• Title/Summary/Keyword: 고유진동수 및 모드형상 변화

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Analysis of sound radiation by floor vibration in the closed sound field (실내의 바닥진동에 의한 음향방사해석)

  • 최석주
    • Proceedings of the Acoustical Society of Korea Conference
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    • 1992.06a
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    • pp.137-140
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    • 1992
  • 실내 바닥슬래브의 휨진동에 의한 음향방사문제에 대하여 유한요소법을 적용하여 검토하였다. 단순한 형상의 판이 휨진동하여 자유공간에 음을 방사하는 문제에 대해서는 이론적인 해를 구할 수 있으나, 임의형상의 판이 휨진동하여 실내에 음을 방사하는 문제에 대해서는 검토되지 않았다. 따라서 본 연구에서는 이와같은 문제를 단순화한 해석법으로서 먼저 유한요소법을 이용하여 판의 휨진동에 대한 고유모드의 상대변위를 구하고, 다음 상대변위를 진동속도로 변환한 결과를 입력조건으로 하여 유한요소법에 의한 3차원 음장해석을 하였다. 그 결과 실내 바닥슬래브의 휨진동에 의한 음향방사파워는 슬래브의 진동모드, 실내음향모드 및 벽흡음율 등의 조건에 따라 크게 변화된다는 것을 확인하였다.

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Structural Analysis Modeling of Disaster Resilient Greenhouse Structures (내재해형 온실구조의 해석을 위한 구조모델)

  • Jung, Ji-Eun;Kim, Dae-Jin;Kim, Hong-Jin;Shin, Seung-Hoon;Kim, Jin-Won
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.30 no.1
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    • pp.7-15
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    • 2017
  • This paper presents the results of the parametric study to investigate the effects of several analysis modeling parameters such as support conditions, member connectivities and cable member stiffness on the main mode shapes and natural frequencies of a representative disaster resilient greenhouse structure. In addition, an ambient vibration test was performed on the representative greenhouse structure and its main mode shapes and natural frequencies were obtained. By comparing the experimental and analysis results, a proper analysis modeling method of the representative greenhouse structure was proposed.

Structural Damage Evaluation of Large Span Roof Structure using Artificial Neural Network (인공신경망을 이용한 대공간구조물 구조손상평가)

  • Cho, Ja-Ock;Kim, Ji-Young;Yu, Eun-Jong;Kim, Mi-Jin;Kim, Dae-Young
    • Proceedings of the Computational Structural Engineering Institute Conference
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    • 2010.04a
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    • pp.335-338
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    • 2010
  • 구조물의 상태평가는 구조물 고유의 동특성을 분석함으로써 평가할 수 있다. 구조물은 태풍, 지진 및 기타 외적 환경 등에 의하여 손상이 발생하고 이러한 구조물의 손상은 강성의 변화로 이어져 구조물의 동특성에 변화를 일으킨다. 따라서 손상 발생 전후의 동적응답을 각각 계측한 후 구조물 식별(Structural System Idetification)을 통하여 고유진동수 및 모드형상을 추출하고 수학적인 기법을 사용하여 구조물을 구성하고 있는 개별 부재 혹은 부재 그룹의 강성을 비교함으로써 손상의 발생여부 및 손상정도를 추정할 수 있다. 본 연구에서는 지붕트러스 구조물에 대하여 손상평가를 수행하고 이를 검증할 수 있는 Mock-up 구조물을 설계 및 시공하였다.

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Damage Evaluation of Cracked Laminated Composite Plates Using Experimental Modal Analysis (실험 모드해석을 이용한 균열 적층복합판의 손상평가)

  • Kim, Joo-Woo
    • Journal of Korean Society of Steel Construction
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    • v.24 no.4
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    • pp.399-410
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    • 2012
  • In this study, vibration tests are performed on cantilevered and clamped-clamped laminated composite rectangular plates using experimental modal analysis technique. The damages are simulated by applying progressive line cracks to the laminated composite plates for damage evaluations due to crack growth. The changes of frequency response functions(FRFs), MAC values, and modal parameters (frequency, mode shape and damping ratio) of the damaged composite plates, which are obtained by the modal testing of impact hammer, are investigated. Each experimental modal parameter of the progressively damaged composite plates is compared with natural frequencies and mode shapes obtained by finite element analysis. It is seen that the damage can be evaluated from the changes in the geometric properties and structural behaviors of the laminated composite plates resulting from the model updating process of the finite element model as a benchmark.

Dynamic Modeling of Scissors Structure and Stiffness Analysis Based on Deployed Configuration (전개형 시저스 구조물의 동역학적 모델링 및 전개 완료 형상에 따른 강성 분석)

  • Kim, Tae-Hyun;Suh, Jong-Eun;Han, Jae-Hung
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.47 no.6
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    • pp.405-413
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    • 2019
  • Deployable structures are widely used for space mission because of their advantages in storage and transportation coming from its transformability of configuration. The space structures should be designed with high stiffness to withstand the various types of disturbance that they encounter during operation. Especially for the deployable structures, the internal forces loaded on the component or the stiffness at its deployed configuration should be analyzed since they usually consist of the thin and light structures. In this paper, a dynamic model of the scissors structure is established and its deployment behavior is analyzed, especially focusing on the deployment speed and the internal force on each joint. In addition, modal analysis is carried out for the 1-stage and 2-stage scissors structures in order to analyze the stiffness of the scissors structure based on its deployed configuration. The fundamental mode shapes and natural frequencies are analyzed and discussed.

