• Title/Summary/Keyword: Vibration problem

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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.

Free vibration of symmetric angle-ply layered conical shell frusta of variable thickness under shear deformation theory

  • Viswanathan, K.K.;Javed, Saira;Aziz, Zainal Abdul
    • Structural Engineering and Mechanics
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    • v.45 no.2
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    • pp.259-275
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    • 2013
  • Free vibration of symmetric angle-ply layered conical shell frusta of variable thickness is analyzed under shear deformation theory with different boundary conditions by applying collocation with spline approximation. Linear and exponential variation in thickness of layers are assumed in axial direction. Displacements and rotational functions are approximated by Bickley-type splines of order three and obtained a generalized eigenvalue problem. This problem is solved numerically for an eigenfrequency parameter and an associated eigenvector of spline coefficients. The vibration of three and five-layered conical shells, made up of two different type of materials are considered. Parametric studies are made for analysing the frequencies of the shell with respect to the coefficients of thickness variations, length-to-radius ratio, length-to-thickness ratio and ply angles with different combination of the materials. The results are compared with the available data and new results are presented in terms of tables and graphs.

Trouble Shooting of Environment Noise Problem for Apartment and Residence Place adjacent to Underground Machinery Room (지하기계실에서 발생한 아파트 및 인접거주지역의 소음 발생 원인 분석 및 해결 사례)

  • 김현식;손성완;김한준
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2001.11b
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    • pp.903-909
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    • 2001
  • Apartment and large residence buildings are necessary to ensure a comfortable noise/vibration environment. So. it must be performed a anti-vibration/noise evaluation at early design stage, such as utility room arrangement, machinery installation method and so on. In this paper. environment noise status on problem areas, which was issued by resident. was investigated to understand the noise transmission property generated from underground machinery room and to device a optimized countermeasure in order to enhance noise environment. Also, the measured noise levels before and after modification works are compared to confirm the effectiveness of proposed countermeasure.

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Nonlinear buckling and free vibration of curved CNTs by doublet mechanics

  • Eltaher, Mohamed A.;Mohamed, Nazira;Mohamed, Salwa A.
    • Smart Structures and Systems
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    • v.26 no.2
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    • pp.213-226
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    • 2020
  • In this manuscript, static and dynamic behaviors of geometrically imperfect carbon nanotubes (CNTs) subject to different types of end conditions are investigated. The Doublet Mechanics (DM) theory, which is length scale dependent theory, is used in the analysis. The Euler-Bernoulli kinematic and nonlinear mid-plane stretching effect are considered through analysis. The governing equation of imperfect CNTs is a sixth order nonlinear integro-partial-differential equation. The buckling problem is discretized via the differential-integral-quadrature method (DIQM) and then it is solved using Newton's method. The equation of linear vibration problem is discretized using DIQM and then solved as a linear eigenvalue problem to get natural frequencies and corresponding mode shapes. The DIQM results are compared with analytical ones available in the literature and excellent agreement is obtained. The numerical results are depicted to illustrate the influence of length scale parameter, imperfection amplitude and shear foundation constant on critical buckling load, post-buckling configuration and linear vibration behavior. The current model is effective in designing of NEMS, nano-sensor and nano-actuator manufactured by CNTs.

Exact solutions of vibration and postbuckling response of curved beam rested on nonlinear viscoelastic foundations

  • Nazira Mohamed;Salwa A. Mohamed;Mohamed A. Eltaher
    • Advances in aircraft and spacecraft science
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    • v.11 no.1
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    • pp.55-81
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    • 2024
  • This paper presents the exact solutions and closed forms for of nonlinear stability and vibration behaviors of straight and curved beams with nonlinear viscoelastic boundary conditions, for the first time. The mathematical formulations of the beam are expressed based on Euler-Bernoulli beam theory with the von Karman nonlinearity to include the mid-plane stretching. The classical boundary conditions are replaced by nonlinear viscoelastic boundary conditions on both sides, that are presented by three elements (i.e., linear spring, nonlinear spring, and nonlinear damper). The nonlinear integro-differential equation of buckling problem subjected to nonlinear nonhomogeneous boundary conditions is derived and exactly solved to compute nonlinear static response and critical buckling load. The vibration problem is converted to nonlinear eigenvalue problem and solved analytically to calculate the natural frequencies and to predict the corresponding mode shapes. Parametric studies are carried out to depict the effects of nonlinear boundary conditions and amplitude of initial curvature on nonlinear static response and vibration behaviors of curved beam. Numerical results show that the nonlinear boundary conditions have significant effects on the critical buckling load, nonlinear buckling response and natural frequencies of the curved beam. The proposed model can be exploited in analysis of macrosystem (airfoil, flappers and wings) and microsystem (MEMS, nanosensor and nanoactuators).

Comparison of Assessment method of Blast Vibration (발파 진동 평가의 문제점과 개전방안)

  • Chang, Seo-Il;Lee, Jae-Won;Kim, Hyung-Kon
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2002.11b
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    • pp.553-558
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    • 2002
  • The blast vibration can generate occupants dissatisfy as well as damage of physics nearby building. Then blast vibration estimation issue important problems. But, now blast vibration prediction inside-outside country not established objective method to express magnitude of vibration according to blast number. In this study, Our propose show our country problem of blast vibration about blast vibration measurement and this problems be able to find improve method.

