Even when the initial condition exceed 1 the system is able to converge to the right solution with no problem.
But with first order approximation the system doesn't work. Ernesto Em 2012-12-05 16:51, Roy Stogner escreveu: > On Wed, 5 Dec 2012, ernestol wrote: > >> I will try to set the nodal value directly, thank you. > > This *still* won't give you a ringing-free solution. Imagine you're > trying to interpolate a step function which changes from 0 to 1 less > than halfway through a 3-node quadratic line element. You'll set the > first node to 0, the second node to 1, and the third to 1, and the > quadratic function will peak 3/4 of the way through the element with > a > value of 9/8, greater than 1. > > What's more, didn't you say you're doing Cahn-Hilliard with the > typical polynomial free energy functional with a trough at 1? > In that case even the *true solution* can temporarily exceed 1, IIRC > - > the local free energy term penalizes but doesn't forbid such excess, > and in the transient case the local term can be temporarily dominated > by the interfacial free energy effects. If you're coupling > Cahn-Hilliard to another equation that NaNs or goes unstable or > whatever when it sees c>1, you'll need to either truncate c in the > coupling or use something like a Flory-Huggins free energy that > really > does prevent c>1 solutions. > --- > Roy ------------------------------------------------------------------------------ LogMeIn Rescue: Anywhere, Anytime Remote support for IT. Free Trial Remotely access PCs and mobile devices and provide instant support Improve your efficiency, and focus on delivering more value-add services Discover what IT Professionals Know. Rescue delivers http://p.sf.net/sfu/logmein_12329d2d _______________________________________________ Libmesh-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/libmesh-users
