Melting and burning solids into liquids and gases

Lattice-Boltzmann and Eulerian Hybrid for Solid Burning Simulation

We propose a new hybrid simulation method to model burning solid interactions. Unlike gas fuel, fire and smoke interactions that have been relatively well studied in the past, simulations of solid fuel combustion processes remain largely unaddressed. These include pyrolysis/smoldering, interactions with oxygen and flow inside porous solid. To advance this simulation problem, we designed a new hybrid of the Lattice-Boltzmann method (LBM) and a Eulerian grid based Navier-Stokes equation (NSE). It uses the LBM, which has symmetrical directions of particle velocities in a cell, for inside the solid fuel and the NSE, which has a representative velocity in a cell, for outside the solid. At the interface where the two methods join, we develop a novel method to exchange physical quantities and show a natural transition between the two methods. Since LBM allows us to directly manage the quantity of exchanges from the microscopic perspective, that is, between lattice points, we can easily simulate the burning speed and the shape change of burning an inhomogeneous solid. Also, we derive an LBM version of the previously proposed porous Navier-Stokes equation to simulate gas flow inside the porous solid. In addition, we use the NS solver outside the solid where macroscopic behavior is much more dominant and, hence, LBM is less efficient than NS solver. Our results show us the physical stability and accuracy and visual realism.

Real-Time High-Fidelity Surface Flow Simulation

Surface flow phenomena, such as rain water flowing down a tree trunk and progressive water front in a shower room, are common in real life. However, compared with the 3D spatial fluid flow, these surface flow problems have been much less studied in the graphics community. To tackle this research gap, we present an efficient, robust and high-fidelity simulation approach based on the shallow-water equations. Specifically, the standard shallow-water flow model is extended to general triangle meshes with a feature-based bottom friction model, and a series of coherent mathematical formulations are derived to represent the full range of physical effects that are important for real-world surface flow phenomena. In addition, by achieving compatibility with existing 3D fluid simulators and by supporting physically realistic interactions with multiple fluids and solid surfaces, the new model is flexible and readily extensible for coupled phenomena. A wide range of simulation examples are presented to demonstrate the performance of the new approach.

Strain-based diffusion solver for realistic representation of diffusion front in physical reactions

When simulating fluids, such as water or fire, interacting with solids, it is a challenging problem to represent details of diffusion front in physical reaction. Previous approaches commonly use isotropic or anisotropic diffusion to model the transport of a quantity through a medium or long interface. We have identified unrealistic monotonous patterns with previous approaches and therefore, propose to extend these approaches by integrating the deformation of the material with the diffusion process. Specifically, stretching deformation represented by strain is incorporated in a divergence-constrained diffusion model. A novel diffusion model is introduced to increase the global rate at which the solid acquires relevant quantities, such as heat or saturation. This ensures that the equations describing fluid flow are linked to the change of solid geometry, and also satisfy the divergence-free condition. Experiments show that our method produces convincing results.

Fluid simulation with articulated bodies

We present an algorithm for creating realistic animations of characters that are swimming through fluids. Our approach combines dynamic simulation with data-driven kinematic motions (motion capture data) to produce realistic animation in a fluid. The interaction of the articulated body with the fluid is performed by incorporating joint constraints with rigid animation and by extending a solid/fluid coupling method to handle articulated chains. Our solver takes as input the current state of the simulation and calculates the angular and linear accelerations of the connected bodies needed to match a particular motion sequence for the articulated body. These accelerations are used to estimate the forces and torques that are then applied to each joint. Based on this approach, we demonstrate simulated swimming results for a variety of different strokes, including crawl, backstroke, breaststroke, and butterfly. The ability to have articulated bodies interact with fluids also allows us to generate simulations of simple water creatures that are driven by simple controllers.

Two-way coupled SPH and particle level set fluid simulation

Grid-based methods have difficulty resolving features on or below the scale of the underlying grid. Although adaptive methods (e.g. RLE, octrees) can alleviate this to some degree, separate techniques are still required for simulating small-scale phenomena such as spray and foam, especially since these more diffuse materials typically behave quite differently than their denser counterparts. In this paper, we propose a two-way coupled simulation framework that uses the particle level set method to efficiently model dense liquid volumes and a smoothed particle hydrodynamics (SPH) method to simulate diffuse regions such as sprays. Our novel SPH method allows us to simulate both dense and diffuse water volumes, fully incorporates the particles that are automatically generated by the particle level set method in under-resolved regions, and allows for two way mixing between dense SPH volumes and grid-based liquid representations.