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Studies on Coupled Vibration of Diesel Engine Propulsion Shafting (디젤기관 추진축계의 연성진동에 관한 연구 (제1보:연성이 고유진동수와 그의 모드에 미치는 영향))

  • 김의간
    • Proceedings of the Korean Society of Marine Engineers Conference
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    • 2000.05a
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    • pp.60-71
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    • 2000
  • When the crankshaft of Diesel engine has more than 3 throws which are arranged in a different plane its vibration induces coupled motions especially the coupled torsional and axial vibration. Nowadays the torsional vibration which is influenced rather weak than axial one can be theoretically calculated fairly accurately but theoretical calculation results of the axial vibration which is influenced strongly from torsional vibration is not so good. To get accurate calculation results of axial vibration coupled axial-torsional vibration must be treated. in this investigation coupled effects of vibration of Diesel engine propulsion shafting are analyzed theoretically and some more simple calculation methods are also studied. On this first report effects of coupling on natural frequencies and their modes are mainly studied setting the each mass in 4 degrees of freedom. later this problem may be studied again by setting each mass as 6 degrees of freedom.

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A Study on the Calculation of Vibration Transfer Formula for Ground Vibration (지반의 진동전달식 산정에 관한 연구)

  • 홍갑표;전호민
    • Journal of KSNVE
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    • v.8 no.5
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    • pp.799-806
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    • 1998
  • Noise and vibration due to railway traffic are major causes of environmental pollution in the city. In course of judging, assessing and coping with the problem, it becomes imperative to predict the vibration level induced by railway traffic passing through downtown in the city. The vibration due to railway traffic is transferred to the neighbouring buildings through the ground. In this study, as a method predicting vibration level of the buildings near railway, a vibration transfer formula is suggested. This formula is used to calculate vibration level occuring at the bottom of the neighbouring buildings, which are located at a certain distance from railway.

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Performance Test of Isolator for Reaction Wheel Micro-Vibration (인공위성 반작용휠 미소진동 감쇠기의 성능 측정)

  • Oh, Shi-Hwan;Seo, Hyun-Ho;Yim, Jo-Ryeong;Rhee, Seung-Wu
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2006.05a
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    • pp.376-379
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    • 2006
  • Reaction Wheel Assembly (RWA) is one of the major disturbance sources that have influence upon the Line of Sight (LOS) of payload. A micro-vibration induced by RWA is propagated through the satellite structure and decrease the LOS stability performance of payload. This effect shall be analyzed through the jitter analysis. If a requirement or specification of payload jitter level is found to be not satisfied according to the jitter analysis campaign, some modification or redesign should be done on the satellite structure or a couple of isolator should be attached on the RWA interface in order to reduce the transmitted vibration level of RWA. The purpose of ???RWA isolator test? is to roughly evaluate the performance of vibration suppression level with a passive RWA isolator made of rubber. For this test, actual RWA is used as a vibration source and a couple of cube-shaped rubber mount designed for satellite is used as a passive isolator. There may be several considerations in order to accommodate RWA isolator to spacecraft such as not only vibration reduction performance but also thermal conduction problem, mechanical size, RWA alignment problem, etc. But in this report the feasibility of RWA isolator is analyzed only in a vibration suppression point of view. As a result, high frequency vibration of RWA above 50Hz is perfectly attenuated with isolators, however, first harmonic components below 50Hz became larger due to the additional low frequency resonance modes of roll, pitch, yaw rigid body motion of RWA+bracket.

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Nonlinear vibration of unsymmetrical laminated composite beam on elastic foundation

  • Pakar, I.;Bayat, M.;Cveticanin, L.
    • Steel and Composite Structures
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    • v.26 no.4
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    • pp.453-461
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    • 2018
  • In this paper, nonlinear vibrations of the unsymmetrical laminated composite beam (LCB) on a nonlinear elastic foundation are studied. The governing equation of the problem is derived by using Galerkin method. Two different end conditions are considered: the simple-simple and the clamped-clamped one. The Hamiltonian Approach (HA) method is adopted and applied for solving of the equation of motion. The advantage of the suggested method is that it does not need any linearization of the problem and the obtained approximate solution has a high accuracy. The method is used for frequency calculation. The frequency of the nonlinear system is compared with the frequency of the linear system. The influence of the parameters of the foundation nonlinearity on the frequency of vibration is considered. The differential equation of vibration is solved also numerically. The analytical and numerical results are compared and is concluded that the difference is negligible. In the paper the new method for error estimation of the analytical solution in comparison to the exact one is developed. The method is based on comparison of the calculation energy and the exact energy of the system. For certain numerical data the accuracy of the approximate frequency of vibration is determined by applying of the suggested method of error estimation. Finally, it has been indicated that the proposed Hamiltonian Approach gives enough accurate result.