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Modifying equation system in Mechanical application mode

Posted 2010/02/19 0:29 GMT-5 3 Replies

Rakesh Dhote
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Hi Everybody,

I need to modify equation system in mechanical application mode to accommodate for 5'th order stress-strain relationship. Does anybody know how to change the equation system (Physics > Equation System > Subdomain Settings) ? It would be great if you share some examples.

Please share your expertise.

Thanks in advance,

Cheers,
Rakesh
3 Replies Last Post 2010/04/09 11:08 GMT-4
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 2 decades ago 2010/02/19 11:57 GMT-5
Hi
basically you can do whatever you want with the equations under Physics Equation Systems Subdomain Settings Variables Pan

The only thing/caveat is that if you modify something such as the sx_... variables, your domain will be flagged with a keylock which indicating that COMSOL willnot and cannot update this domain as COMSOL is not programmed to understand what is going on when you change your physics this way.
So that, if you add some new physics, variables might not follow or be updated correctly.

You can always backtrack by hitting the Reset Equation

From thereon I'll leave it to you to update your physics, because I'm not sure I understand correctly what exactly you want to do, so I do not think I can help much further.

In anycase good luck, with COMSOL we are back doing physics, finally

Ivar
Hi basically you can do whatever you want with the equations under Physics Equation Systems Subdomain Settings Variables Pan The only thing/caveat is that if you modify something such as the sx_... variables, your domain will be flagged with a keylock which indicating that COMSOL willnot and cannot update this domain as COMSOL is not programmed to understand what is going on when you change your physics this way. So that, if you add some new physics, variables might not follow or be updated correctly. You can always backtrack by hitting the Reset Equation From thereon I'll leave it to you to update your physics, because I'm not sure I understand correctly what exactly you want to do, so I do not think I can help much further. In anycase good luck, with COMSOL we are back doing physics, finally Ivar
Stefan Wolf
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Posted: 2 decades ago 2010/04/09 10:26 GMT-4
Dear Ivar,
I am also manipulating the Physics Equations System -Subdomain Setting.

In my case, I do change the way stress is calculated. Instead of the linear Hookian Stress-Strain relation, I do use Anand's relation. Therefore I do introduce a new variable for the strain e_ij in addition to the linear-elastic Hookian strain. To calculate the stress, I do subtract the Anand-strain from the corresponding sx=E_smps*(ex_...-ex_anand)...
Basically the same idea as used in "Viscoplastic Creep in Solder Joints" Model ID: 4488.

Can you help me to understand how the variable sx_... flagged with a keylock does effect the computation? I am not sure, what is meant by updating a domain, and whether this affects my transient simulation of creep. Do you know some sources for further reading?

Best regards,
Stefan Wolf
Dear Ivar, I am also manipulating the Physics Equations System -Subdomain Setting. In my case, I do change the way stress is calculated. Instead of the linear Hookian Stress-Strain relation, I do use Anand's relation. Therefore I do introduce a new variable for the strain e_ij in addition to the linear-elastic Hookian strain. To calculate the stress, I do subtract the Anand-strain from the corresponding sx=E_smps*(ex_...-ex_anand)... Basically the same idea as used in "Viscoplastic Creep in Solder Joints" Model ID: 4488. Can you help me to understand how the variable sx_... flagged with a keylock does effect the computation? I am not sure, what is meant by updating a domain, and whether this affects my transient simulation of creep. Do you know some sources for further reading? Best regards, Stefan Wolf
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 2 decades ago 2010/04/09 11:08 GMT-4
Hi

The only thing I know is that the "lock" is there when you change the equations directly in such a way that COMSOL cannot understand it anymore. Because, when you change modes, physics etc, COMSOL updates the equations, but it does not touch "locked" equations because that's "your" responsability.

But I'm not sure how COMSOL flags any warning if it wants to change soemthing that you have locked, you might have some surprises such as expecting COMSOL to update something but this is NOT done as the equations are locked.

I have a couple of examples of locked equations too (the last one is the most up to date) in the paralle thread where I have dumped some of my thought/tests about torque loads and rotation restraints in solid structural. the example is 2 but protable to 3D. look carefully through loads and the physics equations as there are several "locks" in there on boundaries and on points

www.comsol.com/community/forums/general/thread/3566/#p11777

Good luck
Ivar
Hi The only thing I know is that the "lock" is there when you change the equations directly in such a way that COMSOL cannot understand it anymore. Because, when you change modes, physics etc, COMSOL updates the equations, but it does not touch "locked" equations because that's "your" responsability. But I'm not sure how COMSOL flags any warning if it wants to change soemthing that you have locked, you might have some surprises such as expecting COMSOL to update something but this is NOT done as the equations are locked. I have a couple of examples of locked equations too (the last one is the most up to date) in the paralle thread where I have dumped some of my thought/tests about torque loads and rotation restraints in solid structural. the example is 2 but protable to 3D. look carefully through loads and the physics equations as there are several "locks" in there on boundaries and on points http://www.comsol.com/community/forums/general/thread/3566/#p11777 Good luck Ivar

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