P5-1: FSI2 with the fluid on the overset — fsi2_harness/overset.rs (the background without a body, the cylinder–flag patch regenerated around the deformed flag every pass via set_patch_mesh, the wall velocity from the interface velocities along the wetted polygon, the load from the patch's wall faces into WettedSurface::transfer_load — no probes, no clamp, no smoothing), fsi2_harness/overset_march.rs (the harness's rigid phase / release / subiterated coupling with its acceptance rule, no rescue machinery, death returned not panicked), tests/turek_hron_fsi2_overset.rs (RTX_FSI2O_* knobs); rtx-cfd: CurvilinearPisoSolver::wall_tractions (per-face pressure + full-stress traction, surface_force sums the same terms bit-identically); Interface::edges (bottom/tip/top for the generator); cylinder_flag_mms RTX_CF_BEND (P5-0 gate iv: Stokes orders 2.14 / 2.09 on the flag bent to 80 mm)

Co-Authored-By: Claude Fable 5.1 <[email protected]>
Claude-Session: https://claude.ai/code/session_0116sg1Qz1gMv9hdcKP1XUam

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

@@ -0,0 +1,97 @@
+//! P5 (`docs/overset_metal_campaign.md` §5.12): Turek–Hron FSI2 with the
+//! fluid on the OVERSET — the body-fitted patch following the flag. The
+//! structure, coupling and acceptance are the FSI2 harness's; the fluid
+//! side is `fsi2_harness::overset`. Defaults are the P5-1 gate run
+//! (ny = 41, s = 1, a short march); `RTX_FSI2O_*` knobs as the harness's.
+//! Reference (Turek–Hron FSI2): uy(A) 1.23 ± 80.6 mm at 2.0 Hz, ux(A)
+//! −14.58 ± 12.44 mm, drag 208.83 ± 73.75, lift 0.88 ± 234.2.
+
+mod fsi2_harness;
+
+use fsi2_harness::overset_march::{run_march_overset, OversetMarchConfig};
+use fsi2_harness::{case_from_env, FSI2};
+
+const REF_UY_AMP: f64 = 80.6e-3;
+const REF_UY_FREQ: f64 = 2.0;
+const REF_UX_MEAN: f64 = -14.58e-3;
+const REF_UX_AMP: f64 = 12.44e-3;
+const REF_DRAG_MEAN: f64 = 208.83;
+const REF_LIFT_AMP: f64 = 234.2;
+
+#[test]
+fn fsi2_on_the_overset() {
+    let config = OversetMarchConfig::from_env(
+        "FSI2O",
+        OversetMarchConfig {
+            ny: 41,
+            flag_nx: 35,
+            t_release: 6.0,
+            t_end: 7.0,
+            subcycle: 1,
+            tol_floor: 2e-4,
+            rtol: 1e-2,
+            stall_accept: 5.0,
+            max_subiterations: 12,
+            coupler: "aitken".into(),
+            reuse: 2,
+            initial_relaxation: 0.5,
+            c1_interface: false,
+            predictor: "structure".into(),
+            sweeps: 100,
+            max_rounds: 3,
+            csv_path: None,
+            trace_steps: 0,
+        },
+    );
+    let case = case_from_env("FSI2O", FSI2);
+    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 1.23 ± {:.1}), ux(A) = {:.3} ± {:.3} mm (ref {:.2} ± {:.2}), f = {:?} Hz (ref {REF_UY_FREQ}); drag {:.2} ± {:.2} (ref {REF_DRAG_MEAN} ± 73.75), lift {:.2} ± {:.2} (ref 0.88 ± {REF_LIFT_AMP}); onset amp {:.3e} → {:.3e} m; rigid drag {:.2}",
+        config.ny,
+        config.flag_nx,
+        m.dt,
+        config.subcycle,
+        config.sweeps,
+        config.max_rounds,
+        config.coupler,
+        m.coupled_steps,
+        m.elapsed,
+        m.mean_subiterations,
+        m.max_subiterations,
+        m.stalled_steps,
+        m.retried_steps,
+        m.worst_stall,
+        m.worst_conservation,
+        r.faces_used,
+        m.newton_rescues,
+        r.rounds_mean,
+        r.reclassified_mean,
+        r.fresh_mean,
+        r.regen_count,
+        r.regen_seconds,
+        r.fluid_seconds,
+        r.structure_seconds,
+        r.death,
+        w.t_start,
+        config.t_end,
+        w.uy_mid * 1e3,
+        w.uy_amp * 1e3,
+        REF_UY_AMP * 1e3,
+        w.ux_mid * 1e3,
+        w.ux_amp * 1e3,
+        REF_UX_MEAN * 1e3,
+        REF_UX_AMP * 1e3,
+        w.frequency,
+        w.drag_mid,
+        w.drag_amp,
+        w.lift_mid,
+        w.lift_amp,
+        w.amp_early,
+        w.amp_late,
+        m.rigid_drag
+    );
+    assert!(m.final_state_finite, "the flag's state is not finite");
+    assert!(r.death.is_none(), "the coupling died: {:?}", r.death);
+}