Estimation of response amplitude operators for ships via the circular-hyperbolic decomposition

The frequency-domain analysis is commonly used to determine ship-motion cha racteristics, such as transfer functions and Response Amplitude Operators ( RAOs), The Discrete Fourier Transform (DFT) has been the most widely used t echnique to conduct such an analysis. Nevertheless, application of the DFT is not always desirable because of leakage. This problem cannot be eliminat ed unless the frequency content of a signal is known and all frequency comp onents are rational multiples of each other. in this paper, we apply a rece ntly developed closed-form decomposition technique, called the circular-hyp erbolic decomposition (CHD), to estimate the RAOs of coupled heave and pitc h motions using evenly sampled discrete ship-motion data. We show the advan tages of the new technique over the DFT when leakage is present. We also in troduce enhancements to the CHD in terms of a decimation parameter and a ge neralization for multiple signals. The results show that it is a promising technique.