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-   -   [ANSYS Meshing] Problem with meshing a complex Geometry (Hex) (https://www.cfd-online.com/Forums/ansys-meshing/108391-problem-meshing-complex-geometry-hex.html)

 fluent_beiyo October 22, 2012 13:50

Problem with meshing a complex Geometry (Hex)

Hi everyone,
I just started to work with CFD Fluent and have a few Problems now with the meshing. I have to do a windenergypotential analysis for a building on my College campus. The Task is to make sort of a tutorial for other people, so that they have a better starting point.

My Professor wants me to mesh the Geometry with Hexaeders. The Problem is now that the Geometry is very complex and there are still some tetraeders in the mesh, especially around the building, which is bad because that are the important zones. I have really no clue how to mesh the Geometry, so that the quality is good enough. :( Here is a photo of the actual meshing and the problem zones.

http://imageshack.us/photo/my-images/96/bild6r.gif/

the big cuboid is of course the enveloping body. I did that with the boolean operation and sliced the Result in the middle, so that you can see the problem zones.

I meshed that with Hexadominant, because there were no sweepable bodies available. Anyone an idea, how to solve that problem?

Thank you very much :)

 diamondx October 23, 2012 20:57

if you want to mesh it with hexa, you can get better control by using icem cfd.
It's difficult to get hexa in ansys meshing if you don't have sweepable bodies....

 Sixkillers October 24, 2012 03:02

Quote:
 I meshed that with Hexadominant, because there were no sweepable bodies available. Anyone an idea, how to solve that problem?
Start slicing your geometry in DM until each volume become sweepable. In addition you should have all these volumes into one part, so you will have conformal mesh.

 fluent_beiyo October 24, 2012 07:31

Quote:
 Originally Posted by diamondx (Post 388215) if you want to mesh it with hexa, you can get better control by using icem cfd. It's difficult to get hexa in ansys meshing if you don't have sweepable bodies....
Hey ,
thanks for your answers. Yes I already heard that meshing with hexa in ansys meshing isn't working very good, but we dont have the possibility to use icem cfd.

@sixkillers
could you explain how to do that, in a more detailed way? I dont know how to slice the Building exactly - here is another picture of the geometry:

http://imageshack.us/photo/my-images/196/geometryc.jpg/

Edit: Referring to the first picture that i posted, how can I generate an Inflation Layer between the Building (Hexa) and the "Air" (Tetra)around the building??

 Sixkillers October 25, 2012 02:20

Hi!

Here are some tips:

1) Hexa dominant method in ANSYS Meshing isn't designed for CFD, but for FEA.

2) When you are doing external aero your computational domain (fluid domain) has to be large enough, so your final solution wont be affected by boundary conditions. What I see on the first picture is completely unacceptable. Your fluid box should be almost 10 larger that your build in each dimension.

3) As was mentioned earlier you have to divide your fluid domain into several swepable bodies to use method sweep. The most common way to do that is by using command slice (by surface) in DM. But before doing that I would simplify your building by merging several smaller faces into a larger one (command merge in DM).

4) For a sweep method boundary layer can be simply done by specifying bias factor and refining cells near a surface.

5) If you don't what to bother with creation of mesh too much. Just create your fluid domain in DM (again large enough) and load agdb file into ICEM CFD and create a tet mesh with hexa elements in core (chech Create Hexa-Core in ICEM). Definitely watch this two youtube tutorials:

 Far November 6, 2012 09:28

did you make the mesh?

 nkme2007 November 8, 2012 09:36

Hi...

Mine is also a similar problem in meshing with GAMBIT. I want to model a building in GAMBIT 3D. Finally, aim of my project is to simulate the temperatures of the walls of building when water flows through pipes inserted in the ceiling (using Ansys Fluent). Is it possible to solve?? :confused:

 Far November 11, 2012 09:33

4 Attachment(s)
Hey

Are you still working on it. Any progress!

I am working on it. Wanted to ask can you simplify some details (Fig. 4)?

You want to mesh it inside or outside this domain?

 mechatronicstudent April 26, 2014 04:55

FATAL error in meshing

hello everybody!
I'm new in ANSYS. I have some problems in modeling & meshing.
I'm trying with : ANSYS15-x64 and in Mechanical APDL.
my system is : Intel core(i5) 2.27 with 4G RAM.
O.S : Windows 8-x64.
I create this rectangle :
wp x = 0
wp y = 0
width = 2
height = 1
I meshed it in default mode. with PLANE55 element.
Then I could Extrude it in " Cylindrical " Active C.S & with SOLID278 with " Extrude Area by XYZ" tool.
It meshed & Extruded exactly.
MY PROBLEM IS :
But when I'm trying to Extrude it in " Cylindrical-Y " Active C.S it happens this error :

*** FATAL *** CP = 4.094 TIME= 12:30:54
An allocation was made with a negative length requested: -8