Investigation of the Applicability of the Third Degree Functional Polynomial Model to Non-Linear Ship Motions Problems.

摘要

The objectives of the present work were to explore the applicability of the third degree functional polynomial model to nonlinear seakeeping problems, and to attempt the development of an approach by which third degree nonlinearities in observed responses of ships to waves might be interpreted. Basic approaches to the deterministic characterization of such systems are discussed, and basic identification theory for the random sea case is developed. The latter involves the estimation of a new entity called the cross-tri-spectrum. Simulations of the response of a system with quadratic and cubic nonlinearities was carried out for random excitation. The qualitative influence of cubic nonlinearities on random time domain response as well as response spectra are discussed. A first attempt was made at cross-tri-spectral identification of cubic response from samples of random excitation and response. Though this attempt was partially successful, the numerical method employed was not satisfactory in an important way and further development is indicated. (Author)