Mass-conserving Eulerian liquid simulation

We present a GPU friendly, Eulerian, free surface fluid simulation method that conserves mass locally and globally without the use of Lagrangian components. Local mass conservation prevents small-scale details of the free surface from disappearing, a problem that plagues many previous approaches, while global mass conservation ensures that the total volume of the liquid does not decrease over time. Our method handles moving solid boundaries as well as cells that are partially filled with solids. Due to its stability, it allows the use of large time steps that makes it suitable for both offline and real-time applications. We achieve this by using density-based surface tracking with a novel, unconditionally stable, conservative advection scheme. We also propose mass conserving methods to sharpen the interface and to reveal subgrid features of the liquid. While our approach conserves mass, volume loss is still possible but only temporarily. With constant mass, local volume loss causes a local increase of the density used for surface tracking which we detect and correct over time. We show the effectiveness of the proposed methods in several practical examples all running either at interactive rates or in real time.