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Inquiry about how to put constraint on PDE dependent variable
Posted Nov 11, 2014, 8:01 p.m. EST Modeling Tools & Definitions, Parameters, Variables, & Functions Version 5.2a 1 Reply
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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 Nov 11, 2014, 9:30 p.m. EST
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Posted:
9 years 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.