David Le Touzé

SPH modeling of shallow-water coastal flows

In the present paper, a Smoothed Particle Hydrodynamics (SPH) modeling of the shallow water equations is presented. The objective of this modeling is to perform flooding simulations involving complex bathymetries of sea bottom and dry land. The formulation is first detailed. Its implementation is then described, including specific procedures making possible to follow the expansion of the fluid domain during flooding simulations. An anisotropic kernel with variable smoothing length is especially used, as well as a periodic redistribution of the particles.A number of validation tests are performed. The model results are first checked on the case of a dam break on a flat dry bottom in one and two dimensions. Then more complex two-dimensional cases are simulated and compared to other models and experiments, e.g. a dam break flooding a slope of complex shape, and a solitary wave running up an island.

Analysis of free-surface flows through energy considerations: Single-phase versus two-phase modeling.

The study of energetic free-surface flows is challenging because of the large range of interface scales involved due to multiple fragmentations and reconnections of the air-water interface with the formation of drops and bubbles. Because of their complexity the investigation of such phenomena through numerical simulation largely increased during recent years. Actually, in the last decades different numerical models have been developed to study these flows, especially in the context of particle methods. In the latter a single-phase approximation is usually adopted to reduce the computational costs and the model complexity. While it is well known that the role of air largely affects the local flow evolution, it is still not clear whether this single-phase approximation is able to predict global flow features like the evolution of the global mechanical energy dissipation. The present work is dedicated to this topic through the study of a selected problem simulated with both single-phase and two-phase models. It is shown that, interestingly, even though flow evolutions are different, energy evolutions can be similar when including or not the presence of air. This is remarkable since, in the problem considered, with the two-phase model about half of the energy is lost in the air phase while in the one-phase model the energy is mainly dissipated by cavity collapses.

A Potential/RANSE Approach for Regular Water Wave Diffraction about 2-d Structures

Abstract A new formulation is proposed for the simulation of viscous flows around structures in waves. It consists in modifying the Reynolds-averaged Navier-Stokes equations: velocity, pressure or free-surface elevation fields are split into incident and diffracted fields to compute the diffracted flow only. The incident flow may be explicitly given by a stream function theory for non-linear regular waves, or by a spectral method for irregular waves. This method avoids classical problems (large CPU time, poor quality of generated wave) of numerical generation of waves in a viscous flow solver. The 2D flow around an immersed square in regular waves demonstrates the effectiveness of the method.