The Operational Modal Analysis And The Dynamic Optimization Of Vibration Reduction For Ship Stiffened Structure

A ship is operated under an extremely complex environment, in which waves and winds are assumed to be the stochastic excitations. Moreover, the propeller, host and mechanical equipment can also induce the harmonic responses. In order to reduce structural vibration, it is important to obtain the modal parameters information of a ship. However, the traditional modal parameter identification methods are not suitable since the excitation information is difficult to obtain. Operational modal analysis can identify modal parameters only from the response signals, so it is convenient and feasible in application and has great engineering significance. According to the modal parameters, vibration source can be found, and then one can strengthen the large amplitude positions to reduce the vibration level. There must be a best structural modification plan which fits the vibration reduction requirement. Hence, the FEM and the dynamic optimization theories would be needed here.In this work, the significance of the research and the background of OMA and dynamic optimization have been discussed firstly. Then with the theoretical derivation of two time domain method NExT-ERA and SSI, relevant computer programs are compiled in Fortran. After that, in order to explain the influence of filtering technology, harmonic excitation, SNR and ballast condition on identification accuracy, a large number of contrast experiments are carried out. NExT-ERA is also used to identify the modal parameters of local structures for a real ship. Finally, studies are surrounded with the subjects how to add a typical excitation of ship on a stiffened plate and how to utilize the adaptive ES method for optimizing the position and the stiffness of the springs. They are aimed at finding the best vibration reduction method. According to all the studies in this paper, the results of operational modal analysis and dynamic optimization are relatively ideal, they can be applied in engineering practice.