Added TMOP solver to improve mesh conditioning#2
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tboudreaux wants to merge 2 commits into4D-STAR:mainfrom
Open
Added TMOP solver to improve mesh conditioning#2tboudreaux wants to merge 2 commits into4D-STAR:mainfrom
tboudreaux wants to merge 2 commits into4D-STAR:mainfrom
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Meshes generated purley algebraically tend to be poorly conditioned. Incorporated MFEM's TMOP support based on a metric of ideal shape and unit size
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Meshes are generated as a three domain system, the core, envelope, and vacuum. We need this multi-domain approach as a Cartesian mesh is useful in the core to avoid singularities, a spherical mesh is useful in the envelope to model deformation, and the vacuum is needed to apply boundary conditions. A challenge though is that the boundary between the core and envelope mesh can introduce artificial stiffness into the shape function Jacobians. This resulted in the boundary between these two domains acting as an artificial material change.
I've explored some analytic ways to resolve this; however, generally they have not prooven useful. Instead we use MFEM's built in Target Matrix Optimization Problem (TMOP) solver to automatically deform the nodes interior to the stellar surface following the
IDEAL_SHAPE_UNIT_SIZEmetric and the302TMOP metric. These choices can be adjusted in the future; however, they seem to work well to smooth out the interface boundary.Note that these metrics involve computing the dense Hessian for the shape functions and then solving a PDE accross the domain. This means that when TMOP is enabled (through the
[main.optimization_modes.tmop]parameter in the config filestroidruntime can increase up to 10 -> 30 minutes depending on mesh resolution. This is not a problem as we do not expect to be generating meshes on the fly.