Showing papers on "Modal testing published in 2013"
TL;DR: This paper proposes a novel “frequency-domain damping design” using high-pass filter for ABC using modal space analysis and the validity of the proposed control system is confirmed by some experimental results.
Abstract: Time delay in bilateral control system seriously deteriorates performance and stability. Acceleration-based bilateral control (ABC) is hybrid of position and force control in the acceleration dimension based on a disturbance observer. It can be divided into two modal spaces: common and differential modal spaces. The sum of master force and slave force is controlled to be zero in common modal space to realize the law of action-reaction. The difference of master position and slave position is controlled to be zero in differential modal space for position tracking. This paper analyzes the stability of each modal space under time delay. Based on modal space analysis, this paper proposes a novel “frequency-domain damping design” using high-pass filter for ABC. The validity of the proposed control system is confirmed by some experimental results.
99 citations
TL;DR: In this paper, the authors examined three different inverse algorithms for solving the non-linear equations to predict the interface, lengthwise location and size of delamination: direct of solution using a graphical method, artificial neural network (ANN) and surrogate-based optimization.
92 citations
TL;DR: In this paper, an algorithm is proposed that efficiently estimates the covariances on modal parameters obtained from this multi-setup subspace identification, which merges the data from different setups prior to the identification step, taking the possibly different ambient excitation characteristics between the measurements into account.
91 citations
TL;DR: In this paper, an experimental calibration of a three-dimensional numerical model of an Alfa Pendular train vehicle based on modal parameters was performed using a submodeling/multistep approach involving two phases.
Abstract: This article describes the experimental calibration of a three-dimensional numerical model of an Alfa Pendular train vehicle based on modal parameters. The dynamic tests of the carbody and bogie of the vehicle allowed the determination of the frequencies and modal configurations of 13 vibration modes, by applying the data-driven stochastic subspace identification method. In addition, a dynamic characterisation test of the passenger-seat system was also conducted. The calibration of the model was performed using a submodelling/multistep approach involving two phases, the first one focused on the calibration of the model of the bogie under test conditions and the second one focused on the calibration of the complete model of the vehicle. The calibration was performed through an iterative method based on a genetic algorithm and allowed to obtain optimal values of 17 parameters of the numerical model. For the pairing of the vibration modes, real and complex, a recent technique was used based on the calculation of the modal strain energy. The stability of a significant number of parameters considering different initial populations demonstrated the robustness of the algorithm. The comparison of experimental and numerical responses before and after calibration revealed significant improvements in the numerical model and a very good correlation between the responses obtained with the calibrated model and the experimental responses.
75 citations
TL;DR: In this article, the authors focus on the dynamic tests of two historic structures, performed in operational conditions at different levels of ambient excitation, aimed at checking the invariance of the dynamic characteristics (i.e., natural frequencies and mode shapes) with increasing excitation amplitude.
74 citations
TL;DR: In this article, the authors proposed a method based on the existing second-order blind identification of underdetermined mixtures technique for identifying the modal characteristics, namely, natural frequencies, damping ratio, and real-valued partial mode shapes of all contributing modes.
Abstract: SUMMARY
Herein, we propose a method based on the existing second-order blind identification of underdetermined mixtures technique for identifying the modal characteristics—namely, natural frequencies, damping ratio, and real-valued partial mode shapes of all contributing modes—of structures with a limited number of sensors from recorded free/ambient vibration data. In the second-order blind identification approach, second-order statistics of recorded signals are used to recover modal coordinates and mode shapes. Conventional versions of this approach require the number of sensors to be equal to or greater than the number of active modes. In the present study, we first employ a parallel factor technique to decompose the covariance tensor into rank-one tensors so that the partial mode shapes at the recording locations (sensors) can be estimated. The mode shape matrix identified in this manner is not square, which precludes the use of a simple inversion to extract the modal coordinates. As such, the natural frequencies are identified from the recovered modal coordinates' Autocovariances. The damping ratios are extracted using a least-squares technique from modal free vibrations, as they are not directly recoverable because of the inherent smearing produced by windowing processes. Finally, a Bayesian model updating approach is employed to complete the partial mode shapes—that is, to extract the mode shapes at the DOFs without sensors. We use simulated and physical data for verifying and validating this new identification method, and explore optimal sensor distribution in multistory structures for a given (limited) number of sensors. Copyright © 2012 John Wiley & Sons, Ltd.
70 citations
TL;DR: In this paper, the authors proposed a time-frequency domain decomposition method for the modal identification of ambient vibration testing, where the continuous wavelet transform of the matrix of response correlation functions is first computed from raw data and then decomposed using singular value decomposition, leading to singular values and singular vectors.
55 citations
TL;DR: The results for the resistive and reactive sound power obtained from the superposition of the individual modal sound power contributions are compared to the harmonic solution of the forced problem.
