Showing papers on "Modal testing published in 2016"
TL;DR: In this paper, a field experiment was conducted on an actual simply supported steel truss bridge with four artificial damage scenarios applied sequentially, and the results of modal-parameter identification and vibration-based damage detection were presented.
138 citations
TL;DR: In this article, new variance computation schemes for modal parameters are developed for four subspace algorithms, including output-only and input/output methods, as well as data-driven and covariance-driven methods.
63 citations
TL;DR: In this article, a frequency and spatial domain decomposition method for operational modal analysis making use of strain measurements is presented, which can be applied to various engineering problems more commonly due to its advantages in real life implementations.
59 citations
TL;DR: In this article, a two-dimensional Fourier spectral method is employed to conduct the two dimensional modal curvature estimation in composite structures, where the spectral calculations for spatial derivatives are implemented in global space, thus noise can be suppressed.
57 citations
TL;DR: In this paper, the seismic modal dynamic identification of frame structures by a refined Frequency Domain Decomposition (rFDD) algorithm, autonomously formulated and implemented within MATLAB, is discussed.
56 citations
TL;DR: In this article, a methodology for quantitative crack identification is proposed based on multivariable wavelet finite element method and particle swarm optimization, which can achieve more accurate vibration analysis results because it interpolates all the solving variables at one time.
47 citations
TL;DR: In this paper, a Bayesian statistical approach is developed for modal identification using the free vibration response of structures, and a frequency domain formulation is proposed that makes statistical inference based on the Fast Fourier Transform (FFT) of the data in a selected frequency band.
46 citations
TL;DR: In this paper, an innovative method, developed by authors to evaluate, in frequency domain, the fatigue damage of mechanical components modeled by modal approach and subjected to random dynamic loads is presented.
39 citations
TL;DR: In this article, a wavelet packet transform (WPT) is used to decompose free vibration response of structure and then the decomposed signal is used for modal parameter identification using peak picking method.
Abstract: Damage identification problem involves detection, localization and assessment of the extent of damage in a structure so that the remaining life could be predicted. Visual or nondestructive experimental damage detection methods such as ultrasonic and acoustic emission ones are based on a local evaluation in easily accessible areas, and therefore, they require a certain prior knowledge of the damage distribution. With the purpose of providing global damage detection methods applicable to complex structures, techniques based on modal testing and signal processing constitute a promising approach for damage identification. These methods examine changes in the dynamic characteristics of structure, such as natural frequencies and mode shapes to detect the structural damage. Modal parameters including natural frequencies, mode shapes and damping ratios are known as essential parameters for analyzing the dynamic behavior of a structure. This paper deals with identification of modal parameters of structures using a two-step algorithm. In the proposed method, free vibration response of structure is decomposed using wavelet packet transform. Then, decomposed signal, which has the same energy with the main signal, is used for modal parameter identification using peak picking method. The performance of the proposed method is verified against the results of an experimental benchmark problem.
38 citations
TL;DR: In this paper, a fast Bayesian FFT method is used for operational modal analysis on the basis of measured acceleration data, where probability is used as a measure for the relative plausibility of outcomes given a model of the structure and measured data.
Abstract: The Canton Tower is a high-rise slender structure with a height of 610 m. A structural health monitoring system has been instrumented on the structure, by which data is continuously monitored. This paper presents an investigation on the identified modal properties of the Canton Tower using ambient vibration data collected during a whole day (24 hours). A recently developed Fast Bayesian FFT method is utilized for operational modal analysis on the basis of the measured acceleration data. The approach views modal identification as an inference problem where probability is used as a measure for the relative plausibility of outcomes given a model of the structure and measured data. Focusing on the first several modes, the modal properties of this supertall slender structure are identified on non-overlapping time windows during the whole day under normal wind speed. With the identified modal parameters and the associated posterior uncertainty, the distribution of the modal parameters in the future is predicted and assessed. By defining the modal root-mean-square value in terms of the power spectral density of modal force identified, the identified natural frequencies and damping ratios versus the vibration amplitude are investigated with the associated posterior uncertainty considered. Meanwhile, the correlations between modal parameters and temperature, modal parameters and wind speed are studied. For comparison purpose, the frequency domain decomposition (FDD) method is also utilized to identify the modal parameters. The identified results obtained by the Bayesian method, the FDD method and a finite element model are compared and discussed.
38 citations
TL;DR: In this article, a modal parameter estimation method to directly establish modal models of structural dynamic systems satisfying two physically motivated constraints is presented, i.e., reciprocity of the frequency response functions (FRFs) and the estimation of normal (real) modes.
TL;DR: In this article, high structural modal frequencies of car body are beneficial as they ensure better vibration control and enhance ride quality of railway vehicles. Modal sensitivity optimization and elastic suspens...
