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PATRAN Beginner’s Guide
Arul M BrittoApril 15, 2005
Contents 1
Introduction
How to Start a PATRAN Session
Creating a New Database
Opening New Database
Leaving a PATRAN Session
Resuming a Previous Session
Steps Involved in an analysis
Units
Create Geometry
Geometry..............................................
Create Points
Create Curves.......................................
Checking and Correcting Mistakes
Check the Points.....................................
Check the Curves
Deleting Points and Curves...............................
Error and Warning Messages
Entity Labels............................................
Checking the Surface Normal
Loads and Boundary Conditions
Define the Load variation function
Loads and Boundary Conditions
Load Application
Define Element Properties
Define Material Properties....................................
Element Properties
Finite Element Mesh
Create Mesh Seeds
Create the Mesh..........................................
Unpost the Geometry.......................................
Equivalence and Optimize....................................
Check Load/BCs
Loads/BCs.............................................
Create a Load Case
CONTENTS
CONTENTS
Perform the Analysis
Submit a ABAQUS Analysis...................................
Accessing the ABAQUS Results from PATRAN........................
Post Processing
Changing Display Parameters..................................
Hard Copy of Plot.........................................
Stress Fringe Plot
Using Graph (XY) Plot to plot Stress variation.........................
To Quit from PATRAN
10 Files
11 Troubleshooting
12 Frequently Asked Questions
HOW TO START A PATRAN SESSION
1
Introduction PATRAN is a pre and post processing package for the finite element program ABAQUS. In additionit has the capability of finite element analysis. This manual has been prepared for users who want touse ABAQUS for finite element analysis. It also describes how once the ABAQUS analysis is run onecould carry out some post processing.
This manual tells the user how to run PATRAN in the Teaching system. It also has an example prob- lem on how to set up the data for an ABAQUS analysis using PATRAN. It explains how a ABAQUSjob can be submitted from within PATRAN and after the successful completion of the job how to usethe post processing facilities. 2
How to Start a PATRAN Session Find a suitable terminal for running PATRAN. These are the X-terminals in the main area of the DPO,the PC-based X-terminals at the East end of the DPO, and the PC-based X-terminals in the EIET Lab(Inglis building).
- Log in using your user ID and password.2. Run a window manager (example :
twm&
). This is recommended. It is useful in the sense that
the PATRAN windows can be moved around and scaled. Do not run
start, fvwm or fvwm
- Create a subdirectory and move to it.
Type
mkdir patran
(you need to do this only once.)
Type
cd patran
(you need to do this for each session.)
It is a good idea to re-start PATRAN in the directory in which the database resides. Even thoughit is possible to start PATRAN in any directory and then change to the directory in which thedatabase is, it is not recommended. The reason is any new files created by PATRAN (examplesession files) will be placed in the directory from which PATRAN was started.If you do not know which is your current directory then type
pwd
. This will list the name of the
current working directory.Some useful unix commands : ls^
-l^
- will list all the files in the current directory.
cd
- to return to your HOME directory. rm
file-name
- to delete a file. Replace
file-name
with name of file to be deleted. Example
: rm bracket.datHere the subdirectory is called patran. All the PATRAN related files will be placed in this di-rectory. When you start a session of PATRAN ensure that there is enough unused disk spaceavailable within your quota to complete the current exercise. Contact the Computer Operators ifyou require the quota to be increased.Alternatively you can work in the
/tmp
directory. However files created in the
/tmp
directory
are deleted automatically after 48 hours. Therefore if you require these files please copy them toyour home directory within that time. First check whether there is enough free disk space. If thefree disk space is less than 10 Mbytes do not use the
/tmp
directory.
Type
bdf
/tmp
Check the amount available under the heading
avail
. This will be in KBytes.
Type
cd
/tmp
Type
mkdir
userid
. Here substitute your user-id for
userid
Type
cd
userid
to move to this directory.
If you start PATRAN from here then all the files created will be placed in this directory.
HOW TO START A PATRAN SESSION
Show
Reset graphics
Undo
Refresh graphics
Heartbeat
Labels
HideLabels
FrontView
Interrupt
Figure 1: Main Form
- Type
patran
(Note : must be in lower case)
Warning
Warning : Do not use the
start
or
fvwm
window manager or any of its derivatives
(fvwm2). In the past some problems have been encountered while running PATRAN withfvwm.
The MSC/PATRAN
Main form
( Figure 1
, also see Appendix A, page 3) should appear
across the top of the screen.
At the top of the main form are1. the pull-down menus, the on-line help, system icon buttons and the heartbeat.
Below that are
- the application radio buttons3. the toolbar icons4. the history window area5. the text command line
in that order (See Figure A1, in Appendix A).The following message should appear in the history window : MSC.PATRAN 2004 r2 has obtained 1 concurrent license(s) from FLEXlm .... Then all is well.
The MSC/PATRAN status indicator is displayed between the “interrupt” and
“undo” icons. This is the “ heartbeat”.
- Green means ready and waiting.2. Blue means busy, but can be interrupted.3. Red means busy but not interruptible. However if you find that PATRAN is taking a long time
to carry out routine tasks try clicking the Middle Mouse button in the viewport area. However if you get a message saying that PATRAN could not get a licence then try typing
patran
again. If you still get the same message please contact the Computer Operators ([email protected])and they should be able to sort out the problem.
If the licence was obtained successfully then wait for the heartbeat to turn Green. Only the ‘File’ command along the top row will appear in black. At this point that is the only command that can beselected. The rest of the menus are greyed out.
In the rest of this document the actions to be taken by the user for completing the exercise is denoted by the symbol
Before starting the exercise
HOW TO START A PATRAN SESSION
Opening New Database
Template Database Name
New Database
Filter
/amd_tmp/needle−16/usersn/userid/patran/*.db
Directories
Database List
Change Template ...
Click on this
.........................................../patran/............................................/patran/.. bracket
OK
/export/../patran2004r2/template.db
Modify Preferences ...
