Assessment of residual ultimate strength of an asymmetrically damaged tanker considering rotational and translational shifts of neutral axis plane

This paper provides two convergence criteria to find translational and rotational locations of the neutral axis plane (NAP) for intact and damaged vessels. Definition of three types of asymmetries of a ship section is proposed: material-, load-, and geometry-induced asymmetries. Concept of moment plane (MP) is introduced to define the heeling angle of ship section. It is suggested that force equilibrium and force vector equilibrium criteria are simultaneously necessary to determine new position of NAP due to both translational and rotational shifts. In order to verify the applicability of the convergence criteria, midship section of a VLCC is selected with two types of asymmetries: one is due to heeling of a section and the other due to hull damages. 0° and 30° heeling conditions and collision-induced and grounding-induced damage extents based on ABS Guides and DNV Ship Rules are taken into account. The various section properties are compared according to the area reduction ratios for each heeling and damage cases. It is shown that ultimate hull girder capacities are closely related to the area reduction due to the damages. Using new convergence criterion, mobility of NAPs and force centroids in elastic and inelastic regimes are visually provided.

► A new convergence criterion for rotational movement of neutral axis are proposed.
► Three asymmetry conditions of hull sections are defined; material-, load-, and geometry-induced asymmetries.
► Deterministic damages due to collision and grounding by DNV and ABS are provided.
► Mobility of the instantaneous neutral axis is graphically shown at elastic and plastic moment stages.