Abstract: High structural modal frequencies of car body are beneficial as they ensure better vibration control and enhance ride quality of railway vehicles. Modal sensitivity optimization and elastic suspens...
TL;DR: In this paper, a series of full-scale field vibration tests (including ambient, forced, and free vibration tests) were carried out on a pedestrian bridge at City University of Hong Kong (CityU).
Abstract: Many spectacular pedestrian bridges were designed and constructed recently. Owing to their special shapes, it is expected that various types and a wide range of vibration frequency components will be induced by pedestrians. To avoid accidents and reduce risk, the vibration characteristics of pedestrian bridges during their service life must be carefully assessed. The most direct and reliable way to study the vibration characteristics of a structural system is through field vibration tests. In this paper, a series of full-scale field vibration tests (including ambient, forced, and free vibration tests) were carried out on a pedestrian bridge at City University of Hong Kong (CityU). The difficulties encountered in the field tests are reported. The recently developed Bayesian methods were utilized to determine the modal parameters of the bridge based on measurements from all three kinds of tests. In addition to the most probable values (MPVs) of modal parameters, the associated posterior uncertainties were also analytically calculated. Four modes were identified, including three vertical bending modes and one torsional mode. The accuracy of the identified modal parameters was assessed through the posterior uncertainty. Because the amplitudes of the vibration in the three kinds of tests were different, the modal parameters determined from these kinds of tests were compared and discussed. Suggestions related to the proper use and potential vibration problems during the lifecycle of pedestrian bridges were provided based on the analysis results.
TL;DR: A simulation based damage detection method is used that incorporates the Concrete Damaged Plasticity model and shows significant sensitivity to estimate damage and that it can be integrated with modal testing to assess the current condition of the structure without the need for baseline data.
TL;DR: In this article, a low-cost vibration-monitoring system was developed and installed on an urban steel-plated stress-ribbon footbridge, where the system continuously measured the acceleration [using 18 triaxial microelectromechanical system (MEMS) accelerometers distributed along the structure], ambient temperature, and the wind velocity and direction.
Abstract: A low-cost vibration-monitoring system was developed and installed on an urban steel-plated stress-ribbon footbridge. The system continuously measures the acceleration [using 18 triaxial microelectromechanical system (MEMS) accelerometers distributed along the structure), the ambient temperature, and the wind velocity and direction. Automated output-only modal parameter estimation based on the stochastic subspace identification (SSI) was carried out to extract the modal parameters (i.e., the natural frequencies, damping ratios, and modal shapes). Thus, this study analyzed the time evolution of the modal parameters over data monitoring for 1 year. First, for similar environmental/operational factors, the uncertainties associated with the SSI-based techniques used and to the acceleration records used were studied and quantified. Second, a methodology for tracking the vibration modes was established, because several of them with closely spaced natural frequencies were identified. Third, the modal par...
Journal Article•
TL;DR: A thorough comparison of EMA and OMA tests of a Plexiglas plate is presented and it is concluded that no significant differences were found between modal parameters obtained by OMA and EMA.
TL;DR: In this paper, the use of wireless inertial measurement units (IMUs), designed for biomechanics motion capture applications, was used for the modal testing of a 109m footbridge.
TL;DR: In this article, the use of piezoelectric disk buzzers, usual in stringed musical instruments to acquire sound as a voltage signal, for experimental modal analysis is presented.
Abstract: We present the use of piezoelectric disk buzzers, usual in stringed musical instruments to acquire sound as a voltage signal, for experimental modal analysis. These transducers helped in extracting natural frequencies and mode shapes of an aluminium beam and a steel arch in the laboratory. The results are compared with theoretical predictions and experimental values obtained by accelerometers and a laser displacement transducer. High accuracy, small dimensions, low weight, easy usage, and low cost, make piezoelectric pickups an attractive tool for the experimental modal analysis of engineering structures.
TL;DR: In this article, the effect of the damage length, its location and severity and also the effects of rotational speed and amplitude of loading on the wind turbine blade is studied. And the importance of geometric nonlinearity in the damage detection of the modern wind turbines is demonstrated.
TL;DR: This paper investigates the posterior uncertainty of the modal parameters in terms of their posterior covariance matrix, which is mathematically equal to the inverse of the Hessian of the negative log-likelihood function (NLLF) evaluated at the MPVs.
TL;DR: In this paper, the authors present a strategy for testing and validating structures connected together with bolted joints, which are the most common components in mechanical structures, by using modal testing performed under controlled response amplitude, and two test structures, a simple bolted flange test case and a sector of a RollsRoyce aero-engine casing, are tested under high level of vibrations.
