Convention Differences (+3)

Convention Differences

• AQWA: ISO 6954 (phase lead) — A * cos(wt + phi)
• OrcaWave: Orcina (phase lag) — A * cos(wt - phi)
• Conversion: phi_Orcina = -phi_ISO (negate AQWA phases)

Implementation

Normalize at extraction time, not at comparison time. Use Orcina (phase lag) as the canonical convention:

# In AQWA extraction, after building each RAOComponent:
component.phase = -component.phase  # ISO 6954 → Orcina lag
results.phase_convention = "orcina_lag"

Track convention metadata on DiffractionResults:

phase_convention: str = "unknown"  # "orcina_lag" or "iso_lead"
unit_system: str = "SI"            # "SI" (kg,m,s) or "orcaflex" (te,m,s)

M24/M42 Sway-Roll Coupling Sign Fix

AQWA sway-roll coupling terms (M24/M42) have opposite sign to OrcaWave. Empirically determined from barge geometry; needs AQWA Theory Manual Section 4.3 confirmation.

# Negate Sway-Roll coupling in AQWA extraction
# Added mass AND damping matrices
matrix[1, 3] = -matrix[1, 3]  # M24
matrix[3, 1] = -matrix[3, 1]  # M42

Scope: Only M24/M42 — other roll-coupling terms (M14, M34, M46) are near-zero for typical barge geometries and cannot be verified.

Unit System

• AQWA: SI (kg, m, s)
• OrcaWave: OrcaFlex (te, m, s) — factor ~1000x
• Pearson correlation is scale-invariant, so units don't affect correlation-based comparison
• Track in metadata for absolute value comparisons