73 lines
3.3 KiB
Markdown
73 lines
3.3 KiB
Markdown
# Prescribed in-line oscillation: Dütsch Re 100 / KC 5 — PROTOCOL DRAFT (not frozen)
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Production under test: `claude/moving-bodies-s3a` at `653fd997` (unchanged).
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Primary source: Dütsch, Durst, Becker & Lienhart, J. Fluid Mech. 360, 249–271
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(1998), doi:10.1017/S002211209800860X. Items marked ⟨verify⟩ must be taken from
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the paper itself (Grok) before freezing; nothing here is read from plots.
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## Criteria (kept separate)
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- Same-grid frame consistency (G4, frozen 2%): already evaluated; not reused here.
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- Cross-resolution criterion: every reported observable's error against the
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reference, and the fine-pair difference, must decrease monotonically over the
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resolution ladder. No numeric grid threshold and no order label is added.
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- Reference agreement: only against values with provenance (section 6).
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## 1. Kinematics
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- In-line only: `x(t) = -A sin(2 pi t / T)`, `u(t) = -U_max cos(2 pi t / T)`
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⟨verify sign and phase origin⟩; `KC = U_max T / D = 2 pi A / D = 5`,
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`Re = U_max D / nu = 100`, so `A = 5 D / (2 pi)`.
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- Prescribed per step through `set_body(offset, vx)` + `run(1)`, offset and
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velocity evaluated analytically at step n (no differencing).
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- Start: the paper's motion from rest ⟨verify Dütsch start⟩. Measured window:
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whole cycles 4–6, fixed now, never shortened afterwards. A one-cycle smooth
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ramp is a separately named variant that only checks start independence.
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## 2. Resolution ladder (uniform only, fixed Mach)
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| D (cells) | U_max | nu_lat | tau | steps / period |
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|---|---|---|---|---|
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| 20 | .04 | .008 | .524 | 2,500 |
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| 40 | .04 | .016 | .548 | 5,000 |
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| 80 | .04 | .032 | .596 | 10,000 |
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- MRT collision (SRT at tau ≈ .524 is the recorded unstable regime).
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- Mach check: U_max .02 vs .04 at D = 40 (separate, labelled).
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## 3. Domain and boundaries
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- Square still-fluid box, default 40 D; domain check 20 D vs 40 D at D = 40
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⟨verify Dütsch domain extent⟩.
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- Boundary family declared by the runner owner before running (x-periodic /
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y free-slip or closed walls, whatever the dense runner supports without
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production change); swept band ±A + R + 2 clear of any seam.
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- Per-step displacement ≤ .04 cells (bound .5).
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## 4. Observables (raw, per step, preserved)
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- `obs` Fx, Fy (CME) and the diagnostics columns (`MovingTables.DIAG`):
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CME, CME + Wen, CME + cover − uncover reported separately; crossings,
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eq_only, no_donor.
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- Velocity u, v on lines at the paper's x-stations relative to the mean
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cylinder position and at its phase angles ⟨verify stations and phases⟩;
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cell-centred values, documented bilinear interpolation in physical units.
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## 5. Metrics
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- Morison C_D, C_M by least squares over the measured cycles with the paper's
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force definition and sign ⟨verify formula⟩; per-cycle RMS force; force
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phase history; phase-resolved velocity profiles.
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- Unit map for each candidate stated with `k = rho dx^3 / dt^2` per span.
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## 6. Reference data provenance
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- Accepted: values from the paper's tables, or digitized figure curves with
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figure number, tool and uncertainty recorded. Curves without provenance are
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qualitative only. Values quoted by later papers are secondary until checked.
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## 7. Order
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Protocol review → test driver (no production change) → runs → physical
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validation verdict → only then single-cylinder VIV. No AMR, no pinball.
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