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#1 2019-12-31 01:51:47

maxmss
Member
Registered: 2019-09-03
Posts: 25

how to create a mesh for ECHANGE_PAROI

Hi everyone,

I am developing a thermal analysis in Code_Aster,  what I need to do is define the heat exchange values between several solids with ECHANGE_PAROI. To do this I need two heat exchange interfaces for every two solids in contact. I use Make.Partition in order to obtain the interfaces of the solids in contact but the problem comes when i try to create a face groups for interfaces, because I only get a single interface of two solids in contact,  for example: in two stacked solids the interface created in a lower solid has the same face id created in the upper solid (the same mesh group instead two). Then with make.Compound do another assembly in order to obtain two different face id groups for interfaces, and finally mesh the Compound but apparently it is not enough because in Code_Aster I get the following error: Les deux listes && CAECHP.LLIST1 et && CAECHP.LLIST2, it seems a problem with the number of nodes of each interface group.


I have some questions:

What is the correct way to mesh for ECHANGE_PAROI?

Is it necessary that there is a gap between two solids in contact?

Is it desirable that the two groups of meshes for ECHANGE_PARAOI be the same?

To apply boundary conditions on an assembly of different geometries, it is necessary to have one (with groups of meshes for each solid) single mesh or should each element be individually meshed?

In the attached file is my 3D model that I want to mesh in order to create interfaces of contact of a couple solids.

Regards,
Max

Last edited by maxmss (2019-12-31 02:14:52)


Attachments:
Screenshot from 2019-12-21 14-52-23.png, Size: 32.47 KiB, Downloads: 159

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#2 2020-07-23 15:02:08

Rémi CHOUVIN
Member
Registered: 2020-07-23
Posts: 2

Re: how to create a mesh for ECHANGE_PAROI

Hi everyone,

I have exactly the same question than Max if someone know how to respond.

Thanks

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#3 2020-07-30 16:56:27

mf
Member
Registered: 2019-06-18
Posts: 261

Re: how to create a mesh for ECHANGE_PAROI

Hi,

I also have the same question, I never managed to get it right. If I remember correctly, the 2 opposite faces must be exactly identical (same number of elements with exactly opposing nodes). This is not even possible with 2 simple touching cubes, as the generated mesh (with tets) is vice-versa the same. But the two opposite faces are not.

Mario.

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#4 2020-07-30 18:46:09

mf
Member
Registered: 2019-06-18
Posts: 261

Re: how to create a mesh for ECHANGE_PAROI

I set up a little example and I get the error, that is probably most common with ECHANGE_PAROI if the two surfaces do not match perfectly:

!-------------------------------------------------------------------------------------!
   ! <EXCEPTION> <MODELISA6_22>                                                          !
   !                                                                                     !
   !  Les deux listes &&CAECHP.LLIST1  et  &&CAECHP.LLIST2  ne sont pas de même longueur !
   !-------------------------------------------------------------------------------------!

I did the following:
1.) draw two tubes in GEO-Editor.
2.) meshed the 2 tubes and their contacting surfaces TUBE1_OUTER and TUBE2_INNER exactly the same with a tetmesh size = 5mm (tried quad-dominated also, same result).
3.) Built a compound with merge nodes and a tolerance = 16mm (more than 3 times the element size, otherwise I do not get the same number of nodes in the 2 surfaces). As far as I can judge, the contacting surface meshes are the same, so ECHANGE_PAROI should work?

In the mess file I even get the same number of nodes in these 2 groups, so were is the mistake, if both surface meshes are exactly the same?

NOMBRE DE GROUPES DE NOEUDS                8
                              GrTUBE1_Nodes                      660
                              TUBE1_INNER                        194
                              GrTUBE2_Nodes                      845
                              TUBE1_OUTER                        454
                              TUBE2_INNER                        454
                              TUBE1_OUTER_edge                    62
                              TUBE2_INNER_edge                    62
                              TUBE2_OUTER                        385


Any ideas welcome, thank you in advance,

Mario.

Last edited by mf (2020-07-30 18:47:26)


Attachments:
TEST_ECHANGE_PAROI.zip, Size: 91.56 KiB, Downloads: 148

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#5 2020-07-30 19:09:20

mf
Member
Registered: 2019-06-18
Posts: 261

Re: how to create a mesh for ECHANGE_PAROI

I found the mistake: although the nodes are exactly the same, the surface triangles are not always the same.

See attached image, one group is semi-transparent, the yellow triangles are not exactly like their neighbours underneath. You can tell the difference by the crossing lines.

How can this problem be overcome?


Attachments:
Both_surface_groups_TUBE2_inner_transparent.png, Size: 217.16 KiB, Downloads: 138

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#6 2020-07-30 20:30:43

mf
Member
Registered: 2019-06-18
Posts: 261

Re: how to create a mesh for ECHANGE_PAROI

Ok, I think I got the solution.

It is all about the mesh. IT IS NOT IMPORTANT TO GET THE TOLERANCE IN GENERATE MESH COMPOUND RIGHT TO GENERATE EXACTLY THE SAME NODES as I did in the last post.

In this example, I did the following:
1.) Create a compound with the standard tolerance of 1e-5.
2.) Open the 'Duplicate Nodes and/or Elements' Dialogue and use it on the compound. Choose the second option 'duplicate nodes and border elements'. Choose the face group to duplicate (in this example TUBE1_OUTER), choose the face group to replace (here: TUBE2_INNER, but beware, this group also remains). Press 'Generate', press 'Apply and Close'. There will be a new group with ending _double (here:TUBE1_OUTER_double), which will be the second Group_MA in ECHANGE_PAROI. It is a copy of the first group (so it's exactly the same, no modifications needed), but somehow takes the place (I guess via internal ID?) of the group it should replace.

Mesh, .comm and .mess are attached. In the example above are 2 additional errors: 1.) In LAMsteel it should be TEMP instead of INST, and 2.) a second BC is missing.

If this is not the correct way to do it, please respond. I will do further testing with finer meshes. The attached mesh is quite coarse because of the upload limit, so there are only 2 temperature zones visible.

Mario.

Last edited by mf (2020-07-30 20:38:15)


Attachments:
TEST_ECHANGE_PAROI2.zip, Size: 159.62 KiB, Downloads: 167

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#7 2021-09-21 14:38:44

mf
Member
Registered: 2019-06-18
Posts: 261

Re: how to create a mesh for ECHANGE_PAROI

Hello all,

accidentally, today I found another solution for this problem in an OpenFoam-Tutorial. It is even simpler (no need to duplicate parts of the mesh..) and I am quite embarrassed it took me so long to find out. So here it goes:

1) design your bodies in Salome
2) mark all bodies that are supposed to exchange heat in the GEOMETRY module
3) create a PARTITION with all of the marked bodies (IMPORTANT: put them all in 'Objects', put nothing in 'Tool Objects'). You'll get one body/object WITH all partitions! (I never tried that before...)
4) create volume groups of your bodies (the once separated bodies in 1) ), create groups of your surfaces for ECHANGE_PAROI WITHIN those volume groups.
5) mesh your body
6) Create Groups from Geometry

Voila, your two heat exchanging surfaces have exactly the same mesh (in fact, the two groups refer to the same nodes/elements)! I did not test the ECHANGE_PAROI part of this, but it should work..

Simple example with two boxes attached, let me know if it doesn't work,

Mario.

Last edited by mf (2021-09-21 14:50:11)


Attachments:
MESH_FOR_ECHANGE_PAROI_3.hdf, Size: 242.77 KiB, Downloads: 10

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