Abstract

The paper presents a verification of 1D and 2D wave spectral formulations against measured data, aiming at validating and possibly improving the empirical formulas used in the definition of spectral parameters. Jonswap spectral formulation has been employed, with Mitsuyasu-like directional spreading function. The verifications of the empirical formulations commonly used in engineering practice, have highlighted a reasonable agreement with measured data, although extremely dispersed.

INTRODUCTION

In the engineering application, a sea state is generally completely described using spectral forms. The most common spectral forms for describing the frequency distribution of the energy of a sea state are usually the Jonswap and Ochi-Hubble formulations. Their efficacy has been demonstrated by numerous studies and publications related to various world locations such as the one by Gao et al. (2020) and Piscopia et al. (2003). To describe the directional distribution, equations such as the one proposed by Mitsuyasu et al. (1975) or the Wrapped Normal one, are generally used. The parameters of these relationships would require calibration based on spectral measured data at the site of interest. However, measurements of spectral data are rarely available, and, for this reason, empirical correlations from literature are often used.

In this study, Jonswap spectral formulation have been employed, with Mitsuyasu-like directional spreading function. For Jonswap spectrum, the relationships for spectral parameters proposed by DNVGL-RPC205 and the HYPA relation for spectral amplitude have been considered. The aim of this paper is to use a series of measured spectral data from Mediterranean Sea and Barents Sea, to verify how these empirical relationships correctly estimate the measured spectra. In particular, as for 1D spectra, the reconstructed spectra from measured data will be compared with the Jonswap formulations while, as regards 2D spectra, the results obtained using the directional spreading function reconstructed from measure data, will be compared with those obtained using the empirical spreading function of Mitsuyasu et al. (1975) and the expression of Goda and Suzuki (1975) for the spreading parameter which can be improved by a slight modification of coefficients. The measured data have however shown high dispersion. It can therefore be said that any empirical relationship does not always provide an exhaustive description of the spectrum. These uncertainties should be considered in engineering practice by introducing appropriate precautions into design.

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