research: one-shot Dütsch Re100/KC5 prescribed-oscillation driver (no production change)
protocol.py holds the pure arithmetic (phase/cycle bookkeeping from the right
turning point, 1-degree bins, interval-averaged Morison bases and fit with
added-mass c_i, solid-aware bilinear sampling, settling and common-window
rules). run.py drives the existing Simulation API (set_body + run(1) +
read_force + moving_diagnostics; macroscopic fields and flags only inside the
three phase bins) and writes raw data outside the checkout. analyze.py builds
the cycle ledger, K_case, the common window, Morison fits, Fy sanity and the
cross-resolution waveform difference. CPU tests cover the §6a arithmetic.
Carries the protocol doc from claude/duetsch-protocol 8c1f3c4d.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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Claude
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Claude Opus 5.5
Claude Opus 5.5
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# Prescribed in-line oscillation: Dütsch Re 100 / KC 5 — PROTOCOL (review draft)
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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. Source facts below were verified from
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the paper (Slack C0C78UFKGRM/1793335557.460509, TRON 1793356317–1793356724,
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page numbers given). Everything marked ENGINEERING is our a-priori choice,
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fixed before any benchmark result; it is not a paper uncertainty.
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## 0. Source facts (with provenance)
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- Motion (p.251): `x_c = -A sin(2 pi f t)`; paper phase phi = 0 is the mean
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position moving left at `-U_max`. KC = 5 gives `A/D = 5/(2 pi) = .7957747`.
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- Start (p.254): the computation starts a quarter cycle before phi = 0, at
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`x = +A` with zero velocity (phi = -90°).
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- Experiment (pp.252, 254–256): D = 10 mm, L = .65 m, tank 1.2 × .7 × .7 m,
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rho = 998.2 kg/m³, mu = 1.00818 mPa·s, Re = 100, KC = 5; LDA with 1° phase
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bins and 200 samples per node and degree; no quantified experimental error
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recovered.
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- Profiles (Fig. 8, p.260): LAB-FIXED stations x1 = -6, 0, 6, 12 mm, i.e.
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x/D = -.6, 0, .6, 1.2, at phi = 180°, 210°, 330°; u1 and u2 versus x2.
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- Original numerics (§2): cylinder-fixed accelerated frame (`x_i = x~_i +
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x_i,s`, outer velocity `-u_c`, inertial source `-rho du_c/dt`), O-grid outer
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diameter 120 D, illustrated 192 circumferential nodes, 720 steps/cycle; tank
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influence neglected.
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- Force fit (verified): force ON THE BODY per unit span
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`F1 = -0.5 rho D c_d xdot|xdot| - (pi/4) rho D² c_i xddot` with `x = -A sin phi`;
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normalized by `0.5 rho D U_max²`: `c_d cos phi |cos phi| - (pi² c_i / KC) sin phi`.
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`c_i` is the ADDED-MASS coefficient; total inertia `c_m = c_i + 1` is a
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different convention and is not used.
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- Table 1 computed Morison coefficients (c_d, c_i) for 96 / 192 / 384 perimeter
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nodes at dt/T = 1/720: (2.15, 1.42), (2.10, 1.45), (2.09, 1.45). These are
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fitted computed coefficients, not a measured force and not an error bar. The
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paper states the coarse direct force is closer to the finest direct force
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than the Morison fit, but gives no waveform-error norm.
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## 1. Kinematics, time levels and phase bookkeeping
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- Our run is in the LAB frame: the circle moves, the fluid is initially at rest
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(rho = 1, u = 0); no fictitious inertial source is added. Lab-fixed profile
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stations are compared directly (no frame transform needed).
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- Geometry reference: the circle's base centre is the INITIAL position, the
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right turning point `x_mean + A`; the declared offset box is x in [-2A, 0],
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y = 0. The body is never teleported: offset 0 at s = 0.
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- Elapsed time s = n dt from the start. Analytic position relative to the mean
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`x(s) = A cos(2 pi s / T)`, velocity `u(s) = -U_max sin(2 pi s / T)`; paper
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phase `phi = (360 s / T - 90) mod 360`.
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- Step n moves from s_n to s_{n+1}: target offset `x(s_{n+1}) - A`; wall
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velocity = the single-step interval average `(x(s_{n+1}) - x(s_n)) / dt`
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(analytic, supplied, not differenced from stored offsets). The per-step
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force of `run(1)` / `read_force(normalize=True)` is attributed to that same
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interval.
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- Paper cycle k = 1, 2, ... spans `s in [T/4 + (k-1) T, T/4 + k T)`; the
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initial quarter cycle (s < T/4) is cycle 0 and never scored. Every logged
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sample carries (k, phi). Example: phi = 330° of cycle 1 is at s = 7T/6.
