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Author	SHA1	Message	Date
Omar SobhandClaude Fable 5	327da7ff47	rtx-cfd: multigrid-PCG projection — 30x faster, same answers — and the CFD1 refinement study ... Falsifier 4 of the Turek–Hron geometry decision fired (the SOR projection cost 0.09 s/step at 250x41 and an hour per run at 5 mm); this answers it. solvers::incompressible::poisson: PoissonProblem (cell-centred five-point SPD operator as per-cell face coefficients + Dirichlet diagonal extra + active mask) and solve_multigrid_pcg — conjugate gradient preconditioned by one V-cycle of geometric multigrid: aggregation by 2 per direction (odd sizes absorbed, coarse cell active iff any child is), the Galerkin coarse operator for piecewise-constant prolongation / summation restriction, symmetric Gauss–Seidel smoothing, coarse correction scaled by 2 (Braess's under-correction of unsmoothed aggregation; scalar, so the preconditioner stays symmetric and positive on range(A)), L1 TRUE-residual stop with a stagnation guard. Singular systems are handled per connected component of the active cells (mean projection and level per pure-Neumann component; the anchor's component to p[anchor] = 0). PoissonSolverKind::{Sor, Multigrid} on PisoParameters / EmbeddedParameters; Sor is the default and its code is byte-for-byte untouched; an unconverged multigrid solve falls back to the SOR sweeps for that projection. Verified (poisson/tests.rs, tests/poisson_equivalence.rs): - PCG iterations to cut the residual 1e-8 on the closed Neumann box at 32^2..256^2: 4, 4, 4, 4; ragged masked domains 8/8/8; - manufactured recoveries to ~1e-14; Galerkin identity A_c v = R A P v to 7e-15 on every level (masked, outlet column, non-uniform conductances); V-cycle symmetric to 1e-14; NaN-poisoned inactive cells untouched; - two Neumann components with opposite imbalances, and a Dirichlet component beside an imbalanced Neumann one (review scenarios): converge, each component right up to its own constant; - speed vs plain SOR at the same stop: 22.7x (128^2), 41x (256^2); - same answers as SOR: PISO MMS 4.6e-8 relative, Taylor–Green divergence 1.4e-9 every step, embedded-circle MMS 7e-8, no-body bit-identity with MG on both solvers, channel+outlet+circle 1.4e-10; CFD1 loads identical to four digits at 0.003 s/step vs 0.094 (30x). CFD1 refinement study (tests/turek_hron_cfd.rs, three grids, 257 s): h = 10 / 6.6 / 5 mm -> control-volume drag 15.6156 / 15.2829 / 15.0988 vs 14.2929 (+9.25 / +6.93 / +5.64%), apparent order 0.71, Richardson extrapolate 14.04; surface route and lift not monotone (flag 2/3/4 cells thick) — the test asserts the measured band at the finest grid. Built with a 4-agent workflow (core, integration, refinement study, adversarial review); the review found no defects and four risks, three fixed here (per-component projection, one symmetric smoother-sweep parameter, acting on `converged` with an SOR fallback) and one recorded (isotropic aggregation loses grid-independence on anisotropic cells). rtx-cfd 301 -> 318 green. Co-Authored-By: Claude Fable 5 <[email protected]>	2026-08-20 10:20:25 -07:00
Omar SobhandClaude Fable 5	c25f15b3c4	rtx-cfd + rtx-fea: embedded-boundary PISO and total-Lagrangian SVK — the first two Turek–Hron rungs ... The Turek–Hron geometry decision (omni-cortex docs/turek_hron_geometry_decision.md) chose an embedded boundary on the fixed Cartesian MAC grid over body-fitted unstructured ALE; this commit builds the first rung on each side of the ladder, verified MMS-first. rtx-cfd — solvers::incompressible::{embedded, embedded_body}: EmbeddedPisoSolver is the fixed-grid PISO predictor/projection with per-side domain boundaries (ALE's SideBoundary semantics, so the channel has an outlet), a (x, y, t) boundary-velocity function, and an optional EmbeddedBody (signed distance + surface velocity; circle / rectangle / union). EmbeddedMask classifies cells (fluid iff phi > 0 at the centre) and faces (fluid iff both cells fluid; ghost within 1.5 h; solid deeper); the predictor updates fluid faces only, the projection enforces continuity on fluid cells with zero coefficient across prescribed faces, ghost faces are re-imposed after each projection from a boundary-intercept least-squares linear fit (exact for linear fields), the net ghost mass flux is removed uniformly so a Neumann projection stays compatible, and loads come by two routes: surface-stress reconstruction (full viscous traction) and a control-volume momentum balance. Verified (tests/embedded_mms.rs, tests/turek_hron_cfd.rs): - no body, closed box: bit-identical to PisoSolver over 200 steps; - embedded off-centre circle MMS 16/32/64: velocity orders 0.92, 0.97 (plain PISO 0.85, 0.91), pressure 0.96, 0.90, max |div u| <= 9e-8 on every fluid cell, compatibility correction 6e-4 -> 3e-5; force on the circle vs the exact surface integral: surface route 0.52 -> 0.29 -> 0.15, control-volume route 0.61 -> 0.30 -> 0.15 (both first order, two unrelated readings of the same solution); - Turek–Hron CFD1 (Re 20, h = 10 mm, flag two cells thick), settled to four digits: surface drag 15.71 / lift 0.94, control-volume drag 15.62 / lift 1.08 vs reference 14.29 / 1.119 — the drag routes agree to 0.6%, both +9.5%. A coarse first number; the refinement study waits on a multigrid projection (SOR: 0.1 s/step at 250x41 in the test profile). Fourteenth defect of the campaign: the fixed-grid PISO predictor zeroes the transverse convective face velocity on its domain sides (exact for walls); carried into a solver with an outlet it dropped the OUTGOING momentum flux through the outlet side of the v control volumes, the last column accumulated, and CFD1 went NaN at t ~ 4 s. Found by printing where max |u| lived (x = 2.5) after halving dt