docs: VIV predeclare — source-verified box/position, seed, response-cycle window, instability definition

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/validation/leontini_viv_predeclare.md

@@ -8,9 +8,15 @@ this page is jointly agreed.
 
 ## Primary case (one case)
 
-- Reference: Kolahdouz et al., arXiv:2003.12046, §4.1.1 (setup) and Qin et
-  al., arXiv:2003.12186, §4.5 (maximum amplitudes at U_red = 3…8: .075, .551,
-  .520, .459, .370, .084 D, as quoted by Grok/Astra from the text).
+- Reference: Qin et al., arXiv:2003.12186, §4.5 (maximum amplitudes at
+  U_red = 3…8: .075, .551, .520, .459, .370, .084 D in the text, as quoted by
+  Grok/Astra) for the target; setup from Kolahdouz et al., arXiv:2003.12046,
+  §4.1.1 (read 2026-10-30 via ar5iv): U* sweep 3–8 with amplitudes only in
+  Fig. 3(b) (no text values), domain [−30, 45] D × [−30, 30] D with the
+  cylinder "initially at rest and centered at the origin", uniform inflow on
+  the left, zero normal traction and tangential velocity at the outlet, zero
+  normal velocity and tangential traction on y = ±30 D; no initial
+  perturbation and no total simulated time stated.
 - Re = 150, U* = U/(f_n D) = 5, m/(rho D²) = 2 (m* = rho_s/rho_f = 8/pi),
   zeta = 0, f_n = sqrt(K/M)/(2 pi) in vacuum. Transverse DOF only.
 - Target: A_max = .520 D (peak amplitude, Qin §4.5). Multi-code reference
@@ -21,8 +27,8 @@ this page is jointly agreed.
 
 - D = 40, MRT, dense double buffer; U_lat = .04, nu = U D / 150 = .010667,
   tau = .532.
-- Box 75 D × 60 D (3000 × 2400, Kolahdouz class); cylinder position as in
-  Kolahdouz (OPEN: confirm; default 20 D from the inlet, centred in y).
+- Box 75 D × 60 D (3000 × 2400) with the cylinder 30 D from the inlet, 45 D
+  from the outlet, centred in y (Kolahdouz §4.1.1).
 - Boundaries: uniform Zou–He inlet, NEQ outlet (rho = 1, backflow clamp),
   free-slip y walls. Kolahdouz uses a traction outlet: declared mismatch.
 - Qin's own VIV box (40 D × 20 D) is not used; a smaller box would be a
@@ -49,12 +55,25 @@ this page is jointly agreed.
 
 ## Window, failure semantics, acceptance (engineering, development stage)
 
-- Settled when the per-cycle peak |y| changes ≤ 2 % between consecutive
-  10-cycle windows and the last 5 cycle peaks agree within 1 %; cap 150
-  oscillation cycles.
+- Start: fluid at rest at U = 0 except the uniform inlet (impulsive start as
+  in the reference), body at rest. The reference states no perturbation; a
+  numerically symmetric start can delay or suppress lift, so one declared
+  seed is used: initial structural displacement y0 = +.05 D (2 cells) with
+  v0 = 0, released at t = 0. No other perturbation; not changed afterwards.
+- Response cycles: delimited by consecutive upward zero crossings of y about
+  its running mean; per-cycle peak = max |y − mean| in that cycle.
+- Settled when the per-cycle peak changes ≤ 2 % between consecutive 10-cycle
+  windows and the last 5 cycle peaks agree within 1 %. The 20 scoring cycles
+  follow settling and are included in the cap of 150 response cycles from
+  t = 0 (about 150 × 5,000 = 750,000 steps, t U/D ≈ 750); total steps and
+  t U/D are reported.
+- Growth transient vs instability: amplitude growth from the seed that stays
+  below 1.0 D (about twice the largest reference peak, .551 D) is a physical
+  transient and is not a failure by itself. Instability = |y| > 1.0 D, a
+  non-finite value, or the offset box being reached.
 - FAIL-CLOSED and reported (no sub-iteration, no RHS or parameter retune):
-  unsettled at the cap, |y| beyond the declared offset box, no_donor > 0, or a
-  growing/diverging amplitude (coupling instability at m* ≈ 2.55).
+  unsettled at the cap, instability as defined above (possible weak-coupling
+  instability at m* ≈ 2.55), or no_donor > 0.
 - Score over the 20 cycles after settling: A_max/D (mean of cycle peaks) and
   f/f_n (reported; no target).
 - Acceptance: |A_max − .520 D| ≤ .052 D (±10 %), stated together with the