Solver for Mystran
Moderator: bernd
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Re: Solver for Mystran
Wait a second though... It is plenty tall though.
I bet other solvers can do this with no problem right?
There's something strange about it not being able to do this.
We're working on it. Sorry for the inconvenience.
I bet other solvers can do this with no problem right?
There's something strange about it not being able to do this.
We're working on it. Sorry for the inconvenience.
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- Posts: 118
- Joined: Fri Apr 09, 2021 3:26 am
Re: Solver for Mystran
We've just confirmed that NX Nastran can solve this.
I'm upgrading this to an official bug! Congragulations Bernd, we did it!
I'll be trying to figure out why this specific combination of inputs makes such strange results, but in the mean time, just know that very large numbers in the property card like this seem to risk the solver not being able to handle it; despite the fact that it stays accurate until it just stops working, which is good I guess.
I'm upgrading this to an official bug! Congragulations Bernd, we did it!
I'll be trying to figure out why this specific combination of inputs makes such strange results, but in the mean time, just know that very large numbers in the property card like this seem to risk the solver not being able to handle it; despite the fact that it stays accurate until it just stops working, which is good I guess.
Re: Solver for Mystran
Hi,
A bit late in the conversation, but I wrote a quite simple Neutral Parser (working on FEMAP and MYSTRAN neutral file): https://framagit.org/numenic/femap_neutral_parser. I'm quite happy with it, although I'm eagerly waiting for Steve's OP2 implementation to discard it!
I'm also working on a declarative MYSTRAN test-suite runner: https://framagit.org/numenic/mystran-validation.
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Re: Solver for Mystran
Oh hey Numenic!
Good to see you here!
I hadn't thought to ask you for your neutral file parser, but I'm elated to take this opportunity to take a look.
Also! I have reason to believe that the CBAR example that Bernd was using may have been wrong in an obvious way! I need to check that I just got home one moment--
Good to see you here!
I hadn't thought to ask you for your neutral file parser, but I'm elated to take this opportunity to take a look.
Also! I have reason to believe that the CBAR example that Bernd was using may have been wrong in an obvious way! I need to check that I just got home one moment--
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- Posts: 118
- Joined: Fri Apr 09, 2021 3:26 am
Re: Solver for Mystran
Okay Bernd! I have a solution.bernd wrote: ↑Tue Aug 03, 2021 6:49 pm I have Mystran solver errors on beam analysis just because I changed cross section geometry ... Could some of the Mystran cracks around help. https://www.mystran.com/forums/showthre ... 268#pid268
Here's what's wrong.
1.) The deflections are very large.
If you're ever not trusting linear analysis checks where you have very large deflections, it could be for a few reasons.
There's a subroutine in Nastran and mystran called AUTOSPC. This stands for automatic-single-point-constraint. Basically, if a node is flying away, or is not really attached to anything, mystran automatically reaches out and tries to fix it in place. It checks for this early in the solution, and tells the user when this happens in the F06 file. Here's it in your f06 file.
2.) Sometimes, very, very rarely, you have models that can't be solved by sparse matrices. This is very, very rare, and is what I thought was going on for your model, Bernd.
*INFORMATION: AUTOSPC Summary, Stage 3 after identification of AUTOSPC's to eliminate N-set DOFs with stiffness ratios < PARAM AUTOSPC_RAT
AUTOSPC_RAT = 1.000000E-06
Number of DOF's identified for AUTOSPC in component 1 = 0
Number of DOF's identified for AUTOSPC in component 2 = 1
Number of DOF's identified for AUTOSPC in component 3 = 1
Number of DOF's identified for AUTOSPC in component 4 = 0
Number of DOF's identified for AUTOSPC in component 5 = 0
Number of DOF's identified for AUTOSPC in component 6 = 0
------------
Total number of DOF's identified in this stage = 2
*INFORMATION: AUTOSPC Summary, Overall: after identification of all AUTOSPC's
AUTOSPC_RAT = 1.000000E-06
Number of DOF's identified for AUTOSPC in component 1 = 0
Number of DOF's identified for AUTOSPC in component 2 = 1
Number of DOF's identified for AUTOSPC in component 3 = 1
Number of DOF's identified for AUTOSPC in component 4 = 0
Number of DOF's identified for AUTOSPC in component 5 = 0
Number of DOF's identified for AUTOSPC in component 6 = 0
------------
Total number of DOF's identified overall = 2
This can be fixed by making mystran solve the full matrix, with a parameter called MATSPARS. Also, you can run MATSPARS when you switch from the SUPERLU sparse solver to the full BANDED solver.
