# B vector in mhd module.

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 August 3, 2011, 09:45 B vector in mhd module. #1 New Member   Adam Join Date: Feb 2011 Posts: 6 Rep Power: 7 Hello I need advice. I am using Fluent with MHD module to simulate my object. In MHD I can define value of vector B but only of external field. Now I need to calculate B of internal magnetic field (means: field made by current flowing by the fluid). Is any simple method to do this calculations. I am thinking some time over this problem. Do I have to write some kind of my own mhd module or I can use this in Fluent. I will appreciate your help.

 August 3, 2011, 15:19 #2 Senior Member     Amir Join Date: May 2009 Location: Montreal, QC Posts: 739 Blog Entries: 1 Rep Power: 15 Hi Adam, you can simply add any source terms to your N-S equations. I didn't use MHD module before, but it reasonably add appropriate source terms and properties to your solver; in other words, you can do any thing that this module do by your self without any restrictions with some UDFs. Bests, Amir

 August 8, 2011, 06:17 #3 New Member   Adam Join Date: Feb 2011 Posts: 6 Rep Power: 7 I thought over what you have written. I suppose you mean to add sources to momentum equ. (in my case something like: JxB) and to energy equ. (in my case something like: (Jx^2 + Jy^2 + Jz^2)/conductance). My question is how to describe it in UDF - I mean how to put J (current density) which is "created" in MHD.

August 8, 2011, 06:25
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Amir
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Quote:
 Originally Posted by adamo I thought over what you have written. I suppose you mean to add sources to momentum equ. (in my case something like: JxB) and to energy equ. (in my case something like: (Jx^2 + Jy^2 + Jz^2)/conductance). My question is how to describe it in UDF - I mean how to put J (current density) which is "created" in MHD.
If you know how this vector is created, the problem is resolved. Even if this vector is obtained from sth like transport eqn, you can handle that by UDS implementation.
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August 9, 2011, 05:07
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Quote:
 Originally Posted by Amir If you know how this vector is created, the problem is resolved. Even if this vector is obtained from sth like transport eqn, you can handle that by UDS implementation.
Yet I have no idea how the J vector is created. MHD defines it and makes calculations. I know that values of the vector is placed in UDM by MHD module. When the iterates are finished I can draw charts of J, B, A (electric vector potential), V (electric scalar potential).
The problem is to define J equation. My fluid shape is a little bit irregular and I am not sure how to create model of current flow in it.
What do you mean: "this vector is obtained from sth"?

August 9, 2011, 05:22
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Amir
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Quote:
 Originally Posted by adamo Yet I have no idea how the J vector is created. MHD defines it and makes calculations. I know that values of the vector is placed in UDM by MHD module. When the iterates are finished I can draw charts of J, B, A (electric vector potential), V (electric scalar potential). The problem is to define J equation. My fluid shape is a little bit irregular and I am not sure how to create model of current flow in it. What do you mean: "this vector is obtained from sth"?
I meant that this vector may created from something like algebraic equation (explicit relation) or you may have to solve a transport eqn. for that (more probable) which both of them can simply be modeled without use of MHD module.
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Last edited by Amir; August 9, 2011 at 09:06.

 August 9, 2011, 06:41 #7 New Member   Adam Join Date: Feb 2011 Posts: 6 Rep Power: 7 That means that I should turn off MHD module and write my own transport equations to solve it. I have never done it before so I have to read sth about UDSs and UDMs. Thanks a lot Amir. Probably I will have further questions later. Best wishes, Adam

May 22, 2012, 06:26
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Quote:
 Originally Posted by adamo That means that I should turn off MHD module and write my own transport equations to solve it. I have never done it before so I have to read sth about UDSs and UDMs. Thanks a lot Amir. Probably I will have further questions later. Best wishes, Adam
Hello，i encounter the same question of you that in the MHD the UDM of B（magnetic field azimuthal component）comes to 0.Have you already solved your problem？