New code only: Flag3d builds the Turek-Hron flag as a structured Hex20
plate (x-major serendipity lattice), the root clamp with free or
plane-strain (u_z = 0) lateral faces, the TL-SVK Newmark analysis with the
2-D harness's settings (beta = (gamma + 1/2)^2/4, 60 Newton), the wetted
Quad8 faces with outward orientation, and consistent nodal forces of a
traction field on the current faces. The dynamic stepper and the TL path
were already dimension-generic; nothing existing changes.
Gates (tests/flag3d_structure.rs): mass = rho V, face-force totals;
plane-strain 3-D reproduces the 2-D 35x2 Quad8 CSM1 to rounding and the
first 60 CSM3 steps to 9e-16 m. Instruments (#[ignore]): CSM1 table,
CSM3 march, modal K/M dump.
Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>
