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-   -   ICEM Edge Params Bunching laws (https://www.cfd-online.com/Forums/ansys-meshing/68384-icem-edge-params-bunching-laws.html)

 twsloss September 17, 2009 08:20

ICEM Edge Params Bunching laws

I am trying to make an automated front end for some blocking based grids I am making in icem, because I have to do a lot of them, and want to make it so people not familiar with icem can make grids. I want to be able to update the number of nodes to use on certain edges based on their length, but have been unable to figure out how the bi-geometric bunching law works. Thank you for any incite or help.

 PSYMN October 16, 2009 09:33

Search the Help

Look in the help... You can type Bigeometric into the search...

Look under Bunching laws for the description... Many of the other laws give the equations, but not this one.

Bunching Laws

BiGeometric The default bunching law. The two initial heights and ratios define parabolas in a coordinate system where the number of node points is the X-axis and the cumulative distance along the edge is the Y-axis. The parabolas are truncated where their tangent lines are identical; the spacing is linear between these points. If there are not enough nodal points to form this linear segment, a hyperbolic law is used and the ratios are ignored.

 Bastisendling August 21, 2011 15:31

Hello!
I'm having the same trouble. For a parametrisation i also need information on the Bigeometric bunching law. But i find the help info somewhat incomplete.
How exactly do the spacings and ratios define the parabolas?
My first guess would be:
The forumula for a parabola is f(x)=a*x^b
with a=Spacing and b=ratio.
Is this correct?
I really need the correct definition.
Thank you for help!

 zampa September 13, 2011 15:45

Yesterday, I had the same problem.

It´s not so difficult.
BiGeometric distribution use for the initial and end bunching law two parabol-functions: y(x)=a+bx+cx².

Using initial and end height and ratios, you can define this two parabolas.

The second target is to know where both parabols have the same tangent. You can express this using two ecuactions, and getting the start and end point where to distribute the cells uniformly.

Check the definition and think about it.

 TrII4d July 14, 2014 08:43

i know this topic was discussed long time before, but i do not understand what you mean exactly.

if i have the parabol function: y(x)=a+bx+cx²

what are the variables a,b,c ? if i have two functions i become 6 unknown variables ... however 4 variables are discussed (spacing 1 and 2; ratio 1 and 2)

i'm really confused at the moment :confused: ... kindly help

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