Building animation tools for fluid-like motions is an important and challenging problem with many applications in computer graphics. The use of physics-based models for fluid flow can greatly assist in creating such tools. Physical models, unlike key frame or procedural based techniques, permit an animator to almost effortlessly create interesting, swirling fluid-like behaviors. Also, the interaction of flows with objects and virtual forces is handled elegantly. Until recently, it was believed that physical fluid models were too expensive to allow real-time interaction. This was largely due to the fact that previous models used unstable schemes to solve the physical equations governing a fluid. In this paper, for the first time, we propose an unconditionally stable model which still produces complex fluid-like flows. As well, our method is very easy to implement. The stability of our model allows us to take larger time steps and therefore achieve faster simulations. We have used our model in conjuction with advecting solid textures to create many fluid-like animations interactively in two- and three-dimensions.

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...

This paper proposes a simple and computationally inexpensive method for animation of clouds. The cloud evolution is simulated using cellular automaton that simplifies the dynamics of cloud formation. The dynamics are expressed by several simple transition rules and their complex motion can be simulated with a small amount of computation. Realistic images are then created using one of the standard graphics APIs, OpenGL. This makes it possible to utilize graphics hardware, resulting in fast image generation. The proposed method can realize the realistic motion of clouds, shadows cast on the ground, and shafts of light through clouds.

Flow volumes are the volumetric equivalent of stream lines. They provide more information about the vector field being visualized than do stream lines or ribbons. Presented is an efficient method for producing flow volumes, composed of transparently rendered tetrahedra, for use in an interactive system. The problems of rendering, subdivision, sorting,compositing artifacts, and user interaction are dealt with. Efficiency comes from rendering only the volume of the smoke, using hardware texturing and compositing.

We present a method for visualizing unsteady flow by displaying its vortices. The vortices are identified by using a vorticity-predictor pressure-corrector scheme that follows vortex cores. The cross-sections of a vortex at each point along the core can be represented by a Fourier series. A vortex can be faithfully reconstructed from the series as a simple quadrilateral mesh, or its reconstruction can be enhanced to indicate helical motion. The mesh can reduce the representation of the flow features by a factor of one thousand or more compared with the volumetric dataset. With this amount of reduction it is possible to implement an interactive system on a graphics workstation to permit a viewer to examine, in three dimensions, the evolution of the vortical structures in a complex, unsteady flow.

this paper, we show how texture mapping hardware can produce near-real-time texture motion,

Flow visualization has been a very attractive component of scientific visualization research for a long time. Usually very large multivariate datasets require processing. These datasets often consist of a large number of sample locations and several time steps. The steadily increasing performance of computers has recently become a driving factor for a reemergence in flow visualization research, especially in texture-based techniques. In this paper, dense, texture-based flow visualization techniques are discussed. This class of techniques attempts to provide a complete, dense representation of the flow field with high spatio-temporal coherency. An attempt of categorizing closely related solutions is incorporated and presented. Fundamentals are shortly addressed as well as advantages and disadvantages of the methods. Categories and Subject Descriptors (according to ACM CCS): I.3 [Computer Graphics]: visualization, flow visualization, computational flow visualization

Current techniques for direct volume visualization offer only the ability to examine scalar fields. However most scientific explorations require the examination of vector and possibly tensor fields as well as numerous scalar fields. This paper describes an algorithm to directly render three-dimensional scalar and vector fields. The algorithm uses a combination of sampling and splatting techniques, that are extended to integrate the display of vector field data within the image.

We present hardware-accelerated texture advection techniques to visualize the motion of particles in steady or time-varying vector fields given on Cartesian grids. We propose an implementation of 2D texture advection which exploits advanced and programmable texture fetch and per-pixel blending operations on an nVidia GeForce 3. For 3D vector field visualization, we present an algorithm for SGI's VPro, based on pixel textures and 3D textures. Moreover, we sketch how 3D texture advection could be implemented on future graphics boards that provide programmable fetch operations for 3D textures. Since all implementations exclusively use graphics hardware without intermediate data transfer to main memory, extremely high frame rates are achieved, e.g., up to 90 frames per second for advecting a calculatory number of one million particles in a 2D flow. The proposed techniques are especially useful for the interactive visualization of vector fields. 1

We present a direct volume rendering algorithm to speed up volume animation for flow visualizations. Data coherency between consecutive simulation time steps is used to avoid casting rays from those pixels retaining color values assigned to the previous image. The algorithm calculates the differential information among a sequence of 3D volumetric simulation data. At each time step the differential information is used to compute the locations of pixels that need updating and a ray-casting method is utilized to produce the updated image. We illustrate the utility and speed of the differential volume rendering algorithm with simulation data from computational bioelectric and fluid dynamics applications. We can achieve considerable disk-space savings and nearly real-time rendering of 3D flows using low-cost, single processor workstations* for models which contain hundreds of thousands of data points.