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rustytorch/crates/specialized/rtx-fsi/Cargo.toml
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Omar SobhandClaude Fable 5 b82f307cae rtx-fsi + rtx-cfd + rtx-fea: FSI1 — the coupled cylinder and flag
The summit rung C1: all the verified pieces joined into the first coupled
Turek–Hron computation (rtx-fsi/tests/turek_hron_fsi1.rs). The embedded
fluid computes tractions on the DEFORMED flag surface
(EmbeddedMask::traction_at, factored from surface_force); the flag's
wetted boundary is a polygon whose vertex list sits behind a lock, so the
moving-body mask rebuild picks up every shape update
(EmbeddedBody::polygon + pub polygon_signed_distance); WettedSurface —
rebuilt on the deformed interface every subiteration — carries the loads
to the flag's boundary nodes (NonlinearStaticAnalysis::set_nodal_forces);
Subiterated::aitken drives the exchange, each pass marching the fluid to
flag-load stagnation so the coupling map is a function of geometry, not
of the fluid's transient.

Result (ny = 62, 6 Aitken passes, 420 s): coupled drag 15.360 (+7.5%,
the rigid CFD1 band at this grid), lift 0.7977 (+4.4%), ux(A) 2.647e-5
vs 2.270e-5 (+16.6%; +6.1% at ny = 82), uy(A) 3.90e-4 vs 8.21e-4 at
h = 6.6 mm and 1.124e-3 (+37%) at h = 5 mm — the resolutions BRACKET the
reference through the flag's 3 -> 4-cell thickness transition, like the
rigid-flag lift; conservation 7.4e-12 every pass. Bands asserted are the
measured ones; RTX_FSI1_NY runs studies.

Two real rtx-fsi defects found by this rung (15th and 16th of the
campaign), both regression-tested (tests/transfer_curved_edge.rs):

1. solve_weights built its constraint Gram from RAW coordinates: the
   condition number grows as (position/spacing)^2 — ~1e4 for a flag edge
   at x ~ 0.26 with 5 mm spacing — and the 4x4 SVD pseudo-inverse lost
   enough accuracy that the (correctly strict) partition-of-unity /
   reproduction verification rejected healthy neighbourhoods: the
   operator's behaviour depended on WHERE the interface sat. Now centred
   on the face and scaled by the neighbourhood radius — identical
   constraints, O(1) conditioning, translation-invariant.

2. A NEARLY collinear neighbourhood (the nearest nodes of a face on a
   smoothly deformed edge: y is almost linear in x, off by the curvature
   sagitta) cannot satisfy exact centroid reproduction with bounded
   weights — the offending singular value is too large to truncate and
   too small to invert. The recruitment now widens (8 -> 16 -> 32 -> all)
   until the verified constraints hold; for a thin structure that pulls
   in the opposite face, exactly the transverse spread the system needs.

Findings measured before believed: the transfer is faithful (a strictly
local two-node split of the same tractions moved the tip by 2%); the
uy error is the sampled lift PROFILE on a 3-cell flag (a uniform
distribution of the same net lift bends 4x more), confirmed by the
resolution study; TVD limiter chatter (+-0.5% steady load — limited
schemes stall short of machine steady state) defeats steady fixed-point
coupling, so steady coupled cases run upwind while the time-marched
FSI2/FSI3 keep TVD; and the mask never chattered at FSI1's sub-cell
amplitude (fluid-cell count constant through every pass).

rtx-fsi 29 -> 31 green (lib 27, piston 2, curved-edge 1, FSI1 1).

Co-Authored-By: Claude Fable 5 <[email protected]>
2026-08-20 17:22:27 -07:00

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TOML

[package]
name = "rtx-fsi"
version = "1.0.0"
edition.workspace = true
rust-version = "1.92"
authors = ["RustyTorch Team"]
license = "MIT OR Apache-2.0"
description = "Partitioned fluid-structure interaction coupling: conservative load and motion transfer across non-matching interfaces"
keywords = ["fsi", "fluid-structure", "coupling", "aeroelasticity", "simulation"]
categories = ["science", "simulation"]
repository = "https://github.com/rustytorch/rustytorch"
[dependencies]
nalgebra = { workspace = true }
thiserror = { workspace = true }
[dev-dependencies]
# The coupled benchmarks drive the real fluid and structure solvers; the
# coupling library itself still depends on no solver.
futures = { workspace = true }
rtx-cfd = { workspace = true }
rtx-fea = { workspace = true }
[lints]
workspace = true