| Abstract: | We present a new signal processing and testing technique by using a higher statistical moment, the bispectrum, to determine the damping ratio and natural frequency of offshore structures excited by both unexpected Gaussian forces and known non-Gaussian driving forces. Due to unexpected exciting forces, such as turbulence, in the ocean, environment, the transfer functions of offshore structures are not determined through operating a known driving force and measuring its response. In order to overcome this problem, some of the existing techniques try to model the unexpected forces as white Gaussian forces or almost white Gaussian forces and determine the modal parameters from the response only. Others try to average the input and output to suppress unexpected parts. Our method uses third-order moments to keep the influence of the unexpected Gaussian forces away from the determination of the transfer function of the structure which has linear properties. We model the third-order moment property of the response function with a bispectral model. The modal parameters can be calculated from the estimated model's coefficients. The method has been proven by a number of simulations. |
