Research On Multi-shaft Coupling Vibration And Dry Friction Damper With Dual Rub Impact Of Helicopter Tail Driveline

Helicopters play an important role in disaster relief,transportation,and military.One of the three key components in helicopters is the transmission system,among which the tail-rotor driveline is responsible for transmitting power to the tail-rotor.The supercritical design of the driveline in domestic and foreign helicopters has many advantages,but the vibration amplitude increases sharply when it crosses the critical speed.It will easily cause overload or make the shaft collide with other components if the vibration is not properly suppressed,a damper should be added to the driveline.This thesis focuses on a dry friction damper.The damper structure,material,and parameter range are only designed empirically,lacking quantitative parameter guidance.It is costly to analyze these parameters completely by experiments.Therefore,it is necessary to model and simulate the dynamics of the system to obtain the dynamic response region and boundary,and to understand the influence of each parameter,which is important for the reasonable configuration of the damper parameter.The research of this thesis includes:(1)Considering the continuous parameter distribution of the flexible shaft,the energy equation of bending and twisting vibration of the shaft is established.On the basis of the structure of hexagonal diaphragm coupling,the static misalignment and dynamic misalignment amount are superimposed to obtain the forces acting on each bolt connected due to the deformation of the diaphragm.The parallel and angular misalignment forces acting on the shaft are obtained,considering the rotation effect of the shaft.The multi-shaft coupling vibration equation of the tail driveline is obtained by using the Galerkin method and Lagrange equation.Based on the supercritical tail driveline of a helicopter,the high-order harmonic and subcritical resonance caused by misalignment are analyzed.(2)The damping stages of the dry friction damper are divided and the switching conditions of each stage are analyzed.Rub impact model of each stage is established with the change of DOF of the damper and the interaction of internal components.The dampers are modeled as a suspended double nest stator to form a dual rub impact model with the shaft.The variable impact stiffness of the inner layer rub impact is obtained by FEA and the contact theory.The nonlinear impact stiffness of the outer layer rub impact is obtained from the damper’s structure.Finally,the dynamic equation of vibration suppression of helicopter tail driveline is derived.The improved Adams-bashforth method is utilized for numerical simulation.The damping characteristics of the damper at each stage are analyzed;The variation of the periodic solution and its stability throughout the transcritical speed process is studied;The coupling vibration characteristics of misalignment and rub impact damping are analyzed.(3)To provide all-round responses and boundaries of the helicopter tail driveline,the boundary speed entering the rub impact region is analytically deduced.The dynamic stiffness decoupling is proposed to obtain the periodic solution of each stage and the boundary conditions of synchronous full annual rub.The intrinsic frequency of the coupled system of the shaft and damping ring is derived.Based on this frequency,the trigger speed of the reverse whirl considering forward eccentric excitation is derived by the multiscale method.The backward whirl frequency of the shaft is derived.Simulation is conducted to analyze the response characteristics of the multi-stage period solution and stability state change of solution;The effects of variable rub impact stiffness,friction coefficient,the mass of damping ring,suspension stiffness,and internal and external damping on the response regions of no rub impact,synchronous full annual rub,partial rub,and backward whirl and their boundaries are studied;The development of backward whirl and its frequency characteristics at different friction coefficients are studied.(4)To investigate the stability and phase difference of the shaft and dry friction damper system with viscous internal damping and gyroscopic moment,the polar coordinate rub impact equation is established.The relationship between the speed of phase difference variation and the system parameters and the criteria of stability and bifurcation are derived.Based on the helicopter tail driveline,analytical and numerical simulations are used to analyze and verify the variations of phase difference and stable period solution regions,as well as several turning points where the variations occur.The effects of the system’s parameters,especially the viscous internal damping and the gyroscopic moment of the rub impact solution,are analyzed.(5)With the requirement analysis,the overall framework of the software named “platform for parameter analysis and optimization of Dry Friction Damper”,and the block diagram of each module and function realization are designed;The interfaces and underlying algorithm of the software are designed based on Matlab App Designer;The analytical solution and multi-objective intelligent optimization algorithm are combined to realize the parameter optimization function.Numerical simulations of the software were tested and found to produce accurate and abundant dynamical responses.Better damping performance and stability were obtained through parameter optimization;A new damping ring form is obtained through structural optimization,uniforming frictional stiffness and reducing frictional wear.(6)A test rig of the helicopter tail driveline is designed based on similar principles.The maximum amplitude error between simulation and experiment with different parameters was found to be about 7% by the dynamics model verification experiment.The verification for coupling effects of misalignment and rub impact are designed,and the experimental results were similar to the simulation results.The phase difference characteristic verification was conducted by speed tracking angular domain resampling,and the phase difference change in the experiments was similar to the simulation with a slight delay.The gyroscopic moment and internal damping effect verification experiments were designed,and the phase difference and orbits changes were consistent with the simulation.There are 91 figures,27 tables,and 220 references.