Note: This discussion is about an older version of the COMSOL Multiphysics® software. The information provided may be out of date.
Discussion Closed This discussion was created more than 6 months ago and has been closed. To start a new discussion with a link back to this one, click here.
Cannot evaluate the expression
Posted Mar 10, 2011, 4:30 p.m. EST Studies & Solvers Version 4.1 1 Reply
Please login with a confirmed email address before reporting spam
Hi,
I've spent weeks trying to figure out what was wrong with the model i was building ,
when i solve i get the error message
Cannot evaluate expression
Failure to evaluate variable
- Variable: mod1.T
-Geometry:1
-Boundary:17
Failure to evaluate expression
-Expression: mod1.T
-Plot: Surf1 (surface)
I've spent weeks trying to figure out what was wrong with the model i was building ,
when i solve i get the error message
Cannot evaluate expression
Failure to evaluate variable
- Variable: mod1.T
-Geometry:1
-Boundary:17
Failure to evaluate expression
-Expression: mod1.T
-Plot: Surf1 (surface)
1 Reply Last Post Mar 11, 2011, 1:23 a.m. EST
Please login with a confirmed email address before reporting spam
Posted:
1 decade ago
Hi
difficult to say something useful without a model to look at but already from the few lines I interpret:
the dependent variable T (probably temperature of model 1) is not defined on the Boundary 17 of your geometry 1
This appears in a surface plot (probably in the Results / post processing)
Questions to test:
1) Why isn't T defined on surface 17 (use the Selection list in Boundary mode in 3D or Domain mode in 2D for surfaces to identify it)
2) is the surface plot selection correct ? should it be an edge plot ? or a 3D plot
General note: if T is defined on a domain, the boundaries get a value of T value from their adjacent domains ("by heritage") if for any reason the left domain is at T0 and the right at T1 different from T0, then COMSOL usually uses an average value for the temperature on the boundary (more complex to define for a point intersecting with many edges and domains). If its an external boundary and its isolated thermally then the boundary temperature should be the surface temperature. If for some reason the boundary conditions are not well defined, COSMOL might have an issue how to define T and would leave it undefined (I have not seen that case yet).
But before you kill your PC with a hammer, send the model to support they shoudl be able to help you ;)
And do not forget to update to latest patch that helps, sometimes ;)
--
Good luck
Ivar
difficult to say something useful without a model to look at but already from the few lines I interpret:
the dependent variable T (probably temperature of model 1) is not defined on the Boundary 17 of your geometry 1
This appears in a surface plot (probably in the Results / post processing)
Questions to test:
1) Why isn't T defined on surface 17 (use the Selection list in Boundary mode in 3D or Domain mode in 2D for surfaces to identify it)
2) is the surface plot selection correct ? should it be an edge plot ? or a 3D plot
General note: if T is defined on a domain, the boundaries get a value of T value from their adjacent domains ("by heritage") if for any reason the left domain is at T0 and the right at T1 different from T0, then COMSOL usually uses an average value for the temperature on the boundary (more complex to define for a point intersecting with many edges and domains). If its an external boundary and its isolated thermally then the boundary temperature should be the surface temperature. If for some reason the boundary conditions are not well defined, COSMOL might have an issue how to define T and would leave it undefined (I have not seen that case yet).
But before you kill your PC with a hammer, send the model to support they shoudl be able to help you ;)
And do not forget to update to latest patch that helps, sometimes ;)
--
Good luck
Ivar