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- T is chosen as a multiple of 360 native steps, so phi = 180°, 210°, 330° fall
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exactly on step boundaries and 1° bins hold whole steps.
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## 2. Resolution ladder (uniform grid, fixed Mach), ENGINEERING
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| D (cells) | T (steps) | U_max = 5 D / T | nu_lat = U_max D / 100 | tau (3 nu + .5) |
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|---|---|---|---|---|
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| 20 | 2,520 | .039683 | .0079365 | .5238 |
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| 40 | 5,040 | .039683 | .015873 | .5476 |
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| 80 | 10,080 | .039683 | .031746 | .5952 |
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- MRT collision. Mach fixed (Ma ≈ .0687); a separate Mach check at D = 40
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with T = 10,080 (U_max halved, tau .5238) is labelled MACH and not part of the
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ladder.
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- Per-step displacement ≤ U_max ≈ .04 cells (bound .5).
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## 3. Domain and boundaries (finite-domain reproduction), ENGINEERING
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The paper's 120 D O-grid is not reproduced; our rectangular box is a
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reproduction choice. The native dense channel (zero-velocity inlet,
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pressure-NEQ outlet, bounce-back y walls) is a finite-domain approximation,
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not infinite still fluid. The G4 x-periodic / y-slip override is a separately
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labelled sensitivity family and never mixed into the primary ladder. The
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runner owner confirms the zero-velocity inlet is supported as configured
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before any run.
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Order (closed):
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1. Smoke + ledger at D = 40, native BC, 40 D × 40 D (finite box).
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2. Domain sensitivity before any literature statement: same BC, D = 40,
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L ∈ {20 D, 40 D, 60 D}; record the change in Fx waveform, c_d, c_i and the
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scored profiles.
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3. Optional labelled BC sensitivity: one x-periodic / y-slip case at D = 40,
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40 D; reported as a delta against native only.
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4. Only after step 2 passes: the D = 20 / 40 / 80 ladder on the chosen BC and
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domain (default 40 D if, against 60 D, `RMS(dFx)/F_ref` and |dc_d|, |dc_i|
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stay inside the section 6 bands).
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- Memory/runtime: measured by a smoke run before each new size; measurements
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inform scheduling only, never tolerances.
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## 4. Observables (raw, per step, preserved)
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- `obs` Fx, Fy (CME) and all `MovingTables.DIAG` columns per step: CME,
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CME + Wen and CME + cover − uncover reported separately; crossings, eq_only,
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no_donor (no_donor must stay 0).
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- Velocity u1, u2 on lab-fixed lines x/D = -.6, 0, .6, 1.2 (relative to the
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mean cylinder position) versus x2, at the scored phases. Lab frame
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throughout; if any body-frame intermediate is used, position and velocity
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are both transformed.
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- Sampling cost: raw force and diagnostics counters are read every step
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(small). Flags and velocity fields are read only at the steps inside the
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three prescribed 1° phase bins (φ ∈ [180, 181), [210, 211), [330, 331),
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T/360 steps each) of the cycles needed for settling and scoring, plus
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sparse declared audits; never every step.
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- Point set: fixed x2/D sample points per station, identical on every grid
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and declared before running; per point the interpolation weights are
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recorded; the scored set is the common subset valid on all compared grids
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at that phase, with its coverage recorded; point sets never change silently.
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- Interpolation: bilinear on cell centres using only cells that are fluid at
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that step (flags read back via `get_flags()`); weights renormalized over the
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fluid corners; a sample with no fluid corner, or inside the circle at that
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step, is MISSING and logged, never set to zero. One-degree bins keep valid
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fluid weights. The numerical average need not mimic the 200 LDA samples.
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## 5. Periodic-regime gate (every case, before any statistic), ENGINEERING
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Ledger rows, same schema for every case: dx, dt (in D and T units); U_max, nu,
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Re, KC (lattice and nondimensional); T (native steps, nondimensional);
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duration (native steps, s/T, paper cycles); discard; accepted window; cycle
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ledger; verdict PASS or FAIL-CLOSED.
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Scales: `F_ref = 0.5 rho U_max² D`, `U_ref = U_max`; never a near-zero mean
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force as denominator.
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- Settling metrics, cycle k−1 → k, phase-aligned by step within the cycle:
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- waveform `RMS(dFx) / F_ref ≤ .02`;
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- `|d mean|`, `|d RMS|`, `|d peak|` of Fx, each `/ F_ref ≤ .01`;
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- scored profiles (fluid-only) `|du| / U_max`, `|dv| / U_max ≤ .03` at the
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three phases × four stations;
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- Morison `|dc_d| ≤ .02`, `|dc_i| ≤ .02`.
