The capabilities of the postprocessing program CANDI (Color Animation of Nastran DIsplacements) were expanded to accept results from axisymmetric analysis. An auxiliary program, ANIMATE, was developed to allow color display of CANDI output on the IRIS 4D-series workstations. The user can interactively manipulate the graphics display by three-dimensional rotations, translations, and scaling through the use of the keyboard and/or dials box. The user can also specify what portion of the model is displayed. These developments are limited to the display of complex displacements calculated with the NASHUA/NASTRAN procedure for structural acoustics analysis

Fales, Janine L.

English

NASA Technical Reports Server

N9!-20514
COMPUTER ANIMATION OF NASTRAN DISPLACEMENTS
ON IRIS 4D-SERIES WORKSTATIONS:
CANDI/ANIMATE POSTPROCESSING OF NASHUA RESULTS
Janine L. Fales
Los Alamos National Laboratory
Advanced Engineering Technology (MEE-13)
Los Alamos, New Mexico 87545
SUMMARY
The capabilities of the postprocessing program CANDI (Color
Animation of Nastran Displacements) [1] have been
expanded to accept results from axisymmetric analyses. An
auxiliary program, ANIMATE, has been developed to allow
color display of CANDI output on the IRIS 4D-series
workstations. The user can interactively manipulate the
graphics display by three-dimensional rotations, translations,
and scaling through the use of the keyboard and/or dials box.
The user can also specify what portion of the model is
displayed. These developments are limited to the display of
complex displacements calcuIated with the
NASHUA/NASTRAN procedure for structural acoustics
analyses [2].
INTRODUCTION
Animation of results has become an increasingly popular method of
postprocessing because of the wealth of information conveyed to the
analyst in a short amount of time. Animation allows the analyst to
visualize time-dependent results that previously could only be
imagined from a series of static plots. Through animation, the
analyst is able to focus on the interpretation of the results, having
been freed from the burden of envisioning their time dependency.
The advantages of animation were recognized by Lipman at David
Taylor Research Center (DTRC), in the development of the
postprocessing computer program, CANDI (Color Animation of
Nastran Displacements) [1]. CANDI was originally written to
76
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interface with an Evans & Sutherland PS-330 interactive graphics
system [3] for the graphics display. Unfortunately, the usefulness of
CANDI was limited to those with access to this specific hardware.
A postprocessing tool was required for displaying complex
displacements obtained with the NASHUA/NASTRAN procedure
(hereafter referred to as NASHUA). NASHUA, developed by
Everstine and Quezon at DTRC, is a coupled finite element/boundary
element capability built around NASTRAN for calculating the low-
frequency, far-field acoustic pressure field radiated or scattered by
an arbitrary, submerged, elastic structure subjected to either
internal, time-harmonic, mechanical loads or external, time-
harmonic, incident loadings [2]. The structure can be axisymmetric
or three-dimensional. CANDI was one postprocessing option for
three-dimensional NASHUA analyses. An axisymmetric tool was also
required.
Rather than replicate the work of Lipman, an auxiliary computer
program, ANIMATE, was developed to accept, as input, the output
from CANDI and display the results on the IRIS 4D-series
workstations, manufactured by Silicon Graphics, Incorporated (SGI).
The choice of the IRIS workstation was based on its three-
dimensional, graphics display capabilities. CANDI was also expanded
to postprocess results from axisymmetric NASHUA analyses.
Because the work described here was done to accomplish specific,
programmatic needs, the scope of the computer program developed
is limited to the display of complex displacements calculated with
NASHUA. Although CANDI is able to postprocess results from other
