Support bounded shared transverse motion and steady pinball demo

tests/unit/test_steady_pinball.py

@@ -0,0 +1,54 @@
+"""Real config loading and pure structural update for the frozen development case."""
+import importlib.util
+import math
+from pathlib import Path
+
+import numpy as np
+import pytest
+
+path = Path(__file__).resolve().parents[2] / 'research/steady_pinball/run.py'
+spec = importlib.util.spec_from_file_location('steady_pinball_run', path)
+runner = importlib.util.module_from_spec(spec)
+spec.loader.exec_module(runner)
+
+
+def test_actual_loader_and_paper_geometry(tmp_path):
+    import json
+    from CelerisLab.config import load_lbm_config
+    p = tmp_path/'config.json'
+    p.write_text(json.dumps(runner.config()))
+    cfg = load_lbm_config(str(p))
+    cfg.validate()
+    assert (cfg.nx, cfg.ny, cfg.viscosity, cfg.velocity) == (1280, 512, .004, .01)
+    assert cfg.collision == 'MRT' and cfg.y_wall_bc == 'bounce_back'
+    assert runner.U * runner.D / runner.NU == 50.
+    assert runner.CENTRES == ((600., 255.5), (626., 270.5), (626., 240.5))
+
+
+def test_structure_rest_equilibrium_and_energy_decay():
+    s = runner.Structure()
+    assert s.candidate(0.) == (0., 0.)
+    assert s.mass == pytest.approx(10*3*math.pi*100)
+    s.y, s.v = .2, 0.
+    # One damped period: independent continuous solution at total elapsed time.
+    for _ in range(runner.PERIOD):
+        s.y, s.v = s.candidate(0.)
+    t = runner.PERIOD
+    a = s.zeta*s.omega
+    w = s.omega*math.sqrt(1-s.zeta**2)
+    expected = .2*math.exp(-a*t)*(math.cos(w*t)+a/w*math.sin(w*t))
+    assert s.y == pytest.approx(expected, abs=2e-12)
+    assert .5*s.mass*s.v*s.v+.5*s.stiffness*s.y*s.y < .5*s.stiffness*.2**2
+    s.y, s.v = .3, 0.
+    assert s.candidate(s.stiffness*.3) == pytest.approx((.3, 0.), abs=1e-15)
+
+
+def test_report_uses_completed_rows_and_net_force():
+    rows = np.zeros((4, 15))
+    rows[:, 0] = np.arange(1, 5)
+    rows[:, 1] = 2.
+    rows[:, 3:9] = 1.
+    got = runner.summarize(rows)
+    assert got[0]['end_step'] == 4
+    assert got[0]['y_rms_D'] == .1
+    assert got[0]['fy_rms'] == 6.