The motions of air, water, and smoke are typical natural phenomena, and examples of fluid motion that we come across in our daily lives. The modeling and simulation of fluid motion, however, is not a trivial task in scientific computing or computer animation. Research on animating fluid motion has a very long history, and such animations have many applications in the entertainment and advertising industries. This paper proposes a novel approach to controlling the density and motion of smoke, so that the synthetic appearance of the smoke resembles a still or moving object. The approach uses a combination of a compressible fluid model and level set method.

In the proposed method, the smoke’s density distribution is described by an implicit function that satisfies a certain differential equation, and the boundary of the smoke is described as a specific iso-surface of the density function. Given the boundary of the target object at each point in time, the task is to control the boundary of the smoke in relation to the boundary of the target object. Artificial feedback forces are applied at the smoke boundary to enable the smoke boundary to approach the target boundary. These forces are simulated by velocity adjustments and constraints. As a result of the applied forces, the smoke region evolves into a regular object, and follows the motion of the object, while maintaining its smoke appearance.

For readers who are interested in computer animation, especially in physics-based animation, this paper is definitely worth reading.