• 제목/요약/키워드: modal testing

검색결과 307건 처리시간 0.024초

디지털 실험장치를 이용한 판의 모우드 해석 (Model Analysis of Plate using by Digital Test System)

  • 홍봉기;배동명;배성용
    • 수산해양기술연구
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    • 제29권1호
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    • pp.39-55
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    • 1993
  • Modal Analysis is the process of characterizing the dynamic properties of an elastic structure by identifying its modes of vibration. A mode of vibration is a global property of an elastic structure. That is, a mode has a specific natural frequency and damping factor which can be identified from response data at practically any point on a structure, and it has a characteristic mode shape which identifies the mode spatially over the entire structure. Modal testing is able to be performed on structural and mechanical structure in an effort to learn more about their elastic behavior. Once the dynamic properties of a structure are known its behavior can be predicted and therefore controlled or corrected. Resonant frequencies, damping factors and mode shape data can be used directly by a mechanical designer to pin point weak spots in a structure design, or this data can also be used to confirm or synthesize equations of motion for the elastic structure. These differential equations can be used to simulate structural response to know input forces and to examine the effects of pertubations in the distributed mass, stiffness and damping properties of the structure in more detail. In this paper the measurement of transfer functions in digital form, and the application of digital parameter identification techniques to identify modal parameters from the measured transfer function data are discussed. It is first shown that the transfer matrix, which is a complete dynamic model of an elastic plate structure can be written in terms of the structural modes of vibration. This special mathematical form allows one to identify the complete dynamics of the structure from a much reduced set of test data, and is the essence of the modal approach to identifying the dynamics of a structure. Finally, the application of transfer function models and identification techniques for obtaining modal parameters from the transfer function data are discussed. Characteristics on vibration response of elastic plate structure obtained from the dynamic analysis by Finite Element Method are compared with results of modal analysis.

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고낙차 수력 펌프/터빈 런너에 대한 진동 모드해석 및 실험 (Modal Analysis and Testing of a High Head Pump/Turbine Runner)

  • 류석주;하현천
    • 소음진동
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    • 제8권6호
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    • pp.1062-1068
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    • 1998
  • This paper describes the vibration characteristics of a high head pump-turbine runner. with nine blades and an outer diameter of 4.410 mm. of the pumped storage power plant. Mode shapes and natural frequencies were obtained by means of both the finite element analysis and modal testing. both in air and in water. The natural frequencies in air were calculated using the finite element method by ANSYS software. In order to confirm calculation results. the natural frequencies and mode shapes of the runner were measured using a hydraulic exciter both in air and in water. Natural frequencies of the pump-turbine runner were found at 174. 310 Hz in air, and at 107. 184 Hz in water. The first mode shape is flat plate mode with two nodal diameter and the second one is also flat plate mode with three nodal diameter. It can be shown that the natural frequencies of the pump-turbine runner in water is reduced approximately 40 % due to additional mass effect. Natural frequencies in air predicted by ANSYS software are in good agreement with test results.

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이방성을 고려한 회전기기 고정자 코어의 동적 모델링 (Dynamic Modeling of the Stator Core of the Electrical Machine Using Orthotroic Characteristics)

  • 김희원;이수목;김관영;배종국
    • 한국소음진동공학회:학술대회논문집
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    • 한국소음진동공학회 2002년도 추계학술대회논문집
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    • pp.1044-1048
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    • 2002
  • The experimental modal testing has been carried out for the stator of a generator to confirm the vibrational mode shapes and the corresponding natural frequencies. The model of the stator for the vibration analysis was developed and a series of vibration analyses was carried out. And the properties of the solid element were updated to reduce the differences of the natural frequencies between the measured and the analysed. In the vibration anlyses, the axial, radial and circumferential properties of the solid element were separately varied to take into account the orthotropic effect of the laminated structure and to match the primary modes of the stator core which were extracted from the modal testing. After several attempts to match the measured natural frequencies and model shapes, the properties of the stator model were determined. Comparison of the vibration analyses results based on the determined properties showed fairly good coincidence with the measured data.

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토글가새와 납-고무 제진장치를 적용한 구조물 진동제어 실험 (Experiments for the Vibration Control of Steel Frame Structure Using Toggle Brace and Lead Rubber Damper)

  • 박정우;박진영;이완하;김기만;박건록
    • 한국소음진동공학회:학술대회논문집
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    • 한국소음진동공학회 2011년도 춘계학술대회 논문집
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    • pp.171-176
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    • 2011
  • The purposes of the research were to evaluate system performance and response of building structure under external load for full scale modal-testing-tower applied toggle bracing and lead rubber damper(LRD). The dynamic properties of the structure were measured before and after installing damper under harmonic excitation using the AMD and the results were compared. The harmonic excitation condition is to increase 0.01Hz sine sweep signal from 0.49Hz to 0.63Hz. As a result of measuring resonant frequency, before installing damper is 0.55Hz and after installing damper is 0.62Hz. The experimental results after installing damper were also distinguished from simulation results and the main cause of this results is temperature dependency property of rubber material.

