Collision of multi-particle and general shape objects in a viscous fluid

The dynamics of particle-particle collisions in a viscous fluid are numerically investigated. A distributed-Lagrange-multiplier-based computational method in a solid-fluid system is developed and a collision strategy for general shape objects is presented. In earlier methods, a repulsive force is applied to the particles when their separation is less than a critical value and, depending on the magnitude of this repulsive force, collision may not be prevented or particles may bounce unrealistically. In the present method, upon collision of two or more particles, a uniformly distributed force is added to each particle. The contact force is calculated and the relative velocity of the particles along their line of center vanishes. For non-spherical (or non-cylindrical in 2-D) particles the force due to collision may lead to a torque around the center of mass of each particle. In this situation, the uniform distributed force is modified in order to create a net torque around the center of mass of each particle without changing the net force applied to that particle. The contact force is impulsive at the onset of the collision process and decreases smoothly to zero when contact ends. Particles separate from each other when the contact force vanishes and subsequently, a rigidity constraint is satisfied for each particle separately. Results for systems of multi-particle and general shape objects in a viscous fluid are presented.