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How to define this two equation using PDE

Posted Aug 19, 2014, 8:41 p.m. EDT 6 Replies

Humphrey Winfree
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Hi，
In my 2D model，the governing equations are

.
The and are the variables I want to solve on the whole plane.Other variables , are all known.The direction of the magnetic field is normal to the 2D plane.
And I want to solve this two equations together, which means the plane has two governing equations. And the coefficient Form PDE is very convenient to define both equations.But the coefficient form PED is overriden,I can‘t add another coefficient form PDE.This bothers me a lot.
your kind help is very much appreciated.
Thank you very much
6 Replies Last Post Sep 6, 2016, 5:09 a.m. EDT
Humphrey Winfree
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Posted: 1 decade ago Aug 20, 2014, 9:38 a.m. EDT
Is there anyone know how to solve this problem. I have been trobuled by this problem for half a month.
I'm really desperate to solve this problem.
Thank you very very very much.
Is there anyone know how to solve this problem. I have been trobuled by this problem for half a month. I'm really desperate to solve this problem. Thank you very very very much.
Martijn Weterings
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Posted: 1 decade ago Aug 21, 2014, 12:13 p.m. EDT
"But the coefficient form PED is overriden, I can‘t add another coefficient form PDE."

If you have two dependent variables then you can define two PDEs.

- Either add the PDE module two times when you select the physics. (which seems the best in your case as J and phi are different units/fields)
- Or define two dependent variables in a single PDE physics node.


There are several points where you can make these two options happen. Either during the first screens when setting up the physics or later by adding or editing the physics.

See also attached image with an example of multiple added physics nodes and multiple defined dependent variables.
"But the coefficient form PED is overriden, I can‘t add another coefficient form PDE." If you have two dependent variables then you can define two PDEs. - Either add the PDE module two times when you select the physics. (which seems the best in your case as J and phi are different units/fields) - Or define two dependent variables in a single PDE physics node. There are several points where you can make these two options happen. Either during the first screens when setting up the physics or later by adding or editing the physics. See also attached image with an example of multiple added physics nodes and multiple defined dependent variables.

Attachments:

Humphrey Winfree
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Posted: 1 decade ago Aug 21, 2014, 8:40 p.m. EDT
Hi,Martijn
Thank you .I know how to do this now
Hi,Martijn Thank you .I know how to do this now
Krishnaraj KP
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Posted: 9 years ago Jul 1, 2015, 2:28 a.m. EDT
Hi Martijn,

I wish to solve the navier stokes equation for the flow of fluid through a cylindrical tube. But in the equation there are 2 variables velocity and pressure. How do I solve this using equation based modelling and also how to define the inlet and outlet pressure conditions.

Please I have been stuck in this for a long time.

Thank You.
Hi Martijn, I wish to solve the navier stokes equation for the flow of fluid through a cylindrical tube. But in the equation there are 2 variables velocity and pressure. How do I solve this using equation based modelling and also how to define the inlet and outlet pressure conditions. Please I have been stuck in this for a long time. Thank You.
Aparna Neettiyath
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Posted: 9 years ago Mar 30, 2016, 1:31 a.m. EDT
Hi
I am using coupled global PDE form for three dependent variables.
how to define relation between dependent variables?

when I do it outside in the variables section, it says duplication of variable.

Thank you very much
Hi I am using coupled global PDE form for three dependent variables. how to define relation between dependent variables? when I do it outside in the variables section, it says duplication of variable. Thank you very much
Di Shen
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Posted: 8 years ago Sep 6, 2016, 5:09 a.m. EDT
Hi Krishnaraj

I got a pretty similar problem as you, basically I am simulating pipe flow using incompressible N-S eqn in general PDE interface, it seems the equations didn't quite accept a pressure inlet + pressure outlet boundary conditions case. Have you figure out how to do it?

I will be very appreciated if you can give me some advice.

Best
Di Shen
Hi Krishnaraj I got a pretty similar problem as you, basically I am simulating pipe flow using incompressible N-S eqn in general PDE interface, it seems the equations didn't quite accept a pressure inlet + pressure outlet boundary conditions case. Have you figure out how to do it? I will be very appreciated if you can give me some advice. Best Di Shen

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