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Showing papers on "Modal testing published in 2008"


Journal ArticleDOI
TL;DR: In this paper, the variance estimation procedure uses the first-order sensitivity of the modal parameter estimates to perturbations of the measured output-only data, which is applicable for the reference-based covariance-driven stochastic subspace identification algorithm.

350 citations


Journal ArticleDOI
TL;DR: In this paper, the use of the combined deterministic-stochastic subspace identification algorithm for the experimental modal analysis of mechanical structures is discussed The algorithm requires artificial forces to be applied to the structure, so it can also be used for operational modality analysis (OMA), since the excitation level of the artificial forces can be low compared to the ambient forces.

293 citations


Journal ArticleDOI
TL;DR: In this article, the authors presented the physical meaning of the frequency domain decomposition (FDD) method to estimate the modal parameters of a nine-storey reinforced concrete (RC) dwelling in Grenoble (France).

163 citations


Journal ArticleDOI
TL;DR: In this paper, the authors presented two modal identification methods that extract dynamic characteristics from output-only data sets collected by a low-cost and rapid-to-deploy wireless structural monitoring system installed upon a long-span cable-stayed bridge.

125 citations


Journal ArticleDOI
TL;DR: In this paper, a base-excitation modal testing technique is adopted to measure the natural frequencies and mode shapes of dragonfly wings severed from thoraxes and glued onto the base of a shaker, which is capable of inducing translational motion in the lateral direction of the wing plane.

108 citations


Journal ArticleDOI
TL;DR: In this article, a seismic damage identification method for buildings with steel moment-frame structure is presented, which is based on artificial neural networks and modal variables, and the results are successful as concern as the robustness of the method.

99 citations


Journal ArticleDOI
TL;DR: In this paper, the effects on tree behavior under forced vibration are not firmly established on 17 olive trees (Olea europaea L) growing in an intensively-managed orchard using modal testing techniques.
Abstract: The mechanical harvesting of fruit for oil production in an intensive olive tree orchard is generally accomplished by applying vibration to the tree’s trunk. This vibration is consequently transmitted to the branches, causing the fruit to detach. Although this practice is commonly used, the effects on tree behavior under forced vibration are not firmly established. Dynamic analysis was performed on 17 olive trees (Olea europaea L.) growing in an intensively-managed orchard using modal testing techniques. Modal parameter identification was focused inside the range excitation frequency used by the most commonly available trunk shakers on the market. The olive trees featuring a low morphological variability and modal parameters were obtained for a representative olive tree. The first two modes of vibration of the main tree frame were identified with damping ratios of 26.9 and 17.1% and natural frequencies of 20.2 and 37.7 Hz, respectively. A third mode of vibration of less importance was found at a higher frequency. Therefore, many local modes of vibration were detected near these natural frequencies, primarily located on secondary branches. During the testing, the olive trees behaved like a damped harmonic oscillator with predominantly mass damping in these modes.

70 citations


Patent
16 May 2008
TL;DR: In this paper, a system and method for detecting structural damage is provided that utilizes a general order perturbation methodology involving multiple perturbations parameters, which is used iteratively in conjunction with an optimization method to identify the stiffness parameters of structures using natural frequencies and/or mode shape information.
Abstract: A system and method for detecting structural damage is provided that utilizes a general order perturbation methodology involving multiple perturbation parameters. The perturbation methodology is used iteratively in conjunction with an optimization method to identify the stiffness parameters of structures using natural frequencies and/or mode shape information. The stiffness parameters are then used to determine the location and extent of damage in a structure. A novel stochastic model is developed to model the random impact series produced manually or to generate a random impact series in a random impact device. The random impact series method or the random impact device can be used to excite a structure and generate vibration information used to obtain the stiffness parameters of the structure. The method or the device can also just be used for modal testing purposes. The random impact device is a high energy, random, and high signal-to-noise ratio system.

