Research On Diagnosis Method Of Typical Rotor Faults Based On Nonlinear Output Frequency Response Functions

As one of the most common structures in mechanical products,rotor structures are widely used in various power and chemical machinery.With the continuous operation of rotor structures,the probability of failure of rotor system will further increase.How to diagnose rotor faults has become a very important research content.The occurrence of faults often manifests as a further enhancement of system nonlinearity.By performing real-time quantitative detection of the nonlinearity of rotor system,we can probably know the severity and location of faults,so that it is fully prepared for the next step of maintenance.Therefore,the analysis and study of the nonlinearity of rotor system has important theoretical and practical value.Nonlinear output frequency response functions is a nonlinear analysis method developed on the basis of Volterra series.It is very advantageous in terms of nonlinear design and optimization of the mechanical system as well as fault detection.Especially in the aspect of fault detection,this method has the characteristics of simple,convenient and high efficiency,and has been successfully applied in many fields.In this paper,typical faults of rotor system are taken as research objects,and the nonlinear output frequency response functions is taken as the research method.Based on the basic theory of rotor dynamics,the research on the method of fault detection and diagnosis is carried out.The main contents include:(1)Taking rotor crack fault as a research object,its finite element model is established.The dynamics model is solved by Newmark-β method,and the vibration response signals of the system under different rotor crack depths are obtained.The vibration signals are further analyzed by the nonlinear output frequency response functions.We analyzed the correlation between the depth and location of rotor cracks and NOFRFs.Based on this,the depth and location of the rotor crack are identified.Finally,the correctness of the simulation analysis was verified by experiments with rotor crack fault test bench.(2)According to the characteristics of the nonlinear output frequency response functions and its existing related indicators,and by combining the relative theory of feature weighting and contribution rate,the weighted contribution rate of the nonlinear output frequency response functions is proposed.Its relative theoretical formulas are deduced in detail.The advantages of the weighted contribution rate of the nonlinear output frequency response functions in the enhancement of weak fault characteristics are introduced in detail.The difference and relationship between the weighted contribution rate of the nonlinear output frequency response functions and its existing related indicators are compared and analyzed.Finally,the feasibility of the method for rotor crack fault detection is verified from two aspects of simulation and experiment.(3)According to the characteristics of the rub-impact of rotating parts,Kuhn-Tucker condition of Coulomb friction law and augmented Lagrangian method are used to deal with contact constraints.The dynamic model of a rub-impact rotor system is established.The differential equation of motion of the system is derived.The numerical solutions of the vibration response of the system under different rub-impact conditions are obtained by Newton-Raphson iterative solution.The weighted contribution rate of the nonlinear output frequency response functions of the system under different rubbing conditions is obtained by the algorithm proposed in this paper.The relationship between the method and rub-impact condition is found.Finally,the correctness of theoretical analysis was verified by setting up a rotor rub-impact fault test bench.This paper has innovated in the theoretical development and specific application of nonlinear output frequency response functions.In particular,the weighted contribution rate of the nonlinear output frequency response functions proposed in the paper is a summary and innovation based on the work done by predecessors.The proposed method has important theoretical significance for the enhancement of weak fault characteristics.The simulation and experimental research on typical rotor faults demonstrates the advantages of this method in the field of rotor fault diagnosis,and further shows enormous economic value of the method.