• Title/Summary/Keyword: modal analysis

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Modal transformation tools in structural dynamics and wind engineering

  • Solari, Giovanni;Carassale, Luigi
    • Wind and Structures
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    • v.3 no.4
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    • pp.221-241
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    • 2000
  • Structural dynamics usually applies modal transformation rules aimed at de-coupling and/or minimizing the equations of motion. Proper orthogonal decomposition provides mathematical and conceptual tools to define suitable transformed spaces where a multi-variate and/or multi-dimensional random process is represented as a linear combination of one-variate and one-dimensional uncorrelated processes. Double modal transformation is the joint application of modal analysis and proper orthogonal decomposition applied to the loading process. By adopting this method the structural response is expressed as a double series expansion in which structural and loading mode contributions are superimposed. The simultaneous use of the structural modal truncation, the loading modal truncation and the cross-modal orthogonality property leads to efficient solutions that take into account only a few structural and loading modes. In addition the physical mechanisms of the dynamic response are clarified and interpreted.

Blind modal identification of output-only non-proportionally-damped structures by time-frequency complex independent component analysis

  • Nagarajaiah, Satish;Yang, Yongchao
    • Smart Structures and Systems
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    • v.15 no.1
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    • pp.81-97
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    • 2015
  • Recently, a new output-only modal identification method based on time-frequency independent component analysis (ICA) has been developed by the authors and shown to be useful for even highly-damped structures. In many cases, it is of interest to identify the complex modes of structures with non-proportional damping. This study extends the time-frequency ICA based method to a complex ICA formulation for output-only modal identification of non-proportionally-damped structures. The connection is established between complex ICA model and the complex-valued modal expansion with sparse time-frequency representation, thereby blindly separating the measured structural responses into the complex mode matrix and complex-valued modal responses. Numerical simulation on a non-proportionally-damped system, laboratory experiment on a highly-damped three-story frame, and a real-world highly-damped base-isolated structure identification example demonstrate the capability of the time-frequency complex ICA method for identification of structures with complex modes in a straightforward and efficient manner.

Fluid effect on the modal characteristics of a square tank

  • Jhung, Myung Jo;Kang, Sung-Sik
    • Nuclear Engineering and Technology
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    • v.51 no.4
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    • pp.1117-1131
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    • 2019
  • Tanks are used extensively in many engineering areas for spent fuel pool structures at nuclear power plants or for water storage tanks in bulk carriers. To ensure the structural integrity of such tanks when under dynamic loads, modal characteristics such as natural frequencies, participation factors and mode shapes should be known. Investigated in this study are the modal characteristics of a square tank by the finite element method. This approach can be used with subsequent dynamic analyses such as a response spectrum analysis or a harmonic analysis. Finite element models are prepared to determine the natural frequencies and mode shapes, which are easy to find the modal characteristics of a fluid-filled square tank. The effects of the fluid contained in the tank and the boundary conditions at top and bottom ends on the modal characteristics are assessed by several finite element analyses.

Operational Modal Analysis of a Wind Turbine Wing Using Acoustical Excitation (음향가진을 이용한 풍동터빈 날개의 운전형상 변형 분석)

  • Herlufsen, H.;Konstantin-Hansen, H.;Moller, N.
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2002.11a
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    • pp.385.1-385
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    • 2002
  • Operational Modal Analysis also known as Ambient Modal Analysis has an increasing interest in mechanical cngineering. Especially on big structures where the excitation and not less important the determination of the forces is most often a problem. In a structure like a wind turbine wing where the modes occur both close in frequency and bi-directional the Ambient excitation has big advantages. (omitted)

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Frequency domain analysis of concrete arch dams by decoupled modal approach

  • Lotfi, Vahid
    • Structural Engineering and Mechanics
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    • v.21 no.4
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    • pp.423-435
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    • 2005
  • A modal approach is proposed for dynamic analysis of concrete arch dam-reservoir systems in frequency domain. The technique relies on mode shapes extracted by considering the symmetric parts of total mass and stiffness matrices. Based on this method, a previously developed program is modified, and the response of Morrow Point arch dam is studied for various conditions. The method is proved to be very effective and it is an extremely convenient modal technique for dynamic analysis of concrete arch dams.

Modal Analysis of Suspension System with Kinematic Constraints and Elastic Elements (기구학적 구속조건과 탄성요소를 가진 현가계의 모드해석)

  • 이장무;강주석;윤중락;배상우;탁태오
    • Transactions of the Korean Society of Automotive Engineers
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    • v.8 no.1
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    • pp.110-123
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    • 2000
  • In this Study, the dynamic equation for vibration analysis of mechanical systems with kinematic constraints is derived. This equations are derived in terms of small displacements of Cartesian coordinates, and are applied to compute the dynamic response and the natural modes of the suspension system of a vehicle. The results are validated through the comparison with the results from conventional nonlinear dynamic analysis and modal test.

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Stability Investigation of Rotor Systems by Complex Modal Analysis (복소 모드해석을 이용한 회전체의 안정성 분석)

  • Han, Dongju
    • Journal of Aerospace System Engineering
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    • v.7 no.4
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    • pp.27-35
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    • 2013
  • Identifying the stability of rotor systems is prerequisite for clear determination of the parameter identification and safety, through which operating conditions may be rationally ascertained. For this purpose, the complex modal analysis of periodically time-varying system has been introduced by transforming the relation between periodic eigen-vectors and the corresponding adjoint vectors into the latent value problem. Stability investigation associated with modal features for rotor systems is performed using numerical simulation based upon the analysis model.

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.

Voice Analysis of Highest Falsetto and Lowest Modal Voice (가성구와 흉성구의 객관적인 음성분석)

  • 진성민;송윤경;권기환;이경철;반재호
    • Journal of the Korean Society of Laryngology, Phoniatrics and Logopedics
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    • v.13 no.2
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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.

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Modal Testing of Mechanical Structures Subject to Operational Excitation Forces

  • Gade, Svend;Moller, Nis B.;Herlufsen, Henrik;Brincker, Rune;Andersen, Palle
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2001.11b
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    • pp.1162-1165
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    • 2001
  • Operational Modal Analysis also known as Output Only Modal Analysis has in the recent years been used for extracting modal parameters of civil engineering structures and is now becoming popular for mechanical structures. The advantage of the method is that no artificial excitation need to be applied to the structure or force signals to be measured. All the parameter estimation is based upon the response signals, thereby minimising the work of preparation for the test. This test case is a controlled lab set-up enabling different parameter estimation methods techniques to be used and compared to the Operational Modal Analysis. For Operational Modal Analysis two different estimation techniques are used: a non-parametric technique based on Frequency Domain Decomposition (FDD), and a parametric technique working on the raw data in time domain, a data driven Stochastic Subspace Identification (SS!) algorithm. These are compared to other methods such as traditional Modal Analysis.

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