Objectives Ships are essential for waterborne transportation, and the safety of their structures is of utmost importance. However, during operation, ships may encounter various accidents such as collisions and groundings, which may damage the hull integrity. Such accidents not only pose risks to the safety of the crew and cargo but can also cause significant environmental damage. To ensure ships maintain sufficient safety reserves after damage and avoid catastrophic consequences, accurately evaluating the residual strength of ships in extreme collision scenarios is essential. This study aims to deeply analyze factors such as the shape, area, and location of hull breaches to comprehensively understand their impact on the residual ultimate strength of the hull, providing a basis for assessing residual strength and responding to emergencies after collisions.

Methods First, a simplified numerical calculation method was employed to conduct a series of collision structure response calculations. By considering different speeds, angles, and impact locations, the damage conditions of the hull structure were obtained. Specifically, based on a reference experiment, finite element models of the struck and impact ships were established. The fluid's influence on the ships was simulated using the added mass coefficient to improve calculation efficiency. After verifying the accuracy of the simplified numerical calculation method by comparing with experimental results, it was applied to the collision response calculation of the Coast Guard 2501 ship. Then, using the nonlinear finite-element software Abaqus-Explicit, the residual ultimate strength of the ship was studied. The quasi-static method calculated the residual ultimate strength of the damaged cabin section under collision loads, and explored the influence of different breach forms on the residual ultimate strength of the ship structure.

Results The research results show that two key factors significantly affecting the residual ultimate strength of the ship are the breach area and location. The breach shape has a smaller effect on the residual ultimate strength magnitude but a greater impact on the structural fracture pattern. As the breach area increases with the same shape, the residual ultimate strength of the structure continuously decreases. For example, in the case of a 30-degree impact angle and a speed of 15 kn, the residual ultimate strength decreased by 10% in the hogging state and 18% in the sagging state. When the breach areas are similar in size, as the breach edge becomes sharper, the angle between the fracture path and the middle cross-section of the cabin section gradually decreases, and the fracture location moves towards the center of the structure. In addition, the impact speed has the most significant effect on the breach area, showing a positive correlation. As the impact angle changes, the breach shape also changes. When the impact angle is small, damage along the ship's length is larger, and as the angle increases, damage along the ship's width gradually increases. When the impact angle is 90 degrees, the side breach forms an isosceles triangle, causing greater damage to the internal structure.

Conclusions These findings provide a foundation for evaluating the residual ultimate strength of ships. By varying the impact speed, angle, and location, the effects of the breach area, shape, and location on the residual ultimate strength of the structure can be equivalently simulated. This provides important reference for emergency handling after ships encounter collisions during navigation, helping formulate more scientific and reasonable emergency response strategies and improving ship safety after accidents.