Estimation of the Effect of Green Water and Bow Flare Slamming on the Wave-Induced Vertical Bending Moment Using Closed-Form Ex-pressions

ABSTRACT: The effect of impulsive loads like slamming and green water on deck on the wave-induced bending mo-ment is estimated by a semi-analytical approach. The impulse loads leading to transient vibrations are described in terms of magnitude, phase lag relative to the wave-induced peak and decay rate. These loads can be due to bow flare slamming, bottom slamming or green water loads as they all can be characterised by a short duration relative to the wave cycle. The magnitude of the bow flare slamming loads is estimated using accurate results from wedge-shaped sections, Zhao and Faltinsen (1993) and for green water loads the results from Buchner (1995) and Wang et al .(1998) are applied. The phase lag relative to the wave-induced peak and the decay rate are derived mainly from published experimental results, Sikora, (1998). The results are given in closed-form expressions and the required input information for the procedure is restricted to the main ship dimensions: Length, breadth, draught, block coefficient and bow flare coefficient together with speed and heading. The formulas make it simple to obtain quick estimates in the conceptual design phase and to perform a sensi-tivity study of the variation of the ship¿s main dimensions and operational profile. The procedure is applied to three tankers of different length and to a high speed ferry sailing in restricted water. The re-sults obtained are compared to results obtained by use of current classification rules.