Whipping identification of a flexible ship using wavelet cross-correlation

This paper presents a methodology through which the whipping event can be identified both in terms of the time and magnitude based on the cross-correlation of a continuous Morlet wavelet transform. The scale-averaged cross-correlation of the wavelet power spectrum was introduced to examine the correlation between the two signals with ease and flexibility. First, the cross-correlation of the wavelet power spectrum was checked for an artificially-generated ideal free decaying whipping signal buried in the wave-induced signal. While checking the similitude, the frequency band was adjusted to avoid the effects of the forced vibration component, i.e. wave-induced components, so that only the free vibration component is captured. In addition, the local similitude of the two signals at a given time range was examined using a wavelet coherence function. Finally, the proposed methodology was applied to a more realistic signal that was obtained by running the 3D hydroelastic program, WISH-Flex, where both springing and whipping together with wave-induced signal were all combined. The correspondence of the identified whipping instances between the results, one from the proposed method and the other from the calculated slamming modal force, was excellent (C) 2013 Elsevier Ltd. All rights reserved.