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

2012 ◽  
Vol 19 (5) ◽  
pp. 1071-1083 ◽  
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.

scholarly journals Operational Modal Analysis on a 3D Scaled Model of a 3-Storey Aluminium Structure

2018 ◽  
Vol 7 (4.27) ◽  
pp. 78
Author(s):  
M. Fadhil Shazmir ◽  
N. Ayuni Safari ◽  
M. Azhan Anuar ◽  
A. A.Mat Isa ◽  
Zamri A.R
Keyword(s):  
Domain Decomposition ◽  
Modal Analysis ◽  
Frequency Domain ◽  
Natural Frequencies ◽  
Operational Modal Analysis ◽  
Mode Shapes ◽  
Modal Parameters ◽  
Modal Assurance Criterion ◽  
Scaled Model ◽  
Frequency Domain Decomposition

Obtaining a good experimental modal data is essential in modal analysis in order to ensure accurate extraction of modal parameters. The parameters are compared with other extraction methods to ascertain its consistency and validity. This paper demonstrates the extraction of modal parameters using various identification algorithms in Operational Modal Analysis (OMA) on a 3D scaled model of a 3-storey aluminium structure. Algorithms such as Frequency Domain Decomposition (FDD), Enhanced Frequency Domain Decomposition (EFDD) and Stochastic Subspace Identification (SSI) are applied in this study to obtain modal parameters. The model test structure is fabricated of aluminium and assembled using bolts and nuts. Accelerometers were used to collect the responses and the commercial post processing software was used to obtain the modal parameters. The resulting natural frequencies and mode shapes using FDD method are then compared with other OMA parametric technique such as EFDD and SSI algorithm by comparing the natural frequencies and Modal Assurance Criterion (MAC). Comparison of these techniques will be shown to justify the validity of each technique used and hence confirming the accuracy of the measurement taken.    

Combined Deterministic-Stochastic Frequency-Domain Subspace Identification for Experimental and Operational Modal Analysis

Volume 1 ◽  
2004 ◽  
Author(s):  
Bart Cauberghe ◽  
Patrick Guillaume ◽  
Peter Verboven ◽  
Eli Parloo ◽  
Steve Vanlanduit
Keyword(s):  
Modal Analysis ◽  
Frequency Domain ◽  
Real Life ◽  
Power Spectra ◽  
Operational Modal Analysis ◽  
Subspace Identification ◽  
Input Output ◽  
Deterministic Models ◽  
Subspace Algorithm ◽  
Subspace Algorithms

Until recently frequency-domain subspace algorithms were limited to identify deterministic models from input/output measurements. In this paper, a combined deterministic-stochastic frequency-domain subspace algorithm is presented to estimate models from input/output spectra, frequency response functions or power spectra for application as experimental and operational modal analysis. The relation with time-domain subspace identification is elaborated. It is shown by both simulations and real-life test examples that the presented method outperforms traditional frequency-domain subspace methods.

Modal Characterization of MEMS Switches via Output Only and Input/Output Identification Methods

2011 ◽  
Author(s):  
Joel M. Book ◽  
Samuel F. Asokanthan
Keyword(s):  
Modal Analysis ◽  
Noise Signal ◽  
Experimental Modal Analysis ◽  
Modal Parameters ◽  
Identification Algorithm ◽  
Base Excitation ◽  
Mems Devices ◽  
Stochastic Subspace Identification ◽  
Output Only

MEMS devices typically have moving or oscillating mechanical parts, and characterization of their dynamics, including their modal parameters, is highly desirable. This paper is concerned with experimental implementation of a Stochastic Subspace Identification (SSI) algorithm as well a base excitation based identification algorithm for experimental modal analysis of a micro-cantilever switch. A white noise signal applied to the built-in electrostatic actuator in the switches excited a response measured using microscanning Laser Doppler Vibrometry (LDV). In the case of identification via the SSI, only the output response was used while the base excitation based algorithm employed the input and the output signals. The modal parameters found using MACEC matched well with those predicted by theory, and the results obtained via the two experimental identification approaches are in good agreement, thus providing confidence in using the SSI approach for experimental modal analysis of MEMS structures.

Effect of Bass Bar Tension on Modal Parameters of a Violin's Top Plate

2015 ◽  
Vol 39 (1) ◽  
pp. 145-149 ◽  
Author(s):  
Ewa B. Skrodzka ◽  
Bogumił B.J. Linde ◽  
Antoni Krupa
Keyword(s):  
Modal Analysis ◽  
Experimental Modal Analysis ◽  
Mode Shapes ◽  
Modal Parameters ◽  
Normal Value ◽  
Modal Damping

Abstract Experimental modal analysis of a violin with three different tensions of a bass bar has been performed. The bass bar tension is the only intentionally introduced modification of the instrument. The aim of the study was to find differences and similarities between top plate modal parameters determined by a bass bar perfectly fitting the shape of the top plate, the bass bar with a tension usually applied by luthiers (normal), and the tension higher than the normal value. In the modal analysis four signature modes are taken into account. Bass bar tension does not change the sequence of mode shapes. Changes in modal damping are insignificant. An increase in bass bar tension causes an increase in modal frequencies A0 and B(1+) and does not change the frequencies of modes CBR and B(1-).

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

Procedia CIRP ◽  
2018 ◽  
Vol 77 ◽  
pp. 473-476 ◽  
Author(s):  
Jan Berthold ◽  
Martin Kolouch ◽  
Volker Wittstock ◽  
Matthias Putz
Keyword(s):  
Modal Analysis ◽  
Machine Tools ◽  
Operational Modal Analysis ◽  
Modal Parameters

Frequency-Domain System Identification Techniques for Experimental and Operational Modal Analysis

2003 ◽  
Vol 36 (16) ◽  
pp. 1609-1614 ◽  
Author(s):  
Patrick Guillaume ◽  
Peter Verboven ◽  
Bart Cauberghe ◽  
Steve Vanlanduit ◽  
Eli Parloo ◽  
...  
Keyword(s):  
System Identification ◽  
Modal Analysis ◽  
Frequency Domain ◽  
Operational Modal Analysis ◽  
Identification Techniques

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

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>

scholarly journals Output-Only Modal Analysis Based on Improved Empirical Mode Decomposition Method

2015 ◽  
Vol 2015 ◽  
pp. 1-12 ◽  
Author(s):  
Shiqiang Qin ◽  
Qiuping Wang ◽  
Juntao Kang
Keyword(s):  
Modal Analysis ◽  
Empirical Mode Decomposition ◽  
Modal Parameters ◽  
Band Pass Filter ◽  
Pass Filter ◽  
Random Decrement Technique ◽  
Mode Decomposition ◽  
Frequency Components ◽  
Output Only ◽  
Emd Method

The output-only modal analysis for bridge structures based on improved empirical mode decomposition (EMD) is investigated in this study. First, a bandwidth restricted EMD is proposed for decomposing nonstationary output measurements with close frequency components. The advantage of bandwidth restricted EMD to standard EMD is illustrated by a numerical simulation. Next, the modal parameters are extracted from intrinsic mode function obtained from the improved EMD by both random decrement technique and stochastic subspace identification. Finally, output-only modal analysis of a railway bridge is presented. The study demonstrates the mode mixing issues of standard EMD can be restrained by introducing bandwidth restricted signal. Further, with the improved EMD method, band-pass filter is no longer needed for separating the closely spaced frequency components. The modal parameters extracted based on the improved EMD method show good agreement with those extracted by conventional modal identification algorithms.

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

2018 ◽  
Vol 141 (2) ◽  
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.

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

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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