• Title/Summary/Keyword: vibration modes

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Suppression of Sound Radiation from Composite Plate Structures Using Piezoelectric Materials (압전재료를 이용한 복합재료 평판 구조물의 음향파워 억제)

  • 윤기원;김승조
    • Journal of KSNVE
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    • v.6 no.6
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    • pp.781-790
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    • 1996
  • The goal of current research is to suppress the acoustic noise radiated from vibration of composite plate structure. The induced noise can be reduced through the control of the corresponding structural vibration modes by using the piezoelectric materials as actuator. The acoustic fields are to be analyzed through the boundary element method (BEM) based on the Rayleigh intergral equation and structural system through the finite element method (FEM). The suppression of rediated sound is studied by adaping the piezoelectric material as the distributed actuator. Numerical results are presented on the sound radiation from composite plate of arbitrary boundary conditions, the noise reduction adapting the piezoelectric materials as distributed actuator. The results show the effectiveness and possibility of piezoelectric actuator in the control of sound radiation from composite structure.

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Lens-Holder Design in Pick-up Actuator using Sensitivity Analysis (감도해석을 이용한 광픽업 엑추에이터의 렌즈홀더 설계)

  • 이동주;이경택;김철진;박노철;양현석;박영필
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2001.05a
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    • pp.712-717
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    • 2001
  • In order to modify flexible mode frequencies, finite element analysis is applied for a lens-holder in pick-up actuator. Several design parameters like shape and local dimension of a lens-holder were selected adequately and sensitivities of the design variables for vibration modes were obtained by FE analysis and this result was used for updating FE model. A sensitivity matrix between the natural frequencies and the design variables was calculated by finite difference method. By comparing the calculated natural frequencies with target frequencies, modification of the design variables was acquired and used for improving FE model. Calculated natural frequencies after several iterations by FE analysis coincided with target frequencies and the errors between them were minimized.

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Mechanism of ovalling vibrations of cylindrical shells in cross flow

  • Uematsu, Yasushi;Tsujiguchi, Noboru;Yamada, Motohiko
    • Wind and Structures
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    • v.4 no.2
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    • pp.85-100
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    • 2001
  • The mechanism of wind-induced ovalling vibrations of cylindrical shells is numerically investigated by using a vortex method. The subject of this paper is limited to a two-dimensional structure in the subcritical regime. The aerodynamic stability of the ovalling vibrations in the second to fourth circumferential modes is discussed, based on the results of a forced-vibration test. In the analysis, two modal configurations are considered; one is symmetric and the other is anti-symmetric with respect to a diameter parallel to the flow direction. The unsteady pressures acting on a vibrating cylinder are simulated and the work done by them for one cycle of a harmonic motion is computed. The effects of a splitter plate on the flow around the cylinder as well as on the aerodynamic stability of the ovalling vibrations are also discussed. The consideration on the mechanism of ovalling vibrations is verified by the results of a free-vibration test.

Ambient vibration tests of XV century Renaissance Palace after 2012 Emilia earthquake in Northern Italy

  • Cimellaro, Gian Paolo;De Stefano, Alessandro
    • Structural Monitoring and Maintenance
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    • v.1 no.2
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    • pp.231-247
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    • 2014
  • This paper focuses on the dynamic behaviour of Mirandola City Hall (a XV century Renaissance Palace) that was severely damaged during May 2012 Emilia earthquake in Northern Italy. Experimental investigations have been carried out on this monumental building. Firstly, detailed investigations have been carried out to identify the identification of the geometry of the main constructional parts as well as the mechanical features of the constituting materials of the palace. Then, Ambient Vibration Tests (AVT) have been applied, for the detection of the main dynamic features. Three output-only identification methods have been compared: (i) the Frequency Domain Decomposition, (ii) the Random Decrement (RD) and the (iii) Eigensystem Realization Algorithm (ERA). The modal parameters of the Palace were difficult to be identified due to the severe structural damage; however the two bending modes in the perpendicular directions were identified. The comparison of the three experimental techniques showed a good agreement confirming the reliability of the three identification methods.

An Experimental Study on the Structural Vibration Control Using Orificed Fluid Dampers (Orificed Fluid Dapper를 이용한 구조물 진동계어의 실험적 연구)

  • 정태영;임채욱;김병현
    • Proceedings of the Earthquake Engineering Society of Korea Conference
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    • 2001.09a
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    • pp.364-372
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    • 2001
  • An orifices fluid damper(OFD) having the capacity of about 2 tons was designed and fabricated and applied to a 6-story steel structure under random excitation and seismic excitation for the confirmation of its validity on structural vibration absorbtion. The experimental results demonstrated that the addition of an OFD to the test structure is very effective in reduction of vibration level of the higher modes as well as the fundamental mode. Maxwell model was adopted to described the frequency-dependent characteristics of the fabricated OFD and the numerical simulation was carried for the test structure. It was confirmed that the experimental and numerically simulated results agree well.

