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Interactions between waves and new generations of brakewaters with small footprint

Abstract : Nowadays the respect of the environment is an obligation in maritime works. Vertical concrete caissons with porous plates are often the number one technical solution to enlarge existing ports and/or to improve the agitation of the basins. The footprint is reduced and the demand in quarry materials is less important compared to classical riprap breakwaters. Recently, alternative systems to vertical concrete caissons have been designed. Vertical riprap breakwaters are made of a metal framework enclosing blocks. This kind of structure offers environmental benefits, permeability for currents and a good hydrodynamic performance. This thesis work looks at developing a new 3D-BEM code that is easy to use and integrates porous media. Innovative geometries are tested like spaced gabions with damping chamber or a mix of porous plates and porous media.Describing flows in porous media is an complex issue. Volume averaging method is the common mathematical process used to model porous media flows without drawing every grain of a porous medium. The well-known extended Forchheimer equation describes the volumetric forces applied to the flow by a porous medium through resistance and inertial coefficients. These researches were the occasion to look into this coefficients, especially the one of poorly understood inertia in the case of a porous medium. It plays a major role in very low-KC flows currently occurring in porous breakwaters apart from armour layer.First, a literature review on porous media flows was undertaken. In parallel, the numerical code called Diffra3D was produced. It was then used to look for resistance coefficients of porous media through data coming from three experimental campaigns : one sloshing test on hexapode and two classical reflection-transmission studies in a wave tank. These campaigns were also the occasion to test and calibrate the code. New geometries of porous structures were then tested experimentally and numerically. Two new values of resistance coefficients of a porous medium are proposed. Some interesting features concerning the inertia coefficient CM of a porous medium are also developed. In simulations, we observe that the hydrodynamic behaviour of porous structures in low-KC flows is very sensitive to the coefficient of inertia. This research topic would still deserve further studies in order to find empirical law(s) for the inertia coefficient of a porous medium. The code Diffra3D performs well to model porous media flows. However, it is limited to waves with low steepness. The challenge is to properly characterise the porous medium. This research has shown that innovative porous structures like spaced gabions have proven their place as environmentally-friendly damping breakwaters. They may be commonly used in the future.
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Paul Milesi. Interactions between waves and new generations of brakewaters with small footprint. Fluids mechanics [physics.class-ph]. Ecole Centrale Marseille, 2019. English. ⟨NNT : 2019ECDM0003⟩. ⟨tel-02383932⟩

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