Ground Vibration Test of KF- 16D (KF-16D 지상진동시험)

  • Byun, Kwan-Hwa;Park, Chan-Yik;Kim, Jong-Heon
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.33 no.5
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    • pp.41-49
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    • 2005
  • This paper discusses the test procedure, instrumentation, verification methodology and the results of the ground vibration test(GVT) performed on the KF-16D aircraft to estimate experimentally dynamic characteristics of the aircraft. The modal tests for 7 external store configurations were conducted to estimate effects of external stores on the aircraft vibration modes. To emulate free-free boundary conditions the test aircraft was mounted on its landing gear structure with deflated tires during the GVT. The airframe modal tests were done by burst random excitations with 6 to 8 shakers and about 200 accelerometers. Frequency response functions(FRFs) were measured for each test, and the FRFs were reduced and analyzed to identify the dynamic parameters interested. The analyses were carried out in two steps. To extract modal parameters such as, frequencies and damping ratios, the poly-reference least square complex exponential method was used in the time domain. The mode shape coefficients were estimated with the least squares frequency domain method to identify the vibration modes.

Determination of Degraded Properties of Vibrating Laminated Composite Plates for Different Layup Sequences (적층배열 변화에 따른 진동하는 복합재료 적층 구조의 미시역학적 물성변화 추정)

  • Kim, Gyu-Dong;Lee, Sang-Youl
    • Composites Research
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    • v.28 no.5
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    • pp.277-284
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    • 2015
  • This paper presents a method to detect the fiber property variation of laminated GFRP plates from natural frequency response data. The combined finite element analysis using ABAQUS and the inverse algorithm described in this paper may allow us not only to detect the deteriorated elements from the mirco-mechanical point of view but also to find their numbers, locations, and the extent of damage. To solve the inverse problem using the combined method, this study uses several natural frequencies instead of mode shapes in a structure as the measured data. Several numerical results show that the proposed system is computationally efficient in identifying fiber stiffness degradation for complex structures such as composites with various layup sequences.

Vibration Analysis of Rotating Cantilever Plates with a Concentrated Mass (집중 질량을 가진 회전하는 외팔 평판의 진동 해석)

  • 양정식;유홍희
    • Journal of KSNVE
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    • v.8 no.6
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    • pp.1130-1136
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    • 1998
  • A modelling method for the vibration analysis of rotating cantilever plates with a concentrated mass is presented. The equations of motion for the rotating plates with a concentrated mass located in an arbitrary position are derived and transformed into a dimensionless form. For the mathematical modelling of the concentrated mass. a mass density Dirac delta function is used. The effects of concentrated mass and its location. angular speed. plate aspect ratio. and hub radius of the rotating plate on the natural frequencies are studied. Particularly. mode shape variations due to some parameter variations are investigated.

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Non-destructive Reliability Evaluation of Electronic Device by ESPI (ESPI를 이용한 전자부품 비파괴 신뢰성평가)

  • Yoon, Sung-Un;Kim, Koung-Suk;Jo, Seon-Hyung;Kang, Ki-Soo
    • Journal of the Korean Society for Nondestructive Testing
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    • v.21 no.6
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    • pp.630-633
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    • 2001
  • This paper propose electronic speckle pattern interferometry(ESPI) for reliability evaluation of electronic device. Especially, vibration problem in a fan of air conditioner, motor of washing machine and etc. is important factor to design the devices. But, it is difficult to apply previous method, accelerometer to the devices with complex geometry. ESPI, non-contact measurement technique applies a commercial fan of air conditioner to vibration analysis. Vibration mode shapes, natural frequency and the range of the frequency are decided and compared with that of FEM analysis. In mechanical deign of new product, ESPI adds weak point of previous method to supply effective design information.

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Variability of Mid-plane Symmetric Functionally Graded Material Beams in Free Vibration (중립면 대칭 기능경사재료 보의 자유진동 변화도)

  • Nguyen, Van Thuan;Noh, Hyuk-Chun
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.31 no.3
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    • pp.127-132
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    • 2018
  • In this paper, a scheme for the evaluation of variability in the eigen-modes of functionally graded material(FGM) beams is proposed within the framework of perturbation-based stochastic analysis. As a random parameter, the spatially varying elastic modulus of FGM along the axial direction at the mid-surface of the beam is chosen, and the thru-thickness variation of the elastic modulus is assumed to follow the original form of exponential variation. In deriving the formulation, the first order Taylor expansion on the eigen-modes is employed. As an example, a simply supported FGM beam having symmetric elastic modulus with respect to the mid-surface is chosen. Monte Carlo analysis is also performed to check if the proposed scheme gives reasonable outcomes. From the analyses it is found that the two schemes give almost identical results of the mean and standard deviation of eigen-modes. With the propose scheme, the standard deviation shape of respective eigen-modes can be evaluated easily. The deviated mode shape is found to have one more zero-slope points than the mother modes shapes, irrespective of order of modes. The amount of deviation from the mean is found to have larger values for the higher modes than the lower modes.