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Unable to evaluate an expression

Posted Feb 4, 2016, 6:40 a.m. EST Fluid & Heat, Heat Transfer & Phase Change, Computational Fluid Dynamics (CFD), Mesh Version 5.2 8 Replies

Apurva Gajwani
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Excuse me, I am getting an error as

Attempt to evaluate real square root of negative number.
Function: sqrt
Failed to evaluate expression.
Expression: nojac(min(1,(sqrt((comp1.fsi.h2GNS*((comp1.fsi.rho^2)*(((comp1.u fluid-d(r,TIME))^2)+((comp1.w fluid-d(z,TIME))^2)))))/(comp1.fsi.mu*24))))
Failed to evaluate variable.
Variable: comp1.fsi.xi m, Defined as: nojac(min(1,(sqrt((comp1.fsi.h2GNS*((comp1.fsi.rho^2)*(((comp1.u fluid-d(r,TIME))^2)+((comp1.w fluid-d(z,TIME))^2)))))/(comp1.fsi.mu*24))))
Failed to evaluate variable.
Variable: comp1.fsi.vhNS lin, Defined as: ((0.5*sqrt((max((comp1.fsi.tau m*(((comp1.fsi.res u*comp1.fsi.xi m)^2)+((comp1.fsi.res v*comp1.fsi.xi m)^2))),0)*comp1.fsi.B0YigijtauNorm2)))/(comp1.fsi.B0YigijtauNorm2+eps))
Failed to evaluate expression.
Expression: nojac(((1.4142135623730951^(1-shapeorder(comp1.u fluid)))*max((comp1.fsi.vhNS lin-comp1.fsi.vhNS quad),0)))
Failed to evaluate variable.
Variable: comp1.fsi.vhNS, Defined as: nojac(((1.4142135623730951^(1-shapeorder(comp1.u fluid)))*max((comp1.fsi.vhNS lin-comp1.fsi.vhNS quad),0)))
Failed to evaluate temporary symbolic derivative variable.
Variable: comp1.fsi.crosswindnsVDN${test8}, Defined as: ((comp1.fsi.rho*comp1.fsi.vhNS)*((comp1.u fluidr*(-comp1.fsi.gijrr))-(comp1.u fluidz*comp1.fsi.gijrz)))
Failed to evaluate expression.
Expression: d((2*comp1.fsi.crosswindns*pi*r)*(dvol spatial),{test8})
Last time step is not converged.

Can Any one answer this pls
8 Replies Last Post Jul 3, 2017, 7:46 p.m. EDT
COMSOL Moderator

Hello Apurva Gajwani

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永宾 张
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Posted: 9 years ago May 22, 2016, 10:53 p.m. EDT
I have got the same problem，do you have any solution?
I have got the same problem，do you have any solution?
Joe Alexandersen
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Posted: 8 years ago Sep 30, 2016, 3:14 a.m. EDT
Me too! But for conjugate heat transfer. I am assuming it has something to do with a particular poor quality mesh. But I have tried to change the mesh significantly and it does not seem to work.
Me too! But for conjugate heat transfer. I am assuming it has something to do with a particular poor quality mesh. But I have tried to change the mesh significantly and it does not seem to work.
Joe Alexandersen
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Posted: 8 years ago Sep 30, 2016, 3:42 a.m. EDT
For me, it just helped to turn off crosswind stabilisation, as that is where the error message stems from.
For me, it just helped to turn off crosswind stabilisation, as that is where the error message stems from.
Jordan Chase
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Posted: 8 years ago Apr 10, 2017, 4:57 p.m. EDT
I have the same issue in a model with NITF physics. Please advise! Thank you.
I have the same issue in a model with NITF physics. Please advise! Thank you.
Tina Maake
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Posted: 7 years ago May 30, 2017, 7:08 a.m. EDT
I got the same Problem,
and I just can not figure out where the Problem is...
I got the same Problem, and I just can not figure out where the Problem is...
Abdul Haq Mohammed
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Posted: 7 years ago Jul 2, 2017, 4:30 p.m. EDT
Hey,

I am facing the same issue with conjugate heat transfer.

Did anyone got a solution to the problem.

Thanks in advance
Hey, I am facing the same issue with conjugate heat transfer. Did anyone got a solution to the problem. Thanks in advance
Mohammad Amin Kazemi
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Posted: 7 years ago Jul 3, 2017, 12:21 p.m. EDT
Hi,
I would get a similar error earlier. As far as I remember, the issue was with the initial conditions that were far from the final solution.
To resolve that, solve the heat transfer at first (using u,v,w=0), then use the solution as an initial condition for the combined study.
Hope this helps you.
Amin,
Hi, I would get a similar error earlier. As far as I remember, the issue was with the initial conditions that were far from the final solution. To resolve that, solve the heat transfer at first (using u,v,w=0), then use the solution as an initial condition for the combined study. Hope this helps you. Amin,
Abdul Haq Mohammed
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Posted: 7 years ago Jul 3, 2017, 7:46 p.m. EDT
Thanks
Thanks

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