The external loads and ultimate load-carrying capacity are two important aspects to evaluate the safety and reliability of the ship. In this study, fluid-structural interaction calculation and model collapse test are combined together to obtain the ultimate strength of an aluminum alloy model with three holds. Distributed optical fiber sensors and fiber bragg grating sensors are used to establish a monitoring system. The deformation form, stress distribution, and ultimate strength of ship structure in waves are obtained. The results show that out-of-plane distortion increases and initial yielding occurs earlier because of water pressure, which leading to the reduction of structural ultimate strength. This study has great significance for structural health monitoring and structural design of large opening hull structures.
It is reported that the economies of the Yangtze River Economic Belt make up about 46% of China's GDP in 2020, and more than 10% of it comes from the shipping industry of the Yangtze River. With the active development of the Yangtze River Golden Waterway, the design and manufacturing of river-sea-going container ship, which has many advantages such as energy-saving, economical, environment-friendly, and efficient, are in short supply. However, the river-sea-going container ship sails both in the rivers and along the coast, and the wave load varies greatly. The feature of a large opening leads to the low bending and torsional strength of the structure. If the external load exceeds the ultimate load-carrying capacity of the structure, the ship will collapse. Therefore, it is essential to research the external load and ultimate load-carrying capacity of the ship structure to ensure the riversea- going container ships with large opening navigating safety.
Since the concept of ultimate strength was proposed by Caldwell (1965), scholars around the world have done a lot of research. In earlier research, structural safety was evaluated without considering the interaction between load and structure. This method is more convenient but less accurate. With the improvement of computer performance, more and more scholars pay attention to the load-structure integrated computational analysis considering the fluid-structure interaction. Yao (2009) used the three-dimensional Singularity Distribution Method to calculate the modal and external load distribution of the ship. The nonlinear finite element method and the ideal structural element method were combined together to analyze the collapse process of ship structure in waves. The calculated numerical results were consistent with the theoretical analysis, which expanded the research direction of threedimensional potential flow theory for the structural response analysis of ship hull in waves. On the basis of Yao's research, Pei (2015) proposed an ultimate strength evaluation system combining fluid-structural interaction calculation and idealized structural unit method. The collapse response and progressive collapse behavior of the structure in the midship could be obtained through comprehensive analysis. Takami (2018) developed and validated a simulation method to predict global and local hydroelastic response of a ship that couples CFD and FEA. The result calculated by CFD-FEA was compared with linear/nonlinear strip method, 3D panel method, and towing tank test results. The effectiveness of the CFD-FEA coupling method is confirmed. On this basis, Takami (2021) introduced the combination of the Reduced Order Method (ROM) and the First Order Reliability Method (FORM) to replace the CFD-FEA method to predict the extreme value of wave bending moment.
