Fluid Simulation Quality with Violated CFL Condition

Philipp Erler

Supervisor(s): Christian Hafner, Michael Wimmer

TU Wien

Abstract: Fluid simulation for movies and games is still an active field of research, although the fundamental Navier-Stokes equations have been known for almost 200 years. The required computational power is extremely high, even with many approximations. Also, the visual quality still has room for improvement. Our fluid simulation focuses on easy and fast exchange of algorithms. For example, we can switch semi-Lagrangian advection with the modified MacCormack's scheme, while the pressure projection is done with the finite element method in both variants. If the Courant-Friedrichs-Lewy (CFL) condition is met, the pressure projection can be accurate. However, this condition can be willingly violated, e.g. for performance reasons. In our simulation with strongly violated CFL condition, we investigate how mass conservation and visual quality change with different advection methods. Also, we show the influence of a higher grid resolution and shorter time steps. Our results show that the mass conservation is not perfect, neither with the semi-Lagrangian nor the modified MacCormack's scheme. Semi-Lagrangian advection conserves more mass in most cases. On the other hand, MacCormack's gives slightly better visual results. A shorter time step results in better fluid conservation. The visual quality can be increased by using a higher resolution and a shorter time step.
Keywords: Scientific Visualization
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Year: 2017