Abstract: A modal decomposition technique to analyze individual modal contributions to the sound power radiated from an externally excited structure submerged in a heavy fluid is presented. The fluid-loaded structural modes are calculated by means of a polynomial approximation and symmetric linearization of the underlying nonlinear eigenvalue problem. The eigenvalues and eigenfunctions of a fluid loaded sphere with and without internal structures are presented. The modal sound power contributions using both fluid-loaded structural modes and acoustic radiation modes are presented. The results for the resistive and reactive sound power obtained from the superposition of the individual modal sound power contributions are compared to the harmonic solution of the forced problem.
53 citations
TL;DR: In this paper, a more simple methodology is proposed based on scaling the experimental mode shapes of a structure using the mass matrix of a finite element model, and two approaches are compared; one approach is reduced to the set of measurement points using SEREP and a second approach is expanded to all DOFs in the model using a newly published principle called the local correspondence principle.
46 citations
TL;DR: In this article, a mass-change structural modification method was used for the mass normalization in an operational modal analysis, without using a motion sensor, and the mass-normalized displacement and strain mode shapes were obtained using a combination of the proposed approach and the strain EMA.
45 citations
TL;DR: In this paper, a distributed frequency domain algorithm for real-time modal estimation of large power systems using ambient synchrophasor data is proposed, which is tested on known test systems and archived real power system data from eastern and western power systems.
Abstract: This paper provides a distributed frequency domain algorithm for real-time modal estimation of large power systems using ambient synchrophasor data. By dividing the computation between a supervisory central computer and local optimizations at the substation level, the algorithm efficiently estimates multiple dominant mode frequencies, damping ratios and mode shapes from wide-area power system measurements. The algorithm, called distributed frequency domain optimization, is tested on known test systems and archived real power system data from eastern and western power systems.
TL;DR: In this paper, the authors presented an optimization methodology to reduce magnetically induced vibrations of a spoke-type interior permanent magnet (IPM) motor that was developed by performing magnetic and structural finite element analyses and optimization.
Abstract: We present an optimization methodology to reduce magnetically induced vibrations of a spoke-type interior permanent magnet (IPM) motor that we developed by performing magnetic and structural finite element analyses and optimization. The magnetic forces acting on the teeth of the stator were calculated by magnetic finite element analysis and the Maxwell stress tensor method. The natural frequencies and mode shapes of the stator were calculated by structural finite element analysis and verified by modal testing. The vibration of the motor due to the rotating magnetic force was calculated by the mode superposition method, and it was compared with the measured vibration. Finally, two optimization problems were formulated and solved to reduce magnetically induced vibration: minimization of magnetic force and minimization of acceleration. We showed that minimization of acceleration was more effective than minimization of magnetic force at reducing magnetically induced vibrations, because the former method effectively decreased the amplitudes of the excitation frequencies of magnetic force by considering the transfer function of the motor.
TL;DR: In this paper, the effect of accelerometer and transducer mass loading effects from measured frequency response functions (including point FRF and transfer FRF) in shaker modal testing is investigated.
TL;DR: In this article, the aim of active vibration control is to contain these phenomena, and the aim is to prevent the system from becoming susceptible to dangerous vibratory phenomena, such as small damping.
Abstract: Many systems have, by their nature, a small damping and they are therefore potentially subjected to dangerous vibratory phenomena. The aim of active vibration control is to contain these phenomena,...
TL;DR: In this paper, the effect of fluid-structure interaction on global dynamic properties such as vibrational frequency, mode shape, modal curvature, as well as free vibrational responses along E-glass composite, carbon composite, and aluminum beams, respectively, was examined.
TL;DR: In this article, a multivariate autoregressive model is presented for the automatic identification of the spectrum and modal parameters of an operational modal analysis using multi sensors, and its parameters are estimated by least squares via the implementation of QR factorization.
TL;DR: In this article, a multidirectional-modal-parameter-based visual inspection with high-frame-rate (HFR) stereo video analysis is proposed for determining the dynamic properties of a vibrating object.
Abstract: This paper proposes the concept of multidirectional-modal-parameter-based visual inspection with high-frame-rate (HFR) stereo video analysis as a novel active sensing methodology for determining the dynamic properties of a vibrating object. HFR stereo video is used for observing the 3-D vibration distribution of an object under unknown excitations in the audio-frequency range, and the projections of the vibration displacement vectors along multiple directions can be verified using output-only modal analysis that can estimate their modal parameters such as resonant frequencies and mode shapes. Through implementing a fast output-only modal parameter estimation algorithm on a 10000-fps stereo vision platform, we developed a real-time multidirectional-modal-parameter-based visual inspection system; it can measure the 3-D vibration displacement vectors of 30 points on a beam-shaped object from 512 × 96 pixel stereo images at 10000 fps and can determine its resonant frequencies and mode shapes along 72 different directions around its beam axis as its input-invariant modal parameters. To demonstrate the performance of our system in modal-parameter-based visual inspection, the asymmetric dynamic properties, caused by cracks, of several steel beams vibrating at dozens of hertz and having artificial cracks were inspected in real time by determining the modal parameters along 72 directions around their beam axes.
