To meet the lightweight design requirements of ship composite structures, this paper proposes a multi-objective optimization method for composite laminate layup. The method integrates the NSGA-II algorithm with the micromechanical Voigt-Reuss model and classical lamination theory. Furthermore, a novel tiered constraint strategy, tailored to the loading characteristics of ship structures, is introduced for the first time in the industry, successfully achieving the multi-objective (dual-objective) optimization of laminate layups. Taking a 40-layer carbon-fiber laminate as an example, the optimized design achieves a 14.6% increase in stiffness and a 98% satisfaction rate of manufacturing constraints compared to conventional methods. Finite-element verification under clamped boundary conditions shows a 32% reduction in maximum stress and a 12% increase in the first-order natural frequency. The application of this method to a high-speed composite catamaran demonstrates that the optimized hull-girder design leads to a 10% reduction in deflection and a 15.6% decrease in the fiber stress utilization factor in longitudinal strength calculations. This study provides a valuable reference for advancing ply-optimization design techniques for ship composite structures.

The structural analysis of the Ro-Ro access demands further investigation due to its complexity and the applicability problems in the requirements of the vehicle deck size of the China Classification Society Rules for Classification of Sea-going Steel Ships. The plate, beam structure and primary supporting members of the Ro-Ro access are studied to establish the descriptive requirements of the vehicle deck plate thickness and the stiffener scantlings by using the theoretical formula derivation and the numerical fitting method. At the same time, the direct calculation requirements for the primary supporting members of the access that meet the unified requirements of the International Association of Classification Societies (IACS) and cover all kinds of loads are formed and then verified through case calculations. The results show that the optimized descriptive requirements and direct calculation requirements have good applicability. This study is of great significance for improving the safety and lightweight level of the Ro-Ro access structure design.