Paddle Generated Waves in Laboratory Channels

The wave field generated by single frequency and biharmonic motion of a plane paddle wavemaker is investigated theoretically and in laboratory experiments. Regardless of the detailed paddle geometry, nonlinear effects associated with the paddle boundary conditions introduce free waves which are the order of forced nonlinear corrections (Stokes type) associated with nonlinearities of the surface boundary conditions. For simple harmonic paddle motion at frequency σ, the largest free waves have frequency 2σ. For biharmonic paddle motions of frequencies σ₁ and σ₂, additional free difference frequency (—σ₁—σ₂—) long waves are generated. These can resonate in a closed basin, leading to undesired modulations of breaker location and other shallow water phenomenon.