Hui Ma

Stability of periodic motion on the rotor-bearing system with coupling faults of crack and rub-impact

A dynamic model was set up for the rotor-bearing system with coupling faults of crack and rub-impact. Using the continuation-shooting algorithm for periodic solution of nonlinear non-autonomous system, the stability of the system periodic motion was studied by the Floquet theory. The saddle-node bifurcation, periodic-doubling bifurcation and the Hopf bifurcation were found. There are peculiar dynamic characteristics of the rotor-bearing system with coupling faults of crack and rub-impact that differs from single fault. The conclusions provide theoretic basis reference for the failure diagnosis of the rotor-bearing system with coupling faults of crack and rub-impact fault.

Numerical Simulation and Experimental Research on Pedestal Looseness of a Rotor System

The mechanical model of looseness of fastening bolt on the bearing pedestal is set up based on the project practice. Using the nonlinear oil-film model put forward by Adiletta, the dynamic characteristics were investigated by numerical Runge-Kutta method. At last, the experiment is performed to investigate the pedestal looseness by a test rig and the fault signals are analyzed by the spectrum cascade and reassigned wavelet scalogram. Numerical simulation and experiment all show that system motion state changes frequently with the increase of the rotating speed. And the experimental results coincide with the simulation results.Copyright

Feature Extraction of Rotor Systems with Coupling Fault with Crack and Rub-Impact

In practical rotor systems, rotor-stator rub-impact may occur because crack fault causes the increase of vibration amplitude, which is called coupling fault with crack and rub-impact. The vibration signal is non-stationary due to the strong nonlinear characteristics of the coupling fault. In this paper, a rotor test rig was designed to research on nonlinear vibration characteristics of rotor systems with this fault. Some meticulous experiments were performed to simulate crack fault, rub-impact fault and coupling fault of both. The vibration signals were collected in the process of speed up-down running. The rough time-frequency features are extracted by spectrum cascade. For extracting the fault features better, the wavelet time-frequency method is adopted to accurately analyze the local unstable signal. The results show that the fault features can be well extracted by combining the two methods.

Feature Analysis of Oil-Film Instability Fault Based on Time-Frequency Methods in Rotor Systems

Aiming at oil-film instability fault often occurring in the project, fault simulation experiment was simulated by using a rotor test rig, and vibration signals of two groups were collected by adjusting thickness of disc and shaft length. Fault features were extracted by using spectrum cascades, reassigned wavelet scalograms and rotor trajectories. Some new interesting features are obtained by feature analysis and fault mechanism corresponding to theses features is explained. The results will provide theoretical references for diagnosing this kind of fault.

Experiment Research of Two-Span Rotor-Bearing System with Rub-Impact and Crack Faults

The test rig of two-span rotor-bearing system with rub-impact and crack faults was constructed. The vibration of the rotor-bearing system was observed for different conditions, such as single rub-impact fault, double rub-impact faults and coupling faults of rubbing and crack. The 3D-waterfall spectrum of rotor system was used to analyze the dynamic characteristics of the system during faults. The results indicate there appears 6-superharmonic frequency component on double rub-impact faults. The amplitudes of subharmonic frequencies decrease obviously and it of superharmonic frequencies increases on coupling faults of rubbing and crack, and the superharmonic frequency components are different obviously in different span.

Bearing Parameter Optimization of a Compressor Rotor System Based on Orthogonal Experimental Design

A Low-pressure cylinder rotor of certain large centrifugal compressor units was studied by combing orthogonal experiments and finite element method. The effect of bearing parameters (length-diameter ratio, clearance ratio, dynamic viscosity of lubricating oil and preload) to bearing-rotor system stability and journal vibration was evaluated and optimum bearing parameters were determined. The significant and non-significant factors influencing on system stability and journal vibration were determined by variance analysis and F test. These conclusions will provide guidance to compressor rotor system design.

Study on Parametric Modeling Based on Visual Optimization Design of Mechanical Product

Visual optimization design (VOD) is a sort of modern design method based three-dimensional model and modeling speed impacts the research efficiency of VOD directly. The technology of parametric modeling can build model rapidly by parameter drive, so it can provide good serving for VOD. In the paper, the method of parametric modeling is studied based on VOD of mechanical product. The relation of parametric modeling and VOD is analyzed and the general flow of opening parametric modeling system is proposed, which includes confirming functional module, analyzing parameters, parametric modeling for parts and automatism assembly and so on. At last, a 3-PPT parallel kinematics machine tool is taken as research object, a parametric modeling system is opened based on VOD by VB in the Solidworks. The validity is proved by this case.

Research on Modeling Flow of Volumetric Error for Five-Axis NC Machine Tools

Based on the achievements of early works, a volumetric error modeling flow which is based on multi-body system theory is put forward. The flow includes 4 key steps mainly: describing structure, setting up coordinate system, creating characteristic matrix and generating volumetric error model are respectively. The operating method of every step is discussed in detail and the solving formula is given. At last, taking the VMC650 machining center of milling and boring which is developed by a machine tool factory as example, the validity of modeling flow is verified. This study can be used as a reference for opening automatic modeling system.

Research on Dynamics of Rotor Systems in Large Centrifugal Compressor

It is important to study system vibration characteristics for improving product quality and ensuring safety operation of units. In this paper, some dynamics of rotor systems are studied in large centrifugal compressor. The models of diaphragm coupling and tilting pad bearing are established by appropriate simplification. The finite element model of rotors with bearing and coupling is set up by taking interrelation of these subsystems into account. The unbalance responses of journal are computed based on the relative standard. The effect of bearing parameters (length-diameter ratio, clearance ratio and lubricating oil number) to journal vibration of rotor systems is analyzed. Finally test results and theoretical results are compared and errors are analyzed. The research results will provide theoretical basis for improving the bearing design of compressor rotor systems.

Dynamics Analysis of Rotor Systems in Large Centrifugal Compressor

It is important to study system vibration characteristics for improving product quality and insuring safety operation of machine. In this paper, dynamics of rotor systems are studied in a large centrifugal compressor. The models of subsystems, such as coupling and bearing, are established by appropriate simplification. The finite element model of rotors is set up by taking interrelation of these subsystems into account. The unbalance responses and system stability are analyzed for overall unit and single cylinder. The results show that the critical speed and journal amplitude at working speed in the overall unit are greater than those of low pressure cylinder. The conclusion will provide guidance to compressor rotor system design.