Strange mechanical behavior in FSI

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Hello,

I am a student, new to COMSOL, and I'm trying to compute a fluid-structure interaction study where the sinusoidal body load applied to the mechanism induces a motion in the fluid. Everything seems to run smoothly but when I observe the results, something odd is displayed. While the solid body is deformed (cf attached file), it seems the the motion in the fluid is computed taking into account a not deformed solid(cf attached file).

It is problematic since the fluid solution is antiisymetric, while the solid behavior is not, and I'm not sure the results are right. Do any of you happen to know where the problem might come from? Is it a PEBKAC?

Regards



2 Replies Last Post 18.10.2019, 03:46 GMT-4
Henrik Sönnerlind COMSOL Employee

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Posted: 2 months ago 18.10.2019, 01:54 GMT-4

Hi,

I never heard about a PEBKAC, but it seems to be the same as a PICNIC :-)

The two reasons that come to my mind are:

  1. Just a plotting problem. Wrong scale factor in Deformation node, or wrong frame in the dataset.
  2. You are running a Fluid-Structure Interaction, Fixed Geometry type of analysis, when there is no Moving Mesh. Then this type of plot makes sense: The fluid domain geometry does not change, but it gets its velocity boundary condition from the solid deformation (which is upscaled in the plot).

Regards,
Henrik

Hi, I never heard about a PEBKAC, but it seems to be the same as a PICNIC :-) The two reasons that come to my mind are: 1. Just a plotting problem. Wrong scale factor in Deformation node, or wrong frame in the dataset. 2. You are running a Fluid-Structure Interaction, Fixed Geometry type of analysis, when there is no Moving Mesh. Then this type of plot makes sense: The fluid domain geometry does not change, but it gets its velocity boundary condition from the solid deformation (which is upscaled in the plot). Regards, Henrik

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Posted: 2 months ago 18.10.2019, 03:46 GMT-4

Hello Henrik,

Thank you for your reply, yeah, PICNIC and PEBKAC are quite similar.

I changed the sulod surface plot in order to plot the total deformation and it seems that you are right, I had the wrong scale factor in Deformation and I was misguided. One more PICNIC to my long list. Thank you very much for your help.

Regards, Edouard

Hello Henrik, Thank you for your reply, yeah, PICNIC and PEBKAC are quite similar. I changed the sulod surface plot in order to plot the total deformation and it seems that you are right, I had the wrong scale factor in Deformation and I was misguided. One more PICNIC to my long list. Thank you very much for your help. Regards, Edouard

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