Stress initialization
Altair EmployeeHello everybody,
I have some problems with stress initialization simulation of solid element: I'd like to do a simulation made of two step where the second step shall take into account strain and stress of first step.
I have try to use \inista but there is something wrong because in second step, at first frame, the part have no stress.
The procedure I have used is:
- STEP I: /IOFLAG
- eport solver deck from HyperView for the deformed shape
- STEP II: /INISTA
In attach the file .rad of simulation.
Thank you in advance for your help!
Marta
Answers
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Hi @marta
Have you gone through this post regarding initial stress?
https://community.altair.com/community?id=community_question&sys_id=bb76483a1b2bd0908017dc61ec4bcb820 -
yes, I've read the post, the Radioss reference guide and I've watched the video but I don't fully understand the procedure.
Coud you check the file and could you point what I'm doing wrong?
Thanks a lot.
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Hi Marta,
I suggest using .sta files instead of .sty files, which is a legacy format.
The procedure to carry over stress and strain state of elements is to create STATE engine cards in the 1. step:
/STATE/BRICK/STRAIN/FULL
/STATE/BRICK/STRES/FULLif there are shells also create additional cards (search Radioss help with keyword: STATE)
/STATE/DT(define start time and frequency to write state files and declare components to be included)
Run the simulation which creates model_name.sta file, which is then imported into the original model. It will overwrite the original mesh with deformed and there should also be Tables entry in the model browser (stress & strain information for each element that can be edited).
Attached are the modified files and also some tips about STATE files.
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Hi @Ivan,
thank you so much for your suggestion! I've try and ereything is working as planned but I've an other problem: when I run the second step this messages appears:
MESSAGE ID : 259
** WARNING ZERO OR NEGATIVE VOLUME : 3D-ELEMENT ID : 483
ELEMENT IS SWITCHED TO SMALL STRAIN OPTION**ERROR : TIME STEP LESS OR EQUAL DTMIN FOR SOLID ELEMENTS
**ERROR : NEGATIVE STIFFNESS NODE 1
**ERROR : NEGATIVE STIFFNESS NODE 273
**ERROR : TIME STEP LESS OR EQUAL ZERO
How can I solve this problem?
Thank you a lot!
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Nothing regarding material. I used /inista card and I modified interface to avoid initial penetration ( I reduced gap minimum). Nothing else.
Thanks
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I think negative stiffness is due to added mass at the beginning of the cycle.
Can you change Istiff to 1 or maybe advanced penalty methods?
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can you share the troublesome model?
The NEGATIVE VOLUME error happens when solid elements are very deformed and their characteristic length goes to 0. For large strain formulation the time step of an element goes to 0 when the element is compressed. In RADIOSS Starter input file (Runname_0000.rad), use Ismstr =2 in the solid property and in RADIOSS Engine file (Runname_0001.rad) use the option/DT/BRICK/CST which will set the time step value tmin at which the solid elements will switch to small strain. This means that the solid elements using Ismstr =2 will use large strain formulation while their time step remains greater than tmin, and will then switch to small strain formulation.
**ERROR : NEGATIVE STIFFNESS NODE is probably due to initial penetrations so you should clear those.
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in the STEPII files you shared, there is reference to .sty files (/INISTA control card).
Instead, I have turned off this card and imported .sta file (with FE overwrite) from STEPI and the simulation runs fine.
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Thank you @Ivan, I really, really appreciate for all the help you gave me!
Now the simulation runs fine!
Thank you again!
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Altair Forum User said:
in the STEPII files you shared, there is reference to .sty files (/INISTA control card).
Hello Ivan,
I have same issue & gone through all suggestions but the file uploaded, i'm unable to open bcz of version issue as below..
Error: The file is not a 4.1 or 4.2 or 4.4 or 5.1 or 9.0 or 10.0 or 11.0 or 12.0 or 13.0 or 14.0 Radioss Block File (file version = 2017)
Resolution: Quitting..due to that i'm unable to see how u used /INISTA control card to make reference of STATE files (/STATE/BRICK/STRAIN/FULL
/STATE/BRICK/STRES/FULL).Every time i tried to simulate it shows error as below image.
Plz help.
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Hi Gajendra,
attached is the HM model saved in 140 Radioss profile. The rad files already shared should not cause compatibility issues.
Acutally, I have turned the /INISTA control card off.
STATE files are imported with FE overwrite option (to initialize deformed shape). After import there should be Tables entry in the browser.
<?xml version="1.0" encoding="UTF-8"?>
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Thanks Ivan,
I think that previously FE overwrite option was unchecked and that may cause of dual input condition. Simulation has done.
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