• Title/Summary/Keyword: modal analysis

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Experimental Modal Analysis of Machining Centers

  • Guoyi Ji;Park, Dong-Keun;Chung, Won-Jee;Lee, Choon-Man
    • Proceedings of the Korean Society of Machine Tool Engineers Conference
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    • pp.82-87
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    • 2004
  • Experimental modal analysis is an effective tool to investigate the dynamic behavior of machining centers. This paper presents the measurement system and experimental investigation on the modal analysis of machining centers. The modal analysis shows the weak part of the machining center. An important local model of spindle in our experiment, which influences the dynamics of machining process, is proposed in this paper. The results provide the foundation of structure modification for good dynamic behaviors.

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Generalized modal analysis of asymmetrical rotor system using modulated coordinates (변조 좌표계를 이용한 비대칭 회전체계의 일반화된 모드해석)

  • 서정환;홍성욱;이종원
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • pp.526-531
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    • 2003
  • Conventional modal analysis techniques are known to be inappropriate for asymmetrical rotor systems. when the equations of motion are written in the stationary coordinates, due to the presence of time varying parameters. This paper presents a generalized modal analysis method for asymmetrical rotor systems in the stationary coordinates, employing the modulated coordinates and the lambda matrix formulation. A numerical example with a flexible asymmetric rotor model is provided to demonstrate the effectiveness of the proposed modal analysis method. As an application of the proposed method, modal analysis is also performed with an open cracked rotor system.

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Generalized Modal Analysis of Asymmetrical Rotor System Using Modulated Coordinates (변조 좌표계를 이용한 비대칭 회전체계의 일반화된 모드해석)

  • 서정환;홍성욱;이종원
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.13 no.10
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    • pp.813-820
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    • 2003
  • Conventional modal analysis techniques are known to be inappropriate for asymmetrical rotor systems, when the equations of motion are written in the stationary coordinates, due to the presence of time varying parameters. This paper presents a generalized modal analysis method for asymmetrical rotor systems in the stationary coordinates, employing the modulated coordinates and the lambda matrix formulation. A numerical example with a flexible asymmetric rotor model is provided to demonstrate the effectiveness of the proposed modal analysis method. As an application of the proposed method, modal analysis is also performed with an open cracked rotor system.

Mode shape identification using response spectrum in experimental modal analysis

  • Babakhani, Behrouz;Rahami, Hossein;Mohammadi, Reza Karami
    • Structural Monitoring and Maintenance
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    • v.5 no.3
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    • pp.345-361
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    • 2018
  • The set of processes performed to determine the dynamic characteristics of the constructed structures is named experimental modal analysis. Using experimental modal analysis and interpreting its results, structural failure can be assessed and then it would be possible to plan for their repair and maintenance. The purpose of the experimental modal analysis is to determine the resonance frequencies, mode shapes and Mode damping for the structure. Diverse methods for determining the shape of the mode by various researchers have been presented. There are pros and cons for each of these methods. This paper presents a method for determining the mode shape of the structures using the response spectrum in the experimental modal analysis. In the first part, the principles of the proposed method are described. Then, to check the accuracy of the results obtained from the proposed method, single and multiple degrees of freedom models were numerically and experimentally investigated.

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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    • 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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A Study on the Improvement of Finite Element Model for Scaled Frame by Considering Eigenvectors and Eigenvalues (고유벡터와 고유치를 고려한 모형 프레임의 유한요소 모델 개선에 관한 연구)

  • 김병곤;정태진;이종길;허덕재
    • Journal of KSNVE
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    • v.10 no.6
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    • pp.1009-1016
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    • 2000
  • This paper describes the procedure of increasing the efficiency of experimental modal analysis and updating the quality of FE model using the scaled commercial vehicle frame. In this study, it was found that the experimental modal analysis could be more efficient when the measurements were made on the areas with high kinetic energies. Such areas could be located with the aid of FE modal analysis. Also, the number of measurement points could be decided by considering the dynamic characteristics of full FE model. The correlation of FE model and experimental modal analysis was assessed by the differences between the natural frequencies and MAC matrix, which is based on normal modes. These differences of modal parameters were reduced through the sensitivity and optimization analysis of which objective function consisted of the errors of natural frequencies and the diagonal terms of MAC matrix.

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Buckling Analysis of the Large Span Spatial Structures by Modal Analysis (Modal Analysis법에 의한 무주대공간 구조물의 좌굴해석)

  • 한상을;권택진
    • Proceedings of the Computational Structural Engineering Institute Conference
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    • pp.195-201
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    • 1996
  • This paper is mainly forcused on the application of modal analysis In analyze the geometrically non-linear buckling behaviors of large span spatial structures, and the evaluation of each eigen mode affected post-buckling behaviors and buckling loads. Modal analysis is applied . to derivation of the system matrices transforming actual displacement space into generalized coordinates space represented by coefficients multiplied in the linear combination of eigen modes which are independent and orthogonal each other. By using modal analysis method, it will be expected to save the calculating time by computer extremely. For example, we can obtain the satisfactorily good results by using about 7% of total eigen modes only in case of single layer latticed dome. And we can decrease the possibility of divergence on the bifurcation point in the calculation of post-buckling path. Arc-length method and Newton-Raphson iteration method are used to calculate the nonlinear equilibrium path.

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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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    • 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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Modal analysis of asymmetric/anisotropic rotor system using modulated coordinates (변조좌표계를 이용한 비대칭/비등방 회전체의 모드 해석)

  • 서정환;홍성욱;이종원
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • pp.304-309
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    • 2003
  • A new modal analysis method for rotor systems with periodically time-varying parameters is proposed. The essence of method is to introduce modulated coordinates to derive the equivalent time-invariant equation. This paper presents a modal analysis method using modulated coordinates fur general rotors, of which rotating and stationary parts both possess asymmetric properties. The equation of motion with time-varying parameters is transformed to an infinite order matrix equation with the time-invariant parameters. A theory of modal analysis for the system is presented with the infinite order equation and a couple of reduced order equations. A numerical example with simple asymmetric rotor is provided to demonstrate the effectiveness of the proposed method

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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.