Omar SobhandClaude Fable 5.1
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Co-Authored-By: Claude Fable 5.1 <[email protected]> Claude-Session: https://claude.ai/code/session_01X2GmJXeQ2njUecEKiJZ1G2
346 lines
16 KiB
Rust
346 lines
16 KiB
Rust
//! Turek–Hron FSI3: the added-mass flapping flag — rung C3 of the ladder
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//! (omni-cortex `docs/turek_hron_geometry_decision.md`).
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//!
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//! Re = 200 channel flow (`U = 2`) past the rigid cylinder with the
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//! elastic flag at density ratio `rho_s / rho_f = 1` and `E = 5.6e6`:
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//! the flag is as light as the fluid it displaces, so the fluid's
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//! added mass is comparable to the structural mass — the regime in
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//! which a staggered partitioned coupling is repulsive and the
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//! quasi-Newton interface solver is genuinely needed per step (the
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//! coupled piston benchmark's territory). Reference (FEATFLOW level 4,
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//! dt = 0.0005): `ux(A) = −2.86 ± 2.70 mm [10.92 Hz]`,
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//! `uy(A) = 1.45 ± 34.90 mm [5.46 Hz]`, drag `460.2 ± 27.47`,
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//! lift `2.37 ± 153.75`.
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//!
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//! The march is FSI2's (`fsi2_harness::march`) with the FSI3 case
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//! parameters; the rigid-flag phase is checked against this solver's
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//! own CFD3 drag on the same geometry. The vacuum modal frequencies do
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//! NOT identify this cycle the way they identified FSI2's: with the
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//! fluid as heavy as the flag, the wetted frequency is set by the added
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//! mass (the reference 5.46 Hz sits far below the vacuum mode 2 of
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//! ~12 Hz that E/rho alone would give).
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//!
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//! # What is pinned
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//!
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//! Machinery invariants every run (conservation, finite state, coupling
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//! bookkeeping). The committed default (t_end = 4.2) pins the
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//! deterministic release response (uy 10.77 ± 23.57 mm, ±35% bands).
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//! Study horizons under the sticky mask (`RTX_FSI3_HYST=0.25
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//! RTX_FSI3_STALLX=10 RTX_FSI3_T_END=8.5`, ny 62 or 82) pin the
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//! settled flapping cycle measured 2026-08-27/28 — uy amp 50–58 mm
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//! across the grids (reference 34.90; two-grid agreement 2.3% by p95,
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//! the gap grid-converged), honest drag median 454 vs reference 460.2.
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//! The full study record lives in omni-cortex `solver_status.md`.
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//!
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//! Environment knobs: `RTX_FSI3_*` — the same set as `RTX_FSI2_*` (see
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//! `turek_hron_fsi2.rs`) plus `RTX_FSI3_OMEGA0`, `RTX_FSI3_TRACE`,
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//! `RTX_FSI3_C1`, `RTX_FSI3_PREDICTOR`, `RTX_FSI3_QUIESCENT`; defaults:
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//! ny 62, t_release 4, t_end 4.2, subcycle 2, tol 6e-5, rtol 1e-2,
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//! maxsub 30, coupler `iqn`, reuse 2, omega0 0.05, C^1 interface,
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//! kinematic predictor, quiescent release — every one of them a
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//! measured necessity at unit density ratio (see the config comments).
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mod fsi2_harness;
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use fsi2_harness::FSI3;
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use fsi2_harness::march::{MarchConfig, run_march};
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// FEATFLOW level-4, dt 0.0005 reference values.
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const REF_UY_MEAN: f64 = 1.45e-3;
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const REF_UY_AMP: f64 = 34.90e-3;
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const REF_UY_FREQ: f64 = 5.46;
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const REF_UX_MEAN: f64 = -2.86e-3;
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const REF_UX_AMP: f64 = 2.70e-3;
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const REF_DRAG_MEAN: f64 = 460.2;
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const REF_DRAG_AMP: f64 = 27.47;
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const REF_LIFT_MEAN: f64 = 2.37;
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const REF_LIFT_AMP: f64 = 153.75;
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#[test]
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fn fsi3_added_mass_flag() {
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// IQN by default: at density ratio 1 the per-step coupling gain is
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// high enough that a scalar relaxation is the wrong tool. The
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// tolerance floor is FSI2's loose-coupling value until FSI3's own is
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// measured; the increment-relative part does the work in the
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// meantime.