changed nothing. Fluxes now come from the stored boundary faces on every side. rtx-fea — elements::total_lagrangian + NonlinearStaticAnalysis:: with_total_lagrangian(): Green–Lagrange strain, second Piola–Kirchhoff stress from a St. Venant–Kirchhoff law on the material's Lamé parameters (plane strain in 2-D), B_L of the current deformation, material plus geometric tangent; dead-load body force per reference volume. Verified (tests/total_lagrangian_svk.rs): - zero displacement: the plane-strain stiffness to 1e-13; - tangent = d f_int/du by central differences at 20% random displacement (Quad4, Quad8, Hex8): relative < 1e-7, symmetric to 1e-12; - a 34-degree rigid rotation produces no internal force; the small-strain routine does (negative control); - manufactured finite-strain solution, body force by FD of the exact P = F S: Quad4 orders 1.95, 1.98; Quad8 2.93, 3.03, 3.02 (an 8% amplitude, Green–Lagrange strain to -0.25 near SVK's compressive limit E = -1/3, broke Newton on fine meshes — the material, not the code; 3% is clean); - Turek–Hron CSM1 at 70x4 Quad8: u(A) = (-7.060, -65.43) mm vs (-7.188, -66.10), 1.0% / 1.8%, converging from below (35x2: -65.14); CSM2: (-0.4604, -16.79) vs (-0.4690, -16.97), 1.1% / 1.8%. rtx-cfd 293 -> 301 green (5 unit + 3 integration), rtx-fea 559 -> 564. Co-Authored-By: Claude Fable 5 <[email protected]>	2026-08-20 08:51:32 -07:00
Omar SobhandClaude Fable 5	4bd98b5264	rtx-cfd + rtx-fsi: the added-mass piston — partitioned FSI on the real ALE fluid ... The first coupled fluid-structure computation in the workspace, verified against a closed form, and the first time rtx-fsi's added-mass claims run against a real discretised fluid rather than a linear model map. ALE extensions: per-side boundaries (Velocity / SlipWall / PressureOutlet) and moving boundary lines. A moving Velocity side is a material wall whose prescribed normal velocity must equal the line's own motion; a pressure outlet takes Dirichlet p' = 0 in the projection (replacing the Neumann anchor) with a zero-gradient predictor on its faces. Fluid half verified alone (tests/ale_piston_channel.rs): prescribed piston motion, slip walls, outlet. The incompressible rigid column is exact DISCRETELY - continuity forces every u to the wall's discrete velocity (8e-12) and the projected pressure is exactly linear with gradient rho times the wall's backward-difference acceleration (2.5e-9). Coupled benchmark (rtx-fsi/tests/piston_added_mass.rs): elastic piston (Newmark average acceleration) against added mass rho*L*H at mass ratio 6.25, rtx-fsi's Subiterated driving a real fluid/structure pass per step: - plain staggered diverges in 7 subiterations (Causin-Gerbeau-Nobile on a real solver); - Aitken converges at 3.0 subiterations/step onto T = 1.07009 vs the closed form 1.06999 - 9.8e-5 relative, halving with dt; - outlet flux matches the piston sweep to ~1e-9 every step. Discrete-analysis finding: Newmark beta scales the staggered added-mass threshold - the iteration gain is beta*m_a/(M + K*beta*dt^2), so the continuous ratio 2.5 CONVERGES at beta = 1/4 (gain 0.625, measured ~17 passes/step) and the benchmark needs ratio 6.25 (gain 1.56). Two real defects found and fixed, twelfth and thirteenth of the campaign: 1. rtx-cfd ale::advance re-stamped boundary faces at t_old from the current boundary function, which in a coupling loop carries the NEW interval's wall velocity - the predictor's old state had interior u = w0 but wall face u = w1, leaving an O(dt) pressure artifact confined to the wall-adjacent cells (p exact to 6e-11 everywhere except the wall cell at 4.7e-5). The start-of-step boundary faces are whatever the previous step's end-of-step application left there. 2. rtx-fsi aitken_factor guarded its denominator - a SQUARED residual- difference norm - against a bare f64::EPSILON, silently disabling Aitken below residual ~1e-8 and degrading to unit relaxation exactly in the well-converged regime; the repulsive fixed point then amplified 1e-9 residuals back up and the coupling diverged. Third instance of the absolute-threshold species (NNLS, ECSW). The guard is relative now; aitken_is_scale_invariant pins it at initial residual 1e-9. rtx-cfd 293 green (+1), rtx-fsi 29 green (+3). rtx-fsi's lib gains only the relative guard; the coupling layer still depends on no solver (rtx-cfd is a dev-dependency of its tests). Co-Authored-By: Claude Fable 5 <[email protected]>	2026-08-20 06:10:13 -07:00
Omar SobhandClaude Fable 5	259c5baa63	rtx-cfd: ALE on a moving tensor-product grid, DGCL-exact by construction ... The first brick of the Turek-Hron frontier: PISO (explicit conservative predictor + SOR projection) generalised to a staggered grid whose x- and y-lines move arbitrarily each step while the domain boundary stays fixed. The discretisation choice that carries everything: time-averaged face areas (A^n + A^{n+1})/2 in both the fluid fluxes and the face-swept volumes. For tensor-product motion the discrete geometric conservation law then holds as an algebraic identity, so uniform flow is a machine-precision fixed point, not a truncation-order one: - DGCL test: uniform (0.7, -0.4) on a 16x12 grid with interior lines wiggling out of phase, 400 steps: max deviation 7.9e-15 (~35 ulp). Negative control with end-of-step areas (per-step cell error exactly dw*dh/V, the cross term the identity absorbs): 1.5e-2 - a 1e12 separation, so the test can fail. - Degeneracy: zero motion on a uniform grid vs fixed-grid PISO over Taylor-Green steps: max difference 2.2e-16 - one ulp - pinning every geometric generalisation to the verified implementation. - Physics under motion: Taylor-Green on the wiggling mesh, L2 error 2.42e-2 -> 1.07e-2 (n=16 -> 32, order 1.17); moving-mesh error at n=32 sits below the fixed-mesh 1.1532e-2 (PISO's published value to four digits); energy decay unchanged by the motion. One trap documented in the test: the projection's inner-stop floor (0.1 * tolerance * reference_flux) at an engineering tolerance lets a one-sweep partial p' accumulate into p, whose gradient perturbs the velocities at ~1e-11 with the geometry blameless. The DGCL run must use a rounding-level tolerance because machine-precision preservation is the claim under test. Measured: 3.6e-11 at tol 1e-9, 7.9e-15 at 1e-13. Incompressibility needs no mesh-velocity term: subtracting the GCL from moving-cell mass conservation leaves plain div(u) = 0 on the current geometry, so the projection is the fixed-grid one with non-uniform coefficients. 292 rtx-cfd tests green (288 + 4). Co-Authored-By: Claude Fable 5 <[email protected]>	2026-08-20 05:31:12 -07:00
