Study on the transient response and wavelet time—frequency feature of a cracked rotor passage through a subcritical speed

2003 ◽  
Vol 38 (3) ◽  
pp. 269-276 ◽  
Author(s):  
J Zou ◽  
J Chen ◽  
J. C Niu ◽  
Z. M Geng
Keyword(s):  
Numerical Simulation ◽  
Transient Response ◽  
Crack Model ◽  
Cracked Rotor ◽  
Time Frequency ◽  
Stiffness Variation ◽  
The Difference ◽  
Frequency Features ◽  
Cracked Rotor System ◽  
Subcritical Speed

The dynamic model in dimensionless form of the transient response of a cracked rotor system is derived, which is based on the simple hinge crack model. By numerical simulation, the transient responses of the uncracked rotor and the cracked rotor are obtained and the subharmonic resonance of the cracked rotor is analysed. The influence of the unbalance, the inhabiting angle and the stiffness variation on the transient response is investigated. The wavelet time-frequency features of the cracked rotor and the uncracked rotor are studied, and the difference between them is discussed. The numerical simulation demonstrates that the wavelet analysis algorithm is valid for the identification of cracked rotor.

Application of the Wigner-Ville distribution to identification of a cracked rotor

2003 ◽  
Vol 217 (5) ◽  
pp. 551-556 ◽  
Author(s):  
J Zou ◽  
J Chen ◽  
J C Niu ◽  
Z M Geng
Keyword(s):  
Numerical Simulation ◽  
Transient Response ◽  
Crack Model ◽  
Cracked Rotor ◽  
Simulation Research ◽  
Time Frequency ◽  
Stiffness Variation ◽  
Engineering Practices ◽  
Frequency Features ◽  
Frequency Feature

The dynamic equation of transient response in a cracked rotor is modelled, and is based on the simple hinge crack model. The numerical simulation solutions of the uncracked rotor and the cracked rotor are obtained from the model. Using the Wigner-Ville distribution, the time-frequency features of the cracked rotor and the uncracked rotor are compared, and a new algorithm using the Wigner-Ville distribution to identify the cracked rotor is proposed. By simulation research, the sensitivity of the Wigner-Ville distribution to the stiffness variation is investigated, and the influence of the unbalance and the inhabiting angle on the time-frequency feature is discussed. The Wigner-Ville time-frequency feature is unique, and can be used as the criterion for identification of a cracked rotor in engineering practices.

On the wavelet time-frequency analysis algorithm in identification of a cracked rotor

2002 ◽  
Vol 37 (3) ◽  
pp. 239-246 ◽  
Author(s):  
J Zou ◽  
J Chen ◽  
Y P Pu ◽  
P Zhong
Keyword(s):  
Numerical Simulation ◽  
Detection Algorithm ◽  
Sampling Frequency ◽  
Crack Model ◽  
Cracked Rotor ◽  
Simulation Research ◽  
Time Frequency ◽  
Local Flexibility ◽  
The Difference ◽  
Frequency Properties

Based on the hinge crack model and the local flexibility theorem, the local flexibility of a cracked rotor due to the crack and the modified function of the opening and closing of the crack are given; the corresponding dynamic equation of the cracked rotor is modelled; the numerical simulation solutions of the cracked rotor and the uncracked rotor are obtained. By the continuous wavelet time—frequency transform, the wavelet time-frequency properties of the uncracked rotor and the cracked rotor are discussed; the difference between the wavelet time-frequency properties of the cracked rotor and those of the uncracked rotor is presented. A new detection algorithm that uses the wavelet time-frequency transform to identify the crack is proposed. The influence of the sampling frequency on the accuracy and validity of the wavelet time-frequency transform is analysed by numerical simulation research; the preferred sampling frequency is suggested. The experiments on the cracked rotor and the uncracked rotor demonstrate the validity and availability of the algorithm in the identification of the cracked rotor in engineering practices.

