The Study On Modal Parameters Identification For Ship Structures Based On Ambient Excitation

Modal parameters are very important factors on dynamic performance of structures. Whether the modal parameters are proper influences the performance of structures directly. While, the traditional methods of experimental modal test can't be very satisfactory because of the difficulty in getting the complete information of input and output, and the difficulty in exciting such big structures like ships. Modal parameters identification method based on ambient excitation can get the modal parameters just knowing the vibration responses, which has a wide application prospects in mega-structures.In this paper, research is mainly focused on the application on ship structures of this method. The algorithm which combines Natural Excitation Technique and Eigensystem Realization Algorithm (NExT/ERA) is used in the identification process. And through a series of model experiments and a ship structure test, its validity and feasibility in ship structures are verified.First, the importance of modal parameters to engineering structures is discussed, and in this paper, the difference between the modal parameters identification methods under ambient excitation and traditional modal test are discussed; What's more, theories and characteristics of algorithms on modal parameters identification based on ambient excitation are introduced.Second, characteristics of the ambient excitation of ship structures are discussed, and the excitation can be assumed as a combination of white noise and harmonic components.Third, the NExT/ERA method is introduced in detail, and the corresponding Matlab program is written, then experiments of a simply supported beam, a ship structural model and a stiffened plate model are done to verify the feasibility of the program. Through calculation and experiments, the treating methods in the situation that harmonic excitation exists are discussed.At last, by an actual ship structure's operational modal analysis, the feasibility of modal parameters identification method based on the ambient excitation that used in ship structures is verified, which provides experimental and theoretical bases for the subsequent work.