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How to get this body meshed, Urgent please ?

Pioneer
Pioneer

Hi All,

 

I have different models of the same geometry yet only an interior object has a different rotation. (see attached please). For the importance of mesh consistency among different models, I am looking for a way to design similar mesh for the different cases (orientation degrees for the interior slit).

 

My understanding is to keep the whole model partition the same. by isolating the interior zone where the only difference. Then do partition for the interior zone in a similar way. However, I got some irregular zones where it kind of hard to mesh uniformly (with element shape does not distort due to sharp edges)

 

I am going to simulate 3D models. The partition is so challenging here. simply the error of the loop is not closed to extrude which revealed that the curves are not connected fully for two reasons. the first is there is a hole. second even I draw and trim curve in NX, I found NX itself leave a gap between curves.so they are not connected. 

 

The following are some inquiries around this problem

1- Is the suggested way practical/acceptable or even is necessary for your opinion for consistency (I mean in the results for all model)  ..do you recommend it or it has its issue that needs to avoid. 

2-Do you have any suggestions in this regards (meshing such models) please or could you refer to similar examples to study them and follow their concepts. 

3-For such a model, using dependent mesh (for mesh around the hole sides (hatched in brown color)  as it could be regarded as a type of symmetric (I mean both should have the same displacement and deformation in my case).

4- do you recommend using a discontinuous mesh that will be glued by edges-to-edge in 2D, or surface to surface in 3D.

 

Your comments are so much appreciated 

 

Thanks

 

 

 

18 REPLIES

Re: How to get this body meshed, please ?

Phenom
Phenom
  1. post an example of the mesh achirved for Case A so that we can see what you have so far
  2. Make the partition (split Body/Splite face) of the slot "parameteric" so that when you rate the slot geometry teh partion is alway there (Datume, Bissector on teh 2 faces of the slots)
  3. do you need a full model? Coudl a 1/4 model do
  4. Have you looked at using the Contact/Glue option? then you only need to remodel the centre feature. The mesh main body stay the same. If the "interface" is far enough from teh stress concnetration it shouldn't be an issue
  5. Is the issue because you wan to use Hex and not Tet?
Production: NX9.0.3.4, NX10.0.2.6
Development: VB.NET (amateur level !)

Re: How to get this body meshed, please ?

Pioneer
Pioneer
Selex_ct

Thanks for your comments and the valuable suggestions

1&5 -Yes, I'm trying to use the Hex instead of Tet element. Therefore, the partition needs more consideration. I am still trying to get a first try mesh and will attach it soon hopefully.

3- I do not I think I can use 1/4 the geometry as there is no symmetry in x, & y but only through the thickness (half thickness model can be used).

However, I have the feeling that (cyclic symmetry and/or dihedral symmetry, & dependent mesh features) can help to simplify the model geometry or the analysis in a similar way to the symmetry feature. Unfortunately, I do not know exactly if this is possible for this model or how to employ these features.

4- Yes, I mentioned in my post that I like to use this feature (glue contact, i.e. surface_to_surface gluing) in a way can transmit the mesh from fine to coarse. I have not used it before (I am a new user of NX) I will try it and hopefully itll work.

Thanks

Re: How to get this body meshed, please ?

Pioneer
Pioneer

Hi 

I got this partitioned now, but the first mesh fails at the slot. I keep trying to modifying it. 

I planned to use the surface contact for later so the mesh was not always continuous. However, I could not have that many coarse elements far from the area of interest as the smallest element size though thickness (it is size related to the size of the smallest element at the slot based on the aspect ratio criteria) in some way limit the maximum element size in the model.

 

 

Re: How to get this body meshed, please ?

Phenom
Phenom

I have found that quite often if you split the faces/bodies like you did i.e. overthinking then you are not helping NX mesher - sometime less is more! I think in your case you have created to many split. With fewer splits the starting pont is not too bad. Transition zone will be the "problem" orange blue meshes on the attached pdf

 

If you are planning to use the contact-glue option them one might be able to create a circular "split" and then manualy rotate the mesh to create the different slots position -it means that you contact gluedges are now on that circluar cut. mind you this could work even with coincident meshes

 

Still do not kwno whay 1/4 model would not work

 

 

Production: NX9.0.3.4, NX10.0.2.6
Development: VB.NET (amateur level !)

Re: How to get this body meshed, please ?

Pioneer
Pioneer
Hi Selex_ct

Thank you for your comments. It is so much appreciated.

I cannot use the 1/4 model for all the other cases where the slot is oriented, where there is no symmetry for those cases. I did not use it here as well (even though it is applicable as you implied to) as my interest is solving the other models which require using all the model without symmetry. Starting with the case shown here (symmetric case) is a simple way (as I think) to generalized for other (I mean the partition scheme and the applied conditions for mesh necessity ie. gluing or mating)

I am using surface gluing only if it is needed for FE meshing purpose. which I expected for the presence of small slot (its effect on the global meshing sizes).