Omar SobhandClaude Fable 5	b321a9aba7	rtx-cfd: Taylor-Green validates PISO's transient path — and fixes the projection's inner solve ... With k = pi the decaying Taylor-Green vortex has zero normal velocity on the unit box for all time, so it fits the closed staggered domain exactly, with ZERO body force: convection is balanced identically by the true TG pressure and the decay comes from viscosity alone. This exercises exactly what the steady MMS harness cannot see — the time derivative, the unsteady pressure coupling and the projection's splitting error. The time-decaying tangential wall velocity enters by re-setting the wall hook each step. Measured (16/32/64, dt ~ h^2): L2 velocity 2.267e-2, 1.153e-2, 5.841e-3 — orders 0.97 and 0.98, first-order upwind's rate — and the kinetic-energy deficit against the exact e^(-4 nu pi^2 T) halves per refinement (0.0690, 0.0360, 0.0185; ratios 1.92, 1.95), within 2.3% on the finest mesh. Every step divergence-free to ~1e-7. Its first run caught two defects in the projection's inner solver: - The inner Gauss-Seidel stop summed the per-sweep iterate CHANGE — the same movement-not-residual pseudo-criterion the SIMPLE census flagged: slow modes move little per sweep while their residual is still large. - Plain GS contracts smooth modes by only 1 - O(h^2) per sweep, so the 400-sweep cap left max |div u| ~ 1e-2, GROWING with mesh size (8e-3 at 16^2 to 2e-2 at 64^2). The inner stop now measures the true equation residual, the sweep is SOR at the optimal Poisson factor omega = 2/(1 + sin(pi h)), and it converges relative to each projection's own source with a floor tied to the outer mass tolerance — so a long steady march no longer burns a hundred sweeps per step polishing negligible corrections. The steady MMS harness had masked all of this: a march to steady state iterates the projection to death regardless, which is why its divergence read 1e-9 while a 205-step transient left 1e-2. mms_piso's steady-state criterion is 1e-6 (was 1e-7): per-step projection noise at the mass tolerance floors |du/dt| just below 1e-6, and the L2 errors under measurement are 1e-2 to 1e-3. Its results are unchanged to six figures and still match SIMPLE's. 288 rtx-cfd tests, 0 failing. Co-Authored-By: Claude Fable 5 <[email protected]>	2026-08-20 00:35:06 -07:00
Omar SobhandClaude Fable 5	d8a30db155	rtx-cfd: Ghia Re=400 as a quantitative claim — and the stopping-tolerance trap ... The Re=400 lid-driven cavity, 128^2 TVD on an exactly-unit domain, sampled on the staggered faces that lie exactly on the centrelines, against Ghia, Ghia & Shin (1982) — reference values sourced from two independent transcriptions that agree digit for digit (Mramor/Vertnik/Sarler CMC 2013 Table 1, and the ivan-pi benchmark collection): u_min -0.32667 at y = 0.2852 (Ghia: -0.32726 at 0.2813 — 0.18%) v_min -0.45024 at x = 0.8633 (Ghia: -0.44993 at 0.8594 — 0.07%) v_max 0.30044 at x = 0.2305 (Ghia: 0.30203 at 0.2266 — 0.53%) max |u - Ghia| over 15 profile stations: 0.0051 Ghia's own values carry ~0.3% discretisation error (Sahin & Owens 2003 put u_min at -0.32838), so this is at the reference's own accuracy. The finding worth the commit message: the first run used the Re=100 test's residual tolerance of 1e-4 and read u_min = -0.31987 — "converged", 2.3% shy — and refining to 192^2 made it WORSE (-0.30879, profile deviation doubled from 0.034 to 0.074). The residual had dropped below tolerance while the field was still developing, and the effect grows with mesh size because SIMPLE's per-iteration contraction weakens as h -> 0: at fixed residual tolerance the finer mesh stops at an EARLIER stage of convergence. Tightening the stop (3e-5, then 1.5e-5, until the movement per halving fell below the reference's own error) was the fix, and the test's bands are set so the premature-stop state fails all of them. "The residual converged" must never stand in for "the answer stopped moving". Co-Authored-By: Claude Fable 5 <[email protected]>	2026-08-19 23:23:32 -07:00
Omar SobhandClaude Fable 5	e94ad1be6b	rtx-cfd: Poiseuille closed-form validation with exact-zero assertions ... Plane channel driven by a uniform body force: u(y) = G/(2mu) y(1-y), v = 0, p exactly constant. Convection vanishes identically, so this isolates diffusion, the half-cell wall treatment and the pressure coupling — and two of the three answers are exact zeros, which no benchmark comparison offers. The ends are clamped to the profile the DISCRETISATION prefers — the 1-D tridiagonal with half-cell wall closures, solved directly in the test — rather than to the continuous parabola. That makes (u_hat, 0, const) an exact fixed point of the 2-D discretisation, and the solver must sit on it: |u - u_hat| ~ 1e-10, max |v| ~ 1e-10, p spread ~ 8e-10 (16^2) A first version clamped the ends to the continuous parabola instead; the O(h^2) incompatibility between that profile and the discrete one drove a weak secondary flow near the ends (max |v| = 1.3e-3) — a property of the mismatched boundary data, not of the solver, recorded in the test docs so nobody rediscovers it as a bug. The wall treatment's own truncation is measured in isolation as |u_hat - parabola|: 3.906e-3 at 16, 9.766e-4 at 32 — refinement ratio exactly 4.00, second order, in closed form c h^2 / 4. Co-Authored-By: Claude Fable 5 <[email protected]>	2026-08-19 19:32:37 -07:00
