• Title, Summary, Keyword: modal analysis

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Modeling of Beam Structures from Modal Parameters (모달 파라미터를 이용한 보 구조물의 모델링)

  • Hwang, Woo-Seok
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • pp.519-522
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    • 2006
  • Accurate modeling of a dynamic system from experimental data is the bases for the model updating or heath monitoring of the system. Modal analysis or modal test is a routine process to get the modal parameters of a dynamic system. The modal parameters include the natural frequencies, damping ratios and mode shapes. This paper presents a new method that can derive the equations of motion for a dynamic system from the modal parameters obtained by the modal analysis or modal test. The present method based on the relation between the eigenvalues and eigenvectors of the state space equation derives the mass, damping and stiffness matrices of the system. The modeling of a cantilevered beam from modal parameters is an example to prove the efficiency and accuracy of the present method. Using the lateral displacements only, not the rotations, gives limited information for the system. The numerical verification up to now gives reasonable results and the verification with the test data is scheduled.

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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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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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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.

Experimental Method of a Super Structure (선체 상부구조물의 실험적 해석)

  • 박석주;박성현;오창근;제해광
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • pp.328-334
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    • 2001
  • Up to now. vibration analysis and vibration engineering have been developed, encompassing the aspects of both experimental and analytical techniques. Using experimental modal analysis or modal testing, the mode shapes and frequencies of practical structure can be measured accurately. Curve-Fitting Method is realized through experimental modal identification. In the experimental modal parameter estimation, the estimation of modal damping factor is difficult for complicated and large structure. Also numbers of Selected mode are determined before the procedure. This paper describes the vibration shape of the super-structure model of ship through experimental modal analysis.

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Application assessments of concrete piezoelectric smart module in civil engineering

  • Zhang, Nan;Su, Huaizhi
    • Smart Structures and Systems
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    • v.19 no.5
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    • pp.499-512
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    • 2017
  • Traditional structural dynamic analysis and Structural Health Monitoring (SHM) of large scale concrete civil structures rely on manufactured embedding transducers to obtain structural dynamic properties. However, the embedding of manufactured transducers is very expensive and low efficiency for signal acquisition. In dynamic structural analysis and SHM areas, piezoelectric transducers are more and more popular due to the advantages like quick response, low cost and adaptability to different sizes. In this paper, the applicable feasibility assessment of the designed "artificial" piezoelectric transducers called Concrete Piezoelectric Smart Module (CPSM) in dynamic structural analysis is performed via three major experiments. Experimental Modal Analysis (EMA) based on Ibrahim Time Domain (ITD) Method is applied to experimentally extract modal parameters. Numerical modal analysis by finite element method (FEM) modeling is also performed for comparison. First ten order modal parameters are identified by EMA using CPSMs, PCBs and FEM modeling. Comparisons are made between CPSMs and PCBs, between FEM and CPSMs extracted modal parameters. Results show that Power Spectral Density by CPSMs and PCBs are similar, CPSMs acquired signal amplitudes can be used to predict concrete compressive strength. Modal parameter (natural frequencies) identified from CPSMs acquired signal and PCBs acquired signal are different in a very small range (~3%), and extracted natural frequencies from CPSMs acquired signal and FEM results are in an allowable small range (~5%) as well. Therefore, CPSMs are applicable for signal acquisition of dynamic responses and can be used in dynamic modal analysis, structural health monitoring and related areas.

CORRECTION TECHNIQUES OF MASS-LOADING EFFECTS OF TRANSDUCERS IN MODAL TESTING

  • Guoyi Ji;Chung, Won-Jee;Lee, Choon-Man;Park, Dong-Keun
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • pp.188-188
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    • 2004
  • Modal testing and analysis is a primary tool for obtaining reliable models to represent the dynamics of structures. When a structure is tested in order to collect measured data in modal testing, we usually use attached accelerometers to pick up the response data. Change in modal parameters due to the mass of transducers in modal testing is a well-known problem. The disadvantages are the shift of measured modal frequencies and the change of modal shapes, which can cause inaccurate results in further analysis. Modal analysis methods in frequency domain are based on a set of measured frequency response functions(FRF).(omitted)

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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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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.

Mode identifiability of a cable-stayed bridge using modal contribution index

  • Huang, Tian-Li;Chen, Hua-Peng
    • Smart Structures and Systems
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    • v.20 no.2
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    • pp.115-126
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    • 2017
  • The modal identification of large civil structures such as bridges under the ambient vibrational conditions has been widely investigated during the past decade. Many operational modal analysis methods have been proposed and successfully used for identifying the dynamic characteristics of the constructed bridges in service. However, there is very limited research available on reliable criteria for the robustness of these identified modal parameters of the bridge structures. In this study, two time-domain operational modal analysis methods, the data-driven stochastic subspace identification (SSI-DATA) method and the covariance-driven stochastic subspace identification (SSI-COV) method, are employed to identify the modal parameters from field recorded ambient acceleration data. On the basis of the SSI-DATA method, the modal contribution indexes of all identified modes to the measured acceleration data are computed by using the Kalman filter, and their applicability to evaluate the robustness of identified modes is also investigated. Here, the benchmark problem, developed by Hong Kong Polytechnic University with field acceleration measurements under different excitation conditions of a cable-stayed bridge, is adopted to show the effectiveness of the proposed method. The results from the benchmark study show that the robustness of identified modes can be judged by using their modal contributions to the measured vibration data. A critical value of modal contribution index of 2% for a reliable identifiability of modal parameters is roughly suggested for the benchmark problem.