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- Rule: all metrics for N = 3 consecutive whole paper cycles → settled.
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Cycle indexing (worked example, binding). Paper cycle k spans
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`s/T in [0.25 + (k-1), 0.25 + k)`, i.e. φ0 → φ0; cycle 0 is the startup
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quarter `s/T < 0.25`. Pair p_k compares cycle k−1 with cycle k.
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- Discarded: cycles 0, 1, 2 (s/T < 2.25). Pairs are formed only between
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cycles ≥ 3, so the first pair is p_4 (3 → 4).
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- Settling proof for a case: three consecutive pairs all pass; K_case = the
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first cycle AFTER the last of those pairs. Earliest possible: pairs 3→4,
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4→5, 5→6 pass ⇒ K_case = 7.
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- Common window: K = max over compared cases of K_case; every case scores the
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same three complete cycles K, K+1, K+2 and must stay settled throughout:
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pairs (K−1→K), (K→K+1), (K+1→K+2) must pass on every case, otherwise that
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case is FAIL-CLOSED (an earlier local settle does not waive this).
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- Cap: cycle k ends at s/T = k + 0.25, so the last admissible scored cycle is
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11 (ends 11.25 T) and K ≤ 9. Examples: K = 7 → cycles 7–9 (ends 9.25 T);
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K = 9 → cycles 9–11 (ends 11.25 T); any K_case > 9 → FAIL-CLOSED.
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- Every case is run to the end of cycle K + 2 (proportionally more native
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steps on finer grids).
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- Discard: the initial quarter cycle plus the first 2 full paper cycles
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(s/T < 2.25). Settling is searched from cycle 3; cap 12 periods from s = 0;
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unsettled → FAIL-CLOSED (no literature, cross-resolution or VIV statistic).
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- Common window: K = the largest first-settled cycle index over all compared
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cases; every case is scored on the same 3 cycles K .. K + 2 and must reach
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them within the cap (proportionally more native steps on finer grids), or
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the comparison is FAIL-CLOSED.
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- The earlier G4 timing check (100 coarse vs 400 diffusive-fine steps) was a
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matched short transient, not periodic evidence.
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## 6. Metrics and per-observable criteria (ENGINEERING, not paper uncertainty)
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Three criteria stay separate; the G4 same-grid 2% target is not reused.
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- Morison fit: least squares of the normalized per-step force over the
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accepted window against the two basis functions, each averaged over its
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single step interval, fixed paper phase, no free phase shift; c_d and
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added-mass c_i per force candidate.
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- Cross-resolution: every scored observable's error against its reference must
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decrease monotonically D20 → D40 → D80 (necessary, not sufficient).
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- Against Table 1 (computed fit, not measured force): at D ≥ 40,
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`|c_d - 2.09| ≤ .15` and `|c_i - 1.45| ≤ .15`, and monotone.
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- Force waveform against its own Morison reconstruction: residual reported
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only, no pass/fail (the paper reports fit error above its coarse numerical
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error and gives no percentage).
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- Fig. 8 LDA profiles: QUALITATIVE ONLY. The original figure could not be
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accessed or rendered; no digitized ordinates and no measurement uncertainty
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exist. After a digitization with figure number, tool and uncertainty note:
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`RMS(|du|, |dv|) / U_max ≤ .15` at D ≥ 40 and monotone; LDA error stays
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UNQUANTIFIED and is stated with every comparison.
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- Fy sanity (not literature): `|mean Fy| / F_ref ≤ .05` in the accepted window.
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- No force candidate is selected for an RHS by these results; each is
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reported.
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Superseded (earlier drafts): the velocity-jump start, guessed stations and
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phases, "C_M" for c_i, and the uncertainty wording; cycles 4–6, the 30-cycle
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cap and the earlier tolerance numbers.
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## 6a. Driver unit tests (CPU, before any run)
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- Phase/cycle arithmetic: s ↔ (k, φ), cycle boundaries, bin membership,
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window/cap selection for K = 7, 8, 9, 10.
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- Solid-aware interpolation: all-fluid, partial-solid (renormalized weights),
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no-fluid (MISSING) and inside-circle cases.
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- Interval-averaged Morison bases and the two-parameter fit on a synthetic
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waveform with known c_d, c_i.
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## 7. Order and scope
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Protocol review → one-shot Dütsch driver (analytic `set_body` + `run(1)`,
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cycle ledger, lab-fixed fluid-only station sampler, two-basis Morison fit; no
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reusable runner until the first smoke shows shared helpers pay off; no
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production change) → smoke (memory/runtime) → domain sensitivity →
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ladder → physical-validation verdict → only then single-cylinder VIV. No AMR,
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no pinball, no manuscript work.
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