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Query concerning Stitched body FEA Analysis

Builder
Builder

Hello everyone,

 

I have prepared some porous structure using voronoi techniques.

There were lot of part was opened therefore I couldn’t able to perform the FEA.

Now I closed most of the part using solid works software. And some part I stitched suing automatic FEMAP ability. Attached please see the pics of structure with geometry information.

I want to know can I able to perform FEA now Using FEMAP. Or Do I need to make first the complete solid as an one object.

I would be very glad for the understanding.

Looking forward to hear from somebody soon.

Your Sincerely

Varun

7 REPLIES

Re: Query concerning Stitched body FEA Analysis

Phenom
Phenom
If you want to run any form of valid static analysis, then either
(a) the solid must be made as one solid, or
(b) each separate solid will have to have its own constraints, or
(c) any solid part(s) which don't have constraints will need to be glued or otherwise connected (eg. via rigid elements or springs etc.) to a solid part which does have constraints.

AND
(d) the elements must be of sufficient quality (ie. well enough shaped for the size of the geometry) to form a proper stiffness matrix.
Otherwise, you will get a User Fatal 9137 error due to the inability for the software to calculate a unique static equilibrium to the applied loads and constraints.

You could run natural frequency analysis without constraints. You will get 6 x zero Hz modes for each separate part which is not constrained. If the model is "big" (eg, say > 500k nodes) and there are more than, say 5 or 6 separate parts, then your computer will need to be "above average specification" to do the natural frequency calculation. I am not sure what the purpose of the analysis would be if the parts are separated, but you haven't said anything about the sort of FEA you would like to conduct. If you do want natural frequency, make sure your material(s) have a density specified using consistent units (ie. Tonnes per mm^3 if your model is sized in mm)

Re: Query concerning Stitched body FEA Analysis

Builder
Builder

Thank you very much sir for the reply, well I want to perform the crushing model in terms of strress and strains. I had a lot of gap which are open and self intersection. but with the applications of cleanup and stithed I was able to fix most of the error.

 

Please attached see the image of my geomtry and please let me know if now the geomtry is complete or still need to be closed again.

 

Re: Query concerning Stitched body FEA Analysis

Phenom
Phenom
The Geometry icons in your model info tree suggest two real solids and three sheet solids. The three sheet solids probably have geometry free edges (ie. not fully closed)
Femap has a few methods (mainly Mesh -> Geometry -> Solids from Elements ) where you can mesh the surfaces of the (sheet or real) solid, then create a solid mesh from the elements. But the surface elements must form a closed volume (no free edges of elements) if this method is to work.

You have 5 distinct parts. FEA is all about connection. If mesh is not connected by common nodes, or glue, or other methods like rigid elements or contact or constraint equations, then these parts know nothing of each other and will not interact in any way. Forces must "flow" from where they are applied to the "supports" (ie. constraints). That path must be present by the means suggested above for any form of static analysis to work (ie. equilibrium possible at any proportion of applied load).
Non-linear transient (time history with inertia) analysis with general 3D contact (ie. via the Advanced Non-linear add-on) can get around some of the requirements of static equilibrium, but I will politely suggest that IF you are new to FEA, then non-linear transient is never the place to start.

Re: Query concerning Stitched body FEA Analysis

Builder
Builder

sir I did what you said, but still 2 parts are coming in as a sheet solid. 

could you please tell me how can I can oovercome this problem.

Re: Query concerning Stitched body FEA Analysis

Phenom
Phenom
If the geometry came from SolidWorks, you should confirm that the geometry is definitely also a solid in SolidWorks. Eg. Export (eg. as parasolid) the single solid and reimport the single solid and check that Solid Works can calculate values like volume and mass. If SW thinks it is a sheet instead of a real solid you should tidy it up in SolidWorks before exporting (also as parasolid)
If it is definitely a real (filled) solid in SolidWorks, perhaps you should export and import into Femap one at a time.

Femap has very strict /precise rules for real solids:
(a) must be a closed volume of surfaces (can include internal voids which MUST also be a closed collection of surfaces)
(b) EVERY surface edge MUST be shared by exactly two surfaces (eg. if you try to get a cube and add it to another cube where the cubes share one common edge, this cannot form a real solid because that common edge would then be shared with four surfaces, not two).

If the conditions above are satisfied, then Geometry -> Solid -> Stitch will successfully create a real solid. If it fails to do so, then closer inspection of the geometry is required. If modelling in mm, the default stitching tolerance may be too tight - you may need to try other (likely larger) tolerance, but don't go too large, otherwise the geometry will become corrupted. Eg. if the smallest dimension of interest is about 1 unit, then a stitch tolerance larger than 0.01should be avoided.

Re: Query concerning Stitched body FEA Analysis

Builder
Builder

sir I created the geomtry using Voronoi tesselation techniques. I was using the ZW3D software not solid works.

in zw3d it was showing a complete solid but when i import it shows 2 area are not closed.

 

Re: Query concerning Stitched body FEA Analysis

Phenom
Phenom
I support Femap clients commercially. I usually give general advice on these free forums, but you need to do the careful investigation and repair. Usually, when you stitch surfaces to become a solid in Femap, it will highlight the failed/free edges if the stitch fails to form a real solid. It should also label the free edge curves (If Window -> Show Entities is set to show labels). This will highlight why the geometry failed as a solid, allowing you to fix the problem either in ZW3D or Femap itself.
Maybe one of the other generous contributors will troubleshoot the model for you, but unfortunately I don't have time for that, sorry.