2.7 THE
CAD CONVERTER Z88X
2.7.1
OVERVIEW Z88X
The CAD converter Z88X
works in two directions:
(I) You design your
component in a CAD system and generate Z88 data. You cover in the CAD system your component
with a FE mesh or a super-structure following certain rules which follow below,
and add if necessary boundary conditions and material informations. Then make
your CAD system generating a DXF file and start the CAD converter Z88X. The Z88
entry files are produced by Z88X and you can start with the FE analysis.
Windows:
Z88X,
> Type Conversion > 4 from Z88X.DXF to Z88I1.TXT
Z88X,
> Type Conversion > 5 from Z88X.DXF to Z88I* . TXT (default)
Z88X,
> Type Conversion > 6 from Z88X.DXF to Z88NI.TXT
... and > Compute > Go
UNIX:
z88x
-i1fx (Z88X.DXF to Z88I1.TXT, "I1 from X")
z88x
-iafx ( Z88X.DXF to Z88I* . TXT, "I all from X", )
z88x
-nifx (Z88X.DXF to Z88NI.TXT, "NI from X")
... or
use the Z88-Commander with the proper option for Z88X
(II) Convert your Z88
entry files into CAD data. This is very interesting for Z88 data sets already existing, for
controls, for completions of the FE structure, but also for plotting the FE
structure by CAD program.
Windows:
Z88X,
> Type Conversion > 1 from Z88I1.TXT to Z88X.DXF
Z88X,
> Type Conversion > 2 from Z88I* . TXT to Z88X.DXF
Z88X,
> Type Conversion > 3 from Z88NI.TXT to Z88X.DXF
... and
> Compute > Go
UNIX:
z88x
-i1tx (Z88I1.TXT to Z88X.DXF, "I1 to X")
z88x -iatx (
Z88I* . TXT to Z88X.DXF, "I all to X", )
z88x
-nitx (Z88NI.TXT to Z88X.DXF, "NI to X")
... or
use the Z88-Commander with the proper option for Z88X
Since the converter is
completely compatible in both directions, you can execute the possibilities I
and II in succession as you wish. You will not find any data loss!
That makes a most
interesting variant:
(III) Mixed Operation, e.g.
- Component-and
super-structural layout done in CAD program
- Conversion CAD --->
Z88
- Meshing in Z88
- Conversion Z88 --->
CAD
- Complete FE structure in
CAD e.g. with not-mesh generator capable elements
- Conversion CAD --->
Z88
- Change e.g. material
informations in Z88
- Conversion Z88 --- >
CAD
- Installation of the
boundary conditions in CAD
- Conversion CAD --->
Z88
- FE analysis in Z88
- Etcetera
Which CAD systems can
cooperate with Z88 ?
Well, any CAD systems which
can import (read) and export (write) DXF files. However, we cannot guarantee
any success as some of the CAD guys are changing their DXF definitions from
month to month. Z88 V10 has been intensively tested together with the different
AutoCAD LT versions for Windows of Autodesk, and AutoDesk's DXF guidelines have
been rgarded as the inventor of the DXF interface, according to AC1009 and
AC1012.
The general philosophy
of a CAD - FEA data interchange:
CAD files containe nondirectional
informations. It is
only a wild collections of lines, points and texts, stored in the order of its
production to make things worse.
Basically, a FEA system
needs topological information which most CAD systems cannot supply. The FEA system must know that these
and those lines form a finite element and that these and those points are
included in this element. This could be made on principle if one would design
in the CAD system in a quite firmly predefined order. Experiments showed that,
indeed, this is possible for very simple components, but it will not work for
complex components. And, yes, this is what one wants to do in practice: FE
analysis on complex structures !
These difficulties are
known for a long time and appear at the data interchange of CAD - NC data
likewise. As a proper work-around, integrated CAD - FEM systems do exist which
are only to acquire at a very high price.
Another attempt enlarges
(better: blows up) the CAD system by e.g. additional modules or macros to such
an extend, that partly utilizable FEA data can be produced. This is done
frequently. It bears the disadvantage that it neither works well for all CAD programs
nor works quite exactly even for the same products of one CAD program
manufacturer.
Another attempt does
nothing in the CAD system. The FEA system, however, contains a kind of mini- or
semi-CAD system, in order to process or rework the raw and totally useless CAD
data into FEA data, but only by massive support of the operator. The
disadvantage is here, that the operator must master two CAD systems, and the
integrated semi-CAD system has not got the performance and power of the real
CAD system.
