Asymmetry in Directional Spreading Function of Random Waves due to Refraction

Abstract

In this study, a more general directional spreading function is developed that allows for asymmetric directional distributions. For multidirectional random waves that approach the shore obliquely over a planar slope, we demonstrate that directional asymmetry is generated due to wave refraction. The asymmetry created by refraction increases with the offshore peak wave direction. The present spreading function is compared to a preexisting symmetric spreading function and is shown to better capture changes in the directional distribution that occur in a refracting, random wave field. Finally, the new asymmetric spreading function is compared to a long time series of wave directional spectra measured at a nearshore field site. The results demonstrate that refraction-induced asymmetry is common in the nearshore and the asymmetric spreading function gives an improved analytic representation of the overall directional distribution as compared to the symmetric function.