Omar SobhandClaude Fable 5	9b097fca0d	rtx-cfd: PISO validated by manufactured solution — after fixing the inverted projection ... PisoSolver was the only major solver in the workspace with no verification of any kind. Writing the MMS harness for it (tests/mms_piso.rs) and inspecting the implementation found the census's defect species again: - The pressure correction had its SIGN inverted: it solved -lap(p') = +rho div(u*)/dt and then corrected with u = u* - (dt/rho) grad(p'), so each projection DOUBLED the divergence instead of removing it. - The momentum sweeps froze the near-wall lines (1..ny-1) and the pressure correction skipped the outer ring of cells (1..nx-1) — both exactly the defects repaired in SIMPLE. - The "explicit" predictor read neighbours the same sweep had already overwritten, so the step depended on sweep order. - The pressure gradient was dropped entirely on the last interior face. Rewritten as a genuinely explicit predictor plus anchored-Neumann projection on the staggered grid, with the conventions SIMPLE now embodies: near-wall lines are unknowns with half-cell wall diffusion, continuity on every cell, boundary faces are prescribed data. Momentum-source and wall-velocity hooks added so the manufactured solution can reach it. Measured (16 -> 32 -> 64): L2 velocity 3.516214e-2, 1.953750e-2, 1.037512e-2 — orders 0.85 and 0.91, first-order upwind's rate — with max |div u| ~ 1e-9 in every cell. The errors agree with SIMPLE's on the same meshes to six or seven significant figures: an implicit under-relaxed outer iteration and an explicit time-marching projection land on the same discrete steady solution, which is what sharing a spatial discretisation must produce and is very hard for two independently wrong solvers to fake. 285 tests, 0 failing. Co-Authored-By: Claude Fable 5 <[email protected]>	2026-08-19 19:28:39 -07:00
Omar SobhandClaude Fable 5	796cf173e6	rtx-cfd: second-order convection by deferred-correction TVD; MMS order 1.84, cavity closes on Ghia ... First-order upwind's O(h) numerical viscosity was the measured limit on the whole discretisation: MMS order ~0.9 at Re = 20 against 2.05 in the Stokes limit. This adds a ConvectionScheme parameter to SimPLE — Upwind (default, behaviour unchanged), TvdVanAlbada, TvdVanLeer — implemented by deferred correction: the upwind operator stays implicit, so a_p = sum(a_nb) and diagonal dominance survive unconditionally, and the limited high-order-minus-upwind flux difference enters the source explicitly at the current iterate. At a fixed point the two agree, so the converged answer is the TVD discretisation. Faces whose far-upwind node lies outside the domain fall back to pure upwind; wall faces pass no mass, so no correction enters. Measured by the manufactured solution (van Albada, 16 -> 32 -> 64): L2 velocity 1.325e-3 4.406e-4 1.232e-4 orders 1.59, 1.84 (upwind) 3.516e-2 1.954e-2 1.038e-2 orders 0.85, 0.91 The error is 27x to 84x below upwind's at equal resolution, the order climbs toward 2 (the shortfall is limiter clipping plus the boundary fallback, both of which shrink with h), the pressure error falls at the same rate, and continuity still holds to solver tolerance in every cell. On the Re = 100 lid-driven cavity at 65^2 the centreline minimum moves from -0.1932 (upwind) to -0.2036 against Ghia's -0.2109 — 59% of the remaining gap closed at equal resolution, converged in 790 iterations — and the vortex position moves from 0.5000 to 0.4844 toward Ghia's 0.4531. Both new cavity bounds exclude the upwind values, so falling back to first order fails them. 284 tests, 0 failing. Co-Authored-By: Claude Fable 5 <[email protected]>	2026-08-19 19:16:48 -07:00
Omar SobhandClaude Opus 5	1a740e0b2c	rtx-cfd: the wall treatment is second order, not first — correct the record ... The manufactured-solution test carried a hypothesis for why the observed order sits below 1: that `(u_P - u_wall)/(dy/2)` approximates the wall gradient at y = dy/4 rather than at the wall, making the near-wall rows first order. Measuring in the Stokes limit refutes it. With convection negligible every remaining operator is second order, so the observed rate there reports the wall treatment directly: rho = 1.000 (Re = 20.00) 3.52e-2 1.95e-2 1.04e-2 orders 0.85 0.91 rho = 0.001 (Re = 0.02) 2.21e-3 5.35e-4 1.28e-4 orders 2.05 2.06 2.05 and 2.06. The half-cell wall term is second-order accurate and the Stokes discretisation reaches its nominal rate. The shortfall at Re = 20 is first-order upwind and nothing else, which is what a first-order convection scheme is supposed to give. Comment corrected rather than left standing: a plausible explanation that happens to be wrong is worse than none, because it sends the next person to fix something that is not broken. Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>	2026-08-19 17:42:14 -07:00
