Thanks Daniel. I think I understand now. What would I do to multiply through by r in writing a FiPy equation? Should I some how create a spatial variable for r? Such as r= Variable? Do I have to somehow give it a range of possible values? (I didn't see an example for this online)
Then I could use a standard mesh, correct? mesh = Grid1D(nx=nx,dx=dx) and then the equation becomes? eqT = TransientTerm(r * rho_b * Cp_b*1000/MW_b, var=T) == DiffusionTerm(coeff = L_eff, var=T) + r*S Sorry to have so many questions. On Thu, Aug 30, 2018 at 10:20 AM Daniel Wheeler <daniel.wheel...@gmail.com> wrote: > There are two ways to solve on a cylindrical domain in FiPy. You can > either use the standard diffusion equation in Cartesian coordinates (2nd > equation below) and with a mesh that is actually cylindrical in shape or > you can use the diffusion equation formulated on a cylindrical coordinate > system (1st equation below) and use a standard 2D / 1D grid mesh. I think > you're confused about "multiplying through by R". The problem with the > first equation in FiPy (cylindrical) is that FiPy can't have a coefficient > outside the first derivative, which occurs in the diffusion term of the > first equation. Of course that isn't an issue for constant coefficient like > density etc., but r, however, is not constant. We can get around that > problem by multiplying the first equation by r (small r) because the r can > come inside the time derivative in the transient term and just be a > multiplier on the source term, which is fine. Your equation then looks like > this. > > > Hope that helps. > > Cheers, > > Daniel > > On Wed, Aug 29, 2018 at 9:13 AM Daniel DeSantis <desan...@gmail.com> > wrote: > >> Daniel, >> >> Thanks again for getting back to me. Sorry to keep coming back to the >> same problem. It does seem like there's a problem with the >> CylindricalGrid1D mesh. I noticed that running the most basic 1D diffusion >> example with a cylindrical grid doesn't seem to work correctly. With that >> said, I hope I can impose on you one more time and ask how I should convert >> a cylindrical coordinate PDE into a rectangular coordinate PDE for FiPy, >> essentially turning this >> [image: image.png] >> into this: >> [image: image.png]. >> Previously you said to multiply through by r. Assuming R is the maximum >> of the variable r, am I looking at this equation >> [image: image.png] or should I be using this? >> [image: image.png]If r should still be in the variable format, how would >> I make that work in FiPy? >> >> Thanks, >> Dan DeSantis >> > > > -- > Daniel Wheeler > _______________________________________________ > fipy mailing list > fipy@nist.gov > http://www.ctcms.nist.gov/fipy > [ NIST internal ONLY: https://email.nist.gov/mailman/listinfo/fipy ] > -- Daniel DeSantis
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