• Title/Summary/Keyword: Forced vibration analysis

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Ambient and forced vibration testing with numerical identification for RC buildings

  • Aras, Fuat
    • Earthquakes and Structures
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    • v.11 no.5
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    • pp.809-822
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    • 2016
  • Reinforced concrete buildings constitute the majority of the building stock of Turkey and much of them, do not comply the earthquake codes. Recently there is a great tendency for strengthening to heal their earthquake performance. The performance evaluations are usually executed by the numerical investigations performed in computer packages. However, the numerical models are often far from representing the real behaviour of the existing buildings. In this condition, experimental modal analysis fills a gap to correct the numerical models to be used in further analysis. On the other hand, there have been a few dynamic tests performed on the existing reinforced concrete buildings. Especially forced vibration survey is not preferred due to the inherent difficulties, high cost and probable risk of damage. This study applies both ambient and forced vibration surveys to investigate the dynamic properties of a six-story residential building in Istanbul. Mode shapes, modal frequencies and damping ration were determined. Later on numerical analysis with finite element method was performed. Based on the first three modes of the building, a model updating strategy was employed. The study enabled to compare the results of ambient and forced vibration surveys and check the accuracy of the numerical models used for the performance evaluation of the reinforced concrete buildings.

Forced Vibration Analysis of Pipe Conveying Harmonically Excited Fluid (조화 맥동 유체를 포함하는 직관의 강제진동응답 해석)

  • 오준석;정의봉;서영수
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2003.11a
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    • pp.277-283
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    • 2003
  • It is well known that the natural frequencies of the pipe come to be lower as internal fluid velocity and pressure increase, and the pipe will be unstable if the fluid velocity is higher than critical velocity. But even if the velocity of the fluid below the critical velocity, resonance will be caused by pulsation of the fluid. So it should be also taken into consideration that the effect of pulsating fluid in pipe design. The research of the piping system vibration due to a fluid pulsation has been studied by many people. But almost is dealt with determining the boundary between stable and unstable region without analyzing forced response in the stable region. In this study, not only stability analysis but also forced response analysis, which is caused by harmonically excited fluid especially, is conducted.

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Modal analysis of viscoelastic nanorods under an axially harmonic load

  • Akbas, Seref D.
    • Advances in nano research
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    • v.8 no.4
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    • pp.277-282
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    • 2020
  • Axially damped forced vibration responses of viscoelastic nanorods are investigated within the frame of the modal analysis. The nonlocal elasticity theory is used in the constitutive relation of the nanorod with the Kelvin-Voigt viscoelastic model. In the forced vibration problem, a cantilever nanorod subjected to a harmonic load at the free end of the nanorod is considered in the numerical examples. By using the modal technique, the modal expressions of the viscoelastic nanorods are presented and solved exactly in the nonlocal elasticity theory. In the numerical results, the effects of the nonlocal parameter, damping coefficient, geometry and dynamic load parameters on the dynamic responses of the viscoelastic nanobem are presented and discussed. In addition, the difference between the nonlocal theory and classical theory is investigated for the damped forced vibration problem.

Analysis of local vibrations in the stay cables of an existing cable-stayed bridge under wind gusts

  • Wu, Qingxiong;Takahashi, Kazuo;Chen, Baochun
    • Structural Engineering and Mechanics
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    • v.30 no.5
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    • pp.513-534
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    • 2008
  • This paper examines local vibrations in the stay cables of a cable-stayed bridge subjected to wind gusts. The wind loads, including the self-excited load and the buffeting load, are converted into time-domain values using the rational function approximation and the multidimensional autoregressive process, respectively. The global motion of the girder, which is generated by the wind gusts, is analyzed using the modal analysis method. The local vibration of stay cables is calculated using a model in which an inclined cable is subjected to time-varying displacement at one support under global vibration. This model can consider both forced vibration and parametric vibration. The response characteristics of the local vibrations in the stay cables under wind gusts are described using an existing cable-stayed bridge. The results of the numerical analysis show a significant difference between the combined parametric and forced vibrations and the forced vibration.

Investigation on Forced Vibration Behavior of WIG Craft Main Wing Structure Excited by Propulsion System

  • Kong, Chang-Duk;Yoon, Jae-Huy;Park, Hyun-Bum
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2008.03a
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    • pp.810-812
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    • 2008
  • Previously study on structural design of the main wing of the twenty-seat class WIG(Wing in Ground Effect) craft. In the final design, three spars construction was selected for safety in the critical flight load, and the Carbon-Epoxy material was selected for lightness and structural stability. In this study, the forced vibration analysis was performed on the composite main wing structure of the twenty-seat class WIG craft with two-stroke pusher type reciprocating engine. The vibration analysis based on the finite element method was performed using a commercial FEM code, MSC/NASTRAN. Excitations for the frequency response analysis were assumed as the H-mode(horizontal mode), the V-mode(vertical mode) and the X-mode(twisted mode) which are typical main vibration modes of engine. And excitations for the transient response analysis were assumed as the L-mode(longitudinal mode) with the oscillating propeller thrust which occurs in operation. According to the result of forced vibration analysis, structural design was modified to reduce the vibrations.

