Mesh a model

tienbk95

hello everyone. when I make a model is a hemisphere with hollow, I want to mesh it by C3D8R element type. But I can't do it in Salome Meca.

How can I do to mesh model like that image which I attached below.

I glad when receive a help.

Attached file:
Capture1.PNG, 78792kb

mecour

Hello,

meshing of such shapes with hexahedral elements is not its strength. Here you have only 2 circles as edges, it is necessary to add more. You can partition the shape with some planes in geom module to get more surface edges. Then the hexa mesh is possible.

tienbk95

Thanks Mecour very much. I try to partition but the model always has face with 3 sides, so I can't mesh with C3D8R element type.when I compute, the monitor has error: " unexpected geomery. Face must have 4 sides but not 3.

You can see the model which I partitioned below. and you can help me with this model?

I look forward your reply.

Attached file:
1.PNG, 35372kb

mecour

Hello,

I tried more strategies but unfortunately I am not able to create such mesh as you want. What I know about hexahedral meshing, there is no general algorithm as for example delauay for tetrahedral meshing. So every software (especially commercial) uses own internal algorithm to produce hexahedral mesh. There are only few opensource hexahedral mesh generators.

My strategy is using tetrahedral mesh in such curvilinear shapes and sometime is good to use the quadratic mesh to get better results.

tienbk95

Thanks for your reply. I hope you are always healthy and successful.

Nicolas

Here is one solution. The main difficulty is the edge that générâtes the sphères. It implies a translation for the partition.

Attached file:
hemisphere.py, 5337kb

Nicolas

If you can rotate the spheres, the influence of the generatrices disappears.

Attached file:
hemisphere.py, 5320kb

mecour

Hello,

thanks to Nicolas I also created quite similar mesh. Thank you for this instructions. I always fight with hexahedral mesh at curvaceous shapes.

Attached file:
pic.png, 349607kb

tienbk95

Thanks to Nicolas. When I received your answer, I was very happy. I've just used Salome Meca, so I hard to do these problems. So, Thanks a lot.

sb1966

mecour wrote

thanks to Nicolas I also created quite similar mesh.

Hi,

Would you please share your python file? I need to do similar meshing for an ellipsoidal skin with thickness. I think your file would be helpful for me too.

BTW, another question to experts in gmsh:

How to do similar meshing in gmsh? I hope that it would be a lot easier in gmsh.

Thanks in advance.

Regards.

Sukumar

mecour

Hello,

I will try prepare python file also for some ellpsoid, now i know how to start.

In gmsh is aslo possible create hexahedral mesh, but as in salome the meshing of curvaceous shape requires some geometrical operation

sb1966

mecour wrote:

I will try prepare python file also for some ellpsoid, now i know how to start.

Dear mecour,

Thanks a lot for your kind gesture. Would sincerely wait for your file(s).

In gmsh (it) is also possible create hexahedral mesh, but as in salome the meshing of curvaceous shape requires some geometrical operation

Thank you for your suggestion. I will try after about a week due to my other preoccupations.

With Best regards

Sukumar

sb1966

Hi,

While surfing, I got the following blog, which might be useful for hexahedral meshing using gmsh:

http.blogspot.com/2013/12/building-hexagonal-meshes-with-gmsh.html

Thanks and regards.

mecour

Hello,

As I promise last week I tried to prepare ellipsoidal shape with hexa element. Attachment is python file prepared in salome 8.5.0. I hope it will help. I used Nicolas 's procedure and some sub-meshing to obtain better mesh.

Before using of this mesh please check double elements and nodes.

Attached file:
elipsoid.py, 4949kb

sb1966

mecour wrote

As I promise last week I tried to prepare ellipsoidal shape with hexa element.

Dear Mecour,

Thank you so much for your file. I would try to understand it. However, unlike the file given by Nicolas, I am unable to see the mesh in your file.

I am using the latest Salome-meca (2018.0.1) which uses Salome 8.5.0.

Do I need to do something else to activate the mesh?

Thank you very much again for your kind gesture.

Regards.

Sukumar

ib-guder

hi!

maybe this one helps. Its a bit messy, because i played around a bit.

tom

ps: its made with salome18

Attached file:
Study1.hdf, 987908kb

ib-guder

or this one. Its about mapping a cube into and onto a sphere for getting a hexaedral mesh of a sphere.

Attached file:
Study2.hdf, 910306kb

ib-guder

here a picture of the geometry.

Attached file:
geom.png, 90756kb

ib-guder

and of the mesh. I deleted some elements to reveal the mesh-quality.

Attached file:
mesh.png, 74898kb