THE VELOCITY-FIELD BENEATH WIND-WAVES - OBSERVATIONS AND INFERENCES

An extensive set of measurements taken from a fixed tower is used to study the velocity field under wind waves. Velocity measurements, made with miniature drag spheres, arc compared with linear theory estimates of the orbital velocities obtained from measured surface elevation. Results are presented in the context of how well linear theory is able to predict wave-induced forces on cylindrical structural members. Linear theory is seen to predict the flow velocities to within about 7%. Furthermore, both the inertial and drag forces are generally well predicted by linear theory. although small scale turbulent motions not accounted for by linear theory can result in significantly higher inertial forces on smaller structural members.