Menu

Discussion Forum

New Discussion
Filtra

Note: This discussion is about an older version of the COMSOL Multiphysics® software. The information provided may be out of date.

Discussion Closed This discussion was created more than 6 months ago and has been closed. To start a new discussion with a link back to this one, click here.

How to solve 6 Coupled Mode Non linear Partial Differential Equation

Posted 20 feb 2014, 00:35 GMT-5 Parameters, Variables, & Functions, Studies & Solvers Version 4.3a, Version 4.3b 4 Replies

Upendra Hatiya
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

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.

Attachments:

4 Replies Last Post 27 feb 2014, 12:07 GMT-5
Suresh Seetharam
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 25 feb 2014, 16:02 GMT-5
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
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 26 feb 2014, 03:12 GMT-5
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
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 26 feb 2014, 11:19 GMT-5
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
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 27 feb 2014, 12:07 GMT-5
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..??

Note that while COMSOL employees may participate in the discussion forum, COMSOL® software users who are on-subscription should submit their questions via the Support Center for a more comprehensive response from the Technical Support team.

Suggested Content