Research On Physically Based Fluid Animation Modeling

Fluids are an essential substance in our daily life and have attracted the attention of many researchers. Recent developments in computer graphics has enabled physically based computer animation understanding to be applied to the production of simulations, films, animations and games. Physics makes more realistic. However, the complexity of the physical computation often leads to serious performance degradation, so it is necessary to investigate on the physically based techniques. This thesis aims to solve the problem by seeking for a trade off between the realistic effects and real time performance, to meet the needs from various applications.This thesis focuses on low speed incompressible flow modeling, including, Navier-Stockes and Lattice Boltzmann simulations, animation of free surface, modeling large scale fluids, non-Newton fluid and etc. In the process of theory researching and algorithm practicing, based on contents to be researched and problems to be resolved, some creative algorithms and methods have been proposed. In detail, the highlighted ideas and main contributions of this thesis are described as follows:A free surface simulation method based on macroscopic control equations is proposed in conclusion of comprehensive comparison about VOF, SPH, and Level Set. In this paper, we present an efficient semi-Lagrangian based improved Level Set. method for the accurate capturing of interfaces. This method retains the robust topological properties of the Level Set. method without the adverse effects of numerical dissipation .The simulation algorithm based on the lattice Boltzmann method is proposed. This method has been chosen due to the overall computational efficiency of the basic lattice Boltzmann algorithm, and its ability to deal with complex geometries and topologies. The basic algorithm is extended to compute the motion of free surfaces in three dimensions while conserving the overall mass. Adaptive time steps and grids, in combination with a turbulence model, allow stable and efficient simulations of detailed fluids. In combination with boundary conditions for moving and deforming objects, an approach to perform this fluid control, without disturbing the natural fluid behavior is also proposed. The algorithm represents a flexible basis for free surface simulations. The hybrid 2D/3D simulation algorithm of large open water surfaces is proposed. Shallow water simulations can be performed using the LBM. Instead of considering the fluid pressure, a height value is computed for each cell, both the streaming step and relaxation towards the equilibrium are still valid. An explanation of how to perform such simulations using a combination of two-dimensional and three-dimensional techniques is given, in combination with a particle based drop model.This thesis describes a technique for animating the behavior of non-Newton fluid, which exhibit a materials combination of both fluid and solid characteristics. The algorithm builds upon prior Eulerian methods for animating incompressible fluids with free surfaces by including additional elastic terms in the basic Navier-Stokes equations. The elastic terms are computed by integrating and advecting strain-rate throughout the fluid. As evidenced by their widespread use, these methods can efficiently produce results that are realistic enough for applications in the demanding visual effects industry.This thesis present a discrete particle based method capable of creating very realistic animations of bubbles in fluids. It allows for the generation of bubbles from gas dissolved in the fluid, the motion of the discrete bubbles including bubble collisions and drag interactions with the liquid which could be undergoing complex free surface motion, the formation and motion of coupled foams and the final dissipation of bubbles. This allows comprehensive simulations of dynamic bubble behavior. This model contains significant bubble scale physics and allows, in principle, the capturing of many important processes that cannot be directly modeled by traditional methods.Based on the research work of this thesis, some practices from theory to application are implemented for low speed incompressible flow modeling, which promote the combination between computational fluid dynamics and computer graphics, and build solid ground for other relevant theories and applications.