Unbalance-Misalignment Vibration Analysis Of Double Span Rotor-Diaphragm Coupling System

The helicopter tail drive shaft is a typical double-span or multispan slender rotor-diaphragm coupling structure,which transmits power to the tail rotor and is an extremely important part.When passing the critical speed,the bending amplitude of the rotor increases sharply,and the misalignment will adversely affect the vibration of the rotor.Therefore,studying the dynamic characteristics of unbalance and misalignment faults of double-span rotor system has a certain engineering reference significance for vibration reduction,fault monitoring and diagnosis of the actual rotor system.In this paper,according to the structure of the helicopter tail drive shaft system and based on the similarity principle,the test rig of the doublespan rotor-diaphragm coupling system is designed,and its related vibration characteristics are studied.The main research contents are as follows:(1)The structure and working principle of the diaphragm coupling are described.The stiffness is analyzed by mathematical formula and ANSYS Workbench software static simulation.The stiffness value shows that the axial and angular compensation ability of diaphragm coupling is good.(2)Considering the coupling factor of the diaphragm coupling,the dynamic equation of the double span rotor-diaphragm coupling system is established by the finite element method,in which the shaft segment model uses the Rayleigh beam.The first and second order speed and mode shapes of the system are calculated and compared by finite element method and ADAMS rigid-flexible coupling model simulation.The maximum error of ADAMS simulation results is 10.6%,and the vibration mode is consistent.The influence of unbalance magnitude,position and phase difference on coupling vibration of the system is analyzed.The results show that the vibration amplitude of the system increases linearly with the unbalance magnitude.When the difference of unbalance phase between the rotor increases,the amplitude of each rotor shows an opposite trend.(3)According to the deformation and force relation of the diaphragm of the coupling,the expression of the relation between the additional force or moment of the quadrangle and hexagon diaphragm on the rotational speed and misalignment is deduced under the two cases of parallel or angular misalignment.At the same time,considering the dynamic misalignment force at both ends of the diaphragm coupling caused by the vibration of the transmission shaft,the misalignment force is decomposed into two directions of the coordinate system,and the misalignment dynamic equation of the double-span rotor-diaphragm coupling system is finally established.The dynamic response of the system under different misalignments is analyzed,and it is found that the misalignment can cause subcritical resonance phenomenon during the acceleration of the rotor system.The effects of different shapes of diaphragm misalignment and the magnitude of misalignment on the steady-state response of the system are analyzed.The results show that the variation period of the misalignment excitation force caused by the two types of diaphragms is different.(4)A double span rotor system test rig is built and the control and data acquisition system is implemented.Aiming at the difficulty of initial static misalignment measurement,a machine vision detection scheme is proposed.The maximum error of measuring parallel misalignment is0.03 mm.The unbalance dynamic and steady-state response experiments of the system are designed.The first and second order critical speed is basically consistent with the simulation results,and the maximum error is12.6%.The main vibration characteristics are consistent with the simulation results.The steady-state response experiments with different parallel and angular misalignments are carried out by adding gaskets,and the vibration orbit,frequency domain and variation law of the drive shaft are similar to the simulation results.