Assessment of the ultimate and residual strength of a ship's hull
Abstract
The Common Structural Rules (CSR) developed by the International Association of Classification Societies (IACS) stipulate the incremental-iterative method as one of the standard methods for assessing the ultimate/residual strength of an intact or damaged ship's hull. Based on the force equilibrium condition (FEC), the position of the neutral axis (NA) of the cross-section is determined at each increment of curvature. However, in cases of non-uniform loading or damage due to collision/grounding, which lead to asymmetry in the ship's hull cross-section, the NA undergoes both translational and rotational motion simultaneously. To account for the rotational motion of the NA, the force equilibrium condition is extended to a vector equilibrium condition (VEC), and the Sequential Least Squares Quadratic Programming (SLSQP) algorithm is employed to simultaneously determine both motions of the NA. For a container ship under upright, intact condition, the numerical calculation results show good agreement with existing methods, including those outlined in the reports of the International Ship and Offshore Structures Congress (ISSC). The influence of the NA rotation angle on the ultimate/residual strength at various ship heel angles is discussed. Owing to the improved convergence rate and required accuracy of the SLSQP algorithm, the proposed method can be used for a rapid and rational assessment of hull strength under adverse conditions.
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