Feature investigation of a cracked rotor with initial deflection

2003 ◽  
Vol 217 (7) ◽  
pp. 787-796 ◽  
Author(s):  
J Zou ◽  
J Chen ◽  
G M Dong
Keyword(s):  
Numerical Simulation ◽  
Dynamic Equation ◽  
Subharmonic Resonance ◽  
Initial Deflection ◽  
Crack Model ◽  
Cracked Rotor ◽  
Simulation Research ◽  
Vibrational Characteristics ◽  
Frequency Components ◽  
Stiffness Variation

The dynamic equation of a cracked rotor with initial deflection is modelled, which is based on the simple hinge crack model; the numerical simulation solutions are obtained from the model. The subharmonic resonance of the cracked rotor is analysed and the frequency components of the cracked rotor with initial deflection and without initial deflection are investigated. By simulation research, the influence of the stiffness variation, the initial deflection, the unbalance, the unbalance angle and the orientation of the initial deflection on the vibrational characteristics is studied, which can be used as the criterion for identification of a cracked rotor.

On the Modeling of Open and Breathing Cracks of a Cracked Rotor System

2010 ◽  
Author(s):  
Mohammad A. AL-Shudeifat ◽  
Eric A. Butcher
Keyword(s):  
Finite Element ◽  
Crack Detection ◽  
Linear Time ◽  
Harmonic Balance Method ◽  
Rotor System ◽  
Crack Model ◽  
Open Crack ◽  
Cracked Rotor ◽  
Critical Rotational Speed ◽  
Cracked Rotor System

The modeling of a cracked rotor system with an open or breathing transverse crack is addressed here. The cracked rotor with an open crack model behaves as an asymmetric shaft. Hence, the time-varying area moments of inertia of the cracked section are employed in formulating the periodic finite element stiffness matrix for both crack models which yields a linear time-periodic system. The harmonic balance method (HB) is used in solving the finite element (FE) equations of motions for studying the dynamic behavior of the cracked rotor system. The unique behavior of the whirl orbits during the passage through the subcritical rotational speeds and the sensitivity of these orbits to the unbalance force direction can be used for early crack detection of the cracked rotor for both crack models. These whirl orbits were verified experimentally for the open crack model in the neighborhood of 1/2 of the first critical rotational speed where a good match with the theoretical whirl orbits was observed.

Cracked Rotor Diagnostics Using Soft Computing

2007 ◽  
Author(s):  
B. Samanta ◽  
C. Nataraj
Keyword(s):  
Soft Computing ◽  
Transient Response ◽  
Fuzzy Inference ◽  
Cracked Rotor ◽  
Inference System ◽  
Time Frequency ◽  
Wavelet Energy ◽  
Soft Computing Techniques ◽  
Detection And Diagnosis ◽  
Run Up

A study is presented for detection and diagnostics of cracked rotors using soft computing techniques like adaptive neuro-fuzzy inference system (ANFIS), artificial neural networks (ANN) and genetic algorithms (GA). A simple model for a cracked rotor is used to simulate its transient response during startup for different levels of cracks. The transient response is processed through continuous wavelet transform (CWT) to extract time-frequency features for the normal and cracked conditions of the rotor. Several features including the wavelet energy distributions and the grey moment vectors (GMV) of the CWT scalograms are used as inputs for diagnosis of crack level. The parameters of the classifiers, ANFIS and ANN, along with the features from wavelet energy distribution and grey moment vectors are selected using GA maximizing the diagnostic success. The classifiers are trained with a subset of the data with known crack levels and tested using the other set of data (testing data), not used in training. The procedure is illustrated using the simulation data of a simple de Laval rotor with a ‘breathing’ crack for different crack levels during run-up through its critical speed. A comparison of diagnostic performance for the classifiers is presented. Results show the effectiveness of the proposed approach in detection and diagnosis of cracked rotors.

