linear elastic: force on a surface which should not tilt

Numerical methods and mathematical models of Elmer
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saxonfahrer
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Joined: 27 Jan 2011, 13:47

linear elastic: force on a surface which should not tilt

Post by saxonfahrer »

Hello,
i like to model a vertical beam (fixed on bottom), wich is bended by a force (at top to the side in x-direction) and wich gets a pressure on top (z direction). Please see attached picture.
Therefore i would set a displacement for x-direction and i also need to set a pressure in z-direction.
But: the upper surface should be always parallel to the bottom surface. So the upper surface is not allowed to tilt. I assume one can handle this with "Displacement Condition i" in Elmer.
Could someone tell me how to use these condition or what is the right strategy to deal with this problem?

Best regards,
alex
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raback
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Re: linear elastic: force on a surface which should not tilt

Post by raback »

Hi

The condtional Dirichlet condition is not a solution here. This sounds more like some kind of constraint problem i.e. you know the sum of forces acting on the top level but all the displacement in the vertical direction should be the same. There are some features in that respect but I don't remember how they would be applicable. If this is something that you need to do only a small number of times fix the vertical displacement to some value, apply horizontal force, and calculate sum of reaction forces in vertical direction. Then get the correct vertical displacement from linear interpolation finding a vertical displacement so that reaction forces and applied vertical force coinside.

-Peter
skoushik
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Re: linear elastic: force on a surface which should not tilt

Post by skoushik »

In this case, as well as a general clarification with ELMER, Is it not a good idea to fix the rotation of the top face..?

Is it possible to prescribe rotation in ELMER...? If yes how...?
raback
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Re: linear elastic: force on a surface which should not tilt

Post by raback »

Hi

You can add a linear constraint such that

Code: Select all

Boundary Condition 1
  Name = "Upper"
  ...
  Displacement 3 Constant = Logical True
End 
See test cases ConstantBC*

-Peter
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