68 citations


Journal ArticleDOI
TL;DR: In this paper, an approximation approach of seismic analysis of two-way asymmetric building systems under bi-directional seismic ground motions is proposed, where a three-degree-of-freedom (3DOF) modal stick is developed to simulate the modal pushover curve with the stated bifurcating characteristic.
Abstract: An approximation approach of seismic analysis of two-way asymmetric building systems under bi-directional seismic ground motions is proposed. The procedures of uncoupled modal response history analysis (UMRHA) are extended to two-way asymmetric buildings simultaneously excited by two horizontal components of ground motion. Constructing the relationships of two-way base shears versus two-way roof translations and base torque versus roof rotation in ADRS format for a two-way asymmetric building, each modal pushover curve bifurcates into three curves in an inelastic state. A three-degree-of-freedom (3DOF) modal stick is developed to simulate the modal pushover curve with the stated bifurcating characteristic. It requires the calculation of the synthetic earthquake and angle β. It is confirmed that the 3DOF modal stick is consistent with single-degree-of-freedom modal stick in an elastic state. A two-way asymmetric three-story building was analyzed by UMRHA procedure incorporating the proposed 3DOF modal sticks. The analytical results are compared with those obtained from nonlinear response history analysis. It is shown that the 3DOF modal sticks are more rational and effective in dealing with the assessment of two-way asymmetric building systems under two-directional seismic ground motions.

68 citations


Journal ArticleDOI
TL;DR: The framework presented in this paper will allow to investigate the effects of various realistic damage scenarios in long-span cable-supported (suspension and cable-stayed) bridges on changes in modal identification results.
Abstract: In this paper, wind-induced vibration response of Vincent Thomas Bridge, a suspension bridge located in San Pedro near Los Angeles, California, is simulated using a detailed three-dimensional finite element model of the bridge and a state-of-the-art stochastic wind excitation model. Based on the simulated wind-induced vibration data, the modal parameters (natural frequencies, damping ratios, and mode shapes) of the bridge are identified using the data-driven stochastic subspace identification method. The identified modal parameters are verified by the computed eigenproperties of the bridge model. Finally, effects of measurement noise on the system identification results are studied by adding zero-mean Gaussian white noise processes to the simulated response data. Statistical properties of the identified modal parameters are investigated under increasing level of measurement noise. The framework presented in this paper will allow to investigate the effects of various realistic damage scenarios in long-span cable-supported (suspension and cable-stayed) bridges on changes in modal identification results. Such studies are required in order to develop robust and reliable vibration-based structural health monitoring methods for this type of bridges, which is a long-term research objective of the authors.

65 citations



Journal ArticleDOI
TL;DR: In this paper, the radial electromagnetic force distribution along the air gap, which is the main source of vibration, is calculated and developed into a double Fourier series in space and time.
Abstract: A method for determining the signatures of dynamic eccentricity in the airgap force distribution and vibration pattern of induction machine is presented. The radial electromagnetic force distribution along the airgap, which is the main source of vibration, is calculated and developed into a double Fourier series in space and time. Finite element simulations of faulty and healthy machines are performed. They show that the electromagnetic force distribution is a sensible parameter to the changes in the machine condition. The computations show the existence of low frequency and low order force distributions, which can be used as identifiable signatures of the motor condition by measuring the corresponding low order vibration components. These findings are supported by vibration measurements and modal testing. The low frequency components offer an alternative way to the monitoring of slot passing frequencies, bringing new components that allow to discriminate between dynamic eccentricity and rotor mechanical unbalance. The method also revealed a non linear relationship between loading, stress waves and vibration during dynamic eccentricity.

Journal ArticleDOI
TL;DR: In this paper, the authors present the most relevant results obtained from the application of different output-only modal identification methods to data collected in dynamic tests of the new Braga Sports Stadium suspended roof and the subsequent finite element model correlation analysis.

Journal ArticleDOI
TL;DR: In this article, different criteria based on frequencies or mode shapes are applied to detect damage in reinforced concrete beams for which a few natural frequencies and/or mode shapes, obtained by experimental modal analysis, are available.

Journal ArticleDOI
TL;DR: In this paper, the smooth orthogonal decomposition eigenvalue problem formulated from white-noise induced response data can be tied to the unforced structural eigen value problem, and thus can be used for modal parameter estimation.

