A theoretical model is developed for wave heights and set-up in a surf zone. In the time averaged equations of energy and momentum the energy flux, radiation stress and energy dissipation are determined by simple approximations which include the surface roller in the breaker. Comparison with measurements shows good agreement. Also the transitions immediately after breaking are analysed and shown to be in accordance with the above mentioned ideas and results.

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Wave Heights and Set-up in a Surf Zone

https://hal.archives-ouvertes.fr/hal-00294092/document

Three-dimensional Large Eddy Simulation of air entrainment under plunging breaking waves

Scientists and engineers have observed for some time that tidal amplitudes at many locations are shifting considerably due to non-astronomical factors. Here we review comprehensively these important changes in tidal properties, many of which remain poorly understood. Over long geological time-scales, tectonic processes drive variations in basin size, depth, and shape, and hence the resonant properties of ocean basins. On shorter geological time-scales, changes in oceanic tidal properties are dominated by variations in water depth. A growing number of studies have identified widespread, sometimes regionally-coherent, positive and negative trends in tidal constituents and levels during the 19th, 20th and early 21st centuries. Determining the causes is challenging because a tide measured at a coastal gauge integrates the effects of local, regional, and oceanic changes. Here, we highlight six main factors that can cause changes in measured tidal statistics on local scales, and a further eight possible regional/global driving mechanisms. Since only a few studies have combined observations and models, or modelled at a temporal/spatial resolution capable of resolving both ultra-local and large-scale global changes, the individual contributions from local and regional mechanisms remain uncertain. Nonetheless, modelling studies project that sea-level rise and climate change will continue to alter tides over the next several centuries, with regionally coherent modes of change caused by alterations to coastal morphology and ice sheet extent. Hence, a better understanding of the causes and consequences of tidal variations is needed to help assess the implications for coastal defense, risk assessment, and ecological change.

The Tides They Are a-Changin’: A Comprehensive Review of Past and Future Nonastronomical Changes in Tides, their Driving Mechanisms and Future Implications

Gravity waves generated by a moving obstacle in a two-layer stratified fluid are investigated. The experimental configuration is three-dimensional with an axisymmetric obstacle which is towed in one of the two layers. The experimental method used in the present study is based on a stereoscopic technique allowing the 3D reconstruction of the interface between the two layers. Investigation into the wave pattern as a function of the Froude number, Fr, based on the relative density of the fluid layers and the velocity of the towed obstacle is presented. Specific attention is paid to the transcritical regime for which Fr is close to one. Potential energy trapped in the wave field patterns is also extracted from the experimental results and is analyzed as a function of both the Froude number, Fr, and the transcritical similarity parameter $$\varGamma$$
 . In particular, a remarkable increase in the potential energy around Fr = 1 is observed and a scaling allowing to assemble data resulting from different experimental parameters is proposed.

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Wave patterns generated by an axisymmetric obstacle in a two-layer flow

A variety of host-fabric elements (HE) cut by cross-cutting elements (CE) in rocks defines flanking structures (FS) on mesoscopic and microscopic scales. There has been renewed interest in studying and classifying the FS for their morphologies, useful as shear sense indicators and geneses. Existing non-genetic morphologic parameters for the FS are reviewed, and two new classification schemes are presented. One of these is based on the nature of the CE and whether HE penetrates it. The other scheme takes account of all the potential combinations of drag/no drag and slip/no slip of the HE. Deciphering the shear sense of the rock body from FS is complicated because the angular relationship between the CE and the primary shear planes might be opposite to what is found between S- and C- ductile shear fabrics. Further, single CEs can curve and several similar FS occur in reverse forms. As with mineral fish, the shape asymmetries of microscopic CEs indicate the shear sense. Conjugate FS (with non-parallel CEs) with interfering perturbation fields around the CEs are more reliable shear-sense indicators than FS with single CE. During low but increasing bulk strains, FS may evolve from one type to another, e.g. from a- to s-type. At high strain, FS can resemble intrafolial or sheath fold. Whether the drag is normal or reverse depends fundamentally on the initial angle between the HE and the CE and the relative magnitudes of throw and vertical separation.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0016756813001088

Review of flanking structures in meso- and micro-scales

Richards [1980] conjectured that megaripples of the continental shelf are due to a seabed instability in the presence of seabed ripples. Towards a better understanding of this megaripple formation process, we use a morphodynamical numerical model to investigate the bed roughness influence on the bed load?induced linear stability of a sandy bed. We find that the linearly most amplified mode shifts from a dune mode (grain roughness) towards a megaripple mode (large bed roughness). Then, we discuss how megaripples could be generated over a flat bed and over dunes.

