Crack Detection in an Overhung Rotor System Using External Harmonic Excitation

2020 ◽  
pp. 159-169
Author(s):  
R. Tamrakar ◽  
N. D. Mittal
Keyword(s):  
Crack Detection ◽  
Harmonic Excitation ◽  
Rotor System

scholarly journals Exact receptance function and receptance curvature of a clamped-clamped continuous cracked beam

2019 ◽  
Vol 41 (4) ◽  
pp. 349-361
Author(s):  
Nguyen Viet Khoa ◽  
Cao Van Mai ◽  
Dao Thi Bich Thao
Keyword(s):  
Numerical Simulations ◽  
Frequency Domain ◽  
Crack Detection ◽  
Harmonic Excitation ◽  
Second Derivative ◽  
Cracked Beam ◽  
Cracked Beams

The receptance function has been studied and applied widely since it interrelates the harmonic excitation and the response of a structure in the frequency domain. This paper presents the derivation of the exact receptance function of continuous cracked beams and its application for crack detection. The receptance curvature is defined as the second derivative of the receptance. The influence of the crack on the receptance and receptance curvature is investigated. It is concluded that when there are cracks the receptance curvature has sharp changes at the crack positions. This can be applied for the crack detection purpose. In this paper, the numerical simulations are provided.

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.

Rotor Transverse Crack Detection and Diagnosis Using Embedded Modeling

Manufacturing ◽  
2003 ◽  
Author(s):  
Kristoffer K. McKee ◽  
C. James Li
Keyword(s):  
Crack Detection ◽  
Complex Geometry ◽  
Universal Function ◽  
Rotor System ◽  
Modeling Methodology ◽  
Stiffness Reduction ◽  
Embedded Modeling ◽  
Function Approximator ◽  
High Level ◽  
Local Stiffness

This study proposes an embedded modeling methodology for identifying the crack-induced local stiffness reduction in a shaft from its horizontal and vertical vibrations. An embedded model integrating a dynamic model of the rotor system, and the unknown local stiffness reduction in the form of a universal function approximator i.e., neural network, is established. As a FEM model, it can describe rotors of complex geometry. A solution method is then established to identify the local stiffness reduction of the shaft due to a crack. Subsequently, a method is then used to find the location and size of the crack along the shaft. Simulated studies were conducted to demonstrate that the crack induced stiffness reduction of a Jeffcott rotor system can be identified, and the location, size and shape of the crack can be estimated by the proposed method with high level of accuracy.

Dynamics of Slant Cracked Rotor for a Steam Turbine Generator System

2017 ◽  
Vol 139 (6) ◽  
Author(s):  
Chao Liu ◽  
Dongxiang Jiang
Keyword(s):  
Steam Turbine ◽  
Turbine Unit ◽  
Crack Detection ◽  
Rotor System ◽  
Fault Detection And Isolation ◽  
Cracked Rotor ◽  
Generator System ◽  
Vibration Data ◽  
Torsional Excitation ◽  
Cracked Rotor System

Root causes of several recent crack failures in turbine units are attributed to oscillation and interaction between generator of turbine unit and devices on the grid, where torsional vibration of the rotor bearing system is observed and identified as an important cause. Exploring vibrational (lateral, torsional, and axial) features in the cracked rotor system with torsional excitation (TE) present can provide a novel view in crack detection and isolation. This work presents dynamic analysis of a cracked rotor system in a steam turbine unit (a typical rotor system with multiple rotors, multiple supports, and oscillating loads), and the vibrational features of the cracked rotor system with comparisons to typical features in monitored vibration data. The results show that coupled vibration in both lateral and torsional components is an effective indicator for cracks in the presence of torsional excitation. Also, vibration characteristics evaluated in different locations of the rotor system are beneficial for fault detection and isolation.

scholarly journals Analysis of the Response of a Rotor System Containing a Breathing Crack

2009 ◽  
Vol 413-414 ◽  
pp. 479-486
Author(s):  
Jean Jacques Sinou
Keyword(s):  
Crack Detection ◽  
Crack Depth ◽  
Harmonic Balance Method ◽  
Dynamical Behaviour ◽  
Rotor System ◽  
Harmonic Frequency ◽  
Transverse Cracks ◽  
Frequency Components ◽  
On Line ◽  
Truncated Fourier Series