Type
New Database Name
Cancel
Filter
bracket
Figure 4: New database
the box below :
Cancel
Filter
OK
Database Template
/export/../patran2004r2/*.db.........................................../patran/............................................/patran/..Template Name
Database Template List
ABAQUS analysis.
abaqus.dbbase.db
Click on this for
Filter Directories
Then this nameshould appear in
template.db
Figure 5: Change template
HOW TO START A PATRAN SESSION
Leaving a PATRAN Session
New Model Preference^ Model Preference for :
bracket.db Tolerance
Analysis CodeAnalysis Type :Structural
This should display ABAQUS
Change this to 100.
Approximate MaximumModel Dimension :
Use the
This is the largest dimensionof the example problem being considered.
based on ModelDefault
or
Deletechar
Reset
OK
key
to deletecharacters
Delete
ABAQUS
Figure 6: Model Preference
- Creating journal file bracket.db.jou at
date
time
Note that “.db” is automatically appended to the name. This denotes “database”. An empty view- port should appear with a black background.
The axes will be displayed.
The cross hair symbol
represents the origin. The name of the database is displayed at the top of the viewport.
Appendix A contains a brief review of the notations used in PATRAN. It also explains the purpose of the five icons (repaint, window layering, cleanup, abort and undo) displayed at the top right handcorner.
When a new database is opened, the following form appears (see
Figure 6
^ Click on the box marked ‘Model Dimension’ and change the 10 to 100.For the current example problem this is the
largest dimension
. The Tolerance parameter which
is used later is calculated based on this value. Therefore it is important to get this right approx-imately. Getting this wrong can create a few problems later. The tolerance is taken as 0.0005 ofthe largest dimension, so it will 0.05 for the current example. More on tolerance later. Click on the OK button. This will close that form. In general when entering/editing data in boxes in a form you need to click on the box
first
to
indicate to the program that you wish to do so. In the rest of this document when reference is made toentering data in a box it will be assumed that you have to click on that box first even though this maynot be explicitly stated. Where there are exceptions to this rule it will be pointed out.
The next step is to create the geometry.
Leaving a PATRAN Session
You can quit the current session at any time you wish. Make sure that the heartbeat is Green.
^ Then Click on the
Quit
button.
STEPS INVOLVED IN AN ANALYSIS
Resuming a Previous Session
All the information input and actions taken are stored in the PATRAN database so there is noneed to save before quitting.However if for some reason you want to save a copy of the database (for example to use it as atemplate) then Click on the
File
button Choose the
Save a copy...
option. Set the toggle to save a copy of the
journal file. Enter an appropriate name for the saved database.Always save a copy of the journal file : *.db.jou (here * represents the name of the database). Then wait for the Green light and choose the
Quit
option.
Another situation where you may want to save a copy of the databse is if you want to save the results of the current analysis before making some changes (for example using a different elementtype) and re-running the analysis and comparing the two sets of results. Then it will be a good idea towork on a copy of the original database.
However you have to have enough spare disk space (quota) to be able to save a second copy of the database.
First time users can skip the next section (section 2.3). It explains how to open an existing database
to continue a previous session. 2.
Resuming a Previous PATRAN Session Change to the directory where the the PATRAN database are present by typing ‘cd patran’. Choose
Open...
instead of
New...
from the
File
menu.
^ Select the appropriate
db
file from the list of ‘available files’, by clicking on it.
That file name should appear in the box marked ‘Existing Database Name’. Then click on the ‘OK’ button to choose that file. It is recommended that you use separate databases for each new analysis.If you want to look at a different PATRAN databsse then use
File / Close
to close the current
database and then open the other database. 3
Steps Involved in an analysis The following is the order adopted for the various steps required for the current example.
- Decide on what units to use2. Create Geometry3. Specify Boundary Conditions and Loading on the Geometry4. Specify Material properties5. Assign material properties to geometry6. Create finite element mesh7. Create a loadcase8. Carry out the analysis9. Read results10. Post processing of the results
CREATE GEOMETRY
Units
But one does not have to strictly adhere to this sequence. PATRAN provides flexibility. The user can choose the sequence best suited for the problem in hand.
For example it is better to assign the material properties to the geometry rather than the finite element mesh. This way if you decide to change the mesh you don’t have to re-assign the materialproperties.
Similarly where necessary the specification of the boundary conditions or loading can be delayed until after the mesh has been generated. In general boundary conditions and loading are specified inthe geometry.
The finite element mesh can be created immediately after the geometry has been created. But there
are good reasons to delay it. 3.
Units
There is no default set of units assumed with ABAQUS. It is the user’s responsibilty to choose anappropriate set of units and enter all values using the correct units. For example the x co-ordinate of apoint is 20 mm. If you are using
for Length the value to be entered is
. However if you are using
^ for Length then you need to enter
^20
. The same applies to all numbers being entered which have
units associated with it.
From the PATRAN program’s point of view units doesn’t mean anything (all numerical entries are just numbers). It means that all numerical input are treated as just numbers by PATRAN. For structuralproblem the user should decide on the units for Length and Force. For time dependent problems theunit for Time also has to be chosen. Example :
Length -
(metres)
Force -
(Newtons)
Time -
(seconds)
Then all dependent parameters must be specified in a consistent set of units. For example stiffness should be specified in
and density in
For the example given here the SI(mm) units are used.^ Quantity
SI
SI(mm)
SI
US Unit(ft)
US Unit(inch)
Length
Force
Mass
(
Time
s^
s^
s^
s^
s
Stress
(N/
)
(N/
(
)
Energy
(
J)
Density
lbf
Note
Always choose your set of units before starting to create the geometry ie entering the point co-ordinates.
Because this affects the stiffness parameters, loading etc.
This will
avoid unnecessary scaling of the results later. 4
Create Geometry The model is a simple L bracket which is fixed along one side (vertical) in both x andy directions.
Part of the other side (horizontal) is subjected to a triangular distribution
which varies from 100
to 0 at the tip
(Figure 7)
. This is an elastic analysis and
contains a single load step. The analysis consists of a single increment. The
SI(mm)
units have been
chosen for the present example.
