Association Technique Maritime et Aéronautique

Numéro : 2212 - Year : 1993

On the extreme bending moment long term prediction

D. BOOTE, Instituto Policattedra di Ingegneria Navale, Universita di Genova
D. BRUZZONE, Instituto Policattedra di Ingegneria Navale, Universita di Genova
A. CAMPANILE, Dipartimento di Ingegneria Navale, Universita "Federico II" di Napoli


The probabilistic nature of the load effects acting on a ship is well established. The prediction of the long term extreme values is gradually becoming more important with the adoption of reliability-based methods. In this study attention bas been focused on the bending moment: it is commonly divided into two components, the still water and the wave-induced bending moment, which have both probabilistic nature but different variability characteristics. The statistical properties of the total bending moment depend in general on the individual statistical properties of the two components and on their correlation, if any. Based on the short term probability distributions of the bending moment peak and maximum values, a general expression for the prediction of the long term distributions is derived. The reduced form, in the case of the statistical independence of statical and dynamic components, is given as weIl. A set of numerical calculations has been carried out with reference to three typical merchant ships: a bulk carrier, a container ship and a big cru de carrier. Some load conditions have been considered obtaining a set of study cases for each ship. For each load condition the still water moment as well as the wave induced moments for an appropriate set of wave direction and mean zero-crossing period values has been evaluated. Obtained results are analysed in order to identify, from the statistical point of view, the correlation of the moment. On this basis, the dependence of the two load effects under examination is verified.

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