• Title/Summary/Keyword: forced vibration system

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Evaluation on the Effect of Whole Body Vibration on EEG Frequency-Fluctuation (인체진동이 뇌파변동리듬에 미치는 영향평가)

  • Min, Byung-Chan;Kim, Hyoung-Wook;Kim, Ji-Kwan
    • Journal of Korean Society of Industrial and Systems Engineering
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    • v.30 no.4
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    • pp.71-77
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    • 2007
  • In this study, reactions of central nervous systems working against different conditions of forced frequency and acceleration were measured and analyzed. The experiment are conducted with health men. The steady vibration conditions of forced frequency (0.315m/s2-1.0Hz, 0.315m/s2-10Hz and 10Hz-1.0m/s2) are used and the waves of EEG (Electroencephalogram) are measured. As a result, this paper shows that the ${\alpha}-wave$ of frontal lobe transfers from low to high frequency band under the vibration environment. Additionally, the average frequency of ${\alpha}-wave$ is higher under the vibration than under non-vibration environment. In the case of forced frequency of 1.0Hz-0.315m/s2, the feeling with the vibration are nearly same compared with the non-vibration condition. But in the case of 10Hz-1.0m/s2, uncomfortable feeling increased compared with the non-vibration condition. This study also shows the relationship between fluctuation slop and feeling. From this study, it is found that the effect of vibration on human depends on acceleration characteristics. Highly accelerating vibration is more harmful to human.

A Forced Vibration Analysis of Soil-Pile Interaction System (지반-말뚝 상호작용계의 강제진동해석)

  • 김민규
    • Proceedings of the Earthquake Engineering Society of Korea Conference
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    • 2001.04a
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    • pp.136-143
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    • 2001
  • In this study, a numerical analysis for soil-pile interaction systems in multi-layered half planes under a forced vibration is presented. The soil-pile interaction system is divided into two parts, so called near field and far field. The near field soil using finite elements and piles using beam elements are modeled. The far field soil media is implemented using boundary elements those can automatically satisfy the condition of wave radiation. These two fields are numerically coupled by imposing displacement compatibility condition at the interface between the near field and the far field. For the verification, the forced vibration test was simulated and the response under horizontal and vertical harmonic loads at the pile cap in the layered half plane was determined. The results are compared to the theoretical and experimental results of the literatures to verify the proposed soil-pile interaction analysis formulation.

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A 3-DOF forced vibration system for time-domain aeroelastic parameter identification

  • Sauder, Heather Scot;Sarkar, Partha P.
    • Wind and Structures
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    • v.24 no.5
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    • pp.481-500
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    • 2017
  • A novel three-degree-of-freedom (DOF) forced vibration system has been developed for identification of aeroelastic (self-excited) load parameters used in time-domain response analysis of wind-excited flexible structures. This system is capable of forcing sinusoidal motions on a section model of a structure that is used in wind tunnel aeroelastic studies along all three degrees of freedom - along-wind, cross-wind, and torsional - simultaneously or in any combination thereof. It utilizes three linear actuators to force vibrations at a consistent frequency but varying amplitudes between the three. This system was designed to identify all the parameters, namely, aeroelastic- damping and stiffness that appear in self-excited (motion-dependent) load formulation either in time-domain (rational functions) or frequency-domain (flutter derivatives). Relatively large displacements (at low frequencies) can be generated by the system, if required. Results from three experiments, airfoil, streamlined bridge deck and a bluff-shaped bridge deck, are presented to demonstrate the functionality and robustness of the system and its applicability to multiple cross-section types. The system will allow routine identification of aeroelastic parameters through wind tunnel tests that can be used to predict response of flexible structures in extreme and transient wind conditions.