Omar SobhandClaude Opus 5	698c844926	solvers: near-wall momentum, Newmark dynamics, QM6, and MMS across elements ... Four parallel work items plus two defects found while integrating them. 561 -> 592 tests, 0 failing, verified stable over repeated runs. ## rtx-cfd: solve the near-wall velocity lines Every u row sits at y = (j+0.5) dy and every v column at x = (i+0.5) dx -- strictly interior. The sweeps froze rows 0 and ny-1 and columns 0 and nx-1 and treated whatever was stored there as a boundary condition, which imposed wall values half a cell inside the domain. They are now unknowns, with the wall entering through the control volume's half-cell conductance (mu dx / (dy/2)), zero convective flux through the wall, and the wall's tangential velocity in the source. That in turn makes continuity enforceable on every cell, with a neighbour coefficient zero only for a genuine boundary face. Extending continuity had been tried before and broke convergence; it works now because the near-wall lines are no longer frozen. Order matters here. Manufactured solutions, which is how any of this is known: n L2 velocity order max |p - p_exact| 16 3.516212e-2 - 9.245576e-2 32 1.953751e-2 0.85 5.225739e-2 64 1.037523e-2 0.91 2.796415e-2 Velocity error is 7.4x smaller at n=16, and the observed order rises from 0.48 toward 1. The pressure error was 0.408 -> 0.624 -> 0.756, *growing* with refinement; it now falls. Divergence on the outer ring of cells goes from 1.0e1 to 2.5e-10. A separate defect found on the way: u_source_term was computed and never called, so the x-momentum equation carried no body force at all while the y-momentum one did. That is exactly the u-versus-v asymmetry the earlier diagnosis had flagged as an unexplained clue. Cavity at 65^2, against Ghia's u_min = -0.2109 at y = 0.4531: -0.1792 at 0.3906 before, -0.1932 at 0.5000 after, in 733 iterations rather than 971. The cavity test now sets FreeSlipWall on all four sides plus the lid through the new set_wall_velocity hook. That is not a weakened benchmark: on a staggered grid the only velocity component living *on* a boundary is the normal one, which is what FreeSlipWall prescribes, and the tangential no-slip arrives through the half-cell wall term with wall velocity zero on the three stationary walls. Prescribing whole u rows and v columns, as before, pins lines half a cell inside the domain and over-determines the cells beside them once every cell has a continuity equation. ## rtx-fea: DynamicAnalysis, previously a stub returning zeros Newmark-beta in acceleration form -- the displacement form divides by beta dt^2, singular at beta = 0 -- with Rayleigh damping, the effective matrix Cholesky-factorised once and reused. Initial acceleration is solved from M a0 = F0 - C v0 - K u0 rather than assumed zero, which would destroy the second-order rate. Verified two ways that cannot both be faked: against the closed-form single-degree-of-freedom response, undamped and damped, with the measured order of accuracy; and against the free-vibration period of the same bar whose modal frequencies are already validated. Time domain and frequency domain come from different code paths. ## rtx-fea: QM6 incompatible modes Wilson's Q6 with Taylor's correction, added alongside compute_stiffness_ matrix rather than replacing it -- the existing method is byte-identical, which matters because the manufactured-solution verification depends on it. Internal modes statically condensed; the incompatible strain block evaluated at the element centre, which is what makes the patch test pass on distorted elements. ## rtx-fea: manufactured solutions across the element library Quad4 order 2.00 Tri3 order 1.98 Quad8 order 3.00 Hex8 order 1.96 (new 3-D solution) Each element asserts its own theoretical rate. ## Two defects found while integrating Reverse Cuthill-McKee node ordering was nondeterministic. All three of its orderings -- seed selection, neighbour ordering, and the trailing sweep -- were decided by HashMap/HashSet iteration order, which std randomises per process. On a rectangular mesh every corner ties at minimum degree, so two calls to displacement_only on the same mesh in the same process returned different DOF indices for the same node, agreeing in only 5 of 20 measured runs. Ties now break by node id. This surfaced as a coin-flip test failure -- 12 in 25 runs -- and would have been dismissed as flaky rather than diagnosed had the integration pass not re-run it. Quadrature: triangle(3) weights summed to 0.25 against a reference area of 0.5, and tetrahedron(3) to 1/36 against a volume of 1/6. Both divided weights that were already tabulated for the reference measure by that measure again, so both rules integrated everything to a fraction of its value -- invisibly, since a scaled quadrature leaves the stiffness matrix symmetric, the mass matrix positive definite and the rigid-body modes exact. New test asserts every rule integrates 1 to its reference measure, across every family and order, plus Gauss-Legendre exactness to degree 2n-1. Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>	2026-08-19 15:39:20 -07:00
Omar SobhandClaude Opus 5	b5814a304f	rtx-cfd: manufactured solution finds the diffusion conductances were 1/h too ... large Applies MMS to the SIMPLE solver. It found a major discretisation error on the first run, which is the point of the method. The diffusion conductances read `mu / dx` and `mu / dy`. Finite volume requires `Gamma * A / delta` — the face area over the distance between the nodes it separates — so they should be `mu * dy / dx` and `mu * dx / dy`. The face area was missing entirely, making viscosity too large by a factor of `1/h`: sixty-five times on a 65x65 mesh. Every other term in the equation was already a force (`dp * dy` for pressure, `rho u dy` for the convective flux), so the mismatch was confined to diffusion. The consequence was that the solver ran at an effective Reynolds number far below the one requested. Before the fix the manufactured-solution error did not reduce under refinement at all — observed order about -0.05, because the spurious viscosity grows with the mesh. After it, the error falls monotonically. This also explains an apparent regression that is really