Hydrodynamic interactions for single dissipative-particle-dynamics particles and their clusters and filaments.

We have investigated low Reynolds number flow past single dissipative-particle-dynamics particles (point centers of repulsion), their clusters, and their filaments using dissipative-particle-dynamics (DPD) simulations. The objective of our study was to verify whether DPD particles immersed in a sea of DPD particles behave like Langevin particles suspended in a continuous Newtonian fluid solvent, the basis of Brownian dynamics. Our principal test is to compare two effective DPD radii calculated by independent means. From the calculated coefficients of self-diffusion and viscosity the Stokes-Einstein equation yields an intrinsic radius, and from simulations of flow past a single fixed DPD particle a second radius is calculated from Stokes law. In the limit of small Reynolds number the two radii were found to approach each other. Hydrodynamic interactions were studied with Stokes flow past two DPD particles, and single DPD particles in bounded uniform flow and in-plane Poiseuille flow. Additional simulations examined closely spaced multiparticle clusters (straight-chains and hexagonal-packed aggregates). For all cases of rigid bodies the simulation results are in good agreement with predictions derived analytically from the continuum Stokes system. Elastic filaments, DPD-particle chains with bending resistance, were also simulated to examine hydrodynamically induced distortions, and the results show that the model captures the correct hydrodynamic interactions among filament beads.