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Limiting variables in Monolithic solver

Posted 27.08.2024, 18:57 GMT-4 Studies & Solvers, Structural Mechanics, Material Models 4 Replies

Aida Bouaziz
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Hello COMSOL Community,

In the typical segregated approach, it’s possible to limit a variable between an upper and lower bound. In the case of, the phase field variable needs to remain between 0 and 1. However, when using the monolithic or fully coupled solver, I haven’t found a way to enforce these limits.

My question is: How can I ensure that the phase field variable stays within the range of 0 to 1 when calculating energy, which depends on this variable, while using the monolithic solver?

I would appreciate any insights or suggestions on how to approach this issue.

Thank you!

4 Replies Last Post 04.09.2024, 05:29 GMT-4
Adam Wahlsten COMSOL Employee

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Posted: 7 months ago 28.08.2024, 04:48 GMT-4

Hi Aida,

If possible, it is usually better to enforce the limit on the phase field from the governing equations instead of setting a limit in the solver, since the latter will disregard the equations where your bound is violated. This means that you can get an arbitrarily large residual.

In version 6.2, with the Phase Field in Solids interface, you can use the Bounds subnode to a Phase Field Model node to specify these kind of inequality constraints.

If you are working with a phase field damage model like AT1, which is unbounded, an alternative approach to adding inequality constraints is to analytically derive the minimum energy that is necessary for a zero solution and add this as an additional source term in the phase field equation.

Best regards,
Adam Wahlsten
COMSOL

Hi Aida, If possible, it is usually better to enforce the limit on the phase field from the governing equations instead of setting a limit in the solver, since the latter will disregard the equations where your bound is violated. This means that you can get an arbitrarily large residual. In version 6.2, with the Phase Field in Solids interface, you can use the Bounds subnode to a Phase Field Model node to specify these kind of inequality constraints. If you are working with a phase field damage model like AT1, which is unbounded, an alternative approach to adding inequality constraints is to analytically derive the minimum energy that is necessary for a zero solution and add this as an additional source term in the phase field equation. Best regards, Adam Wahlsten COMSOL
Aida Bouaziz
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Posted: 7 months ago 30.08.2024, 10:38 GMT-4

Thank you for your response, Mr Adam
However, I've noticed that the "Weak Contribution" sub-node doesn't exist under the " Phase Field in Solids" node. How can I resolve this issue?

Thank you for your response, Mr Adam However, I've noticed that the "Weak Contribution" sub-node doesn't exist under the " Phase Field in Solids" node. How can I resolve this issue?
Magnus Ringh COMSOL Employee

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Posted: 7 months ago 02.09.2024, 03:42 GMT-4

Hi Aida,

Could it be that you have not yet activated the Equation-Based Contributions checkbox in the Show More Options window (which you open from the top of the Model Builder window). Then you should be able to add Weak Contribution subnodes.

Best regards,

Magnus

Hi Aida, Could it be that you have not yet activated the **Equation-Based Contributions** checkbox in the **Show More Options** window (which you open from the top of the **Model Builder** window). Then you should be able to add **Weak Contribution** subnodes. Best regards, Magnus
Aida Bouaziz
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Posted: 7 months ago 04.09.2024, 05:29 GMT-4

Hi Magnus,

Thank you for the suggestion! I tried to add the Weak Contribution subnodes as needed, and it worked perfectly. Thanks again for your help!

Best regards, Aida

Hi Magnus, Thank you for the suggestion! I tried to add the Weak Contribution subnodes as needed, and it worked perfectly. Thanks again for your help! Best regards, Aida

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