The bracket is 100 mm long along its side and is 20 mm thick and is 75 mm wide. This is to be anlysed as a
Plane Stress
problem.
Points, Curves and Surfaces and Solids (for 3D) form the Geometric Entity. The Nodes and Ele- ments of the FE mesh form the FE Entities.
The bracket is to be divided into 3 surfaces. There are a number of ways to create a surface with straight edges.
CREATE GEOMETRY
Geometry
Internal
(^2080)
Y Z
X
3
5 3
2
1
2 1 1
6 surface 1.
2
surface 2.
surface 1.
surface 3.
surface 3.
4
8
20
80
7
ofsurface edges.
curves,
numbering
surface
Figure 9: L Bracket : The Surfaces
The
Figure 9
shows the bracket divided into three surfaces. It is created using eight points and two
curves.
The geometry form is shown in
Figure 10
. You will also notice a column of icons with the heading
‘Pick’ displayed alongside the form. This is known as the
Select Menu
If you move the cursor from icon to icon in the select menu, text explaining each icon will pop up. This is useful when picking entities. You choose an appropriate icon from this menu when needed.
The default icon is the first one (shown in reverse video ie highlighted). This icon means that the coordinates of the points are directly entered. More on this later. 4.1.
Create Points
The default setting of this form is for specifying directly the XYZ coordinates for the points. Notice the2 boxes labelled ‘Point ID List’ and ‘Point Coordinates List’. The first point is to be placed at the origin.
^ Click on the
Apply
button to create the first point at the origin ( [0, 0, 0] ).
The point number is automatically incremented for the next point. Click on the ‘Point Coordinates List’ and enter the coordinates 20 0 0 and click on the
APPLY
button. Note that the co-ordinates are enclosed by square brackets ( [ ] ). If you make any mistakes click on the ‘undo’ icon next the MSC label (top right hand corner, last icon). This will undo the last command. In general, you can only undo the last command.
CREATE GEOMETRY
Geometry
At this stage you could enter the co-ordinates [ 0 80 0 ] for the 3rd point and finally [ 20 80 0 ] for the 4th point co-ordinates, in order to create the first surface. However instead of that let us use a differentmethod to create the surface.
Figure 10: Geometry Form
Create Curves ^ Change the ‘Object’ to ‘Curve’. This is done by pressing the left mouse button over ‘Point’ andchoosing ‘Curve’ by moving the mouse (while holding down the left mouse button) to that menuoption and releasing the mouse button. ^ Now check that the ‘Method’ is set to ‘Point’. The form should be as shown in
Figure 11
Notice the cursor (indicated by I) at the box marked ‘ Starting Point List’. The bottom 2 boxeswhere PATRAN expects data to be entered both deal with
Points
. Whichever point is selected
would be automatically placed in the first box marked ‘Starting Point List’. Click on
Point 1
PATRAN now anticipates that the next selection will be the ’Ending Point’. So without clickingon the box marked ‘Ending Point List’ click on the
Point 2
Now this label should appear in the 2nd box and without having to click on APPLY (because AutoExcecute is SET) the 1st Curve will be created and displayed. The curve and its label will be inYellow.
The entity selection (Selecting Point 2) for the last box acts as a trigger and executes the above command.
First time users might find this a little disconcerting. The ‘Auto Execute’ button can be de-activated by clicking on it. Then you need to click on APPLY to complete the action.
The next step is to create the
Curve 2
by translating
Curve 1
CREATE GEOMETRY
Geometry
Figure 11: Constructing lines
^ Choose the Action : ‘Transform’ instead of ‘Create’.Notice that the Curve ID List is displaying 2 in readiness for the next curve. ^ Change the ‘Object’ to ‘Curve’ and the ‘Method’ to ‘Translate’.The form is as shown in
Figure 12
The curve 2 is created by translating curve 1 in the y direction by 80 mms.^
This is done by changing the ’Translation Vector’ to
.
Here DO NOT press the RETURN key after entering the ’Translation Vector’ because the form is not complete.
Otherwise a Window will appear with an error message.
If it does click on OK to
acknowledge it in order to proceed.
Pressing the RETURN key in any of the boxes where the data are typed has the same effect as executing the current task i.e. clicking on the APPLY button.
Therefore as a rule when typing in data refrain from pressing the RETURN key even if it is the last box or entry which would complete the data input to that form.
This might lead to the tendency of pressing the RETURN key automatically whenever typing in data in a box even when the form is not complete.
Leave the repeat count at 1, because we only require 1 curve to be created.^
Click on the box marked ‘Curve List’ and then click on Curve 1. The Curve 2 will be displayedwithout having to click on ‘APPLY’, if ‘Auto Execute’ is ON.The next step is to create the surface using these 2 curves. Change the ‘Action’ to ‘Create’. Change the ‘Object’ to ‘Surface’ and the ‘Method’ to ‘Curve’.The form should be as shown in
Figure 13
:^15
CREATE GEOMETRY
Geometry
Figure 12: Translate Curve
CREATE GEOMETRY
Checking and Correcting Mistakes
Figure 15: Creating surface - XYZ method
^ Click on the second box (marked ‘Vector Coordinates List’) and then change it to
.
Leave the repeat count at 1, because only 1 surface is to be created. Click in the box marked ‘Origin Coordinates List’ and then click on ‘Point 4’.This should draw the surface in Green and display its number (Surface 3 ). At this point you should have the 8 Points and 3 surfaces on the screen. However if you had made
mistakes you will find that you have more than 8 Points and/or 3 surfaces; do not panic. The nextsection explains how mistakes can be detected and corrected. If there are no mistakes then skip tosection 4.3. 4.
Checking and Correcting Mistakes
If you think that you have made no mistakes then skip the rest of this section (goto section 4.3).
Sometimes the mistakes made may be too many to be able to rectify it. Then it will be quicker to delete everything and make a fresh start. For this
^ Change the ‘Action’ to ‘Delete’ and the ‘Object’ to ‘Any’.Make sure that the ‘Autoexceute’ option is UNSET (In case you want to change your mind).This is a drastic step. With a single action you are going to delete all Geometric entities (Points,Curves, Surfaces).