The purpose of this paper is to investigate the influence of the presence of transverse cracks in rotors. The dynamic response of the cracked rotor is evaluated by expanding the changing stiffness of the crack (i.e. the breathing mechanism) as a truncated Fourier series and then using the Harmonic Balance Method. The crack detection is based on the use of the 2X and 3X super-harmonic frequency components of the non-linear dynamical behaviour at the associated sub-critical resonant peaks. Various parametric studies including the effects of the crack depth and location, and the crack–unbalance interaction on the dynamic of a crack rotor are undertaken. It will be illustrated that the emerging of super-harmonic frequency components and/or antiresonances can provide useful information on the presence of cracks and may be used on an on-line crack monitoring rotor system for small levels of damage.

scholarly journals Exact Receptance Function of Cracked Beams and Its Application for Crack Detection

2019 ◽  
Vol 2019 ◽  
pp. 1-19
Author(s):  
Khoa Viet Nguyen ◽  
Mai Van Cao
Keyword(s):  
Boundary Conditions ◽  
Numerical Simulations ◽  
Frequency Domain ◽  
Crack Detection ◽  
Harmonic Excitation ◽  
General Boundary ◽  
Second Derivative ◽  
General Boundary Conditions ◽  
Cracked Beams

The receptance function is very important which interrelates the harmonic excitation and the response of a structure in the frequency domain. This paper presents the exact receptance function of cracked beams. In this work, the “receptance curvature” is defined as the second derivative of the receptance. The influence of the crack on the receptance curvature is investigated. The results show that when there are cracks, the receptance curvature is influenced significantly at crack positions. This might be useful for the detection of cracks. In this paper, the derivation of exact receptance of the beam with general boundary conditions is presented, and the numerical simulations are provided.

A Nonlinear Analysis of the Axial Steady State Response of the Hydrodynamic Thrust Bearing-Rotor System Subjected to a Harmonic Excitation

2005 ◽  
Author(s):  
T. N. Shiau ◽  
W. C. Hsu
Keyword(s):  
Steady State ◽  
Reynolds Equation ◽  
Thrust Bearing ◽  
Harmonic Excitation ◽  
Rotor System ◽  
Time Dependent ◽  
Steady State Response ◽  
Harmonic Force ◽  
Oil Film ◽  
State Response

The purpose of this study is to investigate the nonlinear axial response of a thrust bearing-rotor system, which is subjected to an axial harmonic force. For the axial vibration of the rotor, the system forces include the external axial harmonic force and the reacting oil film forces, which are obtained by solving a time-dependent Reynolds Equation within the thrust pads of the thrust bearing. The time-dependent Reynolds Equation is solved by a finite difference method, and the system equation of motion is solved by the fourth-order Runge-Kutta method. A linear analysis is attempted in to evaluate its suitability for the situation under consideration. And the bearing stiffness and damping coefficients are investigated with parameters including the dimensionless wedge thickness, the initial oil film thickness and the rotor spin speed. The results show that the average steady state response will decrease as the harmonic axial force intensifies its fluctuating magnitude. The results also indicate that it will induce ultra-super harmonics when the axial harmonic force intensifies its fluctuating magnitude.

scholarly journals Stability Analysis of a Breathing Cracked Rotor with Imposed Mass Eccentricity

2015 ◽  
Vol 2015 ◽  
pp. 1-17 ◽  
Author(s):  
Huichun Peng ◽  
Qing He ◽  
Yaxin Zhen
Keyword(s):  
Crack Detection ◽  
Rotation Speed ◽  
Rotor System ◽  
Critical Ratio ◽  
Cracked Rotor ◽  
Stability Diagrams ◽  
Mass Eccentricity ◽  
Stability And Bifurcations ◽  
The Stability ◽  
Cracked Rotor System

The investigation of the effects of mass eccentricity on stability of a gravity dominated cracked Jeffcott rotor would generally provide practical applicability to crack detection and instability control of the heavy loading turbo-machinery system. Based upon the numerical Floquet method, the stability and bifurcations of the periodic time-dependent rotor with a transverse breathing crack are studied with respect to the varied mass eccentricity at different rotation speed, and the stability diagrams in the parameter plane are obtained which the previous studies have not covered. The numerical response of the cracked rotor system is also analyzed by the frequency spectrum to present the vibration characters while the rotation speed approaches the critical ratio. The detailed numerical eigenvalues of the transition matrix are applied to analyze the types of the bifurcations of the cracked rotor system. Three types of bifurcations are found and responses of the cracked rotor system at these bifurcations are presented for the visualized comparisons.

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