engleski

Hull-girder reliability of new generation oil tankers

A series of new generation oil tankers is presently under construction. These ships differ from traditional oil tankers by their unusual form and therefore direct hydrodynamic analysis is used to determine design vertical wave bending moments instead of adopting IACS rule values. The purpose of the paper is to quantify changes in hull-girder reliability resulting from the new design features. To achieve this, first-order reliability analysis is carried out with respect to ultimate collapse bending moment of the midship cross section of a new generation oil tanker and of a conventional “ rule” designed oil tanker. The stochastic model of wave induced bending moment is derived from direct hydrodynamic analysis performed according to IACS Recommendation No.34 (2000). The probability distribution of the still water bending moment is assumed based on data from loading manuals. The model uncertainties of linear wave loads, non-linearity of the response as well as load combination factors are included in the reliability formulation. The reliability analysis is performed for three relevant loading conditions: full load, ballast and partial load and for two states of the hull: the “ as-built“ hull and “ corroded” hull according to anticipated 20-years corrosion. One of the most interesting conclusions from the study is that the annual hull-girder reliability of new generation oil tanker is increased considerably compared to the conventional oil tanker. Sensitivity and parametric studies are performed with respect to random variables representing modelling uncertainties. The results of a sensitivity study enable sorting of pertinent variables according to their relative importance, while parametric study is used to quantify changes in the reliability indices for moderate variation of input parameters. Fruthermore, some other results and discussions are presented pointing out the benefits of introducing the ship reliability methods in design practice, especially if this refers to new designs.

tanker structures; longitudinal strength; structural reliability; stochastic model of loads; uncertainties

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