103 lines
5.3 KiB
Markdown
103 lines
5.3 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 before freezing; nothing here is read from plots. All numbers
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marked PROVISIONAL (ladder, window, domain, boundaries) are my choices and stay
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non-normative until the primary-spec packet and Astra's feasibility check land.
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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), with an
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observable-specific error/uncertainty criterion declared per observable
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before runs (OPEN). Monotone decrease alone is not a literature pass.
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- Duration/periodicity gate (section 1a) must pass before any statistic is
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collected.
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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⟩. A one-cycle smooth
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ramp is a separately named variant that only checks start independence.
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- Phase convention: the motion uses the analytic offset/velocity at the step's
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time level n; the per-step force (`run(1)`, `read_force(normalize=True)`) is
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attributed to the same n. Whether the paper's phases refer to endpoint
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values or interval averages is ⟨verify⟩; comparisons state which.
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## 1a. Duration and periodic-state gate (auditable, every case)
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- Recorded per case: dx, dt, D, U_max, nu (lattice and nondimensional), steps
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per period, total steps, total nondimensional duration t U_max / D and in
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periods, number of discarded cycles, accepted cycle window.
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- Every case in a comparison uses the SAME accepted window in periods (finer
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grids run proportionately more native steps for the same physical time).
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- Periodic-state adequacy is demonstrated, not assumed: per-cycle mean and RMS
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of Fx and the Morison fit per cycle must change by less than a predeclared
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cycle-to-cycle tolerance (OPEN) over the last cycles before the window;
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otherwise the run is extended and the window moved by whole periods, and the
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failure is recorded. Cycles 4–6 is PROVISIONAL only.
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- The G4 timing check (100 coarse vs 400 diffusive-fine steps) is a matched
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short transient, not evidence of periodic convergence.
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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; size PROVISIONAL (e.g. 20 D vs 40 D check at D = 40)
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⟨verify Dütsch domain extent⟩; no generic size is normative.
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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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- Reference types kept separate: (a) phase-averaged LDA velocity measurements;
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(b) the paper's computed results, including forces and Morison fits — a
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computed reference, not a measured force. The paper itself reports the
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Morison-fit error as larger than its coarse grid/time numerical error, so
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C_D, C_M agreement is judged against that stated fit uncertainty.
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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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- No cost estimate is normative; Astra's smoke run measures it.
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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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