# [ICEM] Growth ratio ICEM

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 February 3, 2013, 14:38 Growth ratio ICEM #1 New Member   Marijo Join Date: Jan 2011 Posts: 12 Rep Power: 7 Hello, How can I set a "real" growth ratio of, for example 20% growth, for hexa mesh in ICEM? If bigeometric bunching law is set, for a given initial height there is a range of number of elements that could be applied for the same growth ratio. In other words, there is no unique number of elements for a given growth ratio. Thanks!

February 4, 2013, 10:18
#2
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Christoph
Join Date: May 2011
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Quote:
 Originally Posted by krembil Hello, How can I set a "real" growth ratio of, for example 20% growth, for hexa mesh in ICEM? If bigeometric bunching law is set, for a given initial height there is a range of number of elements that could be applied for the same growth ratio. In other words, there is no unique number of elements for a given growth ratio. Thanks!
depends on mesh law and if you determine spacing 1 (let's say your intitial height) and spacing 2.

so if you choose bigeometric as mesh law and set your spacing 1 to 0.1 and ratio 1 to 1.2, the nodes will be distributed on this edge with these settings.

BUT: if you set a spacing 2 to a determinated value (other than 0), Icem will retain the initial spacing 1 and spacing 2 and grow ratio, but the max. space will change OR, if it isn't possible (to less or to many nodes), you have to change to number of nodes to achieve the intended grow ratio.

February 4, 2013, 18:54
#3
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Simon Pereira
Join Date: Mar 2009
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Krembil,

Bunching gives you too many controls, and
Quote:
 with great power comes great responsibility...
So, you could specify a small initial size and a small growth ratio, but not enough nodes to make it mathematically work out... In which case, it would just increase your ratio so it works...

Inversely, you could put too many nodes, in which case, the ratio could drop down to 1 (uniform) and your initial height could even be reduced.

You could also be setting things up on one edge and copy to another with a different overall length and end up with a different effective ratio.

This is why there are two columns in the Hexa Parameters panel... The first is what you would like... So you could put something like ratio = 1.1 in there. The second column is what you get... so if you don't have enough nodes, you could see that as ratio = 1.8...

To make the two line up, you can increase the number of nodes until you see something similar in the second column.

Do you get it? Play with it a bit and you will.
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 February 5, 2013, 04:32 #4 New Member   Marijo Join Date: Jan 2011 Posts: 12 Rep Power: 7 Thank you for your answer. It's clear now. Marijo

 April 20, 2015, 05:41 Growth ratio in Unstructured meshing #5 New Member   Manjunatha S Join Date: Mar 2015 Posts: 8 Rep Power: 3 Hi .. How can we control the growth rate of tetra elements in ICEM. I want smaller grid size near the wall and larger size elements away from the wall. Please suggest me how to create it with out using prism layers.? Regards Manjunatha S

 April 20, 2015, 06:18 #6 Senior Member     shereez Join Date: Jan 2014 Location: England Posts: 188 Rep Power: 4 I do not know if this is the best way but this works for me. I use density boxes to define tetra sizes and ratios. It can be created for octree and delaunay volume meshes. Read simon's ticks and trips document. ( search in google for it, it comes to the 1st page of google search)

 April 21, 2015, 00:48 #7 New Member   Manjunatha S Join Date: Mar 2015 Posts: 8 Rep Power: 3 Hi Shereez, Thank you for your reply. I want to know how can i mesh without using density option. Is there any method to give ratio's ? What is that simon's ticks and trips page? I am not getting anything relevant to this topic..!

April 21, 2015, 09:46
#8
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shereez
Join Date: Jan 2014
Location: England
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Quote:
 Originally Posted by manju Hi Shereez, Thank you for your reply. I want to know how can i mesh without using density option. Is there any method to give ratio's ? What is that simon's ticks and trips page? I am not getting anything relevant to this topic..!
Density boxes are a way of controlling tetra sizes. You create these boxes as entity bounds or from points and with a certain ratio you have in mind. But you have to know the appropriate sizes to use other wise it increases the amount of volume mesh rapidly and this is an unwanted situation.

I have uploaded to my dropbox Simon's tips and tricks 2010 google doc and also Simon's Prisms no pyramids. I found them both very useful while learning ICEM CFD. Hope this helps. Here are the links. Let me know if you can access them now.

Simon's tips and tricks
https://www.dropbox.com/s/2m53u2c7w9...s2010.pdf?dl=0

Simon's Prisms no Pyramids:
https://www.dropbox.com/s/l0ddrxaw7h...amids.pdf?dl=0

I have also posted a mesh which i made a month ago for tetra meshing of an aircraft with density boxes. just to give you an idea I will show you a photo of it:
https://www.dropbox.com/s/hsmakw8fig...BOXES.jpg?dl=0

Regards
Shereez

 April 22, 2015, 07:56 #9 New Member   Manjunatha S Join Date: Mar 2015 Posts: 8 Rep Power: 3 Hi Shareez, Thank you very much for your valuable information and documents.. Thanks a lot.. Regards, Manjunatha S

 December 30, 2015, 01:46 bunching law #10 New Member   Amit soni Join Date: Jul 2015 Posts: 10 Rep Power: 3 Dear sir , from where i can get the details of bunching law used by icem

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