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Failed to evaluate variable: freq
Posted 2012年12月21日 GMT+1 06:24RF & Microwave EngineeringVersion 5.28 Replies
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Hi COMSOL Users,
I'm new to using the v4.x series of COMSOL, so perhaps I've missed something simple, but I get an error when trying to plot body volume force variables. The error message states:
"Cannot evaluate expression.
Failed to evaluate variable.
- Variable: freq
- Geometry: 1
- Domain: 1
Failed to evaluate variable.
- Variable: mod1.acpr.freq
- Defined as: freq
..."
and continues down to mod1.spf.Fx which I am trying to plot (see attached image).
I have used the Pressure Acoustics module along with the Laminar Flow module. I set the solver to first solve Pressure Acoustics in the frequency domain (Step 1), then a combination of parameters from Pressure Acoustics is used to calculate body forces in the Laminar Flow module. Stationary analysis is used to solve for the Laminar Flow physics (Step 2).
Has anyone had this problem before? Is there an easy way to fix this problem?
Thanks in advance,
Ian
I'm new to using the v4.x series of COMSOL, so perhaps I've missed something simple, but I get an error when trying to plot body volume force variables. The error message states:
"Cannot evaluate expression.
Failed to evaluate variable.
- Variable: freq
- Geometry: 1
- Domain: 1
Failed to evaluate variable.
- Variable: mod1.acpr.freq
- Defined as: freq
..."
and continues down to mod1.spf.Fx which I am trying to plot (see attached image).
I have used the Pressure Acoustics module along with the Laminar Flow module. I set the solver to first solve Pressure Acoustics in the frequency domain (Step 1), then a combination of parameters from Pressure Acoustics is used to calculate body forces in the Laminar Flow module. Stationary analysis is used to solve for the Laminar Flow physics (Step 2).
Has anyone had this problem before? Is there an easy way to fix this problem?
Thanks in advance,
Ian
Attachments:
8 Replies
Last Post 2016年2月27日 GMT+1 22:41
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Posted:
1 decade ago
Hi
Have you defined the frequency in the first tab in the frequency solver node ? I suspect your field is blank
--
Good luck
Ivar
Have you defined the frequency in the first tab in the frequency solver node ? I suspect your field is blank
--
Good luck
Ivar
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Posted:
1 decade ago
Ian,
Try the following:
Under Global Definitions>Parameters, define variable “freq” and assign the same numerical value of the frequency you are using in the Study Step.
Update the model and plot your results again.
Regards,
Sergei
Try the following:
Under Global Definitions>Parameters, define variable “freq” and assign the same numerical value of the frequency you are using in the Study Step.
Update the model and plot your results again.
Regards,
Sergei
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Posted:
1 decade ago
Hi Ivar, Sergei,
Thanks for your help and apologies for the delayed reply. The trick of defining a new parameter "freq" under Global Parameters worked.
Regards,
Ian
Thanks for your help and apologies for the delayed reply. The trick of defining a new parameter "freq" under Global Parameters worked.
Regards,
Ian
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Posted:
1 decade ago
Hi
probably the same effect as when you run a stationary sover before a time series, with BC equations depending on "t" the time, but "t" is defined only when the time dependent solver is active not during the stationary solver, therefore one must add the variable name as a Parameter (typically t=0[s]).
For the frequency domain, "freq" is defined when that solver is active, but not for any other solver, so you need to add it in the Parameter list too.
A Parameter might be overwritten later by COMSOL as a parameter is loaded once at first solver run and only updated via a "Parameter sweep" or "Continuation sweep" sovler node
--
Good luck
Ivar
probably the same effect as when you run a stationary sover before a time series, with BC equations depending on "t" the time, but "t" is defined only when the time dependent solver is active not during the stationary solver, therefore one must add the variable name as a Parameter (typically t=0[s]).
For the frequency domain, "freq" is defined when that solver is active, but not for any other solver, so you need to add it in the Parameter list too.
A Parameter might be overwritten later by COMSOL as a parameter is loaded once at first solver run and only updated via a "Parameter sweep" or "Continuation sweep" sovler node
--
Good luck
Ivar
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Posted:
1 decade ago
Hi, Sergei,
I think I have the pretty similar trouble as the one you solved. Could you take a quick look at the attached file and help me fix the problems.
Thanks in advance on your comment.
Best,
Ji
I think I have the pretty similar trouble as the one you solved. Could you take a quick look at the attached file and help me fix the problems.
Thanks in advance on your comment.
Best,
Ji
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Posted:
1 decade ago
Thank you Sergei,
This bug still exists in 4.4!
This bug still exists in 4.4!
Ian,
Try the following:
Under Global Definitions>Parameters, define variable “freq” and assign the same numerical value of the frequency you are using in the Study Step.
Update the model and plot your results again.
Regards,
Sergei
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Posted:
9 years ago
And 5.1 too.
Thank you Sergei,
This bug still exists in 4.4!
Ian,
Try the following:
Under Global Definitions>Parameters, define variable “freq” and assign the same numerical value of the frequency you are using in the Study Step.
Update the model and plot your results again.
Regards,
Sergei
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Posted:
8 years ago
Has anyone figured out how to deal with this problem when you are running a study with two steps, each of which uses frequency domain RF, but at different frequencies?
When doing the last step, it seems to want to update the solution of the previous step using the new frequency that it sees when I don't want it to do that.
Update: never mind, I figured out how to do it in COMSOL 5.2. If you go to the topmost list (i.e Electromagnetic waves (emw) ), then go to the equation tab, there are now options to choose from. The default seems to be "study controlled", but if you change it to frequency domain, it gives you the option to enter any frequency you want with a different variable name.
When doing the last step, it seems to want to update the solution of the previous step using the new frequency that it sees when I don't want it to do that.
Update: never mind, I figured out how to do it in COMSOL 5.2. If you go to the topmost list (i.e Electromagnetic waves (emw) ), then go to the equation tab, there are now options to choose from. The default seems to be "study controlled", but if you change it to frequency domain, it gives you the option to enter any frequency you want with a different variable name.