
ID	0125
Class	KNOWN-LIMITATION
Severity	2
Status	blocked

Models: —

Found: 2026-10-20, feature m2-hydro-doc-gaps (split from ENV-0120 on the owner's ruling of 2026-10-20; prototype report plans/env0120-angle-form-prototype.md in fhsim_workspace, open question Q5)

Decision needed: lift angle form. Which form of the lift angle factor for LocalThroughFlow: one pinned at C_L(45°) like the drag factor of ENV-0120 (so MF2022 L1 stays), or another form? Lift is separate from the drag fix and needs its own study and ruling. The Løland lift (pure sin 2θ, KF2012 Eq. 4) lies 27 to 46 % above MF2022 Eq. 10 at 45°, so the two datasets disagree about the level too.

Evidence

The default lift is C_L(θ) = c_l [(1 + b6) sin 2θ + b4 sin 4θ + b6 sin 6θ] with b4 = 0.036, b6 = 0 (owner ruling R1, MARE-0131, 2026-10-20; kf2012::LiftAngleFactor). Disabled tests at HEAD, measured against tolerance:

PanelLoadLaw_Rudi.DISABLED_L5_LiftAngleDependence_LocalThroughFlow (0.08): C_L(30)/C_L(45) = 0.897 against 1.000 (Sn 0.130, −0.103), 1.091 (0.144, −0.194), 1.000 (0.184, −0.103), 1.019 (0.317, −0.122); C_L(80)/C_L(45) = 0.319 against 0.455 (0.130, −0.136) and 0.636 (0.144, −0.317). The 60° rows pass with b4 = 0.036 (they failed by −0.130 with b4 = 0.10).
PanelLoadLaw_Loland.DISABLED_L6_LiftCoefficient_LocalThroughFlow (±25 %): 15 of 80 rows outside tolerance; worst −33.3 % (Sn 0.317, 80°, Re 2000) and +25.0 % (Sn 0.130, 30°, Re 500) (doc/user/hydrodynamics.md Section 11.4, tests/PanelLoadLaw_Loland_Test.cpp:132). Løland's lift lies 27–46 % above MF2022 Eq. 10 at 45° for the four Rudi nets, and its pure sin 2θ differs from b4 sin 4θ.
PanelLoadLaw_Consistency.DISABLED_L9_DefaultHarmonicsSatisfyL5AndL8: 17 of 66 checks fail; 6 of them are L5 lift rows. It stays failing with every drag option of the ENV-0120 prototype.

The prototype of ENV-0120 left lift untouched: with a3 + a5 = 0.07 kept, lift at 45° and every lift test is unchanged.

Effect

Inclined net panels at 30° and above 60° take a lift ratio that is too low against Rudi (up to −0.317 of C_L(45°)), and the level against Løland is off by up to a third. Lift of a trawl panel at small angles of attack is where this shows.

Possible fix

A lift angle factor pinned at C_L(45°) = 1, fitted to Rudi and Løland by leave-one-dataset-out, as was done for the drag in ENV-0120 (same method, same checks). Decide first whether Løland's level (27–46 % above MF2022) is to be followed; MF2022 is the anchor dataset (ME ADR 0005), so probably only the angle shape.

Test that would prove it

DISABLED_L5_LiftAngleDependence_LocalThroughFlow and DISABLED_L6_LiftCoefficient_LocalThroughFlow enabled and passing with untuned tolerances, with MF2022 L1 and L3 still passing.

Risk

Moves the lift of every inclined panel under the default law, so every inclined-net baseline in fhsim_marine_elements moves (regenerate with owner approval).