• Title/Summary/Keyword: Natural Frequency and Mode Shape Variations

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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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Dynamic Characteristic Analysis of Trapezoidal Cantilever Plates Undergoing Translational Acceleration (가속을 받는 사다리꼴 외팔 평판의 동특성 해석)

  • 임홍석;유홍희
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.12 no.10
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    • pp.785-791
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    • 2002
  • A modeling method for the dynamic characteristic analysis of a translationally accelerated trapezoidal cantilever plate is presented in this paper. The equations of motion for the plate are derived and transformed into a dimensionless form. The effects of the inclination angles and the acceleration on the vibration characteristics of the plate are investigated. Incidentally, natural frequency loci veering and associated mode shape variations are observed and discussed.

Dynamic Characteristic Analysis of Trapezoidal Cantilever Plates Undergoing Translational Acceleration (가속을 받는 사다리꼴 외팔 평판의 동특성 해석)

  • 임홍석;유홍희
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2002.05a
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    • pp.268-273
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    • 2002
  • A modeling method for the dynamic characteristic analysis of a translationally accelerated trapezoidal cantilever plate is presented in this paper. The equations of motion for the plate are derived and transformed into a dimensionless form. The effects of the inclination angles and the acceleration on the vibration characteristics of the plate are investigated. Incidentally, natural frequency loci veering and associated mode shape variations are observed and discussed

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Vibration Analysis of Rotating Cantilever Plates with Arbitrary Orientation Angle (임의의 자세를 갖는 외팔평판의 진동해석)

  • Kim, Sung-Kyun;Yoo, Hong-Hee
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.27 no.8
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    • pp.1331-1337
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    • 2003
  • Linearized equations of motion for the vibration analysis of rotating cantilever plates with arbitrary orientation angle are derived in the present work. Two in-plane stretch variables are introduced to be approximated. The use of the two in-plane stretch variables enables one to derive the equations of motion which include proper motion-induced stiffness variation terms. The equations of motion are transformed into dimensionless forms in which dimensionless parameters are identified. The effects of the dimensionless parameters on the modal characteristics of rotating cantilever plates are investigated through numerical study. The natural frequency loci veering along with the associated mode shape variations, which occur while the rotating speed increases, are also presented and discussed.

Bending Vibration of a Pretwisted Rotating Cantilever Beam (초기 비틀림각을 갖는 회전 외팔보의 굽힘 진동)

  • Park, Jung-Hun;Yoo, Hong-Hee
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.20 no.7
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    • pp.2174-2181
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    • 1996
  • Equations of chordwise and flapwise bending motions of pretwisted rotatin cantilever beams are derived. The two motions are coupled to each other due to the pretwist angle of the beam cross section. As the angular speed, hub radius ratio, and pretwist angle vary, the vibration characteristics of the beam change. It is found that engenvalue loci veering phenomena and associated mode shape variations occur between two vibration modes due to the pretwist angle. The effect of the pretwist angle on the critical angular speed is also investigated.

Stiffener Modeling for Rectangular Plates Employing the Dirac's Delta Function and Modal Analysis (충격함수를 이용한 사각평판 보강재의 모델링 및 진동 해석)

  • Hur, Sung-Chul;Yoo, Hong-Hee
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.27 no.5
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    • pp.833-839
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    • 2003
  • The effects of stiffeners on the modal characteristics of rectangular plates are investigated. A modeling method for the modal analysis of rectangular plates with stiffeners is presented. A mass density Dirac's delta function is used to idealize the stiffeners mathematically. The equations of motion for the plates are derived and transformed into a dimensionless form. To confirm the accuracy of the method presented in this study, numerical result are obtained and compared to those of a commercial program. The mode shape variations due to some parameter variations are also exhibited.

