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[ICEM] How to generate sunstructured "all-tri patch-dependant" surface mesh in ICEM? |
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December 3, 2010, 06:18 |
How to generate sunstructured "all-tri patch-dependant" surface mesh in ICEM?
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#1 |
New Member
Jason Sherlock
Join Date: Sep 2010
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Hi all,
Typically when I am running alpha-traverse studies, I am creating an unstructured symmetry mesh of my geometry (left half of the geometry, left half of the far field, and a symmetry plane). I have been using patch-independant surface meshing to create the surface mesh, then advancing-front (smooth) + prisms to fill in the volume mesh. While I am quite happy with the surface mesh on the aircraft, I haven't been happy with the surface mesh generated on the symmetry plane. Since patch-independant surface meshing is using octree to generate the surface triangles, the growth rate on the symmetry plane going from the aircraft to the farfield is very octreeish: aggressive and "boxy". I haven't found a parameter that smooths this out in a nice way. The result is that the advancing-front volume mesh is constrained near the symmetry plane in a way that looks "odd/wrong" when compared to the volume growth away from the symmetry plane (see attached mesh cut-plane, this is looking down the length of the geometry, symmetry plane terminates the mesh on the left side, farfield is off screen on the right side). I've got a feeling that patch-dependant surface meshing is going to generate a surface mesh on the symmetry plane that is more compatible with the advacing-front volume mesh, but I haven't completely gotten the hang of it. Parts of the surface mesh come out beautiful (just what I am hoping for) and others come out twisted. I've checked my surface normals and they are fine. So my questions are: 1.)Is there a tutorial describing how to use patch-dependant surface meshing for unstructured meshes (I haven't been able to locate one in the official Ansys tutorials)? or 2.)Is there an other way to create a surface mesh on the symmetry plane that has a smoother growth ratio going from the aircraft to the farfield? Thanks for any help! |
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December 4, 2010, 14:08 |
Laplace...
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#2 |
Senior Member
Simon Pereira
Join Date: Mar 2009
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There is a tutorial about patch conforming surface mesh on an aircraft, but I always found it more work... (The jist is that you must build topo first and set up sizes on all the curves. Then use the patch dependent surface mesher. You can just mesh a single surface, such as the symmetry plane and then use that when you Octree, or you could mesh the whole thing with patch dependent)
I can dig it up for you if you really want it. In the mean time, I have another suggestion that is easier to implement... Generate your Octree Mesh... (no need for Delaunay yet). Delete all the volume elements (Delete Mesh, then select All volume elements with the selection tool bar). These will be deleted to replace with delaunay eventually, but if you get rid of them now, it is easier to smooth. Then smooth the heck out of the surface mesh using the Laplace option. Make sure to turn on that laplace checkbox option... Try 50 iterations up to 0.6 or something like that. Laplace tries to smooth out angles between elements and the transition (surface area change) between elements. It ends up looking very "delaunay". But it doesn't focus on individual element quality, so... One more round of regular smoothing (10 iterations up to 0.4) (without Delaunay) to finish up. Take a look at the surface on the symmetry plane. It should be pretty good. Then go back to compute mesh => Delaunay to fill the volume and continue on with your regular process... ----------------------------------------- Please help guide development at ANSYS by filling in these surveys Public ANSYS ICEM CFD Users Survey This second one is more general (Gambit, TGrid and ANSYS Meshing users welcome)... CFD Online Users Survey |
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December 4, 2010, 16:23 |
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#3 |
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Jason Sherlock
Join Date: Sep 2010
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Excellent, thanks! I've never tried going that extreme on the smoothing options. Looking forward to trying this out on monday.
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April 19, 2013, 08:40 |
how to generate a mesh
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#4 | |
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tita
Join Date: Apr 2013
Posts: 27
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Quote:
Thanks |
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May 30, 2013, 12:30 |
triangular mesh generation
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#5 |
Member
Harry
Join Date: May 2013
Posts: 68
Rep Power: 13 |
Hello friends. I want to make triangular mesh around 2D airfoil. By default it makes quadrilateral. How should I proceed for tri grid? Please help
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May 30, 2013, 15:08 |
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#6 |
Senior Member
Simon Pereira
Join Date: Mar 2009
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What tool are you using? if ICEM CFD, go to the mesh tab and change the global settings for shell meshing... Or just go to Compute mesh and ask for all tri instead of quad dominant.
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----------------------------------------- Please help guide development at ANSYS by filling in these surveys Public ANSYS ICEM CFD Users Survey This second one is more general (Gambit, TGrid and ANSYS Meshing users welcome)... CFD Online Users Survey |
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May 31, 2013, 07:21 |
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#7 |
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Harry
Join Date: May 2013
Posts: 68
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Thanks PSYMN for your reply.
Yes I am using ICEM. Here I am posting a quick process of mine. I created airfoil and farfield (surface created) curves. Then I changed Shell meshing parameters to "All tri" type. Next, I created block and set some edge parameters under premesh parameters but it still create quad grid.. Also there is no option for 'All tri' under compute mesh... I 'll be really thankful for your help. Here I attached the type of mesh which I want to generate.. |
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May 31, 2013, 12:01 |
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#8 |
Senior Member
Simon Pereira
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Those shell meshing parameters are for shell meshing, not for blocking...
