Study On Stability And Experiments By Complex Rotor-bearing System With Coupling Faults

Rotating machinery is one kind of mechanical equipments most widely used in the industrial department,its stable operation influences the development process of all the industry.With the development of the society,rotating machinery is developing in the direction of high speed,overloading,automation and complexity,which results in more and more questions.As the operating environment is quite bad,complex rotating machinery often breaks down for the nonlinear factors.This makes the system lose stability or even air crash accidents,which cause immeasurable economic losses,casualties and social harms.In the past, simple rotor model was often used to study the nonlinear characteristics and stability,but for the more complex engineering machinery,such model is no longer competent.Therefore, study of the modeling and operational stability of the complex rotor-bearing system has great practical significance.At present many scientific workers at home and abroad begin to realize this question and have achieved some results.This paper is in the background of large-scale compressor rotor vibration experiment system studied by Northeastern University and Shenyang Blower Co.,Ltd.Cycle operation stability and bifurcation characteristics of the complex rotor-bearing system with faults,that single-span double-disk rotor-bearing system with single fault or coupling faults and double-span multiple-disk rotor-bearing system with coupling faults are studied for the purpose of the dynamic design appliance in the framework of the "Integrated Design Method Based on the System Engineering" put forward by Professor Wen Bangchun.Concrete contents are as follows:(1) Continuation targeting algorithm is studied to solve the periodic solutions and to determine the stability and bifurcation of the nonlinear dynamic rotor-bearing system. Nonlinear dynamics toolbox of the rotor-bearing system is developed based on the finite element theory,this toolbox contains about 50 subfunctions,its functions are as follows: calculating critical speed,calculating material damping coefficient,calculating time and frequency domain response of the elastic supporting system,calculating time and frequency domain response of the single-span and double-span nonlinear rotor-bearing system, studying bifurcation,chaos,stability and so on.Nonlinear factors include oil film supporting, crack and rub-impact,etc.To get higher calculation accuracy and save calculation cost,the toolbox contains dimensionless and reduced-processing functions.(2) Nonlinear dynamic model of the double-disk rotor-bearing system supported by oil film is established.Stability and bifurcation behaviors of the system are studied by the continuation targeting algorithm in the parameter domains of eccentric phase,eccentricityrotational speed,bearing aspect ratio-rotational speed,bearing clearance-rotational speed and oil viscosity-rotational speed.Instability characteristics and nonlinear vibration characteristics of the rotor-bearing system supported by oil film are studied by experiments.Research shows that synchronous periodic motion of the system mainly presents as period doubling and quasi periodic bifurcation phenomenon.And with the change of a parameter,the topological structure and domain of attraction of the system will also change,which results in the jump mutations phenomenon of the system bifurcation curve.Generally instability speed will also change as jump change of the bifurcation type.(3) Instability and bifurcation behaviors of the double-disk rotor-bearing system supported by oil film with rub-impact faults are analyzed in the parameter domains of friction coefficient-rotational speed and rub-impact clearance-rotational speed for different rub-impact position.Rub-impact monitoring device and experimental device are established and the main results of the analysis are verified.Research shows that different rub-impact position and eccentric magnitude have great influence on the stability and dynamic characteristics of the system,so it can be said that topological structure of the system can be easily changed by the rub-impact faults.Rub-impact faults can influence the emergence of the oil whirl and oil whip. This can delay the instability speed and double frequency components will appear in the frequency domain response for the reason of rub-impact.(4) Operation stability and instability rules of the double-disk rotor-bearing system supported by oil film with crack faults arc analyzed in the parameter domains of eccentric magnitude- rotational speed,crack depth- rotational speed and crack position- rotational speed. Research shows that existence and location change of the crack have little influence on the system instability speed and instability patterns.As the growth of the crack,instability speed increase slowly.The main reason is that existence of the crack interfere the formation of the oil whirl,but it not means that existence of the crack is beneficial:Its existence would bring about great hidden trouble,numerical calculation may not continue when the crack depth reach a certain level,so crack damage in the rotor system must be avoided.(5) Operation stability and bifurcation rules of the continuous double eccentric rotorbearing system with rub-impact-crack coupling faults are analyzed in the parameter domains of eccentric magnitude- rotational speed,rub-impact clearance-rotational speed and crack depth- rotational speed.Research shows that with the increasing of the eccentric magnitude, instability speed has decreased tendency.When the eccentric magnitude reaches a certain level,instability speed will increase for the restriction of the stator.When the rub-impact clearance decreases,instability speed will increase for the increasing of the rub-impact force. In additon,rub-impact faults have bigger influence than the crack on the rotor-bearing system with rub-impact-crack coupling faults,but existence of the crack would bring about great hidden trouble for the normal operation of the system.(6) Nonlinear dynamic model of the double-span rotor-bearing system with rub-impact-crack coupling faults supported by oil film is established.Stability and bifurcation behaviors of the system with rub-impact-crack coupling faults are studied in the parameter domains of eccentric magnitude- rotational speed,rub-impact clearance-rotational speed and crack depth- rotational speed.Research shows that instability characteristics of the double-span rotor-bearing system are different from that of the single-span system.Mutations phenomenon of bifurcation type and instability speed did not appear in the double-span rotor-bearing system,which is main decided by the structural characteristics of the rotor system.Study on the double-span rotor-bearing system with coupling faults shows that response of both ends of the rotor one appears strong and the other appears weak for the effect of the elastic coupling.Big eccentric magnitude makes the instability speed of the system increase and characteristic of rub-impact faults appears more obvious.