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Natural Vibration Analysis of Thick Rings (두꺼운 링의 고유진동 해석)

  • Kim Chang-Boo;Park Jung-Woo
    • Proceedings of the KSR Conference
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    • 2005.05a
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    • pp.459-466
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    • 2005
  • In this paper, we have systematically formulated the equations concerned to the in-plane and out-of-plane motions and deformations of a thick circular beam by using the kinetic and strain energies in order to analyse natural frequencies of a thick ring. The effects of variation of radius of curvature across the cross-section and also the effects of bending shear, extension and twist are considered. The equations of motion for natural vibration analysis of a ring are obtained utilizing the cyclic symmetry of vibration modes of the ring. The frequencies calculated using thick ring model and thin ring model are compared and discussed with the ones obtained from finite element analysis using the method of cyclic symmetry with 20-node hexahedral solid elements for rings with the different ratio of radial thickness to mean radius.

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FREE VIBRATION ANALYSIS OF CIRCULAR PLATE WITH ECCENTRIC HOLE SUBMERGED IN FLUID

  • Jhung, Myung-Jo;Choi, Young-Hwan;Ryu, Yong-Ho
    • Nuclear Engineering and Technology
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    • v.41 no.3
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    • pp.355-364
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    • 2009
  • Circular plates with holes are extensively used in mechanical components. The existence of a hole in a circular plate results in a significant change in the natural frequencies and mode shapes of the structure. Especially if the hole is located eccentrically, the vibration behavior of these structures is expected to deviate significantly from that of a plate with a concentric hole. In addition, if the plate is in contact with or submerged in fluid, the situation is more complex. Therefore, in this study, an analytical method to determine the modal characteristics of a plate submerged in fluid is developed based on the finite Fourier-Bessel series expansion and Rayleigh-Ritz method and is verified by the finite element analysis using a commercial program. Also, the relationship between parameter variations and vibration modes is investigated. These results can be used as guidance for the modal analysis and damage detection of a circular plate with a hole.

Modeling and Vibration Analysis of Rotating Cantilever Deams Considering Shear and Rotary Inertia Effects (전단 및 단면 관성효과를 고려한 회전 외팔보의 모델링 및 진동해석)

  • 신상하;유홍희
    • Journal of KSNVE
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    • v.6 no.2
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    • pp.179-185
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    • 1996
  • This paper presents a modeling method for the vibration analysis of a rotating beam the slenderness ratio of which is relatively small. The smaller the slenderness ratio becomes, the larger the shear and rotary inertia effects become. Such effects become critical for the accurate estimation of the natural frequencies and modeshapes, especially higher frequencies and modes, as the angular speed increases. It is also shown that the effects are important for the accurate estimation of the critical angular speed of the beam.

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Dynamic Characteristics of the Plate with Structural Damages (구조손상을 갖는 평판의 동적특성)

  • Kim, Nam-In;Lee, U-Sik
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2000.06a
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    • pp.357-362
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    • 2000
  • Though there have been many researches to investigate the relationship between the damage location, damage size and the changes in eigenparameters, there have been few studies on the small-sized damages. Thus, this paper considers the plate with small local damages. The equation of motion for damaged plate is derived in terms of the damage distribution function and then the effects of small damages on the dynamic characteristics of plate are investigated. It is observed that the damage-induced modal coupling and a sufficient number of vibration modes should be considered especially for small damage detections.

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Vibration Analysis of an Exhaust System with Bellows Using the Component Mode Synthesis (부분구조 합성법을 이용한 배기계의 진동해석)

  • Lim, Jae-Moon;Kim, Min-Soo;Lee, Kwi-Young
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.17 no.7 s.94
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    • pp.1833-1840
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    • 1993
  • An efficient vibration analysis method, Component Mode Synthesis(CMS), for an exhaust system with bellows is presented. Analyses are performed for two types of bellows, where characteristics of vibration modes affecting idle shake and interior noise of a vehicle are examined. Also analyzed are the contributions of an exhaust and engine mounting system to the idle shake and interios noise. Comparison between the analysis and test is in good agreement, hence the CMS method is shown to be efficient and valid.