Simon Schirm

Interaction of fluids with deformable solids

In this paper, we present a method for simulating the interaction of fluids with deformable solids. The method is designed for the use in interactive systems such as virtual surgery simulators where the real‐time interplay of liquids and surrounding tissue is important. In computer graphics, a variety of techniques have been proposed to model liquids and deformable objects at interactive rates. As important as the plausible animation of these substances is the fast and stable modeling of their interaction. The method we describe in this paper models the exchange of momentum between Lagrangian particle‐based fluid models and solids represented by polygonal meshes. To model the solid‐fluid interaction we use virtual boundary particles. They are placed on the surface of the solid objects according to Gaussian quadrature rules allowing the computation of smooth interaction potentials that yield stable simulations. We demonstrate our approach in an interactive simulation environment for fluids and deformable solids. Copyright

Real-time simulations of bubbles and foam within a shallow water framework

Bubbles and foam are important fluid phenomena on scales that we encounter in our lives every day. While different techniques to handle these effects were developed in the past years, they require a full 3D fluid solver with free surfaces and surface tension. We present a shallow water based particle model that is coupled with a smoothed particle hydrodynamics simulation to demonstrate that real-time simulations of bubble and foam effects are possible with high frame rates. A shallow water simulation is used to represent the overall water volume. It is coupled to a particle-based bubble simulation with a flow field of spherical vortices. This bubble simulation is interacting with a smoothed particle hydrodynamics simulation including surface tension to handle foam on the fluid surface. The realism and performance of our approach is demonstrated with several test cases that run with high frame rates on a standard PC.

Real-time Breaking Waves for Shallow Water Simulations

We present a new method for enhancing shallow water simulations by the effect of overturning waves. While full 3D fluid simulations can capture the process of wave breaking, this is beyond the capabilities of a pure height field model. 3D simulations, however, are still too expensive for real-time applications, especially when large bodies of water need to be simulated. The extension we propose overcomes this problem and makes it possible to simulate scenes such as waves near a beach, and surf riding characters in real-time. In a first step, steep wave fronts in the height field are detected and marked by line segments. These segments then spawn sheets of fluid represented by connected particles. When the sheets impinge on the water surface, they are absorbed and result in the creation of particles representing drops and foam. To enable interesting applications, we furthermore present a two-way coupling of rigid bodies with the fluid simulation. The capabilities and efficiency of the method will be demonstrated with several scenes, which run in real-time on todays commodity hardware.Animations of two avatars tangled with each other often appear in battle or fighting scenes in movies or games. However, creating such scenes is difficult due to the limitations of the tracking devices and the complex interactions of the avatars during such motions. In this paper, we propose a new method to generate animations of two persons tangled with each other based on individually captured motions. We use wrestling as an example. The inputs to the system are two individually captured motions and the topological relationship of the two avatars computed using Gauss Linking Integral (GLI). Then the system edits the captured motions so that they satisfy the given topological relationship. Using our method, it is possible to create / edit close-contact motions with minimum effort by the animators. The method can be used not only for wrestling, but also for any movement that requires the body to be tangled with others, such as holding a shoulder of an elderly to walk or a soldier piggy-backing another injured soldier.

Screen space meshes

We present a simple yet powerful approach for the generation and rendering of surfaces defined by the boundary of a three-dimensional point cloud. First, a depth map plus internal and external silhouettes of the surface are generated in screen space. These are used to construct a 2D screen space triangle mesh with a new technique that is derived from Marching Squares. The resulting mesh is transformed back to 3D world space for the computation of occlusions, reflections, refraction, and other shading effects. One of the main applications for screen space meshes is the visualization of Lagrangian, particle-based fluids models. Our new method has several advantages over the full 3D Marching Cubes approach. The algorithm only generates surface where it is visible, view-dependent level of detail comes for free, and interesting visual effects are possible by filtering in screen space.