• Title/Summary/Keyword: modal analysis

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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.

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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    • 2003.05a
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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.

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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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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    • 2004.04a
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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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Optimum amount of additive mass in scaling of operational mode shapes

  • Khatibi, M.M.;Ashory, M.R.;Albooyeh, A.R.
    • Structural Engineering and Mechanics
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    • v.39 no.5
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    • pp.733-750
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    • 2011
  • Recently, identification of modal parameters using the response only data has attracted considerable attention particularly where the classic modal testing methods is difficult to conduct. One drawback of the response only data, also known as Operational Modal Analysis (OMA), is that only the unscaled mode shapes can be obtained which restricts the applications of OMA. The Mass change method is a usual way to scale the operational mode shapes. In this article a new method is proposed to optimize the additive mass for scaling of the unscaled mode shapes from OMA for which a priori knowledge of the Finite Element model of structure is required. It is shown that the total error of the scaled mode shapes is minimized using the proposed method. The method is validated using a numerical case study of a beam. Moreover, the experimental results of a clamped-clamped beam demonstrate the applicability of the method.

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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    • 2003.11a
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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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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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Application of Substructure Synthesis Method for Analysis of Acoustic System (음향계의 해석을 위한 부분구조합성법의 적용)

  • 오재응;고상철;조용구
    • Journal of KSNVE
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    • v.7 no.5
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    • pp.737-746
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    • 1997
  • The substructure synthesis method is used for making it easy to analyze vibration systems generally in vibration field. In the past, this method has been to be used mainly because of shortage of computer memory and CPU time. But recently this method is used for analyzing complex structure or identifying the characteristics of systems precisely. The purpose of this study is to develop acoustic substructure synthesis method that can be applied to acoustic modal analysis of complex acoustic systems. Acoustic modal analysis method to be introduced here is a method that analyze acoustic natural mode shape of the complex acoustic system by the principle of CMS(component mode synthesis method). This paper describes the acoustic modal analysis of the acoustic finite element model of simple expansion pipe by acoustic substructure synthesis method. The resutls of acoustic modal analysis analyzed by Acoustic substructure synthesis method and the results by FEM(finite element method) shows good agreement.

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Operational Modal Analysis of a Wind Turbine Wing Using Acoustical Excitation

  • H. Konstantin Hansen;H. Herlufsen;N. Moller
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2002.11b
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    • pp.863-868
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    • 2002
  • Operational Modal Analysis also known as Ambient Modal Analysis has an increasing interest in mechanical engineering. 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 hi-directional the ambient excitation has big advantages. In this paper modal parameters are identified from the wing by operational modal analysis. For the parameter identification both parametric and non-parametric techniques are used. Advantages and disadvantages are discussed and results from the different techniques are compared

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