Technical Brief

A Performance Study of Controlled Impact Timing on Harmonics Reduction in Operational Modal Testing

[+] Author and Article Information
Hong Cheet Lim

Mechanical Engineering Department,
Faculty of Engineering,
University of Malaya,
Kuala Lumpur 50603, Malaysia
e-mail: h_chet_l@siswa.um.edu.my

Zhi Chao Ong

Mechanical Engineering Department,
Faculty of Engineering,
University of Malaya,
Kuala Lumpur 50603, Malaysia
e-mails: zhichao83@gmail.com; alexongzc@um.edu.my

Zubaidah Ismail

Civil Engineering Department,
Faculty of Engineering,
University of Malaya,
Kuala Lumpur 50603, Malaysia
e-mail: zu_ismail@um.edu.my

Shin Yee Khoo

Mechanical Engineering Department,
Faculty of Engineering,
University of Malaya,
Kuala Lumpur 50603, Malaysia
e-mail: khooshinyee@um.edu.my

1Corresponding author.

Contributed by the Dynamic Systems Division of ASME for publication in the JOURNAL OF DYNAMIC SYSTEMS, MEASUREMENT,AND CONTROL. Manuscript received July 5, 2017; final manuscript received September 27, 2018; published online November 8, 2018. Assoc. Editor: Douglas Bristow.

J. Dyn. Sys., Meas., Control 141(3), 034501 (Nov 08, 2018) (6 pages) Paper No: DS-17-1338; doi: 10.1115/1.4041609 History: Received July 05, 2017; Revised September 27, 2018

As an alternative to operational modal analysis and classical experimental modal analysis (EMA), a novel method was introduced previously, namely impact-synchronous modal analysis (ISMA). The effectiveness ISMA on rotor and structural dynamic systems has been proven in previous literature. More recently, an automated impact device (AID) was introduced which utilized tachometer pulse as initiation signal and its effectiveness on ISMA was proven. An attempt to further enhance this device in term of equipment and cost is then proposed by replacing the tachometer with the in-use tri-axial accelerometer through utilizing the filtered response of cyclic load component as an initiation signal to control the impact device, which is also the primary aim for this study. Prior to modal testing, accuracy of this device is illustrated at desired phase angles of 0 deg, 90 deg, 180 deg, and 270 deg. Subsequently, frequency response function (FRF) estimations obtained for ISMA using enhanced AID has demonstrated the suppression capabilities of this device on disturbances, i.e., reduction of 93.58% at 30 Hz and 57.78% at 60 Hz, resulting in a high correlation for signature assurance criterion (SAC) and cross signature assurance criterion (CSAC). Modal parameters extracted from the EMA and ISMA using impact device are presented and compared, for the first three natural modes of the test rig. It is found that natural frequencies are deviating by less than 6%, whereas modal assurance criterion (MAC) values between the mode shapes of the two tests are found to be above 0.9.

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Ong, Z. C. , Lim, H. C. , Khoo, S. Y. , Ismail, Z. , Kong, K. K. , and Rahman, A. G. A. , 2017, “ Assessment of the Phase Synchronization Effect in Modal Testing During Operation,” J. Zhejiang Univ.-Sci., A, 18(2), pp. 92–105. [CrossRef]
Rahman, A. G. A. , Ismail, Z. , Noroozi, S. , and Ong, Z. C. , 2014, “ Enhancement of Impact-Synchronous Modal Analysis With Number of Averages,” J. Vib. Control, 20(11), pp. 1645–1655. [CrossRef]
Chao, O. Z. , Cheet, L. H. , Yee, K. S. , Rahman, A. G. A. , and Ismail, Z. , 2016, “ An Experimental Investigation on the Effects of Exponential Window and Impact Force Level on Harmonic Reduction in Impact-Synchronous Modal Analysis,” J. Mech. Sci. Technol., 30(8), pp. 3523–3532. [CrossRef]
Ong, Z. C. , and Lee, C. C. , 2015, “ Investigation of Impact Profile and Isolation Effect in Automated Impact Device Design and Control for Operational Modal Analysis,” ASME J. Dyn. Syst. Meas. Control, 137(9), p. 094504. [CrossRef]
Chao, O. Z. , Kor, M. A. M. A. , and Brandt, A. , 2015, “ Experimental Validation of Phase Synchronisation Effects in Optimising Impact-Synchronous Time Averaging,” Sixth International Operational Modal Analysis Conference (IOMAC-15), Gijon, Spain, May 12–14, pp. 629–636. https://www.researchgate.net/publication/282301845_Experimental_validation_of_phase_synchronisation_effects_in_optimising_Impact-Synchronous_Time_Averaging
Lim, H. C. , Ong, Z. C. , and Brandt, A. , 2018, “ Implementation of Phase Controlled Impact Device for Enhancement of Frequency Response Function in Operational Modal Testing,” J. Franklin Inst., 355(1), pp. 291–313. [CrossRef]
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Fig. 1

Filtered cyclic load component and dominant cyclic load component used for the calculation of the actual counter time. Response due to impact is expected at crest of periodic response from cyclic load.

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Fig. 2

Equipment setup with test rig defined by 20 measurement points. Manual impact hammer was used for static test and enhanced AID was used for 30 Hz test can be seen.

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Fig. 3

Starting position of response due to impacts (a) Φp = 0 deg, (b) Φp = 90 deg, (c) Φp = 180 deg, and (d) Φp = 270 deg can be seen

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Fig. 4

Frequency response function estimations for ISMA using enhanced AID with one average

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Fig. 5

Frequency response function estimations for ISMA using enhanced AID with 12 averages

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Fig. 7

Results of CSAC correlation between EMA and ISMA using enhanced AID for all measurement DOFs

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Fig. 6

Results of SAC correlation between EMA and ISMA using enhanced AID in the range of 8–27 Hz



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