Bang Chun Wen

EXPERIMENT OF OIL-FILM WHIRL IN ROTOR SYSTEM AND WAVELET FRACTAL ANALYSES

An oil-film whirl experiment is carried out in a rotor test rig and some nonlinear analyses are achieved in the paper. Firstly, the experiment schemes for measuring oil-whirl of a rotor system are introduced. The shaft vibrations are measured both in stable rotating process and running up and coast down. And then, the detailed signals of level 3, reconstructed by wavelet transform, representing the oil-film whirl motions are analyzed. At last, a wavelet fractal method is proposed, based on wavelet package transform and fractal geometry theory, and the correlative dimensions of signals in every frequency bands are calculated. This method describes the chaotic properties of the oil-film whirl vibration well, and wavelet fractals prove to be more effective than any other nonlinear parameters of the corresponding original shaft vibration signals.© 2005 ASME

Hybrid Model Based Identification of Local Rubbing Fault in Rotor Systems

A quantitative identification procedure for local rubbing fault in rotor systems based on a hybrid model is proposed. The hybrid model combines finite element model of rotor and rigid discs, online identified oil film stiffness and elastic supports. The identification algorithm of oil film parameters is stated in detail. The hybrid model based diagnosis process for local rubbing fault is described with assumption of periodic rubbing forces. With the help of modal expansion technique, the estimated rubbing forces at each node along rotor are checked for the rubbing position. The estimated rubbing forces at ascertained position are then used in fault severity assessing quantitatively next. These approaches have been tested successfully on a test rig with single rotor double discs.

Simulations of a Dual-Rotor System with Local Rub-Impacts Based on Rigid-Flexible Multi-Body Model

The nonlinear dynamical analyses of a dual-rotor system of an aero-engine are investigated with considering local rub-impacts based on rigid-flexible multi-body simulations. The dual-rotor system is set up from a practical aero-engine prototype, which includes an inner shaft (lower-pressure shaft) and an outer shaft (higher-pressure shaft). The two shafts are in internal-external arrangement and connected by six different rolling bearings. Firstly, a rigid-flexible multi-body model of the dual-rotor system with local rub-impacts is established with MSC.Adams. Then, for the rub-impacts happening between the higher-pressure disk and the fixed elastic rod, the rub-impact forces are described as a nonlinear one with piecewise stiffness and a constant friction. At last, the transverse vibrations of the dual-rotor system are simulated. From the obtained frequency spectra and shaft center orbits of given shaft nodes, many of them are composed of multi-frequencies and demonstrate nonlinear motion patterns.

Model Based Online Diagnosis of Rotating Machinery Structural Damage

Structural damage often happens in rotating machinery such as steam engines, aircraft engines, and compressors due to the high-speed rotating of the shaft. The most common structural damages in rotating machinery are rotor shaft crack, rotor to stator rub, and bolts looseness and so on. In the present paper, the model based identification method is used to detect single structural damage such as crack, rotor to stator rub, pedestal looseness, and also, coupling fault such as rotor to stator rub and crack, crack and pedestal looseness. Utilizing the characteristic that equivalent loads of rub forces are internal forces, and the equivalent loads of the crack are external moments, the coupling faults of crack and rub-impact and crack and pedestal looseness are analyzed and exampled. The merit of the method is that it is an online diagnosis method, which provides early warning of machine failure. Theoretical simulation and laboratory testing are conducted to validate the method.

The Self-Synchronization of a Novel Vibrating Mechanism Excited by Two Unbalanced Rotors

This paper proposes an analytical approach to study self-synchronous motion and stabilizing conditions of a novel vibrating mechanism excited by two unbalanced rotors. This approach begins with utilizing Lagrange equation to establish differential motion equations of the system, and then obtains the dimensionless coupled equation of the unbalanced rotors with a modified average small parameter method. The zero solutions of dimensionless coupled equations are used to achieve the condition to implement self-synchronization of the vibrating system, and finally the Routh-Hurwitz criterion is used to derive the conditions of self-synchronous motion stability.

Pedestal Looseness Fault Analysis of Overhanging Dual-Disc Rotor-Bearing

Looseness fault can occur in rotor part, bearing and pedestal for the vibration caused by alteration of operating craft and inappropriate installation. In the paper, a new pedestal looseness model is proposed by comprehensively considering the advantages and disadvantages of current models of pedestal looseness. By using nonlinear finite element method, the nonlinear characters of overhanging dual-disc rotor bearing for pedestal looseness fault are studied. The work has important significance on safe running and prolonging the life span of machines.

ANN-Based Crack Identification in Rotor System with Multi-Crack in Shaft

Rotating machinery, such as steam turbo, compressor, and aeroengine etc., are widely used in many industrial fields. Among the important rotor faults, the fatigue crack fault, which can lead to catastrophic failure and cause injuries and severe damage to machinery if undetected in its early stages, is most difficult to detect efficiently with traditional methods. In the paper, based on the truth of the change of the mode shapes of the cracked structure, a new method by combining accurate finite element model of rotor with multi-crack in shaft and artificial neural network (ANN) is proposed to identify the location and depth of cracks in rotating machinery. First, based on fracture mechanics and the energy principle of Paris, the accurate FE model of the rotor system considering several localized on-edge non-propagating open cracks with different depth, is built to produce the specific mode shapes. Then a set of different mode shapes of a rotor system with localized cracks in several different positions and depths, which will be treated as the input of the designed ANN model, can be obtained by repeating the above step. At last, with several selected crack cases, the errors between the results obtained by using the trained ANN model and FEM ones are compared and illustrated. Meanwhile, the influences of crack in the different position on the identification success are analyzed. The method is validated on the test-rig and proved to have good effectiveness in identification process.

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

Diagnosis of Local Fault and Identification of Transient Fault Force in Rotating Machinery

Model based fault identification techniques can be used to diagnose local faults in rotating machinery; the equivalent loads that represent fault forces can be used to identify the fault location. But in some cases the equivalent loads smeared over many nodes, and make it hard to identify accurate fault location and transient fault force. In this paper, the fault location is identified using least squares fitting approach by the system’s vibration shape when the fault signal is periodic or quasi-periodic. And after the fault location is ascertained, the transient fault forces can be identified by transient residual vibration using simple matrix multiplications and additions. Numerical simulations and experiment on rotor to stator rub are used to test the method, which proved the efficiency of the method.

Research on the Product Quality Control Based on the Systematic Design Process

It expounded the design quality connotation, product generalized quality was “the integrated embodiment of product function and performance”, the generalized product quality and the whole function and performance are equivalent. Clearly it made the design quality concretized into the product function and three performances. Expounded the concept of product design quality control, analyzed the influencing factors of product design quality, formed the design idea of quality control; aiming at the existing problems of traditional product design, established design quality control preliminary model by applying systematic design theory.