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timestep in stationary study?

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I am modeling laminar flow at steady-state. Error message:

Undefined variable.
- Variable: timestep
- Geometry: geom1
- Domain: 2
Failed to evaluate expression.
- Expression: nojac((0.5/sqrt(((((comp1.spf.rho^2)/(timestep^2))+(((6*comp1.spf.mu)^2)*emetric2))+((comp1.spf.rho^2)*emetric(comp1.u,comp1.w))))))
Failed to evaluate variable.
- Variable: comp1.spf.tau_m
- Defined as: nojac((0.5/sqrt(((((comp1.spf.rho^2)/(timestep^2))+(((6*comp1.spf.mu)^2)*emetric2))+((comp1.spf.rho^2)*emetric(comp1.u,comp1.w))))))
Failed to evaluate temporary symbolic derivative variable.
- Variable: comp1.spf.streamlinens@VDN${test@30}
- Defined as: (((-comp1.spf.tau_c)*comp1.spf.res_p)-((nojac((comp1.u*comp1.spf.rho))*comp1.spf.tau_m)*comp1.spf.res_u))
Failed to evaluate expression.
- Expression: d((2*comp1.spf.streamlinens*pi*r)*(dvol),{test@30})

It might be related to a very thin domain in the geometry.

br
Lasse

1 Reply Last Post 6 sept. 2017, 19:28 UTC−4
COMSOL Moderator

Hello Lasse Murtomäki

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Bo Gao Certified Consultant

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Posted: 7 years ago 6 sept. 2017, 19:28 UTC−4
Hi Lasse,

Hope you have resolved your problem and you do not need any solution now. But if you still need help for this problem, maybe I can provide you a possible reason and solution. Try to check your "equation form" in the settings of laminar flow. If it is "time dependent", please change it to "study controlled" or "stationary". Please remind that if you use "stationary", it will be only valid for steady-state solver; while if you use "study controlled", COMSOL will be self-adaptive according to your steady-state or transient solver.
Hi Lasse, Hope you have resolved your problem and you do not need any solution now. But if you still need help for this problem, maybe I can provide you a possible reason and solution. Try to check your "equation form" in the settings of laminar flow. If it is "time dependent", please change it to "study controlled" or "stationary". Please remind that if you use "stationary", it will be only valid for steady-state solver; while if you use "study controlled", COMSOL will be self-adaptive according to your steady-state or transient solver.

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