Midship Bending Moments Acting on a Destroyer in Irregular Seas

Abstract

In the previous paper, the authors presented the results of theoretical evaluation of heave, pitch, .shearing forces and bending moments of a destroyer in regular head waves. In this paper, they tried the theoretical evaluation of heave, pitch and midship bending moments of the same destroyer in oblique head waves, and eslimated the statistical values of them in irregular head seas by means of St. Denis and Pierson's method. The derived statistical values were compared with those calculated approximately in long-crested irregular head waves.The statistical heaving amplitudes in irregular head seas are nearly equal to the approximately calculated values in long-crested irregular head waves. However, those of pitch and midship bending moment are rather smaller than the approximately calculated values.The amplitude of midship bending moment calculated by the conventional method without Smith's effects is nearly equal to the average of 10% highest values in not-fully developed storm seas corresponding ot 25m/sec. winds of 40 hours duration, and that caluclated with Smith's effects is nearly equal to the average of 10% highest values in fully developed storm seas corresponding to 20 m/sec. winds.