This warning is mainly for future reference whence dealing with a more
complex/detailed situation. There is no going back. Here it is not that critical (if you make thewrong choice) Draw a box around all the entities in the viewport.It should all change colour to light red.
CREATE GEOMETRY
Checking and Correcting Mistakes
^ Click on APPLY.Otherwise the first thing to check is whether there are any duplicate points and lines. 4.2.
Check the Points ^ Click on ‘Create’ label in the Geometry form and change it to ‘Show’. ^ Also change the other 2 options so that you have Show/Point/Location for Action/Object/Info.The ‘Total in Model’ will display the total number of points that have been created. This shouldbe 8. ^ Click on the box marked ‘Point List’ and type ‘Point 1’, and click on ’Apply’.This will display a form with the heading ‘Show Point Location Information’. Check that theco-ordinates are correct for this point. ^ Repeat this procedure for the 2nd point. ^ Click on ‘Cancel’ to close that form.The next section shows how to check the curve data. 4.2.
Check the Curves ^ Change the options so that you have Show/Curve/Attributes for Action/Object/Info.This will display the total number of lines that have been created. ^ Click on the box marked ‘Curve List’ and click on ‘Curve 1’.This will display a form with the heading ‘Show Curve Attribute Information’. It will list theStart and End Points. Check with figure 9 whether that information is correct. ^ Click on the ‘Cancel’ button on this form to close it.Click on the box marked ‘Curve List’ and click on the ‘Curve 2’. Check the information for this line. By now you should be able to identify any mistakes that have been made. 4.2.
Deleting Points and Curves
If you need to delete any entities then do it in the reverse order these were created. For example todelete points, curves and surfaces, delete the Surfaces first then the Curves and then finally the Points.
This is because of the dependency. Since the Surface creation is dependent on Curves and Points. So if you try to delete such a Point then PATRAN will remind you of the dependence and ask whetheryou want to delete the surface as well. To avoid these questions follow the order described.
^ If you need to delete any Curves then change the ‘Action’ to ‘Delete’.
Change the ‘Object’ to
‘Curve’. Click on the box marked ‘Curve List’ and enter the line numbers you want to delete. Then click on the ‘Apply’ button. If you need to delete any points then change the ‘Action’ to ‘Delete’. The ‘Object’ will change to‘Any’. Click on ‘Any’ and change this to ‘Point’. Click on the box marked ‘Point List’ and enter the point numbers you want to delete. Then click on the ‘Apply’ button. Make the necessary corrections and re-create any points, curves and surfaces so that the labels match the
Figure 9
. Otherwise cannot make progress with the exercise.
CREATE GEOMETRY
Error and Warning Messages
Error and Warning Messages
If you have made a mistake then PATRAN may put up an error message in a window. If an OK buttonis displayed then click on this to acknowledge the error. You need to do this in order to continue.
Note
If you find that PATRAN is putting up error messages when you think you have not made any mistakes then it could be because after entering data in the boxes of a formyou pressed the RETURN key. Use the
Apply
or OK button at the bottom of the form
once you have completed all the entries. If there are more than one box of data to beinput, and if you press the return key at the first box after entering the data, then theform is incomplete and this will generate an error message.
Therefore pressing the return key in a box is same as clicking on the
Apply
button.
Avoid pressing the RETURN key after entering data in any of the boxes.
Entity Labels
The label entities are all colour coded (the points Cyan, lines Yellow and surfaces (Green)).
The Show labels/Hide Labels icons in the tool bar operate on the labels/numbers collectively. To use it selectively
^ Click on the pull-down menu
Display
and choose the option
Entity Color/Label/Render...
This will bring up a form which will display the complete list of all the colour coding. Click on ‘Hide All Entity labels’ and ‘Apply’ and this will erase all the geometry entity labels. Torestore it click on ‘Show All Entity labels’ and ‘Apply’. Click on the
Cancel
button to close this form.
This form allows one to selectively choose entity labels to be displayed. ’Label Font Size’ controls the size of the characters.
It is also possible to change the colour used for any of the entities. Just click and hold on the colour
for a selected entity and then select the colour from the palette. You need to make sure that anotherentity does not use the same colour. 4.
Checking the Surface Normal
At this stage it is important to check that the created geometry will give a valid finite element mesh.This is done by checking the direction of the normal to the surface ie the surface’s C3 parametric direc-tion. Using the right hand rule, the C3 direction is determined by crossing the surface’s C1 directionwith the C2 direction. Here the right hand rule is used. The positive surface normal should be in thesame direction as the positive Z axis.
If not the created finite elements will not be accepted by the
analysis module.
^ To check this change ‘Action’ from ‘Create’ to ‘Edit’. Change the ‘Object’ to ‘Surface’ and the‘Method’ to ‘Reverse’ (see
Figure 16
^ Check the square button marked ‘Auto Execute’ to make sure it is
unset
^ Click on the box marked ‘Surface List’ and click on the Surface label 1. ^ Then Click on the box marked ‘Draw Normal Vectors’. ^ Now using the middle mouse button tilt the geometry (Hold down the middle mouse buttonand move the mouse until you can see the direction of the normal vector clearly). The vectorstarts at the centre of the surface and is directed normal to it.If the normal vector is in the same direction as the positive Z axis then the current geometry willcreate a valid finite element mesh.If the normal vector is in the same direction as the positive Z axis
CREATE GEOMETRY
Checking the Surface Normal
Figure 16: Check Surface Normal
x z^
y
Front View Icon
^ then DO NOT click on
Apply
^ If not then you can use the
Apply
button to reverse it. This can be used selectively on individual
surfaces. Note
Note that this check only needs to be carried out for analysing 2D problems (Plane Stress or Plane Strain). However this check is not required if using 3D solid elementsor shell elements.
