A direct calculation approach of determining extreme combined bending moments for fast fine form ships

摘要

For fast fine form ships, direct calculation approaches play more and more important roles towards rational structural design. In this paper, the coupling effects between the higher order harmonic components and whipping components of nonlinear vertical bending moments are described. To further investigate this phenomenon and other nonlinear dynamic effects of wave loadings, a nonlinear time domain strip theory is developed and validated. The nonlinear wave-induced bending moments and nonlinear combined bending moments including whipping components are obtained. Considering the coupling effects and the speed losses of ships in waves, a direct calculation approach of determining extreme combined bending moments for fast fine form ships are presented. Taking the combined bending moments as the dominant load parameter in head sea condition, the matched ship motions, nonlinear wave-induced wave loads and design operational conditions (design wave and ship speed) are obtained at the instant when the combined bending moments reach their maximum to ensure that the most unfavorable responses are achieved. Finally, an application example for a fast containership is presented.