Drew - I'm glad we were able to get things working for you.
I recommend learning git/github just because I think it'll help you keep track of your own work. Jumbles of renamed files are a sure-fire way to lose things. I recommend the [Software Carpentry lesson](http://swcarpentry.github.io/git-novice/); it only takes a few hours. - Jon > On Dec 18, 2018, at 12:43 AM, Drew Davidson <davidson...@gmail.com> wrote: > > Hi Dr. Guyer, > > I updated my code with your changes. It now matches the analytical solution > pretty well, after several grid refinements. This is of course not a > comprehensive test. > > The Python script: > https://github.com/cashTangoTangoCash/Convection2DFiPyExample01/blob/master/ConvectionTestProblem2D_01_20181215Version.py > > A report showing agreement between FiPy and analytical solution: > https://github.com/cashTangoTangoCash/Convection2DFiPyExample01/blob/master/Report20181216.pdf > > The README.md of my repo has been updated to provide a better explanation of > what is going on. > > I apologize for not learning git/github well enough to have github properly > track changes between us as we went along. Instead, I put comments at the > top of my scripts to document how I was looking at your code and > documentation. > > Thanks > > > On Fri, Dec 14, 2018 at 8:20 PM Guyer, Jonathan E. Dr. (Fed) via fipy > <fipy@nist.gov> wrote: > Drew - > > I had found the same sign error in the denominator. You're also correct that > the units didn't agree. Multiplying by the face areas is redundant to taking > the divergence. > > I've updated our notes: > > https://github.com/usnistgov/fipy/blob/dd3420fb71884d74850051ad2280bff525301824/documentation/USAGE.rst > > and your latest code: > > https://github.com/guyer/Convection2DFiPyExample01/commit/ca59e8955319545f9965705c8fadfcbb5abd5951 > > With these changes, the results look much more plausible. > > - Jon > > > On Dec 12, 2018, at 1:22 PM, Drew Davidson <davidson...@gmail.com> wrote: > > > > Hi Dr. Guyer, > > > > I looked over your more recent documentation: > > https://github.com/usnistgov/fipy/blob/70b72b7abb267c85ada47886b8b3573e1819fffc/documentation/USAGE.rst > > > > I am embarrassed I did not understand how to choose values for a and b in > > the Robin condition before. > > > > I also cloned your repo to my local computer and ran it: > > https://github.com/guyer/Convection2DFiPyExample01 > > > > When I run the code in your repo, the viewer does show a variation in T > > with respect to r, but the size of that variation is extremely tiny. > > Essentially, the solution is pinned at the initial temperature. The > > variation also has the wrong sign (solid object is warming up), as the > > ambient air is colder than the solid object (T_infinity < T_initial), and > > the solid object should be cooling down. Maybe this is due to confusion I > > sowed by having var be T minus T_infinity; sorry. > > > > I tried another script in my repo: > > > > https://github.com/cashTangoTangoCash/Convection2DFiPyExample01/blob/master/ConvectionTestProblem2D_01_20181211Version.py > > > > This script is upgraded in that now, the log file contains information > > about the solution (max and min temperatures). I obtain max and min > > temperatures using var.value.min() and var.value.max() in order to rule out > > goof-ups in my get_solution_along_ray function. > > > > The solution variable var is now exactly the temperature, in order to get > > rid of the previous source of confusion in which var was T minus T_infinity. > > > > The solution in my script is still pinned at the initial temperature. This > > persists even if I crank up the convection coefficient to a huge value > > (keep multiplying it by 1000 over and over and still seeing solution pinned > > at initial condition). > > > > I made handwritten notes on top of a pdf I made via Kile Editor of your > > more recent documentation: > > > > https://github.com/cashTangoTangoCash/Convection2DFiPyExample01/blob/master/RobinBoundaryConditionsFiPyUsage20181211_Annot_CTTC.pdf > > > > It seems to me that the units of the source terms should match the units of > > the terms in the partial differential equation for heat conduction. I > > thought that is how it worked from the FiPy examples, but I haven’t gone > > back and