# Octree Grid Refinement

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 September 24, 2008, 14:38 Octree Grid Refinement #1 Tristan Guest   Posts: n/a I've been playing around with ICEM to make a tet mesh. I have a global maximum element size of 3.5 mm and then I specify a smaller maximum element size on some parts where I need local grid refinement. Here's a sequence of (part maximum element size-total number of elements) pairs for my domain (global maximum element size is always 3.5 mm): (1.5 - 3,298,490); (1.0 - 11,166,651); (0.875 - 2,2465,04); (0.7 - 4,293,775); (0.6 - 6,766,108); (0.4375 - 2,811,941) This doesn't make a whole lot of sense. Clearly, powers of 2 in the ratio between the global max element size and the part max element size are golden. If I don't use a power of two then I see grid refinement throughout the whole domain instead of just in the region near the parts with the smaller maximum element size. Is there a general rule here for Octree meshing that you should always make your local grid refinements in powers of 2? Thanks, Tristan

 September 25, 2008, 09:39 Re: Octree Grid Refinement #2 rohit Guest   Posts: n/a I have not exactly understand your problem, but i can make out that you need local refinement in some areas. Try using "mesh density" for local refinements..it is available under the mesh tab.

 September 25, 2008, 13:13 Re: Octree Grid Refinement #3 Tristan Guest   Posts: n/a Rohit, The problem is that as I decrease the maximum size on the parts where I need grid refinement, the total number of elements in my domain does not increase monotonically. When I set the maximum size on some of my parts (surfaces where I need a finer grid) to 1 mm (global maximum size is 3.5 mm), I end up with over 11 million total elements. However, if I set the maximum part size slightly smaller to 0.875 mm (which is exactly one fourth of the global maximum size) then I get just over 2 million elements. I'll take a look at using a mesh density. Tristan

 September 26, 2008, 05:33 Re: Octree Grid Refinement #4 rohit Guest   Posts: n/a Tristan, It's a strange problem, but can i know whether you are defining a surface size for the rest of the surface apart form the ones where you need refinement. I would suggest you do define a surface size of 3.5mm(i.e, your global mesh size) to all the remaining surface, and lets us see how it behaves with both the refinement sizes. Rohit.

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