Proceedings ArticleDOI
01 Jan 2008
TL;DR: In this article, a non-linear modal analysis of mechanical systems with contact and friction interfaces is proposed, based on a frequency domain formulation of the dynamical system's equations of motion.
Abstract: A method for non-linear modal analysis of mechanical sys- tems with contact and friction interfaces is proposed. It is based on a frequency domain formulation of the dynamical system's equations of motion. The dissipative aspects of these non- linearities result in complex eigensolutions and the modal pa- rameters (natural frequency and modal damping) can be obtained without any assumptions on the external excitation. The gener- ality of this approach makes it possible to address any kind of periodic regimes, in free and forced response. In particular, sta- bility analysis in flutter applications can be performed. Applications for the design of friction ring dampers for blisks and for the dynamical simulation of bladed disk with dove- tail attachment are proposed. Finally, we propose a study of dy- namical behaviour coupling with the calculation of fretting-wear at the interfaces based on non-linear modal characterization.

Journal ArticleDOI
TL;DR: In this paper, a historical masonry minaret, its finite element modeling, modal testing, and finite element model calibration is described. Butler et al. presented a 3D finite element modelling of the minaret to obtain the analytical frequencies and mode shapes.
Abstract: This paper describes a historical masonry minaret, its finite element modeling, modal testing, and finite element model calibration. Iskenderpasa historical masonry minaret located in Trabzon City Center, Turkey, is selected as an application. Modal analysis is performed on the developed 3-D finite element model of the minaret to obtain the analytical frequencies and mode shapes. The ambient vibration tests on the minaret under environmental excitations, such as traffic loads and wind, are conducted. The output-only modal parameter identification is carried out by using peak picking of the average normalized power spectral densities in the frequency domain and stochastic subspace identification in the time domain. Dynamic characteristics such as natural frequencies, mode shapes, and damping ratios are determined. The finite element model of the minaret is calibrated to minimize the differences between analytically and experimentally estimated modal properties by changing some uncertain modeling parameters such as material properties and boundary conditions. At the end of the study, maximum differences in the natural frequencies are reduced on an average from 27 % to 5 %. A good agreement is also found between analytical and experimental natural frequencies and mode shapes after model calibration.

Journal ArticleDOI
TL;DR: In this article, a modal controller is implemented on a digital controller board, and experimental tests with the floor panel and center panel of a car body are carried out to validate the proposed concept.

Journal ArticleDOI
TL;DR: In this article, a semi-adaptive modal control strategy in deferred time is proposed to attenuate the problems of initial operating conditions such as boundary conditions, and the sensitivity of control performance to modal parameter variation is presented.
Abstract: Modal active control, based on a state model, is an efficient method of increasing the lifetime of electronic boards by using piezoelectric components. In the case of industrial mass production, dispersions lead to changes in mechanical and electromechanical properties. Moreover, initial operating conditions such as boundary conditions can change during the lifetime of the control and modify its efficiency and stability. Therefore, a semi-adaptive modal control strategy in deferred time is proposed to attenuate these problems. Firstly modal control gains are calculated by using a classical linear quadratic Gaussian algorithm with the nominal model including mode shapes. Then control I/O data are collected by an identification system that uses on-board piezoelectric components. A subspace method is implemented to estimate modal matrices in order to update the controller. The sensitivity of control performance to modal parameter variation is presented. Estimated control frequencies and modal damping are finally used to update modal control gains. The effectiveness of the proposed method is examined through numerical simulation and experimental tests in the case of boundary condition modifications. This adaptive modal control/identification design greatly increases the nominal robustness of the controller in the case of frequency shifts.

Journal ArticleDOI
TL;DR: In this article, the structural displacement response in free vibration condition was measured and as the input to the modal parameter extraction algorithm such that all of the structural modal frequencies and mode shapes of the system can be determined successfully.