At Z88 these
difficulties are solved as follows:
1: FROM
CAD SYSTEM TO Z88:
1.1 in the CAD
system:
Remark: This point case
1.1 will be explained in greater detail in chapter 2.7.2. This is a summary.
(1) Design your component. Order
and layers as you like.
(2) Define the FEA
structure or the super structure by lines and points. Any order and layers,
therefore unproblematic and fast.
(3) Number the nodes with
the TEXT function on the layer Z88KNR. Any order, therefore unproblematic and
fast.
(4) Write the element
information with the TEXT function on the layer Z88EIO. Any order, therefore
unproblematic and fast.
(5) Outline each element
with the LINE function on the layer Z88NET. The only section with firm work
rules and orders (because of the topological informations).
(6) Write general
information, material information and control information for the stress
processor Z88D on the Layer Z88GEN.
(7) Define the boundary
conditions on the layer Z88RBD.
(8) Export or store your
3-D model or 2-D drawing under the name Z88X.DXF.
1.2 in Z88: Starts
the CAD converter Z88X
You can choose depending on
your input data whether
* A mesh generator file
Z88NI.TXT or
* A file of the general
structure data Z88I1.TXT or
* A complete Z88 data
set with Z88I1.TXT, Z88I2.TXT and Z88I3.TXT
is produced. Everything
else runs automatically.
1.3 in Z88: Starts
other Z88 modules
Check output files produced
by Z88X once more with the Filechecker Z88V.
Run the FEM analysis by
starting the different Z88 modules at your choice:
*
Iteration Solver Z88I1/Z88I2
2: FROM
Z88 TO CAD PROGRAM
2.1 in Z88: Input
files Z88xx.TXT
You have produced the input
files
*
Mesh generator file Z88NI.TXT or
* File of the general
structure data Z88I1.TXT or
* complete Z88 data set
with Z88I1.TXT, Z88I2.TXT and Z88I3.TXT
either by an editor, a
word processing program, EXCEL or an own routine or by modifying data files that came from the CAD
converter Z88X.
2.2 in Z88: Launch
CAD converter Z88X
Define which Z88 input
files shall be converted. The DXF-file produced by Z88X is Z88X.DXF. If the
input files contained polar- or cylindrical coordinates, they are converted
into cartesian coordinates.
2.3 in the CAD
system:
Import the DXF file
Z88X.DXF. Save the loaded model or drawing under a valid CAD name (e.g. at
AutoCAD name.DWG) and work with the drawing. You can switch off and switch on
the different Z88-layers as you like.
2.7.2
Z88X IN DETAIL
Proceed in the following
steps and reserve the following layers
Z88GEN: Layer for general information (1st
input group in the mesh generator input file Z88NI.TXT and general structure data file Z88I1.TXT). Include further the material
information (4th input group in the mesh generator input file Z88NI.TXT and
general structure data file Z88I1.TXT). Add, if necessary, the data of the
stress parameter Z88I3.TXT.
Z88KNR: Layer including the node numbers.
Z88EIO: Layer including the element information
like element type and in the case of mesh generator input file Z88NI.TXT
control information for the mesh generator.
Z88NET: Layer containing the mesh which was
drawn or outlined in defined order.
Z88RBD: Layer containing the contents of
the boundary conditions file Z88I2.TXT.
A further layer, Z88PKT,
is produced by Z88X if you convert from Z88 to CAD. It shows all nodes with a
point marker so that one better recognizes the nodes. For the reverse step,
from CAD to Z88, it is completely insignificant.
1st step: Design your component in the CAD
system as usual. You do not need to maintain a definite order and you can use
any layers. It is highly recommended to put symbols on one layer, edges on
another layer, dimensions on a third layer, invisible lines and center lines on
a forth layer and so on. This enables you to remove all unnecessary information
in the next step.
2nd step: Plan your mesh subdivision, that
means suitable finite element types and their distribution. Subdivide the FE
structure or the super structure into elements by lines, insert all
points which are not yet existing (for example intersection points or
end-points of lines are usable). Any order and layer. However, it is
recommended not to use the Z88-layers like Z88NET, Z88GEN, Z88PKT, Z88KNR,
Z88EIO and Z88RBD. Better define any new layer for this or use already
available layers from step 1.