Thank you for the suggested method for the partition that can be generalized for all cases. However, the transition zone you have highlighted might be still an issue here as well.
Also the time we rotate the circle part (include the slot), we will get the slot's bisector lines will be rotated as well, and then need another treatment/partition. However, I think it is the best option I got thankfully so far.

Noted that I have a 3D model. I am thinking how much fine I can go with elements at the slot without having element fails (aspect ratio, Taper, skew). I mean the element dimension on the surface to that through the thickness. The same thing with the coarse element (beyond the gluing line).
In another word, am I correct to think that having elements with huge different size (one at the slot, the other at the coarse element-far from the slot), one of them will be affected by the element size through the thickness (no. of layers). I means the aspect ratio, or we have to mesh each zone with different no of layers and the gluing the zones edges.

Please accept my apologies for much details/questions

Regards



Re: How to get this body meshed, please ?

Solution Partner Phenom Solution Partner Phenom
Solution Partner Phenom

Dear Wazy,

Here you are some ideas for meshing the part with 3-D solid CHEXA 8-nodes elements, I run FEMAP but you can do the same using NX AdvSim. The key is to define a PAD around the slot. Also, do not split bodies, simply divide surfaces in the idealization environment, later when 2-D QUAD4 mesh available simply extrude to create 3-D solid HEX mesh.

The key is to split top surfaces like the following picture:

2-D-split-geometry.png

And mesh using CQUAD4 elements: the mesh quality is perfect, it pass all the minimum NX NASTRAN control quality checks:

Check Element Quality
745 Element(s) Selected...
No Elements Outside of Maximum NX NASTRAN Allowable Value.

   Quality Check               Number Failed      Worst Value
      Quad Skew                          0           44.97235
      Quad Taper                         0           0.256011
      Quad Warp                          0                 0.
      Quad IAMin                         0           43.83203
      Quad IAMax                         0           135.0003
      Quad AR                            0           2.650163
 
   0 Elements Failed out of 745 Checked.

2-D-MESH.png

You can perform a mesh transition, but do not use a ratio bigger than 2.0 because remember you have to extrude the 2-D QUAD mesh to generate the 3-D solid CHEXA elements.

2-D-MESH-transition.png

This is the full 2-D mesh (all are QUADs, not any triangle exist):

2-D-MESH-full.png

And finally extrude the 2-D mesh to generate the 3-D solid CHEXA elements: I have used and element size = 0.2, resulting in 25 divisions in the direction of extrusion, and here you are the resulting element quality checks, the maximum aspect ratio is 5.1. If you want to reduce it, simply use 30 elements in the extrusion direction:

Check Element Quality
267775 Element(s) Selected...
No Elements Outside of Maximum NX NASTRAN Allowable Value.

   Quality Check               Number Failed      Worst Value
      Hex AR                             0           5.107534
      Hex DetJ                           0       0.0000548154
      Hex Warp                           0                 1.
 
   0 Elements Failed out of 267775 Checked.

3-D-MESH-full.png

Best regards,
Blas.

Blas Molero Hidalgo, Ingeniero Industrial, Director
IBERISA • 48004 BILBAO (SPAIN)
WEB: http://www.iberisa.com
Blog Femap-NX Nastran: http://iberisa.wordpress.com/

Re: How to get this body meshed, please ?

Pioneer
Pioneer
Dear Blas,

That's great! thank you for the great idea. there is a lot to learn from this post.

My only concern here is the model size that I was trying to use transition mesh with gluing. You have used a symmetry above but for my main purpose, I will not have a symmetry for the oriented slot. I hope you have a suggestion for such a case (see the photos attached please).
A related issue is the allocated memory for NX to run such a big model. I have a physical memory of 32GB, available 19GB which is quite good. However, the model I posted earlier which still smaller than this one but has stopped due to
(System fatal message 3000 (SITDELC: iterative solution failed due to insufficient memory), 'the result file is in a wrong format'

Your comment is appreciated
Regards

Re: How to get this body meshed, please ?

Solution Partner Phenom Solution Partner Phenom
Solution Partner Phenom

Hello!,

32 GB RAM is not too bad, but you can cut the model size more if instead to performing a mesh transition from local to global you use GLUE SURFACE-TO-SURFACE condition, this is a valid feature, I use it a lot as well. You can split the body and perform local mesh with best quality, and then gradually use GLUE in different stages, I suggest to keep the ratio 2:1 for every mesh transition, this way the quality & accuracy of both mesh & results won't be at risk.

Best regards,
Blas.

Blas Molero Hidalgo, Ingeniero Industrial, Director
IBERISA • 48004 BILBAO (SPAIN)
WEB: http://www.iberisa.com
Blog Femap-NX Nastran: http://iberisa.wordpress.com/

Re: How to get this body meshed, please ?

Pioneer
Pioneer
Hi Blas,

while with using surface gluing, we can transit from fine to coarse mesh on the surface, what about the thickness in both fine and coarse zones. Can we have a transition in the thickness (so can control the element aspect ratio in different zones) or we have to keep the thickness constant through the whole model as usual.

Regards