Predeclare zero-damping pinball development cases

docs/steady_pinball_fiv.md

@@ -5,7 +5,8 @@ rho=1, mean U=.01, nu=.004, D=20, Re_D=50. Centres are (600,255.5),
 (626,270.5), (626,240.5), radius10. No upstream cylinder. Passive probes stay
 at (800,295.5), (800,255.5), (800,215.5), radius5. Every omega is zero.
 Parabolic inlet, regularized NEQ damping1; y bounce-back planes .5/510.5;
-NEQ-extrapolated outlet with existing backflow clamp/blending. Initial fluid is
+NEQ-extrapolated outlet with backflow clamp (the configured blend is inactive in
+this MRT route). Initial fluid is
 parabolic equilibrium. Fixed warmup is 4 NX/U=512000 steps.
 
 Geometry and fluid parameters follow DynamisLab 609116ec26f19766f5e9ce2b0df427d4e24faae8,
@@ -71,3 +72,33 @@ This stage makes no claim of physical grid convergence or vibration suppression.
 Run from checkout with PYTHONPATH=src and the existing Python environment:
 `python research/steady_pinball/run.py --smoke --out <new-external-directory>`
 then separately `--out <new-free-directory>` and `--fixed --out <new-fixed-directory>`.
+
+## Zero-damping development follow-up (predeclared 2026-10-31)
+
+The original d0bcefa run and its zeta=.01 results remain historical evidence.
+The current runner exposes three fixed `--case` choices, all with C=0 as requested:
+
+| Case | M / (rho 3 pi D^2/4) | fn | M | K | Purpose |
+|---|---:|---:|---:|---:|---|
+| Z0 | 10 | .0001 | 9424.77796 | .00372075320 | Remove damping only |
+| M2 | 2 | .0001 | 1884.95559 | .000744150640 | Reduce mass and stiffness together at fixed fn |
+| R2 | 2 | .00006 | 1884.95559 | .000267894231 | Change stiffness only relative to M2 |
+
+R2 deliberately places fn at the retained fixed-body lift peak, f=.00006
+(St=.12 on mean U). This is an informed development choice, not independent
+physical validation or a promise of lock-in. All geometries, fluid settings,
+512000-step fixed warmup, y0=v0=0, force time level and unfiltered RHS are unchanged.
+No run result may select a replacement parameter or an automatic extension.
+
+Each case has a 600000-step cap, the same 300 D/U physical duration. This equals
+60 natural periods for Z0/M2 and 36 for R2. Compare the common final200000 native
+steps, and six100000-step blocks, retaining actual natural/response frequencies
+and ongoing drift. Do not call those blocks ten R2 periods. No settled-VIV claim
+follows from a larger displacement. Report all three outcomes, including quiet
+responses or stopped cases, alongside the existing fixed and damped-free records.
+
+Unchanged stops: |y|>D, invalid move/speed, nonfinite values or no_donor. A 1800s
+per-case wall cap and GPU headroom check bound resource use. Preserve partial rows;
+do not add damping, clip trajectories, filter forces, or relax any stop. Each
+case adds72MB of scalar history, no full fields. The separate Legacy/modern
+baseline diagnosis does not change this FSI protocol.