State-of-the-art and prospects of direct stability assessment methods for second-generation intact stability criteria

Intact stability of ships in waves is a fundamental guarantee for navigation safety. The direct stability assessment methods associated with the Second Generation Intact Stability Criteria (SGISC) remain undeveloped and have become a key focus of current research. This study aims to systematically review global research progress and critical challenges in direct stability assessment for SGISC. Methodologically, it summarizes numerical prediction techniques (including potential flow methods, viscous flow methods, hybrid viscous-potential flow algorithms, and intelligent computational methods) applied to five stability failure modes: parametric rolling, pure loss of stability, surf-riding/broaching, excessive acceleration, and dead ship stability. Additionally, three categories of statistical extrapolation methods, designed to address the rarity of stability failures, are analyzed in detail, namely extreme value theory approaches, critical wave groups and wave episode methods, and environmental condition extrapolation techniques. The results show that potential flow and viscous flow methods have achieved remarkable results in predicting most failure modes, while intelligent methods and hybrid viscous-potential flow algorithms demonstrate application potential. However, several key challenges remain unresolved, such as the high dependence of intelligent methods on high-quality data, insufficient simulation accuracy for multi-degree-of-freedom coupling in pure loss of stability and surf-riding/broaching, the need for improved propeller-rudder emergence models, and the high computational cost associated with full viscous flow simulations. In conclusion, future research directions are proposed, such as enhancing experimental data validation, optimizing the integration of viscous flow methods with extrapolation techniques, investigating the suitability of different extrapolation methods for various failure modes, performing more calculations on sample ships, and standardizing databases to support intelligent methods. This study provides a reference for the engineering application of direct stability assessment technologies under the SGISC framework.