# [ICEM] Difference between Octree and Delaunay Mesh

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 January 25, 2019, 13:03 Difference between Octree and Delaunay Mesh #1 New Member   Adil Khan Join Date: Jan 2019 Posts: 3 Rep Power: 7 Dear all, I am a student who is just starting to venture into the world of CFD. I was trying to learn meshing on ANSYS ICEM and had to use Octree and Delaunay meshes. I know this might come across as a very basic question, but can someone explain me the difference between the two? I read about both types online, but would like someone to explain the merits and demerits of both compared to the other. Thanking you in advance, Adil Khan

 January 25, 2019, 13:56 #2 Senior Member   Gert-Jan Join Date: Oct 2012 Location: Europe Posts: 1,835 Rep Power: 27 Octree creates a large cube around your geometry and splits this over and over into smaller tetrahedral elements until it reaches the mesh requirements. Then it project elements on the geometry. The elements outside the geometry are thrown away. Delauney first creates a mesh on the surfaces of your geometry. From there it start to grow the mesh inside your geometry, untill it is completely filled with elements.

January 28, 2019, 11:09
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 Originally Posted by Gert-Jan Octree creates a large cube around your geometry and splits this over and over into smaller tetrahedral elements until it reaches the mesh requirements. Then it project elements on the geometry. The elements outside the geometry are thrown away. Delauney first creates a mesh on the surfaces of your geometry. From there it start to grow the mesh inside your geometry, untill it is completely filled with elements.
Thank you for the prompt reply. However, I am still not sure about when I should choose Octree over Delauney or vice versa. If you could shed some light on this, I would be very glad.
Regards,

 January 28, 2019, 11:56 #4 Senior Member   Gert-Jan Join Date: Oct 2012 Location: Europe Posts: 1,835 Rep Power: 27 I don't know. I never use Delauney in ICEM. I only use ICEM if the surfaces in my geometry are crap. Then Octree is very helpful since it is foregiven for sloppy geometry (overlapping, holes, gaps, etc). If my customer provides me a watertight geometry, then I use the Workbench mesher, which uses a Delauney approach. Adil_Khan likes this.

 January 29, 2019, 11:50 Icem cfd #5 New Member   Milad Join Date: Jan 2019 Posts: 3 Rep Power: 7 The Quick (Delaunay) option will generate a tetra mesh using a bottom-up meshing approach (Delaunay Tetra algorithm). This algorithm requires an existing, closed surface mesh. If this has not yet been created, it will automatically create the surface mesh from the geometry as defined by the Global Mesh Setup settings (or the Surface Mesh option). The volume mesh will then be generated from this surface mesh. You can also run this in two steps by creating/importing a surface mesh first and then running this mesher. If a surface mesh exists, you can also specify the Input as Existing Mesh when Compute Mesh is applied. The Robust (Octree) option will generate a tetra mesh using a top-down meshing approach. An Octree mesher does not require an existing surface mesh because one is created by the Octree process. It will accept a variety of parameters in a more general way. For instance, curve sizes are respected, but specific curve node spacing distributions are not. For a better understanding of the Octree meshing methodology https://cfdgroup.ir/product/course-icem-cfd/ Adil_Khan likes this.

 Tags delaunay, octree