ere, the normal MPC particles are replaced by dumbbells with harmonic or finite-extensible nonlinear elastic (FENE) springs. We have studied the properties of FENE-dumbbell fluids under simple shear flow. Shear-thinning behavior is found for shear rates larger than the inverse characteristic dumbbell relaxation time. We have applied this approach to the flow behavior of a colloid in a shear-thinning viscoelastic fluid.
(Y.-G. Tao, S. Ji, I.O. Goetze, R. Jiang, R.G. Winkler, G. Gompper)
Importance of Angular Momentum Conservation in Mesoscale Hydrodynamics Simulations
Angular momentum is conserved in fluids -- with a few exceptions such as ferrofluids in an external field. However, it can be violated locally in fluid simulations to reduce computational costs. We have developed a version of multiparticle collision dynamics (MPC), a particle- based simulation method, in which angular-momentum conservation can be switched on or off. To investigate the effects of angular-momentum violation, we have studied circular Couette flows between concentric and eccentric cylinders. Non-physical torques due to the lack of the angular-momentum conservation are found, whereas the velocity field is not affected. In addition, in simulations of fluids with different viscosities in contact, incorrect angular velocities are shown to occur. These results quantitatively agree with the theoretical predictions based on the macroscopic stress tensor, which contains an antisymmetric contribution in the absence of angular momentum conservation.
(I.O. Goetze, H. Noguchi, and G. Gompper)
Multiparticle collision dynamics (MPC)
The dynamics of complex fluids is often governed by the hydrodynamic behavior of the solvent. Due to a large separation of length and time scales between the atomic scale of the solvent molecules and the mesoscopic scale of the solute, direct simulation approaches with atomistic solvent are prohibitively costly in computer time. This has stimulated the development of several mesoscale simulation techniques in recent years.
MPC is a particle-based mesoscale simulation technique. The fluid is modeled by N point particles. Positions and velocities evolve in discrete increments of time. The algorithm consists of two steps. In the streaming step the particles move ballistically. In the collision step, the particles are sorted into collision boxes, and the velocities relative to the centre of mass motion perform a random rotation.
( M. Ripoll R. G. Winkler , G. Gompper )