Hi Jed, I'm mainly interested in the parameter limits -- I know how to specify them, but I don't see any explanation of valid values in the code. So for ex20, how large can beta get and still be meaningful?
For ex29, are you saying that it's always generating a singular linear system, or only for low viscosity and resistivity? Thanks! Boyana -- Boyana Norris, Ph.D., Computer Scientist, Argonne National Laboratory norris at mcs.anl.gov, +1.630.252.7908, http://www.mcs.anl.gov/~norris/ On May 14, 2011, at 1:14 PM, Jed Brown wrote: > On Sat, May 14, 2011 at 02:53, Barry Smith <bsmith at mcs.anl.gov> wrote: > Do you know what the valid values for the various model parameters in snes > ex20 and ex29 are? We are looking for something we can vary similar to how we > change the lid velocity and grashof parameters in the driven cavity problems, > in order to generate linear systems with different characteristics. > > The options are given in the help strings. Do you want the names of the > non-dimensional parameters? Do you want to know how various parameters affect > the system? > > In the case of ex20, the exponent beta is the only free parameter. If > temperature is always positive, I believe there are no well-posedness issues > for any beta. Positive beta becomes degenerate as T -> 0, negative beta > becomes singular in that limit. It appears that the method works for all > positive beta. When beta is negative, this discretization (or maybe just the > line search) is not monotone so it may compute negative temperatures (program > crashes). Negative beta is physical for other heat transport problems. > > I can't give a similarly detailed explanation of ex29, but low viscosity and > low resistivity should tend to make it less diffusive (closer to ideal MHD > which is hyperbolic). This discretization seems to produce singular linear > systems. -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20110514/0d448405/attachment.htm>