/pdf/influence-of-bed-roughness-on-dune-and-megaripple-generation-5apz9190vr.pdf

Influence of bed roughness on dune and megaripple generation

Numerical Modeling And Experiments For SolitaryWave Shoaling And Breaking Over a Sloping Beach

A stereoscopic method for rapid monitoring of the spatio-temporal evolution of the sand-bed elevation in the swash zone

Linear and nonlinear behavior of large-scale underwater bedform patterns like sandbanks are studied using linear stability analysis and numerical modeling. The model is based on depth-integrated hydrodynamics equations with a quadratic bottom friction law and a bed load sediment transport model including a bottom slope effect. First, the linear stability analysis of a flat erodible bottom subject to a steady current is performed. The direction of the most amplified bedform is controlled by the current, whereas its wavelength is selected by the gravity driven sediment flow. The instability proved to be due to the velocity component parallel to the mean flow, whereas the transverse velocity and the bottom slope effect are damping processes. The growth rate is then related to the spatial phase-lag between flow velocity and bathymetry. In order to validate the numerical model in this linear regime, the growth rate and the phase celerity of an infinitesimal bottom perturbation are computed as a function of its wavevector. A good agreement with linear stability results is found. Second, using the property that the growth rates for block-function and steady current are the same, the nonlinear behavior of the instability is investigated for a simple tidal current. The saturation height of the theoretically most amplified mode is estimated using the numerical model. The analysis of the sediment fluxes gradients shows that the saturation is mostly due to the hydrodynamic processes, although the saturation height slightly depends on the value of the bottom slope effect coefficient. Third, a Landau equation, whose coefficients are computed from the previous results, is used to predict the temporal evolution of the bedform amplitude from the initial infinitesimal perturbation to the saturation. A comparison with the characteristics of continental shelf sandbanks shows that the model gives a reasonable estimation of the temporal dynamics of these large-scale bedforms. However, the saturation height seems to be slightly overestimated. The limitations of the method are also discussed.

/pdf/analytical-and-numerical-modeling-of-sandbanks-dynamics-3ansn0lfk6.pdf

Analytical and numerical modeling of sandbanks dynamics

This research deals with the validation of fluid dynamic models,used for simulating shoaling and breaking solitary waves on slopes,based on experiments performed at the Ecole Sup'erieure d'Ing'enieurs deMarseille's (ESIM) laboratory. A separate paper, also presented at thisconference, reports on experiments. In a first part of this work, a fullynonlinear potential flow model based on a Boundary Element Method(BEM) developed at the University of Rhode Island (URI), is used togenerate and propagate solitary waves over a slope, up to overturning,in a set-up closely reproducing the laboratory tank geometry andwavemaker system. The BEM model uses a boundary integral equationmethod for the solution of governing potential flow equations and anexplicit Lagrangian time stepping for time integration. In a secondpart, several Navier-Stokes (NS) models, developed respectively atTREFLE-ENSCPB, IMFT, IRPHE and LSEET are initialized based onthe BEM solution and used for modeling breaking solitary waves ina finely discretized region encompassing the top of the slope and thesurfzone. The NS models are based on the Volume of Fluid Method(VOF). This paper mostly deals with the first part, which includescalibration and comparison of BEM results with experiments, for thegeneration of solitary waves in the physical wave tank. Thus, parametersof the physical wave tank were numerically matched, including tankgeometry and motion of the wavemaker paddle corresponding to thegeneration of solitary waves. Use and coupling of the BEM and VOFmodels for the simulation of solitary wave breaking is discussed in the paper.

https://hal.archives-ouvertes.fr/hal-00084408/document

Dominique Astruc

Papers

Influence of bed roughness on dune and megaripple generation

Numerical Modeling And Experiments For SolitaryWave Shoaling And Breaking Over a Sloping Beach

A stereoscopic method for rapid monitoring of the spatio-temporal evolution of the sand-bed elevation in the swash zone

Analytical and numerical modeling of sandbanks dynamics

Numerical Modeling and Experiments for Solitary Wave Shoaling and Breaking over a Sloping Beach