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#1 2021-11-14 15:59:11

mihe
Member
From: ENGCALengineeringcalculations
Registered: 2008-04-08
Posts: 259

HEXA20_27, PENTA15_18 and the conformity of the mesh

Hi, A Question about CREA_MAILLAGE HEXA20_27, PENTA15_18 and the conformity of the mesh.

HEXA27 is recommended for contact analysis(u4.44.11, u2.04.04, u4.23.02) and my experience is that for contact with friction it is a huge difference in converges compared to other elements. At least for FORMULATION='CONTINUE’.

But there is extra effort building the mesh. Building a combined mesh with HEXA20 and PENTA15 can often be easier. However it may then become complicated to convert the mesh into a HEXA27 mesh since CREA_MAILLAGE with keyword HEXA20_27 only modifies QUAD8  and HEXA20 elements (into QUAD 9 and HEXA27).

If you convert a combined HEXA20+PENTA15 mesh using HEXA20_27=_F(TOUT='OUI’) , then on the QUAD sides of the PENTA15 you will get QUAD9 elements that do not conform with the underlying PENTA15. The problem is not solved by sequentially adding the PENTA15_18 operation. QUAD9 elements will then exist on the quad sides of the PENTA18 but the elements will not be joined at the mid side node. The end result is a mesh where you can not use the quad side elements of the pentas.

Questions:
1 -If converting a combined mesh HEXA20+PENTA15 mesh using HEXA20_27=_F(TOUT='OUI’) and then only using the quad sides of the HEXA27 and the triangular sides of the PENTA15 elements: -Will this be ok? –Or will the nonconformity between then voluminal HEXA27(with mid side node) and the PENTA15(without midside node) reduce the accuracy of the stresses and the deformations?

2 -For a HEXA20_27=_F(TOUT='OUI’) + PENTA15_18=_F(TOUT='OUI’) mesh a way to attach the QUAD9 side to the PENTA18 could be to merge the mid side nodes manually (for example by importing them into Salome + merge + export). –Would this be good way to solve this issue if you want to be able to use also the quad sides of the pentas? –Or is there another way? (The documentation says not “At present, mixed grids made up at the same time ofHEXA20 and of PENTA15 are not transformable by CREA_MAILLAGE”) –Still Would the presented “manual merge” idea work?

3 –For a mesh with only PENTA18 (created with the PENTA15_18 =_F(TOUT='OUI’) operation) will the QUAD9 sides perform as good in contact as if the underlying element was a HEXA27?

4 -Anyone want to recommend an automatic hex-mesher?   -Are the Salome plugins DISTENE "MG-" algorithms good?

Thank you for your inputs!
BR/Micke

Last edited by mihe (2021-11-14 16:02:08)


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Salome Meca 2019 on Ubuntu 18

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#2 2022-03-18 13:47:13

jonas loenartz
Member
Registered: 2021-10-01
Posts: 51

Re: HEXA20_27, PENTA15_18 and the conformity of the mesh

Hello,

Have you found an answer to this issue? Because I am very interested in this topic, too. I use a pre-processor, that is not able to create bi-quadratic meshs and so far I only used CREA_MAILLAGE, to get bi-quadratic shell-elements. I have found it increasingly difficult to get contact-problems to converge with simple quadratic 3D-elements. It would be great, to be able to transform mixed meshes as well.

In principal it is possible to transform mixed quadratic meshes into bi-quadratic meshes using the mesh module in Salome-Meca. It would be great though, if this extra step were not neccessary.

Jonas

Last edited by jonas loenartz (2022-03-23 11:26:42)

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#3 2022-04-05 15:16:05

mihe
Member
From: ENGCALengineeringcalculations
Registered: 2008-04-08
Posts: 259

Re: HEXA20_27, PENTA15_18 and the conformity of the mesh

Hi, No I have not wound a answer.

Regarding the contact problems, -are you using Salome meca 2021? -Have you seen this post:https://code-aster.org/forum2/viewtopic.php?id=26047

I tried your idea with salome bi-quadratic but it seems this does not create PENTA18. It creates PENTA20. I am not sure CA will be able to handle them.
BR/Micke

Last edited by mihe (2022-04-06 11:25:10)


Salome Meca 2019 on Ubuntu 18

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