Analysis Of Mechanical Characteristics Of Bolted Rotor System

Bolt joint structure is one of the most important connection in all kinds of mechanical equipment.It has been widely used in the mechanical structure of rotor system because of its simple processing,easy assembly,strong bearing capacity,convenient disassembly,convenient maintenance,good operability,high reliability and so on.However,the mechanical characteristics of bolt connection structure are complex because of the multiple nonlinear characteristics of the bolt joint surface,and the running state of bolt connection structure has a direct impact on the mechanics characteristics of connection surface,and then affects the normal operation of mechanical equipment.In recent years,the rotor mechanical structure develops continuously towards high speed and thrust weight ratio,and the influence of bolt connection structure on mechanical behavior of the rotor system is becoming more and more important.Bolt connection problems also become more and more prominent.Therefore,it is rather necessity to analyze the mechanical characteristics of the rotor mechanical system with bolt joint.This paper researches on the joint stiffness characteristics,natrual characteristics and vibration characteristics of bolt connection structure through establishing the finite element model of thin cylindrical shell structure and rotor drum structure with bolt joint.The research contents of this paper include:(1)The bolt connection of thin cylindrical shell structures are established in this paper based on the ANSYS software.The correctness and the reasonableness of five kinds of different simulation modeling method with bolt connection structure(solid element modeling method with surface contact,mixed element modeling method,interface rigid binding modeling method,thin-layer element modeling method and spring element modeling method)are verified through comparising the results obtained in the literature.(2)A drum rotor structure connected with bolts is established by five simulation modeling methods mentioned above.The natrual characteristics of drum rotor structure are analysed under the free boundary and the boundary conditions with bearing.The simulation results are compared with the experimental results so as to further illustrate the reliability and the accuracy of five methods for simulating bolt joint structures in certain circumstances.Finally,the influences of the inherent characteristics of speed and preload on the system are explored.(3)Based on the research of the inherent characteristics of the bolted rotor drum structures,the reduction modeling method is introduced.A reduced model with beam shell and spring element is established,and the validity and superiority of the reduced model are explained through comparing with the results obtained with solid element model.Based on the statics solution method,the time-varying stiffness of the contact surface is obtained,it is imported into reduced model.Finally,the mechanical characteristics of drum rotor system are analysed,and the influences of bolt number,system speed and bolt pretightening force on the system vibration response are discussed.(4)The influence of bolt looseness on the time-varying stiffness and vibration characteristics of drum rotor system is analysed on the base of researching on the healthy drum rotor system in this paper.And the effects of the number of loose bolts,the total number of bolt,rotational speed,the preload and the style of bolt loosening on the characteristics of the vibration system are studied.The results show that with the reduction of the number of loose bolts,the increase of the total number,system speed and preload,the fluctuation degree of the time-varying stiffness curve in 6 directions decreases,but the stiffness value is increasing,which leads to obviously reduce for amplitude amplification phenomenon of the vibration response of drum rotor system in high frequency band.In addition,the nonlinear also further weakened,and the bolt looseness form on the mechanical characteristics of bolt loosening drum rotor system is of great influence.