2 Commits

Include renames

Author	SHA1	Message	Date
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	8615fc5783	rtx-fea: verify elastostatics by manufactured solution — second order confirmed ... Adds the Method of Manufactured Solutions to this crate, and it immediately paid for itself by finding a bug that every existing test missed. MMS asserts something stronger than "close enough to a value someone believed": that the discretisation converges to the exact solution at the rate the theory predicts. Choose a smooth field, substitute it into the governing equations, and whatever they fail to balance is the body force that makes it exact. Solve, refine, read off log2(e_h / e_h/2). Observed order for Quad4 displacement in L2: n = 8 L2 error = 7.816681e-3 order - n = 16 L2 error = 1.962845e-3 order 1.99 n = 32 L2 error = 4.912786e-4 order 2.00 (n = 64 reads 2.00 as well, at ten times the cost) That verifies the whole chain at once -- element matrices, quadrature, Jacobian, assembly, DOF numbering, constraints and the linear solver -- against a solution none of them can represent exactly. It is the check that none of the sixteen defects fixed in this crate would have survived. The manufactured field is u = sin(pi x) sin(pi y), v = x^2(1-x) y(1-y): smooth, not in the bilinear element space, with the two components different in form and a non-zero shear strain, so the shear block of the constitutive matrix is exercised rather than skipped. Found by it: `compute_shape_functions` inferred how many parametric coordinates to pass from the coordinate *values* -- match coords.eta() { 0.0 if coords.zeta() == 0.0 => vec![coords.xi()], // 1 component ... -- so any evaluation on an axis was handed a one-component slice, which every 2-D and 3-D element rejects. That includes the element centre and the middle point of every odd-order Gauss rule. It survived only because the default 2-point rule never samples zero; asking for a 3-point rule to integrate the error was enough to trip it. Dimensionality now comes from the element, which is where it belongs. Two prerequisites, both real functional gaps rather than test scaffolding: - Consistent body-force integration. `BodyForceBC` distributed load as force * volume / num_nodes, which is exact only for a constant force on a symmetric element and otherwise first-order -- enough to cap the measured order of the whole solver at 1 regardless of the element. `ElementMatrixComputer::compute_body_force_vector` now integrates the consistent form, taking the force as a closure so a spatially varying load can be expressed at all. - Non-homogeneous Dirichlet conditions did not exist. `StaticLinearAnalysis` read the prescribed value out of the boundary condition and discarded it, and `extract_free_system` built the reduced right-hand side without the K_fc u_c coupling, so every Dirichlet condition behaved as zero whatever the caller asked for. `GlobalSystem::set_prescribed_value` and the coupling term close that, reusing `extract_submatrix` and `multiply_vector` rather than a dof-by-dof loop. 560 tests across the three crates, 0 failing. Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>	2026-08-19 12:04:46 -07:00