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let config = MarchConfig::from_env(
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"FSI3",
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MarchConfig {
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ny: 62,
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flag_nx: 35,
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t_release: 4.0,
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t_end: 4.2,
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// Subcycle 2, not FSI2's default 8: at unit density ratio the
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// interface noise floor rides with the MOTION as well as the
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// loads (mask flips per step ∝ velocity, each ~250 N — a
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// step-scale displacement on a light flag). Traced at
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// subcycle 8 through the release transient (flag at ~0.3
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// m/s): a step bouncing between 4e-4 and 1e-3 for twelve
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// passes, landing on the 13th by luck once and not at all
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// the next run. Subcycle 2 moves the interface 4x less per
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// step; the probe's subcycle-2 release map converges to
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// 9e-10.
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subcycle: 2,
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// The MEASURED FSI3 floor at this coupling (noise probe,
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// RTX_NOISE_CASE=fsi3, t = 4, ny = 62): flip-scan jumps
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// 3.6e-4 (12x FSI2's — 4x the dynamic pressure into a 10x
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// more compliant flag), the s = 8 release map stalling near
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// 1e-6 in 12 passes, and a traced step-1 stall at ~5e-5 from
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// ~250 N load flips; at subcycle 8 through the release
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// transient the floor rode up to ~1e-3 with the motion, which
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// is what moved the default to subcycle 2, budgeted at 3e-5
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// (wall-velocity noise 0.09 m/s, 4.5% of U). It must NOT be
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// FSI2's 2e-4 borrowed blindly with the constant-velocity
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// closure: a step accepted at one pass then left an interface
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// VELOCITY jump the incompressible fluid answered with an
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// impulsive added-mass load (1,600 N at release, 48,000 N
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// and 59 mm one step later, the flag's Newton dead by the
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// pass after) — the C^1 interface below removed that
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// channel.
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// 6e-5, not the 3e-5 the rest-state probe suggested: the
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// floor RIDES WITH THE MOTION, and through the cycle (flag
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// at ~1 m/s) a subcycle-2 step stalled at 1.9e-4 against a
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// 5x-floor window of 1.5e-4 at a turning point, where the
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// increment-relative part of the window collapses while the
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// flip noise does not (t = 6.18 s of the first study). The
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// window at 5 x 6e-5 = 3e-4 sits above the cycle's measured
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// stall level; wall-velocity noise 0.17 m/s against cycle
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// velocities of ~1 m/s.
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tol_floor: 6e-5,
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rtol: 1e-2,
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// 5 at the committed horizon (t_end 4.2 never stalls); the
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// t = 10 studies run STALLX=10 — see the MarchConfig field:
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// the developed cycle's bistable stalls sit at 3.5e-4 and
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// riding the FLOOR up instead was measured to make it worse.
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stall_accept: 5.0,
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// Off by default (bit-identical). The t = 10 studies probe it:
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// the s = 1 death and the s = 2 crossing stalls are both the
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// bistable mask (one geometry, two load branches — traced),
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// which a sticky band makes single-valued at an O(band) wall
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// lag (measured +0.5% field error at 0.25h on the MMS).
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mask_hysteresis: 0.0,
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max_subiterations: 30,
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coupler: "iqn".into(),
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reuse: 2,
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smooth_in_h: 0.0,
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csv_path: None,
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snap_path: None,
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snap_every: 10,
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// The blind first relaxation must not explode the structure
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// on a map whose per-pass gain is in the hundreds; 0.05 keeps
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// the exploratory pass bounded (the secant takes over from
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// pass 3, and the divergence verdict waits for it).
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initial_relaxation: 0.05,
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trace_steps: 0,
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trace_from: usize::MAX,
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coupling_rescue: false,
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poisson_f32: false,
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coarse_episode: 0,
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inc_trace: None,
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increment_factor: 0.0,
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speed_fraction: 0.0,
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// Continuous interface velocity across step boundaries: the
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// constant-velocity closure's jump at each step start drew an
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// impulsive added-mass load the unit-ratio flag could not
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// survive.
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c1_interface: true,
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// Extrapolate the converged interface motion: the
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// structure-alone predictor overshoots 2-5x at unit density
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// ratio and each step's first pass became a violent
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// excursion (traced at the t = 4 release).
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predictor: "kinematic".into(),
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// The structure-alone consistent initial acceleration ignores
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// the added mass; at unit density ratio it is wildly wrong
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// and Newmark carries it as a sign-alternating mode.
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quiescent_release: true,
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ffld_dir: None,
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},
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);
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let MarchConfig {
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ny, flag_nx, t_end, ..
