I dislike any Job which is monotanamous so whenever I encouter anything
like that I will write a Program or a Macro to make my life bearable. I
thought I will share these stuf with the other peoples and maybe get something
else in return. I have too much stuff let me add one by one.
As you know almost all real life problems includes
contact. But we neglect contact in most of the simple problems where it
is not very important, the decision is entirely based on engineer's judgement.
In some cases the contact may be important but in the other hand it may
not ask for a full fledged contact analysis say using ABAQUS or any other
Non-Linear solver.
When the contact is very simple let us say between a plate and a Bracket and no friciton effects are required, Then using a complicated non-linear analysis is not asked for, so usually engineers
employ very simple contact procedure using linear analysis using NASTRAN
SOL 101.
The Contact is modelled by node-to-node CBAR or CROD element with only axial stiffness. Output of the member forces are taken and the contact elements with tensile forces are removed. The procedure is repeated till there is no tensile elements or to some satisfactory level, say 3 iterations or more.
You can use many inefficient and time consuming methods to modify the bulk data file to remove the tensile elements, so I wrote a simple script based on Python to read the member forces directly from PUNCH file and modify the Bulkdata accordingly. The same program is written in Perl and Python to deploy it in many flavours of UNIX and Windows workstation. Here I am sharing the Windows version in self extracting EXE file. It is created under Windows 2000. Other editions of Windows I am not sure. If you need I can send you XP compiled one or the source code itself. Please let me know.
Download the Program Here
After downloading the NastranContact.zip rename it as NastranContact.exe to get the self extracting file Geocities is not allowing exe files to be uploaded so I have changed the extension.
Contact Modeling in SOL 101 in Nastran by Linear Gap.
This contact methodology is called as Linear Gap procedure because the analysis is done under SOL 101, a linear solver. The contact state is obtained by solving MPC equations for open and close condition iteratively.
Generally in Nastran solving a Contact problem using CGAP elements with SOL 106 is little difficult as you need to decide on various parameters like NLPARM and PGAP etc. and it also takes comparatively more time. To obtain faster solution and to keep the problem simpler a new approach called Linear GAP procedure is introduced in Nastran from 70.5. For more detail on this method please refer my PPT available here Linear Gap PPT
But this method also poses some problem as it requires creation of data cards which are not supported by the common pre-processors [Patran has a PCL utility] and creating manually is also very cumbersome, so I tried to create a tool that can create this MPC, SUPPORT, SPOINT and DMIG cards automatically based on the user input.
Using this is very simple, create the Nastran Deck as if it is a Linear analysis and define the CGAP node-node elements for Contact, no PGAP or NLPARM are required just CGAP. The Linear Gap tool takes the Nastran input file and replaces all CGAP to Linear Gap equations it also creates other necessary cards like DMIG to define the initial status of the contact. It also modifies the SPC and MPC cards in the CASE CONTROL section so the output file should be ready for analysis without any modifications.
The usage is:
lingap.exe input_file.dat gap_distance
Example: lingap.exe bracket.dat 0.01
input_file.dat: Nastran input file you have created with CGAP elements.
gap_distance: Initial gap opening.
The tool creates an output file with the same name but with the ".gap" extension. For example you will get an output file named bracket.gap for the input above.
Limitations:
1. The Nodes involved in the contact must have the same Reference and Analysis co-ordinate systems. If you are not using any local co-ordinate systems the do not worry about this.
2. Many Subcases or not allowed, Currently it can process only one subcase, or only a Global case. In case if you want to analyze many Subcases you can hand edit the file.
3. It creates MPC and SPC sets with id's 101 and 102 so you cannot have them in your input date file.
Note:
1. Same node cannot be used by the SPC and Lingap Equation so make sure that you are not defining any CGAP elements on constrained nodes.
If you have any trouble contact me.
This is created using a programming language called PYTHON and Compiled using PY2EXE under windows 2000.
Keywords: Lingap, Linear-Gap, Linear Gap, Nastran, Contact.
Download the Program Here LinearGap Tool
Meshing is one of the area where we end up spending lot of our valuable
time. Some time it is very frustationg by on the other hand I do not prefer
people doing only meshing for my as the modelling is very important.
Hypermesh has lot of customisation options and I used it to the full
extent from Templates to Point creation. Some of my customisations scripts
and macros are availabe Here