• Journal of Mechanical Science and Technology
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• 제18권7호
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• pp.1086-1093
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• 2004

The modal characteristics of constrained multibody systems undergoing constant accelerated motions are investigated in this paper. Relative coordinates are employed to derive the equations of motion, which are generally nonlinear in terms of the coordinates. The dynamic equilibrium position of a constrained multibody system needs to be obtained from the nonlinear equations of motion, which are then linearized at the dynamic equilibrium position. The mass and the stiffness matrices for the modal analysis can be obtained from the linearized equations of motion. To verify the effectiveness and the accuracy of the proposed method, two numerical examples are solved and the results obtained by using the proposed method are compared with those obtained by analytical and other numerical methods. The proposed method is found to be accurate as well as effective in predicting the modal characteristics of constrained multibody systems undergoing constant accelerated motions.

• Earthquakes and Structures
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• 제16권3호
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• pp.321-327
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• 2019

This study investigated the possibility of using the recorded micro tremor data on ground level as ambient vibration input excitation data for investigation and application Operational Modal Analysis (OMA) on the bench-scale earthquake simulator (The Quanser Shake Table) for model chimney. As known OMA methods (such as EFDD, SSI and so on) are supposed to deal with the ambient responses. For this purpose, analytical and experimental modal analysis of a model chimney for dynamic characteristics was performed. 3D Finite element model of the chimney was evaluated based on the design drawing. Ambient excitation was provided by shake table from the recorded micro tremor ambient vibration data on ground level. Enhanced Frequency Domain Decomposition is used for the output only modal identification. From this study, best correlation is found between mode shapes. Natural frequencies and analytical frequencies in average (only) 1.996% are different.

• Smart Structures and Systems
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• 제10권4_5호
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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.

• Structural Engineering and Mechanics
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• 제17권3_4호
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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.

• 대한후두음성언어의학회지
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• 제13권2호
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• pp.151-154
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• 2002

Background and Objectives : The pitch range of the human voice is variable, extending from chest register to falsetto register. Although numerous studies have investigated after laryngeal mechanism description of falsetto tone, systematic and objective studies were lack. The purpose of this study was to systematically analyze and compare modal with falsetto voice. Materials and Methods : Seven adult baritones were selected from a larger population of volunteers at choir. Simultaneous measurements of acoustic, electroglottographic and aerodynamic study were made during /e/ sustained in two vocal registers, lowest modal and highest falsetto. Statistical analysis was performed using Wilkoxson signed rankes test. Results : In the acoustic analysis, shimmer was increased in flasetto voice(p<0.05). In the electroglottographic analysis, closed quotient(CQ), speed quotient(SQ) at the modal voice were higher than at the falsetto voice(p<0.05). In the aerodynamic analysis, and airflow rate(MFR) of falsetto voice was higher than modal voice(p<0.05). Conclusions : In the results of the study indicate that, falsetto register ineffective, inefficient, generally unpleasant because it was produced by incomplete clousure of true vocal cord. We anticipated that further study with large samples can provide an objective criteria for status and classification of singer's modal and falsetto voice.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 1998년도 추계종합학술대회 논문집
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• pp.359-362
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• 1998

The electromagnetic properties of leaky-waves guided by metal-strip grating configurations can be phrased in rigorous modal theory. Such a modal solution expressed by simple electrical transmissionline networks is utilized to analyze the leakage and filtering characteristics of metal-strip gratings. In particular, the modal transmission-line theory can serve as a template for computational algorithms that systematically evaluate the radiation effects that are not readily obtained by other methods.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2000년도 춘계학술대회논문집
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• pp.1925-1932
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• 2000

Damage detection methods using vibration modes are investigated on ring structures and. modal behavior of the slightly asymmetric rings is examined. Mode shapes changes, MSER(modal strain energy ratio) and MCR(modal curvature ratio) are applied to identify the locations of faults or damages. Parameters are calculated and compared by finite element analysis on rings with designed local damages. Damages are modeled as reduced stiffness in the analysis. The results show MSER and MCR can be proper factors to detect local damages in ring structures.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2008년도 제39회 하계학술대회
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• pp.1436-1437
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• 2008

In this work, we investigate the electrical and electromagnetic behaviors of the power-bus with a variety of shapes of aperture, on the signal integrity, using a rigorous methods(Modal or MoM) along with Modal analysis method.

• 한국해양공학회지
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• 제14권1호
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• pp.80-87
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• 2000

Despite many combined research efforts outstanding needs exist to develop robust safety-estimation methods for large complex structures. This paper presents a practical damage identification scheme which can be applied to truss structures using only limited modal responses. firstly a theory of pattern recognition (PR) is described. Secondly existing damage-detection algorithms are outlined and a newly-derived algorithms for truss structures. Finally the feasibility of the proposed scheme is evaluated using numerical examples of plane truss structures.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2000년도 ITC-CSCC -2
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• pp.945-948
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• 2000

The coupling properties of supermodes guided by grating-assisted directional couplers (GADCs) can be phrased in rigorous modal theory. Such a modal solution for TE modes expressed by simple electrical transmission-line networks is utilized to analyze the power distribution of GADCS with three guiding channels. In particular, the modal transmission-line theory can serve as a template for computational algorithms that systematically evaluate the coupling efficiency that are not readily obtained by other methods.