Forced Vibration Testing of Full-scale Non-seismic Reinforced Concrete Frame Structure Retrofitted Using FRP Jacketing System (FRP자켓 시스템이 보강된 비내진 철근콘크리트 골조의 실물 크기 강제 진동 실험)

  • Shin, Jiuk
    • Journal of the Earthquake Engineering Society of Korea
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    • v.22 no.5
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    • pp.281-289
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    • 2018
  • Existing reinforced concrete building structures have seismic vulnerabilities due to their seismically-deficient details resulting in non-ductile behavior. The seismic vulnerabilities can be mitigated by retrofitting the buildings using a fiber-reinforced polymer column jacketing system, which can provide additional confining pressures to existing columns to improve their lateral resisting capacities. This study presents dynamic responses of a full-scale non-ductile reinforced concrete frame retrofitted using a fiber-reinforced polymer column jacketing system. A series of forced-vibration testing was performed to measure the dynamic responses (e.g. natural frequencies, story drifts and column/beam rotations). Additionally, the dynamic responses of the retrofitted frame were compared to those of the non-retrofitted frame to investigate effectiveness of the retrofit system. The experimental results demonstrate that the retrofit system installed on the first story columns contributed to reducing story drifts and column rotations. Additionally, the retrofit scheme helped mitigate damage concentration on the first story columns as compared to the non-retrofitted frame.

Vibration Analysis of Frame Structural Systems by the Receptance Method

  • Han, S.Y.;Kim, K.C.
    • Selected Papers of The Society of Naval Architects of Korea
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    • v.1 no.1
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    • pp.52-64
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    • 1993
  • There exist many frame structural systems having some attachments reducible to damped spring-mass systems, concentracted masses and spring supports. For free and forced vibration analyses of such a system an analytical method based on the receptance method is presented. A framed structure having attachments is considered as a combined system composed of various Timoshenko beam and bar elements and the attachments. So, the vibration characteristics of the system are calculated by synthesizing receptances and Support Displacement Transfer Ratio (SDTR) of beam and bar elements In spectral and/or closed forms, and receptances of the attachments. In forced vibration analysis, arbitrary excitation forces at a point on the structure and displacement excitations at boundaries are considered. Numerical investigations are carried out for verification of the presented method, and the results show good accuracy and very high computational efficiency.

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Longitudinal vibration of double nanorod systems using doublet mechanics theory

  • Aydogdu, Metin;Gul, Ufuk
    • Structural Engineering and Mechanics
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    • v.73 no.1
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    • pp.37-52
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    • 2020
  • This paper investigates the free and forced longitudinal vibration of a double nanorod system using doublet mechanics theory. The doublet mechanics theory is a multiscale theory spanning between lattice dynamics and continuum mechanics. Equations of motion and boundary conditions for the double nanorod system are obtained using Hamilton's principle. Clamped-clamped and clamped-free boundary conditions are considered. Frequencies and dynamic displacements are determined to demonstrate the effects of length scale parameter of considered material and geometry of the nanorods. It is shown that frequencies obtained by the doublet mechanics theory are bounded from above (van Hove singularity) and unlike classical elasticity theory doublet mechanics theory predicts finite number of modes depending on the length of the nanotube. The present doublet mechanics results have been compared to molecular dynamics, experimental and nonlocal theory results and good agreement is observed between the present and other mentioned results. The difference between wave frequencies of graphite is less than 10% between doublet mechanics and experimental results near to the end of the first Brillouin zone.

Size-dependent forced vibration response of embedded micro cylindrical shells reinforced with agglomerated CNTs using strain gradient theory

  • Tohidi, H.;Hosseini-Hashemi, S.H.;Maghsoudpour, A.
    • Smart Structures and Systems
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    • v.22 no.5
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    • pp.527-546
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    • 2018
  • This article presents an analysis into the nonlinear forced vibration of a micro cylindrical shell reinforced by carbon nanotubes (CNTs) with considering agglomeration effects. The structure is subjected to magnetic field and transverse harmonic mechanical load. Mindlin theory is employed to model the structure and the strain gradient theory (SGT) is also used to capture the size effect. Mori-Tanaka approach is used to estimate the equivalent material properties of the nanocomposite cylindrical shell and consider the CNTs agglomeration effect. The motion equations are derived using Hamilton's principle and the differential quadrature method (DQM) is employed to solve them for obtaining nonlinear frequency response of the cylindrical shells. The effect of different parameters including magnetic field, CNTs volume percent and agglomeration effect, boundary conditions, size effect and length to thickness ratio on the nonlinear forced vibrational characteristic of the of the system is studied. Numerical results indicate that by enhancing the CNTs volume percent, the amplitude of system decreases while considering the CNTs agglomeration effect has an inverse effect.

