DETERMINISTIC DECOMPOSITION OF DEEP-WATER SHORT-CRESTED IRREGULAR GRAVITY-WAVES

A method is developed for the deterministic decomposition of nonlinear short-crested irregular ocean waves accurate up to second order in wa ve Steepness. Initially, an alternative maximum likelihood method is u sed to determine the directional spreading of wave energy. Then a leas t squares fitting scheme is used to calculate the initial phases of di rectional free-wave components. The effects df nonlinear wave-wave int eractions among these free-wave components are calculated using a conv entional second-order wave-wave interaction model and subtracted from the measurements; The final results are obtained through an iterative process of computing the free-wave components and their nonlinear inte ractions. Given an ocean wave field defined by multiple fixed-point me asurements, the method is capable of decomposing the wave field into a set of directional free-wave components. On the basis of the derived free-wave components, the wave characteristics of the wave field can b e predicted in the vicinity of the measurements. The method has been a pplied to two sets of ocean wave pressure measurements which were coll ected from an array of sensors mounted on an offshore production platf orm near the California coast. satisfactory agreement between the pred ictions based on the decomposed free-wave components and related measu rements indicates the proposed method is reliable. It is expected that this method will have a variety of applications to ocean science and engineering.