DYNAMIC BEHAVIOR OF VERTICAL CYLINDER DUE TO WAVE FORCE

Abstract

This paper describes the dynamic behavior of a fixed cylindrical pile due to both the in-line or longitudinal force and lift or transverse force in regular waves. Resonant response of the pile due to the lift force in the direction normal to the wave propagation direction is discovered at the period ratios of Tw/Tn=2,3,4,5 and 6 (Tw : the wave period, Tn : the natural period of the pile). Furthermore, the resonant responses in the wave propagation direction due to the in-line force also appear at the same period ratios, in addition to the well known resonance point of Tw/Tn=l. Moreover, dynamic displacements of the pile in the direction normal to the wave propagation direction are longer than those in the wave propagation direction when the period ratio is longer than 1.6 and Keulegan-Carpenter number is larger than 6. Next, for the purpose of the ocean structural design, the methods of estimating the dynamic displacements in both directions and of estimating the dynamic displacements considering both are derived by using Morison's equation and lift force equation formulated by the authors. The displacements calculated are compared exactly with the experimental results to investigate the validity of the proposed method.