3rd step: Define the Z88-Layer Z88KNR and
make it the active layer. Catch or trap every FE node, which were already defined
in the 1st step by your construction or have been completed in the 2nd step,
and number them. Write to every node P blank node-number e.g. P 33,
with the TEXT function of the CAD program. Be very careful to snap exactly the
node and attach the number exactly to the node's location. Take your time ! With
the snap modes of AutoCAD (intersection point, end-point, point etc.) this
works well. Choose any order of the work consequence as you like, you can well
number the node 1 (P 1), then the node 99 (P 99) and then node 21
(P21). However, the numbering of the nodes must make sense and must be
meaningfull for a FE analysis. You define which node in node 99 and
which other node reads 21. Bad node numbering can cause heavy (but not really
necessary) storage needs and computing times. Consult a good FEA book for this
aspects.
4th step: Define the Layer Z88EIO and make it
the active layer. Write the element information with the TEXT function anywhere
(of course, it looks nicer with the element infos placed in middle of the
respective finite element or super element). The order of the work consequence
is up to you. You can describe element 1 first, step to the attaching element
17 and then proceed with element 8. However, your element choice and
description must make sense for a FE analysis. The following information have
to be written:
For all
finite element types from 1 to 20 (not 16 and 17):
FE Element number
Element type
Write into one line,
separate each item by at least one blank.
Example: An Isoparametric
Serendipity Plane Stress Element No.7 is supposed to get the element no. 23. Write
e.g. into the middle of the element with the TEXT function FE 23 7
For
super-elements 2-dimensional No. 7, 8, 11, 12 and 20
SE
Element number
Super-element type
Type of the finite elements to be produced by meshing
Subdivision in local x direction
Type of subdivision in local x direction
Subdivision in local y direction
Type of subdivision in local y direction
Write into one line,
separate each item by at least one blank.
Example: Sudivide an
Isoparametric Serendipity Plane Stress Element with 12 nodes ( Element type 11)
used as super-element into finite elements of type 7, i.e. Isoparametric
Serendipity Plane Stress Elements with 8 nodes (Element type 7). Subdivide in
local x direction three times equidistantly and subdivide in local y direction
5 times ascending geometrically. The super element is supposed to have the
number 31. Write e.g. into the middle of the element with the TEXT function: SE
31 11 7 3 E 5 L (e or E for equidistant is equivalent)
For
super-elements 3-dimensional Hexahedrons No.10
SE
Element number
Super-element type
Type of the finite elements to be produced by meshing
Subdivision in local x direction
Type of subdivision in local x direction
Subdivision in local y direction
Type of subdivision in local y direction
Subdivision in local z direction
Type of subdivision in local z direction
Write into one line,
separate each item by at least one blank.
Example: Subdivide an
Isoparametric Serendipity Hexahedron with 20 nodes (Element type 10) as super
element into finite elements of the type Isoparametric Hexahedrons with 8 nodes
(Element type 1). Subdivide equidistantly three times in local x direction, 5
times ascending geometrically in local y direction and subdivide equidistantly
4 times in local z direction. The super element is supposed to have the number
19. Write e.g. into the middle of the element with the TEXT function:
SE 19 10 1 3 E 5 L 4 E (e or E for equidistant is
equivalent)
5th step: Define the Layer Z88NET and make it
the active layer You need concentration for this step, because a firm and rigid
work consequence must now be kept because of the topological information. One
of the most important information, the coincidence, is defined in this step,
that means which elements are defined or outlined by which nodes. Choose a
proper color which differates well from the colors used till now and remove all
superfluous information by switching off unused layers.
Select the LINE command and
select the proper snap options e.g. points, intersection points and, if
necessary, end-points.
Start at the first element.
For Z88 the first element is the element with which you start now, that means
the one which you have chosen for your first element (SE 1 or FE 1). Select
the node you want to be the first node of this element (this can be e.g.
globally the node 150) and draw a line to the node which shall be the second
node of this element (this can be e.g. globally the node 67). From there, draw
a line to the third node of this element (this can be e.g. globally the node
45). Connect all required nodes with lines and draw at last a line to the
starting point, the first node, then quit the LINE function.
Then you do the same with
the second element. Remember: You determine with this order which of the
elements will be the real second element now. In the previous 4th step you
have only defined what kind of element the second element is. You determine
here how the element is defined topologically.
The third element follows
and so on. If you should make a mistake at the outlining of an element then
delete all previous lines of this element (e.g. with an UNDO function) and
start again at the first point of the questionable element. But if you notice
now just outlining element 17 that you have made a mistake at element 9 , then
you must delete all lines of the elements 9 to 17 and restart with element 9.
