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webhaw July 24, 2007 08:08

ICEM clustering of mesh points and multiple edges
As, I am meshing a aircraft, i have imported the geometry from solid works and try to mesh it.

a) As i am giving command for meshing using tetra cells. It generates the mesh. But the mesh is not growing (from surface) as per the expansion funtion, mesh density & tetra cell ratio, i have given . It generate N (number of cells) uniform size mesh cells from the surface, after that the mesh cell size is limited to maximum size element and just filling the volume.

Can anybody help me for the proper(without much jump) expansion of mesh from the surface in tetra mesh?

b) Some how i genearted mesh with the tetra cells without clustering and all. After the mesh check, it shows Multiple edges in some area. When i zoom the area, i find it is not desirable. But i really don't know how to remove them.

can you help me regarding Multiple edges, how to avoid them?

please help me.......

Thanks for reading this msg

Robin July 24, 2007 10:17

Re: ICEM clustering of mesh points and multiple ed
Hi Webhaw,

a) The octree algorithm can only give 2:1 expansion ratios. If you specify an expansion ratio, it will reduce the target size, but keep creating elements of the same size until the target size is 1/2 or 2x the current size. To get a smoother mesh, turn on the "Smooth Transitions" option. This will make tetra automatically throw away the volume mesh and fill the volume from the surface mesh using a Delauney algorithm. You can also do this manually by deleting the volume elements and remeshing from the surface using Delauney. If you have version 11.0 installed, you can also use "Advancing Front" or TGrid Delauney (the delauney mesher from FLUENT TGrid).

b) If you delete the curve, ICEM CFD will not resolve it. You can do this manually, or run the "Build Topology' function to do it for you. You should be able to find examples of this in the tutorials or the on-line demos.

Regards, Robin

webhaw July 25, 2007 02:04

Re: ICEM clustering of mesh points and multiple ed
Thanks robin....for a quick reply.

I m having ICEM CFD 10.0...

i can understand the first answer and i am trying as u sugested. Des it mean that i have to give tetra ratio or expansion 2 only?

but i couldn't understand the second answer....can u elborate it...

Robin July 25, 2007 10:10

Re: ICEM clustering of mesh points and multiple ed
Hi Webhaw,

You don't need to specify a ratio of 2. With the Octree (tetra) method, if you specify a surface size of 1 and an expansion ratio of 1.2 the first layer will be size 1, the second layer will have a target size of 1.2, but since tetra can only expand the cell size by a factor of two, it will maintain a cell size of 1. The next layer will have a target size of 1.44 (1.2^2) and again will have an actual size of 1. This will continue until the target size is greater than or equal to 2, at which point the cell size will double.

At the very least specifying an expansion ratio will delay the change and keep more layers at the smaller size.

On the second point, there is a "smooth transitions" option when you run tetra. This will run an automated process which will use tetra to create the surface mesh (the volume mesh is intersected with the surface to get a surface mesh, rather than starting from the surface). The volume mesh is then deleted and a Delauney method is used to fill the volume from the surface mesh obtained in the first step.

Version 11.0 offers some additional volume meshing options such as the Delauney method from TGrid and the Advancing Front method from CFX-Mesh. Each of these offer further advantages in terms of element quality with TGrid Delauney being faster and Advancing Front having the highest quality but a bit longer to run.

Regards, Robin

myron July 25, 2007 16:29

Re: ICEM clustering of mesh points and multiple ed
In other words - leave the 'tetra expansion ratio' at the default of 0. If you want a few layers of the same size before expanding - you can set 'Num Layers' to 2 or 3.

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