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Why can I not use `solid.d` in the Symmetry node?
Posted Jul 31, 2023, 6:21 a.m. EDT Structural Mechanics Version 5.5 1 Reply
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I have a Solid Mechanics plane strain physics problem, where I use a Symmetry node. If I use a Normal Direction Condition -> Prescribed force, I want to scale the result by the depth of the problem. So logically, I would want to say Fn = 1[MPa] * solid.d * height or similar. However, then I get an error, "Undefined variable. - Variable: comp1.solid.d". If I use solid.d in other context (e.g., a Boundary Load or a Weak Contribution) it works fine.
Is this a bug or is there a subtlety of COMSOL I'm not getting?
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The subtle issue is that 'solid.d' is a field which, in principle, can vary over the boundary you are constraining. The force you are prescribing is, however, a single (global) variable. Which value to use is thus not well defined.
One way of handling this is to create a global variable with the same value by picking a value from the domain using a probe or an average operator.
The quickest solution in your case is probably to add a parameter and use it both for prescribing the thickness and the force.
-------------------Henrik Sönnerlind
COMSOL