Generalized drag force for particle-based simulations

Computing the forces acting from a surrounding air phase onto a particle-based fluid or rigid object is challenging. Simulating the air phase and modeling the interactions using a multiphase approach is computationally expensive. Furthermore, stability issues may arise in such multiphase simulations. In contrast, the effects from the air can be approximated efficiently by employing a drag equation. Here, for plausible effects, the parameterization is important but challenging. We present a drag force discretization based on the drag equation that acts on each particle separately. It is used to compute the effects of air onto particle-based fluids and rigid objects. Our presented approach calculates the exposed surface area and drag coefficient of each particle. For fluid particles, we approximate their deformation to improve the drag coefficient estimation. The resulting effects are validated by comparing them to the results of multiphase SPH simulations. We further show the practicality of our approach by combining it with different types of SPH fluid solvers and by simulating multiple, complex scenes.