Multiparticle collision framework for active polar fluids.

Area of Science:

• Soft Matter Physics
• Active Matter Simulations
• Mesoscale Hydrodynamics

Background:

• Dense active suspensions, common in biology, are modeled as active fluids with orientational symmetry.
• Existing mesoscale simulations focus on active nematic fluids, while polar fluids lack comparable methods.
• Simulating polar fluids requires mesoscale approaches for complex geometries and as suspension solvents.

Purpose of the Study:

• To develop a mesoscale numerical approach for simulating polar active fluids.
• To adapt the multiparticle collision dynamics (MPCD) framework for active polar systems.
• To investigate the behavior of active polar fluids under various conditions.

Main Methods:

• Applied the coarse-graining multiparticle collision dynamics (MPCD) framework.
• Developed three active-polar MPCD (AP-MPCD) variants based on the Vicsek model.
• Incorporated Andersen and Langevin thermostats for particle speed relaxation.

Main Results:

• Each AP-MPCD variant demonstrated a flocking transition at critical activity.
• Observed banding phenomena near the flocking transition point.
• Explored flocking under external fields (destroying banding) and anisotropic obstacles (biasing direction).

Conclusions:

• The AP-MPCD method effectively captures known polar active suspension phenomenology.
• Demonstrated the versatility of AP-MPCD for studying active polar fluids in complex scenarios.
• Provides a valuable tool for simulating active polar fluids in biological and soft matter systems.