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UDF to define the vector transport equation

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Old   August 31, 2012, 05:47
Default UDF to define the vector transport equation
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Hi

Through the UDS, scalar transport equation can be defined. I would like to define the vector transport equation. How can i define it?

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Old   August 31, 2012, 08:14
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Hi,

You would need 3 UDSs as each component!

Bests,
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Old   September 3, 2012, 00:03
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Hi Amir

Can you describe how and which UDS to use?

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Old   September 3, 2012, 03:38
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Quote:
Originally Posted by mvee View Post
Hi Amir

Can you describe how and which UDS to use?

Mvee
Suppose you wanna model momentum equation via UDS. You have to define 3 UDSs; u, v and w; and provide appropriate transport terms such as convection, diffusion, unsteady and source terms for each of them. A UDS has a general form of transport equation which you can modify for your purpose.

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Old   September 3, 2012, 04:07
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Hi Amir

Problem: Welding arc simulation
Description:
1) No. of zones: 3
2) Solid zone: electrode and workpiece (copper)
3) Fluid: argon (electrically conductive)

Current is imposed on the electrode which passes from the fluid and workpiece (which is at zero potential). Due to the current electro-magnetic field is generated which is governed by Maxwell’s equation (consists of current continuity and potential vector equation). These equations are having same form as that of our NS equations.

I have defined one UDS for voltage to solve current continuity equation. In the similar form do you mean to define UDS for vector A. Can you describe how shall I follow for the physics mentioned above? Also the output of this UDS will go as source term in momentum equation.

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Old   September 3, 2012, 05:29
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Quote:
Originally Posted by mvee View Post
I have defined one UDS for voltage to solve current continuity equation. In the similar form do you mean to define UDS for vector A. Can you describe how shall I follow for the physics mentioned above? Also the output of this UDS will go as source term in momentum equation.
Hi,

Ok, you'll also need a vector transport equation. You can consider a vector transport equation as 3 scalar transport equation (one for each component) and model each of them via a UDS. Here you have a vector A, so define 3 UDS as Ax, Ay and Az as its components. So consider your vector equation and decompose it into 3 scalar equation. Finally with simple UDFs you can add each component of your added equations into each momentum components without any trouble.

Bests,
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Old   September 3, 2012, 06:13
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Hi Amir

Thank you very much for your help, still have some doubt.
My algorithm will work in following manner -

(1) Current continuit equation: \Delta\Phi=0 /*\Phi = applied voltage and \Delta = Laplacian operator*/

(2) current density, j = -\sigma\nabla\Phi

(3) Potential vector equation: \Delta\vec{A}=\mu\vec{j}

First and third point can be applied through UDS. How to interface (required to solve point 2) between point 1 and 3? Is it required UDF?
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Old   September 3, 2012, 07:34
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Quote:
Originally Posted by mvee View Post
(1) Current continuit equation: \Delta\Phi=0 /*\Phi = applied voltage and \Delta = Laplacian operator*/

(2) current density, j = -\sigma\nabla\Phi

(3) Potential vector equation: \Delta\vec{A}=\mu\vec{j}

First and third point can be applied through UDS. How to interface (required to solve point 2) between point 1 and 3? Is it required UDF?
Dear friend,

It depends. It doesn't need to evaluate j explicitly if you just want to obtain A! you can substitute j from equation 2 into 3 directly and remove the j variable. But if you want to obtain j as well; yes, you'll need a UDF to store the phi gradient into a UDM. It should be noted that you would also need UDFs for defining source terms of equation 3.

Bests,
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Old   September 10, 2012, 01:27
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Hi Amir

Thank you very much for your kind co-operation. I have solved these equations.

Thank you
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