Floating breakwater field assessment program, Friday Harbor, Washington

A theoretical model for predicting the dynamic behavior of a floating breakwater is presented along with a report on a field experiment designed to provide basic data for verifying the model. Additional data were taken from the literature and from auxiliary laboratory experiments. The dynamic behavior characteristics investigated were: (1) Total transmitted and reflected waves and their components; (2) wave forces on the breakwater; (3) motions of the breakwater; and (4) forces on the mooring lines. The prediction model was developed from two-dimensional, linearized solutions of the hydrodynamical equations formulated in terms of a boundary value problem for the velocity potential. Some nonlinear effects are considered. Results for the predicted transmission coefficients were in good agreement with laboratory and field data, and they showed how the influence of fixed-body transmission, and of sway, heave, and roll motions on the transmission coefficient changed with increasing values of the parameter, beam (width) to wavelength ratio. The shape of the curves predicting the mooring line forces as a function of the beam (width) to wavelength ratio (or of wave frequency) followed those for the measured responses, but predicted magnitudes did not agree closely with measured values. The floating breakwater at Friday Harbor, was instrumented. Statistical summaries of all data are presented with analyses of selected transmitted waves, transmission coefficients, and acceleration components.