>Viscous fluxes are messier with DG: they have tunable parameters and the >tradeoffs are never satisfying.
I almost never tune those parameters. Interior penalty can be problematic in case of very stretched elements but BR2 works great in 2D and 3D with stability parameter \eta= 3, 4 or number of element faces (as the theory suggests). I think that the major difference is the convergence rates of iterative solvers, with cG you need far less iterations. That's the reason why I use cG for the pressure solvers in operator splitting algorithms for incompressible flows. Lorenzo On Fri, Apr 19, 2013 at 1:29 AM, Jed Brown <[email protected]> wrote: > "Kirk, Benjamin (JSC-EG311)" <[email protected]> writes: > > > well you probably should clarify that - you are certainly "unwinding" > > at the cell interfaces to get an upwind bias in the scheme, right? So > > that could be alternatively looked at as a central + diffusive > > discretrization… So I would contend the artificial viscosity is (i) > > less direct and (ii) physically based, but could be thought of as > > viscosity nonetheless. > > 1. "upwinding" here means the solution of a Riemann problem. If you use > a Godunov flux, then the "upwinding" is introducing no numerical > viscosity. I think of Riemann problems as being very fundamental when > solving problems that do not have continuous solutions. > > 2. Numerical dissipation introduced by an approximate Riemann solver is > decoupled from the convergence rate of the method. The Riemann solve > has no tunable parameters, does not depend on the grid, and can attain > any order of accuracy purely by raising the order of reconstruction (in > FV) or the basis order (in DG). Compare this to SUPG, for example, > which has an O(h) term. > > Viscous fluxes are messier with DG: they have tunable parameters and the > tradeoffs are never satisfying. > > > Certainly if you computed the interface cell flux as the average of > > the neighbors things would go to hell in a hurry? > > Yes, that's unstable. > ------------------------------------------------------------------------------ Precog is a next-generation analytics platform capable of advanced analytics on semi-structured data. The platform includes APIs for building apps and a phenomenal toolset for data science. Developers can use our toolset for easy data analysis & visualization. Get a free account! http://www2.precog.com/precogplatform/slashdotnewsletter _______________________________________________ Libmesh-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/libmesh-users