^ First click on the box marked ‘Reset Graphics’ in this form. This will erase thenormal vector. ^ Repeat the above steps for surfaces 2 and 3. ^ As a final check draw the normal vector for all 3 surfaces.
This is one of the
dialogue boxes where you don’t automatically click on APPLY. This is only done
if necessary.
^ Click on the ‘Front View’ icon in the toolbar. Click on the ‘Fit View’ icon if neces-sary.
LOADS AND BOUNDARY CONDITIONS
Loads and Boundary Conditions
B A
fixed
CreateDisplacement
New set Name
Nodal
DO NOT press
Action:Object:
Click in this box and
Input Data ...
Select this box
−Apply−
OK
enter name ’fixed’.
Click on the "curve" icon to select it. It is the 3rd icon in the select menu.
Click in this box and enter 2 zeroesseparated by spaces between
Type:
eithe geometry or the finite element
Select menu
Pick
Then click on line A. The label ‘surface 1.1’ should
Click on this and the information shouldappear the ‘Application Region’.
Select Application Region...
This selection filters screen picking. In this case only the lines will beselected, although there may be surfaces or points in the area.
Translations <T1,T2,T3>Rotations <R1,R2,R3>
<^
OK
the angled brackets.
GeometryFEM
The Loads and BCs can be associated withmodel. The default pick is "Geometry".
Select Geometry Entities
Click in this box.
Add
appear in the box marked ‘select Geometry Entities’.
Leave this unchanged.
the RETURN key.
Load/Boundary Conditions
Key
Repeat this by selecting line B (label Surface 2.1).
Figure 19: Load/BC Form
LOADS AND BOUNDARY CONDITIONS
Loads and Boundary Conditions
This is the set name given to the fixity boundary condition about to be specified. Each load andboundary conditions has to be given a
set
name. The user is free to choose a meaningful name
for the set.This needs two subforms to be filled. In the first of these you specify the type of fixity. The secondsubform is for selecting the region to which the boundary condition is applied. To execute thecommand you need to click on the
Apply
button in the original form.
^ Now click on the box marked ‘Input Data...’.This will open a new form. ^ Click on the box under the heading ‘Translations’ and enter 2 zeroes separated by spaces betweenthe angled brackets (
This is to indicate zero displacements in the 2 directions (x and y).Leave the rest of the data in the default setting. Click on the OK button. Then in the original form click on the ‘Select Application Region...’.This is to specify which part of the boundary is to be fixed. Notice the
Geometry which is
selected. Click on the box marked ‘Select Geometry Entities’. Now choose the ‘curve’ icon (3rd icon) fromthe select menu next to the form.This selection filters the picking. In this case only lines will be selected. Surfaces and points willbe ignored when you cursor pick entities.As you move the mouse around you will notice that the various curves getting highlighted andchanging colour. PATRAN is indicating what is the current selection and highlighting entitieswhich are likely to be selected.
This should help in informing you what is the current icon
selection. Now click on the left hand side vertical line A.This line should change colour to indicate that it has been selected.The label of the line should also appear in the box marked ‘Select Geometry Entities’. Howeverif this does not happen then check the ‘Select Menu’ to see that the ‘curve’ icon is chosen. Click on the ‘Add’ button. The label should appear in the box marked ‘Application Region’. Now click on line B and again click on the ‘Add’ button.If you had not made any mistakes then click on the OK button to close that form.If by mistake you had selected a different line, then use the ‘Remove’ button on that form toremove it from the list. Click on the line which was wrongly selected. Then check the label in thebox marked ‘Select Geometry Entities’ and click on the ‘Remove’ button. This should remove itfrom the ‘Application Region’ list. In the original form click on the
Apply
button.
Blue cones indicate the restraints applied to the left hand side boundary. There should be 2 sets of cones at each location. The numbers 1 and 2 indicate which directions are restrained. The tip andorientation of the cone indicates which direction the edge is restrained. If the tip is pointing in thehorizontal direction then that line is restrained in the horizontal direction.
If the blue cones are not displayed then you must have made a mistake. Change the ‘Action’ from ‘Create’ to ‘Modify’. Check the ‘Input Data’ and ‘Application Region’. Make sure that the correct iconwas chosen from the ‘Select Menu’. You can also change the ‘Action’ to ‘Show Tabular’ to check theinput data.
DEFINE ELEMENT PROPERTIES
Load Application
Load Application
Along the top, the side on the right hand is to be subjected to a vertical triangular distributed loadwhich varies from 100
to 0.
The load distribution function has already been specified in the previous section.^
To specify this, set the ’Action’ to ’Create’ and change the ‘Object’ to ‘Pressure’. Enter
dstld
(short
for distributed loading) in the box marked ‘New Set Name’.This is the label by which the load will be identified (
Figure 20
^ Click on the ‘Input Data...’ button and click on the box marked ‘Edge pressure (2-D Solids)’ andclick on the label
triang
in the field box marked ‘Field’. The label
f:triang
should be displayed in
that box. Click on the OK button. Then click on ‘Select Applications Region...’. Click on the box marked ‘Select Geometry Entities’.Choose the ‘Curve’ icon from the ‘Select Menu’ (it is the 1st icon). Then click on curve marked Cin
Figure 20
The label ‘Surface 3.2’ should appear in the box marked ‘Select Geometry Entities’. Click on the ‘Add’ button. The label ‘Surface 3.2’ should appear in the box marked ‘ApplicationRegion’. Then click on the OK button to close that form. In the original form click on the
Apply
button.
This completes the specification of the load.
The load vector should be displayed in Red.
The
values 100 and 0 should be displayed at either ends. If this does not happen then you must have madea mistake. Change the ‘Action’ from ‘Create’ to ‘Modify’. Check that the ‘Input Data’ and ‘ApplicationRegion’ are correct for the above load application. You can also change the ‘Action’ to ‘Show Tabular’to check the input data. Then proceed with the exercise.
The next step is to input the material properties. 6
Define Element Properties First a material called
steel
is created and the properties defined (E,
).^
Then these properties are
assigned to the bracket and the thickness is also specified. These are defined in two different forms. 6.
