Numerical simulation and preliminary analysis of spectral slope and tail characteristics using nested WAM-SWAN in a shallow water application off Visakhapatnam

Abstract

Over the past several decades, understanding the nature and slope of high frequency tail in wind-wave modelling studies is extremely important, and its uncertainty amongst −4 and −5 frequency exponent representation was an area of major significance. Hence, an attempt has been made to estimate the slope of the high frequency tail of the wind-wave frequency spectrum off coastal Visakhapatnam using measured data for the period November 2011 to December 2015. The investigation reveals that the high frequency slope of the spectra varied seasonally in the range between −1.80 and −3.77. Annually 75.11% of wave conditions were dominated by swells and the rest 24.89% by wind-seas. Further, the validation of 1D wave spectra at the coastal location utilizing the nested WAM-SWAN setup was promising enough indicating a departure in capturing the peak energies. With the aid of spectral fitting method, the JONSWAP spectra was compared with the measured spectra; which demonstrated significant deviations from the measured spectra revealing high Scatter Index ranging from 0.24 to 1.73. The study aims to report on the uncertainty in the correct slope for the high frequency tail; and the concept of a unified slope at any coastal location remains unpredictable for the oceanographic community.