Bottom Particles Segregation: Experiments and Numerical Simulations Using Non-linear Diffusion Equation

Tien Dat Chu (1) , François Marin (1) , Armelle Jarno-Druaux (1) , Djillali Tiguercha (2) , Anne-Claire Bennis (2) , Alexander B. Ezersky (2)

1 LOMC - Laboratoire Ondes et Milieux Complexes
2 M2C - Morphodynamique Continentale et Côtière

We report experimental and theoretical results on segregation of particles in sandy bottom under the action of oscillating velocity field due to surface waves. Experiments were performed in-situ and in wave flume. Segregation in the mixtures of light and heavy particles of the same diameter and small and large particles of the same density was observed. It was found that segregation appears on the background of sand ripples generation in the upper «active» zone of the bottom. The thickness of this zone is proportional to the amplitude of velocity oscillation. The topology of segregation patterns depends on particle size differences, on particle density differences as well as on particle percentage composition in the mixture. It was revealed that small particles with small percentage are concentrated below sandy ripples crest. If percentage composition of small and large particles are approximately equal, the large particles are concentrated below the ripples crests. Light particles quite the «active» zone where concentration of heavy particles increases. To investigate the segregation of particles we use non-linear diffusion equations in the presence of gravity field like it was done recently in paper of Fernandez et al (Physica A, 2003, 327, 94–98). The main idea of this model is to take into account the different sizes and densities of particles using mobility coefficients in diffusion equations for concentration of particles. We extended one dimensional model of Fernandez et al for two dimensional case. Numerical simulations demonstrate good qualitative coincidence with experimental data. In particular, zones with high concentration of small and large particles below ripples crest were obtained in numerical simulations depending on percentage composition of particles. Formation of the layer where the concentration of light particles sufficiently decreases was also found in numerical simulations. Importance of segregation processes for biological and environmental problems is discussed.

Mots clés: Segregation; sand ripples; surface wave; sea bottom; non-linear diffusion equation

Domaines: Mécanique des fluides [physics.class-ph]; Sciences de la Terre; Océanographie

Tien Dat Chu, François Marin, Armelle Jarno-Druaux, Djillali Tiguercha, Anne-Claire Bennis, et al.. Bottom Particles Segregation: Experiments and Numerical Simulations Using Non-linear Diffusion Equation. Chaotic Modeling and Simulation (CMSIM), 2015, 1, pp.85-93. ⟨hal-01534131⟩