This paper describes a new animation technique for modeling the turbulent rotational motion that occurs when a hot gas interacts with solid objects and the surrounding medium. The method is especially useful for scenes involving swirling steam, rolling or billowing smoke, and gusting wind. It can also model gas motion due to fans and heat convection. The method combines specialized forms of the equations of motion of a hot gas with an efficient method for solving volumetric differential equations at low resolutions. Particular emphasis is given to issues of computational efficiency and ease-of-use of the method by an animator. We present the details of our model, together with examples illustrating its use.

Developing a visually convincing model of fire, smoke, and other gaseous phenomenais among the most difficult and attractive problems in computer graphics. We have created new methods of animating a wide range of gaseous phenomena, including the particularly subtle problem of modelling “wispy ” smoke and steam, using far fewer primitives than before. One significant innovation is the reformulation and solution of the advection-diffusion equation for densities composed of “warped blobs”. These blobs more accurately model the distortions that gases undergo when advected by wind fields. We also introduce a simple model for the flame of a fire and its spread. Lastly, we present an efficient formulation and implementation of global illumination in the presence of gases and fire. Our models are specifically designed to permit a significant degree of user control over the evolution of gaseous phenomena.

The realistic depiction of smoke, steam, mist and water reacting to a turbulent field such as wind is an attractive and challenging problem. Its solution requires interlocking models for turbulent fields, gaseous flow, and realistic illumination. We present a model for turbulent wind flow having a deterministic component to specify large-scale behaviour, and a stochastic component to model turbulent small-scale behaviour. The small-scale component is generated using space-time Fourier synthesis. Turbulent wind fields can be superposed interactively to create subtle behaviour. An advection-diffusion model is used to animate particle-based gaseous phenomena embedded in a wind field, and we derive an efficient physically-based illumination model for rendering the system. Because the number of particles can be quite large, we present a clustering algorithm for efficient animation and rendering. CR Categories and Subject Descriptors: I.3.7 [Com- puter Graphics]: Three-Dimensional Graphics...

Realistic rendering of participating media like clouds requires multiple anisotropic light scattering. This paper presents a propagation approximation for light scattered into M direction bins, which reduces the "ray effect" problem in the traditional "discrete ordinates" method. For a regular grid volume of n 3 elements, it takes O(M n 3 log n + M 2 n 3 ) time and O(M n 3 + M 2 ) space. This document is reprinted from the proceedings of the Fifth Eurographics Workshop on Rendering, Darmstadt, Germany, June 13 - 15, 1994 1. Introduction To render realistic images of clouds, one must take into account absorption and multiple scattering of incoming illumination. In addition, to produce the bright edges surrounding a cloud when the sun is behind it, one must account for the anisotropic, mainly forward, scattering of light from the water droplets. In 1984, Jim Kajiya and Brian Von Herzen [Kaj84] proposed two methods for rendering clouds. The first was the two-pass "slab" me...

This article presents a simple, fast and stable method for the animation and visualisation of turbulent gaseous fluids in two dimensions. We draw on well known methods from computational fluid dynamics to model the fluid using vorticity and velocity fields. While the vorticity is transported by a particle system, we use a uniform grid to compute velocities and displacements for each particle. This mixed approach where free particles move on a fixed grid requires little computational power, making it suitable for computer animation. The method simulates the behaviour of fluids in situations where the contact between fluid masses with different velocities generates an intermediate mixing layer which can give rise to turbulence phenomena. Unlike previous algorithms, it is possible to generate quasi-turbulent patterns, where large scale coherent vortex structures are still discernible in the flow.

This paper proposes an image-based modeling of clouds where realistic clouds are created from satellite images using metaballs. The intention of the paper is for applications to space flight simulators, the visualization of the weather information, and the simulation of surveys of the earth. In the proposed method, the density distribution inside the clouds is defined by a set of metaballs. Parameters of metaballs, such as center positions, radii, and density values, are automatically determined so that a synthesized image of clouds modeled by using metaballs is similar to the original satellite image. We also propose an animation method for clouds generated by a sequence of satellite images taken at some interval. The usefulness of the proposed method is demonstrated by several examples of clouds generated from satellite images of typhoons passing through Japan. 1.

This paper presents a new animation framework for the modeling of gaseous phenomena. We combine particle and grid based techniques in an innovative way. Based on this framework, our system allows for an incremental design of animations. In the first stage, an animator uses particle methods to model the evolution and appearance of gases. Grid based techniques are subsequently employed to compute high quality animations. Central to the success of our technique is a new algorithm to efficiently advect densities on grids. To demonstrate the effectiveness of our approach, we have included many animations.

A new method for simulating and rendering explosion phenomena is presented. It is based on an improvement of the SPH (Smoothed Particle Hydrodynamics) model introduced by Monaghan. Choosing polynomial kernel functions allows to approximate the attenuation term and compute an analytical solution for the illumination integral in the ray-tracing algorithm. Dynamics uses well-known SPH evolution rules whose parameters are inspired from chemical rules and measured data. A parallel computation on a CM5 machine is performed by the message passing method using the PVM library and a space subdivision approach; the programming scheme is used both for rendering the scene and dazzle postprocessing. VIRTUAL EXPLOSIONS FOR TESTING REAL ALGORITHMS Information systems are crucial in any modern military conflict. Fitted with a video input, computers are used for enhancing and processing images as well as detecting targets. After decades of technological improvements, an important question still rem...

Recently, displaying natural phenomena such as smoke has become a topic of interest in computer graphics. The ability to simulate the complex shapes and motion of the smoke particles is not only important but is also a difficult problem to solve. In this paper, we propose a method of displaying swirling smoke, including the consideration of its passage round obstacles . By using the idea of metaballs, we can easily represent the 3-dimensional density distribution of smoke. We solve the physical equation of the flow, and represent the vortices by using the vorticity vector. Therefore, we can make a model of the smoke flow even if there are obstacles in it's path. Keywords and phrases: Smoke, Metaballs, Vorticity, Computational Fluid Dynamics, Natural Phenomena. 1. Introduction Methods of displaying smoke are used in various fields, such as visual simulation, entertainment, etc. Therefore , there is quite a demand in several industries to mimic the appearance and motion of smoke. The p...

We present a technique to animate amorphous materials such as fire, smoke and dust in real-time on graphics hardware with dedicated texture memory. Our method uses a coarse voxel grid to model object dynamics, and texture cycling to create local and global dynamics. Detail is added by encoding high-frequency components, which are normally spread uniformly throughout the volume, into the volume integration. The individual voxels are rendered using a splatting approach with a table of anisotropic footprint functions. Our method produces a truly three-dimensional volume effect that can interact with the rest of the environment. Using different spectral scales for the volume’s appearance allows for motion at three distinct and disjoint scales. Local dynamics are achieved by phase-shifting through a set of textures within a voxel. Global dynamics, such as eddies, are propagated through the volume using inter-voxel dynamics. Object dynamics are achieved using procedural or keyframe animation techniques on the low-resolution voxel grid. We also develop an automated technique for texture selection by sampling a single large image having various frequency components.