Journal ArticleDOI
TL;DR: In this article, a pre-test design and test technique for validating wind turbine blade structural models is discussed, and the importance of proper pre-testing and test techniques for wind turbine model validation is demonstrated.
Abstract: The focus of this paper is a test program designed for wind turbine blades. Model validation is a comprehensive undertaking which requires carefully designing and executing experiments, proposing appropriate physics-based models, and applying correlation techniques to improve these models based on the test data. Structural models are useful for making decisions when designing a new blade or assessing blade performance, and the process of model validation is needed to ensure the quality of these models. Blade modal testing is essential for validation of blade structural models, and this report discusses modal test techniques required to achieve validation. Choices made in the design of a modal test can significantly affect the final test result. This study aims to demonstrate the importance of the proper pre-test design and test technique for validating blade structural models.

Journal ArticleDOI
TL;DR: In this article, a Turkish reinforced concrete minaret and its modal analysis is performed to obtain analytical frequencies and mode shapes using ANSYS finite element program, and the earthquake behavior of the minaret is investigated using 1992 Erzincan earthquake before and after finite element model updating.
Abstract: This paper describes a Turkish style reinforced concrete minaret, its finite element model, modal testing, finite element model updating and earthquake behaviour, before and after model updating. The minaret of a mosque located in Trabzon, Turkey is selected as an application. A three-dimensional (3D) model of the minaret and its modal analysis is performed to obtain analytical frequencies and mode shapes using ANSYS finite element program. The ambient vibration tests are conducted on the minaret under natural excitations such as wind effects and human movement. The output-only modal parameter identification is carried out by Enhanced Frequency Domain Decomposition and Stochastic Subspace Identification methods in Operational Modal Analysis software and in doing so, dynamic characteristics (natural frequencies, mode shapes and damping ratios) are determined. A 3D finite element model of the minaret is updated to minimize the differences between analytical and experimental modal properties by changing some uncertain modelling parameters such as material properties and boundary conditions. The earthquake behaviour of the minaret is investigated using 1992 Erzincan earthquake before and after finite element model updating. Maximum differences in the natural frequencies are reduced from 21% to 8%, and good agreement is found between analytical and experimental natural frequencies. In addition to this, it is realized that finite element model updating is effective on the earthquake behaviour of the minaret. Copyright © 2008 John Wiley & Sons, Ltd.

Journal ArticleDOI
Keyu Qi1, Zhengjia He, Zhen Li1, Yanyang Zi1, Xuefeng Chen1 
TL;DR: In this paper, a novel method is proposed for operational modal analysis OMA of linear rotor systems, combined with correction technique of spectrum analysis (CTSA), harmonic wavelet filtering (HWF), random decrement technique (RDT) and Hilbert transform (HT) method.

Journal ArticleDOI
TL;DR: In this article, the authors investigated the use of an iterative Guyan expansion for mass weighting of target modes for sensor placement analogous to the common iterative Gaussian reduction technique.

Journal ArticleDOI
TL;DR: In this paper, a damage detection methodology applied specifically to frame-resistant buildings designed according to the capacity criterion is proposed, based on the observation that, for ductile frames, the damage resulting from a strong earthquake should be limited to the plastic hinge zones, typically distributed throughout the structure, according to weak-beam/strong-column principle.

Journal ArticleDOI
TL;DR: In this article, an advanced structural health monitoring (SHM) strategy based on distributed fiber optic sensing techniques has been proposed to utilize the strain responses throughout the full or some partial areas of structures to detect the arbitrary and unforeseen damages.
Abstract: In a recent study by the authors, an advanced structural health monitoring (SHM) strategy based on distributed fiber optic sensing techniques has been proposed to utilize the strain responses throughout the full or some partial areas of structures to detect the arbitrary and unforeseen damages As one of the essential components, a two-level scheme based on modal parameters from distributed dynamic macro-strain responses has been developed for damage locating and quantifying This work further investigates the superiority and some concerns of using distributed long-gage fiber optic sensing technique for vibration based SHM through a theoretical modal analysis on the dynamic macro-strain distribution Modal testing is also carried out to verify the performance of macro-strain frequency response function (FRF) and identify the modal parameters including resonant frequency, damping ratio, and modal macro-strain vector (MMSV) From the SHM point of view, their applications are summarized finally

