Abstract
The method for the prediction of extreme vertical wave bending moments on a passenger ship based on the hindcast database along the shipping route is presented. Operability analysis is performed to identify sea states when the ship is not able to normally operate and which are likely to be avoided. Closed-form expressions are used for the calculation of transfer functions of ship motions and loads. Multiple operability criteria are used and compared to the corresponding limiting values. The most probable extreme wave bending moments for the short-term sea states at discrete locations along the shipping route are calculated, and annual maximum extreme values are determined. Gumbel probability distribution is then fitted to the annual extreme values, and wave bending moments corresponding to a return period of 20 years are determined for discrete locations. The system reliability approach is used to calculate combined extreme vertical wave bending moment along the shipping route. The method is employed on the example of a passenger ship sailing across the Adriatic Sea (Split, Croatia, to Ancona, Italy). The contribution of the study is the method for the extreme values of wave loads using the hindcast wave database and accounting for ship operational restrictions.
Highlights
The extreme wave loads on ships are usually determined by weighting short-term sea state responses by their probabilities of occurrences
Extreme value adopted as the design value of global wave load is usually calculated from the long-term distribution for exceeding probability of 10−8
The procedure recommended by the International Association of Classification Societies (IACS) for the computation of long-term global wave loads on ships is given in [1]
Summary
The extreme wave loads on ships are usually determined by weighting short-term sea state responses by their probabilities of occurrences. The possibility that the shipmaster changes heading angle in extreme sea conditions is not considered [2] Such maneuvers are normally taken to reduce excessive ship responses in heavy weather, most often the ship rolling motion [3]. To efficiently employ the wave hindcast database for the computation of wave loads on ships, it is essential to account appropriately for weather routing effects. A method is proposed to calculate extreme wave loads that a ship encounters along a specific route using the hindcast database and accounting for operational restrictions. The most probable short-term extreme vertical wave bending moments are determined for each sea state that the ship could encounter.
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