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October 23, 2019, 10:41 
UDf current density integration

#1 
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Domagoj
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Hello,
i need to integrate current density in my axisymmetric Fluent model in order to obtain selfinduced azimuthal magnetic field (Ampere circuital law)  see attached picture. Z is symmetry axis, r is radial distance. How to write UDF for this problem? Is it possible to loop cells for various z=const from r=0 to the right boundary while replacing integral with sum of finite values calculated in cell center? Any suggestions? Thanks. 

October 23, 2019, 22:25 

#2 
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Alexander
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there is build in electric potential model in fluent
did you try to use it?
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October 24, 2019, 02:38 

#3  
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Domagoj
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Quote:
Also, there is advanced addon module called MHD but it solves problems with externallyimposed magnetic field. In my case magnetic field is selfinduced and I do not see how to apply it? My final goal is to obtain Lorentz force from current density and magnetic field and use it as momentum source. Than I could solve fluid stirring problem. Last edited by Domagoj; October 24, 2019 at 09:25. Reason: t 

October 25, 2019, 01:07 

#4 
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Alexander
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I'm not sure how to do it step by step.
But it seems you should use userdefined scalar to define your magnetic field read Ansys Fluent Customization manual for more information regarding UDS
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October 25, 2019, 01:10 

#5 
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Alexander
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does current field predefined? or you should solve some equation to get current distribution?
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October 25, 2019, 02:26 

#6  
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Domagoj
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Quote:
It should be relatively simple numerical integration but I am not sure how to locate and loop cells from some constant zcoordinate (and r=0) to the right boundary end perform summation instead of integral. 

October 25, 2019, 03:24 

#7 
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Alexander
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inside cell loop you may check if the cell is inside region (z> your_boundary_coord) and make summation if True.
using C_CENTROID macro you can get coordinate of cell detail information in Ansys Customization Manual
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October 25, 2019, 06:45 

#8  
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Domagoj
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Quote:
I thought that someone already has something similar that could be modified for my case. 

August 25, 2022, 18:52 

#9 
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Rodrigo Villarreal
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I have the very same problem but in ANSYS CFX. It seems that I cannot integrate using the NLOC array. Is there a way to perform numerical integration using User Fortran?


September 30, 2022, 08:22 

#10 
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Domagoj
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Hello,
In the end I obtained Lorentz force using magnetic vector potential method. I can't remember the implementation details (UDS were used), it was long time ago, but read this paper carefully. https://iopscience.iop.org/article/1...3727/37/6/013 

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