Journal ArticleDOI
TL;DR: In this paper, the structural parameters of a fixed end beam with and without added mass were identified by using the first natural frequency of the beam and the theoretical frequencies obtained using the identified structural parameters also close to the measured frequencies.
Abstract: Structural parameter identification based on the measured dynamic responses has become very popular recently. This paper presents structural parameter identification of fixed end beams by inverse method using measured natural frequencies. An added mass is used as a modification tool. The measurements of the flexural vibrations of a fixed end beam with and without added mass are performed by using experimental modal testing. The solution of free bending transverse vibration of the beam is obtained by solving the differential equation motion of Bernoulli-Euler beam. By introducing the natural frequencies from experimental measurements into the solution of differential equation, the structural parameters of the fixed end beam are calculated. It is seen from the results that the values of the mass distribution and elasticity modulus identified using the first natural frequency of the beam nearly close to the real values. Besides, the theoretical frequencies obtained using the identified structural parameters also close to the measured frequencies.

Journal ArticleDOI
H.-J. Cho1, C.-D. Cho1
TL;DR: In this paper, numerical and experimental analyses are performed in accordance with disc thickness, pressurization type of caliper, and lining arc length, considering thermal and mechanical instability simultaneously, and results on disc brake performances considering the disc and pad design are discussed in terms of hot spots and squeal problems.
Abstract: The thermal distortion induced by thermoelastic instability (TEI) results in hot spots on the surface of the brake disc. This can incur low-frequency vibration known as judder. In pad-induced squeal noise, mode coupling occurs owing to the variation in the friction coefficient between the disc and pad, inducing high-frequency noise. Through a coupled analysis of hot spots and squeal phenomena, an optimum disc and pad design can be designed for higher thermal and mechanical performance. In this study, numerical and experimental analyses are performed in accordance with disc thickness, pressurization type of caliper, and lining arc length, considering thermal and mechanical instability simultaneously. Thermal deformation and pressure distribution are calculated using a finite element analysis (FEA). For evaluating TEI performance, experiments are performed using a chassis dynamometer and a high-speed infrared camera, and the results are correlated with FEA results. A complex eigenvalue analysis is conducted to evaluate mechanical instability using an FEA. Modal testing and simulations are conducted to correlate a real model and an FE model, and the corrected simulation results are applied for a complex eigenvalue problem to analyse coupled modes according to rotor and pad shapes. The results on disc brake performances considering the disc and pad design are discussed in terms of hot spots and squeal problems.

Journal ArticleDOI
TL;DR: In this paper, a multipurpose finite element solution module with the theoretical groundwork originated from principles of rotordynamics was developed to solve rotating machine problems such as of the high speed gas bearing spindles and the electric machines.

Journal ArticleDOI
TL;DR: In this article, a neural network model was proposed to correlate the modal frequency of each vibration mode with wind speed and temperature simultaneously, and it was shown that using significant components of wind speeds and temperatures rather than the whole measurement components as input to neural network can enhance the prediction capability.
Abstract: Wind and temperature have been shown to be the critical sources causing changes in the modal properties of large-scale bridges. While the individual effects of wind and temperature on modal variability have been widely studied, the investigation about the effects of multiple environmental factors on structural modal properties was scarcely reported. This paper addresses the modeling of the simultaneous effects of wind and temperature on the modal frequencies of an instrumented cable-stayed bridge. Making use of the long-term monitoring data from anemometers, temperature sensors and accelerometers, a neural network model is formulated to correlate the modal frequency of each vibration mode with wind speed and temperature simultaneously. Research efforts have been made on enhancing the prediction capability of the neural network model through optimal selection of the number of hidden nodes and an analysis of relative strength of effect (RSE) for input reconstruction. The generalization performance of the formulated model is verified with a set of new testing data that have not been used in formulating the model. It is shown that using the significant components of wind speeds and temperatures rather than the whole measurement components as input to neural network can enhance the prediction capability. For the fundamental mode of the bridge investigated, wind and temperature together apply an overall negative action on the modal frequency, and the change in wind condition contributes less to the modal variability than the change in temperature.