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boundary integration in podtprocessing

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Dear all,

I have a simple question about comression simulation.

I have a cube in mechanical module.
I applied a prescribed displacement(in -y direction)as a boundary settings for upper boundary.
bottom boundary is fixed.

In Postprocessing/boundary integration I clicked on upper boundary and chose reaction force in y direction.

This reaction force has negative value!!!!!!!

How it can be that I press on cube and cube's reaction force is negative?

Thanks in advance,
Alex

4 Replies Last Post Aug 11, 2010, 2:26 a.m. EDT
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)

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Posted: 1 decade ago Mar 14, 2010, 1:24 p.m. EDT
Hi

I would expect that the reaction force sign is defined with respect to the surface normal = direction pointing "outwards" of the volume.

Therefore I find the signs rather coherent that way, but I agree it's a convention issue

Do you agree ?

Good luck
Ivar
Hi I would expect that the reaction force sign is defined with respect to the surface normal = direction pointing "outwards" of the volume. Therefore I find the signs rather coherent that way, but I agree it's a convention issue Do you agree ? Good luck Ivar

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Posted: 1 decade ago Mar 15, 2010, 6:18 a.m. EDT
Hi Ivar,

of course it is but the problem is that in my case it works only in x and z directions.
It should be that reaction force directed according axes but this rule works only in x and z directions...
in y direction(where my prescribed displacement applied) it works in opposite way...

Thank you in advance,
Alex
Hi Ivar, of course it is but the problem is that in my case it works only in x and z directions. It should be that reaction force directed according axes but this rule works only in x and z directions... in y direction(where my prescribed displacement applied) it works in opposite way... Thank you in advance, Alex

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Posted: 1 decade ago Aug 10, 2010, 5:14 p.m. EDT
Hi Alex:

I am having a similar issue, I was wondering if you can help me. I am modeling the insertion of a probe into the a cube. The probe I am having in post processing is that using point evaluation on vertices or boundary integration on the probe boundaries, the reaction force is always zero (in the z-direction of insertion).

I am looking for the resistance force that the probe is experiencing during the insertion - this is the reaction force right?
Also, for those points on the surface of the cube that are not part of the geometry, I cannot do point evaluation of any parameters on those points, any idea why?

I am attaching a simple version of this simulation.

Thank you,

Joe
Hi Alex: I am having a similar issue, I was wondering if you can help me. I am modeling the insertion of a probe into the a cube. The probe I am having in post processing is that using point evaluation on vertices or boundary integration on the probe boundaries, the reaction force is always zero (in the z-direction of insertion). I am looking for the resistance force that the probe is experiencing during the insertion - this is the reaction force right? Also, for those points on the surface of the cube that are not part of the geometry, I cannot do point evaluation of any parameters on those points, any idea why? I am attaching a simple version of this simulation. Thank you, Joe


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Posted: 1 decade ago Aug 11, 2010, 2:26 a.m. EDT
Hi Ivar:

I am having a similar issue, I was wondering if you can help me. I am modeling the insertion of a probe into the a cube. The probe I am having in post processing is that using point evaluation on vertices or boundary integration on the probe boundaries, the reaction force is always zero (in the z-direction of insertion).

I am looking for the resistance force that the probe is experiencing during the insertion - this is the reaction force right?
Also, for those points on the surface of the cube that are not part of the geometry, I cannot do point evaluation of any parameters on those points, any idea why?

I am attaching a simple version of this simulation.

Thank you,

Joe

Hi Ivar: I am having a similar issue, I was wondering if you can help me. I am modeling the insertion of a probe into the a cube. The probe I am having in post processing is that using point evaluation on vertices or boundary integration on the probe boundaries, the reaction force is always zero (in the z-direction of insertion). I am looking for the resistance force that the probe is experiencing during the insertion - this is the reaction force right? Also, for those points on the surface of the cube that are not part of the geometry, I cannot do point evaluation of any parameters on those points, any idea why? I am attaching a simple version of this simulation. Thank you, Joe

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