Hi Dan, Wow. I did not expect that at all, thanks for that important information! I just tried searching for ways to implement the Robin BCs in FiPy. This site example < http://www.ctcms.nist.gov/fipy/examples/convection/generated/examples.convection.robin.html> appears to show that the var.faceGrad.constrain(0, where=m.exteriorFaces) command I mentioned earlier handles only the advection component, while, I presume, the diffusion component is subject to Neumann BCs by default. If that is so, then it's even more puzzling why having that line in my code blows up the solution, yet the solution seems well-behaved under just the Neumann BCs. Am I missing something else here?
Thanks, Yun On Wed, Aug 24, 2016 at 8:24 PM, Daniel Farrell <[email protected]> wrote: > Hello Yun, > > I just briefly looked at the code. Seems like you are solving something > like an advection diffusion problem. This might not help but just I case > ... > > If you want a closed boundary you need to apply Robin boundary conditions > because by definition the flux contains two components: one related to the > diffusion process and one the advection process. > > For example, http://scicomp.stackexchange.com/a/10576/3691 > > Dan > > On 24 Aug 2016, at 22:56, Yun Tao <[email protected]> wrote: > > Hi all, > > I'm experiencing a bizarre issue when trying to implement zero-flux > external boundary condition when solving for transient solutions. My > understanding is that it is the default setting in FiPy 3. Indeed, without > specifying it, the solutions (attached) remains at unity throughout the > simulation duration. However, when I manually tried to fix the exterior > face gradient to zero with *var.faceGrad.constrain(0, > where=m.exteriorFaces)*, the solution began to blow up (as shown in the > printed statements). Why does this happen? Is there a hidden conflict in > conservation settings I should be careful of? > > Thanks, > Yun > > > -- > Yun Tao > Postdoc > Center for Infectious Disease Dynamics > Pennsylvania State University > State College, PA 16803 > > <0flux_bc_fipylistserve.py> > > _______________________________________________ > fipy mailing list > [email protected] > http://www.ctcms.nist.gov/fipy > [ NIST internal ONLY: https://email.nist.gov/mailman/listinfo/fipy ] > > > _______________________________________________ > fipy mailing list > [email protected] > http://www.ctcms.nist.gov/fipy > [ NIST internal ONLY: https://email.nist.gov/mailman/listinfo/fipy ] > > -- Yun Tao Postdoc Center for Infectious Disease Dynamics Pennsylvania State University State College, PA 16803
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