fsi2 overset harness: RTX_FSI2O_CASE=FSI3 (the FSI3 constants with FEATFLOW level-4 references in the summary), RTX_FSI2O_SAVE_FROM (instants only from a time on — a dense last period for the viewer)

Co-Authored-By: Claude Fable 5.1 <[email protected]>
Claude-Session: https://claude.ai/code/session_01LzcjQX7tvgn87CQCyg9Cfr

crates/specialized/rtx-fsi/tests/fsi2_harness/overset_march.rs

@@ -283,6 +283,10 @@ pub fn run_march_overset(case: BenchmarkCase, config: &OversetMarchConfig) -> Ov
     });
     let (t_fluid, t_structure) = (std::cell::Cell::new(0.0_f64), std::cell::Cell::new(0.0_f64));
     let prev_area = std::cell::Cell::new(fluid.borrow().shared.read().unwrap().area());
+    let save_from: f64 = std::env::var("RTX_FSI2O_SAVE_FROM")
+        .ok()
+        .and_then(|v| v.parse().ok())
+        .unwrap_or(0.0);
     let save_every: usize = std::env::var("RTX_FSI2O_SAVE_EVERY")
         .ok()
         .and_then(|v| v.parse().ok())
@@ -418,7 +422,9 @@ pub fn run_march_overset(case: BenchmarkCase, config: &OversetMarchConfig) -> Ov
         fluid.borrow_mut().commit_base();
         // `RTX_FSI2O_SAVE_EVERY=N` (+ `RTX_FSI2O_SAVE`): the composite at
         // every N-th committed step, for the offline chain audit.
-        if save_every > 0 && (step + 1) % save_every == 0 {
+        // `RTX_FSI2O_SAVE_FROM=t` (0): instants only from t on — a dense
+        // last period for the viewer without a gigabyte of the onset.
+        if save_every > 0 && (step + 1) % save_every == 0 && t_now >= save_from {
             if let Ok(dir) = std::env::var("RTX_FSI2O_SAVE") {
                 let d_now = extract(&flag_state);
                 let dd_now = extract_velocity(&flag_state);

crates/specialized/rtx-fsi/tests/turek_hron_fsi2_overset.rs

@@ -9,21 +9,53 @@
 mod fsi2_harness;
 
 use fsi2_harness::overset_march::{OversetMarchConfig, run_march_overset};
-use fsi2_harness::{FSI2, case_from_env};
+use fsi2_harness::{FSI2, FSI3, case_from_env};
 
-// Reference: FEATFLOW's FSI2 table (Turek's group), level 4, Δt = 0.01 —
-// uy 1.24 ± 81.7 mm at 1.93 Hz, ux −14.87 ± 12.73 mm, drag 215.18 ± 77.78,
-// lift 0.87 ± 238.0 (`docs/research_sweep_2026-09.md` §1). The 2006 paper's
-// table is level 2 (80.6 mm, drag 208.83) and rounds the frequency to 2.0.
-const REF_UY_MEAN: f64 = 1.24e-3;
-const REF_UY_AMP: f64 = 81.7e-3;
-const REF_UY_FREQ: f64 = 1.93;
-const REF_UX_MEAN: f64 = -14.87e-3;
-const REF_UX_AMP: f64 = 12.73e-3;
-const REF_DRAG_MEAN: f64 = 215.18;
-const REF_DRAG_AMP: f64 = 77.78;
-const REF_LIFT_MEAN: f64 = 0.87;
-const REF_LIFT_AMP: f64 = 238.0;
+/// The benchmark's reference cycle (FEATFLOW's tables, level 4 — FSI2 at
+/// Δt = 0.01: uy 1.24 ± 81.7 mm at 1.93 Hz, ux −14.87 ± 12.73, drag 215.18 ±
+/// 77.78, lift 0.87 ± 238.0; FSI3 at Δt = 0.0005: uy 1.45 ± 34.90 at 5.46 Hz,
+/// ux −2.86 ± 2.70, drag 460.2 ± 27.47, lift 2.37 ± 153.75;
+/// `docs/research_sweep_2026-09.md` §1. The 2006 paper's FSI2 row is level 2
+/// (80.6 mm, drag 208.83) with the frequency rounded to 2.0).
+struct Refs {
+    uy_mean: f64,
+    uy_amp: f64,
+    uy_freq: f64,
+    ux_mean: f64,
+    ux_amp: f64,
+    drag_mean: f64,
+    drag_amp: f64,
+    lift_mean: f64,
+    lift_amp: f64,
+}
+
+fn refs(case: &str) -> Refs {
+    if case == "FSI3" {
+        Refs {
+            uy_mean: 1.45e-3,
+            uy_amp: 34.90e-3,
+            uy_freq: 5.46,
+            ux_mean: -2.86e-3,
+            ux_amp: 2.70e-3,
+            drag_mean: 460.2,
+            drag_amp: 27.47,
+            lift_mean: 2.37,
+            lift_amp: 153.75,
+        }
+    } else {
+        Refs {
+            uy_mean: 1.24e-3,
+            uy_amp: 81.7e-3,
+            uy_freq: 1.93,
+            ux_mean: -14.87e-3,
+            ux_amp: 12.73e-3,
+            drag_mean: 215.18,
+            drag_amp: 77.78,
+            lift_mean: 0.87,
+            lift_amp: 238.0,
+        }
+    }
+}
 