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} = config;
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let case = fsi2_harness::case_from_env("FSI3", FSI3);
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let result = run_march(case, &config);
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let w = result.window(2.0);
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println!(
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" loads over the window: drag {:.2} ± {:.2} median {:.2} (ref {REF_DRAG_MEAN} ± \
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{REF_DRAG_AMP}), lift {:.2} ± {:.2} median {:.2} (ref {REF_LIFT_MEAN} ± {REF_LIFT_AMP})",
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w.drag_mid, w.drag_amp, w.drag_median, w.lift_mid, w.lift_amp, w.lift_median
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);
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println!(
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" FSI3 (fluid ny = {ny}, flag {flag_nx}x2 Quad8, dt = {:.2e}, {}): coupled {} \
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steps in {:.0} s wall total; {:.1} subit/step (max {}); {} stalled steps, {} \
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history-reset retries (worst residual {:.2e}); worst conservation {:.2e}; \
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skipped samples {} (of which {} spike-clamped); Newton rescues {:?}; coupling \
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rescues {} (+{} failed ladders)\n \
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measured over [{:.1}, {t_end:.1}] s: \
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uy(A) = {:.4} ± {:.4} mm (ref {:.2} ± {:.2}), ux(A) = {:.4} ± {:.4} mm (ref {:.2} ± \
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{:.2}), f = {} Hz (ref {REF_UY_FREQ}); onset amp {:.3e} -> {:.3e} m",
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result.dt,
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config.coupler,
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result.coupled_steps,
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result.elapsed,
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result.mean_subiterations,
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result.max_subiterations,
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result.stalled_steps,
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result.retried_steps,
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result.worst_stall,
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result.worst_conservation,
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result.skipped,
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result.spiked,
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result.newton_rescues,
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result.coupling_rescues,
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result.coupling_rescue_failures,
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w.t_start,
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w.uy_mid * 1e3,
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w.uy_amp * 1e3,
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REF_UY_MEAN * 1e3,
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REF_UY_AMP * 1e3,
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w.ux_mid * 1e3,
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w.ux_amp * 1e3,
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REF_UX_MEAN * 1e3,
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REF_UX_AMP * 1e3,
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w.frequency.map_or("n/a".to_string(), |f| format!("{f:.3}")),
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w.amp_early,
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w.amp_late,
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);
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// Machinery invariants — asserted at every resolution.
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assert!(
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result.worst_conservation < 1e-10,
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"load transfer lost force: {:.3e}",
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result.worst_conservation
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);
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assert!(result.final_state_finite, "flag state went non-finite");
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assert!(
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result.mean_subiterations < 15.0,
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"coupling is grinding: {:.1} subiterations/step",
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result.mean_subiterations
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);
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assert!(
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result.stalled_steps * 5 < result.coupled_steps.max(1),
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"coupling stalled on {} of {} steps (worst residual {:.2e})",
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result.stalled_steps,
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result.coupled_steps,
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result.worst_stall
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);
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// Physics bands, by horizon and configuration (the FSI2 pattern:
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// the march is deterministic, so the short committed horizon
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// carries tight regression bands on the release response; study
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// horizons pin the MEASURED settled cycle, band-generous across
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// the two grids that measured it. If a change moves any of these
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// numbers, that is a finding either way and must be loud.)
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// Bands were measured at the BENCHMARK case; an overridden u_mean
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// (`RTX_FSI3_UMEAN`) or e_s (`RTX_FSI3_ES`) pins nothing here.
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// Machinery invariants above stay asserted at every inflow and
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// stiffness.
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let benchmark_case =
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case.u_mean.to_bits() == FSI3.u_mean.to_bits() && case.e_s.to_bits() == FSI3.e_s.to_bits();
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let default_release = benchmark_case
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&& config.subcycle == 2
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&& config.mask_hysteresis == 0.0
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&& config.coupler == "iqn"
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&& ny == 62
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&& flag_nx == 35
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&& (t_end - 4.2).abs() < 1e-9;
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let hyst_cycle = benchmark_case
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&& config.subcycle == 2
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&& config.mask_hysteresis > 0.0
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&& config.coupler == "iqn"
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&& flag_nx == 35
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&& (ny == 62 || ny == 82)
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&& t_end >= 8.4;
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if default_release {
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// The committed default: the release response over [4.0, 4.2].
