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 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.

Experimental Investigation on Power Consumption in Reactor Coolant Pumps with the Function of the Flywheel

2013 ◽  
Vol 744 ◽  
pp. 58-62
Author(s):  
Chun Ming Gong ◽  
Zheng Qiang Yao ◽  
Yao Zong Hou ◽  
Ya Bo Xue ◽  
De Cheng
Keyword(s):  
Experimental Investigation ◽  
Power Consumption ◽  
Experimental Method ◽  
Dynamic Characteristics ◽  
Nuclear Reactor ◽  
Simulation Analysis ◽  
Rotor System ◽  
Coolant Pump ◽  
Reactor Coolant ◽  
Special Working

This article mainly discusses the dynamic characteristics of the experimental rotor system under the abrupt power shut circumstances, and to search the distribution of the power consumption during special working processes with an experimental method. On the basis of the experimental results, the simulation analysis is carried out on the Andritz RCP, and therefore, the dynamic characteristics of the real nuclear reactor coolant pump can be forecast, which just meets the need of the safety running in nuclear plant.

Three-Dimensional Ultrasonic Crack Detection in Anisotropic Materials

1997 ◽  
Vol 9 (2) ◽  
pp. 59-79 ◽  
Author(s):  
J. Mattsson ◽  
A. J. Niklasson ◽  
A. Eriksson
Keyword(s):  
Crack Detection ◽  
Three Dimensional ◽  
Anisotropic Materials

Experimental Method in Antiquity.

1964 ◽  
Vol 19 (6) ◽  
pp. 419-419
Author(s):  
Frank P. Jones
Keyword(s):  
Experimental Method
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