Sensitivity and Cross-Level Consistency Analysis of Excessive Acceleration Under Variations in Natural Roll Period, Roll Damping, and Loading Condition

Second-Generation Intact Stability Criteria (SGISC) assess excessive acceleration (EA) through successive vulnerability levels, but the consistency between Level 1 and Level 2 under changes in ship-related parameters remains insufficiently understood. This study investigates the effects of natural roll period, roll damping, and loading condition on both levels. A MATLAB(R2022b)-based implementation was verified using the IMO C11 example and subsequently applied to the ITTC A1, KCS, and DTC container ships. Three levels were assigned to each investigated factor, producing 27 combinations per ship and 81 cases overall. Responses were examined through case-wise comparisons, isolated and paired-factor trends, and a sum-of-squares decomposition of response variability. A total of 72 cases failed EA1 (the remaining 9 were outside IMO applicability), while 50 passed EA2 and 22 failed at both levels; no Level 1 PASS–Level 2 FAIL outcome was obtained. Longer natural roll periods generally lowered EA1 lateral acceleration while increasing the EA2 long-term probability index, whereas increased damping reduced both measures. Loading-condition effects varied markedly among ships, especially in EA2. Pooled contributions further showed a change from natural roll period dominance in EA1 to roll damping dominance in EA2. These results indicate that parameter sensitivity is both level- and ship-dependent. Since none of the investigated cases passed EA1, the assessment of PASS/FAIL-based cross-level consistency was necessarily limited; however, parameter-induced response trends were examined in detail across both levels.