Visual Debugging of SPH Simulations

Smoothed particle hydrodynamics (SPH) is a popular mesh-free, particle-based fluid simulation approach for a wide range of applications. There are several numerical variants of SPH along with a variety of models for aspects such as boundary conditions, compressibility or incompressibility, and surface tension. Different combinations of these models lead to varying effects that occur during simulation, and their analysis is a critical challenge for fluid mechanics. In this paper, we address this challenge by presenting a visual debugging application for simulations, which allows users to evaluate the properties of the models and to detect possible computational errors. Our multi-view application uses a combination of interactive 3D visualization of the particles and non-spatial visualizations from the field of information visualization, namely scatter plots and parallel coordinates plots. Our visual debugging environment thus enables a quantitative analysis of the multidimensional simulation attributes, including internal and physical properties contributing to the simulation process. All views support brushing and linking, that is, selections of interesting value ranges in the plots are directly visible in the 3D view and, conversely, the selection of particles in the 3D view highlights the corresponding data points in the plots. Since typical SPH simulations come with large numbers of data points, we employ stochastic subsampling to reduce visual clutter in the non-spatial views and accelerate the rendering speed. We discuss four real-world use cases for visual debugging of fluid simulations that showcase how our visual debugging environment is instrumental for identify code errors and increases the understanding of the simulation models. We also show how the combination of coupled views can reveal internal details, thus serving to improve simulation results.