100 lines
5.1 KiB
Markdown
100 lines
5.1 KiB
Markdown
# Moving-boundary force spikes: evidence and source index
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Updated 2026-10-31.
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This note indexes supplied audited observations and primary-source extractions.
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It does not report a newly measured cure or implement an alternative method.
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Paper details below were supplied by the parent investigation; no new source
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retrieval or independent paper verification was performed for this note.
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## Current implementation and interpretation
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- Celeris M1 reconstructs a fresh node as `feq(rho_bar, u_wall) + donor NEQ`.
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- In exact arithmetic, the donor non-equilibrium component has zero mass and
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momentum when formed against the donor's own equilibrium moments.
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- Re-projecting that same reconstruction onto the same wall velocity therefore
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does not, by itself, change its mass or momentum or supply a cure for spikes.
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- Floating-point residuals should be measured separately from this algebraic fact.
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- Peng's alternative differs upstream: extrapolate PDFs from three donors, then
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replace selected moments. It is not simply another projection of current M1.
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- PPO interval-force observations and native per-step FSI right-hand-side forces
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are distinct signals; comparisons must identify which signal is being used.
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## Audited run observations supplied to this note
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- D40 revision: `e9213dd2cc9cfed0e8487a3cf4ebdd94d23dc64d`.
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- Window: first `97.303 D/U` of physical time.
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- Maximum displacement: `max |y|/D = 0.304893`.
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- Maximum native force-coefficient increment: `max |ΔCy| = 0.66688`.
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- D20 over the same physical-time window: `max |ΔCy| = 1.80735`.
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- The largest D40 event involved 30 nodes.
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- These are supplied audited observations, not measurements made for this note.
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- Time steps and trajectories differ between runs. This comparison establishes
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neither spatial convergence nor a unique cause for the force spikes.
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Evidence locations supplied by the investigation:
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- Horsea: `/tmp/celeris-results-pinball-resolution`.
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- Mac: `validation-evidence/pinball-force-diagnosis`.
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These locations index run evidence, not local copies of the cited papers.
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## Tao, Hu, and Guo (2016): time-step decoupling
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Computers & Fluids **133**, 1–14. DOI:
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[10.1016/j.compfluid.2016.04.009](https://doi.org/10.1016/j.compfluid.2016.04.009).
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[Publisher abstract](https://www.sciencedirect.com/science/article/pii/S0045793016301116).
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- Abstract-level support only: non-equilibrium refill reduces oscillations.
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- With local iteration, the compared refill methods give similar oscillation magnitudes.
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- Time-step decoupling reduces oscillations further in the reported sedimentation,
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Couette, and Poiseuille examples.
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- The exact decoupling schedule and time-step ratios have not been verified.
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- This abstract does not establish equivalence to an arbitrary force filter.
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- Do not implement a claimed reproduction until the actual methods are available.
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## Marson et al. (2021): local iterations
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Physical Review E **103**, 053308. DOI:
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[10.1103/PhysRevE.103.053308](https://doi.org/10.1103/PhysRevE.103.053308).
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[Open repository record](https://archive-ouverte.unige.ch/unige:151868).
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- §VI, p. 18 discusses pressure waves associated with fresh nodes.
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- Appendix E.3, p. 25 and Fig. 18, p. 24 describe the local procedure.
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- Copy a local sublattice, perform local collision and streaming, write the fresh
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nodes, and repeat before the global collision and streaming operation.
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- One to three iterations performed best in the reported tests; this is not a
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universal iteration-count recommendation.
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- The reported smoothed torque-noise assessment is qualitative here.
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- Its thin-shell setting differs from the current moving-body configuration.
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## Peng (2016): extrapolation and moment replacement
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Computers & Mathematics with Applications **72**, 349–374. DOI:
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[10.1016/j.camwa.2015.08.027](https://doi.org/10.1016/j.camwa.2015.08.027).
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- §5.1.2, Eq. (50), p. 368: extrapolate PDFs along an outward normal direction:
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`f_new(x) = 3 f(x + e) - 3 f(x + 2e) + f(x + 3e)`.
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- §5.1.3, Eq. (51): wall equilibrium plus donor non-equilibrium is the family
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containing the current M1 reconstruction.
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- §5.1.4, Eqs. (52)–(54): in MRT space, replace momentum with `j = rho0 u_wall`,
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preserve the other moments, then apply the inverse transform.
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- A compressible Celeris adaptation must choose the appropriate density;
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copying the paper's `rho0` blindly is not justified.
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- Three valid donors require new eligibility checks and fallback behavior beyond
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the current one-link shared-body clearance rule.
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- §§5.2–5.3 retain nonzero fluctuations in specific configurations; these results
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do not promise elimination of force spikes in the present problem.
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## Bounded next investigation
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1. Retain current M1 as the baseline and compare matched prescribed trajectories
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over matched physical-time windows.
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2. Record raw force RHS, node crossings, donor moments, mass and momentum changes,
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impulse, spectra, and trajectory response together.
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3. Evaluate local iterations, Peng-style reconstruction, and force filtering as
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separate interventions, with explicit definitions and diagnostics.
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4. Obtain the actual time-step-decoupling methods before implementing that method.
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The current task indexes evidence only; it makes no alternative-method change.
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