Identification of modal parameters of machine tools during cutting by operational modal analysis

In high-precision machining, it is very important to obtain operational modal parameters of machine tools to ensure the quality of machined parts. More specifically, the prediction of free chatter boundary is a critical requirement for improving productivity, which requires accurate dynamic parameters under operational conditions. Operational modal analysis is an effective method to estimate dynamic parameters of the tested system. However, for machine tools, the direct application of the operational modal analysis method is not feasible. In measured responses, periodic components are very preponderant during cutting, which is mainly caused by the periodic cutting force. In order to overcome this issue and to extract operational modal parameters of machine tools, the method of time-synchronous-subtraction based on the principle of time-synchronization-averaging is proposed. The correctness of the proposed approach is demonstrated by a simulation experiment, and the feasibility is verified through a milling experiment. The results show that the time-synchronous-subtraction method can well eliminate harmonics in the vibration response under the real cutting condition. The method is not only accurate but also simple in calculation.

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Evaluation of the effect of operational modal analysis algorithms on identified modal parameters of railway bridges

10.2749/ghent.2021.0441 ◽

2021 ◽

Author(s):

Mohammadreza Salehi ◽

Kultigin Demirlioglu ◽

Emrah Erduran

Keyword(s):

Modal Analysis ◽

Health Monitoring ◽

Iron Ore ◽

Operational Modal Analysis ◽

Modal Parameters ◽

Vibration Source ◽

Light Weight ◽

Railway Bridges ◽

Different Types ◽

Vibration Responses

<p>The accuracy of modal parameters identified by Operational Modal Analysis (OMA) algorithms is of vital importance in vibration-based health monitoring. This paper reports the effects of using different OMA algorithms on identified modal parameters of railway bridges. For this purpose, comparison and application of three different OMA methods including FDD, ARX, SSI-COV are discussed. The vibration measurements are conducted on two railway bridges in Northern Norway for using five triaxial accelerometers. The first bridge is a single-span bridge with the length of 50 m, while the second is a two-span bridge with a total length of 85m. OMA has been conducted on the free vibration responses after passage of different types of trains including light-weight railway vehicles and heavily loaded iron ore trains to evaluate the variation of the identified modal parameters with the chosen algorithm and the vibration source on the OMA results.</p>

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Signal Processing for Operational Modal Analysis of a Jacket-Type Offshore Platform: Sea Test Study

Journal of Offshore Mechanics and Arctic Engineering ◽

10.1115/1.4041510 ◽

2018 ◽

Vol 141 (2) ◽

Cited By ~ 1

Author(s):

Xingxian Bao ◽

Zhihui Liu ◽

Chen Shi

Keyword(s):

Noise Reduction ◽

Modal Analysis ◽

Measured Data ◽

Offshore Platform ◽

Operational Modal Analysis ◽

Ambient Vibration ◽

Data Matrix ◽

Modal Parameters ◽

Stability Diagrams ◽

Free Decay

Operational modal analysis (OMA) has been widely used for large structures. However, measured signals are inevitably contaminated with noise and may not be clean enough for identifying the modal parameters with proper accuracy. The traditional methods to estimate modal parameters in noisy situation are usually absorbing the “noise modes” first, and then using the stability diagrams to distinguish the true modes from the “noise modes.” However, it is still difficult to sort out true modes because the “noise modes” will also tend to be stable as the model order increases. This study develops a noise reduction procedure for polyreference complex exponential (PRCE) modal analysis based on ambient vibration responses. In the procedure, natural excitation technique (NExT) is first applied to get free decay responses from measured (noisy) ambient vibration data, and then the noise reduction method based on solving the partially described inverse singular value problem (PDISVP) is implemented to reconstruct a filtered data matrix from the measured data matrix. In our case, the measured data matrix is block Hankel structured, which is constructed based on the free decay responses. The filtered data matrix should maintain the block Hankel structure and be lowered in rank. When the filtered data matrix is obtained, the PRCE method is applied to estimate the modal parameters. The proposed NExT-PDISVP-PRCE scheme is applied to field test of a jacket type offshore platform. Results indicate that the proposed method can improve the accuracy of OMA.

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Operational modal analysis of a nonlinear oscillation system under a harmonic excitation

Proceedings of the Institution of Mechanical Engineers Part C Journal of Mechanical Engineering Science ◽

10.1177/0954406220977550 ◽

2020 ◽

pp. 095440622097755

Author(s):

Xuchu Jiang ◽

Feng Jiang ◽

Biao Zhang

Keyword(s):

Modal Analysis ◽

Nonlinear Oscillation ◽

Normal Modes ◽

Nonlinear Normal Modes ◽

Harmonic Excitation ◽

Forced Response ◽

Operational Modal Analysis ◽

Single Frequency ◽

Modal Parameters ◽

Oscillation System

Operational modal analysis (OMA) is a procedure that allows the modal parameters of a structure to be extracted from the measured response to an unknown excitation generated during operation. Nonlinearity is inevitably and frequently encountered in OMA. The problem: The traditional OMA method based on linear modal theory cannot be applied to a nonlinear oscillation system. The solution: This paper aims to propose a nonlinear OMA method for nonlinear oscillation systems. The new OMA method is based on the following: (1) a self-excitation phenomenon is caused by nonlinear components; (2) the nonlinear normal modes (NNMs) of the system appear under a single-frequency harmonic excitation; and (3) using forced response data, the symbolic regression method (SR) can be used to automatically search for the NNMs of the system, whose modal parameters are implicit in the expression structure expressing each NNM. The simulation result of a three-degree-of-freedom (3-DOF) nonlinear system verifies the correctness of the proposed OMA method. Then, a disc-rod rotor model is considered, and the proposed OMA method’s capability is further evaluated.