On Development of Vibration Analysis Algorithm of Beam with Multi - Joints(II) (다관절 보의 진동해석 알고리즘 개발에 관한 연구 (II))

  • 문덕홍;최명수;홍숭수;강현석
    • Journal of Advanced Marine Engineering and Technology
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    • v.21 no.3
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    • pp.256-266
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    • 1997
  • The authors apply the transfer influence coefficient method to the 3. dimensional vibration analysis of beam with multi - joints and formulate a general algorithm to analyse the longitudinal, flexural and torsional coupled forced vibration. In this paper, a structure which is mainly found in the robot arms, cranes and so on, has some crooked parts, subsystems and joints, but has no closed loop in this system. It is modeled as the beam of a distributed mass system with massless translational, rotational and torsional springs in each node, and joint elements of release or roll at node which the displacement vector is discontinuous. The superiority of the present method to the transfer matrix method in the computation accuracy was confirmed from the numerical computation results. Moreover, we confirmed that boundary and intermediate conditions could be controlled by varying the values of the spring constants.

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Nonlinear Forced Torsional Vibration for the Engine Shafting System With Viscous Damper (점성댐퍼를 갖는 엔진 축계의 비선형 비틀림강제진동)

  • 박용남;송성옥;김의간;전효중
    • Journal of Advanced Marine Engineering and Technology
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    • v.20 no.4
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    • pp.50-58
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    • 1996
  • The torsional vibration of the propulsion shafting system equipped with viscous damper is investigated. The equivalent system is modeled by a two mass softening system with Duffing's oscillator and the vibratory motion is described by non-linear differential equations of second order. The damper casing is fixed at the front-end of crankshaft and the damper's inertia ring floats in viscous silicon fluid inside of the camper casing. The excitation frenquency is proportional to the rotational speed of engine. The steady state response of the equivalent system is analyzed by the computer and for this analyzing, the harmonic balance method is adopted as a non-linear vibration analysis technique. Frequency response curves are obtained for 1st order resonance only. Jump phenomena are explained. The discriminant for the solutions of the steady state response is derived. Both theoretical and measured results of the propulsion shafting system are compared with and evaluated. As a result of comparisions with both data, it was confirmed that Duffing's oscillator can be used in the modeling of the propulsion shafting system attached with viscous damper with non-linear stiffness.

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Nonlinear Forced Torsional Vibration for the Engine Shafting System With Viscous Damper (점성댐퍼를 갖는 엔진 축계의 비선형 비틀림강제진동)

  • Park, Y.N;Song, S.O;Kim, U.K;Jeon, H.J
    • Journal of Advanced Marine Engineering and Technology
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    • v.20 no.4
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    • pp.372-372
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    • 1996
  • The torsional vibration of the propulsion shafting system equipped with viscous damper is investigated. The equivalent system is modeled by a two mass softening system with Duffing's oscillator and the vibratory motion is described by non-linear differential equations of second order. The damper casing is fixed at the front-end of crankshaft and the damper's inertia ring floats in viscous silicon fluid inside of the camper casing. The excitation frenquency is proportional to the rotational speed of engine. The steady state response of the equivalent system is analyzed by the computer and for this analyzing, the harmonic balance method is adopted as a non-linear vibration analysis technique. Frequency response curves are obtained for 1st order resonance only. Jump phenomena are explained. The discriminant for the solutions of the steady state response is derived. Both theoretical and measured results of the propulsion shafting system are compared with and evaluated. As a result of comparisions with both data, it was confirmed that Duffing's oscillator can be used in the modeling of the propulsion shafting system attached with viscous damper with non-linear stiffness.