 /// `RTX_FSI2O_AUDIT=dir`: the solver-metric chain on every saved instant
 /// under `dir` (`inst_*`, from `RTX_FSI2O_SAVE_EVERY`), no march.
@@ -112,12 +144,27 @@ fn fsi2_on_the_overset() {
             trace_steps: 0,
         },
     );
-    let case = case_from_env("FSI2O", FSI2);
+    // `RTX_FSI2O_CASE=FSI3` runs the FSI3 constants (Re 200, ρ_s = ρ_f, E 5.6e6).
+    let base = if std::env::var("RTX_FSI2O_CASE").as_deref() == Ok("FSI3") {
+        FSI3
+    } else {
+        FSI2
+    };
+    let case = case_from_env("FSI2O", base);
+    let rf = refs(case.name);
+    let (cname, ruf, rdm, rda, rlm, rla) = (
+        case.name,
+        rf.uy_freq,
+        rf.drag_mean,
+        rf.drag_amp,
+        rf.lift_mean,
+        rf.lift_amp,
+    );
     let r = run_march_overset(case, &config);
     let m = &r.result;
     let w = m.window(3.0);
     println!(
-        "  FSI2 OVERSET (ny = {}, flag {}x2 Quad8, dt = {:.2e}, s = {}, sweeps {}, rounds cap {}, {}): coupled {} steps in {:.0} s wall; {:.1} subit/step (max {}); {} stalled, {} retries (worst residual {:.2e}); conservation {:.2e}; {} wall faces; Newton rescues {:?}; rounds mean {:.2}; reclassified/step {:.2} (fresh {:.2}); patch regenerations {} in {:.0} s; fluid {:.0} s, structure {:.0} s; death {:?}\n  measured over [{:.1}, {:.1}] s: uy(A) = {:.3} ± {:.3} mm (ref {:.2} ± {:.1}), ux(A) = {:.3} ± {:.3} mm (ref {:.2} ± {:.2}), f = {:?} Hz (ref {REF_UY_FREQ}); drag {:.2} ± {:.2} (ref {REF_DRAG_MEAN} ± {REF_DRAG_AMP}), lift {:.2} ± {:.2} (ref {REF_LIFT_MEAN} ± {REF_LIFT_AMP}); onset amp {:.3e} → {:.3e} m; rigid drag {:.2}",
+        "  {cname} OVERSET (ny = {}, flag {}x2 Quad8, dt = {:.2e}, s = {}, sweeps {}, rounds cap {}, {}): coupled {} steps in {:.0} s wall; {:.1} subit/step (max {}); {} stalled, {} retries (worst residual {:.2e}); conservation {:.2e}; {} wall faces; Newton rescues {:?}; rounds mean {:.2}; reclassified/step {:.2} (fresh {:.2}); patch regenerations {} in {:.0} s; fluid {:.0} s, structure {:.0} s; death {:?}\n  measured over [{:.1}, {:.1}] s: uy(A) = {:.3} ± {:.3} mm (ref {:.2} ± {:.1}), ux(A) = {:.3} ± {:.3} mm (ref {:.2} ± {:.2}), f = {:?} Hz (ref {ruf}); drag {:.2} ± {:.2} (ref {rdm} ± {rda}), lift {:.2} ± {:.2} (ref {rlm} ± {rla}); onset amp {:.3e} → {:.3e} m; rigid drag {:.2}",
         config.ny,
         config.flag_nx,
         m.dt,
@@ -147,12 +194,12 @@ fn fsi2_on_the_overset() {
         config.t_end,
         w.uy_mid * 1e3,
         w.uy_amp * 1e3,
-        REF_UY_MEAN * 1e3,
-        REF_UY_AMP * 1e3,
+        rf.uy_mean * 1e3,
+        rf.uy_amp * 1e3,
         w.ux_mid * 1e3,
         w.ux_amp * 1e3,
-        REF_UX_MEAN * 1e3,
-        REF_UX_AMP * 1e3,
+        rf.ux_mean * 1e3,
+        rf.ux_amp * 1e3,
         w.frequency,
         w.drag_mid,
         w.drag_amp,