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How to solve 6 Coupled Mode Non linear Partial Differential Equation

Posted Feb 20, 2014, 12:35 a.m. EST Parameters, Variables, & Functions, Studies & Solvers Version 4.3a, Version 4.3b 4 Replies

Upendra Hatiya
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I am having 6 variables Ap_plus, Ap_minus, As_plus, As_minus, Q_plus, Q_minus
Equations are in attached pdf

variables have dependency of both time and space.

I have tried pdepe Matlab but having problem with boundary conditions.

Please tell me which model i should use and and how should i define those coupled equations and i need solution in time at a constant distance, so which study i should use.

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4 Replies Last Post Feb 27, 2014, 12:07 p.m. EST
Suresh Seetharam
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Posted: 1 decade ago Feb 25, 2014, 4:02 p.m. EST
Hi,


Did you try PDE coefficient form? You can either create 6 PDE nodes or just one PDE node and define 6 dependent variables. Comsol manual is easy to follow.


Suresh
Hi, Did you try PDE coefficient form? You can either create 6 PDE nodes or just one PDE node and define 6 dependent variables. Comsol manual is easy to follow. Suresh
Upendra Hatiya
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Posted: 1 decade ago Feb 26, 2014, 3:12 a.m. EST
Thank you Suresh for your respose.

I tried that way but comsol is not allowing me to initialize variables with respect to time. There are two options only whether i can go for initialization of variables with respect to coordinates or initialization of derivative of variables with respect to time.

I want to initialize variables for all times at starting point i.e. at a constant distance(zero in my case) for all time values variables can be user defined.

Thank you Suresh for your respose. I tried that way but comsol is not allowing me to initialize variables with respect to time. There are two options only whether i can go for initialization of variables with respect to coordinates or initialization of derivative of variables with respect to time. I want to initialize variables for all times at starting point i.e. at a constant distance(zero in my case) for all time values variables can be user defined.
Suresh Seetharam
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Posted: 1 decade ago Feb 26, 2014, 11:19 a.m. EST
Hi,


If you want to fix values of the primary variables at a point for all times, then you are talking about a particular type of boundary condition called Dirichlet. You cannot impose this in the "domain" node where you can only provide initial value and initial time derivative, applicable spatially at time zero. Are you doing this? If yes, it is not correct.

Instead you should go to "boundaries" node and select Dirichlet boundary condition for all your primary variables at a give point, in your case x=0. I think this is what you want?


Suresh
Hi, If you want to fix values of the primary variables at a point for all times, then you are talking about a particular type of boundary condition called Dirichlet. You cannot impose this in the "domain" node where you can only provide initial value and initial time derivative, applicable spatially at time zero. Are you doing this? If yes, it is not correct. Instead you should go to "boundaries" node and select Dirichlet boundary condition for all your primary variables at a give point, in your case x=0. I think this is what you want? Suresh
Upendra Hatiya
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Posted: 1 decade ago Feb 27, 2014, 12:07 p.m. EST
well Suresh, you got my problem and your provided solution was appropriate, Thank you for that , I can now able to set values for time at starting point.

But my solution is not converging... wht u think.. wht could be a possible cause of that..??
well Suresh, you got my problem and your provided solution was appropriate, Thank you for that , I can now able to set values for time at starting point. But my solution is not converging... wht u think.. wht could be a possible cause of that..??

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