Laboratory Investigation of Nonlinear Irregular Wave Kinematics

A comprehensive experimental study was conducted to produce benchmark wave kinematics data sets for moderate/steep regular and irregular waves. The experiments were conducted in a narrow glass-walled wave tank at Texas A&M University and velocities were measured using an LDV. The time series of surface elevation and wave kinematics were obtained at nine vertical positions including two points above still water level (SWL). The experimental data were compared with linear theory and fully nonlinear numerical wave tank (NWT) simulations based on potential theory, mixed Eulerian-Lagrangian approach, and boundary element method. For both regular and irregular waves, the linear theory tends to overestimate the measured kinematics especially above the SWL, and the fully nonlinear NWT simulations correlate better with experimental data. It is also shown that the exceedance probability for irregular wave crest heights is underestimated by the Rayleigh distribution, while the opposite is true for crest velocities. The joint distribution plots of wave crest/wave period and particle velocity/wave period reveal that there exists strong correlation between them.