TL;DR: In this article, a finite element model is constructed representing the vibration behavior of the cutting platform of a combine in order to recognize and reduce its vibration problem, and the mass change strategy is used to estimate the scaling-factor and frequency response function (FRF) matrix.
TL;DR: In this paper, an existing OMA technique, the Natural Excitation Technique (NExT) was studied and implemented in order to achieve, from the wind force, the modal parameters of the Vega Launcher, the new European launcher vehicle for small and medium satellites.
TL;DR: The principle of equal modal damping is used to give a unified presentation and calibration of resonant control of structures for different control formats, based on velocity, acceleration and position as mentioned in this paper.
Abstract: The principle of equal modal damping is used to give a unified presentation and calibration of resonant control of structures for different control formats, based on velocity, acceleration–position...
TL;DR: In this article, a non-contact experimental technique for measuring modal parameters of a rectangular aluminum plate with free boundaries using only the output data was presented, with the intention to apply the technique to turbine blades.
TL;DR: In this article, a new control technique called dependent modal space control (DMSC) is proposed for reducing vibration in flexible structures, which is based on the modal approach and can impose not only frequency and damping but also the controlled mode shapes.
Abstract: This paper presents a new control technique for reducing vibration in flexible structures. It is based on the modal approach and is called dependent modal space control (DMSC). The well-known independent modal space control (IMSC) method, devised in the 1980s, allows the frequency and damping of the controlled modes to be changed using diagonal control gain matrices, leaving the mode shapes unaltered. DMSC, on the other hand, can impose not only frequency and damping but also the controlled mode shapes by using full control gain matrices. In many applications, owing to the limited number of sensors–actuators available for control and the increasing spillover effects, generic assignment of eigenvectors is not possible.However, an optimal eigenstructure assignment can be computed to reduce structure vibration by minimizing an input–output performance index. To demonstrate the advantages of this new method, we compare IMSC and DMSC using numerical simulation on a finite element method model of a cantilevered beam.
TL;DR: In this article, an innovative hybrid dynamic model of the tooling system in internal turning, based on FE beams and empirical models, is presented, which is based on physical and geometrical assumptions and it was refined by using experimental observations derived from modal testing of boring bars with different geometries and made of different materials, i.e. alloy steel and high-damping carbide.
TL;DR: In this paper, the authors employed modal filters for simultaneous and independent control of multiple vibration modes of a flexible structure embedded with a non-collocated pair of sensor and actuator.
TL;DR: In this article, a new method for operational modal identification is proposed to deal with output-only vibration measurements contaminated by noise, which is a challenging task for modal analysis.
Abstract: Operational modal analysis is a challenging task to deal with output-only vibration measurements contaminated by noise. This paper proposes a new method for operational modal identification...
TL;DR: In this paper, the modal information of composite plates is statistically evaluated by the discrete singular convolution method with random boundary conditions, and the proposed methodology not only provides an efficient use of SEA method in high frequency vibration analysis of composite structures, but also enhances SEA accuracy in mid frequency region in which conventional SEA fails.
TL;DR: In this article, a new concept of combining the modal frequencies and mode shape ratios is explored for developing an accurate method merely based on ambient vibration measurements for determining the effective vibration length of cable.
Abstract: Due to its easy operation and wide applicability, the ambient vibration method is commonly adopted to determine the cable force by first identifying the cable frequencies from the vibration signals. With given vibration length and flexural rigidity, an analytical or empirical formula is then used with these cable frequencies to calculate the cable force. It is, however, usually difficult to decide the two required parameters, especially the vibration length due to uncertain boundary constraints. To tackle this problem, a new concept of combining the modal frequencies and mode shape ratios is fully explored in this study for developing an accurate method merely based on ambient vibration measurements. A simply supported beam
model with an axial tension is adopted and the effective vibration length of cable is then independently
determined based on the mode shape ratios identified from the synchronized measurements. With the effective vibration length obtained and the identified modal frequencies, the cable force and flexural rigidity can then be solved using simple linear regression techniques. The feasibility and accuracy of the proposed method is extensively verified with demonstrative numerical examples and actual applications to different cable-stayed bridges. Furthermore, several important issues in engineering practice such as the number of sensors and selection of modes are also thoroughly investigated.
TL;DR: In this paper, a semi-active control approach using a dry friction damper is presented to reduce transient vibrations of a space truss structure, where the control target is to maximize an equivalent damping ratio of the lowest bending mode, which is considered most dominant in its transient vibrations.
TL;DR: In this paper, the authors describe the modal interaction between a panel and a heavy fluid cavity when the panel is excited by a broad band force in a given frequency band, and study the validity of SEA assumptions for this case.