Define Material Properties
The bracket is made out of steel. Here it is assumed to be isotropic and linear elastic.
^ Click on the
Materials
for specifying the material properties.
Figure 21
shows the form which is used to input the material properties for the bracket.
^ Click on ‘Isotropic’ and look at the other constitutive models that can be chosen. Leave it un-changed for the present. ^ Enter the Material Name
Steel
^ Select ‘Input Properties...’. Enter an Elastic Modulus of ‘2.1E5’ (in MPa), Poisson’s ratio of 0.3.Click on the ‘OK’ in this form and then click on ‘Apply’ in the original form. This completes theinput of material properties.If you need to check the material properties at a later stage, change the ‘Action’ from ‘Create’ to‘Show’. To make any changes, change the ‘Action’ to ‘Modify’.
DEFINE ELEMENT PROPERTIES
Define Material Properties
C
Click on this and the information should
Add
Click in this box and
Click in this box.
The Loads and BCs can be associated with eitherthe geometry or the finite element model.The default pick is "Geometry".
triang^ OK GeometryFEM
Click on this box.
f: triang Select Surfaces or Edges
Click in this box and then click ontriang in the ‘Spatial Fileds’ Box below.This should then display ‘F : triang’.
Key
Select menu
Click on the "Curve" icon to select it. It is the 1st icon in the select menu.This selection filters screen picking. In this case only the curves or edgesThen click on top line in surface 3 (Line C in above). The label ‘Surface 3.2’should appear in the box marked ‘Select Surfaces or Edges’.
Change this from 3D to 2D.
Target Element Type :
Edge Pressure (2D−Solids)Spatial Fields
enter name ’dstld’.
dstld
Pressure
Type:
OK
−Apply−
Load/Boundary Conditions Select Application Region...
appear the ‘Application Region’.
DO NOT press the RETURN key.
Input Data ...
2D
Pick
New set Name
Create Element Uniform
Action:Object:
will be selected, although there may be points or surfaces in the area.
Figure 20: Load Application
FINITE ELEMENT MESH
Click here and enter the Group Name.
New Group Name
Make Current Add Entity Selection
These are the defaults. The current groupis the one which receives all new entities.
Create ... Group
fem
−Apply−^ Cancel
Figure 23: Define a new group
The message
$ # Property set “bracket” created
should appear in the history window.
When the finite element mesh is created later all the elements in the mesh would be assigned the ‘steel’ material properties.
If you need to check the properties at a later stage, change the ‘Action’ from ‘Create’ to ‘Show’. To make any changes, change the ‘Action’ to ‘Modify’.
Note
As mentioned earlier it is possible to assign the properties either to the “geometry” or to the “finite element mesh”. Here it has been assigned to the geometry. 7
Finite Element Mesh Before generating the finite element mesh it is necessary to create a separate group. Thisis to keep the
Geometry
model separate from
Finite Element Model
. This makes it eas-
ier to select and display the Geometry model separately from the Finite Element Model. Groups
are like ‘named components’. Each group has its own name and contains
en-
tities
. If you look at the top of the viewport you will notice the name
default
group
displayed.
That is the default name and the created geometry is part of that group.
Let us leave
‘geometry’ in the
default
group
A new group called
fem
will be created for the finite element model.
^ Click on the
Group
label at the top window (
Figure 23
). Choose the
Create...
option. Enter ‘fem’
in the box with the heading ‘New Group Name’. Click on the
Apply
and
Cancel
buttons respectively.
You will notice that the group name in the viewport title bar has changed from “default
group” to
“fem”. This is the current group (and only one group can be the current group), and it will receiveall new entities that are to be created; i.e. the finite element mesh, nodes and elements. However the“default
group” is still posted. Here posted means ‘on display’.
Create Mesh Seeds
Mesh seeds tell PATRAN how the mesh is to be generated. The mesh is to be created with 2 elementsalong the shorter sides and 8 elements along the longer sides.
^ Click on the
Elements
label which will close the
Loads/BC
form and open the
Finite Elements
form.
FINITE ELEMENT MESH
Create Mesh Seeds
B A
E^ D
C
Then click on line C.
Click on the line D (curve 1) and then click on thelines B and E (surface 2.1 & 2.2) respectively.
Click in this box
Curve List
Auto Execute
Change this to 8.
Display Existing SeedsNumber =
Click in this box and then click on line A.
Curve List Number =
Mesh Seed Uniform
Action:Object:
Create
Type:
Key
Finite ElementsFinite ElementsFinite ElementsFinite Elements
Figure 24: Mesh Seeds
Leave the current setting of Action/Object/Type as Create/Mesh Seed/Uniform (
Figure 24
).^
The
choice of ‘Uniform’ for ‘Type’ means that the generated elements will be of equal width. It is possibleto generate a graded mesh by changing the ‘Type’ to ‘One Way Bias’ or ‘Two Way Bias’. However thiswill not be attempted for this example.
The idea is to create a mesh with 8 noded quadrilateral elements. Here the shorter sides are as- signed 2 and the longer sides 8 seeds respectively. Since opposite sides are meshed identically assignto at least one of each pair.
^ Change the entry in ‘Number’ box to 2. Click on the ‘Curve list’. ^ Now click on the lines marked B, D and E respectively (shown in the Key in Figure 24).The mesh seeds showing how the sides will be divided should appear in the lines. ^ Change the entry in ‘Number’ box to 8. ^ Click on the ‘Curve List’ again and click on the left hand vertical line (Surface 1.1, marked Ain Figure 24). Notice the internal numbering (surface 1 side 1). Where curves were not directlycreated (unlike the curves 1 and 2) the internal numbering of entities will be used.
Don’t be
misled by the reference to ‘Surface’ when you expect ‘Curve’ to appear. Click on line marked C.Yellow circles will be displayed along these lines. These are the ‘Mesh Seeds’. This shows wherethe nodes will be created and the division of the elements.You can use the ‘Display Existing Seeds’ option in this form to check what the current seeding isat a later time.It is sufficient to assign mesh seeds to 2 adjacent sides of any surface. Opposite sides of a surfaceare meshed identically.
