Spectral subtraction-based filter for experimental modal analysis under harmonics excitation force

Che Ku Eddy Nizwan Che Ku Husin,Mohd Fairusham Ghazali,Ahmad Razlan Yusoff

doi:10.15282/jmes.15.4.2021.02.0668

Che Ku Eddy Nizwan Che Ku Husin, Mohd Fairusham Ghazali + Show 1 more

Open Access

https://doi.org/10.15282/jmes.15.4.2021.02.0668

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Abstract

In modal analysis, measurement of input force and vibration response are crucial to accurately measure the transfer function of the structure. However, under operating condition, the force induced by operating machinery is impossible to be measured due to the sensor placement issue. In this case, the ambient response induced by the operating force should be suppressed to minimize the error in the Frequency Response Function (FRF) calculation. This paper presents the utilization of a modified spectral subtraction filter for ambient suppression. The introduction of effective ambient magnitude in gain function calculation has increased the efficiency of spectral subtraction filter. This parameter is calculated based on the phase information of the reconstructed artificial ambient response. The measurement using EMA was carried out on a motor-driven structure to verify the proposed technique. Two sets of data under shutdown and running condition were recorded to observe the effect of ambient operating force. Under the operating condition, the measured FRF show the non-identical features at operating frequencies as compared to the baseline data. The utilization of filtering process shows the ambient features contained in the transfer function was effectively suppressed. The output of filtering algorithm could provide an alternative option to perform EMA procedure under running condition.

Highlights

In structure dynamics study, modal parameters provide vital information to define the behaviour of a structure under dynamic loads
In the experimental modal analysis (EMA) procedure, one or more input forces are induced to the structures and the vibration response are measured at one or several locations to obtain the frequency response function (FRF)
This paper focuses on the development of a modified spectral subtraction filter algorithm to suppress the ambient features contained in the measured vibration response under operating condition

Summary

INTRODUCTION

Modal parameters provide vital information to define the behaviour of a structure under dynamic loads. Modal analysis technique named experimental modal analysis (EMA) was introduced to deliver reliable system identification algorithms for the determination of the modal parameters of a mechanical structure This technique is used to identify a system model for the structure based on the measured forces and the vibration response. Impact Synchronous Modal Analysis (ISMA) is one of the processing technique in the EMA procedure to apply the measurement under running condition This technique utilized the time-averaging method to filter out all the responses contributed by the unaccounted forces, leaving only the response due to the impact hammer [9]. The algorithm utilized the modified spectral subtraction to suppress the ambient response In this method, the phase of the vibration spectrum required a reallocation process to minimize the phase difference for the post-filter signals. A clean vibration response from impact forced is extracted based on the ratio between estimated ambient with measured impact response

EXPERIMENTAL SETUP

AND DISCUSSION

CONCLUSIONS