Research On Rub-impact Vibration Characteristics Of Dual-disc Rotor-bearing System

Nonlinear vibration of mechanical structures and systems is a complex problem in engineering practice.Because there are non-linear factors in geometric relationship,constraint condition,topology,excitation factor,coupling mode,space-time scale,etc.,the mechanism of generation and propagation of non-linear vibration can be studied to design and manufacture mechanical system and structure with good safety and performance,and at the same time,the harm caused by vibration can be effectively prevented.In recent years,dynamics of mechanical systems with non-smooth mechanical factors,such as clearance,constraint,friction and hysteresis,have attracted common attention in mechanical and vibration engineering fields.Especially the coupling action of multiple non-smooth mechanical factors reflecting the actual engineering and the change of parameters may cause the qualitative change of dynamic characteristics of the system.The quality of dynamic performance directly affects the overall performance index of the system and is the key factor to determine whether the system can operate safely,efficiently and harmoniously.Engineering practical problems urgently require people to have a deeper and more comprehensive understanding of the dynamic behavior of non-smooth mechanical system as well as to understand the relationship between the dynamic characteristics and parameters of the system so as to carry out the collaborative optimization and matching design of the dynamic characteristics and functional objectives of the system.Therefore,from the point of view of multi-parameter and system level,taking two-degree-offreedom impact vibration system with multi-gap-elastic constraints as the research object,the multi-parameter bifurcation diagram,phase diagram and Poincaré mapping diagram are obtained by numerical simulation calculation,which reveals the dynamic characteristics of complex mechanical system,and the dynamic performance matching design method is obtained.The relationship between dynamic characteristics of rotor-bearing system and model parameters is further studied,and the mechanism of non-linear low-frequency vibration instability of rotor system is emphatically analyzed.The main research work includes the following aspects.Firstly,a two-degree-of-freedom forced vibration system with multi-gap-elastic constraints is established.Analysis of the relationship between dynamic characteristics of vibration system and model parameters based on multi-objective and multi-parameter cosimulation.And the mode types and bifurcation characteristics of basic periodic vibration group and subharmonic vibration in low frequency domain are analyzed in detail.It is revealed that the irreversibility of the transition between adjacent basic periodic impact vibration induces two types of transition domains(hysteretic and non-hysteretic transition domains)and their nodes(singularities)which are distributed alternately.It is worth mentioning that the nodes(singularities)of the hysteretic and non-hysteretic transition domains on the boundary lines of p/1 and(p+1)/1 adjacent basic periodic impact vibration bifurcations are the double-Grazing bifurcations of the p/1 periodic vibration and the saddle-doubling codimensional bifurcations of the(p+1)/1 periodic vibration.Furthermore,the mechanism of subharmonic vibration in the non-hysteretic transition domain of adjacent basic periodic impact vibration is studied in detail.The influence of different types of constraints on the mode type,intrinsic characteristics and distribution of subharmonic vibration groups in the transition domain is revealed.By studying the mapping relationship between constraints and functional objectives of such mechanical vibration system,the parameter matching rule and reasonable matching range for coordinated optimization of dynamic characteristics and functional objectives of the system are determined.Secondly,the multi-objective and multi-parameter co-simulation analysis method is applied to complex engineering practice.A mechanical model of double-disk rotor system supported by oil-film short bearing considering rub-impact is established.The bifurcation diagram with two parameters,the max rubbing force diagram,the duty cycle diagram and the local bifurcation diagram are obtained by numerical simulation.The rub-impact vibration characteristics of the double-disc rotor system supported by short oil film bearings under different structural parameters are analyzed.It is found that the rotor system in the low frequency domain exhibits a basic periodic vibration group.The results are helpful to determine the physical and geometric parameters such as the static and dynamic characteristics of the product,such as the shape and size of the structure,when designing,predicting,modifying and re-analyzing the mechanical product,and to provide a scientific theoretical basis for the dynamic comprehensive design of the rotor system.Then,the mechanical model of the non-linear supported oil-film long bearing-double disk rotor system considering rub-impact is established.The dynamic characteristics and parameter matching rules of this type of rotor system are studied.The mode type,occurrence area and bifurcation characteristics of periodic rub-impact vibration of rotor system in the(ω,δ)-parameter plane of excitation frequency and gap threshold are analyzed.The maximum rubbing force and the rubbing duty-cycle obtained by numerical calculation reveal the maximum impact force and the rubbing duration for rubbing failure of the system.Rotor system shows basic periodic vibration group in low frequency domain.At the same time,due to the irreversibility of the transitions between adjacent basic periodic vibration of the system,a non-hysteretic transition domain is induced on the bifurcation boundary of the system.There are complex subharmonic periodic vibration such as 2p/2,(2p+1)/2,(3p+1)/3,…,(np+1)/n,2(np+1)/2n,and2(p+1)/2,…,2n(p+1)/2n in the non-hysteretic transition domain.The research results provide theoretical basis for the reasonable matching range of dynamic parameters of such rotor system.Finally,the mechanical model of the active magnetic bearing supported double-disk rotor system is established.The relationship between dynamic characteristics and structural parameters of the rotor system is studied.The mode types,bifurcation characteristics,maximum impact force and duty-cycle of periodic rub-impact vibration of the rotor system are analyzed.The non-linear low frequency vibration characteristics of the rotator system are analyzed emphatically.The distribution and evolution mechanism of various periodic rub-impact vibration of the rotator system in the low frequency domain are revealed.It is noteworthy that severe 0 / 1 all-round rub-impact vibration occurs in the low frequency domain of the rotor system,which can easily cause abnormal vibration and noise of the rotor system.The research results provide theoretical basis for dynamic design and fault diagnosis of rotor system supported by active magnetic bearing.