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Mesh requirements to accurately calculate mass properties
Posted 16 set 2015, 22:41 GMT-4 Mesh, Parameters, Variables, & Functions, Results & Visualization, Studies & Solvers Version 5.0 2 Replies
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I am trying to model the rotation of a dipole in an electric field. I am using mass properties to determine the moment of inertia, etc of the dipole. I kept getting a divide by 0 error so I've looked at the values that have been calculated and compared them to analytic values.
the calculation of the mass and moment of inertia are both out by 15 orders of magnitude! The COM is non-zero in both the x- and y-axes (the dipole is symmetrically positioned in the centre of the geometry).
I have tried shrinking the mesh, which changes the values, but not significantly. Halving the maximum element size of the mesh basically doubled the calculated mass and moment of inertia. Does this mean I have decrease the maximum element size by 15 orders of magnitude (which is obviously not actually going to be possible) before the calculated values will be correct?! Is there some threshold where the calculation will suddenly become accurate?
the calculation of the mass and moment of inertia are both out by 15 orders of magnitude! The COM is non-zero in both the x- and y-axes (the dipole is symmetrically positioned in the centre of the geometry).
I have tried shrinking the mesh, which changes the values, but not significantly. Halving the maximum element size of the mesh basically doubled the calculated mass and moment of inertia. Does this mean I have decrease the maximum element size by 15 orders of magnitude (which is obviously not actually going to be possible) before the calculated values will be correct?! Is there some threshold where the calculation will suddenly become accurate?
2 Replies Last Post 17 set 2015, 05:09 GMT-4
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Posted:
9 years ago
Hi,
On the contrary, the calculation of mass properties is rather insensitive to the mesh size. So there is definitely something else going wrong here.
Try just computing the integral of '1' over the same domain manually. That should give the volume, with an accuracy similar to what you get from the mass property computation.
Can you upload the example?
Regards,
Henrik
On the contrary, the calculation of mass properties is rather insensitive to the mesh size. So there is definitely something else going wrong here.
Try just computing the integral of '1' over the same domain manually. That should give the volume, with an accuracy similar to what you get from the mass property computation.
Can you upload the example?
Regards,
Henrik
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Posted:
9 years ago
Hi Henrik,
thanks for your reply.
Right, that was what I thought; certainly in the examples/tutorials I've looked at, things seem accurate with much larger meshes than I've been using. It, therefore, surprised me when the values changed when I changed the mesh.
I'm not sure how to do this. I've not been using COMSOL long and I'm still fumbling around a little.
I left uni before this reply came through, I can upload it next Monday.
thanks for your reply.
On the contrary, the calculation of mass properties is rather insensitive to the mesh size. So there is definitely something else going wrong here.
Right, that was what I thought; certainly in the examples/tutorials I've looked at, things seem accurate with much larger meshes than I've been using. It, therefore, surprised me when the values changed when I changed the mesh.
Try just computing the integral of '1' over the same domain manually. That should give the volume, with an accuracy similar to what you get from the mass property computation.
I'm not sure how to do this. I've not been using COMSOL long and I'm still fumbling around a little.
Can you upload the example?
I left uni before this reply came through, I can upload it next Monday.