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Solving a Laplace equation for a scalar quantity

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Old   July 13, 2011, 04:40
Default Solving a Laplace equation for a scalar quantity
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Ali
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Hello,

I am trying to solve \nabla^{2}\varphi=0, i.e. homogeneous Laplace equation, in which \varphi is a scalar quantity and is described in a zone(2D or 3D). We know boundary values of \varphi in borders of the zone. This problem is very analogous to head conduction at steady state, yet \varphi is the electric potential here, not temperature.

I am wondering how to implement this problem in FLUENT. I think I have to mesh the zone and use a udf or something like that.

Thanks for your help.
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Old   July 13, 2011, 07:40
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Hi Ali,
you can easily do that by implementing a UDS, user defined scalar; in it's definition, ignore unsteady and convective terms.


Amir
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Old   October 2, 2014, 11:05
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Hi Amir,

Can you elaborate your statement? How can we justify that unsteady and convective terms can be ignored for solving the laplace equation? (i need to find the change in electric field in my geometry)
I think you know how my geometry looks like :P , I have to find the electric field in the rotor domain.
If possible can you share the UDF with me?

Thank you.
-Mark
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Old   October 2, 2014, 13:34
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Quote:
Originally Posted by Clarence91 View Post
Hi Amir,

Can you elaborate your statement? How can we justify that unsteady and convective terms can be ignored for solving the laplace equation? (i need to find the change in electric field in my geometry)
I think you know how my geometry looks like :P , I have to find the electric field in the rotor domain.
If possible can you share the UDF with me?

Thank you.
-Mark
Dear Mark,

"UDS" is "User-Defined Scalar" equation and is available in FLUENT, something like energy equation and totally different from "UDF"! In the process of enabling a UDS, you can manage the unsteady and convective terms. For more info, please refer to the manual.

Bests,
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Old   February 11, 2015, 20:56
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Hi,
Can we solve defined scalar in x, y, z direction separately (for 3D geometry) or how can we see the scalar values in x y z directions using post processing?
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Old   February 12, 2015, 05:02
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Hi,
Can we solve defined scalar in x, y, z direction separately (for 3D geometry) or how can we see the scalar values in x y z directions using post processing?
Regards
Tharanga
Hi,
For sure you cannot solve it separately, but if you want to see the scalar values in a specified direction, you can simply draw a line and plot the scalar values over it...

Bests,
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Old   February 12, 2015, 06:08
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Hey, Thank you for the reply. I have solved the laplace eq (3D) and I need to get surface integration over x y z direction (separately) . Is there any method for that? cheers
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Old   February 12, 2015, 06:12
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If I elaborate more, I cant choose from the drop down menu x-scalar values etc. Therefore, I'm struggling to find x y z values over a surface. Thank you.
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Old   February 12, 2015, 06:24
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With a user defined scalar, you calculate a scalar, not a vector.
A scalar does not have a x-component... So your question does not make any sense.

If you solved an electrostatic problem, your scalar is probably the electric potential. Which component do you want? The x-component of the electric field? You should know the relation between those two.
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Old   February 12, 2015, 06:36
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It is a homogenized flow problem. Ultimately, I need to solve laplace eqn (vector) with BC's . Yes, you are right but there is no other way (I think) than UDS method in fluent to solve Laplace. Please suggest me an alternative method. Thank you
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Old   February 12, 2015, 07:00
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You don't make clear why you need another way. What is wrong with the UDS method?

And are you sure you want a vector laplace equation??? That is very unusual. I don't know why a "homogenized flow problem" would lead to a vector variant of the laplace equation.
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Old   February 16, 2015, 21:42
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Hi, Thank you very much for your kind replies. I solved it as three different problems in fluent. I got the results.

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