types of analyses, there are no expectations on the part of the author
to enable ANIMATE to display these results. It is hoped that the
foundations of the program are sound enough to allow enhancements
by others, if needed.
THE NASHUA/NASTRAN PROCEDURE (NASHUA)
The NASHUA/NASTRAN procedure, also called the NASHUA
capability or NASHUA, is explained, in detail, in Ref. 2. At Los
Alamos National Laboratory, NASHUA is executed on a Cray
supercomputer running under a CTSS operating system. Table 1
summarizes the steps involved in this type of analysis. Rigid Format
8 (direct frequency response) is used for each NASTRAN execution.
All DMAP ALTER sequences are given in Ref. 2. The DMAP ALTER
77
statements needed for the use of CANDI are the OUTPUT2 statements
given in Figure 1. These OUTPUT2 statements produce a binary file,
named utl, containing the information needed by CANDI. To avoid
the need for a file conversion program to move the utl file (in Cray
binary) to another machine for postprocessing, CANDI was ported to
the Cray.
TABLE 1
NASHUA/NASTRAN PROCEDURE SUMMARY
STEP O3DE
1 NASTRAN 1
2
4
SURF
NASTRAN 2
O_OLVE
NASTRAN 3
MERGE
FAROUT
NASTRAN 4
IPLOT
FAFPLOT
CANDI, etc.
5_6 9 ooo
PURPOSE
Define geometry
Form structural mass,
viscous damping, and
stiffness matrices
Form fluid matrices
Set up coupled system
for pressure
Solve coupled system
Recover velocities
Combine multiple
frequencies
Calculate far-field
quantities
Produce deformed
structural plots
Perform additional
postprocessing
78
ALTER
ALTER
ALTER
e . I
OUTPUT2
OUTPUT2
I • I
ENDALTER $
I $ NASHUA STEP 4, COSMIC 1990 RF8
8,8 $
21,170 $
CASECC,BGPDT,ECT,FRL,PUPVC 1//- 1 $
,,,,//-9 $
Figure 1. DMAP ALTER statements required for use of CANDI.
CANDI, THE POSTPROCESSING PROGRAM
CANDI is an interactive program that reads, filters, and outputs
results from a variety of NASTRAN analyses, including static,
eigenvalue, direct frequency response, direct transient response, and
modal frequency response. It reads the binary utl file produced by
including DMAP ALTER statements in the NASTRAN executive control
deck. (For use with NASHUA, the specific DMAP ALTER statements
are given in Figure 1.)
The user is asked a number of interactive questions to determine
what output is desired. Figure 2 shows a sample interactive session.
Through these questions, the user has control over what is displayed
and how it is displayed. For example, portions of the finite element
model can be excluded based on a range of XYZ coordinate values, on
element type, and/or on element id. Coordinate ranges, element
types, and element ids are displayed to assist the user. The user also
has control over which results are output - which subcases and
which frequencies, in the case of a NASHUA analysis. He also
controls how many frames of animation are desired and whether the
deformation scale factor computed by CANDI is used. The scale
factor is computed so that the magnitude of the displacements will
be similar to the dimensions of the finite element model.
Based on the responses, CANDI filters and outputs one or more ASCII
files in vector list format. A sample vector list is given in Figure 3.
To reduce the computational effort required by the display device,
79
xcandi
candi - color animation of nastran displacements
enter file name of the utl file ?
? utl
coordinate limits of the finite element model
xmin= l. O000e-05 ymin= O.O000e+O0 zmin= O.O000e+O0
ymax= 2.1695e+00 ymax= 3.3930e+01 zmax= O.0000e+O0
do you want to exclude elements by coordinate ranges (y/n) ?
9n
3 element type(s) (element type id-element type)
146-cconeax 287-ctriaax 285-ctrapax
do you want to exclude elements by element type (y/n) ?
?n
do you want to exclude elements by element id (y/n)
? n
do you want the vector lists to be
1 - color coded by element type or
2 - depth cued
? 1
id
do you want to color code by element
1 - type (not user-definable)
2- id (user-definable, default=blue)
? 1
enter file name for the undeformed fem vector list 9
? undef
do you want to generate any displacement vector lists (y/n) ?
?y
number of subcases = 2, subcase ids - 1 2
