UDF function for mesh spacing

Jeric · August 16, 2015, 01:54

Dear all,
I want to write a UDF for calculating the mesh spacing in 3D. Actually, I want to campute delta_x,delta_y and delta_z for each cell. my quastion is which function should be used? How can I write this udf?
function :L_S=C_x*(△x*△y*△z)^(1/3)
C_x=0.61
(delta_x means the length of a cell across x direction)

`e` · August 18, 2015, 06:31

First of all, how would you describe these lengths for an arbitrary, unstructured cell? For example, the "mesh spacing" of a tetrahedron would vary across the geometry. Assuming the maximum distance between nodes in each direction might be an overestimation for your physics. The problem is simplified with a structured mesh utilising hexahedron cells.

Start with writing a UDF which loops through each node of a cell using c_node_loop and calculating the lengths with:

$\Delta x = x_{max} - x_{min}$

and then checking if the results are what you expect.

Far · August 19, 2015, 10:15

check the forum, similar udf is already discussed and i am sure you also want it for LES / DES usage

August 16, 2015, 01:54	UDF function for mesh spacing	#1
Jeric New Member Jeric zhang Join Date: May 2015 Posts: 3 Rep Power: 10	Dear all, I want to write a UDF for calculating the mesh spacing in 3D. Actually, I want to campute delta_x,delta_y and delta_z for each cell. my quastion is which function should be used? How can I write this udf? function :L_S=C_x(△x△y*△z)^(1/3) C_x=0.61 (delta_x means the length of a cell across x direction)

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August 18, 2015, 06:31		#2
`e` Senior Member Join Date: Mar 2015 Posts: 892 Rep Power: 18	First of all, how would you describe these lengths for an arbitrary, unstructured cell? For example, the "mesh spacing" of a tetrahedron would vary across the geometry. Assuming the maximum distance between nodes in each direction might be an overestimation for your physics. The problem is simplified with a structured mesh utilising hexahedron cells. Start with writing a UDF which loops through each node of a cell using c_node_loop and calculating the lengths with: $\Delta x = x_{max} - x_{min}$ and then checking if the results are what you expect.

August 19, 2015, 10:15		#3
Far Super Moderator Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,553 Blog Entries: 6 Rep Power: 54	check the forum, similar udf is already discussed and i am sure you also want it for LES / DES usage