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International audience; In recent years, there has been an increased interest in the possibility for tsunami radar remote sensing, owing tothe effects of tsunami-induced changes on the propagation of short sea waves. Well before microwave radars, HFradars have been investigated to detect tsunami induced- current effects on ocean surface waves (Barrick, 1979).Nonetheless no warning system has been proposed with a sufficiently short warning time, say between 5 and20min depending on the shelf width, which is more adapted to tsunami early warning system in coastal regions.Alternatively, the potential use of Ultra High Frequency (UHF) radar technology has been suggested based onrecent observations of modulation processes in radar echoes, which indicates the possibility for the short windwaves to be affected by the tsunami (Troïtskaya and Ermakov, 2005).In addition to current-induced effects on short gravity waves, like for instance current-induced Dopplershift in the apparent wave frequencies, it is well known that short waves modulations could also arise fromother mechanism interactions, such as wind-wave interactions and nonlinear wave-wave interactions. Thus theidentification and quantification of the interaction between short waves and current-induced tsunami is verychallenging, in particular for waves in the submetric range (high frequency).To achieve these tasks, we use a Higher Order Spectral (HOS) method to simulate numerically the nonlinearevolution of gravity waves in the presence of a time-varying current but spatially homogeneous. The HOSformulation of the prognostic equations has been modified to account for the presence of a time-varying current,whereas numerical time integration has been improved by using both an integrating factor method (unconditionallylinearly stable) and an embedded Runge-Kutta method with variable time steps. This paper presentsinitial numerical results obtained with our modified HOS model. To explore the signature of tsunami inducedcurrents on surface waves, we have used our modified HOS model to study different wave dynamics in thepresence of a time-varying current. In this paper, we present the results on wave dynamics obtained with realistictsunami-induced currents that were computed using the tsunami propagation code GEOWAVES.

International audience; In recent years, there has been an increased interest in the possibility for tsunami radar remote sensing, owing to the effects of tsunami-induced changes on the propagation of short sea waves. Well before microwave radars, HF radars have been investigated to detect tsunamis (Barrick, 1979). But so far there has been no system proposed with an appropriate alert real-time mode, the effort being stressed on wind wave and sea surface study. Alternatively, the potential use of Ultra High Frequency (UHF) radar technology has been suggested based on recent observations of modulation processes in radar echoes, which indicates the possibility for the short wind waves to be affected by the tsunami (Troïtskaya and Ermakov, 2005). In fact, when a tsunami reaches the continental shelf, the induced currents that are mostly depth-uniform greatly increases in speed (maybe up to 10-20 cm/s) and can induce significant Doppler shifts in ocean surface waves, particularly for those of smaller wavelength in the submetric ranges (high frequency). However, the identification and quantification of short-wave modulation processes in response to an incoming tsunami are very challenging. This is partly because some of these modulations can be related to wind-wave interactions, short-wave/short-wave interactions as well as long-wave /short-wave interactions. In order to investigate the short-wave modulation processes induced by an incoming tsunami, we propose here to use a numerical approach based on a high-order spectral (HOS) method to model fully nonlinear short gravity waves (down to metric length scales) in the presence of unsteady large-scale depth and current fields. Such current and depth fields can be obtained for selected case studies, e.g., from tsunami propagation modeling, using a standard long wave model. This paper presents initial results of this modeling study, in terms of Doppler shifts and wave shoaling/refraction caused by a slowly varying depth-uniform current. The numerical results are then compared with large-scale laboratory results from a wave-current interaction experiment, which has been performed in the FIRST basin (La Seyne, France).

Des simulations expérimentales de solitons se propageant et déferlant sur une plage, réalisées dans le canal à houle de l’ESIM à Marseille, sont présentées. Ces expériences de laboratoire feront l’objet d’un futur exercice de comparaisons pour des codes numériques, basés sur la résolution des équations de Navier-Stokes en formulation diphasique. Les laboratoires composant le groupe de travail, les différentes méthodes numériques, ainsi que les codes utilisés, sont exposés. L’objectif est d’aboutir à une description plus fine du phénomène du déferlement et à une meilleure compréhension des processus mis en jeu dans la zone d’impact. Ce travail est soutenu financièrement par le programme CNRS-PATOM.

2d and 3D calculation of surface wave breaking on a beach are performed with a semi lagrangian interface tracking method in a coupled BIEM/VOF solver. PIV experiments on waves are presented. Comparison are performed between experiment and numerical simulations.