
ID	0442
Class	KNOWN-LIMITATION
Severity	2
Status	blocked

Models: —

Found: 2026-11-03, test audit of the speed work (feature me-tw-rulings), at e0a3e14

Decision needed: whether to work on the load-law angle form (MARE-0131), the E-modulus and the Freeze schedule to bring these rows inside the 20 % band, or to accept the bounds.

Evidence

tests/NetValidation_LaderCage_Test.cpp, suite NetValidation_LaderCage_Fig14Drag_VALIDATION: the model drag of the three Lader (2009) cages against KF2012 Fig. 14 at k = 0.05 (18 s, Freeze wake, loads read at 18 s). The KF2012 total uncertainty band is +-20 %. Five of the 21 rows are above +20 % (every one above the measurement):

Row	Model [N]	Measured [N]	Error
Sn 0.19, U 0.12 m/s	10.661	8.1	+31.6 %
Sn 0.35, U 0.26 m/s	74.716	57	+31.1 %
Sn 0.43, U 0.26 m/s	88.031	70	+25.8 %
Sn 0.43, U 0.76 m/s	207.915	165.1	+25.9 %
Sn 0.43, U 0.93 m/s	237.731	173	+37.4 %

Close to the band: Sn 0.35 U 0.39 (+19.79 %) and Sn 0.43 U 0.12 (+19.67 %). No row is below -20 %.

Bound: owner ruling 2026-11-03 (2 rows expected, 5 found). The test asserts -20 % <= error <= bound with the error rounded up to the next 5 %: +35, +35, +30, +30 and +40 % in kKnownDragDeviations; all other rows within +-20 %.

Effect

The model over-predicts the drag of the denser cages at low speed and of Sn 0.43 at high speed by up to 37 %.

Possible fix

Known reasons (doc/user/validation/lader2009.md, section "S3 drag against KF2012 Fig. 14"): the default law's angle form (MARE-0131; KF2012 find the same over-prediction for Sn 0.35 and 0.43 and attribute it to the angle harmonics a3, b4: -28 % drag for Sn 0.43 at 1 m/s from a3 = 0 to 0.1); the provisional E-modulus (awaiting the author), which shapes the cage at low speed; the Freeze schedule, whose round has not converged at Sn 0.35 and 0.43 when the loads are read. Not tuned (R20).

Test that would prove it

Remove the entry of the row from kKnownDragDeviations; the row then has to be within 20 %.

Risk

A bound that stays after the cause is fixed hides a regression up to that bound. Lower or remove the bounds when MARE-0131 is resolved.