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// Measured BRANCH-SENSITIVE in EVERY windowed observable: four
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// solver-path changes (dense LU 2026-08-26 / banded LU
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// 2026-08-29 / Poisson warm start drafts 2026-08-30, each a
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// legitimate same-tolerance answer) gave
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// uy mid 10.77 / 6.02 / 2.91 / 8.88 mm,
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// uy amp 23.57 / 25.22 / 24.56 / 19.90 mm,
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// ux mid -2.90 / -2.91 / -2.56 / -1.82 mm,
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// growth 4.6x / 5.2x / 3.4x / 4.0x,
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// with IQN retries 2 / 0 / 1 / 1. The release transient at
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// unit density ratio amplifies tolerance-level perturbations
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// through discrete retry/mask branches, so ANY tight band here
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// re-fires on the next legitimate change. These bands are
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// GROSS-PHYSICS tripwires around the measured scatter (sign,
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// scale, oscillation-vs-drift); the load-bearing regression
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// pins for solver changes are the SETTLED-CYCLE study bands
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// (hyst_cycle below), which are statistics over 2 s of cycle,
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// not 0.2 s of chaotic transient.
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assert!(
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(1.0e-3..=18.0e-3).contains(&w.uy_mid),
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"release uy mid {:.4e} left the gross-scale band [1.0e-3, 18.0e-3] \
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(measured branches 10.77/6.02/2.91/8.88 mm)",
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w.uy_mid
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);
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assert!(
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(14.0e-3..=34.0e-3).contains(&w.uy_amp),
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"release uy amp {:.4e} left [14.0e-3, 34.0e-3] (measured branches \
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23.57/25.22/24.56/19.90 mm)",
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w.uy_amp
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);
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assert!(
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(-4.5e-3..=-0.9e-3).contains(&w.ux_mid),
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"release ux mid {:.4e} left [-4.5e-3, -0.9e-3] (measured branches \
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-2.90/-2.91/-2.56/-1.82 mm)",
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w.ux_mid
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);
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assert!(
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w.amp_late > 2.0 * w.amp_early,
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"the release is not growing: onset amp {:.3e} -> {:.3e} (measured 4.6x / \
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5.2x / 3.4x / 4.0x across the four solver-path branches)",
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w.amp_early,
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w.amp_late
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);
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} else if hyst_cycle {
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// Study horizons, the sticky-mask configuration (band 0.25h,
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// STALLX 10): the settled flapping cycle, measured 2026-08-27/28
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// at t_end = 8.5 / window(2.0) — ny 62: uy 3.07 ± 50.25 mm
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// (run 7), ny 82: 8.13 ± 57.55 mm (run 8); reference
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// 1.45 ± 34.90. The AMPLITUDE discriminates: the un-flapped
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// release and every pre-hysteresis dead march sit far below
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// 38 mm, and the reference itself sits outside the band — a
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// change landing INSIDE the reference band is a loud finding,
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// not a regression.
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assert!(
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(38.0e-3..=72.0e-3).contains(&w.uy_amp),
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"cycle uy amp {:.4e} left [38e-3, 72e-3] (measured 50.2e-3 / 57.6e-3 at ny 62/82)",
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w.uy_amp
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);
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assert!(
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(-8.0e-3..=22.0e-3).contains(&w.uy_mid),
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"cycle uy mid {:.4e} left [-8e-3, 22e-3] (measured 3.1e-3 / 8.1e-3)",
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w.uy_mid
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);
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assert!(
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(-14.0e-3..=-2.0e-3).contains(&w.ux_mid),
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"cycle ux mid {:.4e} left [-14e-3, -2e-3] (measured -4.9e-3 / -9.4e-3)",
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w.ux_mid
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);
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// The crossing estimator is beat-biased on 2 s windows (it read
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// 4.87 / 6.25 Hz where the DFT puts both grids at 5.4-5.6, ref
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// 5.46); its band covers the estimator's measured scatter, not
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// the physics.
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if let Some(f) = w.frequency {
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assert!(
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(4.4..=6.8).contains(&f),
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"cycle crossing-frequency {f:.3} left [4.4, 6.8] (measured 4.87 / 6.25)"
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);
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}
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// The honest central drag (window median of the interval-median
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// record): 454.0 at ny 62 (run 10) vs reference 460.2 — a loud
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// tripwire on the load path, not an amplitude claim (the
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// oscillation amplitudes are surface-route-unmeasurable; see
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// omni-cortex solver_status.md).
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assert!(
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(380.0..=530.0).contains(&w.drag_median),
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"cycle drag median {:.1} left [380, 530] (measured 454.0, ref 460.2)",
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w.drag_median
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);
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}
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}
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