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 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.

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.

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.

Structural Change Quantification in Rotor Systems Based on Measured Resonance and Antiresonance Frequencies

2013 ◽  
Author(s):  
Adam C. Wroblewski ◽  
Alexander H. Pesch ◽  
Jerzy T. Sawicki
Keyword(s):  
Structural Change ◽  
Frequency Response ◽  
Numerical Optimization ◽  
Element Model ◽  
Sufficient Information ◽  
Response Functions ◽  
Frequency Response Functions ◽  
Magnetic Actuators ◽  
Rotor Systems ◽  
Spatial Domains

A structural change quantification methodology is proposed in which the magnitude and location of a structural alteration is identified experimentally in a rotor system. The resonance and antiresonance frequencies are captured from multiple frequency response functions and are compared with baseline data to extract frequency shifts due to these features. The resulting expression contains sufficient information to identify the dynamic characteristics of the rotor in both the frequency and spatial domains. A finite element model with carefully selected tunable parameters is iteratively adjusted using a numerical optimization algorithm to determine the source of the structural change. The methodology is experimentally demonstrated on a test rig with a laterally damaged rotor and the frequency response functions are acquired through utilization of magnetic actuators positioned near the ball bearings.

Crack Identification in a Rotating Shaft via the Reverse Directional Frequency Response Functions

2009 ◽  
Vol 131 (1) ◽  
Author(s):  
Yun-Ho Seo ◽  
Chong-Won Lee ◽  
K. C. Park
Keyword(s):  
Frequency Response ◽  
Transverse Crack ◽  
Crack Identification ◽  
Response Functions ◽  
Flexible Rotor ◽  
Rotating Shaft ◽  
Frequency Response Functions ◽  
Rotor Systems ◽  
Crack Location ◽  
Reference Map

A method is proposed for identifying the location of an open transverse crack in flexible rotor systems by modeling the crack as a localized element with rotating asymmetry. It exploits the strong correlations between the modal constants of the reverse directional frequency response functions (r-dFRFs) and the degree and location of asymmetry. A map of the modal constants of the r-dFRFs for all elements is constructed to identify the location of crack by comparing the identified modal constants to those of the reference map. This paper also addresses practical issues associated with measurement noises and limited number of sensors. The proposed crack identification method is finally applied to a flexible rotor system with an open transverse crack in order to demonstrate the identification procedure for detection of the crack location.

Sign in / Sign up

Export Citation Format

Share Document