lily-pad
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weymouth
TwoPhase is unstable
Migrated from issue #10.
The attached LilyPad.pde has a circle moving up and down in a two phase flow. If QUICK advection is used, the flow is fine. If the semi-lagrangian advection is used, the flow blows up (infinite velocity near the air/water/body interface) at the end of the first cycle of motion. The semi-lagrangian is much better for interactivity (since the time step can be fixed to a large value), so this instability should be corrected.
The fact that switching advection scheme fixes the problem means this is unlikely to be related to the pressure solver.
Even without a body, and even using QUICK, the TwoPhase solver can become unstable if the waves are sufficiently large and energetic.