Research On Dynamic Characteristic And Fault Diagnosis Of Rotor-basis-ball Bearing System With Multi Coupling Faults

In the service of rotating equipment,faults of the rotor system are usually coupled,and once coupling faults occur,serious consequences will happen,which will shorten life of the equipment,affect the production of factory,and reduce the economic benefits.In severe cases,the occurrence of fatal accidents,resulting in irreparable significant losses.Therefore,it is of great value and necessity to study the mechanism and diagnosis of rotor system with multi coupling faults.Based on this,the inherent characteristics of the rotor-basis-ball bearing system were first studied.Then,various faults such as imbalance,rubbing,crack and pedestal looseness were considered.The dynamic characteristics of the rotor system with multi coupling faults were analyzed,and the multi-fault diagnosis method of the rotor system was explored.The main research of the paper includes:(1)To make the inherent characteristics of the rotor-basis-ball bearing system clear,Timoshenko beam elements and disk elements were assembled by using finite element method.By assembling the model of ball bearing,basis model and the concentrated mass of coupling,the dynamic equations of the rotor-basis-ball bearing system were obtained.Then,the influence of ball bearing contact stiffness,foundation support stiffness and foundation support mass on the system mode and critical speed was studied,and the steady-state response of each node of the system was analyzed.The above studies clarified the vibration modes of the rotor-basis-ball bearing system,the critical speed and the changes of the time domain diagram,spectrum diagram and axis orbits of each node of the system.(2)To analyze nonlinear dynamic characteristics of rotor-basis-ball bearing system with multi coupling faults,the fault models of unbalance,misalignment.rubbing,crack and pedestal loseness were considered,and the dynamic differential equations of the system with multi coupling faults were obtained.The dynamic response of system was obtained using RungeKutta method with variable step length.Then,bifurcation diagrams and poincaré maps of system displacement response varied with speed,unbalance quantity,misalignment quantity,rubbing clearance,crack damage ratio and looseness clearance were obtained.Time domain waveform,axis orbits,phase diagrams and frequency spectrum at the fault areas of different state moments were analyzed.As a result,abundant nonlinear phenomena such as periodic motion,quasi-periodic motion and complex quasi-chaotic motion are found.Additionally,characteristics of faults such as unbalance,misalignment,rubbing,crack and pedestal looseness are indicated during each nonlinear behavior.(3)Aiming at the multi-fault diagnosis of rotor-basis-ball bearing system,the diagnosis method based on entropy was studied.Combined with the established dynamic differential equation of system,the vibration displacement response time series signals corresponding to the position of each node in the system and the comprehensive misalignment,loose clearance,rubbing clearance and crack damage ratio are solved.The sample entropy,fuzzy entropy and permutation entropy were used to diagnose and analyze the above time series signals to study the applicability of each entropy.The results show that the sample entropy and permutation entropy cannot determine the location and degree of faults.Fuzzy entropy can not determine the fault location,and can only diagnose part degree of loose clearance and crack damage ratio.(4)Considering the entropy method can not meet the requirements of multi-fault diagnosis of rotor-basis-ball bearing system,a model-based fault diagnosis method was proposed.Firstly,the location node of fault in multi-fault rotor system was determined by the combination of finite element and harmonic balance theory.Then,the nonlinear output frequency response function(NOFRF)was used to obtain the NOFRFs value of each order mapping relationship between system output and input,and then the NOFRFs value sensitive to the change of fault parameters was selected as the factors for fault degree diagnosis.The diagnosis results show that the fault location determination method based on finite element and harmonic balance theory can determine the fault location in multi-fault rotor system with unbalance,rubbing,crack and pedestal looseness,and comprehensive misalignment quantity,rubbing clearance and pedestal looseness clearance can be integrated by harmonic components of NOFRFs.