This seems like a completely separate issue than any potential changes with dimensionality.
Please define "completely different results". Are you sure that, with your noise term removed, that your Allen-Cahn system is mesh and time step convergent? > On May 9, 2017, at 3:48 AM, Anders Ericsson <anders.erics...@solid.lth.se> > wrote: > > Hi, and thank you for clarifying. > > However I have experienced some issues using the "gaussianNoiseVariable" to > represent thermal fluctuations during nucleation, > http://www.ctcms.nist.gov/fipy/fipy/generated/fipy.variables.html#module-fipy.variables.gaussianNoiseVariable. > > I have noticed that if I change the mesh size or the timestep I seem to get > completely different results, as if the equations changes. I know that the > noise-term contains the cellVolume and the timestep as described in the API, > and many articles state the same thing. > But it seems odd to me that the equations should be meshsize and timestep > dependent, do you know if this is the case or maybe I am doing something > wrong? > > I am using the noise term in an Allen-Cahn equation, implemented such as > below: > > sigmaSqrd = 2 * A * M_phi * kBoltzmann * T / (mesh.cellVolumes * dt) > noise = GaussianNoiseVariable(name = "noise", mesh = mesh, mean = mean, > variance = sigmaSqrd) > > eq = TransientTerm(coeff = 1 / M_phi) == DiffusionTerm(coeff = eps_phi**2) + > S0 + ImplicitSourceTerm(coeff = S1) + noise / M_phi > > I deeply appreciate any help regarding this issue, > > Thank you and best regards, > Anders > > From: fipy-boun...@nist.gov <fipy-boun...@nist.gov> on behalf of Guyer, > Jonathan E. Dr. (Fed) <jonathan.gu...@nist.gov> > Sent: Friday, May 5, 2017 9:58:02 PM > To: FIPY > Subject: Re: How is discretization handled in 1D and 2D? > > FiPy doesn't apply units explicitly (well, it can, but they don't propagate > into the solver matrix and nobody uses them but me AFAICT). > > In 1D you can view > > cell volume as dx x 1 m x 1 m (m**3) > face area as 1 m x 1 m (m**2) > > or > > cell volume as just dx (m) > face area as dimensionless > > > Similarly, in 2D you can view > > cell volume as dx x dy x 1 m (m**3) > face area as w x 1 m (m**2) > > or > > cell volume as just dx x dy (m**2) > face area as w (m) > > > Everything is dimensionally consistent, either way. .faceGrad and .divergence > both have units of m**-1 regardless of the dimensionality of the mesh. > > > > > > > On May 3, 2017, at 4:52 AM, Anders Ericsson <anders.erics...@solid.lth.se> > > wrote: > > > > Hi all, > > > > I am mainly working with 1D and 2D phase-field simulations using FiPy. In > > the documentation there is the discretization section describing how the > > PDE equations are discretized in FiPy in 3D > > (http://www.ctcms.nist.gov/fipy/documentation/numerical/discret.html#). > > > > Maybe this is a stupid question, but I am wondering what the units are for > > the spatial parameters in the discretization when you are running 1D and 2D? > > That is, the CV volume V_p, the area of the face A_f, the distance d_ap. > > > > Thanks and best regards, > > Anders > > _______________________________________________ > > fipy mailing list > > fipy@nist.gov > > http://www.ctcms.nist.gov/fipy > > [ NIST internal ONLY: https://email.nist.gov/mailman/listinfo/fipy ] > > > _______________________________________________ > fipy mailing list > fipy@nist.gov > http://www.ctcms.nist.gov/fipy > [ NIST internal ONLY: https://email.nist.gov/mailman/listinfo/fipy ] > _______________________________________________ > fipy mailing list > fipy@nist.gov > http://www.ctcms.nist.gov/fipy > [ NIST internal ONLY: https://email.nist.gov/mailman/listinfo/fipy ] _______________________________________________ fipy mailing list fipy@nist.gov http://www.ctcms.nist.gov/fipy [ NIST internal ONLY: https://email.nist.gov/mailman/listinfo/fipy ]
