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Error simulating a carbon-nanotube
Posted 16.12.2021, 12:55 GMT-5 Electromagnetics, Structural & Acoustics 2 Replies
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Dear all,
I have been facing a problem with my comsol design. I am trying to do a model of carbon-nanotube cantilever (radius 1.4 nm) that is actuated thanks to an electrode. In order to do so, i have tried doing the meshing by applying a moving mesh on my carbon-nanotube. However, I think there's a problem with the moving mesh that I established for the CNT (the error says : Multiple moving frame specifications on the same selection : the problematic selection is the carbon nanotube) and I can't find the solution. i have looked for several solutions online, tried to redefine the mesh and carefully define where the physics apply depending on the region but nothing.
I have tried replacing the moving mesh by a deformed geometry in the deformed mesh section as suggested in some other forum discussions but I have the following error :
Undefined variable. - Variable: u - Geometry: geom1 - Boundaries: 6-10, 17 Failed to evaluate Jacobian of expression. - Expression: Xg-comp1.material.X_free+u
It seems like comsol doesn't recognize my parameter u put in the mesh displacement variables.
Thank you in advance for your help.
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The fundamental question is what you want to achieve with the moving mesh? Typically, a moving mesh is used in, say, a fluid domain surrounding a structure.
You cannot use a moving mesh in the same domain as where you have Solid Mechanics. That will give the error message you describe. The deformation in the solid is controlled by the solid mechanics solution, and you cannot at the same time prescribe the mesh deformation, since it would in general be a conflict.
-------------------Henrik Sönnerlind
COMSOL
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Dear Henrik,
Thank you for your answer. Indeed, this was the problem as I didn't understand correclty the moving mesh assignement. I have another question if possible. If I use the standard physics mesh suggested by comsol, it gives some warnings as the carbon nanotube is small with respect to the mesh (even for fine meshes). Does the warning mean that the calculations performed are less accurate ? I tried customizing the mesh by using a free triangular swept mesh but it doesn't work correclty for me. I think I still need to master the art of meshing.
Best regards,
Yasser