# [ICEM] Inflation Layers/Prism ICEM

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 February 25, 2015, 11:52 #2 Senior Member     MS Join Date: Jan 2014 Location: England Posts: 346 Blog Entries: 1 Rep Power: 12 Do you perhaps have an image of your mesh? whats your y+ value and whats the initial layer height? If the Aspect ratio is big that means the transition between the octree and the prisms are too large I guess. ?

February 25, 2015, 14:48
Prism ICEM
#3
New Member

Omar Osama Mohamed
Join Date: Nov 2014
Posts: 26
Rep Power: 10
Hi,
I am attaching images of my mesh at outlet and interface as well.
my Y+ didn't exceed 2.5 during Fluent run and I want it to be from 1-1.2 because i am using K-W sst or K-Epsilon family.
my Initial height was 0.02 ( the mesh is in mm ) I want 7-9 layers to reach 0.2 mm total height
Yes I think the same too as you
The inflated or prism cell has very low height because we want to see boundary layer but not very enough width because it will increase all of the mesh elements homogeneously
Thanks again
Attached Images
 MESH.JPG (22.0 KB, 107 views) outlet.JPG (34.7 KB, 84 views) Inflation layers.JPG (48.5 KB, 115 views) Interface.JPG (38.4 KB, 80 views)

February 25, 2015, 19:29
#4
Senior Member

MS
Join Date: Jan 2014
Location: England
Posts: 346
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Rep Power: 12
Quote:
 Originally Posted by Omarspace Hi, The inflated or prism cell has very low height because we want to see boundary layer but not very enough width because it will increase all of the mesh elements homogeneously Thanks again
Sorry for the late reply. My advice would be to make sure you calculate the correct inital height and total number of layers for the prism layers. And have a look into what ratio of prism growth you are using? perhaps 1.2 would be the good to go for I guess. You can use Pointwise website to calculate first layer height etc... And generate the Octree Volume mesh with correct curve sizes and surface triangle sizes..

After you are done convert the Octree mesh to a Delunay mesh ( You can use Delaunay Standard or Tglib with AF if you are using 14.5 or later I guess). before you run make sure you select use existing mesh and disable creating prism layers as they were already generated while octree volume meshing was running. And if you have more problems post a picture of a slice plane. Good luck

 February 25, 2015, 19:33 #5 Senior Member     MS Join Date: Jan 2014 Location: England Posts: 346 Blog Entries: 1 Rep Power: 12 And I forgot to say. The reason for this is Delaunay has a smoother transition than Octree So solvers like fluent like this kind of mesh

February 27, 2015, 17:36
Prism Problem
#6
New Member

Omar Osama Mohamed
Join Date: Nov 2014
Posts: 26
Rep Power: 10
Hi Dear ,
Sorry for my late reply. I have did your recommendations and they affected my mesh greatly. I have realized that despite that overall mesh looks great but there are some elements in critical places with very low orthogonal quality. I am not sure that those are the reason of my divergence but i think so. what do you think ? They are in the inlet of Aortic Arch with almost zero quality + Reverse flow ... maybe really are they the reason of this divergence ? "It is turbulent problem too " I am attaching picture of those elements. Their number is small didn't exceed 50 or 100 while mesh is 500,000 but they are in boundary layer inlets and outlets.
How Can I change their orthogonal quality individually ?
Regards
Omar
Attached Images
 badelements.JPG (18.7 KB, 62 views) inlet.JPG (10.0 KB, 79 views)

 February 27, 2015, 17:43 ICEM prism problem #7 New Member   Omar Osama Mohamed Join Date: Nov 2014 Posts: 26 Rep Power: 10 The actual orthogonal quality in histogram for those elements ranges from 0-0.05

 February 28, 2015, 11:42 #8 Senior Member     MS Join Date: Jan 2014 Location: England Posts: 346 Blog Entries: 1 Rep Power: 12 If you don't mind share the project files from drop box or something. I might be able to have a look into it during this weekend.

 February 28, 2015, 11:48 ICEM prism problem #9 New Member   Omar Osama Mohamed Join Date: Nov 2014 Posts: 26 Rep Power: 10 Oh Thanks for your reply I wish I could but it is unfortunately forbidden by contract Thanks again for your reply Shereez

 February 28, 2015, 15:00 #10 Senior Member     MS Join Date: Jan 2014 Location: England Posts: 346 Blog Entries: 1 Rep Power: 12 Oh okay my bad. My only advice now would be to smooth the mesh with orthogonality option chosen. And also are you using relaxation factors to control the equations in Fluent? turbulence viscosity, energy? which solver settings are you using? If any one else have any experience in this problem please share your views to help out this user.

 February 28, 2015, 15:02 #11 Senior Member     MS Join Date: Jan 2014 Location: England Posts: 346 Blog Entries: 1 Rep Power: 12 Or you could create a subset for the worst orthogonal quality elements and smooth them - I guess

 March 7, 2015, 04:18 ICEM Quality #12 New Member   Omar Osama Mohamed Join Date: Nov 2014 Posts: 26 Rep Power: 10 Hi Shereez, yes thanks a lot I solved it by increasing number of elements it is the only thing that worked. Thanks for you shereez234 likes this.

 April 5, 2015, 16:07 From Stl to Hexa #13 New Member   Omar Osama Mohamed Join Date: Nov 2014 Posts: 26 Rep Power: 10 Hi Dear Sheerez, Sorry to bother you again don't you know how can i mesh this stl geometry into hexa ? There is no points or curves how can i fit my blocks then ? Thanks in Advance

 April 6, 2015, 04:18 #14 Senior Member     MS Join Date: Jan 2014 Location: England Posts: 346 Blog Entries: 1 Rep Power: 12 I have not personally worked with STL geometries. I do not know the exact procedure. Hope some one else helps you around here. But my guess is you run build topology with a small tolerance to extract curves

April 16, 2015, 12:52
#15
Member

Ftab
Join Date: Sep 2011
Posts: 87
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Quote:
 Originally Posted by Omarspace Hi Dear Sheerez, Sorry to bother you again don't you know how can i mesh this stl geometry into hexa ? There is no points or curves how can i fit my blocks then ? Thanks in Advance
Hi Omar,
In biological cases you work more often with STL files received from segmentation of imaging outputs. So I do recommend you to get your hands dirty with them.
With STLs you can even triangulate the surface and base your volumetric mesh on the surface mesh and build up with Delauny.
You just import the STL file, build the topography with appropriate tolerance and then proceed defining the inlets, outlets and walls. Based on the fact that you want to use the already generated surface mesh, or making your own mesh you proceed with Delauny or Octree, respectively.
Checking and smoothing the mesh is also a very import. You can even do the check and smooth step in 2D on surface and make your own mesh from your own surface mesh into 3D with Delauny.
Simon Pereira (PSYMN) has explained the process clearly in several replies in the older posts.
If you need help, I can also give you some hints as I am also working in BioFluid Dynamics and CFD.
Good Luck!

 Tags hemodynamics, mesh quality, prism layers