Abstract: This work presents a strategy for testing and validating structures connected together with bolted joints, which are the most common components in mechanical structures. Considering the great number of coupled mechanical structures and research studies on this subject, the authors focused this research work on bolted flanges of aircraft engine casings. In fact, the coupling of engine casings is generally obtained by a large number of joints which assure the correct sealing at the flanges’ interfaces. From a finite element (FE) modelling perspective, joints are often modelled by either rigid connections or springs, otherwise incurring a very expensive computational time. This modelling approach is not a problem when dealing with low amplitude levels of vibrations. For higher levels of vibrations, joints and flanges cannot be considered rigidly connected and that exerted flexibility at the joints’ area can determine nonlinear dynamic behaviour. This work aims to study the dynamic behaviour of bolted flanges by using modal testing performed under controlled response amplitude. Two test structures, (1) a simple bolted flange test case and (2) a sector of a Rolls-Royce aero-engine casing, are tested under high level of vibrations. Both test structures are modelled by FE method, and nonlinear elements are used for modelling the flanges’ interfaces so as to perform prediction of nonlinear responses. These predictions are eventually correlated with the measured data.
TL;DR: In this article, a new approach based on reverberation time measurements of single resonant frequencies (the modal reverberation times) has been introduced, where two measurement methods have been proposed together with proper measurement procedures: a direct method based on interrupted source signal method, and an indirect method using half bandwidth measurements.
TL;DR: In this paper, a high-temperature transient heating test system and a vibration test system were combined to establish a test system that can perform the thermal/vibration test at 1200°C.
TL;DR: In this paper, the equations to compute the modal parameters from the state space model when input and output data are available (like in combined experimental-operational modal analysis) are derived in detail using invariants of the state-space model.
TL;DR: The analysis results indicate that the natural frequencies and strain mode shapes of the tested pipe acquired by FBG sensors are in good agreement with the results obtained by a reference accelerometer and simulation outputs.
Abstract: Vibration fatigue failure is a critical problem of hydraulic pipes under severe working conditions. Strain modal testing of small and light pipes is a good option for dynamic characteristic evaluation, structural health monitoring and damage identification. Unique features such as small size, light weight, and high multiplexing capability enable Fibre Bragg Grating (FBG) sensors to measure structural dynamic responses where sensor size and placement are critical. In this paper, experimental strain modal analysis of pipes using distributed FBG sensors ispresented. Strain modal analysis and parameter identification methods are introduced. Experimental strain modal testing and finite element analysis for a cantilever pipe have been carried out. The analysis results indicate that the natural frequencies and strain mode shapes of the tested pipe acquired by FBG sensors are in good agreement with the results obtained by a reference accelerometer and simulation outputs. The strain modal parameters of a hydraulic pipe were obtained by the proposed strain modal testing method. FBG sensors have been shown to be useful in the experimental strain modal analysis of small and light pipes in mechanical, aeronautic and aerospace applications.
TL;DR: In this paper, the authors presented experimental results of two damage detection techniques based on modal properties, with the application on a full-size composite helicopter main rotor blade, and remarks concerning sensitivity and robustness of the methods are discussed.
TL;DR: In this article, the authors proposed a new reduction method for predicting the stability analysis of a brake system subjected to friction-induced vibration, which is based on a double modal synthesis.
TL;DR: In this paper, the authors investigated damage identification techniques based on the difference of modal frequencies, shapes and curvatures in the damaged and undamaged states of the structure, and the sensitivity of the identification algorithm with respect to damage parameters is discussed and the minimum number of measured quantities to identify the damage is assessed.
Abstract: This paper investigates damage identification techniques based on the difference of modal frequencies, shapes and curvatures in the damaged and undamaged states of the structure. The sensitivity of the identification algorithm with respect to damage parameters is discussed and the minimum number of measured quantities to identify the damage is assessed. It is shown that modal curvatures can be effectively used to pre-localise the damage and to add a penalty term in the objective function which weighs the difference between natural frequencies and modal displacements. Such a term improves the local convexity of the objective function and enhances the convergence rate of the minimization algorithm. The procedure is validated against the results of the experiments on a parabolic arch carried out by the authors. The advantages of such an approach compared to techniques solely based on frequencies are that the ill-conditioning of the inverse problem is reduced and a more accurate estimate of the damage parameters is achieved.
TL;DR: In this paper, the effect of forcing and response amplitude on the variability of modal parameters of a bridge was examined experimentally, and a finite element model was used to assess the likely levels of structural damage that would have a similar effect on the natural frequencies as the amplitude dependence.
TL;DR: In this paper, the modal parameters of composite flat plate models through Experimental Modal Analysis (EMA) using piezoelectric transducers were estimated using twelve measurement points acquired by laser doppler vibrometry.