FINITE ELEMENT MESH
Create the Mesh
−Apply−
Action: Element Topology
Finite Elements Object:Type:Global Edge Length
Create
click on the Surface labels 1, 2 and 3.The label ‘Surface 1:3’ should appear.
Mesh Surface
Quad5 Quad
Click in this box. Then HOLD the SHIFT key
Paver
Isomesh
Click in this box
Quad Surface List
Figure 25: Create Mesh
Create the Mesh
^ Change Action/Object/method to Create/Mesh/Surface (
Figure 25
). Click on the ‘Quad 4’ set-
ting for ‘Topology’ and look through the available element types. For the present example choosethe
Quad
elements. This is the 8-noded quadrilateral element.
^ Now click on the box marked ‘Surface List’ and then hold the SHIFT key and click in the interiorof the surface or on the label of the 3 Surfaces respectively. Alternately one could have drawn abox around the 3 surfaces.The label ‘Surface 1:3’ should appear in the box marked ‘Surface List’. ^ Then click on the
Apply
button.
The mesh should now be generated and displayed. White lines indicate the element boundary. The numbers in white are the element numbers and the ones in red are the node numbers. There shouldbe 36 elements and 159 nodes in the mesh.
It is sufficient to specify the mesh seed for adjacent lines of a surface.
The opposite sides in a
surface are meshed identically. However if you had left both of a parallel set of sides unseeded thenthe program uses the
Global length
parameter (which has a value of 12.8) as the size of the elements
to be generated along that side. If this is the case then click on the ‘undo’ icon and then click on the‘refresh’ icon. This should delete the finite element mesh. Then change ‘Mesh’ for ‘Object’ to ‘MeshSeed’ and specify the mesh seeds for the sides correctly. Then re-create the mesh. 7.
Unpost the Geometry
Now that the finite element model has been generated we can dispense with the geometry model ieremove it from the view/display. If we had not created the group
fem
just before the f.e. mesh was
created then this would not have been possible.
Then geometric entities (points, curves, surfaces)
would be in the same group (default
group) as the f.e. entities (elements and nodes).
If you had forgotten to create the
fem
group then no harm is done.
Follow the next 3 steps.
Otherwise skip these 3 steps.
FINITE ELEMENT MESH
Equivalence and Optimize
Note that the Loads/BCs go away too,
Group
Post... default_group
Apply fem Cancel
Click on "fem"to select it from the list of posted groups.
because they are in the default_groupwith the geometry.
Select Groups to Post
Figure 26: Select Finite Element Model for viewing
^ Click on the
Group
label at the top window (
Figure 26
). Choose the
Create...
option. Enter ‘fem’
in the box with the heading ‘New Group Name’. Click on ‘Add Entity selection and change it to ‘All F E Entities’. Note that this step is differentfrom the previous instruction in creating a new group. Click on the
Apply
button.
Now to post only the
fem
group.
^ Now change the
Create...
to
Post...
. In the new style dialogue box look at the box marked
Select
Groups to Post
Both
default
group
and
fem
are highlighted (are displayed in reverse video) to indicate that both
are currently selected (
Figure 26
^ Click on the ‘fem’ to select it. Now only the ‘fem’ should appear highlighted. Then click on the^ Apply
button and then the
Cancel
button to close that form.
This should only display the finite element mesh. Click on ‘refresh graphics’ to redraw the mesh.
Equivalence and Optimize
The next two steps are
Equivalence
and
Optimize
. If you click on the ‘Create’ label in the ‘Elements’
form it will display these options.^ Warning
First of all look at the node numbers. If these are not on display switch these ON. You will notice that the nodes along the shared sides of the surfaces have two sets ofnumbers superimposed. These are duplicate nodes.
When PATRAN creates the mesh elements and nodes are created separately on each surface. As a result there are 2 sets of Nodes along shared edges for 2D problems.
The ‘Equivalence’ command gets rid of the duplicate nodes.
If the Equivalence
command is not used then the created f.e. mesh will have unconnected parts ie it willbe fragmented.
If the structure consists of more than one surface use of ‘Equivalence’ is mandatory.
Otherwise you will end up with a mesh which is not connected up. Here the TOLERANCE is usedto determine the duplicate nodes.
Any 2 nodes situated within a distance of the TOLERANCE are
considered to be duplicates. Hence the importance of making sure that the largest dimension on whichthe tolerance is based on is specified reasonably accurately at the beginning
PERFORM THE ANALYSIS
Create a Load Case
Display
Let’s remove the markersfrom the display.
Load / BC / Elem. Props ...
Hide All
Press this to switch it OFF.
Apply Cancel
After clicking on this click on the Reset graphics
icon to clear the markers.
Show on FEM only
Figure 30: Switch Display Off
You can use the ‘refresh’ icon to re-draw the mesh, in case part of the mesh got erased due to the
last command. The next step is to create a load case with the loading and boundary conditions. 8.
Create a Load Case
A load case combines user selected load and boundary conditions. Next step is to create a load case tocombine the boundary condition, ‘fixed’ and the loading ‘dstld’.
^ Choose the
Load cases
. In the box marked ‘Load Case Name’ enter ‘dist
load’.
Then click
on the
Assign/Prioritize Loads/BCs
. This will bring up a new form (
Figure 31
). From ‘Select
Individual Loads/BCs’ select
Disp
fixed
and
Press
dstld
^ If any one of the items makes more than one appearance (by accidentally clicking more thanonce) then ensure that the scale factor is 1.If more than one appearance is made then ^ select the row (by clicking on any cell in that row) and then click on button marked
Remove All
Rows
and repeat the step.
^ Click on the ‘OK’ button and then click on the ‘Apply’ button in the original form.This completes the data input.
The message
Load Case “dist
load” created
should appear in the
history window. 9
Perform the Analysis
Submit a ABAQUS Analysis
We’re ready to analyze the problem we’ve entered in PATRAN.
^ Click on the
Analysis
label.
