#1 2018-06-12 11:40:23

Groguiguy

Member

From: Centrale Lille

Registered: 2017-11-07

Posts: 94

How to eliminate some elements in maillage?

Hi,

I would like to eliminate poorest elements in my mesh, I know it is possible but I don't know how.
I know it is necessary to create groups to subtract poor elements. Currently I use a mesh with a group name is "Poor" and an other group "Global" with all volumetric elements. But when I run this file in Code_Aster, Code_aster say that mesh didn't contain surface element to apply boundary condition.
So, how can I create an element group which contain all elements, 2D and 3D? Or how can I eliminate poorest elements in my mesh?

mesh = LIRE_MAILLAGE(UNITE=20)

DEFI_GROUP(reuse=mesh,MAILLAGE=mesh,CREA_GROUP_MA=_F(NOM='Good_mesh', DIFFE=(('Global','Poor'))))

model = AFFE_MODELE(
  AFFE=_F(
    GROUP_MA=('Global'),
    MODELISATION=('3D', ),
    PHENOMENE='MECANIQUE'
  ),
  MAILLAGE=mesh,
  VERI_JACOBIEN='OUI'
)

Thanks!

ingladisa

Member

Registered: 2017-12-31

Posts: 62

Re: How to eliminate some elements in maillage?

It is not clear what you intend as "poor" elements...
Take into account that in Salome mesh module you can eliminate "bad" elements by the function "merge elements", you can merge also duplicate nodes in the same way (within a tolerance that you can set).

Take also into account that usually a mesh generated by Salome has nodes, 1D linear edge elements, external surface 2D elements, and volume 3D elements. All together. It is up to you what of these to use in analysis.
Until you don't define model in Asterstudy these elements has no meaning.
In the moment that you define:
    MODELISATION=('3D', ),
    PHENOMENE='MECANIQUE'
Aster consider 3D elements ONLY as mechanical elements, but nodes, 1D and 2D elements are useful in case you want apply loads on nodes or surfaces, but they don't have any contribution to the stiffness or mass matrix.

Yes, it is an approach a bit different from other FEM software, where if you have elements in mesh that does not have any meaning for the model there is an error. In Code_Aster you have to decide what of all mesh elements to use for analysis and with which function. But it is absolutely not necessary to remove unused elements (that could be quite hard to do).
For example, I used 2D elements of two faces of a volume mesh to simulate a surface reinforced wall (i.e. a masonry wall with fiber reinforced concrete on its surfaces), applying two modelization criteria, 3D on volume elements and DKT on 2D elements of the two faces (included in a group), all on the same single mesh.

Last edited by ingladisa (2018-06-12 13:22:28)

Groguiguy

Member

From: Centrale Lille

Registered: 2017-11-07

Posts: 94

Re: How to eliminate some elements in maillage?

Thank you ingladisa,

It is not clear what you intend as "poor" elements...

Poor elements = low quality (ratio forme > 20)
I created a group with all of low quality elements, and I would like to simulate my problem without this elements.

I didn't manage to merge this low quality elements.

Yes I understand why Code_aster use 1D,2D,3D elements in the same mesh. I currently, I need to have 2D and 3D elements in "mesh", but I don't know how can I substract low quality group at this TOUT = 'OUI' (Code_aster language).

Have you some tips to do that?

jeanpierreaubry

Guru

From: nantes (france)

Registered: 2009-03-12

Posts: 3,988

Re: How to eliminate some elements in maillage?

hello

what about
GROUP_MA=('Good_mesh',),
in AFFE_MODELE

but this may create a model very different from the one using all elements

.comm and .med file would help to uderstand

jean pierre aubry

---

consider reading my book
freely available here https://framabook.org/beginning-with-code_aster/

ingladisa

Member

Registered: 2017-12-31

Posts: 62

Re: How to eliminate some elements in maillage?

I think you should improve quality of the mesh inside salome mesh module and redefining the whole mesh. If you remove bad elements you create holes and separation in the mesh, that is worse than if you don't do anything...
Try to edit mesh hypothesis, such as Optimize OK, Activate Control Aspect Ratio...
.../salome-tutorials/usage-mesh-2d

Last edited by ingladisa (2018-06-12 15:17:01)