Water Particle Velocities in Regular Waves

Abstract

The Eulerian water particle velocities under paddle‐generated regular waves in a closed channel are not always accurately predicted by a conventional application of Stokes' first, second or fifth order wave theory. Phenomena, which give rise to errqrs, include mass‐transport, the partial clapotis formed by reflection from the spending beach and the free second harmonic wave produced by the sinusoidal motion of the paddle. Measurements taken with a Laser Doppler Anemometer indicate that the amplitudes predicted for the second harmonics of the velocity components can be over 100% in error. Furthermore, there is a mean horizontal velocity which is often greater than the amplitude of the second harmonic and can be 20% of the amplitude of the first harmonic. The observed mean velocities are compared with predictions based on Longuet‐Higgins' conduction solution. Because the design of a wave facility influences the particle kinematics, it is concluded that local empirical data will generally be required to achieve accurate predictions.