Re: Using different Geometries in a model

Fri, 19 Mar 2010 06:58:47 +0000

Hi Martin

Indeed I had forgotten about that, some time since I last played with mesh revolve and multiple geometries ;)

Basically, you are limited to extrude or revolve from one geometry into one other but that one should/must be empty; any previously revolved or extruded geometry in the destionation "GeomN" will dissapear. This I beleive (I do not know truely the interiour of COMSOL I'm just an user as you) is related to the way COMSOL normall generates a mesh:

1) the Draw mode geometry = assembly of shapes that might even overlap that you define
2) the analysed geometry (no overlaps, common borders etc, all based on a "geomanalyse()" of the Drawn geometry, this is where you define the item indexes and later apply the physics and BC's
3) the mesh generated from the analysed geometry, mesh nodes and elements are associated with the corresponding sub-domains = volumes and boundaries = faces, respectively edges and points

For the end user he seldom sees the difference between the geoemtry and the analysed geometry, but when you generate a mesh from another "Geom" COMSOL must create an analysed geometry from the mesh to allow you to derfine physics and BC's. This is done automatically by COMSO, but you do not necessarily generate a "Draw geometry" backwards from the analysed geometry.
You can, there is the command Mesh - Create Geometry from Mesh - slelect Mesh, analysed geoemtry and Draw mode. If you do it you populate your "GeomN" and COMSOL will not allow you to generate a new revolved mesh therein.

now you can draw many shap in one 2D-axi geometry and revolve all in one go into a new 3D GeomN geoemtry but you cannot mix a revovle and an extrude, as these are two separate operations.

How to get around:

1) you can generate several 3D geometries, and just link some equations on the Boundaries to get a global model (it's tedious, but could give some gain in solving time and complexity this gives some kind of "superelement" approach as each geometry is a "superelement" in the terms of some other FEm software.

2) But this loses your nice revolve mesh
you can generate the draw geometry and define your physics separately, then save each geometry and open a new session to "add/merge" them together

When I use "Add components" you add the new GeomN's and you are in the case 1)just above,
If you "Merge component" your 2D axi geom is lost and the new geoemtry created is there but the mesh has gone, as well as the "link" between the 2Daxi and the 3D domain.

Basically, I come to:
create all your geometry in 2D-axi and then revolve all together (this works) but it might not allow you to create the full model the way you wanted it, I do not see how t0 add some simple extruded or prism blocks

So this is worth a question to support on:

How to mix revolved and extruded mes in one geometry

Thanks for the tip, I learned something, hope ihelps you on the way
Good luck
Ivar

Using different Geometries in a model

Thu, 18 Mar 2010 06:47:19 +0000

Hi,

I need some basic advice on the workflow with different geometries.

I want to make a 3D Model extruded from 2D with a mesh also extruded from 2D Mesh.

I start a new 3D simulation and add a 2D geometry (GEOM2) in the model navigator. I then draw in 2D and extrude to GEOM1 what results in a 3D Solid in GEOM1.

Then I create a mesh in the 2D GEOM2 and choose extrude mesh. In the extrude dialog, I can only specify "Extrude to geometry: To new geometry". This creates a mesh in GEOM3.

Now I have the solids (on which I can define the subdomain and boundary settings) in GEOM1 and the mesh in GEOM3.

When I solve the geometry from GEOM1 is taken and a new (default) mesh is created and solved.

How can I tell Comsol to use the mesh in GEOM3 instead?

Thanks for your advice,

Martin

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Re: Using different Geometries in a model

Using different Geometries in a model