On Wed, Jul 24, 2013 at 3:35 PM, Edwin Sze Lun Khoo <[email protected]>wrote:
> Hello, > > I have a couple of quick questions about the use of convection terms and > defining algebraic equations of dependent variables in FiPy: > > 1) What is meant by "an inlet or an outlet boundary condition" in > http://www.ctcms.nist.gov/fipy/documentation/USAGE.html#applying-outlet-or-inlet-boundary-conditions > ? > I think all that it means is that the out or in flux (due to a convection term, there might be another contribution from the diffusion term) will be $\vec{u} \cdot \vec{n} \phi$ if $\phi$ is constrained. If $\phi$ is not constrained, then $\vec{u}$ is assumed to be zero (even if it isn't). This is confusing, but it is maintained for backwards compatibility. > > 2) What is the best way to write algebraic equations that relate > CellVariables in FiPy? For instance, the electroneutrality assumption in > electrochemistry, \sum{z_{i}C_{i} = 0, relates ion concentrations with an > algebraic constraint. > Can't the constrained equation simply be used to eliminate one of the variables? If not, Raymond's solution seems reasonable. -- Daniel Wheeler
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