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EFFECTIVENESS OF OPERATIONAL MODAL ANALYSIS (OMA) FOR DAMAGE DETECTION IN FIBERGLASS REINFORCED EPOXY

Jurnal Teknologi ◽

10.11113/jt.v76.5615 ◽

2015 ◽

Vol 76 (8) ◽

Author(s):

Haizuan Abd Rahman ◽

Ahmad Azlan Mat Isa ◽

Abdul Rahim Bahari

Keyword(s):

Finite Element Method ◽

Boundary Condition ◽

Composite Material ◽

Damage Detection ◽

Modal Analysis ◽

Detection Method ◽

Small Deviation ◽

Operational Modal Analysis ◽

Modal Parameters ◽

Fiber Glass

This study attempts to apply vibration-based damage detection method specifically Operational Modal Analysis (OMA) on fiberglass reinforced epoxy plate. OMA is used on healthy fiber glass reinforced epoxy plate to extract the modal parameters and the procedure is extended to damaged fiberglass reinforced epoxy plate. Both healthy and damaged composite material are tested under different boundary conditions i.e. free-free on 4 edges, 1 edge clamped, 2 edges clamped, 3 edges clamped and 4 edges of free-free boundary condition. The result of frequency from OMA was compared analytically with Finite Element Method (FEM). Nastran software is employed in this study. The FEM using Nastran shows that the result obtained is not accurate enough compared to OMA. Therefore, another method was applied to look at the effectiveness of OMA method using Experimental Modal Analysis (EMA). It was observed that both EMA and OMA methods gave small deviation and good correlation.

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Transmissibilty-Based Operational Modal Analysis for Flight Flutter Testing Using Exogenous Inputs

Shock and Vibration ◽

10.1155/2012/938039 ◽

2012 ◽

Vol 19 (5) ◽

pp. 1071-1083 ◽

Cited By ~ 6

Author(s):

Christof Devriendt ◽

Tim De Troyer ◽

Gert De Sitter ◽

Patrick Guillaume

Keyword(s):

Modal Analysis ◽

Frequency Domain ◽

Experimental Modal Analysis ◽

Operational Modal Analysis ◽

Modal Parameters ◽

Input Output ◽

Output Only ◽

Flutter Testing

During the recent years several new tools have been introduced by the Vrije Universiteit Brussel in the field of Operational Modal Analysis (OMA) such as the transmissibility based approach and the the frequency-domain OMAX concept. One advantage of the transmissibility based approach is that the ambient forces may be coloured (non-white), if they are fully correlated. The main advantage of the OMAX concept is the fact that it combines the advantages of Operational and Experimental Modal Analysis: ambient (unknown) forces as well as artificial (known) forces are processed simultaneously resulting in improved modal parameters. In this paper, the transmissibility based output-only approach is combined with the input/output OMAX concept. This results in a new methodology in the field of operational modal analysis allowing the estimation of (scaled) modal parameters in the presence of arbitrary ambient (unknown) forces and artificial (known) forces.

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Determination of characteristic Parameters of masonry Structures via Operational Modal Analysis

International Journal of Engineering Sciences ◽

10.36224/ijes.120304 ◽

2019 ◽

Vol 12 (3) ◽

Author(s):

Ali Koçak ◽

Burak Toydemir ◽

Melih Bulgur

Keyword(s):

Modal Analysis ◽

Operational Modal Analysis ◽

Physical Models ◽

Mode Shapes ◽

Modal Parameters ◽

Model Parameters ◽

Masonry Structures ◽

Characteristic Parameters ◽

Characteristic Model

Commonly, material and vibration characteristics of masonry structures remain uncertain in the evaluation of existing structures under external loads such as earthquake, heat, wind, etc. In addition, determination of compressive and tensile strength of a masonry walls is not straightforward. However, it is very important to know the characteristic parameters such as eigen values, periods and mode shapes of a structure beforehand in order to create accurate and reliable physical models. Since each historical structure has its own unique wall and bearing characteristics, it is not possible to accept random initial values for the bearing capacity and other parameters of the structure. Besides, conducting vertical and lateral loading experiments is costly and time consuming. An alternative way to determine these parameters that govern the structural behavior is to carry out experimental vibration tests using accelerometers. This method, which is also called as Operational Modal Analysis (OMA), is used to obtain the free and forced vibration response of structures by experimental means and to determine the modal parameters of the structure. OMA is very important for the appropriate use of an analysis method and the model parameters used in the analysis. In this study, two masonry buildings, one of which is historical, are discussed and the modal parameters of buildings are determined experimentally with OMA. Characteristic values obtained from OMA were compared with the three dimensional finite element method by adjusting characteristic model parameters.