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Resin Chock 교반기용 임펠러가 달린 축의 진동해석 (Vibration Analysis of Shaft with Impeller for Resin Chock Mixing Machine)

  • 홍도관;박진우;백황순;안찬우
    • 대한기계학회논문집A
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    • 제32권11호
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    • pp.970-977
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    • 2008
  • This paper deals with the dynamic characteristics of the shaft with impeller model which is the most important part in developing the resin mixing machine. Through reverse engineering, it is possible to make the shaft with impeller geometry model which is necessary vibration characteristic analysis by commercial impeller. The natural frequency analysis and structural analysis using finite element analysis software are performed on the imported commercial shaft with impeller model. The most important fundamental natural frequency of the shaft with impeller model is around 14.5 Hz, which well agrees with modal testing. The most effective design variables were extracted by ANOM(analysis of means) and pareto chart. This paper presents approximation 2nd order polynomial as design variables using RSM(response surface methodology). Generally, RSM take 2 or 3 design variables, but this method uses 5 design variables with table of mixed orthogonal array. Further more, the analyzed result of the commercial shaft with impeller is to be utilized for the structural design of resin chock mixing machine.

Structural identification of concrete arch dams by ambient vibration tests

  • Sevim, Baris;Altunisik, Ahmet Can;Bayraktar, Alemdar
    • Advances in concrete construction
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    • 제1권3호
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    • pp.227-237
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    • 2013
  • Modal testing, widely accepted and applied method for determining the dynamic characteristics of structures for operational conditions, uses known or unknown vibrations in structures. The method's common applications includes estimation of dynamic characteristics and also damage detection and monitoring of structural performance. In this study, the structural identification of concrete arch dams is determined using ambient vibration tests which is one of the modal testing methods. For the purpose, several ambient vibration tests are conducted to an arch dam. Sensitive accelerometers were placed on the different points of the crest and a gallery of the dam, and signals are collected for the process. Enhanced Frequency Domain Decomposition technique is used for the extraction of natural frequencies, mode shapes and damping ratios. A total of eight natural frequencies are attained by experimentally for each test setup, which ranges between 0-12 Hz. The results obtained from each ambient vibration tests are presented and compared with each other in detail. There is a good agreement between the results for all measurements. However, the theoretical fundamental frequency of Berke Arch Dam is a little different from the experimental.

액체가 채워진 원통형 구조물의 진동 특성 규명을 위한 모달 시험 방법 연구 (Study on Modal Test Method for Vibration Characteristics of the Cylindrical Structure Filled with Liquid)

  • 김근상;김문국;김인걸;박재상;박순홍
    • 한국항공우주학회지
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    • 제46권8호
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    • pp.621-630
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    • 2018
  • 액체 추진 발사체는 발사 후 추진제 소모로 인하여 고유진동수가 변화하는데, 이에 대한 영향을 규명하기 위해서는 모달 시험이 필수적이다. 그러나 액체 추진 발사체는 액체 추진제에 의한 액체의 영향과 발사체 구조의 영향이 복합적으로 작용하여, 이를 규명하는 것은 매우 어렵다. 또한 모달 시험에만 의존하여 복합된 특성을 규명하는 경우, 시험에 소요되는 시간이 과도하게 증가하고 특정 모드와 특정 주파수의 판별 및 확인이 쉽지 않다. 본 논문에서는 이러한 단점을 보완하기 위해 유한요소 해석 결과를 이용한 모달 시험 방법을 제안하였다. 액체가 채워진 원통형 구조물을 연구 모델로 선정하여 모달 시험과 유한요소 해석을 수행하였다. 모달 시험은 충격 가진 방식으로 충격망치와 가속도계를 이용하여 수행하였다. 모달 시험과 유한요소 해석 결과 비교를 통해 제안한 유한요소 해석 결과를 이용한 모달 시험 방법의 타당성을 검증하였으며, 액체가 채워진 비율에 따른 원통형 구조물의 자유진동 특성과 그 경향성에 대해 고찰하였다.

Ambient vibration testing and seismic performance of precast I beam bridges on a high-speed railway line

  • Toydemir, Burak;Kocak, Ali;Sevim, Baris;Zengin, Basak
    • Steel and Composite Structures
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    • 제23권5호
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    • pp.557-570
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    • 2017
  • In this study, the seismic performance levels of four bridges are determined using finite element modeling based on ambient vibration testing. The study includes finite element modeling, analytical modal analyses, ambient vibration testing and earthquake analyses of the bridges. For the purpose, four prestressed precast I beam bridges that were constructed for the Ankara-Sivas high speed railway line are selected for analytical and experimental studies. In the study, firstly a literature review related to the dynamic behavior of bridges especially precast beam bridges is given and then the formulation part related to ambient vibration testing and structural performance according to Turkish Seismic Code (2007) is presented. Next, 3D finite element models of the bridge are described and modeled using LARSA 4D software, and analytical dynamic characteristics are obtained. Then ambient vibration testing conducted on the bridges under natural excitations and experimental natural frequencies are estimated. Lastly, time history analyses of the bridges under the 1999 Kocaeli, 1992 Erzincan, and 1999 Duzce Earthquakes are performed and seismic performance levels according to TSC2007 are determined. The results show that the damage on the bridges is all under the minimum damage limit which is in the minimum damage region under all three earthquakes.