Roll-Yaw Coupling Effect of Jeffcott Rotor With Breathing Crack

2015 ◽  
Author(s):  
J. Zhao ◽  
H. A. DeSmidt ◽  
M. Peng ◽  
W. Yao
Keyword(s):  
Coupling Effect ◽  
Rotor System ◽  
Crack Model ◽  
Breathing Crack ◽  
Cracked Rotor ◽  
Lagrange Principle ◽  
Jeffcott Rotor ◽  
Vibration Responses ◽  
Cracked Rotor System ◽  
Rotor Model

A new rotor model is developed in this paper to explore the dynamic coupling effect of roll-yaw motion. The rotor model employs a 6 degree-of-freedom Jeffcott rotor with a breathing crack. Based on the energy method and Lagrange principle, equation of motion is derived in yawing coordinate system with consideration of unbalance mass. The breathing crack model is established by Zero Stress Intensity Factor (SIF) method based on the crack released strain energy concept in fracture mechanics. SIF method is used to determine the crack closure line by computing SIF for opening mode. The vibration responses of the cracked rotor system are solved by Gear’s method. The coupling effect of yawing and rolling motion is studied in this paper to investigate vibration response of cracked rotor system. With the yawing motion, the dynamics of the rotor-bearing system is changed by additional stiffness and force terms. The parametric study is conducted to analyze the effect of yawing rate and acceleration on the crack breathing behavior. Finally, the vibration responses of the nominal and damaged rotor systems are analyzed to find out the indication for the damage detection and health monitoring.

Effect of Unbalance Force Direction on a Cracked Rotor Whirl Response

2017 ◽  
Author(s):  
Hanan Al Hosani ◽  
Mohammad A. AL-Shudeifat ◽  
Adnan S. Saeed ◽  
Shadi Balawi
Keyword(s):  
Numerical Simulation ◽  
Crack Opening ◽  
Crack Model ◽  
Open Crack ◽  
Cracked Rotor ◽  
Force Vector ◽  
Critical Speeds ◽  
Unbalance Force ◽  
Vector Angle ◽  
Time Periodic

The combined effect of the crack and the unbalance force vector angle on the values and locations of the whirl amplitudes at the critical whirl speeds for a cracked rotor-bearing-disk system is numerically and experimentally investigated here. The strongly nonlinear time-periodic equations of motion, which are analogous to Mathieus equation, of the cracked system with an open crack model are formulated according to the finite element time-periodic stiffness matrix. The whirl response during the passage through the critical speeds is obtained via numerical simulation for different unbalance vector angles with respect to the crack opening direction. It is found that the variation in the unbalance force vector angle with respect to the crack opening direction significantly alters the peaks of the critical whirl amplitudes and their corresponding critical whirl speeds. Consequently, the critical speeds of the cracked rotor are either shifted to higher or lower values according to the unbalance force vector angle value. These significant numerical simulation observations are also verified via robust experimental results.

Nonlinear Dynamic Analysis of a Cracked Rotor-Bearing System With Fractional Order Damping

2011 ◽  
Author(s):  
Shiming Xue ◽  
Junyi Cao ◽  
Yangquan Chen
Keyword(s):  
Fractional Order ◽  
Crack Depth ◽  
Nonlinear Dynamic Analysis ◽  
Orientation Angle ◽  
Rotor System ◽  
Speed Ratio ◽  
Crack Model ◽  
Cracked Rotor ◽  
Mass Eccentricity ◽  
Cracked Rotor System

Fatigue cracking of the rotor shaft is an important fault observed in rotating machinery of key industry, which can lead to catastrophic failure. Nonlinear dynamics of a cracked rotor system with fractional order damping is investigated by using a response-dependent breathing crack model. The four-th order Runge-Kutta method and ten-th order CFE-Euler (Continued Fraction Expansion-Euler) method are introduced to simulate the proposed system equation of fractional order cracked rotors. The effects of derivative order of damping, rotating speed ratio, crack depth, orientation angle of imbalance relative to the crack direction and mass eccentricity on the system dynamics are demonstrated by using bifurcation diagram, Poincare map and rotor trajectory diagram. The results show that the rotor system displays chaotic, quasi-periodic and periodic motions as the fractional order increases. It is also found that the imbalance eccentricity level, crack depth, rotational speed, fractional damping and crack angle all have considerable influence on the nonlinear behavior of the cracked rotor system.

