Hello all, After some experimentation it seems to me the values of facesphi do update after every time step and that the approach outlined in the second email is a valid one. If I attempt to use just phi as the variable used to set D I get an error due to the difference in shapes between D and phi. It seems that my second email outlines the correct method to use a coefficient that depends in a piecewise fashion on the variable being solved (were the coeff is defined at the cell faces). Please correct me if I am wrong. Would it be worthwhile to expand the mesh1D diffusion example to include a piecewise version of the final part of that example in which the diffusion coefficient depends linearly on concentration? I am willing to write a new version of the example and post it here if there is interest to make the change.
Cheers, Salomon On Fri, Jan 4, 2013 at 4:30 PM, Salomon Turgman Cohen <[email protected]>wrote: > Hello all, > A possibility is to define the diffusion as a variable (similar to > mesh1D with position dependent diffusion). In this case I can use something > like > > phi = CellVariable(name="Concentration (M)",mesh=mesh,value=0.0) > > and then: > > facesphi=phi.arithmeticFaceValue > > to obtain the concentration at the faces. Can I then use statements in the > form: > > D.setValue(facesphi*slope+intercept,where="concentration rage") > > My concern is that facesphi will not update as the solution is being > obtained. Thanks for any guidance. > > Salomon > > > > > On Fri, Jan 4, 2013 at 2:51 PM, Salomon Turgman Cohen > <[email protected]>wrote: > >> Hello developers and users, >> I am interesting in solving a simple 1D diffusion equation using fipy. >> My requirement is that the diffusion coefficient is concentration >> dependent. Following the mesh1D example I know how to do this if I have a >> simple functional form to describe the diffusion's dependence on >> concentration. However, what I have is just 5 data points of diffusion >> versus concentration. What I want to do is a linear interpolation of the >> diffusion in between the data points. I constructed the following function >> as an example: >> >> def diffusion(phi): >> if (phi>=0.0) & (phi<0.902449): >> return phi*(-7.63256E-8) + 1.05240E-7 >> elif (phi >= 0.902449) & (phi < 1.807062): >> return phi*(-1.37296E-08) + 4.87503E-08 >> elif (phi >= 1.807061587) & (phi < 2.713202143): >> return phi*(-2.23797E-08) + 6.43815E-08 >> elif (phi >= 2.713202143) & (phi < 3.570465711): >> return phi*-1.48121E-09 + 7.67966E-09 >> elif (phi >= 3.570465711) & (phi < 4.425457264): >> return phi*-4.04495E-10 + 3.83529E-09 >> elif (phi >= 4.425457264): >> return phi*-4.62147E-10 + 4.0904E-09 >> >> But it cannot handle the arrays obtained from CellVariables command. What >> would be the right way to do this? >> >> Thanks! >> >> -- >> Salomon Turgman Cohen >> Postdoctoral Associate >> Cornell University >> (919) 341-9650 >> > > > > -- > Salomon Turgman Cohen > Postdoctoral Associate > Cornell University > (919) 341-9650 > -- Salomon Turgman Cohen Postdoctoral Associate Cornell University (919) 341-9650
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