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-   -   stress analysis -Von Mises Theory (http://www.cfd-online.com/Forums/openfoam/80807-stress-analysis-von-mises-theory.html)

watashiwa October 7, 2010 06:29

stress analysis -Von Mises Theory
 
Hi,

I'm doing a 2D modelling stress analysis on a typical cylinder with internal pressure
Using blockMeshDict
Solver-solidDisplacementFoam
-foamCalc components sigma

I would like to know whether I can obtain the result for Von Mises Theory. I have all the stress-->xx, yy, xy and so on but nor von mises.

In fact, in ANSYS can get the result for von mises.
Another way which I can find von mises is by taking the stress-> xx, yy and xy result as a function and put them into the von mises equation.

Not sure whether OpenFoam able to do this or not. Hope to hear from you guys if you have any idea on this.

Regards
watashiwa curious

watashiwa October 14, 2010 10:10

stresseq
 
I have found out that the sigmaeq=von mises theory

I have counter check with ANSYS. not sure this is right or wrong? seems like not many people use OpenFOAM for stress analysis.

bigphil October 14, 2010 12:57

Hi,

Yes SigmaEq is the vonMises stress.

Ye there probably aren't many people that use OpenFOAM for stress analysis, compared to the amount of people using it for CFD.
But there are a few groups that I know of that use it, in Ireland (where I am) and Croatia.

Philip

mturcios777 October 14, 2010 13:04

Looking at calculateStress.H, sigma_eq is calculated by

Code:

sqrt((3.0/2.0)*magSqr(dev(sigma)))
which is the Von-Mises stress according to:

http://en.wikipedia.org/wiki/Von_Mis...ess_conditions

What does the comparison of the results from Ansys tell you?

bigphil October 14, 2010 13:15

EDIT: misinterpreted the question.

watashiwa October 14, 2010 22:01

Hi ,
Hi

I did a comparison using ANSYS(classic) and OpenFOAM. The result seems to be opposite in ANSYS to what I am getting in OpenFOAM. However, both gives the same colour profile especially when I analyzed stress xx, yy, xy and von mises. Von mises in ANSYS shown identical pattern when compare with OpenFOAM.

I have verified my result thick wall cylinder in OpenFOAM with the thoeretical result which is correct but not for ANSYS. As I have mentioned the value obtained in ANsys seems not right but have the identical colour pattern. I will further investigate this.

watashiwa October 14, 2010 22:57

Looking at calculateStress.H, sigma_eq is calculated by


Code:
sqrt((3.0/2.0)*magSqr(dev(sigma)))
Hi Marco, how did you know the sigma_eq equation from the OpenFoam ? from which file and folder? is it require a command to execute in order to obtain the eq?

mturcios777 October 15, 2010 16:43

The file you want to look in is $FOAM_SOLVERS/stressAnalysis/solidDisplacementFoam/calculateStress.H

Checking out the source code is a great way to find out what is happening and how you can change it.


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