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laminar flow: a variable in a certain solid domain is undefined
Posted 2026年4月17日 GMT+8 21:57Fluid & Heat, Computational Fluid Dynamics (CFD), Heat TransferVersion 6.31 Reply
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I am conducting heat transfer simulations in a microchannel. The fluid domain is represented by a rectangular block, and the material is water, while the solid domain is made of copper. Using the laminar flow module, after specifying the inlet velocity, the solver returns the following error message:
Undefined variable. - Variable: comp1.spf.U - Geometry: geom1 - Domain: 80 Cannot compute expression. - Expression: comp1.spf.U - Plot: Volume 1
After that, I looked for domain: 80, which points to a fin, but I don't understand why this fin would cause the laminar flow module to fail. Moreover, the fluid properties and the fluid domain in the laminar flow module do not involve this fin. How should I troubleshoot this error?
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I would start troubleshooting by checking the Physics domains, ensuring that only fluid domain is selected within laminar flow. Can be many other things, for such a simple problem it is more likely that you are not setting up the problem properly. If you still facing this problem I suggest to upload the file or give more details. A tip if you are starting your modeling it is searching on COMSOL Application Gallery for problems similar from yours and checking if you are missing something.
