Simultaneous Coupling of Fluids and Deformable Bodies sketch 0566

We describe a method for simultaneous two-way coupling of fluid and deformable bodies. The interaction between a fluid and deformable body can create complex and interesting motion that would be difficult to convincingly animate by hand. Previous approaches used a time splitting procedure that alternately fixes the fluid pressure while simulating the solid, then fixes the solids velocity while simulating the fluid. While this approach works reasonably well for physical systems with non-stiff coupling, it can lead to instability and visual artifacts for other systems. These problems occur because while solid velocities are fixed they will ignore arbitrarily large fluid pressures, and the converse when the fluid velocities are fixed. For a tightly coupled system like a piston, time splitting becomes untenable and difficulties can still arise even for less tightly coupled systems. Time splitting also requires non-physical fixes for closed systems. By enforcing simultaneous coupling our method avoids these artifacts and allows for substantially larger time steps.