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DISPLACEMENT

Posted May 26, 2016, 11:18 p.m. EDT Structural Mechanics Version 5.0 3 Replies

Bernard Ouma
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Hi All,
I got a small problem and I think someone may be having an idea of how to solve it. I have run my simulation in COMSOL 5.0 and determined the displacement in the color legend. I applied a point load that gave the resultant displacement.
I would like to know the exact displacement at a given point say X (see the attached file). Is there a way I can do this or I have just to approximate from the color variation?
Any suggestions will be highly appreciated.

Best Regards,
Ben

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3 Replies Last Post May 27, 2016, 3:39 a.m. EDT
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 8 years ago May 27, 2016, 1:43 a.m. EDT
Hi

if your "point" is defined as such in the geometry (as an Entitiy) you can "integrate over one point" the value u,v,w which means basically take the sum from 1 to 1 of the value at a given point. But for this you must be able to "select" the point so it must be defined in the geometry (hence it will also automatically be a node of a mesh, except (always one around) if you have suppressed the point from the list of entities to be explicitly meshed). by the way disp=sqrt(u^2+v^2+w^2) in all generality, always positive.

Another way is to use the "Results - Data Set - Cut Point" and then COMSOL will interpolate the value from the surroundings.

One caveat I just encountered: if your point is on a boundary and the dependent variable you are extracting is discontinuous at that boundary, COMSOL will take the Boundary "up" direction value and not the boundary average value (i.e. test it in MF the H value that is often highly discontinuous along an iron boundary)

--
Good luck
Ivar
Hi if your "point" is defined as such in the geometry (as an Entitiy) you can "integrate over one point" the value u,v,w which means basically take the sum from 1 to 1 of the value at a given point. But for this you must be able to "select" the point so it must be defined in the geometry (hence it will also automatically be a node of a mesh, except (always one around) if you have suppressed the point from the list of entities to be explicitly meshed). by the way disp=sqrt(u^2+v^2+w^2) in all generality, always positive. Another way is to use the "Results - Data Set - Cut Point" and then COMSOL will interpolate the value from the surroundings. One caveat I just encountered: if your point is on a boundary and the dependent variable you are extracting is discontinuous at that boundary, COMSOL will take the Boundary "up" direction value and not the boundary average value (i.e. test it in MF the H value that is often highly discontinuous along an iron boundary) -- Good luck Ivar
Bernard Ouma
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Posted: 8 years ago May 27, 2016, 3:20 a.m. EDT
Hi Ivar,
Thank you so much for your prompt response. I have used the second method that you suggested and solved the problem. God bless.

Kind Regards,
Ben
Hi Ivar, Thank you so much for your prompt response. I have used the second method that you suggested and solved the problem. God bless. Kind Regards, Ben
Gunnar Andersson COMSOL Employee

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Posted: 8 years ago May 27, 2016, 3:39 a.m. EDT

I would like to know the exact displacement at a given point say X (see the attached file). Is there a way I can do this or I have just to approximate from the color variation?


An easy way to get the value in a point for which you don't know the coordinates is to select the plot in the Model Builder and click in the graphics window where you want to evaluate. The coordinates and value are shown in a table below the graphics window.

If you know the coordinates of the point and want to know the exact value, then there are two cases:

1. The point is a geometric point: Go to Results > Derived Values and add a Point Evaluation feature. Select the point(s) where you want to evaluate and enter an expression. Click on Evaluate in the toolbar.

2. The point isn't a geometric point: Go to Results > Data Sets and add a Cut Point 3D data set. Enter the coordinates in the Point Data section. Go to Results > Derived Values and add a Point Evaluation feature. Change the Data set to the Cut Point 3D data set you just created. Enter an expression. Click on Evaluate in the toolbar.
[QUOTE] I would like to know the exact displacement at a given point say X (see the attached file). Is there a way I can do this or I have just to approximate from the color variation? [/QUOTE] An easy way to get the value in a point for which you don't know the coordinates is to select the plot in the Model Builder and click in the graphics window where you want to evaluate. The coordinates and value are shown in a table below the graphics window. If you know the coordinates of the point and want to know the exact value, then there are two cases: 1. The point is a geometric point: Go to Results > Derived Values and add a Point Evaluation feature. Select the point(s) where you want to evaluate and enter an expression. Click on Evaluate in the toolbar. 2. The point isn't a geometric point: Go to Results > Data Sets and add a Cut Point 3D data set. Enter the coordinates in the Point Data section. Go to Results > Derived Values and add a Point Evaluation feature. Change the Data set to the Cut Point 3D data set you just created. Enter an expression. Click on Evaluate in the toolbar.

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