You probably just need unstructured shell meshing which you generate with the mesh tab => Compute mesh. Look for a shell meshing tutorial because you will also need to learn how to set the curve params, 2D inflation, etc. If you actually want blocking, you can go to edit block to change the block type from mapped to free (mapped is the default). You can also set the free block to any type of unstructured mesh you want... All tri in your case. You probably want the gambit pave all tri for the smoothest mesh. Note, if you are using blocking, you will need to block out the airfoil interactively or use 2D surface blocking if you want it done automatically. Placing a single 2D block will not capture the airfoil. Best regards,
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----------------------------------------- Please help guide development at ANSYS by filling in these surveys Public ANSYS ICEM CFD Users Survey This second one is more general (Gambit, TGrid and ANSYS Meshing users welcome)... CFD Online Users Survey |
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May 31, 2013, 13:14 |
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#9 |
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Harry
Join Date: May 2013
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Thanks PSYMN for your suggestion. I am now reading tutorial relating to shell meshing. I think for unstructured mesh I will not need blocking. Am I right?
Kind Regards |
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June 1, 2013, 04:09 |
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#11 |
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Harry
Join Date: May 2013
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Dear friends Diamondx and PSYMN, I started learning generating unstructured mesh around airfoil ICEM but one initial problem for me is that after computing it gives me some warning that there is hole in domain. I think it assume airfoil as hole because the mesh ignores the airfoil curves as boundaries and also crosses it. How should I specify the airfoil as walls? please help..
Kind Regards |
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June 1, 2013, 11:56 |
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#12 |
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Ghazlani M. Ali
Join Date: May 2011
Location: Tokyo, Japan
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hello Star,
To specify the airfoil as wall, name those curve "airfoil_wall", then in the output menu specify them as wall. First you have to fix the hole error... would you mind sharing your project via dropbox. i can take a look at it this weed end... |
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June 1, 2013, 13:37 |
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#13 |
Member
Harry
Join Date: May 2013
Posts: 68
Rep Power: 13 |
Thanks diamondx for your reply. By wall i mean to make it solid boundary. I think i can go to output after completing my mesh. I am at the initial stage of mesh generation. I posted here photo of my mesh. you can see what I mean. My 2 main questions regarding my requirements are
1) how to make the airfoil as boundary so that the mesh lines couldn't pass it. 2) how to create more/dense mesh near airfoil boundary. kind Regards Last edited by star; June 1, 2013 at 14:40. |
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June 1, 2013, 23:13 |
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#14 |
Senior Member
Simon Pereira
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2) just set a smaller mesh size on the curves...
1) Delete the surface inside the airfoil and mesh won't generate there.
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----------------------------------------- Please help guide development at ANSYS by filling in these surveys Public ANSYS ICEM CFD Users Survey This second one is more general (Gambit, TGrid and ANSYS Meshing users welcome)... CFD Online Users Survey |
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June 2, 2013, 02:17 |
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#15 |
Member
Harry
Join Date: May 2013
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Thanks PSYMN, your points were much helpful. I trimmed the surface inside airfoil and now it's better...
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June 20, 2013, 14:27 |
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#16 |
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June 20, 2013, 14:39 |
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#17 |
Super Moderator
Ghazlani M. Ali
Join Date: May 2011
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it is a very basic step, under the geometry tab, you have options to delete points, curves, and surface, or everything. just click on delete surface... Do some tutorials to learn more about it
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June 20, 2013, 17:00 |
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#18 | |
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Quote:
thanks a lot for quick reply my friend let me explain more about my problem first i import the airfoil from point data(airfoil curves create not have surface now).then i create the farfield boundary for example like square and create surface in the square. now for shell meshing what can i do? at the moment icem can't recognize the surface inside and the outside of the airfoil? how can split the boundary surface by airfoil curve? i use segment/trim surfaces and select boundary surfaces and airfoil curve but it dose not work and i don't know why? (i have the surface of the farfield boundary and the airfoil curve now ) Best regards |
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July 18, 2013, 16:45 |
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#19 |
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Geometry (tab) => Geometry Repair => Build Diagnostic Topology. This will trim the surface with the airfoil curves and probably turn them red. You can then delete the surface within the airfoil
this is the key that i dont know |
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July 23, 2013, 19:48 |
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#20 |
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Ankur
Join Date: Jan 2013
Location: Austin, USA
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Hi,
I needed a few suggestions regarding meshing in ICEMcfd. Currently I use unstructured tetrahedral mesh with following options, All Tri Shell Meshing, Tetra/Mixed Volume mesh type and Quick Delaunay Volume mesh method. I wanted to know the following 1) My geometry has a rectangular cuboid of dimension 12m X 3m X 3m with a couple of un-meshed cylindrical tubes (12m & 0.15m dia) through it. I entered the maximum size of mesh cell to be 0.3m. I end up getting about 3,000,000 cells!! which really slows down my simulations. [ I do have some inlet/outlet surfaces of dimensions 15 cm over which I applied prism layers of size 3 cm ]. Is there a way I can reduce the no. of cells considerably ? 2) Which one among Delaunay and Octree is better ? 3) Currently I create surface mesh first and the volume and prism together. Is this the correct sequence or directly computing volume mesh without first creating surface mesh is better ? 4) Does structured mesh gives considerable advantage over un-structured mesh ? Thanks, Ankur |
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