Extraction of nearshore spectrum by energy-conserved zero-up crossing method and comparison with the TMA spectrum

Abstract

The present study introduces the zero up-crossing transform (ZUCT) method which includes energy conservation as well as the spectrum of the desired spectral resolution (df) near shore. The wave height obtained from the zero up-crossing method cannot satisfy the variance of surface elevation because it is determined by the difference in vertical height. Therefore, this study suggests a wave height calculation method that conserves energy using the zero up-crossing period, Tz. The wave spectrum obtained by ZUCT was compared with that obtained using the conventional Fourier transform (FT). Furthermore, it also shows satisfactory similarity with the JONSWAP spectrum for a specific df. This ZUCT method was compared with the FT for the data observed in Gonghyunjin and Heukdo, which have markedly different wave characteristics. In addition, considering the observation depth (approximately 30 m), it was compared with the TMA spectrum. As a result of comparison with the TMA spectrum, it was determined that the spectral peak value was not well reproduced because of the constant applied peak enhancement factor γ of 3.3. Therefore, by presenting a method to determine the peak enhancement factor from the dimensionless spectral peak variable, the spectral peak of JONSWAP was accurately reproduced.