Research On Low Frequency Spectrum Optimization Design Of Large And Complex Structure

Since the 21st century, countries around the world in construction of ships and equipment increasingly larger and more complicated, diversified, which lead to serious problem on structural vibration. At the same time,The International Standard Organization 6954:1984, 2000(E) Mechanical Vibration and Shock-The Integrated Evaluation Standard of Commercial Vessel raises higher claim to plat and vessel vibration. Therefore, how to decrease vibratory response of large complicated structure efficiently, especially particular resonance response of line spectrum in low frequency caused by shipboard equipment, has been problem demanding prompt solution in engineering field.Thereby, this thesis elaborates methods to control vibration of ships and marine structures,analyses the disadvantage and difficulty of several kinds of ways to control vibration. The analysis conclusion indicates that: Active Control Technology has not been widely employed in project because ACT needs input of outside energy and some other problem for newly developing, such as intricate technology, high construction cost, and low reliability and so on. Passive Control Technology will be applied better since its simple construction and favorable price. What's more, it is easy to maintain and no need to receive outside energy.Aimed at above questions, the paper based on Principle of Vibration Absorption introduces the dynamic vibration absorber to control vibration of large complicated line spectrum in low frequency,which forms the systematic methods of dynamic vibration absorber applied to vibration-controlling of low frequency of large complicated structure.Firstly,this thesis set forth structural dynamic principle of vibration absorption,establishes mathematical model of dynamic vibration absorption and obtains the amplitude function of steady state response of main structure in the vibration system. Then, the paper discusses value range of the optimal mass ratio, the optimal damping ratio, the optimal frequency ratio and the optimal arrangement quantity and place of dynamic vibration absorption. The result shows that under the condition of other system parameters of dynamic vibration absorber remain unchanged, the steady state response amplitude of main structure in the vibration system changes with the change of mass ratio, damping ratio and frequency ratio, vary with the optimal arrangement quantity and place different. At last, on the basis of theory study, the optimal solution of above theory on the effectiveness of elastomer according to plate frame structure.On such bases, the systematic predicting methods chain of dynamic vibration absorption applied in large complicated line spectrum in low frequency are organized and formed. Take vessel and the typical connected components of marine structures as examples to carry out the effective validation of systematic predicting methods in dynamic vibration absorption. The results show that the systematic predicting methods in dynamic vibration absorption can be applied in vessel and the typical connected components of marine structures well. The vibration response of typical inspection location keeps pace with the changing tendency and theoretical derivation of parameters of dynamic vibration absorber. The effectiveness of systematic predicting methods in dynamic vibration absorption is validated. Methods are provided for large complicated structure line spectrum in low frequency to predict quantitatively and do other research.At last, the paper applies systematic predicting methods of dynamic vibration absorption to the predicting analysis of vibration produced by superstructure of offshore platform, and analyzes the changing tendency of the amplitude of vibration response of typical cabin in the superstructure with the parameters changing of the dynamic vibration and absorber. This thesis also proposed the optimization design to control large complicated structure line spectrum in low frequency and provides the reference to inhibit or decrease the vibration response of full scale structure caused by vessel and marine structure.