modelling thin shells

jake

Dear all,

I'm trying to esablish a workflow for the analysis of slender, thin (cca. 4-30 mm) shell structures - pressure vessels to be exact.

I'm considering to use Mecway as a solver and post-processor. 

My main concern is the pre-processor, which should be an effective solution for the following problem:

- rather simple surfaces: cylinder, torus, sphere...

- union of these, say union of two cylinders intersection each-other or a cylinder going through a sphere or a toroidal surface

- loading is mostly hydrostatic pressure but nodal forces/moments are also a must

- I have the geometry as 3D volume (IGES, STL etc.) from Autodesk Inventor.

- mostly membrane stresses, but bending is not to be neglected.

- Parametric model generation is important - lots of similar models with lots of small differences.

I'm pretty good in python (own opinion!) so solving the problem using scriptable tools is OK.

Right now I'm considering the following options:

- Using the 3D models and solving the problem of hexa meshing. I'd appreciate any suggestions which free mesher to use. foamyHexMesh seems to be an option, but what does it take to import the mesh in Mecway?

- I know about gmesh but have not used it - seems a little weird to me. As I understand gmesh and mecway go along well.

- creating the shells, intersections etc. as surfaces and tri- or quad-meshing them using Blender, writing the mecway input from the blender file. This is something I think sould work (Blender is scriptable and has great geometry tools) - any ideas on this?

Of course I appreciate any other ways.

Sergio

Can you share some simple models to make some tests? Normally for 2D meshes I'm using Gmsh, that gives me more quads (and then hexas by extruding) than Mecway/Netgen. This is about 97-99% of quads, if you need 100% quads then you could use the trial of Roshaz for small-medium size models. I have been looking for good quads/hexas mesher for months, but haven't found nothing better than this in the free/low cost side.

I don't do parametric analisis, but when tests are always the same what I do is separate the mesh file from the boundary conditions (using node and element sets) file in order to have to work only in mesh for the nexts cases.

There is a thread for hexa meshing on Mecway:

mecway.com/forum/discussion/157/best-strategy-to-generate-hex-meshes-within-mecway#latest

Regards

jake

Hello Sergio,

thank you for the fast answer! I attached an stp file. This is not the geometry I described above but shows the main features and proportins. Also, this file this doesn't mesh - must be healed if I remember correctly.

The mesh I need doesn't have to be hexa only, but for the thin parts it should be hexa dominated.

I checked the thread on hexa meshing and I was really surprised that netgen does now hexa dominated meshes - I'm currently installing it and have high hopes that it will word out well.

Sergio

Is there an foamyhexmesh for Windows?????

jake

there seems to be some project to port: http://bluecfd.github.io/Core/2016/08/04/bluecfd-core-2016-1-ongoing-release/

Sergio

Tahnks! I will check it, but for what I read by the moment... looks very ugly, no interface, to much hand writting cards... only for mesh generation!!! I would like to see some real cases of meshes gerated by them, mesh result and mesh procedure.

Regards

Sergio

For the example part I would leave in the CAD program only one side of the part faces, then in Mecway mesh as surface and extrude along element normal this meshes to create hexas/wedges. Then is a matter of using some glue (ccx TIE or Mecway glue contact) to stich all.

MKR

Hi 

 Have you tired Salome CAE HEXABLOCK  module ( free GPL )it is a pure Hex mesher

Another is IOWA IA-FEMESH (free GPL)

jake

I know about the hexa mesher in Salome, but never really tried, the reason being licensing.

http://www.salome-platform.org/downloads/license says: "Below listed products are included into SALOME distribution in a binary form only. These products require obtaining of the commercial license to be used in runtime."

Now, I would like to esablish the workflow at a company - commercial use - and as I understand it, the meshers should the be licensed. So this is a no-go I think - prove me otherwise please!

jake

Sergio, the part can be modified by the guy who makes the 3D-stuff so it consists of one domain and then no contacts are necessary to hold them together.

Sergio

Then guess that will be enough with Mecway/Netgen, 90% or more quads and you need to extrude or use shell elements directly. I prefer in CCX or others to use real hexa elements (by means of extrude) than shells (for sheet metal parts and structural analysis), is easier to postprocess and avoid several mistakes on material side and so one (at least for small parts).

On the side of automatization, well I don't know much about how you could do it. Is a question of make the node sets for boundary conditions in a automatic way. I sow some work done by means of coloring the cad surfaces and then the preproocessador have some intelligence to apply different BC based on this coloring scheme, but was done in Hypermesh.

About modification on the cad to become one domain, well, if is an assembly of real separated and welded parts, I prefer to mesh separately and be carefully with the weld representation, something that you could overestimate in case on having only one continuous domain. Also the representation of the parts will be more accurate.

How much is "a lot of parts"????