Damping ratio identification using a continuous wavelet transform to vortex-induced motion of a Truss Spar

Abstract

The paper presents an application of the continuous wavelet transform (CWT), a time-frequency method based on Gabor wavelet function and widely used in many engineering fields, in ocean engineering for the first time. The advantage of the CWT over commonly used methods like time-domain and frequency-domain methods is its ability to decompose signals simultaneously both in time and frequency. The essential information is the wavelet ridge where the modal parameters like the damping ratio and frequency can be extracted. This paper developed an algorithm to extract the wavelet ridge from the wavelet transform. The method is validated by a numerical example which is similar to the experimental data. Finally the method is applied to estimate the damping ratio and frequency of a Truss Spar in vortex-induced motion. The results indicate that the CWT method performs remarkably well.