[Gmsh] meshing thin membranes in structural analysis

[Matthijs Suijlen]

Dear Mr Geuzaine and Mr Remacle,

Please let me introduce myself and the company I am working for (Innoluce).
Innoluce is a high-tech starter which has spun off from Royal Philips
Electronics three years ago. The core activities of Innoluce are designing
and manufacturing micro MEMS mirrors for different markets where miniature
and accurate laser scanning is required e.g. laser printers, optical
medical devices and laser radar/gesture control. I am responsible for the
mechanical (FEM) analysis of these mirror designs. The reason for writing
this message to you is that we are facing some mesh generation
difficulties/problems and we would appreciate your comments and advice very
much.

For the finite element analysis we use Elmer FEM from the Finnish institute
CSC (www.csc.fi/english/pages/*elmer*‎).
With the Alibre CAD software we model the actual designs. These design
files in STP format are then used as input for the mesh generation in GMSH
and NETGEN. For the post-processing we use own programs written in
Numerical Python and we use Paraview a lot for inspecting output in 3D
projection.

The typical geometries we are facing have all very thin membranes (~10 μm
thick) attached to large anchor blocks (~300 μm thick). Currently we use
unstructured mesh element distributions. For the stress calculations we
would like to use at least two element layers over the thickness of these
thin membranes. The difficulty is to combine coarseness of the mesh with
the double element layer over the thickness. I have attached a model file
which represents this typical geometry. Currently we use attractor fields
to locally refine the mesh but this results in meshes with very large
number of nodes. We believe this could be done more smartly and efficiently
in GMSH. However we do not know how to proceed.

Our thought about the work flow for generating such a mesh would be:

   1. Generate 2D mesh of the membrane including refinement at desired areas
   2. Extrude this 2D mesh in the 10μm thick membrane with at least two
   element layers over the thickness
   3. Use this mesh as input for generating the 3D mesh in the rest of the
   geometry

We would like to get your advice on our mesh problem and secondly we would
like to know if the above work flow is possible with GMSH.

We thank you for your time and effort in advance and are looking forward to
your reaction.

Best regards,

Matthijs Suijlen



  ------------------------------
 Matthijs Suijlen  Development Engineer     Telephone +31-40-8002432 Address
Kerkenbos 1234 unit C  Mobile +31-6-41876748   6546 BE Nijmegen  Skype
matthijs.suijlen   The Netherlands  E-mail
matthijs.suijlen at innoluce.com Internet
http://www.innoluce.com
 Innoluce is an entrepreneurial spin-off of Royal Philips Electronics and
is a leading provider of laser scanner modules built around
state-of-the-art MEMS mirrors.

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