For your comfort, you
must keep the following outline orders which partly differ from the orders
shown at the element descriptions when entering the coincidence by hand. Z88X
then sorts internally correctly.
Example: The coincidence
for the element type 7
is as follows in the element description : First the corner nodes, then the
middle nodes, reads 1-2-3-4-5-6-7-8. The coincidence list must look like this
in the Z88 input files. However, for Z88X' use for comfortably outlining the
elements the order is 1-5-2-6-3-7-4-8-1 (left picture) respectively
A-B-C-D-E-F-G-H-A (right picture):
Following the CAD
outline orders for all elements but No. 16 and No.17 (because these
tetrahedrons can only machine- generated, nearly impossible by hand):
Element No.7 and No.20 :1 - 5 - 2 - 6 - 3
- 7 - 4 - 8 - 1
Element No.8: 1 - 5 - 2 - 6 - 3 - 7 - 4 - 8 - 1
Element No.11: 1 - 5 - 6 - 2 - 7 - 8 - 3 - 9 - 10 - 4 - 11 - 12 - 1
Element No.12: 1 - 5 - 6 - 2 - 7 - 8 - 3 - 9 - 10 - 4 - 11 - 12 - 1
Element
No. 2, 4, 5, 9, 13: Line from node 1
to node 2
Element No.3,
14, 15 and 18 :1 - 4 - 2 - 5 - 3 - 6 - 1
Element No.6: 1 - 2 - 3 - 1
Element No.19: 1 - 2 - 3 - 4 - 5 - 6 - 7 - 8 - 9 -10 - 11 - 12 - 13 - 14 - 15 - 16 - 1
Upper
plane: 1 - 2 - 3 - 4 - 1, quit LINE function
Lower plane: 5 - 6 -7 - 8 - 5, quit LINE function
1 - 5, quit LINE function
2 - 6, quit LINE function
3 - 7, quit LINE function
4 - 8, quit LINE function
Upper
plane: 1 - 9 - 2 - 10 - 3 - 11 - 4 -12 - 1, quit LINE function
Lower plane: 5 - 13 - 6 - 14 - 7 - 15 - 8 - 16 - 5, quit LINE function
1 - 17 - 5, quit LINE function
2 - 18 - 6, quit LINE function
3 - 19 - 7, quit LINE function
4 - 20 - 8, quit LINE function
6th step: Define the layer Z88GEN and switch
it active. Write with the TEXT function into a free space (well into any place
of your drawing):
6.1 general information, i.e. the first input group of the
general structure data Z88I1.TXT or the mesh generator file Z88NI.TXT,
In case of Z88I1.TXT (i.e. FE mesh):
Z88I1.TXT
Dimension of the structure
Number of nodes
Number of finite elements
Number of degrees of freedom DOF
Number of material information lines
Coordinate flag (0 or 1)
Beam flag (0 or 1)
Plate flag (0 or 1)
Write into one line,
separate each item by at least one blank. Definitely write in the layer
Z88GEN.
Example: 3-dimensional FE structure with 150
nodes, 89 finite elements, 450 degrees of freedom, 5 material information
lines. Input with cartesian coordinates, structure contains neither beams No.2
nor beams No.13. Thus Z88I1.TXT 3 150 89 450 5 0 0
In case of Z88NI.TXT (i.e. super structure):
Z88NI.TXT
Dimension of the structure
Number of nodes
Number of super element
Number of degrees of freedom DOF
Number of material information lines
Coordinate flag (0 or 1)
Beam flag (must here be 0!)
Plate flag (0 or 1)
Trap radius header flag (most 0)
Write into one line,
separate each item by at least one blank. Definitely write in the
layer Z88GEN.
Example: 2-dimensional super-structure with
37 nodes, 7 super elements, 74 degrees of freedom, one material information
line. Cartesian coordinates, no beams (anyway forbidden in the mesh generator
file), no plates, use default for trap radius. Thus Z88NI.TXT 2 37 7 74 1 0
0 0 0
6.2 Material information
lines:
For every material
information one
separate line:
MAT
Number of the material information
This material information starts with element no. abc inclusively
This material information ends with element no. xyz inclusively
Young's Modulus
Poisson's Ratio
Integration order (from 1 to 4)
Cross section value (e.g. for plane stress elements thickness, for trusses
cross section area)
... And if beams (but
not plates !) are defined in addition:
Second moment of inertia
yy (bending around yy axis)
Max. distance from neutral axis yy
Second moment of inertia zz (bending around zz axis)
Max. distance from neutral axis zz
Second moment of area (torsion)
Second modulus (torsion)
... And if plates
(but not beams !) are defined in addition:
area load
Write into one line,
separate each item by at least one blank. Make sure to write in the
layer Z88GEN.
