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.
Inquiry about how to put constraint on PDE dependent variable
Posted 2014年11月11日 GMT-5 20:01 Modeling Tools & Definitions, Parameters, Variables, & Functions Version 5.2a 1 Reply
Please login with a confirmed email address before reporting spam
Dear All,
I am carrying a simulation of 3 coupled PDEs (coefficient form PDEs).
One of the PDE (Diffusion-drift equation) is of a dependent variable representing the ion concentration which can't be negative according to its physical definition.
So I am wondering is there a way to implement a constraint of that PDE that will prevent the dependent variable from going negative.
Thanks in advance for your kindly help.
I am carrying a simulation of 3 coupled PDEs (coefficient form PDEs).
One of the PDE (Diffusion-drift equation) is of a dependent variable representing the ion concentration which can't be negative according to its physical definition.
So I am wondering is there a way to implement a constraint of that PDE that will prevent the dependent variable from going negative.
Thanks in advance for your kindly help.
1 Reply Last Post 2014年11月11日 GMT-5 21:30
Please login with a confirmed email address before reporting spam
Posted:
1 decade ago
In addition, the simulation will fail if a single point on the mesh is of a negative ion concentration. (I believe it is because the coupled equation could not converge in this scenario.) Once a negative ion concentration presents, the time-step of the PDE solver will keep on decreasing till the failure message displayed.
Such a failure seems could not be overcame by tuning the damping factor of the newton's method.
My current solution of preventing the negative ion concentration from happening is to add a background initial ion concentration for the corresponding PDE. However, doing so is not physical.
Could any one with the same experience advise on such an issue.
Such a failure seems could not be overcame by tuning the damping factor of the newton's method.
My current solution of preventing the negative ion concentration from happening is to add a background initial ion concentration for the corresponding PDE. However, doing so is not physical.
Could any one with the same experience advise on such an issue.