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A new modal analysis method applied to changing machine tool using clustering

Advances in Mechanical Engineering ◽

10.1177/1687814020968323 ◽

2020 ◽

Vol 12 (10) ◽

pp. 168781402096832

Author(s):

Xuchu Jiang ◽

Xinyong Mao ◽

Yingjie Chen ◽

Caihua Hao

Keyword(s):

Machine Tool ◽

Modal Analysis ◽

Natural Frequency ◽

Efficient Method ◽

Machine Tools ◽

Vibration Signal ◽

Modal Parameters ◽

Analysis Method ◽

Modal Parameter ◽

The Difference

The states of the machine tool, such as the components’ position and the spindle speed, play leading roles in the change of dynamic parameters. However, the traditional modal analysis method that modal parameters manually identified from vibration signal is greatly interfered by harmonics, and the process of eliminating interference is very inefficient and subjective. At present, there is a lack of a standard and efficient method to characterize modal parameter changes in different states of machine tools. This paper proposes a new machine tool modal classification analysis method based on clustering. The characteristics related to the modal parameters are extracted from the response signal in different states, and the clustering results are used to reflect the changes of machine tool modal parameters. After the amplitude of the frequency response function is normalized, the characteristics related to the natural frequency are acquired, and the clustering results further reflect the difference of the natural frequency of the signal. The new method based on clustering can be a standard and efficient method to characterize modal parameter changes in different states of machine tools.

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Chatter prediction based on operational modal analysis and an adaptive complex Morlet filter

Insight - Non-Destructive Testing and Condition Monitoring ◽

10.1784/insi.2020.62.8.484 ◽

2020 ◽

Vol 62 (8) ◽

pp. 484-492

Author(s):

Kai Yang ◽

Guofeng Wang ◽

Kaile Ma

Keyword(s):

Modal Analysis ◽

Machine Tools ◽

Production Efficiency ◽

Stability Boundary ◽

Operational Modal Analysis ◽

Modal Parameter ◽

Local Character ◽

Specific Frequency ◽

Harmonic Components ◽

The Stability

Chatter that occurs between a cutting tool and a workpiece greatly reduces the surface quality and production efficiency. Therefore, it is of great importance to predict and avoid chatter so as to guarantee the stability of the manufacturing process. To realise the accurate prediction of the stability boundary of machine tools, operational modal analysis (OMA) is increasingly receiving attention due to its adequate consideration of variations in working conditions in the industrial environment. However, because of the influence of harmonic components in the response signals, the accuracy in identifying the modal parameters is seriously compromised. In this paper, an adaptive complex Morlet filter (ACMF) is presented to remove the harmonic components by adaptively adjusting the centre frequency and bandwidth according to the local character of the ambient environment in a specific frequency range and filtering out harmonic components that are not strict integer multiples of the fundamental frequency owing to non-rigid periodic motion of the machine tool spindle. In order to show the effectiveness of the proposed method, milling experiments are carried out and experimental modal analysis (EMA) is utilised to make comparisons with the proposed method. Moreover, comparisons between the ACMF and two other typical filtering methods are made. The results indicate that the proposed method performs well in modal parameter recognition for machine tools.

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Application of Operational Modal Analysis on Railway Vehicles Using on Track Measurements

2013 Joint Rail Conference ◽

10.1115/jrc2013-2432 ◽

2013 ◽

Author(s):

Lara Mª Erviti Calvo ◽

Gorka Agirre Castellanos ◽

Igor Alonso Portillo

Keyword(s):

Modal Analysis ◽

Operational Modal Analysis ◽

Modal Parameters ◽

Railway Vehicle ◽

Correct Identification ◽

Static Test ◽

Railway Vehicles ◽

Analysis Techniques ◽

Behavior Design ◽

Nonlinear Components

Nowadays the application of experimental modal analysis techniques on railway vehicles is gaining importance. A correct identification of modal characteristics allows improving the dynamic behavior design of the vehicle and so reaching higher running speeds and accomplishing better comfort levels. So far, in the railway sector only conventional modal analysis techniques have been used. With these techniques, the modal parameters are determined during a static test by measuring the responses of the system to one or multiple known forces. This paper presents the application of the Operational Modal Analysis (OMA) technique on a railway vehicle. This technique determines the modal parameters employing only the responses of the system to an unknown excitation. In this way, the data to be used can be acquired during on track test which presents three main advantages. The first one is that the nonlinear components of the suspensions are working in their normal operating condition which is difficult to achieve during a static test. The second one is that the wheel spinning effect is taken into account. Finally, the test can be combined with other type of track tests, reducing the period of time before delivery of the vehicle to the client. In the case under study, the OMA technique is applied by means of commercial software to measurements performed on a passengers train. The modal parameters obtained for the carbody and one of the bogies are presented.

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