Example: The structure has 34 super elements
type 7 with varying thickness: Elements 1 to 11 have thickness 10 mm, elements
12 to 28 have 15 mm and elements 29 to 34 have 18 mm. Material steel.
Integration order shall be 2.
MAT 1 1 11 206000. 0.3 2
10.
MAT 2 12 28 206000. 0.3 2 15.
MAT 3 29 34 206000. 0.3 2 18.
6.3 Stress parameters:
The input line of the
stress parameter file Z88I3.TXT
Z88I3.TXT
Integration order (0 to 4)
KFLAG (0 or 1)
Von Mises stresses (0 or 1)
Write into one line,
separate each item by at least one blank. Make sure to write in the
layer Z88GEN.
Example: The structure uses finite elements
type 7. The stress calculation is supposed to be carried out in 3*3 Gauss
points per element, stresses are supposed to be calculated in addition radially
and tangentially. Compute von Mises stresses, too. Thus Z88I3.TXT 3 1 1
7th step: Define the Layer Z88RBD and
activate it. Write with the TEXT function into a free space (well into any
place of your drawing):
7.1 number of the
boundary conditions,
i.e. the first input group of the boundary condition file Z88I2.TXT
Z88I2.TXT Number of the
boundary conditions
Write into one line,
separate each item by at least one blank. Make sure to write in the
layer Z88RBD.
Example: The structure has 10 boundary
conditions, e.g. two loads and eight constraints i.e. support reactions. Thus Z88I2.TXT
10
7.2 Boundary conditions, the second input group of the
boundary condition file Z88I2.TXT
RBD
Number of the boundary condition
node number
Degree of freedom
Header flag force/displacement (1 or 2)
Value
Write into one line,
separate each item by at least one blank. Make sure to write in the
layer Z88RBD.
Example: The structure shall be a truss-
framework. Node 1 shall be fixed in Y and Z, node 2 fixed in X and Z. Nodes 7
and 8 have a load of 30,000 N each in Z direction, pointing down. Node 19 is
fixed in X and Z and node 20 is fixed in Y and Z. Thus
RBD |
1 |
1 |
2 |
2 |
0 |
RBD |
2 |
1 |
3 |
2 |
0 |
RBD |
3 |
2 |
1 |
2 |
0 |
RBD |
4 |
2 |
3 |
2 |
0 |
RBD |
5 |
7 |
3 |
1 |
-30000 |
RBD |
6 |
8 |
3 |
1 |
-30000 |
RBD |
7 |
19 |
1 |
2 |
0 |
RBD |
8 |
19 |
3 |
2 |
0 |
RBD |
9 |
20 |
2 |
2 |
0 |
RBD |
10 |
20 |
3 |
2 |
0 |
8th step: Export (store) your model or
drawing under the name Z88X.DXF in the DXF file format. For precision of
decimal positions take the default value which the CAD program suggests. Take
care that you export directly into the Z88-directory or you must copy the file
Z88X.DXF by hand into the Z88-directory, because the CAD converter Z88X expects
the input and output files in the same directory, where Z88X is located.
You may launch the CAD
converter Z88X then.
Note: If you want to convert Z88 text
files as Z88X.DXF to CAD, you can choose the text size which applies to all
texts like node numbers, element numbers etc. This is very important from time
to time because there is no possibility in e.g. AutoCAD to change the text size
globally afterward. From time to time you must make some trys untill you have
found the suitable text size for the respective Z88 file. Simply call Z88X once
more with another text size.
Windows: In Z88X: File
> Textsize
UNIX: z88x -i1tx | -iatx
| -nitx | -i1fx | -iafx | -nifx -ts number
Caution, valuable note: Use the Z88X keywords "P
number, FE values, SE values, MAT, RBD, Z88NI.TXT, Z88I1.TXT, Z88I2.TXT and
Z88I3.TXT" only where they are really needed. Take care that they do
not appear in other drawing items ! Otherwise Z88X cannot interpret the DXF
file properly and will flag error messages !