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Issues with Modeling Rigid Probe Micromotion in Soft Tissue

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Hi all,

I am an undergraduate student working with COMSOL for the first time this summer. I am trying to model the effect of a rigid body moving relative to soft tissue. I designated a prescribed displacement for one surface of the rigid body. My output graph displays stress in the rigid body as a result of the rigid body's contact with the soft tissue during movement. However, the output graph shows stress in the soft tissue to be 0.0 at all points, which doesn't make sense considering its contact with the rigid body.

I know there must be some issue with my model, but I am not sure how to get the tissue included in the analysis. Any advice on this issue would be greatly appreciated! I have attached my .mph file.

Thank you!



1 Reply Last Post 5 Jul 2020, 17:33 GMT-4

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Posted: 8 months ago 5 Jul 2020, 17:33 GMT-4

Hi Will,

I have no experience with this type of model in particular, so instead I'll give you some methodology advices.

  1. It is probrably helpful to debug this on a simpler version of your model, for rapidly identifying the root cause of the problem. What's the simplest model you could build with COMSOL that would exhibit the same issue? Perhaps a 2D model, maybe with revolution symmetry, can be similar enough for testing purposes.
  2. Are you quite sure that you are plotting the right quantity?
  3. Are the equations active on the domain where you want to plot?
  4. If your model stores more than one solution, is your plot taking its input from the correct dataset ? 
  5. When you say the stress is 0.0, is it exactly 0, or too small for the colorbar? It can help to select just one segment, or use log-scale.
  6. Are you confident that the mesh is fine enough?

I know these tips are quite generic but hopefully useful nonetheless

Best, Alexis

Hi Will, I have no experience with this type of model in particular, so instead I'll give you some methodology advices. 1. It is probrably helpful to debug this on a simpler version of your model, for rapidly identifying the root cause of the problem. What's the simplest model you could build with COMSOL that would exhibit the same issue? Perhaps a 2D model, maybe with revolution symmetry, can be similar enough for testing purposes. 2. Are you quite sure that you are plotting the right quantity? 3. Are the equations active on the domain where you want to plot? 4. If your model stores more than one solution, is your plot taking its input from the correct dataset ?  5. When you say the stress is 0.0, is it exactly 0, or too small for the colorbar? It can help to select just one segment, or use log-scale. 6. Are you confident that the mesh is fine enough? I know these tips are quite generic but hopefully useful nonetheless Best, Alexis

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