Study On The Stress Characteristics Of Dropper Under A Dynamic Load

Catenary is a special form of transmission line erected over high-speed railways.Its function is to provide electric energy for electrified trains.Its main components include messenger wire,dropper and contact wire.Dropper is used to keep the contact wire and connect it with messenger wire,which ensures the normal passage of current.Thus,dropp er should have the strong fatigue resistance.The cyclic stress acting on dropper may lead to its fatigue fracture,when the pantograph slides over the contact wire at a high speed.Hence,there is a major hidden danger in driving safety.Therefore,it is of great significance to study the stress characteristics of dropper.The main contents of this paper are as follows:1.The stress calculation equation of dropper is deduced theoretically by using the section method.The partial differential equations of the calculated stress are transformed into the difference equations by using the finite difference method.The flow chart is drawn,which lays the foundation for the subsequent development of MATLAB numerical calculation program.2.The effects of the load location on the stress of dropper are investigated.Firstly,a span of dropper in a simple chain suspension catenary is selected as the research object.Contact wire is treated as the beam element,and the free and forced vibration equations of the equal-section beam are used to derive the contact wire response equation,so as to determine the initial and boundary conditions of each dropper.Secondly,a MATLAB program is compiled to numerically calculate the stress of each dropper,combined with the stres s calculation equations of dropper.Finally,the stress changes of each dropper are observed numerically and the effects of the load location on the stress of each dropper are analyzed by changing the load location.The results show that the stress of dropper increases significantly under a dynamic load in contrast to a static load.There are three stages during the period of the stress changes of dropper,including instant rebound,attenuated vibration and bending compression.The closer distance away from the load is,the larger the vertical displacement of dropper is,which results in the corresponding increases of its stress amplitude and the maximum tensile stress.The load location has a significant impact on the stress changes of dropper.Compared to the condition of the load in the middle,the load acting on the edge of the contact wire could induce the larger tensile stress when both ends of contact wire are considered as free boundaries.Therefore,it is necessary to add supports at both ends of e ach span.3.The effects of contact wire tension on the stress of dropper are performed.Under the condition of adding supports and applying tension at both ends of contact wire,the response equation of contact wire is derived.Furthermore,the initial and boundary conditions of each dropper are determined.Combined with the stress equations of dropper,the stress of each dropper is calculated.The results indicate that the increase of supports and tension make the stress amplitude and the maximum tensile stress of dropper decrease greatly compared to the condition of no supports and no tension.The larger the tension is,the lower the stress amplitude and the maximum tensile stress of dropper are.When the tension is low,there are still three stages during the period of the stress changes of dropper that it locates near the load.Namely,they are instant rebound,attenuated vibration and bending compression stages.However,the attenuated vibration stage disappears when the tension is increased to a certain extent.Therefore,controlling the vibration response of contact wire could effectively reduce the stress amplitude and the maximum tensile stress of dropper,so as to improve the working reliability of dropper.