Vibration Analysis of Rotating Composite Cantilever Plates

  • Kim, Sung-Kyun;Yoo, Hong-Hee
    • Journal of Mechanical Science and Technology
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    • v.16 no.3
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    • pp.320-326
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    • 2002
  • A modeling method for the vibration analysis of rotating composite cantilever plates is presented in this paper. The coupling effects between inplane motions and the bending motion are considered and explicit mass and stiffness matrices are derived for the modal analysis. Numerical results are obtained and some of them are compared to those of a commercial program to confirm the accuracy of the present method. Numerical results show that the coupling effects become important only when laminates are stacked up unsymmetrically. Incidentally, natural frequencies loci veering, loci crossing, and associated mode shape variations are observed.

Dynamic Modeling and Vibration Analysis of Rotating Plate Structures with Stiffeners (보강재를 갖는 회전 평판 구조물의 동역학적 모델링 및 진동해석)

  • 허성철;유홍희
    • Journal of KSNVE
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    • v.10 no.2
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    • pp.312-318
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    • 2000
  • A modeling method for the vibration analysis of rotating cantilever plastes with stiffeners is presented. The equations of motion for the plates aer derived and trnasformed into a dimensionless form. A mass density Dirac's delta function is used to idealize the stiffener mathematically. The effects of stiffeners on the model characteristics of the plate are investigated, and mode shape variations due to some parameter variation are exhibited. It is found that veering phenomena occur between some loci and associated mode shapes change significantly during the veering phenomena.

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Heat and Mass Transfer Enhancement of a pendant droplet on heated horizontal surface by acoustic resonance (가열된 평판위에 매달려 있는 액적의 음향공진에 의한 열 및 물질 전달 촉진에 관한 연구)

  • Moon, Jong-Hoon
    • Proceedings of the SAREK Conference
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    • 2005.11a
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    • pp.335-340
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    • 2005
  • Nonlinear and forced oscillations of supported viscous droplet were focused in the present study. The droplet has a free contact line with solid plate and inviscid fluid. Natural frequencies of a pendant droplet have been investigated experimentally by imposing the acoustic wave while the frequency is being increased at a fixed amplitude. The evaporation was observed at atmosphere pressure. The droplet was recorded throughout the entire evaporation process and transient variations of the volume was measured. The evaporation process of oscillating droplet with thermofoil has been also observed to investigate analyzing the resonance effect on the thermal characteristics of droplet. It is found that a pendant droplet shows the resonant behaviors at each mode similar to the theoretical analysis. During imposing the acoustic wave, the pendant droplet makes a rotating motion in its longitudinal axis which is a new shape oscillation mode. The evaporation rate of a pendant droplet at resonant frequency is significantly enhanced.

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Using frequency response function and wave propagation for locating damage in plates

  • Quek, Ser-Tong;Tua, Puat-Siong
    • Smart Structures and Systems
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    • v.4 no.3
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    • pp.343-365
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    • 2008
  • In this study, the frequency domain method which utilizes the evaluation of changes in the structural mode shape is adopted to identify regions which contain localized damages. Frequency response function (FRF) values corresponding to the modal frequency, analogous to the mode shape coefficients, are used since change in natural frequency of the system is usually insignificant for localized damage. This method requires only few sensors to obtain the dynamic response of the structure at specific locations to determine the FRF via fast-Fourier transform (FFT). Numerical examples of an aluminum plate, which includes damages of varying severity, locations and combinations of multiple locations, are presented to demonstrate the feasibility of the method. An experimental verification of the method is also done using an aluminum plate with two different degrees of damage, namely a half-through notch and a through notch. The inconsistency in attaining the FRF values for practical applications due to varying impact load may be overcome via statistical averaging, although large variations in the loading in terms of the contact duration should still be avoided. Nonetheless, this method needs special attention when the damages induce notable changes in the modal frequency, such as when the damages are of high severity or cover more extensive area or near the boundary where the support condition is modified. This is largely due to the significant decrease in the frequency term compared to the increase in the vibration amplitude. For practical reasons such as the use of limited number of sensors and to facilitate automation, extending the resolution of this method of identification may not be efficient. Hence, methods based on wave propagation can be employed as a complement on the isolated region to provide an accurate localization as well as to trace the geometry of the damage.