67 lines
3.6 KiB
Markdown
67 lines
3.6 KiB
Markdown
# Single-cylinder free transverse VIV — PREDECLARATION DRAFT (not frozen)
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Stage goal (Yanqi via TRON): prescribed Dütsch case + one VIV case both
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"reasonably close" to a predeclared reference = development-stage success, then
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cleanup. The frozen Dütsch settling failure (0/28 pairs at 31.25 T) stays on
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record; nothing here re-scores it. No code until this page is agreed.
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## Reference (primary, provenance required)
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- Leontini, Thompson & Hourigan, J. Fluids Struct. 22 (2006) 857–864,
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doi:10.1016/j.jfluidstructs.2006.04.003. 2-D, one transverse DOF,
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Re = 200, m* = m/m_f = 10, zeta = 0.01; U* = U/(f_N D), f_N natural frequency
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in fluid with inviscid added mass (as read by Grok from the full text).
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- Verified (Grok, primary text, JFS §3.1): U* uses f_N in fluid "assuming an
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inviscid added-mass term applies" (C_A = 1); the paper also plots f/f_N,vac.
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Companion: ANZIAM J. 46(E) C365–C378 (2005), doi:10.21914/anziamj.v46i0.965.
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- c_crit: both papers write zeta = c/c_crit without defining c_crit. OPEN for
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the owners: (a) structural 2 sqrt(k m) or (b) effective 2 sqrt(k (m + m_A)).
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The difference in c is sqrt(11/10) ≈ 5 % at m* = 10; the choice is declared
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before any run and the other is not substituted afterwards.
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- Target: digitized A*/D and f/f_N at U* = 5.0 from Fig. 1 (tool and
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digitization uncertainty recorded). OPEN until that digitization exists; no
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target number is used before it.
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## Case (one locked point; a sweep is a separate decision)
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- U* = 5.0: the paper's own example of a periodic, constant-amplitude,
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stable-phase response (Fig. 3); avoids the intermittent upper-type range
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U* in (4.2, 4.7) (Fig. 2 at U* = 4.6, transition near 4.7). Chosen from the
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paper's prose before any run.
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- D = 40 (matches the prescribed stage), MRT, dense double buffer, native
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channel: uniform inlet U_lat = .04, NEQ outlet, slip y walls; box 40 D × 20 D
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(blockage .05), cylinder 10 D from the inlet — a reproduction choice.
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- nu = U D / 200 = .008, tau = .524. Allowed y offset ±1.5 D; per-step move
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≤ .04 cells (bound .5).
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## Structure and coupling
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- m = m* rho pi D²/4, m_A = rho pi D²/4, k = (m + m_A)(2 pi f_N)², c from zeta
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under the c_crit convention (OPEN).
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- Weak staggered update per step (host driver, `set_body` + `run(1)`, no
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production change): v_{n+1} = v_n + (F_y^n − c v_n − k y_n)/m,
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y_{n+1} = y_n + v_{n+1}. Newmark is the declared alternative only.
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- Force RHS: a coupled run uses exactly one RHS; other candidates are
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diagnostics of that run, not alternative outcomes. Proposal (to agree):
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primary RHS = raw obs/CME (the documented body force); one labelled
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sensitivity run with RHS = CME + Wen. CME + cover − uncover is not used as RHS
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(it failed the G4 same-grid frame target). This is a stage choice, not a
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validated RHS.
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## Window and acceptance (engineering, development stage)
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- Discard the start-up; the response is settled when A_rms changes ≤ 2 %
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between consecutive 10-cycle windows and the last 5 cycle amplitudes agree
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within 1 %; cap 150 oscillation cycles; unsettled → FAIL-CLOSED, reported.
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- Score on the 20 cycles after settling: A*/D and f/f_N (in-fluid f_N;
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vacuum normalisation secondary).
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- Acceptance: |A* − A*_ref| ≤ .15 A*_ref and |f* − f*_ref| ≤ .05 f*_ref,
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each reported together with the digitization uncertainty and the fact that
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the reference is computed (2-D), not experimental.
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- Driver reads force and the small diagnostics per step only; field reads
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only at a few predeclared snapshots.
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## Not in this stage
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D80, literature claims, pinball, AMR, BC redesign, threshold changes.
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