Kinematics measurements of regular, irregular, and rogue waves by PIV/LDV

Abstract

A comprehensive experimental study was conducted to produce benchmark wave kinematics data for five different regular waves and the maxima of four different irregular wave trains. Two of the irregular waves generated are in the category of rogue waves. A series of experiments were conducted in a 2-D wave tank at Texas A&M University to measure wave velocities and accelerations using LDV and PIV systems. The wave crests of regular and rogue waves are the focus of this study. With the measured wave velocity field, the wave accelerations were computed using a centered finite difference scheme. Both local and convective components of the total accelerations are obtained from experimental data. Also, the nonlinear wave forces on a truncated slender cylinder are computed by applying the obtained wave kinematics to the Morison equation. The force results based on measured wave kinematics are compared with those based on the kinematics of linear extrapolation, Wheeler stretching, and modified stretching. The Wheeler stretching method generally underestimates the actual wave kinematics. The linear extrapolation method is very sensitive to the cutoff frequency of the wave spectrum. The modified stretching method tends to predict the maximum value of wave kinematics above the still water level (SWL) well except for the convective acceleration. The magnitude of convective acceleration in the regular waves was negligibly small, whereas the magnitudes of horizontal and vertical convective accelerations in the rogue wave were increased rapidly above the SWL.