A stochastic analysis method is described to predict long term wave induced global design loads for ships in random seas. The method is based on nonlinear wave induced load effects; specifically, on the concept of an ensemble of nonlinear transfer functions, where each transfer function is valid only for a certain range of wave heights. The proposed method constitutes a practical alternative to nonlinear time domain simulations. These so called (nonlinear) pseudo transfer functions were obtained using a nonlinear correction to account for three dimensional effects of the hull shape and the non-vertical sides of the ship's ends as exemplified by local bow and stem flare. Extreme flare, characteristic of many modem containerships, is a common design feature to significantly increase the ship's container deck carrying capacity. Therefore, for these ships, reliable wave induced design load predictions must account for nonlinear effects of this kind that even consider the breaking of higher amplitude waves as they ascend the ship's sides. In the stochastic analysis, there remained one uncertainty regarding the association of the wave height H, used to obtain these pseudo transfer functions, with the significant wave height H{sub}(1/3) of the corresponding natural seaway, used for short-term statistical analyses. Our sample computations of midship vertical bending moment for three modem containerships of different carrying capacities ranging from 600 to 8000 TEU shows that this uncertainty did not significantly affect results. Bending moments based on wave heights equal to the 50 percent fractile (H = 0.59 H{sub}(1/3)) as well as bending moments based on wave heights equal to the average of the 1/10th highest waves (H = 1.27 H{sub}(1/3)) could both be used alternatively without yielding significantly different results. To obtain design values, long-term statistical analyses were then conducted as in the standard linear approach.
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