2.11
THE OPENGL PLOT PROGRAM Z88O
With the new OpenGL plot
program Z88O the Z88 system enters new dimensions. You may illuminate a
structure with three different light sources or plot with hidden lines, both
the undeflected and the deflected structure. You may plot stresses and X, Y and
Z deflections with a color range - like the expensive professional FEA
programs. You may plot a limited range of nodal or element numbers - a nice
feature especially for large structures. A printer or plotter feature is not
included into Z88O - and why - just do a screen shot.
Z88O uses OpenGL so your
computer must be able to deal with OpenGL graphics. This is true for all newer
Windows machines and a quite cheap graphics card will do well. Anyway, it's
always a good idea to control the system settings - sometimes you may turn on
OpenGL hardware acceleration. Compilation (only necessary if you want to add
improvements) under Windows is easy because OpenGL is part of Windows since
Windows95 and the well-known compilers (MS Visual C++, LCC, Borland C++
Builder, OpenWatcom) come with the necessary OpenGL libraries and header files.
Professional UNIX
workstations have always OpenGL features included. If you want to compile the
Z88 system by yourself on a UNIX machine be sure to have the libraries libGLw
and libGL and the header files gl.h, glx.h und GlwMDrawA.h
on your machine in the proper library and include paths. This is also true for
LINUX systems, but LINUX sometimes presents problems with OpenGL and your graphics
card. If so, don't blame Z88O because Z88O was developed on a SGI. And SGI
makes the OpenGL reference machines. But with the newer RedHat and SuSE
distributions it should work after some effort. If Z88O won't work at all: The
approved plot program Z88P which works with the WinAPI or the X11
libraries stays in Z88, ref. Chapter 2.6.
Of course, you may define
your choice of colors, the light features, material properties, the polygon
offset and the fonts (for UNIX) in the parameter files Z88O.OGL (for Windows)
and Z88.FCD (for UNIX). The file Z88.FCD for the UNIX operation system allows
for much more possibilities in changing colors and fonts as well as the sizes
and locations of the pushbuttons, radioboxes etc. You can completely modify the
whole appearance of Z88O for UNIX as you wish. Be careful with changes in
Z88O.OGL (Windows) or Z88.FCD (UNIX/LINUX): You should have some proper
knowledge about OpenGL if you want to change light effects etc. Otherwise you
may pull a long face because nothing will work as you wish. Some hints are
included into Z88O.OGL and Z88.FCD, however, i can not give here an
introduction into OpenGL. Consult the two basic books "OpenGL Programming
Guide" and "OpenGL Reference Manual" from Addison-Wesley.
Start of Rendering: When Z88O was launched the OpenGL
subsystem is started and prepared to go. You'll start rendering under Windows
with the very left icon Go and under UNIX with the pushbutton upper row
right <Run>.
Needed Files |
Super structures |
Undeflected FE struc. |
Deflected FE struct. |
Yes |
No |
No |
|
No |
Yes |
Yes |
|
No |
No |
Yes |
|
No |
Yes, for Mises stresses |
Yes, for Mises stresses |
Rendering with Z88O: For fastest operation Z88O connects
the nodal points - and only the corner points- with straight lines, although
for Serendipity elements the edges of the elements are square or cubic curves. However,
especially illuminated scenes need a huge amount of computational power. Please
keep in mind: If a part renders pretty fast in your CAD system, Pro/ENGNEER for
example, and the same part renders quite slowly in Z88O - this is normal
business because CAD systems are "drawing" only some outline curves. In
contrast, FEA system have to render every finite element i.e. compute
the normal vectors for any element surface, compute light effects for every
tetrahedron etc. Hidden line scenes put very heavy load on the CPU, too.
What can i plot with
Z88O? Nearly
everything if a solver (Z88F or Z88I1 with Z88I2) was run which stored the
deflection file Z88O2.TXT along with a run of the stress processor Z88D which stored the three stress files
Z88O3.TXT (for you to check the stresses), Z88O5.TXT (for Z88P) and Z88O8.TXT
(for Z88O). Even for trusses you may plot the "von Mises" stresses
(i.e. tensile stresses) with different colors. Only beams No.2 and No.13 and cams No.5 allow only the plotting of
deflections and nothing more. Why? Because you must compute for beams and cams
also the notch sensitivity which is impossible for a FEA system which deals
with a whole structure of beams.
Plot of stresses: The kind of plotting the stresses
within FEA programs is truly of philosophical character. As a matter of fact,
numerous experiments and computer studies at the Institute of Engineering
Design and CAD of the University of Bayreuth, Germany, showed, that some
very expensive and well-known professional FEA programs produced incorrect
stress plots in some situations! The best way is the computation of
stresses directly in the Gauss points as realized in Z88P. However, this is odd for OpenGL so i decided
for the following way after a lot of experiments:
Plot of deflections: You may plot the undeflected or the
deflected structure. The enlargement factor is adjustable, with 100 as the
default value for X, Y and Z. In addition, you may plot the deflections for X,
for Y or for Z with color shading. This is a pretty nice feature for large
spatial structures. In contrast to Z88P, you may plot the shaded colors for
stresses or for the deflections with the deflected structure, too.
