulated by the block method without interruption by the oscillation problem that has limited the applicability of many existing computational methods. To evaluate the accuracy of the LBEM method in this paper, simulations are carried out for (i) the dam-break waves, (ii) the wave run-up on plane beach, and (iii) the overtopping of solitary waves over levee. The simulations of the dam-break wave have produced excellent agreement with the exact solutions by Ritter [1] and Stoker [2], and the semi-analytical solution by Sakkas and Strelkoff [3,4]. The simulations of the wave run-up on plane beach agree with the experimental data and the nonlinear theory of Synolakis [5]. The simulations of wave overtopping trapezoidal dike agree with the finite-volume simulations of Stansby [6]. The results have demonstrated the accuracy of the LBEM method and the versatility of the method for general wave simulations over variable terrain.

The effect of bow flare angle on greenwater overtopping is numerically investigated using CFD with a VOF surface capturing scheme. A two dimensional fixed rectangular box with a flare angle is adopted to represent a Floating, Production, Storage and Offloading Unit (FPSO) with flare. Deep water conditions are assumed. The incident waves are focused wave groups based on the New Wave formulation, which represents the most probable free surface elevation around a large crest and includes much of the spectral properties of the underlying random sea state. Bow flare angles of 10, 30 and 50 degrees are analysed, which cover the typical range of a FPSO unit. For the box model, the length L, draft D and freeboard f are modelled as L/D = 15 and f/D = 0.25, which are typical dimensions for a FPSO. A range of wave steepness and relative length are considered, which lead to a variety of overtopping conditions including the hammer fist (HF), plunging plus dam break (PDB) and dam break (DB) greenwater events observed for vessels with no bow flare angle. The numerical simulations are performed using the open source CFD toolbox OpenFOAM of version 2.4.0 together with a fully nonlinear wave generation and absorption utility waves2Foam. The effect of the bow flare angle is quantified by analyzing changes in freeboard exceedance, overtopping volume and horizontal momentum flux of water on deck flow for different bow flare angles. The results indicate that, for the special case in which the vessel is fixed, the bow flare angle can significantly reduce each of these quantities. It is also shown that trends in the overtopping volume and momentum flux can be explained reasonably well using the modified dam break model proposed by Zhang et al. [14].

Large-scale hydraulic model tests and detail numerical model investigations were conducted on recurved wave deflecting structures to aid in the design of wave overtopping mitigation for vertical walls in shallow water. The incident wave and storm surge conditions were characteristic return period events for an offshore island on the North Slope of Alaska. During large storm events, despite depth-limited wave heights, a proposed vertical wall extension was susceptible to wave overtopping, which could potentially cause damage to equipment. Numeric calculations were conducted prior to the experimental tests and were used to establish the relative effectiveness of several recurved parapet concepts. The numerical simulations utilized the COrnell BReaking waves and Structures (COBRAS) fluid modeling program, which is a Volume-of-Fluid (VOF) model based on Reynolds Averaged Navier-Stokes equations [1] [2]. The experimental testing was conducted in the Large Wave Flume (LWF) at Oregon State University, O.H. Hinsdale Wave Research Laboratory. The experimental test directly measured the base shear force, vertical force, and overturning moment applied to the recurved parapets due to wave forcing. Wave impact pressure on the parapet and water particle velocities seaward of the wall were also measured. Results from the experimental testing include probability of exceedance curves for the base shear force, vertical force, and overturning moment for each storm condition. Qualitative comparisons between the experimental tests and the COBRAS simulations show that the numerical model provides realistic flow on and over the parapet.

This paper presents the initial investigations into the ‘Inverse’ concept for wave energy conversion, based on the maximisation of motions and green water. The ‘Inverse’ concept combines aspects of ‘overtopping’, ‘heaving’ and ‘pitching’ wave energy conversion concepts, but also adds specific aspects such as the use of green water. Instead of reducing the motions and green water as is done in normal offshore hydrodynamics, the ‘Inverse’ concepts tries to maximise the motions and green water to generate energy from the waves. Results are presented of frequency domain calculations for the motion (de-) optimisation. Improved Volume Of Fluid (iVOF) simulations are used to simulate the green water flow on the deck. It is concluded that the potential of the ‘Inverse’ concept is clear. As a result of the double connotation of the word ‘green’, this renewable energy concept could also be called the ‘green water’ concept. Further work needs to be carried out on the further optimisation of the concept.

The contribution of wave energy to the renewable energy supply is rising. To extract a considerable amount of wave power, Wave Energy Converters (WECs) are arranged in several rows or in a ‘farm’. WECs in a farm are interacting (e.g. The presence of other WECs influence the operational behaviour of a single WEC) and the overall power absorption is affected. In this paper wake effects in the lee of a single WEC and multiple WECs of the overtopping type, where the water volume of overtopped waves is first captured in a basin above mean sea level and then drains back to the sea through hydro turbines, are studied in a time-dependent mild-slope equation model. The wake behind a single WEC is investigated for uni- and multi-directional incident waves. The wake becomes wider for larger wave peak periods. An increasing directional spreading results in a faster wave regeneration and a shorter wake behind the WEC. The wake in the lee of multiple WECs is calculated for two different farm lay-outs, i.e. an aligned grid and a staggered grid, with varying lateral and longitudinal spacing. In general, the staggered grid results in the highest overall wave power absorption.

Abstract In extreme weather permanently moored FPSOs may be overtopped by large amounts of greenwater, resulting in damage to deck structures and downtime. Thus, the preliminary design process for FPSOs has often included structural protection to mitigate loads from greenwater on deck and ensure structural integrity of top side structures at the bow in harsh sea conditions. This paper numerically investigates greenwater at the bow of an FPSO fitted with a ‘whaleback’ or ‘duck-bill’ shaped forecastle that is represented as an angled extension to the freeboard. In this study, the whaleback forecastle is intended to completely deflect the greenwater flow off the forecastle head. Previously validated numerical models based on OpenFOAM, an open source Computational Fluid Dynamics (CFD) package, are used. The (vertical) run-up height and the forces on the whaleback are analysed based on the CFD results to quantify the effectiveness of the design. It is found that the parameter tan β (FE/λp) that combines the coupled effect of the whaleback geometry and the incoming wave is important for determining the run-up height. The use of this parameter leads to a crude method for fast estimates of the effectiveness of such structures. Increase of the slope of the whaleback forecastle increases the run-up height, thus, increases the horizontal greenwater loading on such structure, however, the direct effect of the slope on the horizontal greenwater loading is found to be limited. An opposite trend is observed for the vertical greenwater loading in which the forecastle slope still plays a significant role even if the effect of run-up height is excluded, as a result of overtopping volume. Additionally, the vertical component of greenwater loading dominates the total greenwater loading on the whaleback forecastle.