a correction. The cavity vortex position moved from y = 0.484 to y = 0.391 against Ghia's 0.4531, which reads as worse agreement. It is not: a strongly over-diffusive cavity approaches Stokes flow, whose vortex sits near mid-height, so the old number was closer to the reference than the scheme deserved. Correcting the viscosity exposed the discretisation's own error. The test now states that disagreement plainly rather than asserting a band around the reference. What MMS reports now, and it is not yet good enough: n = 16 L2 velocity error = 2.586104e-1 order - n = 32 L2 velocity error = 1.797373e-1 order 0.52 n = 64 L2 velocity error = 1.277188e-1 order 0.49 First-order upwind should give 1. It gives about 0.5, and the u component is markedly further from exact than v on the same mesh. Both say there is at least one more defect in the discretisation or its boundary treatment, and the asymmetry between the two momentum equations is the clue. The test asserts only monotone error reduction — what is established — and records the shortfall, because asserting a rate the solver does not achieve would either redden the suite or invite someone to weaken it later. This changes the plan: raising the observed order to 1 is now a precondition for the second-order convection work rather than a consequence of it. There is no value in adding a higher-order scheme to a discretisation that has not demonstrated first order. Supporting changes: - `SimpleSolver::set_momentum_source` applies a volumetric body force, which is what lets a manufactured solution be imposed at all. - Divergence is now detected by growth, not only by NaN. The 8x8 case at Reynolds 10^6 reached 1e149 before anything caught it, because `is_finite` stays true right up until it does not. - `test_simple_solver_workflow` specified water properties on a unit domain, which is Reynolds 10^6 on ten cells: no steady laminar solution exists and the solver diverges on it, correctly. It passed only while the excess diffusion stabilised it. Now set to Reynolds 100. 561 tests across the three crates, 0 failing. Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>	2026-08-19 12:25:52 -07:00
Omar SobhandClaude Opus 5	03a9bdf41f	rtx-cfd: apply boundary conditions to u* before using its divergence ... Closes the relaxation-factor dependence. Converged solutions are now identical for velocity relaxation 0.3, 0.5, 0.7 and 0.9 -- bit for bit -- where they previously spread 18%. The cause was ordering, not formulation. Boundary conditions were applied only at the end of the iteration, so `copy_to_starred` snapshotted a predicted field whose boundary faces held whatever the momentum sweep had written there: values the wall overwrote with zero moments later. The divergence of that field is the pressure equation's source, so those un-constrained faces entered it as a spurious mass source, concentrated at the two lid corners where the moving lid meets a stationary wall. The swept value scales with the relaxation factor, so the spurious source did too -- and so did the answer. Diagnosis is worth recording because the symptom pointed away from the cause. At the stalled state the interior momentum equations were satisfied to machine precision at every relaxation factor: a fresh Gauss-Seidel sweep moved the interior by 1e-15, the pressure correction was 1e-14, and the momentum residual was 3.6e-16. The entire residual floor lived in the *mass* term, and only that term varied with alpha -- 3.7e-4 at 0.3 against 1.6e-4 at 0.9. Each relaxation factor was converging honestly, to the solution of a slightly different problem. The correction also moves the cavity substantially closer to the reference, because the spurious corner source had been suppressing the recirculation: grid before after Ghia (1982) 17^2 -0.068 -0.123 -0.2109 33^2 -0.109 -0.154 65^2 -0.142 -0.174 97^2 -0.157 -0.182 Richardson extrapolation on the two finest grids now gives about -0.199 against Ghia's -0.2109, within 6%, with the remaining gap consistent with first-order upwind's numerical viscosity. The residual floor falls roughly linearly with mesh size (1.6e-3, 5.2e-4, 1.6e-4, 7.8e-5), which is the signature of the corner singularity rather than of an unconverged solve -- the same one Botella & Peyret (1998) subtract analytically. Two further fixes fell out of it: - The solver returned NaN rather than reporting divergence. Asked for an 8x8 cavity at a Reynolds number of a million it now stops, says it did not converge, and reports the last finite residual, instead of handing back a field of NaN that poisons everything downstream. Previously the false transient's large diagonal damped that case into crawling rather than diverging, which hid it. - `apply_boundary_condition` used `start_index` where it meant `end_index` for the bottom wall. The other three arms are correct; with both indices unset the default masked it. 558 tests across the three crates, 0 failing. Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>	2026-08-19 10:27:33 -07:00
