How to impose stick boundary conditions in coarse-grained hydrodynamics of Brownian colloids and semi-flexible fiber rheology

TL;DR

This paper compares two methods for imposing stick boundary conditions in coarse-grained hydrodynamics models of colloids and fibers, enhancing the accuracy of fluid-particle interaction simulations.

Contribution

It introduces and evaluates a collision rule method that exactly enforces stick boundary conditions, improving upon traditional force-based approaches.

Findings

The force coefficient method accurately reproduces friction and torque.

The collision rule method enforces exact stick boundary conditions.

Both methods are validated through numerical simulations.

Abstract

Long-range hydrodynamics between colloidal particles or fibers is modelled by the Fluid Particle Model. Two methods are considered to impose the fluid boundary conditions at colloidal surfaces. In the first method radial and transverse friction forces between particle and solvent are applied such that the correct friction and torque follows for moving or rotating particles. The force coefficients are calculated analytically and checked by numerical simulation. In the second method a collision rule is used between colloidal particle and solvent particle that imposes the stick boundary conditions exactly. The collision rule comprises a generalisation of the Lowe-Anderson thermostat to radial and transverse velocity differences.