**Dense colloids and flow through
porous structures**

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Herrmann, H^{1}

^{1} ETH
Zürich, Switzerland

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I will present simulations of particles dragged by a Non-Newtonian fluid through a porous structure. A generalization of Darcy’s law is possible. The filtering efficiency will be discussed. Three dimensional numerical simulations of model clay consisting of aluminium oxide spheres interacting via DLVO potentials yield viscosity, pair correlation and cluster structure. We find shear thinning in quantitative agreement with experiment. Considering only the hydrodynamic interactions between the particles we produce time series of up to 10**10 time steps under shear and obtain distributions for the velocity components over six orders of magnitude. These compare very well with a simple mean-field theory and show a Gaussian behaviour for small velocities and an exponential tail for large velocities. We can scale them in concentration, viscosity and shear rate and also study the effect of gravity. We also studied the collapse of a fragile granular suspension due to the penetration of an object and the subsequent difficulty in pulling this object out again. This has direct application to quicksand.