Hints for the user for
Zooming, Panning and Rotating:
This option fits well for
limited zooming- and panning ranges and for fast but quite unprecise rotating. You
may in addition use the special keys or pushbuttons but this mixed mode is not
a real feature and may lead to unpredictable results because Z88O uses
different calculations for both modes.
Special key strokes for
Windows:
Prior: increase zoom
Next: decrease zoom
Cursor left: panning X direction
Cursor right: panning X direction
Cursor up: panning Y direction
Cursor down: panning Y direction
Home: panning Z direction
End: panning Z direction
F2: rotate around X axis
F3: rotate around X axis
F4: rotate around Y axis
F5: rotate around Y axis
F6: rotate around Z axis
F7: rotate around Z axis
F8: reset all rotations to 0
Under UNIX use the usual
X and Motif key assignments: Tab key and arrow keys for choice and space bar
for activation.
The "coordinate system": OpenGL works with a Clipping Volume, i.e. with a kind of cube, defined by Xmin and Xmax in horizontal direction, by Ymin and Ymax in vertical direction and Zmin (points towards the user) and Zmax (points away from the user). If you use a too-large zoom factor or if you are panning the structure too near to you then the range of Zmin is exceeded and parts of the structure are laying outside the viewing volume. This offers a nice chance to look into a structure. Otherwise, change the value of Zmin (default entry is -100) to lower values, e.g. -1000: under Windows use Factors > Z limit towards you, under UNIX change the textfield "Zlimit" right side below. The following screenshots are showing the situation:
Windows: piston of a BMW
engine (motorcycle F650GS) Zlimit: default value -100.
Windows: piston of a BMW engine (motorcycle F650GS) Zlimit is -10,
piston has slash cut.
Explanation
of some menu items:
Name of Structure File:
Windows: File >
Structure File
UNIX: Stru. text field directly on window
Choose the structure file
here. Enter name, if necessary with path, press return. The new stucture is
loaded. You'll start rendering under Windows with the very left icon Go
and under UNIX with the pushbutton upper row right <Run>.
Deformation Modes of the
Structure:
Windows: Structure >
Undeflected, Deflected
UNIX: Radio box Undefle., Deflected
Plots the undeflected
structure or the deflected structure. You may do all other rendering operations
with the undeflected structure or the deflected structure.
Caution Deflected: The user must
have executed a calculation of displacements before using this function. Do a
FEA run with Z88F or Z88I1/Z88I2 before using Z88O. Otherwise, some
old files Z88O2.TXT (displacements) from earlier Z88 runs are opened causing
totally wrong results !!
Choice of the 3D
effects:
Windows: 3D-Effekte >
1. Light on,
2. Hidden Line on,
3. Mises stresses (corners),
4. Mises stresses (elements),
5. X Displacements on,
6. Y Displacements on,
7. Z Displacements on
or the appropriate icons
UNIX : Radiobox
1. Light
2. Hide/Mesh,
3. Stress E,
4. Stress M,
5. X displac,
6. Y displac,
7. Z displac
For pos. 3. to 7. the color
range may be edited in the header files Z88O.OGL (Windows) and Z88.FCD (UNIX).
UNIX:
Hidden line plot of the BMW piston, mouse navigation turned on.
Drawing Node and Element
Numbers:
Windows: Labels > No
Labels, Nodes, Elements,
UNIX: Radio box No Labels, Nodes, Elements
Plot the element numbers or
the node numbers or skip numbering. In contrary to Z88P you can define ranges from-to, e.g.
plot the nodal numbers from 11 to 19 or plot the element 3, i.e. from 3 to 3. Z88O
recalls your entries even if you change to No Labels. Keep in mind for
UNIX and LINUX: press immediatelly the Return button after you've filled
in a textfield to enter the value really. This is not a Z88O stupidy but the
normal use of Motif textfields.
Please remember that you'll
only get rendered all desired labels on the surfaces if you are in Hidden
line mode. The other modes may cover some labels. And labels inside a
structure are usually covered by the tetrahedron and hexahedron surfaces. Therefore,
Z88O turnes the hidden line mode temporary off - you'll see the mesh without
hidden lines just as in Z88P. As soon as you switch to No Labels
gehen, the hidden line mode is re-activated.
