Complex Modal Testing Methods for Rotating Machinery

1991 ◽  
Author(s):  
Chong-Won Lee ◽  
Young-Don Joh
Keyword(s):  
Frequency Response ◽  
Rotating Machinery ◽  
Modal Testing ◽  
Response Functions ◽  
Testing Methods ◽  
Complex Signals ◽  
Indirect Assessment ◽  
Testing Method ◽  
Effective Use ◽  
Complex Modal

Abstract Various modal testing methods are proposed for the effective use of complex modal testing for rotating machinery, focusing on excitations and measurements. The proposed methods are developed, based on the input/output relationships for complex signals, for the direct or indirect assessment of frequency response and coherence functions between complex inputs and outputs. The proposed testing methods and the classical modal testing method are compared in consideration of required number of frequency response functions (FRFs) and testing efforts.

Identification of Rotating Asymmetry in Rotating Machines by Using Reverse dFRF

1999 ◽  
Author(s):  
Chong-Won Lee ◽  
Kye-Si Kwon
Keyword(s):  
Frequency Response ◽  
Response Function ◽  
Frequency Response Function ◽  
Modal Testing ◽  
Vibration Sensor ◽  
Response Functions ◽  
Physical Realization ◽  
Simple Method ◽  
Testing Method ◽  
Asymmetric Rotor

Abstract A quick and easy but comprehensive identification method for asymmetry in an asymmetric rotor is proposed based on complex modal testing method. In this work, it is shown that the reverse directional frequency response function (reverse dFRF), which indicates the degree of asymmetry, can be identified with a simple method requiring only one vibration sensor and one exciter. To clarify physical realization associated with estimation of the reverse dFRF, its relation to the conventional frequency response functions, which are defined by the real input (exciter) and output (vibration sensor), are extensively discussed.

Unidirectional Excitation Technique for Complex Modal Testing of Asymmetric Rotor Systems: Application to DTG

1997 ◽  
Author(s):  
Seok-Ku Lee ◽  
Chong-Won Lee
Keyword(s):  
Coordinate System ◽  
Frequency Response ◽  
Modal Testing ◽  
Theoretical Development ◽  
Response Functions ◽  
Rotor Systems ◽  
Numerical Example ◽  
Stationary Coordinate System ◽  
Asymmetric Rotor ◽  
Complex Modal

Abstract Unidirectional excitation technique is presented for the complex modal testing of asymmetric rotor systems. The theoretical development, which is made strictly in the stationary coordinate system, enables the unidirectional excitation to effectively estimate the directional frequency response functions. It far lessens the testing efforts a numerical example of the dynamically tuned gyroscope (DTG) is treated to demonstrate the practicality of the complex modal testing.

Identification of rotating asymmetry in rotating machines by using reverse directional frequency response functions

2001 ◽  
Vol 215 (9) ◽  
pp. 1053-1061
Author(s):  
C-W Lee ◽  
K-S Kwon
Keyword(s):  
Frequency Response ◽  
Frequency Response Function ◽  
Modal Testing ◽  
Vibration Sensor ◽  
Vibration Measurement ◽  
Response Functions ◽  
Physical Realization ◽  
Rotating Machines ◽  
Frequency Response Functions ◽  
Testing Method

A quick and easy but comprehensive identification method for rotating asymmetry in rotating machines is proposed, based on the complex modal testing method. In this work it is shown that the reverse directional frequency response function (reverse dFRF), which indicates the degree of asymmetry, can be identified with a simple testing method requiring only a single vibration sensor and a single exciter. To clarify physical realization associated with estimation of the reverse dFRF, its relation to the conventional frequency response functions, which are defined by the real input (excitation) and output (vibration measurement), are discussed extensively.

Change of modal parameters due to crack growth in a tripod tower platform

1993 ◽  
Vol 20 (5) ◽  
pp. 801-813 ◽  
Author(s):  
Yin Chen ◽  
A. S. J. Swamidas
Keyword(s):  
Finite Element ◽  
Frequency Response ◽  
Response Function ◽  
Frequency Response Function ◽  
Experimental Results ◽  
Modal Testing ◽  
Modal Parameters ◽  
Response Functions ◽  
Frequency Response Functions ◽  
Strain Frequency

Strain gauges, along with an accelerometer and a linear variable displacement transducer, were used in the modal testing to detect a crack in a tripod tower platform structure model. The experimental results showed that the frequency response function of the strain gauge located near the crack had the most sensitivity to cracking. It was observed that the amplitude of the strain frequency response function at resonant points had large changes (around 60% when the crack became a through-thickness crack) when the crack grew in size. By monitoring the change of modal parameters, especially the amplitude of the strain frequency response function near the critical area, it would be very easy to detect the damage that occurs in offshore structures. A numerical computation of the frequency response functions using finite element method was also performed and compared with the experimental results. A good consistency between these two sets of results has been found. All the calculations required for the experimental modal parameters and the finite element analysis were carried out using the computer program SDRC-IDEAS. Key words: modal testing, cracking, strain–displacement–acceleration frequency response functions, frequency–damping–amplitude changes.

Improving Traditional Balancing Methods for High-Speed Rotors

1996 ◽  
Vol 118 (1) ◽  
pp. 95-99 ◽  
Author(s):  
J. Ling ◽  
Y. Cao
Keyword(s):  
Experimental Data ◽  
Frequency Response ◽  
Frequency Response Function ◽  
High Speed ◽  
Rotating Machinery ◽  
Response Functions ◽  
Frequency Response Functions ◽  
Influence Coefficients ◽  
Mathematical Equations ◽  
Rotor Balancing

This paper introduces frequency response functions, analyzes the relationships between the frequency response functions and influence coefficients theoretically, and derives corresponding mathematical equations for high-speed rotor balancing. The relationships between the imbalance masses on the rotor and frequency response functions are also analyzed based upon the modal balancing method, and the equations related to the static and dynamic imbalance masses and the frequency response function are obtained. Experiments on a high-speed rotor balancing rig were performed to verify the theory, and the experimental data agree satisfactorily with the analytical solutions. The improvement on the traditional balancing method proposed in this paper will substantially reduce the number of rotor startups required during the balancing process of rotating machinery.

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