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Vibration Analysis of the End-winding of Large Generator for Fossil Power Plant under Electromagnetic Excitation (대형 화력 발전용 발전기 권선단부의 전자기력에 의한 진동 해석)

  • 김철홍;주영호
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2003.11a
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    • pp.350-355
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    • 2003
  • This paper presents results of vibration analysis of a end-winding of large generator for fossil power plant. A finite element analysis using a commercial S/W is performed to calculate alternating electromagnetic forces, mainly of 120㎐ in 60㎐ machines, acting on the end-winding, and then to calculate forced response of the end-winding under electromagnetic forces. Also, this paper presents analytical and experimental modal analysis results of generator end-winding to validate FE model. We calculated forced response of end-winding on 120㎐, double rotating frequency. These results will be used to evaluate structural reliability of end-winding and applied to update model.

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Forced Vibration Analysis of Elastically Restrained Valve-pipe System (탄성지지된 밸브 배관계의 강제진동 특성)

  • Son, In-Soo;Yoon, Han-Ki;Min, Byoung-Hyun;Hur, Kwan-Do
    • Journal of the Korean Society of Manufacturing Process Engineers
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    • v.11 no.4
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    • pp.90-96
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    • 2012
  • The forced vibration response characteristics of a elastically restrained pipe conveying fluid with attached mass are investigated in this paper. Based on the Euler-Bernoulli beam theory, the equation of motion is derived by using Hamilton's principle. The effects of attached mass and spring constant on the forced vibration characteristics of pipe at conveying fluid are studied. The forced deflection response of pipe with attached mass due to the variation of fluid velocity is also presented. The deflection response is the mid-span deflection of the pipe. The dimensionless forcing frequency is the range from 0 to 16 which is the first natural frequency of the pipe.

Vibration Analysis of a Generator-Stator Core Under Electromagnetic Excitation (전자기력에 의한 발전기 고정자 코어의 진동 해석)

  • 김철홍;주영호;박종포
    • Journal of KSNVE
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    • v.9 no.4
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    • pp.747-753
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    • 1999
  • This paper presents results of vibration analysis of a generator-stator core for 500 MW fossil power plant. A finite element analysis using a commercial S/W is performed to estimate alternating electromagnetic forces, mainly of 120 Hz in 60 Hz machines, acting on the core, and then to calculate forced response of the core. Results are compared with design requirements.

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Forced Vibration of Car Seat and mannequin System (자동차 시트 및 마네킹 시스템의 강제 진동)

  • Kim, Seong-Geol
    • Journal of the Korean Society for Precision Engineering
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    • v.17 no.9
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    • pp.122-132
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    • 2000
  • A simplified modeling approach of forced vibration for occupied car seats was demonstrated by using a mathematical model presented in 'Free Vibration of Car seat and Mannequin System' nonlinear and linear equations of motions were rederived for forced vibration and the transfer function was used to calculate the frequency response function. The experimental apparatus were set up and hydraulic shaker was used to obtain the system responses. Through the tests mannequin's head had a lot of problems and the responses with a head and without a head were measured. To explore the effects of linear dampings and friction moments at the joints linear analyses were performed. New sets of linear spring and damping coefficients and torsional dampings at the joints were calculated through parameter study to match up with experimental results. Good agreement between experimental and simulation frequency response estimates were obtained both in terms of locations of resonances and system deflection shapes at resonance indicating that this is a feasible method of modeling seated occupants.

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Nonlinear analysis of stepped beam with immovable ends for free and forced vibration (양단고정된 변단면보의 자유 및 강제진동의 비선형해석)

  • 심재수;함원식
    • Proceedings of the Computational Structural Engineering Institute Conference
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    • 1990.04a
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    • pp.12-17
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    • 1990
  • Stepped bean with immovable ends for large amplitude of vibration including effects of longitudinal displacement, shear deformation and rotary inertia is investigated for free and forced vibration using finite element method. Modified harmonic force matrix is introduced for analysis of vibration with finite amplitude of the stepped beam under uniform hamonic loading and beam with nonuniform harmonic loading. Numerical examples of stepped beam with various support conditions are analysed for deflections and natural frequencies. Results show that the proposed method is valid and efficient.

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