Zooming:
Windows: PRIOR and
NEXT
UNIX : Pushbuttons Zoom+ and Zoom-
mouse navigation on: left
mouse button pressed
Panning:
Windows:
X: CURSOR LEFT and CURSOR RIGHT
Y: CURSOR UP and CURSOR DOWN
Z: HOME and END
UNIX : Pushbuttons X+,
X-, Y+, Y-, Z+, Z-
mouse navigation on: middle
mouse button pressed
Rotating:
Windows: Faktors >
Rotations 3D
The rotations around X, Y
and Z axises are defined with Factors > Rotations 3-D:ROTX, ROTY and ROTZ. Default
values are 0.
With the F2 . . F7 keys the structure can be revolved in steps of 10 degrees.
UNIX : Pushbuttons RX+,
RX-, RY+, RY-, RZ+, RZ-
Turn in steps of 10
degrees. Pushbutton Rot 0 resets all rotations to 0.
mouse navigation on: right
mouse button pressed
Enlarging Deflections:
Windows: Factors >
Deflections
UNIX: Text fields FUX, FUY and FUZ
Enlarge the computed
deflections with the factors FUX, FUY and FUZ. Default values are 100.
Attention UNIX: As usual for UNIX, the changes only apply at a respective Return.
However, you can type in all three fields without Return and then press
the Pushbutton <Run> .
Some remarks on
stresses:
Windows:
3D-Effects > Mises Stresses (corners) or icon No. 9 from left
3D-Effects > Mises Stresses (elemente) or icon No. 10 from left
UNIX :
Radiobutton Stress C (= corner nodes)
Radiobutton Stress M (= mean value per element)
If you did before a stress
calculation with Z88D (this
is possible and useful for all element types except for beams No.2, No.13 and cams No.5), then you may plot the von
Mises stresses either in the corner nodes or as mean values per each
element. And before running the stress processor Z88D you really had to
calculate the displacements by running Z88F or the iteration solver. Thus, the sequence is:
von Mises stresses in corner nodes. In fact, the stresses are computed not really
in the corner nodes which would lead to very wrong results especially for very
tapered elements but in Gauss points laying in the near of the current corner
nodes. Stresses are computed for just the same number of Gauss points like the
number of corner points. Because often a node is linked to more than one
element the stresses are computed to a mean value from the "corner node"
stresses of all linked elements. This results in pretty balanced stress
shadings which are mostly somewhat lower than the maximum stresses of Z88P,
however. The value of the order of integration INTORD in the header file Z88I3.TXT has no meaning but INTORD should be
greater than 0.
von Mises stresses as a
mean value for each element. The stresses are computed in the Gauss points of the current element,
added and then divided by the current number of Gauss points. This results in a
mean value for the von Mises stress per element. The value of the order
of integration INTORD in the header file Z88I3.TXT is important and INTORD must be
greater than 0. Example: If you enter for INTORD the value 3 when calculating hexahedrons
No.10 then the von
Mises stresses are calculated in 3 x 3 x 3 = 27 Gauss point, added and then
divided by 27.
The stress plot is done by
color shading. You may modify the colors by editing the header files Z88O.OGL
(Windows) or Z88.FCD (UNIX) for your own taste. Of course, for UNIX also the
fonts - this requires some experiments depending on your operating system until
you are (i hope so) satisfied. You need to make this modifications only once or
leave it as it was.
Before that, run a stress
calculation with Z88D. You
did set in the header file Z88I3.TXT the stress flag ISFLAG 1 and the
integration order INTORD > 0. For exact stresses consult the output file
Z88O3.TXT.
Caution: The operator is responsible for
first running a stress calculation by Z88D before using this function. Run Z88F or the Iteration solver Z88I1 and Z88I2 and then Z88D before starting Z88O.
Otherwise some old stress files Z88O8.TXT from earlier calculations are read in
causing totally wrong results !!
Automatic Scaling:
Windows: Autoscale >
No Autoscale, Yes Autoscale
UNIX: Pushbutton AutoS
The Autoscale function
takes care that structures will completely fit on the screen.
Autoscale
activates automatically if a new structure is loaded by File > Structure
File. Autoscale again is deactivated immediately and the hook points to No
Autoscale. You can then scale properly with Autoscale > Yes Autoscale.
However, Autoscale switches again immediately to No Autoscale. Autoscale
> Yes Autoscale is a kind of pushbutton. The explanation above
corresponds to UNIX as well.
Height Ratio:
Windows: File Z88O.OGL
UNIX: file Z88.FCD
The height ratio can be
adjusted to the monitor customization. Therefore, the entry FYCOR exists in
Z88O.OGL (Windows) or Z88.FCD (UNIX). Load a perfectly circular or perfectly
square structure and modify FYCOR untill this structure is plotted perfectly
circular or square on your monitor. Please keep in mind that FYCOR is loaded
with the start of Z88O, so you must re-launch Z88O after a modification in the
files. You need to make this modification only once.
Windows: plot of the von Mises
stresses in the corner nodes of the BMW piston.