Figure 32
shows the form.
^ Click on ‘Step Creation...’
and in the new form enter in the box marked ‘Job Step Name’ :
static
loading
Notice the default option of
Linear Static
for the ‘Solution Type’.
^ In the box marked ‘Job Step Description’ enter ‘Static analysis with pressure loading’.
PERFORM THE ANALYSIS
Submit a ABAQUS Analysis
Displacement Pressure
dstld Assigned Loads/BCs
Remove All Rows
Remove Selected Rows
Add
1.
Add
Scale factor
Type
Priority
1.
fixed
Assign/Prioritize Loads/BCs −Apply−
Select Individual Loads/BCs Displ_fixed
Click on this box andenter name.
Click on this box.
Use these if you makeany mistakes.
Click on the names of the sets we justcreated to select them. Then theseshould appear in the spreadsheet below.
Press_dstld
Load Cases Load Case Name dist_load
OK
Figure 31: Create a Load case
^ Click on the ‘Linear Static’ and this will display other type of analyses that can be carried out.For the present leave this as ‘Linear Static’. ^ Click on the box marked ‘Select Load Cases...’ and in the new form select the ‘dist
load’ from the
available load cases. Then click on the ‘OK’ button to close that form. Click on the label ‘Output Requests...’ and check the default options for future reference. Changethe ‘None’ for ‘Stress Invariants’ to ‘Integ Point’.
Then click on the ‘OK’ button to effect the
changes made. Click on the ‘Apply’ and ‘Cancel’ buttons respectively in the ‘Step Create’ form. This will closethat form. Click on the ‘Step Selection...’ button in the original form. Click on the ‘static
loading’ in the
‘Existing Job Steps’ box and this will appear in the box marked ‘Selected Job Steps’. Then clickon ‘Apply’.Now all the data input is complete. Finally click on the ‘Apply’ button to submit a ABAQUS job. PATRAN creates the input data file called bracket.inp (for this example) and submits a ABAQUS job. The abaqus job is run external to the patran session. The following messages should appear in thehistory window :
- Executing /export/../patran2004r2/bin/pat3aba.2. translator messages may be found in the file ./bracket.msg.01.3. Executing /export/../patran2004r2/bin/AbaqusExecute.
PERFORM THE ANALYSIS
Submit a ABAQUS Analysis
Existing Job StepsSelected Job Steps
Default Static Stepstatic_loading
Click on this to add it to theSelected Job Steps.
static_loading
Method:
Job Step Name^ static_loading
Click in this box and enter name
Solution Type
Click on this for othertype of analysis.
Full Run
Object:
AnalyzeEntire Model
Action:
Leave these unchanged
Analysis
Available Load Cases
Click on this name to select it.
Stress Invariants
Integ Point
Step Creation...
Select Load Cases...
OK
The default is
None.
If we don’t turn these to
Cancel
Step Selection ... Apply
Apply Apply
Integ Point the results plot will be unexciting.
OK
Output Requests...
Output Variables
Option
dst_load
Linear Static
Figure 32: Run an ABAQUS Analysis
PERFORM THE ANALYSIS
Accessing the ABAQUS Results from PATRAN
First the viewport will be closed and the Message
Generating Input for ABAQUS
would appear
in a separate window which would be closed subsequently. At this point he ABAQUS job starts to run(in the background). The viewport should be back on display.
Now move the viewport aside and look in the xterm window from which patran was started. Look for the message :
Sending output to nohup.out
in that window. In the absence of any other message
this would in general mean that the analysis was successful. However in case of errors the followingmessage may appear in the same window.
Error detected ...
Aborting AbaqusExecute
.^
In case of
errors you must find the errors and correct them.
First look in the file called nohup.out.
It might
suggest looking at either bracket.msg or bracket.dat file.
Notice the difference between the files bracket.msg.n and bracket.msg.
The bracket.msg file is
created by ABAQUS and is a report of the analysis whereas bracket.msg.n is a report from PATRANin creating the ABAQUS input file (whether creation of each keyword was successful or not).
The following steps are involved.
First the ABAQUS input file is written to.
The report of this
action is written to a file bracket.msg.01 when it is the first time. If the file(s) bracket.msg.n alreadyexists then a new file with the last 2 digits incremented by 1 will be created. Look for the file with thelargest extension number. The next step in the absence of any errors in the input creation step is to runthe ABAQUS analysis.
Then wait for the abaqus job to finish. Type
top
in the second X-term window and wait till ‘pre.x’
and ‘standard.x’ disappear from the displayed list. Because this is such a small example you will haveto be quick to see this. Type
q
to quit from
top
The files bracket.dat and bracket.fil would have then been created. If either or both these files are missing then there could be an error in the data input. Check the file bracket.msg.01 for error messages.Check also the bracket.inp file.
If both these files (*.dat and *.odb) are successfully created then resume the PATRAN session as described in the next section.
This list summarises the general suggestions on what to do after the analysis is complete.Use one of the other xterm. Make sure that the current directory is
patran
^ more
nohup.out
Read the ABAQUS log file.
^ more
bracket.inp
View contents of ABAQUS input file.
^ more
bracket.msg
View message file.
^ emacs
bracket.dat
View ABAQUS output file using emacs.
^ Use
File / Exit Emacs
to quit from Emacs.
^ rm
nohup.out
Remove this file. It will be recreated.
Accessing the ABAQUS Results from PATRAN
The ABAQUS printed results will be written to bracket.dat (ascii).
The output database is called
bracket.odb (binary). In order to access the results from PATRAN you need to attach the ‘*.odb’ file toPATRAN.
^ Click on the
Analysis
form to re-open it.
^ Change the ‘Action’ from ‘Analyze’ to ‘Read Results’.The form is shown in
Figure 33
^ Click on the label ‘Select Results File...’.This will bring a new form up. Check under the heading ‘Available Files’. If ‘bracket.odb’ doesnot appear in the list then the ABAQUS job has not run so far or there may have been someerrors. ^ Wait for a while and click on the ‘filter’ button to update the list of available files.
