Hemisphere-point loads

Numerical methods and mathematical models of Elmer
mdudek
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Hemisphere-point loads

Post by mdudek »

Dear all,

I am a new user of Elmer and I am really impressed by it;s capabilities. I would like to do a model according to this link:

http://www.caesarsystems.co.uk/NAFEMS_b ... s/le3.html

I am aware of Elmer ShellSolver. I have read the ElmerSolver documentation and unfortunately I didn't find any hints how to apply nodal forces (as in benchmark in link above) with use of ShellSolver. Could you please point me in right direction how this model can be done in Elmer?

Thank you for your help.
Best regards,
Mdudek
kevinarden
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Re: Hemisphere-point loads

Post by kevinarden »

In most of the tutorials and test cases loads are applied with boundary conditions, however you can target nodes instead of a boundary element. This example loads node 1 with 1000000 Newtons


Boundary Condition 1
Target Nodes(1) = 1
Force 2 = 100000.
End
raback
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Re: Hemisphere-point loads

Post by raback »

Hi

This is probably one of the test cases. It is called "Shell_OpenHemisphere" under fem/tests.

-Peter
kevinarden
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Re: Hemisphere-point loads

Post by kevinarden »

Thanks, it is not exactly the same test case but it is an example on how it would be approached.
kevinarden
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Re: Hemisphere-point loads

Post by kevinarden »

I worked through the NAEFEMS case, Elmer gets a 0.182 displacement with this mesh. The NAFEAMS target was 0.185
case.sif
(1.76 KiB) Downloaded 19 times
mesh.zip
(27.62 KiB) Downloaded 21 times
displacement.png
(42.61 KiB) Not downloaded yet
raback
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Re: Hemisphere-point loads

Post by raback »

Hi

Great work Kevin! Do you know how the NAFEMS reference solution is defined? After all, it is pretty old. It would be interesting to know the accurate solution. With such a coarse mesh the reference cannot be one?

-Peter
kevinarden
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Re: Hemisphere-point loads

Post by kevinarden »

It is described in this document which I have not reviewed yet,
https://www.nafems.org/publications/res ... ter/r0006/

Reference solution
This is a test recommended by the National Agency for Finite Element Methods and Standards (U.K.): Test LE3 from NAFEMS publication TNSB, Rev. 3, “The Standard NAFEMS Benchmarks,” October 1990.
mdudek
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Re: Hemisphere-point loads

Post by mdudek »

Thank you for your responses. I have managed to simulate this model thanks to your helpful post. I also found dr Gupta tutorial which explain the syntax of shell solver. I left the link, maybe somebody would find it useful:

https://www.researchgate.net/publicatio ... _is_also_a

Is it possible to simulate such shell with quadratic elements? As far as I noticed Elmer doesn't support QUAD 8 elements in shell solver, but will it be possible with QUAD 9?

And I would like also to ask question: Why U3 = 0 on AC edge is added as boundary condition? If I remove this constraint (according to the NAFEMS benchmark the displacements on the edge AC are free) the result are incorrect (please see attached files). Also point E should be fixed in every direction according to the same benchmark from this site:

https://abaqus-docs.mit.edu/2017/Englis ... -c-le3.htm

Could you please point me why I obtain incorrect results? Thank you for your help.

Regards,
Mdudek
Attachments
case.sif
input
(1.72 KiB) Downloaded 17 times
Screenshot from 2021-03-03 22-34-03.png
displacement
(67.66 KiB) Not downloaded yet
mesh.zip
mesh
(27.62 KiB) Downloaded 18 times
kevinarden
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Re: Hemisphere-point loads

Post by kevinarden »

Without restraining Z along AC it will not obtain the published answer, I tried it both ways in ABAQUS, NASTRAN, and Elmer same result. If you look at the actual ABAQUS input files on the attached link they restrain Z at the point of the load. If Z is not restraint the half symmetry model rotates out of plane.
mdudek
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Re: Hemisphere-point loads

Post by mdudek »

Actually that is not true. I managed to obtain correct result without locking AC edge with Ansys and Code_Aster and friend of mine got correct results with use of Abaqus (please see attached screenshots) so probably model in Elmer is incorrect.
Attachments
Code_Aster
Code_Aster
unknown.png (127.12 KiB) Viewed 348 times
unknown.png
Ansys
(57.33 KiB) Not downloaded yet
Abaqus
Abaqus
unknown.png (41.47 KiB) Viewed 348 times
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