• Title, Summary, Keyword: modal parameter identification

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Determination of Vibration Parameters Using The Improved Time Domain Modal Identification Algorithm (개선된 시간영역 해석기법에 의한 동특성 추정)

  • Jung, Beom-Seok
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.3 no.2
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    • pp.147-154
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    • 1999
  • A new approach to conducting the vibration parameters identification algorithm is proposed. The approach employs the concept of modal amplitude ratio implemented in a mode shape estimation. The accuracy of the improved Ibrahim Time Domain identification algorithm in extracting structural modal parameters from free response functions has been studied using computer simulated data for 9 stations on the two-span continuous beam. Simulated responses from the lumped and distributed parameter system demonstrate that this algorithm produces excellent results, even in the 300% noise response.

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Output-only modal parameter identification of civil engineering structures

  • Ren, Wei-Xin;Zong, Zhou-Hong
    • Structural Engineering and Mechanics
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    • v.17 no.3_4
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    • pp.429-444
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    • 2004
  • The ambient vibration measurement is a kind of output data-only dynamic testing where the traffics and winds are used as agents responsible for natural or environmental excitation. Therefore an experimental modal analysis procedure for ambient vibration testing will need to base itself on output-only data. The modal analysis involving output-only measurements presents a challenge that requires the use of special modal identification technique, which can deal with very small magnitude of ambient vibration contaminated by noise. Two complementary modal analysis methods are implemented. They are rather simple peak picking (PP) method in frequency domain and more advanced stochastic subspace identification (SSI) method in time domain. This paper presents the application of ambient vibration testing and experimental modal analysis on large civil engineering structures. A 15 storey reinforced concrete shear core building and a concrete filled steel tubular arch bridge have been chosen as two case studies. The results have shown that both techniques can identify the frequencies effectively. The stochastic subspace identification technique can detect frequencies that may possibly be missed by the peak picking method and gives a more reasonable mode shapes in most cases.

Output-only modal parameter identification for force-embedded acceleration data in the presence of harmonic and white noise excitations

  • Ku, C.J.;Tamura, Y.;Yoshida, A.;Miyake, K.;Chou, L.S.
    • Wind and Structures
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    • v.16 no.2
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    • pp.157-178
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    • 2013
  • Output-only modal parameter identification is based on the assumption that external forces on a linear structure are white noise. However, harmonic excitations are also often present in real structural vibrations. In particular, it has been realized that the use of forced acceleration responses without knowledge of external forces can pose a problem in the modal parameter identification, because an external force is imparted to its impulse acceleration response function. This paper provides a three-stage identification procedure as a solution to the problem of harmonic and white noise excitations in the acceleration responses of a linear dynamic system. This procedure combines the uses of the mode indicator function, the complex mode indication function, the enhanced frequency response function, an iterative rational fraction polynomial method and mode shape inspection for the correlation-related functions of the force-embedded acceleration responses. The procedure is verified via numerical simulation of a five-floor shear building and a two-dimensional frame and also applied to ambient vibration data of a large-span roof structure. Results show that the modal parameters of these dynamic systems can be satisfactorily identified under the requirement of wide separation between vibration modes and harmonic excitations.

High-order, closely-spaced modal parameter estimation using wavelet analysis

  • Le, Thai-Hoa;Caracoglia, Luca
    • Structural Engineering and Mechanics
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    • v.56 no.3
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    • pp.423-442
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    • 2015
  • This study examines the wavelet transform for output-only system identification of ambient excited engineering structures with emphasis on its utilization for modal parameter estimation of high-order and closely-spaced modes. Sophisticated time-frequency resolution analysis has been carried out by employing the modified complex Morlet wavelet function for better adaption and flexibility of the time-frequency resolution to extract two closely-spaced frequencies. Furthermore, bandwidth refinement techniques such as a bandwidth resolution adaptation, a broadband filtering technique and a narrowband filtering one have been proposed in the study for the special treatments of high-order and closely-spaced modal parameter estimation. Ambient responses of a 5-story steel frame building have been used in the numerical example, using the proposed bandwidth refinement techniques, for estimating the modal parameters of the high-order and closely-spaced modes. The first five natural frequencies and damping ratios of the structure have been estimated; furthermore, the comparison among the various proposed bandwidth refinement techniques has also been examined.

Modal identification of Canton Tower under uncertain environmental conditions

  • Ye, Xijun;Yan, Quansheng;Wang, Weifeng;Yu, Xiaolin
    • Smart Structures and Systems
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    • v.10 no.4_5
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    • pp.353-373
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    • 2012
  • The instrumented Canton Tower is a 610 m high-rise structure, which has been considered as a benchmark problem for structural health monitoring (SHM) research. In this paper, an improved automatic modal identification method is presented based on a natural excitation technique in conjunction with the eigensystem realization algorithm (NExT/ERA). In the proposed modal identification method, damping ratio, consistent mode indicator from observability matrices (CMI_O) and modal amplitude coherence (MAC) are used as criteria to distinguish the physically true modes from spurious modes. Enhanced frequency domain decomposition (EFDD), the data-driven stochastic subspace identification method (SSI-DATA) and the proposed method are respectively applied to extract the modal parameters of the Canton Tower under different environmental conditions. Results of modal parameter identification based on output-only measurements are presented and discussed. User-selected parameters used in those methods are suggested and discussed. Furthermore, the effect of environmental conditions on the dynamic characteristics of Canton tower is investigated.

