This is not intended as a complete review of computer hardware and software that can be used for animation of finite element models and results, but is instead a demonstration of the benefits of visualization using selected hardware and software. The role of raw computational power, graphics speed, and the use of videotape are discussed

Lipman, Robert R.

English

NASA Technical Reports Server

N92-24327
ANIMATION OF FINITE ELEMENT MODELS AND RESULTS
Robert R. Lipman
David Taylor Research Center
Computational Signatures and Structures Branch (Code 1282)
Bethesda, Maryland 20084-5000
SUMMARY
Several years ago, the phrase 'visualization in scientific computing' (ref. 1) was coined for
what we used to call computer graphics. Although computer graphics is part of visualization,
visualization encompasses computer graphics hardware and software, network communications,
user interfaces, computer-aided-design, and more. The purpose of visualization is to provide
insight into the engineer's models and calculations. Animation of finite element models and
results is a visualization process that can provide the insight.
The paper is not intended to be a complete review of computer hardware and software
that can be used for animation of finite element model and results, but is instead a
demonstration of the benefits of visualization using selected hardware and software. Opinions
expressed are solely those of the author and are not those of the David Taylor Research Center,
the Navy, or the Department of Defense. Good reviews of visualization hardware and software
can be found in the following journals: Computer Graphics World, Supercomputing Review,
IEEE Computer Graphics and Applications, and CAE Computer-Aided Engineering. A
videotape showing visualization and animation of finite element models and results is an integral
part of this paper although it is not included in the proceedings.
INTRODUCTION
Visualization and animation give an engineer insight into his finite element model and
results. Wire-frame plots of a finite element mesh do not convey the sense that a 'real' structure
has been modeled. We do not live in a wire-frame world. We live in a world of color, light,
shading, and perspective. A beam is not a line between two points. A beam has a web and a
flange of substantial size and cross-section. The transient motion of a structure cannot be
determined from static plots at selected time steps or plots of the response of a node versus
time. Visualization and animation can be used to show an engineer the realistic configuration
and response of a structure.
The earliest animations of finite element analysis results were made by painstakingly
recording a sequence of static plots on film. Some of the first computer animations of finite
element analysis results were made on Evans & Sutherland graphics hardware (ref. 2). Today,
with the price/performance of computer graphics hardware so low and visualization software
packages becoming more mature, finite element model visualization and animation is now a
desktop tool.
23
https://ntrs.nasa.gov/search.jsp?R=19920015084 2020-03-17T12:09:26+00:00Z
HARDWARE
It seems that computer workstation vendors are announcing faster and less expensive
hardware almost every day. Current Cray X-MP supercomputer computational speeds should bc
available in desktop computer workstations in 1-2 years. By the time this paper is presented,
the 1-2 year time frame may have been reduced from years to months. The cost of memory and
hard disk storage is also falling.
As important as raw computational power is to animation and visualization, graphics
speed is equally important. Graphics speed, usually quoted in polygons per second, is not
increasing as fast as computational speed. Rather, the cost of current graphics power is getting
less expensive. Current peak graphics speeds of 200,000 polygons per second can be found on
the top-of-the-line graphics workstations. The user must beware of the type of polygon that the
vendor uses when quoting graphics speed. Quotes of one million polygons per second are usually
for highly optimized meshes of triangles without light-source shading. For animation of finite ele-
ment models, the graphics speed for independent quadrilateral polygons is more relevant.
When computation and visualization take place in a distributed environment, communica-
tions speed between the client and server is another important issue. Today, animations of finite
clcmcnt analysis results arc typically done in a batch mode. The analysis is done ou a large
mainframe or supercomputcr and the results are sent to a workstation to be used with visualiza-
tion softwarc. In the future, the two processes of analysis and visualization will be more tightly
coupled whcrc thc analysis and visualization are being computed concurrently. For this scenario
to takc place, much higher network communications speed between the computational server
and visualization server will be necessary than current local- and wide-area networks provide.
Finally, animation sequences have to be recorded to videotape. There are two methods
for recording computer graphics animations on videotape: real-time and frame-by-frame. For
real-time recording, the computer graphics display is converted, in real-time, to a television sig-
nal suitable for recording on videotape and being displaycd on a regular television monitor.
Therefore, whatever is being displayed on the computer graphics display can be recorded to
videotape. If the graphics speed is fast enough to animate a finite element model in real-time,
then this process is sufficient.
With graphics hardware that is not fast enough and with visualization software that has a
rendering capability, then frame-by-frame recording can be used. The visualization software
renders individual images that are recorded one-by-one on videotape. The result is a continuous
animation sequence. Frame-by-frame recording also produces higher quality animations and
renderings than real-time animation.
SOFTWARE
Visualization software packages can be separated into three categories: general-purpose,
modular, and application specific. The types of data that the packages can visualize are usually
either structured or unstructured grids. A structured grid is typical for finite-difference applica-
tions such as computational fluid dynamics. A finite element mesh is an example of an unstruc-
tured grid. Many of the general-purpose visualization packages (PV-Wave, Spyglass, Data
Visualizer) are very good with structured grids and less useful for finite element applications.
There are also several application specific visualization packages (Fieldview, Fast, Plot3D) that
2_
canbeusedwith only structuredgrids. The modularvisualizationpackages(AVS, Iris Explorer,
apE) allow users to write their own applicationsspecifc softwaremodulesto be integrated with
the visualization software.
There are few choices for application-specific visualization packages for finite element
analysis animation. The popular finite element pre and postprocessors (Patran, I-DEAS) have
animation capabilities, but are not oriented to the visualization process and to recording video-
tapes. FOTO (ref. 3) is a data visualization software package geared towards finite element
models and animation. FOTO was used to make the videotape that is part of this paper. FOTO
is easy to interface with analysis codes; is user-definable menu driven; has many visualization
types including: color, displacement, contour lines, vectors, transparency, and culling operators;
and has a tightly coupled videotape system.
There are also free visualization software packages available from the national supercom-
purer centers. Because they are free, the source code is provided allowing the user to tailor the
code to his application. However, because they are free, the user will not get the same type of
support or updates to the software that a commercially available package would provide.
THE FUTURE
What is currently possible for finite element animation and visualization is not the final
product, but only a step towards a more interactive, dynamic environment for doing analysis and
visualization. In the future, analysis and visualization will occur concurrently in near real-time
and the engineer will have the capability to interact with the analysis by changing the finite ele-
ment model as the computations are taking place to explore new configurations of the model.
REFERENCES
1. McCormick, B.H., T.A. DeFanti, and M.D. Brown; Editors,
Computing," ACM SIGGRAPH, November 1987.
"Visualization in Scientific
2. Lipman, R.R., "Computer Animation of Modal and Transient Vibrations," in: Proceedings
of 15th NASTRAN Users" Colloquium, 4-8 May 1987, Kansas City, Mo., National Aeronautics
and Space Administration, NASA CP-2481, pp. 111-117, Washington, D.C. (1987).
3. "FOTO User Manual," Cognivision, Inc., Westford, MA, 1992.
25


Animation of finite element models and results

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server