Boundary Model In DPD

this paper we further exploit the idea of freezing DPD particles by presenting a generic model for treatment of the boundaries between solid objects and DPD particles. One would like to apply on the surface of the solid a no-slip boundary condition. This suggest to consider a layer of DPD particles that are stuck (or "frozen") onto the solid. By taking a continuum limit of this layer an effective force due to the solid onto the DPD fluid particles arises. The explicit form of this force will be derived for the case of a flat wall. A crucial ingredient of the model refers to the impermeability of the wall. The wall is a well defined mathematical plane such that whenever a particle crosses the wall it is reinjected into the fluid. Three different models are considered: specular, Maxwellian and bounce back reflections. Very different dynamical behaviour are obtained in each case, as can be observed from numerical simulations, although only the bounce-back is fully consistent with the description of the wall as an ensemble of frozen DPD particles moving as a rigid object. As we will point out later, this is a relevant aspect regarding the modelling of the boundaries carried out in DPD so far. 2. The DPD mode