made sure. I find that for the first source term RobinCoeff*g, the > > units don’t seem to match the units of the terms in the PDE for heat > > conduction (I didn’t check the 2nd source term since it should be the same > > situation). I did this in kind of a hurry so maybe I am goofing up. I have > > not studied the finite volume method, and am just going on a hunch. > > > > It also seemed to me that there might be a minus sign missing in the > > RobinCoeff. The solution I get is still pinned at initial condition > > regardless of a minus sign or no minus sign there. > > > > Thanks > > > > On Fri, Dec 7, 2018 at 6:05 PM Guyer, Jonathan E. Dr. (Fed) via fipy > > <fipy@nist.gov> wrote: > > Drew - > > > > > > Thanks to your notes, I found a couple of errors in our Robin discussion. > > As you noted, the units don't work for the conversion of the divergence of > > gamma grad phi to the sum over faces (midway on page 1 of your notes). The > > left hand side should be integrated over volume. That line is expressing > > the discretization of the divergence theorem. > > > > I also discovered that the .divergence operator in FiPy doesn't work > > reliably on scalars. There's no real reason it should, but I thought I had > > convinced myself that it did. As a result, everything in the Robin terms > > needs to be multiplied by the surface normal > > > > Those changes to the FiPy documentation are > > [here](https://github.com/usnistgov/fipy/pull/615) for now. > > > > Beyond addition that, there are some changes necessary to put your boundary > > condition into Robin form. The point of the Robin condition is that it ties > > the gradient of the field to the value of the field. > > So, g isn't h(T - T_inf) / (-k); it's just -h T_inf / (-k). > > Likewise, \vec{a} isn't zero. Rather, \hat{n}\cdot\vec{a} = h/(-k). > > > > Here are the changes I made to your script to reflect these changes: > > https://github.com/cashTangoTangoCash/Convection2DFiPyExample01/compare/master...guyer:master > > > > I think I got your normalized temperature accounted for properly, and put > > the thermal diffusivity and convection coefficient in the proper places, > > but it's worth checking through. > > > > With these changes, the temperature field is now rotationally symmetric (it > > wasn't before, which is why I had to multiply by the normal before taking > > the divergence). > > > > Heat seems to be fluxing in from the outside, so I probably have the sign > > wrong. > > > > I don't have Octave, so I have no idea how this compares with your > > analytical solution. > > > > - Jon > > > > > On Dec 4, 2018, at 2:34 PM, Drew Davidson <davidson...@gmail.com> wrote: > > > > > > Hi Dr. Guyer, > > > > > > First I tried getting rid of the square brackets in > > > ConvectionTestProblem2D_01.py (commit ‘changed square brackets to > > > parenthesis in convection BC, but get same…’), but results are the same > > > (still wrong). > > > > > > Next: > > > As you directed, I took a look at: > > > > > > https://github.com/usnistgov/fipy/blob/develop/documentation/USAGE.rst#applying-robin-boundary-conditions > > > > > > Firefox was showing me raw latex rather than human-readable equations at > > > that web address, so I made a version I could read using the kile editor: > > > https://github.com/cashTangoTangoCash/Convection2DFiPyExample01/blob/master/RobinBoundaryConditionsFiPyUsage.pdf > > > > > > That material is rather challenging for me. I took a stab at it, > > > resulting in: > > > commit: ‘made a first attempt at a formulation in view of suggestions by > > > fipy …’ > > > > > > ConvectionTestProblem2D_01_2ndTry.py > > > https://github.com/cashTangoTangoCash/Convection2DFiPyExample01/blob/fb47960548650c994eb0c6f990e0db297566e174/ConvectionTestProblem2D_01_2ndTry.py > > > > > > a few handwritten notes indicating what I was thinking: > > > https://github.com/cashTangoTangoCash/Convection2DFiPyExample01/blob/master/RobinBoundaryConditionsFiPyUsageConvectionBC.pdf > > > > > > Here is a bit of the code: > > > > > > #ref: > > > https://github.com/usnistgov/fipy/blob/develop/documentation/USAGE.rst#applying-robin-boundary-conditions > > > > > > #warning: avoid confusion between convectionCoeff in that fipy > > > documentation, which refers to terms involving "a", and convectionCoeff > > > here, which refers to a heat transfer convection coefficient at a boundary > > > > > > Gamma0=D_thermal > > > > > > Gamma = FaceVariable(mesh=mesh, value=Gamma0) > > > > > > mask=surfaceFaces > > > > > > Gamma.setValue(0., where=mask) > > > > > > dPf = FaceVariable(mesh=mesh, value=mesh._faceToCellDistanceRatio * > > > mesh.cellDistanceVectors) > > > > > > Af = FaceVariable(mesh=mesh, value=mesh._faceAreas) > > > > > > #RobinCoeff = (mask * Gamma0 * Af / (dPf.dot(a) + b)).divergence #a is > > > zero in our case > > > > > > b=1. > > > > > > RobinCoeff = (mask * Gamma0 * Af / b).divergence #a is zero in our case > > > > > > #eq = (TransientTerm() == DiffusionTerm(coeff=Gamma) + RobinCoeff * g - > > > ImplicitSourceTerm(coeff=RobinCoeff * mesh.faceNormals.dot(a))) #a is > > > zero in our case > > > > > > # g in this formulation is -convectionCoeff/k*var, where var=T-T_infinity > > > > > > eq = (TransientTerm() == DiffusionTerm(coeff=Gamma) + > > > ImplicitSourceTerm(RobinCoeff * -convectionCoeff/k)) > > > > > > > > > Now the solution variable remains stuck at the initial condition, as if > > > the boundary condition is not being applied. I am sort of out of my depth > > > at this point. I was guessing that an ImplicitSourceTerm was the right > > > thing to do, since 'g' in the Robin condition depends on the solution > > > variable. I did mess around a little in IPython seeing if any terms are > > > coming out all zeros. > > > > > > Again, I put everything at > > > https://github.com/cashTangoTangoCash/Convection2DFiPyExample01. > > > > > > Thanks > > > > > > On Mon, Dec 3, 2018 at 4:21 PM Guyer, Jonathan E. Dr. (Fed) via fipy > > > <fipy@nist.gov> wrote: > > > Drew - > > > > > > Apologies for the delayed reply. > > > > > > There are a couple of issues here: > > > > > > `-convectionCoeff/k*(var.faceValue-T_infinity)` describes a FiPy > > > FaceVariable. > > > > > > `[-convectionCoeff/k*(var.faceValue-T_infinity)]` is a single element > > > Python list that contains a FiPy FaceVariable. > > > > > > Multiplying that list by other elements has rather unpredictable results. > > > > > > In short, get rid of the square brackets. We do our best to treat Python > > > lists like FiPy vector fields, but there's only so much we can do. A list > > > that holds a numpy array is not a vector field. > > > > > > > > > Beyond that, what you've described looks like a Robin boundary condition > > > to me. Our best recommendation for Robin conditions is covered at: > > > > > > > > > https://github.com/usnistgov/fipy/blob/develop/documentation/USAGE.rst#applying-robin-boundary-conditions > > > > > > Please don't hesitate to ask for more clarification if this doesn't get > > > you where you need. > > > > > > - Jon > > > > > > > > > > > > > On Nov 16, 2018, at 11:55 PM, Drew Davidson <davidson...@gmail.com> > > > > wrote: > > > > > > > > Hello, > > > > > > > > I am stuck in how to correctly apply a simple convection boundary > > > > condition in FiPy, in the context of simple transient heat conduction > > > > in 2D. > > > > > > > > Is this correct: > > > > var.faceGrad.constrain([-convectionCoeff/k*(var.faceValue-T_infinity)]*mesh.faceNormals,where=surfaceFaces) > > > > > > > > I have a 2D mesh generated in gmsh. The convection boundary condition > > > > is applied to a curved boundary. > > > > > > > > The code and results are found at: > > > > https://github.com/cashTangoTangoCash/Convection2DFiPyExample01/tree/master > > > > > > > > The project appears to have a heap of files, but It’s a really just a > > > > simple 2D problem with a comparison to an analytical solution. The > > > > basic script is ConvectionTestProblem2D_01.py. Report20181116.pdf shows > > > > current results, which are clearly wrong. > > > > > > > > Am I correctly applying the convection boundary condition in terms of > > > > the FiPy syntax/language for this 2D problem with a gmsh mesh and a > > > > curved boundary? > > > > > > > > Thanks > > > > _______________________________________________ > > > > 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 ] _______________________________________________ fipy mailing list fipy@nist.gov http://www.ctcms.nist.gov/fipy [ NIST internal ONLY: https://email.nist.gov/mailman/listinfo/fipy ]
