In this paper, to disclose the ringing mechanism, properties of numerical simulated freak waves and the response of small diameter vertical cylinder are analyzed by using wavelet transform analysis. Freak waves are generated based on the mechanism of wave focusing in a 2D numerical wave tank. The nonlinear properties of freak waves are analyzed by using wavelet analysis method. It is showed that in the evolution process of freak waves, besides wave energy convergence due to wave focusing, high frequency energy is generated due to wave-wave nonlinear interaction. And high frequency components of freak waves are discussed. The ringing mechanism is disclosed through the spatial and temporal transformation of wave energy and the spectrum of cylinder response by using wavelet transform analysis.

INTRODUCTION

With the development of harbor, coastal and offshore engineering, more and more coastal and offshore structures are being or will be constructed in deep water. These offshore structures may encounter rough sea climate when freak waves act on the offshore structures and may induce high frequency resonance response - ringing. In this paper, to disclose the ringing mechanism, properties of numerical simulated freak waves and the response of small diameter vertical cylinder are analyzed by using wavelet transform analysis. Freak waves are highly transient and non-linear. Therefore it is not genuine to analyze such waves with the classical Fourier analysis, as it is actually a linear as well as a stationary method. So the alternative method of Wavelet analysis is used to analyze the numerical simulated freak waves and the ringing response of vertical cylinder in this paper. Some fundamental theory and function of continuous wavelet transformation were introduced in the first part of the paper. Freak waves are generated based on the mechanism of wave focusing in a 2D numerical wave tank.

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