Hi Raymond, Sorry, it was a typo.
Yes, It is indeed d (phi)/dx, the spatial derivative BC. I shall try setting phi.faceGrad.constrain([k*phi], mesh.facesRight), and see if it will work. Thanks for pointing this out. Krishna From: [email protected] [mailto:[email protected]] On Behalf Of Raymond Smith Sent: 08 June 2016 23:36 To: [email protected] Subject: Re: casting implicit Boundary Conditions in FiPy Hi, Krishna. Just to make sure, do you mean that the boundary condition is a derivative with respect to the spatial variable or with respect to time as-written? If you mean spatial, such that d\phi/dx = k*phi, have you tried phi.faceGrad.constrain(k*phi) and that didn't work? If you mean that its value is prescribed by its rate of change, then I'm not sure the best way to do it. Could you maybe do it explicitly? - Store the values from the last time step with hasOld set to True in the creation of the cell variable - In each time step, calculate the backward-Euler time derivative manually and then set the value of phi with the phi.constrain method. Ray On Wed, Jun 8, 2016 at 6:26 PM, Gopalakrishnan, Krishnakumar <[email protected]<mailto:[email protected]>> wrote: I am trying to solve the standard fickean diffusion equation on a 1D uniform mesh in (0,1) $$\frac{\partial \phi}{\partial t} = \nabla.(D \nabla\phi)$$ with a suitable initial value for $\phi(x,t)$. The problem is that, one of my boundary conditions is implicit, i.e. is a function of the field variable being solved for. $ \frac{\partial\phi}{\partial t} = k \phi $ , at the right boundary edge, k = constant The left BC is not a problem, it is just a standard no-flux BC. How do I cast this implicit BC in FiPy ? Any help/pointers will be much appreciated. Best regards Krishna Imperial College London _______________________________________________ fipy mailing list [email protected]<mailto:[email protected]> http://www.ctcms.nist.gov/fipy [ NIST internal ONLY: https://email.nist.gov/mailman/listinfo/fipy ]
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