Al Globus

A tool for visualizing the topology of three-dimensional vector fields

A description is given of a software system, TOPO, that numerically analyzes and graphically displays topological aspects of a three-dimensional vector field, v, to produce a single, relatively simple picture that characterizes v. The topology of v considered consists of its critical points (where v=0), their invariant manifolds, and the integral curves connecting these invariant manifolds. The field in the neighborhood of each critical point is approximated by the Taylor expansion. The coefficients of the first nonzero term of the Taylor expansion around a critical point are the 3*3 matrix Delta v. Critical points are classified by examining Delta vs eigenvalues. The eigenvectors of Delta v span the invariant manifolds of the linearized field around a critical point. Curves integrated from initial points on the eigenvectors a small distance from a critical point connect with other critical points (or the boundary) to complete the topology. One class of critical surfaces that is important in computational fluid dynamics is analyzed.<<ETX>>

FAST: a multi-processed environment for visualization of computational fluid dynamics

The authors discuss FAST (flow analysis software toolkit), an implementation of a software system for fluid mechanics analysis. Visualization of computational aerodynamics requires flexible, extensible, and adaptable software tools for performing analysis tasks. An overview of FAST is given, and its architecture is discussed. Interactive visualization control is addressed. The advantages and disadvantages of FAST are discussed.<<ETX>>

Automated Antenna Design with Evolutionary Algorithms

Whereas the current practice of designing antennas by hand is severely limited because it is both time and labor intensive and requires a signican t amount of domain knowledge, evolutionary algorithms can be used to search the design space and automatically nd novel antenna designs that are more eectiv e than would otherwise be developed. Here we present automated antenna design and optimization methods based on evolutionary algorithms. We have evolved ecien t antennas for a variety of aerospace applications and here we describe one proof-of-concept study and one project that produced gh t antennas that ew on NASA’s Space Technology 5 (ST5) mission.

Evaluation of visualization software

Visualization software is widely used in scientific and engineering research. But computed visualizations can be very misleading, and the errors are easy to miss. We feel that the software producing the visualizations must be thoroughly evaluated and the evaluation process as well as the results must be made available. Testing and evaluation of visualization software is not a trivial problem. Several methods used in testing other software are helpful, but these methods are (apparently) often not used. When they are used, the description and results are generally not available to the end user. Additional evaluation methods specific to visualization must also be developed. We present several useful approaches to evaluation, ranging from numerical analysis of mathematical portions of algorithms to measurement of human performance while using visualization systems. Along with this brief survey, we present arguments for the importance of evaluations and discussions of appropriate use of some methods.

Optimizing particle tracing in unsteady vector fields

Unsteady 3-D computational fluid dynamics (CFD) results can be very large. Some recent solutions exceed 100 gigabytes. Visualization techniques that access the entire data set will, therefore, be excruciatingly slow. We show that particle tracing in vector fields calculated from disk resident solutions can be accomplished in O(number-of-particles) time, i.e., visualization time is independent of solution size. This is accomplished using memory mapped files to avoid unnecessary disk IO, and lazy evaluation of calculated vector fields to avoid unnecessary CPU operations. A C++ class hierarchy implements lazy evaluation such that visualization algorithms are unaware that the vector field is not stored in memory. A numerical experiment conducted on two solutions differing in size by a factor of 100 showed that particle tracing times varied by only 10-30 percent. Other visualization techniques that do not access the entire solution should also benefit from memory mapping and lazy evaluation.

Evolvable Hardware for Space Applications

This article surveys the research of the Evolvable Systems Group at NASA Ames Research Center. Over the past few years, our group has developed the ability to use evolutionary algorithms in a variety of NASA applications ranging from spacecraft antenna design, fault tolerance for programmable logic chips, atomic force eld parameter tting, analog circuit design, and earth observing satellite scheduling. In some of these applications, evolutionary algorithms match or improve on human performance. In this paper we discuss automated antenna design and self-repairing electronic chips.