Nonlinear Dynamic Analysis of a Cracked Rotor-Bearing System With Fractional Order Damping

2012 ◽  
Vol 8 (3) ◽  
Author(s):  
Junyi Cao ◽  
Shiming Xue ◽  
Jing Lin ◽  
Yangquan Chen
Keyword(s):  
Fractional Order ◽  
Crack Depth ◽  
Nonlinear Dynamic Analysis ◽  
Orientation Angle ◽  
Rotor System ◽  
Speed Ratio ◽  
Crack Model ◽  
Cracked Rotor ◽  
Mass Eccentricity ◽  
Cracked Rotor System

Fatigue cracking of the rotor shaft is an important fault observed in the rotating machinery of key industries, which can lead to catastrophic failure. Nonlinear dynamics of a cracked rotor system with fractional order damping is investigated by using a response-dependent breathing crack model. The fourth-order Runge–Kutta method and tenth-order continued fraction expansion-Euler (CFE-Euler) method are introduced to simulate the proposed system equation of fractional order cracked rotors. The effects of the derivative order of damping, rotating speed ratio, crack depth, orientation angle of imbalance relative to the crack direction, and mass eccentricity on the system dynamics are demonstrated by using a bifurcation diagram, Poincaré map, and rotor trajectory diagram. The simulation results show that the rotor system displays chaotic, quasi-periodic, and periodic motions as the fractional order increases. It is also observed that the imbalance eccentricity level, crack depth, rotational speed, fractional damping, and crack angle all have considerable influence on the nonlinear behavior of the cracked rotor system. Finally, the experimental results verify the effectiveness of the theoretical analysis.

A novel amplitude-independent crack identification method for rotating shaft

2018 ◽  
Vol 232 (22) ◽  
pp. 4098-4112 ◽  
Author(s):  
Laihao Yang ◽  
Xuefeng Chen ◽  
Shibin Wang
Keyword(s):  
Frequency Analysis ◽  
Instantaneous Frequency ◽  
Vibration Signal ◽  
Rotor System ◽  
Crack Identification ◽  
Fast Time ◽  
Time Varying ◽  
Cracked Rotor ◽  
Time Frequency ◽  
Cracked Rotor System

The shaft crack is one of the most common and serious malfunctions in rotating machines and may lead to catastrophic failure if undetected in time. However, the conventional crack identification methods are amplitude-dependent and thus can be only applied to the crack identification under some specific conditions. In this paper, a novel amplitude-independent crack identification method (AiCIM) is significantly proposed to eliminate the amplitude-dependent property and promote the effectiveness of the crack identification. First and foremost, a fast time-varying vibration phenomenon of the cracked-rotor system is newly found. Through the theoretical analysis, the fast time-varying vibration mechanism of the cracked-rotor system is revealed for the first time. It is indicated that the vibration signal of the cracked-rotor system is modulated by the fast-oscillated instantaneous frequency, which is independent of the amplitude of the vibration signal. AiCIM is then put forward on the basis of the fast time-varying vibration mechanism and matching time–frequency analysis theory. Specially, the amplitude-independent instantaneous frequency of the vibration signal is extracted via the matching time–frequency analysis theory, and the time–frequency representation energy-concentration is enhanced along the instantaneous frequency trajectory. Since instantaneous frequency of the vibration signal carrying the critical fault information is employed to identify the shaft crack, AiCIM is only relevant to the phase of the vibration signal, i.e. amplitude independent. As a result, AiCIM successfully eliminates the dependence on the signal amplitude and is more sensitive to the weak crack. Both the numerical and experimental results demonstrate that AiCIM behaves best to extract the fast-oscillated feature of the fast time-varying vibration induced by the shaft crack in comparison with other time–frequency analysis methods, and AiCIM effectively suppress the effect of noises on the instantaneous frequency estimation because of its amplitude-independent property. Influences of the crack parameters on the nonlinear instantaneous frequency are finally discussed with AiCIM. This study provides a potential way to the online crack identification.

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