Here's the bdf with both changes made to it.
Code: Select all
SOL 101
CEND
ECHO = NONE
SUBCASE 1
DISPLACEMENT = ALL
LOAD = 1
SPC = 1
SPCFORCES = ALL
STRESS = ALL
SUBTITLE = Default
BEGIN BULK
PARAM,MATSPARS,N
PARAM,SOLLIB,BANDED
PARAM,AUTOSPC,N
GRID 1 0. 500. 500.
GRID 2 8000. 500. 500.
CBAR 1 1 1 2 0.0 0.0 1.0
PBARL 1 1 BAR
400. 1400. 0.
MAT1 1 210000. .3
$LOADS
LOAD 1 1. 1. 2
FORCE 2 2 9000000. 0. 0. 1.
$SPCs
SPCADD 1 2
SPC1 2 123456 1
ENDDATA
My apologies.
- Aero
Re: Solver for Mystran
Hi Aero,aerospaceweeb wrote: ↑Thu Aug 05, 2021 3:25 am
Okay Bernd! I have a solution.
Here's what's wrong.
2.) Sometimes, very, very rarely, you have models that can't be solved by sparse matrices. This is very, very rare, and is what I thought was going on for your model, Bernd.
This can be fixed by making mystran solve the full matrix, with a parameter called MATSPARS. Also, you can run MATSPARS when you switch from the SUPERLU sparse solver to the full BANDED solver.
Here's the bdf with both changes made to it.
- Aero
Wow, nice option (MATSPARS)! This even does not exist in NX-NASTRAN, as far as I know.
Additionally, testing (and working) with MYSTRAN for a couple of months now, my personal thought is that it is one of the major FEM solver in open-source world. I'm essentially working with structural elements (bars, beams, cbushes and RBE) and there is no alternative i'm aware of! There are still some rough edges though, the major one being outputs formats. Neutral is good, but op2 will be better. (HDF5 would have even be better to me regarding accessibility).
Re: Solver for Mystran
Do not hesitate to provide a feedback.aerospaceweeb wrote: ↑Thu Aug 05, 2021 2:36 am I hadn't thought to ask you for your neutral file parser, but I'm elated to take this opportunity to take a look.
The testing framework (which make use of this neutral parser and use of Steve's pyNastran OP2 reader to automatically compare results) may deserve a look. Maybe it could be used to support Bill for development and unify the Mystran community testing efforts. Let me know your thoughts. (Still struggling for now to understand my CBUSH bug... hehe).
Re: Solver for Mystran
I don't know the license on the NEU parser, but I have no problem incorporating it into pyNastran if it's BSD-3.
Also, the best way I've found to validate OP2s is to just write it to an F06 and diff it. The headers make it a lot easier to compare. Another good strategy is to have a reader/writer combo and you just compare those two. Those should be exact other than NaNs, which thankfully are rare.
Also, the best way I've found to validate OP2s is to just write it to an F06 and diff it. The headers make it a lot easier to compare. Another good strategy is to have a reader/writer combo and you just compare those two. Those should be exact other than NaNs, which thankfully are rare.
Re: Solver for Mystran
I put MIT license, which I think is a very permissive one, but I can change it if required.mesheb82 wrote: ↑Thu Aug 05, 2021 3:53 pm I don't know the license on the NEU parser, but I have no problem incorporating it into pyNastran if it's BSD-3.
Also, the best way I've found to validate OP2s is to just write it to an F06 and diff it. The headers make it a lot easier to compare. Another good strategy is to have a reader/writer combo and you just compare those two. Those should be exact other than NaNs, which thankfully are rare.
For the validation of Mystran, I use the pyNastran's OP2 writer to read the reference results as outputed by NX, and compare them with the Mystran's F06 output.
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- Posts: 118
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Re: Solver for Mystran
A CBUSH elementbug has just been resolved.
There's now nothing standing between mystran and completion of its testing framework.
Bernd, if you were waiting for that bug to be completed, wait no longer!
There's now nothing standing between mystran and completion of its testing framework.
Bernd, if you were waiting for that bug to be completed, wait no longer!