number of frequencies = 4 (number-frequency)
I- 60.00 2- 70.00 3- 80.00 4-
enter a subcase id and frequency number
? 2 3
90.00
enter file name for the displacement vector list 9
? def3
enter number of frames of animation ?
? 16
maximum deformation = 2.1680e-03
computed deformation scale factor (dsf) = 7.8253e+02
do you want to change the computed dsf (y/n) ?
? n
do you want to write another displacement vector list (y/n)
? n
stop
Figure 2. Sample CANDI session of axisymmetric analysis.
8O
CANDI tests whether each side of an element has already been
written to the vector list before adding it. The 'p' and '1' designations
are signals to the graphics device. A 'p' indicates 'move to' the given
coordinates ; an '1' indicates 'draw to' the given coordinates. The
semicolon signals the end of the vector list. In this way, the
undeformed (finite element model) and deformed (results) meshes
are drawn efficiently.
aaa =undeformed vec list
p-I
1-9
1-7
1-5
1-4
085e+00, 1.696e+01, O.O00e+O0
160e-Ol, 1.696e+01, O.O00e+O0
486e-01, 1.693e+01, O.O00e+00
842e-01, 1.690e+01, O.000e+O0
240e-01, 1.684e+01, O.O00e+O0
Figure 3. Portion of vector list for undeformed mesh.
An axisymmetric version of CANDI was required. Structural
acoustics problems frequently require fine mesh densities to capture
the response of the structure accurately. Three-dimensional models
become prohibitive because of computer time required for solution.
Hence, axisymmetric analyses, when applicable, become extremely
important. CANDI was enhanced to recognize the axisymmetric
elements, CCONEAX, CTRIAAX, and CTRAPAX. Other elements could
be added, given the knowledge of card type format 1 for each element
desired. Additional information about CANDI can be found in Ref. 1.
ANIMATE, THE DISPLAY PROGRAM
ANIMATE was developed on a Personal IRIS ® , Model 4D/25TG. It is
written in C and uses the Graphics Library (GL) resident on SGI/IRIS
workstations. ANIMATE reads the vector lists output by CANDI,
calculates, and displays the animation sequence. ControI of the
display is provided through an extensive user interface. Specific
aspects of ANIMATE are discussed in the sections that follow.
1Card type formats are available in Section 2.3 of the "COSMIC/NASTRAN
Programmer's Manual," NASA SP-223(5), August 1987. Header Word 3 is the
element id number.
®Personal IRIS is a registered trademark of Silicon Graphics, Incorporated.
81
HARDWARE / SOFTWARE REQUIREMENTS
The Personal IRIS, Model 4D/25 TG, on which ANIMATE was
developed, was originally purchased for its three-dimensional
capabilities with PATRAN ®. The Personal IRIS (4D/20+) series give
favorable price/performance curves. The need to animate complex
displacements spearheaded the effort to port CANDI to the IRIS
platform. In addition, other postprocessing tools for structural
acoustics analyses had been developed for the IRIS 4D-series
workstations.
The high-level Graphics Library made the graphics programming
relatively easy. However, because the GL was used, ANIMATE is not
universally portable. It is only portable to IRIS 4D-series
workstations, or to IBM machines on which the GL has been installed.
The IRIS Window Manager, based on the NeWS server environment
was used to develop the user interface.
ANIMATE was initially developed using the dials box for the three-
dimensional rotations, translations, and scaling. While the dial box is
an intuitive method to accomplish these transformations, it is an
optional peripheral. Therefore, the same functionality was tied to
keys found on the standard IRIS keyboard. If available, use of the
dial box is preferred.
The minimum hardware requirement to use ANIMATE is an IRIS
4D/20 G workstation. Any graphics workstation of the 4D-series is
acceptable. The dial box is useful, but optional.
CALCULATION OF ANIMATION SEQUENCE
Animation of the harmonic time dependence of the complex
displacements is accomplished according to the following equation.
F i = V u + DSF [ VRe cos0 i - Vim sin0i ]
where F i =
V u =
VRe =
Vim =
ith frame of animation,
