CelerisLab/docs/validation/leontini_viv_predeclare.md

Single-cylinder free transverse VIV — PREDECLARATION DRAFT (not frozen)

Stage goal (Yanqi via TRON): prescribed Dütsch case + one VIV case both "reasonably close" to a predeclared reference = development-stage success, then cleanup. The frozen Dütsch settling failure (0/28 pairs at 31.25 T) stays on record; nothing here re-scores it. No code until this page is agreed.

Reference (primary, provenance required)

• Leontini, Thompson & Hourigan, J. Fluids Struct. 22 (2006) 857–864, doi:10.1016/j.jfluidstructs.2006.04.003. 2-D, one transverse DOF, Re = 200, m* = m/m_f = 10, zeta = 0.01; U* = U/(f_N D), f_N natural frequency in fluid with inviscid added mass (as read by Grok from the full text).
• Verified (Grok, primary text, JFS §3.1): U* uses f_N in fluid "assuming an inviscid added-mass term applies" (C_A = 1); the paper also plots f/f_N,vac. Companion: ANZIAM J. 46(E) C365–C378 (2005), doi:10.21914/anziamj.v46i0.965.
• c_crit: both papers write zeta = c/c_crit without defining c_crit. OPEN for the owners: (a) structural 2 sqrt(k m) or (b) effective 2 sqrt(k (m + m_A)). The difference in c is sqrt(11/10) ≈ 5 % at m* = 10; the choice is declared before any run and the other is not substituted afterwards.
• Target: digitized A*/D and f/f_N at U* = 5.0 from Fig. 1 (tool and digitization uncertainty recorded). OPEN until that digitization exists; no target number is used before it.

Case (one locked point; a sweep is a separate decision)

• U* = 5.0: the paper's own example of a periodic, constant-amplitude, stable-phase response (Fig. 3); avoids the intermittent upper-type range U* in (4.2, 4.7) (Fig. 2 at U* = 4.6, transition near 4.7). Chosen from the paper's prose before any run.
• D = 40 (matches the prescribed stage), MRT, dense double buffer, native channel: uniform inlet U_lat = .04, NEQ outlet, slip y walls; box 40 D × 20 D (blockage .05), cylinder 10 D from the inlet — a reproduction choice.
• nu = U D / 200 = .008, tau = .524. Allowed y offset ±1.5 D; per-step move ≤ .04 cells (bound .5).

Structure and coupling

• m = m* rho pi D²/4, m_A = rho pi D²/4, k = (m + m_A)(2 pi f_N)², c from zeta under the c_crit convention (OPEN).
• Weak staggered update per step (host driver, set_body + run(1), no production change): v_{n+1} = v_n + (F_y^n − c v_n − k y_n)/m, y_{n+1} = y_n + v_{n+1}. Newmark is the declared alternative only.
• Force RHS: a coupled run uses exactly one RHS; other candidates are diagnostics of that run, not alternative outcomes. Proposal (to agree): primary RHS = raw obs/CME (the documented body force); one labelled sensitivity run with RHS = CME + Wen. CME + cover − uncover is not used as RHS (it failed the G4 same-grid frame target). This is a stage choice, not a validated RHS.

Window and acceptance (engineering, development stage)

• Discard the start-up; the response is settled when A_rms changes ≤ 2 % between consecutive 10-cycle windows and the last 5 cycle amplitudes agree within 1 %; cap 150 oscillation cycles; unsettled → FAIL-CLOSED, reported.
• Score on the 20 cycles after settling: A*/D and f/f_N (in-fluid f_N; vacuum normalisation secondary).
• Acceptance: |A* − A*_ref| ≤ .15 A*_ref and |f* − f*_ref| ≤ .05 f*_ref, each reported together with the digitization uncertainty and the fact that the reference is computed (2-D), not experimental.
• Driver reads force and the small diagnostics per step only; field reads only at a few predeclared snapshots.

Not in this stage

D80, literature claims, pinball, AMR, BC redesign, threshold changes.