Water wave diffraction by a cylinder array. Part 1. Regular waves

Diffraction of regular waves by arrays of vertical bottom-mounted circular cylinders is investigated using theoretical, computational, and experimenta l methods. Experiments in an offshore wave basin are designed to measure fr ee surface elevation il at multiple locations in the vicinity of a multi-co lumn structure subjected to regular waves of frequency 0.449 < ka < 0.524 a nd steepness 0.122 < kA < 0.261, where k is the wavenumber, a the cylinder radius and A the wave amplitude. Results from regular wave data analysis fo r first-order amplitudes are compared with those from analytical linear dif fraction theory, which is shown to be accurate for predicting incident wave s of low steepness. Second- and third-order terms are also estimated from t he measured time series, and the effects near a second-order near-trapping frequency are compared to semi-analytical second-order diffraction theory. Linear diffraction theory is shown to be very accurate at predicting the gl obal surface elevation features, even for waves of high steepness. However, violent events and significant nonlinear interactions, including breaking induced by wave scattering, have been observed. Furthermore, second-order n ear-trapping was observed to affect the magnitude of local free surface osc illations as well as scattered far-field radiation.