Re: sources errors in advection/diffusion problems, and one solution

Thank you. I am busy for the week, but then will get a chance to think about this :-) Cheers, Jamie On Tue, Oct 4, 2016 at 1:16 PM, Daniel Wheeler wrote: > Hi James, > > Thanks for this example. I think I understand what is happening. Let's > start with the code for

Re: sources errors in advection/diffusion problems, and one solution

Hi James, Thanks for this example. I think I understand what is happening. Let's start with the code for solving the problem, import fipy import numpy mesh = fipy.Grid1D(nx=10) var = fipy.CellVariable(mesh=mesh) var[:] = 2 * numpy.random.random(mesh.numberOfCells) var.constrain(1.,

Re: sources errors in advection/diffusion problems, and one solution

Interesting. One addition to Zhekai's comment. When I read it, I thought Upwind might be doing better because it is adding additional numerical diffusion (as upwind usually does, at least in finite difference codes). However this is not the case. If you keep the advection u and diffusion D the 1D

Re: sources errors in advection/diffusion problems, and one solution

Hi James, Thanks for providing this demo to illustrate the problem. I don't have any particular ideas exactly why the initial value of psi helps to reduce the error and why transient problem "advect" out. However, I have some findings that may help on this. Finding # 1: I noticed you have tried

Re: sources errors in advection/diffusion problems, and one solution

No worries -- I had to do it to figure out the problem in my more complex domain and equation... The issue which surprised me was that the value the variable was initialized to had an effect on the steady solution. Jamie On Fri, Sep 16, 2016 at 8:14 AM, Guyer, Jonathan E. Dr. (Fed) <

Re: sources errors in advection/diffusion problems, and one solution

James - I think Daniel will have more insight into why this is happening and if there is anything to be done about it besides artificial relaxation, but I just want to say how much I appreciate your putting this together. This is a very lucid illustration. - Jon > On Sep 15, 2016, at 5:13

sources errors in advection/diffusion problems, and one solution

Dear FiPy users -- This is a simple example of how and why fipy may fail to solve a steady advection diffusion problem, and how solving the transient problem can reduce the error. I also found something that was a surprise -- the "initial" condition of a steady problem can affect