Aspect Ratio for 3D Mesh and match percentage in DD

[mtrujil1]

Hello Moldflow user!

im having some problems to fix the aspect ratio in 3D mesh, currently i use a pre-processor to mesh the part, im using ANSA to create tyhe DD mesh (element lenght 4mm) and then i export the mesh as .nas (Nastran).

in MF i imported the .nas file and the next step was review the quality of the mesh, normally i realese the aspect ratio with 6 or 5 value, and after that i change the mesh type to 3D (Edge Lenght 4mm, bias element through the thickness:10, MAx Edge Length through thickness: 2.5, bias ratio: 1.5).

But the Problem is presented when the 3D meshing is done (created in MFI), the aspect Ratio result change dramatically around 140-150.

i know the Aspect ratio recommended for 3D is 50<!

Please support me to solve this issue ans also im having some problems to match the elements.

[madhukeshwart]

Steps 

============ 

1. It is recommended to use mold flow meshing option ( instead of separate pre-processing tool like Hyper mesh/ Ansa). ASMI 2014/2015 captures better mesh.

2. It is not required to maintain  aspect ratio < 6. It is just fine < 30 . If you are going to conver DD mesh in to 3D mesh.

3.  once you have created good quality DD mesh with aspect ratio < 30. Try to elimiate smaller element.

4. Use mesh repair wizard to fix 3D quality - including 3D aspect ratio < 50. 

 5.  If more number of elements are failing in 3D. use diagnostic tool to isolate area of problems and elements with problems

 Try to correct the mesh problem in DD stage. So keep a copy of DD mesh, before converting it into 3D. (refer below image)

Hope this solves most of 3D mesh problems. 

6. If some elements are above the limit. understand the effect of same on results and Judge & interpret results and take decision with caution 

[xusho]

Hello,

Low aspect ratio on surface is not sufficient to generate good 3D meshes.

When you need more layers for a thin model, the surface edge length should be smaller.

The default edge length is based on 6 layers.

Now when you need 10 layers, you need to mesh the surface with smaller edge length, eg. 3mm, 2.5mm instead of still 4mm.

The maximum aspetc ratio on surface can be 30 for 3D.

Shoudong Xu

Moldflow Meshing Team

[mayur_dhumal]

Hi,

I would recommend using Third party meshing software only in case if you need to reduce the number of tetrahedral mesh elements(being a Analyst i know this very well). When you create DD mesh in Third party meshing software, it does not take into account the mesh match %, even though software may have captured geometry well and CAD/FEA model volume is matching it is not advisable.

I suppose that there may not have to be any problem with 3D mesh aspect ratio exceeding in first place; you can always rectify it, repair it using 'Mesh Repair Wizard' which is totally automatic. After this stage if Aspect ratio is failing for few elements then this a indication that you may need to Remesh model with lower edge length.

Try to maintain:
Max Edge length ratio : <2
Max Volume ratio to average volume : <20
Max / average Aspect ratio : <50
Min angle between tetra faces : 2
Max angle between tetra faces : 178

These are all inter-dependent.

Regards,
Mayur