Split-explicit acoustic substepping for low-Mach time integration (with two-tier shock/interface capture)#1619

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Commits on Jun 26, 2026

feat(sim): add acoustic_substepping params and checker exclusions
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feat(sim): advective-CFL timestep and acoustic substep count for split-explicit mode
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feat(sim): HLLC slow-flux variant (p-star removed, contact-speed dissipation) for split mode
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feat(sim): acoustic substep module (forward-backward, EOS, divergence damping)
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feat(sim): split-explicit RK orchestration for acoustic substepping
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fix(sim): guard acoustic_substepping (CFL+RK3 required), gate ICFL abort, CFL example cases
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test(sim): 2D Gresho low-Mach validation case for acoustic substepping
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fix(sim): correct multi-D acoustic substep count and make n_acoustic_substeps a floor
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fix(sim): grad-div divergence damping for acoustic substep (dimensionless, CFL-stable)
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feat(test): 2D isentropic vortex lowmach example + acoustic_substepping golden test
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fix(sim): guard num_fluids==1 for acoustic_substepping, clamp n_substeps overflow, fix cfl_const_dt restart
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perf(sim): slim acoustic substep kernel (direct EOS + per-cell velocity reuse)
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fix(sim): pass acoustic_substepping by value to s_compute_dt_from_cfl (GPU acc-routine-seq portability)
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feat(pre_process): parameterized low-Mach acoustic-pulse hardcoded ICs (hcid 183/264/304)
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feat(sim): generalize acoustic substep kernel to num_fluids>1 (mixture EOS, velocity, slow alpha advection)
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fix(sim): species-mass conservation in acoustic forward sweep via frozen snapshot
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fix(sim): resolve nvhpc OMP-offload ICE in s_compute_dt (firstprivate acoustic_substepping)
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docs: document split-explicit acoustic substepping (low-Mach) integrator
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feat(sim): expose HLLC acoustic-flux entry for the substep robust tier
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feat(sim): WENO reconstruction of acoustic variables in the substep
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feat(sim): two-tier discontinuity criterion (WENO indicators + volume-fraction variation)
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feat(sim): two-tier acoustic flux (cheap central / WENO+HLLC robust, WENO-Z criterion)
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style(sim): wrap long acoustic_substepping recon_type PROHIBIT line
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test(sim): interface + shock-interaction validation for the two-tier substep
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feat(sim): expose HLLC convective-flux entry for the substep robust tier
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feat(sim): conditional full-state reconstruction at flagged faces
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feat(sim): full-HLLC convective transport at flagged faces (shock capture)
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feat(sim): verify second-order time accuracy of the acoustic split scheme
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test(sim): shock-interface validation + docs for shock-capable substep
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feat(sim): live convective momentum at flagged faces via stored slow flux (shock stability)
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test(sim): 2D transverse + multifluid shock-interface validation; docs for shock capture
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feat(sim): robust upwind flux at outflow boundaries for the acoustic substep
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fix(sim): final-review wave — correct frozen-flux comments, drop dead reconstruction, add shock golden
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style(sim): apply ./mfc.sh format to acoustic substep + rhs
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refactor(sim): tidy acoustic substep kernel (dead code, comments, dups)
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feat(sim): reconstruct mixture alpha at flagged faces (multifluid shock EOS accuracy)
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feat(sim): per-face bc_type for outflow-boundary flagging (patch-BC coverage)
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test(sim): 3D shock-capture validation + 3D flagged-face golden
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perf(sim): skip robust-tier delta apply on unflagged stages (smooth-flow speedup)
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feat(sim): expose EE bubble dynamics integrator with explicit step (substep co-subcycling)
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feat(sim): carry bubble state + bubble-aware EOS through the acoustic substep
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Commits on Jun 27, 2026

Commits on Jun 28, 2026

test(sim): 3D low-Mach GPU demonstrators (shock + smooth acoustic pulse)
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