Quantification of nonlinear phenomena in laboratory-generated random sea waves

Abstract

In this paper higher-order statistical signal processing and Volterra series models of nonlinear phenomena are utilized to quantify the role of nonlinear second-order effects in laboratory-generated random seas. It is indicated how higher-order moment spectra may be utilized to determine a frequency-domain Volterra model of the linear and second-order wave physics occurring between two closely spaced points at which the random wave field is sampled. It will be shown that although the amount of ‘‘energy’’ associated with second-order effects is very small, such second-order phenomena play an important role in the generation of large amplitude waves. By inverse Fourier transforming the outputs of the linear and quadratic Volterra filters, it is demonstrated that the generation of large amplitude waves is due to momentary phase locking of the first- and second-order components. All of the phenomena mentioned above will be demonstrated with the aid of experimental data collected at the Offshore Technology Research Center’s Model Basin. [This study was supported by the National Science Foundation Engineering Research Centers Program Grant Number CDR-8721512 through the Offshore Technology Research Center (OTRC). The Volterra modeling techniques were developed under ONR Grant N00014-92-J-1046 and the Joint Services Electronics Program AFOSR F-49620-92-C-0027.]