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Continuity constraint equation
Posted Jul 28, 2020, 2:52 p.m. EDT Structural & Acoustics, General Version 5.5 2 Replies
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I want to modify the equation shown in the equation view node for the continuity boundary condition for an identity pair, to make the velocity rather than displacement continuous across the boundary. However, I am having trouble interpreting the constraint equation shown, for example for the u component of the displacement: if(root.comp1.incontact_ap1&&u_fld_act&&if(root.comp1.incontact_ap1,root.comp1.src2dst_ap1(u_fld_act),0),u-root.comp1.src2dst_ap1(u),0).
In the manual, the src2dst operator is described, but I cannot find an explanation of the root.comp1.incontact variable or the u_fld_act variable, so I'm not sure how to interpret this expression. I'd appreciate any guidance on this.
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root.comp1.incontact_ap1 is a Boolean variable indicating if the boundaries are adjacent to each other or not.
u_fld_act is a Boolean variable indicating that the field 'u' is active on the selection.
These are just safeguards to avoid setting up an invalid constraint.
Why would you be interested in constraining the velocities? If the velocities are equal, so are the displacements. Placing constraints on time derivatives requires special methods, so you cannot directly convert the equation above.
-------------------Henrik Sönnerlind
COMSOL
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Thanks for explaining those variables. I was wanting to constrain the velocities to match the boundary conditions used in some other studies, but in thinking about it more, that is unnecessary and I can just constrain the displacements.