Research On Vibration Control Performance Of The Nonlinear Spatial Suspended Mass Pendulum

The tall and slender structure system is sensitive to the environment of strong wind,earthquake load,and easy to result in the fatigue damage due to the dynamic vibration and even the collapse in extreme conditions.Thus,it is very important to control the vibrations of the high-rise structure,such as transmission towers.As a kind of passive control devices,a suspended mass pendulum(SMP)has the advantages of simple working,better vibration suppression effect,and convenient installation.SMPs and similar pendulum-like devices are widely employed because of their reliability and easy maintenance in contrast to other low-cost devices.The analysis model of a SMP control system is usually simplified as a planar model,which only considers the swing angle in-plane.However,out-of-plane vibrations of a pendulum are inevitable and are significantly more complex than that assumed in the planar model.Due to the impact of multi-dimensional earthquakes,the real pendulum is of a spherical vibration character.Hence,it is necessary to describe its movement in two coordinates ? and ? on a spherical surface.Thus,the spatial vibration modelshould be considered to compute the dynamic response of the SMP.The vibration frequency and characteristics of the new model are very different from the previous ones.The research work in the thesis includes the following aspects:(1)The failure phenomena of the tall and slender structure system are listed.The basic concepts and types of structure vibration control are illustrated.And the research status of suspended mass pendulum are introduced;(2)The kinetic equations of the spatial SMP model coupled with a single-degree-of-freedom(SDOF)structure are established considering the swing angle of SMP in-plane and out-of-plane.The vibration characteristics of the pendulum and their influence on the dynamic response of the structure are numerically analyzed.A parameter study is performed considering the influencing parameters of the control system,including excitation periods,pendulum length,mass ratio,and amplitudes of the horizontal rotation angle at the maximum displacement of the structure.(3)A flexible transmission tower is studied in this dissertation.The Finite Element Model(FEM)of the transmission tower is introduced,and the first six modals(frequencies and mode shapes)are derived by modal analysis.Then the FEM of the transmission tower is simplified,and the comparison between the simplified model and the original is made for proving the accuracy of the simplified model.Themotion equations of the nonlinear spatial SMP coupled with a transmission tower are set up.The comparison between the responses of a planar SMP system and a spatial SMP system excited by El Centro wave(SW)is made for studying the effect of the out-of-plane vibrations.Then eight earthquake records are selected to represent different site conditions.The spatial vibration characteristics are further analyzed by the comparisons of the responses under different site conditions,which also show the necessity of considering the out-of-plane vibrations of the SMP.(4)A two-layer frame model is selected to test the vibration characteristics and the vibration reduction effect of the SMP on the shaking table.Different kinds of sine excitations and seismic excitations are applied to the experimental model and the acceleration data of the shaking table and structure are collected.The vibration reduction effect of the SMP is evaluated by comparing the dynamic responses of the structure with and without control.Comparing the dynamic responses of the structure under the one-way and the two-way excitations,the influence of the out-of-plane vibration on the vibration reduction effect of the SMP is analyzed,which confirms the rationality of the spatial model proposed in this paper.