Omar SobhandClaude Opus 5	2db4e28760	rtx-cfd: make SIMPLE a steady solver; the converged answer no longer depends ... on the pseudo-time step Acting on a literature pass. Standard SIMPLE is a steady-state algorithm: it has no pseudo-time term, and stability comes from under-relaxation folded implicitly into the momentum coefficients. Ours had a false transient *and* an explicit post-hoc blend of the whole field, which is why the converged cavity solution varied with `time_step` -- something a steady state cannot legitimately do. Four changes, in the order they mattered: 1. The convergence measure was `|u - u_old|`, the change between successive iterates. That is not a residual: it reports how far the iteration moved, which depends on how heavily it is damped, and the damping was set by `dt`. Replaced with the imbalance of the discretised momentum equations, `|a_p u_P - sum a_nb u_nb - b|`, normalised by `sum |a_p u_P|` as CFD solvers conventionally report it. An unnormalised sum grows with the cell count and with `dt` through `a_p0`, so the same numeric tolerance meant a different thing on every grid. The residual is measured against the *unrelaxed* equation. Relaxation inflates the diagonal by 1/alpha and adds a matching source; reporting the relaxed system's residual makes one tolerance correspond to a different true error for each alpha. 2. Steady by default: `a_p0 = 0`, and Patankar's implicit under-relaxation -- `a_p / alpha` with `(1-alpha)/alpha * a_p * u_prev` added to the source. At a fixed point the two cancel exactly, so the converged solution is independent of alpha by construction. The explicit velocity blend is removed; it relaxed a second time and undid part of the continuity the pressure correction had just enforced. `steady: false` restores the transient term for genuinely time-dependent problems. Result: dt = 0.001, 0.01 and 0.05 now give bit-identical fields. 3. Dropped the net convective flux from `a_p`. It vanishes identically once continuity holds, but during the iteration it does not, and it can exceed the sum of the neighbour coefficients -- driving `a_p` through zero and the solve to NaN, which is what the workflow tests hit once `a_p0` was no longer there to mask it. Omitting it is what makes `a_p = sum a_nb` positive unconditionally. 4. Anchored one cell of the pressure correction. With velocity prescribed on every boundary the pressure equation is pure Neumann and singular; `p'` is fixed only up to a constant and Gauss-Seidel lets it drift. Enforcing solvability by subtracting the mean source is the textbook remedy and is wrong here -- this source is assembled from face fluxes that include the boundaries, so it need not sum to zero, and subtracting its mean injects a spurious source everywhere. Tried; it diverged. Anchoring a reference cell changes no pressure gradient, which is all the momentum equation uses. Also measured, and it settles the open question about Ghia: the under-prediction is numerical diffusion, not a defect. First-order upwind carries a numerical viscosity of about |u| dx / 2, which at 65^2 is 0.0078 against a physical 0.01 -- an effective Reynolds number near 56, not 100. Refinement moves the centreline minimum monotonically toward the reference: -0.068 at 17^2, -0.109 at 33^2, -0.142 at 65^2, -0.157 at 97^2, against Ghia's -0.2109, with the vortex position tracking 0.375 -> 0.406 -> 0.469 -> 0.490 against Ghia's 0.4531. The cavity test moves to 65^2 and asserts the vortex position tightly (0.40..0.52, Ghia 0.4531) while bounding the strength to the band first-order upwind can reach there. Its tolerance is 1e-4 rather than 1e-6: the two lid corners hold a velocity discontinuity whose discrete imbalance does not reduce with iteration, so the normalised residual floors near 7e-5. That is a property of the problem -- the same singularity Botella & Peyret (1998) subtract analytically -- and the physical assertions, not the stopping rule, are what establish correctness. Still open: converged solutions retain a dependence on the relaxation factor that the implicit formulation should have removed (-0.159 at alpha=0.3 against -0.134 at alpha=0.9 on 65^2, each stable to six decimals over 200k iterations). Recorded rather than papered over. 558 tests across the three crates, 0 failing. Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>	2026-08-19 09:47:46 -07:00
Omar SobhandClaude Opus 5	bfd9f4dfd2	rtx-cfd: repair the pressure-velocity coupling, LBM walls and mesh quality ... Clears the rest of the quarantine. All three crates now run 558 tests with 0 failures and no `#[ignore]` markers. SIMPLE could not converge, and the reason was not slow convergence but wrong physics. The pressure correction equation used a bare Laplacian, 1/dx^2 and 1/dy^2, while the velocity correction divided by a_p = rho dx dy / dt. SIMPLE requires these to be each other's inverse: substituting the corrected velocities into continuity must reproduce the pressure equation, which fixes a_E = rho d dy/dx with d = dV/a_p. The two disagreed by roughly 1/(h^2 dt) -- about 2e4 on a 16x16 cavity -- so the pressure correction was that many times too weak to enforce continuity. The consequence was visible and specific. A lid-driven cavity at Re=100 produced a monotonic profile rising from 0 at the floor to 1 at the lid: Couette flow, with no recirculation anywhere, and a peak pressure of 1.6e-4 against the rho U^2 scale of 1. The return flow in a cavity is driven entirely by the pressure gradient, so with the pressure pinned near zero there was nothing to turn the flow around. With the coefficients made consistent the profile recirculates, the peak pressure is 2.9, and the solver converges. Also in SIMPLE: - `p'` was never reset between outer iterations. It is a correction that `pressure_update_step` folds into `p`, so carrying it forward applied the same correction twice. - The convergence measure was the inner Gauss-Seidel residual, which goes to zero whether or not the flow satisfies continuity. Now the mass imbalance. - The velocity correction used only the transient part of a_p, `rho dV/dt`, rather than the diagonal the momentum equation was actually solved with. - All four convective face fluxes were computed from a single cell-centred velocity, so `fe` and `fw` were the same number, as were `fn` and `fs`. Upwinding then picked the same direction on opposite faces of the control volume. Now interpolated per face on the staggered grid. Not claimed: agreement with Ghia, Ghia & Shin (1982). The vortex centre moves toward their y = 0.4531 under refinement (0.400 at 16^2, 0.419 at 32^2, 0.460 at 64^2) but the minimum centreline velocity reaches only -0.130 against their -0.2109, and the converged field still depends slightly on the pseudo-time step, which a true steady state cannot. The cavity test therefore asserts what is established -- convergence, recirculation, vortex position, and an O(1) pressure field -- and the remaining gap is recorded in omni-cortex/docs/solver_status.md rather than papered over with a loose tolerance. LBM bounce-back was doing neither of the things its name claims. It was written as assignment (`f[2] = f[4]`) rather than a swap, discarding the population being reflected -- bounce-back is a permutation and conserves mass exactly, so the domain leaked 0.013% of its mass every 100 steps and would have kept draining. And the pairs used were 5<->8 and 6<->7, which reverse only the wall-normal component: that is specular reflection, a free-slip wall, so the no-slip condition the walls were supposed to impose never held. Mesh quality: - Quadrilateral aspect ratio included the diagonals in the maximum but not the minimum, so it could never return 1: a unit square reported sqrt(2) and a 2:1 rectangle sqrt(5). - Triangle aspect ratio used longest-over-shortest edge, which does not detect the failure mode that matters. A sliver with vertices (0,0), (10,0), (5,0.1) scores 2.0 -- indistinguishable from a healthy 2:1 triangle -- while its area is a twentieth of what its edges suggest. Now the radius ratio R/2r, which is 1 for equilateral and 1250 for that sliver, and which also fixes the quality histogram. - StructuredMesh aspect ratio took bounding-box extents and guarded the z-extent with `.max(1e-10)`. On a 2-D mesh the depth is exactly zero, so the guard became the minimum and a unit square reported 2e10. Mesh refinement produced meshes that failed their own validation. `subdivide_triangle` reserved midpoint ids as `next_node_id + k`, then advanced the counter by 3, after which `refine_cells` called `add_node` and advanced it three more -- so every refined cell referenced vertices three ids away from the ones actually created. Separately, the position lookup selected by slot rather than by id ("This is simplified, should look up correct midpoint"), so three of four sub-triangles had their areas computed from the wrong points; the quadrilateral version mapped every new id to the cell centre. Fixtures corrected rather than tolerances loosened: a structured mesh test asserted 0.16 for the average cell volume while the comment beside it computed 0.25 from the node-count convention the code actually uses; the Zou-He pressure test built a *velocity* boundary at u = 1.2, far above the lattice speed of sound, making the density negative; and the cavity-setup test required the lid to influence the domain centre 16 rows away in 10 steps, which exceeds the lattice propagation speed. Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>	2026-08-19 08:40:09 -07:00
Omar SobhandClaude Opus 5	cca29aac8f	rtx-fea: repair the eigensolver, and stop the suite lying about the rest ... Lifts the 27 `#[ignore]` markers on rtx-cfd and rtx-fea. 21 of them fail; 6 were stale, marking components that have since been implemented. The suite now reports the truth, which means it is red. The eigensolver had three independent defects, each individually fatal. Found by writing closed-form tests first and confirming red: - The generalized reduction formed M^-1 K and ran Lanczos on it. M^-1 K has the right eigenvalues but is not symmetric even when K and M both are, and Lanczos assumes symmetry -- so it returned a wrong answer rather than an inaccurate one. On a 2-DOF spring-mass chain with M = diag(2,1) it gave 1.633 against an exact root of 1 - sqrt(2)/2 ~= 0.293. Replaced with the Cholesky reduction B = L^-1 (K - sigma M) L^-T. - Output was unsorted. nalgebra's symmetric_eigen gives no ordering guarantee and none was imposed; modal analysis names modes by index, so the ordering is part of the contract. - Eigenvectors could not be transformed back out of the Krylov basis. The Lanczos block was (n x num_iter) and the tridiagonal eigenvectors (min(num_iter, k) x k); whenever those differed the multiply panicked on a dimension mismatch -- that is, on every problem with more DOFs than requested modes, which is every real modal analysis. Lanczos now runs shift-invert by default. Plain Lanczos converges to the eigenvalues of largest magnitude and modal analysis wants the lowest, so without it the solver returns the modes nobody asked for. Also switched to full reorthogonalization, twice per step, so converged eigenvalues do not reappear as ghosts indistinguishable from genuine repeated roots. ModalResults computed f = sqrt(lambda / 2pi) instead of sqrt(lambda) / 2pi. The two agree only at lambda = 2pi, so a smoke test asserting a positive frequency would never separate them. A `#[cfg(disabled)]` module in the same file asserted the correct formula -- the module was disabled rather than the bug fixed. That module is removed; tests/eigenvalue_closed_form.rs supersedes it with every expected value derived analytically. Corrected a fixture rather than loosening its tolerance: implementation_tests expected the smallest eigenvalue of tridiag(-1, 4, -1) at order 3 to be 4 - 2 sqrt(2) ~= 1.172. The eigenvalues of tridiag(c, a, c) are a + 2c cos(k pi / (n+1)), so the true value is 4 - sqrt(2) ~= 2.586. The test had been quarantined for failing to match an expectation that was never right. rtx-fsi is untouched and stays 26/26. Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>	2026-08-19 07:46:01 -07:00
redclawsystems	4d88dc0584	Initial commit	2026-03-04 00:08:42 +00:00