undeformed vector list,
vector list of real components,
vector list of imaginary components,
®PATRAN is a registered trademark of PDA Engineering.
82
and
0 i =
DSF =
angle for F i = 360°/(number of frames),
deformation scale factor.
The equation is obtained by multiplying the time invariant result
(here given by the complex displacements) by the appropriate time
dependency. The simple harmonic variation of the results is given
by the real part of this product [4]. For NASHUA, a harmonic time
dependency of e itot is assumed. Figure 4 illustrates this product
graphically. One complete animation sequence corresponds to a 360 °
rotation of the complex displacement vector. Each frame of the
animation sequence rotates the displacement vector by an angle of
0 i. For smooth animation, the number of frames, i, is normally
specified between 12 and 16.
im
b /_+ib
v
a Re
Time invariant
m
R
X
|m
|m
cos 0 + i sin 0
Re
Time dependent
a cos 0 - b sin 0
Re
Figure 4. Graphic display of animation concept.
83
USER INTERFACE
It was important to develop a user interface that helped, not
hindered the analyst. Thus, the interface was developed as
intuitively as possible, maintaining the function key assignments
found in the original CANDI/Evans & Sutherland system. Specific
key assignments are listed in Figure 5. Dial assignments and
locations are shown in Figure 6. Through this interface, the user has
control over the view and scale of the model, the speed of animation,
and the display of undeformed mesh and/or the coordinate axes. He
can stop and start the animation, or step through it one frame at a
time.
Function Key Definitions
FK1
FK2
FK3
FK4
FK5
FK6
Start animation
Stop animation
Step backwards through animation sequence
Step forwards through animation sequence
Slow down rate of animation
Speed up rate of animation
FK7,8 Not assigned
FK9
FK10
FK11
Reset all rotations and translations
Toggle on/off undeformed mesh
Toggle on/off coordinate axes
Other Key Definitions
x/X
y/Y
z/Z
i/I
j/J
k/K
s/S
ESC
Increase]decrease x-rotation
Increase/decrease y-rotation
Increase/decrease z-rotation
Left/right x-translation
Left/right y-translation
Left/right z-translation
Increase/decrease scale
Exit program
Figure 5. Keyboard definitions for user interface.
84
\SCALE Not Used
Z ROTATION Z TRANSLATION
Y ROTATION
_,,. X ROTATION
Y TRANSLATION
O
X TRANSLATION/
Figure 6. Dial box definitions and dial locations.
85
(i_ _.
REFERENCES
• R. R. Lipman, "Computer Animation of Modal and Transient
Vibrations," Fifteenlh NASTRAN Users' Colloquium, NASA CP-
2481, National Aeronautics and Space Administration,
Washington, D.C., pp 88-97 (May 1987).
= G. C. Everstine and A. J. Quezon, "User's Guide to the Coupled
NASTRAN/Helmholtz Equation Capability (NASHUA) for Acoustic
Radiation and Scattering," Third Ed., DTRC report CMLD-88/03
(February 1988).
. "PS-300 User's Manual," Evans & Sutherland Computer
Corporation, Salt Lake City, Utah, 1985.
. F. Fahy, Sound and Structural Vibration, Radiation, Transmission
and Response, Academic Press, 1985.
86


Computer animation of NASTRAN displacements on IRIS 4D-series workstations: CANDI/ANIMATE postprocessing of NASHUA results

The capabilities of the postprocessing program CANDI (Color Animation of Nastran DIsplacements) have been expanded to accept results from axisymmetric analyses. An auxiliary program, ANIMATE, has been developed to allow color display of CANDI output on the IRIS 4D-series workstations. The user can interactively manipulate the graphics display by three-dimensional rotations, translations, and scaling through the use of the keyboard and/or dials box. The user can also specify what portion of the model is displayed. These developments are limited to the display of complex displacements calculated with the NASHUA/NASTRAN procedure for structural acoustics analyses. 4 refs., 6 figs., 1 tab

Computer animation of NASTRAN displacements on IRIS 4D-series workstations: CANDI/ANIMATE postprocessing of NASHUA results

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