Impact of three-dimensional standing waves on a flat horizontal plate

International audienceA set-up is designed in order to study the wave impact on structures. These structures can be the stern part of cruiser, a fixed structure as a pier or the roof of LNG-tank. The traveling waves impact was already studied by Smith et al. (1998) but it seems difficult to elaborate a model except some empirical formulæ linking the drop height, the wavelength and the wave steepness. Barrholm (2001) as well studied the travelling wave impact underneath decks of platforms. His modelling is based on a two-dimensional Wagner model where the determination of the wetted surface is not a simple task. Here a simplified impact phenomenon is investigated since standing waves are generated

Impact of inflated structures on a liquid free surface.

International audienceThere are many situations where inflated structures may hit violently a liquid free surface. One of them occurs during sea-landing of helicopters. As a matter of fact helicopters are equipped with inflated floaters. Those floaters are made of impermeable tissues which are almost inextensible and their flexural rigidity is small. These mechanical characteristics are difficult to reproduce at model scales, that is why we found more conventional inflated balloons like space hopper. Experiments have been carried out in the flume of Ecole Centrale Marseille. Only qualitative measurements have been performed. High speed camera provided the main features of the phenomenona. This abtract sums up this experimental campaign and the first attempts done in the numerical modellings thus yielding some comparisons. It is shown that simple linearized models- both structural and hydrodynamic models - can reproduce the early stage of penetration when impact occurs

Un modèle de Wagner généralisé: Application à l’impact de sections de formes arbitraires

International audienceA generalized Wagner method for studying water impact of arbitrary section is presented. This method does not require the deadrise angle to be small, unlike the classical linearized Wagner model. It can be applied to asymmetric sections by using conformal mapping. The problem is systematically transformed into an horizontal flat plate problem but it takes into account the exact geometry of the wetting surface. The flow around the flat plate is then calculated by using the theory of Riemann-Hilbert problems. The model is tested against both numerical and experimental results.Une méthode de Wagner généralisée pour l’étude de l’impact de sections de forme arbitraire est présentée. Cette méthode permet de s’affranchir de l’hypothèse de faible angle mort sur laquelle reposent classiquement les méthodes de Wagner linéarisées. Son domaine d’application s’étend à des formes asymétriques. Cela est rendu possible par la transformation systématique du problème en celui d’un écoulement autour d’une plaque plane horizontale, tout en tenant compte de la géométrie exacte de la surface mouillée. La théorie des problèmes de Riemann-Hilbert est utilisée pour résoudre le problème transformé. Les résultats de ce modèle sont comparés à d’autres résultats numériques et expérimentaux

Generalized Wagner model for 2D symmetric and elastic bodies.

International audienceWe propose an algorithm to solve the generalized Wagner problem for two dimensional symmetric and elastic bodies

Generation of focalized wave packet.

International audienceThe generation of focalized wave packets is studied both experimentally and numerically. The exper- imental campaign is carried out in the wave flume of Ecole Centrale Marseille. The purpose is to experimentally generate the focalisation of wave close to a vertical wall thus yielding a database for numerical tools. Two numerical approaches are investigated. The theoretical framework is potential theory. On one hand Boussinesq equations are solved. Boussinesq model is suitable to propagate adequately a wave packet by accounting for most nonlinearities of the gravity wave. From that model, initial conditions are extracted and introduced in a fully nonlinear wave model. The present abstract shows some results illustrating the techniques developed and their validations. Difficulties to reproduce numerically the fine details of the measured overturning crest at the vertical wall are discussed

Contribution a l'etude des non-linearites de surface libre : deux cas d'applications : clapotis dans un bassin rectangulaire, diffraction du second ordre sur un groupe de cylindres verticaux

SIGLECNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Some aspects of the pressure field preceding the onset of critical jets in a breaking wave

We consider in this article two-dimensional nonlinear free surface motions in potential theory. There are situations where the onset of critical jet along a free surface can be predicted by analyzing the temporal and spatial variation of the pressure itself and its successive derivatives. In particular, when a local maximum of pressure appears close enough to a free surface where the pressure vanishes, it is expected a great pressure gradient at the free surface and consequently a large Lagrangian acceleration. The present analysis examines this phenomenon. This analysis is facilitated after identifying a line along which the pressure gradient is parallel to one of the eigenvectors of the Hessian matrix of the pressure. In a standard overturning crest, this line connects the tip of the crest to the bottom of the tank in which the flow is simulated. The analysis of its time evolution gives much information into the onset of critical jets. Other types of critical jet can also appear when a region of positive Gaussian curvature of the pressure suddenly grows in the vicinity of the free surface