Dynamical Characteristic Analysis Of Vibration Isolation System For Marine Power Equipment Based On Fractional-order Theory

Marine power equipment,which is one of the main sources that produce severe vibration and noise,has been an important index for new types of naval ships recent years.The conventional analysis of marine power equipment is mainly based on linear system modeling analysis,which ignored the effect caused by nonlinearity.With the improving requirements for the vibration isolation performance of naval ships,the analytical result that based on linear theory often has a certain error in accuracy.For this reason,based on the fractional order theory,two mechanical models of vibration isolators are established in this article.The main research contents of this article include the following aspects:(1)Grünwald-Letnikov(G-L)fractional-order definition is applied in identification of the discrete numerical solution of vibration isolation system.Then,based on MATLAB GUI platform,The software that used in dynamical characteristic analysis of typical fractional-order vibration isolation system is developed.(2)This article established dynamical equations for semi-active particle damper according to conventional linear mechanical model and fractional-order mechanical model,respectively,and the dynamical parameters of both mechanical model are identified by experimental data.After comparing the semi-active particle damping fractional-order model with its conventional linear mechanical model,it shows that fractional-order dynamical model has a more simper form and better precision than conventional dynamical model.Then a dynamic model of a SDOF nonlinear vibration isolation system with semi-active particle damping equipment is given in this article and its analytical solution that is compared with G-L numerical solution is obtained by averaging method.Finally,the effects of fractional-order parameters change on the amplitude-frequency response of vibration isolation system are analyzed and the nonlinearities caused by the nonlinear parameters are studied.The results show that with the increase of fractional order parameter or the decrease of fractional-order coefficient,the amplitude-frequency response of vibration isolation system will present a downward trend.Besides,the nonlinear stiffness parameter will cause amplitude jump phenomenon and the pitchfork bifurcation phenomenon will be caused by nonlinear damping parameter.(3)The fractional-order theory is used in this article to establish a dynamical model of air spring vibration isolator,whose accuracy is verified by experiments.Then a fractional-order mechanical model is established for investigation of double-layer vibration isolation system with an air spring vibration isolator.The effects of fractional-order coefficient on the vibration isolation system are analyzed continually,and that,with the increase of fractional-order coefficient,the amplitude-frequency response decreases but causes nonlinear phenomenon on the vibration transmission rate of the vibration isolation system.In general,the fractional-order dynamical models of semi-active particle damping equipment and air spring vibration isolator are established in this article,respectively,and the vibration characteristics analysis of fractional-order vibration isolation system that including above isolators are carried out according to experimental test and theoretical analysis.The achievements obtained by this work are aiming to provide experiences for the dynamical analysis of marine power equipment,which also provide references and new thoughts for application and development of vibration isolation in ship engineering field.