Disk deflection

Numerical methods and mathematical models of Elmer
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XHZhu
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Joined: 23 May 2021, 02:03
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Disk deflection

Post by XHZhu »

Hi, I'm a newbie to FEM and Elmer, fascinated by the clean and powerful solver.
I'm working on simulating the deformation of a disk under certain force fields.
Currently, I followed tutorial 9 on the ElmerGUI tutorials to obtain the deflection of a linear plate. I successfully modify the plate shape to a disk and the material for my project. However, I have several questions regarding the solver:
1. Can I apply arbitrary forces/pressures to the disk? I.e., forces in arbitrary directions and locations, and how can I achieve this? Also, I tried to use the deflection tab in "body forces", do these constraints mean apply certain deflections on specific points?
2. From the ParaView, I can observe the deflections' magnitude and XYZ plots, I guess XYZ plots represent deformations' directions and magnitude means deformation distance. Is this correct?
3. I'm trying to use the multiline expressions to define conditions, are there any docs that illustrate the usage?

Many thanks if anyone could give some advice :)
kevinarden
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Re: Disk deflection

Post by kevinarden »

1. Yes, you can create internal boundary elements to apply forces to, or divide the mesh into more than on body. You can target nodes to apply point loads on. A body force is applied to an entire body, applying a deflection to a body would impose that deflection to the body. You can also impose deflection values to boundaries or target nodes.
2. Paraview has the deflections in the x direction, y direction, and z direction. You can view these individually or the magnitude of the vector they form.
3. You should look at the solvers documentation in the model manual, solver manual, The MATC manual documents multline expressions.

https://www.nic.funet.fi/pub/sci/physics/elmer/doc/
XHZhu
Posts: 11
Joined: 23 May 2021, 02:03
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Re: Disk deflection

Post by XHZhu »

Hi Elmer team,
Thanks for your fast reply!
To create an internal boundary, I referred to this post viewtopic.php?t=43.
Specifically, I created a boundary condition specifying deflection on a node, as below.

Code: Select all

Boundary Condition 2
  Target Coordinates(1,2) = Real 0.005 0.005
  Name = "Displacement"
  Deflection 3 = 0.0
  Deflection 1 = 1e-3
  Deflection 2 = 0.0
End

Boundary Condition 3
  Target Nodes(1) = Integer 100
  Name = "Displacement"
  Deflection 3 = 0.0
  Deflection 1 = 1e-3
  Deflection 2 = 0.0
End
It works fine, the deformation makes sense to me.

In tutorial 9, it says that
the 1st component of Deflection is the displacement to normal direction whereas the 2nd and
3rd components are the x- and y-components of the rotation vector
.
I'm wondering does this hold for both boundary conditions and results? I.e., specifying deflection 1 means deformation in the normal direction.
kevinarden
Posts: 2237
Joined: 25 Jan 2019, 01:28
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Re: Disk deflection

Post by kevinarden »

It would hold true for both boundary condition and results, when using that particular solver. However Elmer has many different solvers, and the variables of displacement 1, 2, 3 , U 1 , U 2, U3, etc. vary among the solvers.
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