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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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check entropy inequality in each cell #382

Open BenWibking opened 1 year ago

BenWibking commented 1 year ago

From the expressions given in [1][2][3], we can compute a discrete entropy inequality in each cell, and then fallback to first order when it is violated [3].

More work is needed to generalize to a non-gamma-law EOS.

[1] https://ntrs.nasa.gov/api/citations/19900008060/downloads/19900008060.pdf [2] https://doi.org/10.1016/0168-9274(86)90029-2 [3] https://web.stanford.edu/group/ihmegroup/cgi-bin/MatthiasIhme/wp-content/papercite-data/pdf/ma2017entropy.pdf

psharda commented 1 year ago

Looks like we will need this, because velocities are getting quite large (100 km/s or more) very early on in the PopIII sim

BenWibking commented 1 year ago

We'll need a way to compute the entropy in Microphysics. I think it currently only computes it for constant-gamma gases.

psharda commented 1 year ago

Is entropy an additive property? Is the total entropy of a mixture of ideal gases equal to the sum of the entropies of the individual constituents?

BenWibking commented 1 year ago

Is entropy an additive property? Is the total entropy of a mixture of ideal gases equal to the sum of the entropies of the individual constituents?

Thermodynamics textbook says yes!

I consulted Fundamentals of equilibrium and steady-state thermodynamics, p. 97 (https://www.worldcat.org/title/162130919)

BenWibking commented 1 year ago

It turns out an entropy fallback method has been done for mixtures of ideal gases: https://web.stanford.edu/group/ihmegroup/cgi-bin/MatthiasIhme/wp-content/papercite-data/pdf/ma2017entropy.pdf