In-situ modal testing and parameter identification of active magnetic bearing system by magnetic force measurement and the use of directional frequency response functions (전자기력 측정과 방향성주파수 응답함수를 이용한 능동 자기베어링 시스템의 운전중 모드시험 및 매개변수 규명)

  • Ha, Young-Ho;Lee, Chong-Won
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.21 no.7
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    • pp.1156-1165
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    • 1997
  • Complex modal testing is employed for the in-situ parameter identification of a four-axis active magnetic bearing system while the system is in operation. In the test, magnetic bearings are used as exciters as well as actuators for feedback control. The experimental results show that the directional frequency response function, which is properly defined in the complex domain, is a powerful tool for identification of bearing as well as modal parameters. It is also shown that the position and current stiffnesses can be accurately estimated using the relations between the measured forces, displacements, and currents.

A Modal Identification of Self-Adjoint Distributed Parameter Systems Using Spatial Filter (공간함수 필터를 이용한 자기수반계의 모달판정)

  • 강수준
    • Journal of KSNVE
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    • v.4 no.1
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    • pp.51-57
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    • 1994
  • The objective of this research is to introduce a method of modal identification for self-adjoint distributed parameter systems using Spatial Fiter. To minimize the spillover effects which come from using the finite discrete sensors by means of discrete measurements, a new mechanism, namely spatial filter which is main subject in this research, is introduced for extracting modal coordinates from sensors' output. As an illustration of the proposed method, two simple numerical examples are also examined.

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Modal Parameter Identification of a Generator Stator Frame for Fossil Power Plants (화력 발전용 발전기 고정자 프레임의 모드매개변수 규명)

  • 김철홍;류석주;박종포
    • Journal of KSNVE
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    • v.9 no.3
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    • pp.570-576
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    • 1999
  • This paper presents numerical and experimental results of modal parameter identification in a generator stator frame for 500 MW fossil power plants. A commercial finite element analysis S/W was employed for modal analysis. The generator is excited by alternating electromagnetic forces, mainly of 120 Hz in 60 Hz machines, due to magnetic field and electric current in windings. It is necessary to verify that the stator frame has adequate frequency margin from the excitation frequency to avoid possible resonance when operating. Thus, frequency margin required for the stator frame is established using the numerical and experimental results. The results show that the stator frame meets the frequency-margin requirements. Also, results of modal analysis for design modification in order to reduce weights of the stator frame without deteriorating vibration characteristics are presented.

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Directional ARMAX Model-Based Approach for Rotordynamics Identification, Part 2 : Performance Evaluations and Applications (방향 시계열에 의한 회전체 동특성 규명 : (II) 성능 평가 및 응용)

  • 박종포;이종원
    • Journal of KSNVE
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    • v.9 no.1
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    • pp.60-69
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    • 1999
  • In the first paper of this research$^{(1)}$. a new time series method. directional ARMAX (dARMAX) model-based approach. was proposed for rotordynamics identification. The dARMAX processes complex-valued signals, utilizing the complex modal testing theory which enables the separation of the backward and forward modes in the two-sided frequency domain and makes effective modal parameter identification possible. to account for the dynamic characteristics inherent in rotating machinery. In this second part. an evaluation of its performance characteristics based on both simulated and experimental data is presented. Numerical simulations are carried out to show that the method. a complex time series method. successfully implements the complex modal testing in the time domain. and it is superior in nature to the conventional ARMAX and the frequency-domain methods in the estimation of the modal parameters for isotropic and weakly anisotropic rotor systems. Experiments are carried out to demonstrate the applicability and the effectiveness of the dARMAX model-based approach, following the proposed fitting strategy. for the rotordynamics identification.

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Directional ARMAX Model-Based Approach for Rotordynamics Identification, Part 1 : Modeling and Analysis (방향 시계열에 의한 회전체 동특성 규명: (I) 모델링 및 해석)

  • 박종포;이종원
    • Journal of KSNVE
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    • v.8 no.6
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    • pp.1103-1112
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    • 1998
  • A new time series method, directional ARMAX (dARMAX) model-based approach. is proposed for rotor dynamics identification. The dARMAX processes complex-valued signals, utilizing the complex modal testing theory which enables the separation of the backward and forward modes in the two-sided frequency domain and makes effective modal parameter identification possible, to account for the dynamic characteristics inherent in rotating machinery. This paper is divided into two parts : The dARMAX modeling, analysis. and fitting strategy are presented in the first part. whereas a evaluation of its performance characteristics based on both simulated and experimental data is presented in the second.

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