Finite element assessment of the double bottom structure under static and dynamic ship loads

This paper presents a finite element strength assessment of a ship double bottom structure. A detailed three-dimensional finite element model is developed to describe the structural arrangement and complexity of the double bottom, including plating and longitudinal and transverse stiffening. Static loads represent both uniform and concentrated loads from various cargo types acting on the inner bottom of the cargo hold. Dynamic loads are represented through equivalent load components derived from gravitational forces and inertia effects associated with vessel motions, enabling the evaluation of dynamic loading effects within a quasi-static analysis framework. Structural response is assessed using stress-based criteria in accordance with classification society requirements. Results demonstrate that dynamic ship loads can notably alter stress patterns and increase stresses in critical regions of the double bottom compared to purely static loading. Results show that whether the cargo carried acts as a uniform load or a concentrated load, the double bottom structure should accommodate these changes in loading for ships operating with different types of cargo. The study highlights the importance of explicitly accounting for dynamic loading effects in double bottom strength verification and confirms the effectiveness of finite element analysis as a tool for achieving a more reliable assessment of ship structural strength beyond simplified rule-based approaches.