The dynamic ultimate strength of a hull girder is a crucial parameter for assessing ship safety. In the context of ships being subjected to dynamic loads such as wave-induced and slamming loads during navigation, making accurate calculation of the dynamic ultimate strength of the hull girder is of great significance for ship designers to predict structural performance and ensure ship safety. However, existing research on the calculation of the dynamic ultimate strength of the hull girder remains limited, and traditional methods often face challenges in terms of computational efficiency. Therefore, this study aims to address the challenge of efficiently calculating the dynamic ultimate strength of a hull girder and proposes a more efficient calculation method.

The proposed approach is the dynamic Smith method, which is based on the traditional Smith method. Firstly, considering the strain rate effect of materials under dynamic load, the Cowper−Symonds model is introduced to modify the yield strength of materials. This modification is essential as the dynamic yield strength of materials increases with the increase of strain rate. Secondly, the stress−strain relationship of stiffened plate elements under different strain rates is taken into account. Xiong's empirical formula for the dynamic ultimate strength of stiffened plates is adopted to correct the stress−strain curve, ensuring more accurate calculation of member stress. Finally, the inertia force generated during the dynamic response of the hull girder structure is considered. By calculating the acceleration caused by the change of the neutral axis of the cross-section in the Smith method iteration process, the inertia force of each unit is obtained, and then the impact of inertia force on the dynamic ultimate strength is corrected.

The results show that when the angular velocity of the end-face rotation is less than 1, the error between the dynamic ultimate strength calculated by the dynamic Smith method and that by the finite element method is less than 10%. Specifically, for the box girder model and the hull girder model of a VLCC based on ISSC 2012, the dynamic Smith method shows strong agreement with the finite element results in the low-to-medium angular velocity range. However, when the angular velocity is greater than 1, the error between the two methods becomes larger.

In conclusion, the dynamic Smith method is a significant extension of the traditional Smith method. Compared with the finite element method, it can remarkably improve the calculation efficiency for calculating the dynamic ultimate strength of a hull girder, especially when the end-face rotation angular velocity is less than 1. For the correction of the stress-strain relationship curve in the dynamic Smith method, when the strain rate is less than 0.4, the stress-strain curve is calculated based on strain rate hardening; when the strain rate is greater than or equal to 0.4, the empirical formula is used. This research provides a novel approach to ship safety assessment and provides valuable guidance for ship design and structural strength analysis.

This study analyzes the influence of lateral loads on the ultimate strength and collapse modes of stiffened panels subjected to combined loads.

Nonlinear finite element software ABAQUS is used to set up numerical models and perform numerical simulations under combined loads on different models. The out-of-plane displacement fields are captured and decomposed with buckling modes. The modal amplitude-axial load curves of different models are obtained, and the deformation process of stiffened panels is quantified. The deformation behaviors and collapse modes of stiffened panels in different load cases are then analyzed in combination with cloud diagrams.

The results show that the lateral load in combined load cases causes the yielding of the stiffeners at the endings before the ultimate state, resulting in the increase of the overall buckling mode's amplitude. As the lateral load increases, the overall buckling of the stiffened panels becomes the dominant collapse mode under combined load cases.

The findings of this study reveal the relationship between local and global buckling mode amplitudes and collapse modes during the deformation process of stiffened panels, and can provide useful references for the design of ship frame structures.

This study aims to explore the law of the critical compression stress of stiffened panels under the influence of in-plane shear load, and whether in-plane shear load combined with lateral pressure will introduce a strong coupling effect.

To this end, nonlinear finite element (FE) software ABAQUS is used to perform numerical simulation analysis under combined loads on a group of FE models. A limit state equation/curve is then derived from the dimensionless calculation results based on the minimum square error method.

The results show that the influence law of in-plane shear load on the critical compression stress of stiffened panels is clarified, and a limit state equation of stiffened panels that considers the effect of shear load is obtained.

The limit state equation in this paper can provide references for modifying the ultimate strength of stiffened panels under the influence of in-plane shear load.