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quokka-astro / quokka

Two-moment AMR radiation hydrodynamics (with self-gravity, particles, and chemistry) on CPUs/GPUs for astrophysics
https://quokka-astro.github.io/quokka/
MIT License
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in rare cases, NSCBC outflow produces unphysically high velocities #532

Open BenWibking opened 5 months ago

BenWibking commented 5 months ago

Describe the bug In very rare circumstances, the NSCBC outflow boundary conditions can produce states in isolated cells at the boundary that have unphysically high velocities. An ad hoc (but partially effective) workaround is to revert to zero-gradient extrapolation when the velocity in the ghost cells would otherwise be extremely large (for example, > 1e10 cm/s).

To Reproduce This was observed after about 40,000 timesteps while running the updated shock-cloud problem at 1024x256x256 resolution with no refinement.

Additional context A similar failure mode (but with negative densities instead) was seen in https://github.com/quokka-astro/quokka/pull/472.

psharda commented 3 months ago

@BenWibking is this now resolved by #598 ?

BenWibking commented 3 months ago

@BenWibking is this now resolved by #598 ?

Yes, in the sense that the simple version of the boundary conditions added in #598 doesn't have this problem. No, in the sense that the real NSCBC still has this problem.