Brick mesh vs. tets
Brick mesh vs. tets
(OP)
Hi all,
I have some problems with brick meshing.
Anlyze type: Flotran CFD
Element: FLUID 142
Material: Air
Geometry: block in the middle bottom of the block boundary
Aim: to get accurate results of pressure coefficients (values+distribution)
Questions:
1. How is it possible to apply brick meshing?
2. What gives better results: bricks vs. tets?
Thanks a lot
Robert
I have some problems with brick meshing.
Anlyze type: Flotran CFD
Element: FLUID 142
Material: Air
Geometry: block in the middle bottom of the block boundary
Aim: to get accurate results of pressure coefficients (values+distribution)
Questions:
1. How is it possible to apply brick meshing?
2. What gives better results: bricks vs. tets?
Thanks a lot
Robert





RE: Brick mesh vs. tets
A1) Brick elements can be formed by either creating a mapped mesh of FLUID142 elements or by taking FLUID141 2-D elements and extruding these.
A2) I think the Ansys documentation sums this one up best:
"You will need to make assumptions about where the gradients are expected to be the highest, and you must adjust the mesh accordingly. For example, if you are using the turbulence model, then the region near the walls must have a much denser mesh than would be needed for a laminar problem. If it is too coarse, the original mesh may not capture significant effects brought about through steep gradients in the solution. Conversely, elements may have very large aspect ratios with the long sides along directions with very low gradients.
For the most accurate results, use mapped meshing. It more effectively maintains a consistent mesh pattern along the boundary. You can do this by issuing the command MSHKEY,1 (Main Menu> Preprocessor> Meshing> Mesh> entity> Mapped).
In some cases, you may wish to use hexahedral elements to capture detail in high-gradient regions and tetrahedral elements in less critical regions. As described in Creating Transitional Pyramid Elements in the ANSYS Modeling and Meshing Guide you can instruct ANSYS to automatically create pyramid elements at the interface.
For flow analysis, especially turbulent, you should not use pyramid elements in the region near the walls because it may lead to inaccuracies in the solution.
Wedge elements can be useful when a complex area can be easily meshed with triangles that are then extruded. For a quick solution, you can use wedge elements in the region near the walls. However, for accurate results, you should use hexahedral elements in those regions.
Wedge elements are considered to be degenerate hexahedral elements. When using the ANSYS MeshTool (Main Menu> Preprocessor> Meshing> MeshTool) to sweep triangles into wedges, you must select Hex elements."
Good luck,
-Brian
RE: Brick mesh vs. tets
on the simple shape model with values defined by standards.
After creating the mesh, I will define turbulent model
k-epsilon. Giving the velocity and boundary conditions will follow this step.
But my problem is in creating the brick mesh, because
"Volume 3 has an invalid topology for brick meshing" error
appears.
Volume 3 is creating by substracting the rectangular object
from the rectangular boundary.
How can I find a same example, or step by step method
of creating the brick mesh?
Thanks,
Robert
RE: Brick mesh vs. tets
You must subdivide the area with the property of air into four (or three) trapezes. Then mapped meshing will work!
Regards,
Alex
PS: I would generate the geometry by the 'a' command, instead of 'rectng'.
RE: Brick mesh vs. tets
subdividing the area, not the volume into regular parts????
How could I do this, I don´t use it before.
Thanks
Robert
RE: Brick mesh vs. tets
RE: Brick mesh vs. tets
Your problem is hopefully solved. Here the code:
CODE
aa=1
bb=1
cc=1
dd=0.25
ee=0.25
ff=0.25
/prep7
k,1,-aa/2,-bb/2,0
k,2,aa/2,-bb/2,0
k,3,aa/2,bb/2,0
k,4,-aa/2,bb/2,0
k,5,-aa/2,-bb/2,cc
k,6,aa/2,-bb/2,cc
k,7,aa/2,bb/2,cc
k,8,-aa/2,bb/2,cc
k,9,-dd/2,-ee/2,0
k,10,dd/2,-ee/2,0
k,11,dd/2,ee/2,0
k,12,-dd/2,ee/2,0
k,13,-dd/2,-ee/2,ff
k,14,dd/2,-ee/2,ff
k,15,dd/2,ee/2,ff
k,16,-dd/2,ee/2,ff
v,9,10,11,12,13,14,15,16 ! bloc in the middle
v,5,6,7,8,13,14,15,16 ! pyramid on the top of block
v,1,2,6,5,9,10,14,13 ! pyramid around the block
v,2,3,7,6,10,11,15,14 ! pyramid around the block
v,3,4,8,7,11,12,16,15 ! pyramid around the block
v,4,8,5,1,12,16,13,9 ! pyramid around the block
et,1,solid45
esize,0.1
mshkey,1
vmesh,all
Regards,
Alex
RE: Brick mesh vs. tets
I tried another way of solution:
dividing the volume into blocks by working plane.
That means that I got 9 blocks.
After that I tried to mesh them.
The block in the middle was succesfully meshed,
but the same error (invalid topology) appeared for
the others. I don´t know why?
Thanks,
Robert
RE: Brick mesh vs. tets
vsbw,all,delete
The keyword 'delete' is important!
RE: Brick mesh vs. tets
area of the rectangular object.
So I have now 17 blocks(9x2-1), 5 cutting planes
(rect. object is not meshed).
I use vsbw,all,delete and the brick meshing works now.
Thank you Alex.
Robert