rtx-cfd: mask hysteresis — sticky cell classification against a reference mask

The measured FSI3 killer is the bistable mask: one geometry (|d| identical to 4 digits) samples two load branches (60 vs 120 kN), and the traced s=1 death is the secant walking a 20x load cliff (68,886 -> 1,307,938 N over a 1e-3 candidate change). A sticky band makes the load map single-valued at the crossing: formerly-fluid cells flip only at phi < -band, formerly-solid at phi > band, classified against the mask held at rebuild time — in a coupling loop, the restored committed step-start mask. Band 0 is structurally bit-identical (phi > -0.0 <=> phi > 0.0) and verified digit-for-digit on both committed defaults (FSI2 and FSI3, every physics digit). Measured cost on the translating-circle MMS at band 0.25h: +0.5% field error (u/p ratios 1.17/2.12 vs the no-hysteresis moving levels 1.16/2.11); flip delay = band/(v dt), deterministic. Exposed as RTX_FSI{2,3}_HYST in multiples of h_min. Co-Authored-By: Claude Fable 5 <[email protected]> Claude-Session: https://claude.ai/code/session_01X2GmJXeQ2njUecEKiJZ1G2
2026-08-26 15:27:09 -05:00
parent 3207f2d4c6
commit bff84ccdcc
6 changed files with 340 additions and 4 deletions
@@ -108,6 +108,12 @@ fn fsi3_added_mass_flag() {
            // the developed cycle's bistable stalls sit at 3.5e-4 and
            // riding the FLOOR up instead was measured to make it worse.
            stall_accept: 5.0,
+            // Off by default (bit-identical). The t = 10 studies probe it:
+            // the s = 1 death and the s = 2 crossing stalls are both the
+            // bistable mask (one geometry, two load branches — traced),
+            // which a sticky band makes single-valued at an O(band) wall
+            // lag (measured +0.5% field error at 0.25h on the MMS).
+            mask_hysteresis: 0.0,
            max_subiterations: 30,
            coupler: "iqn".into(),
            reuse: 2,