• Title/Summary/Keyword: Frequency Ratio Model

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Free vibration analysis of chiral double-walled carbon nanotube embedded in an elastic medium using non-local elasticity theory and Euler Bernoulli beam model

  • Dihaj, Ahmed;Zidour, Mohamed;Meradjah, Mustapha;Rakrak, Kaddour;Heireche, Houari;Chemi, Awda
    • Structural Engineering and Mechanics
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    • v.65 no.3
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    • pp.335-342
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    • 2018
  • The transverse free vibration of chiral double-walled carbon nanotube (DWCNTs) embedded in elastic medium is modeled by the non-local elasticity theory and Euler Bernoulli beam model. The governing equations are derived and the solutions of frequency are obtained. According to this study, the vibrational mode number, the small-scale coefficient, the Winkler parameter and chirality of double-walled carbon nanotube on the frequency ratio (xN) of the (DWCNTs) are studied and discussed. The new features of the vibration behavior of (DWCNTs) embedded in an elastic medium and the present solutions can be used for the static and dynamic analyses of double-walled carbon nanotubes.

Experimental study on characteristics of two-phase flow through a bypass-orifice expansion device (바이패스 오리피스 팽창장치의 유동 특성에 관한 실험적 연구)

  • Choi, J.M.;Kim, Y.C.
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.11 no.1
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    • pp.109-116
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    • 1999
  • To establish optimum cycle of the inverter-driven heat pump with a variation of frequency, the bypass orifice, which is a short tube having a bypass hole in the middle, was designed and tested. Flow characteristics of the bypass orifice were measured as a function of orifice geometry and operating conditions. Flow trends with respect to frequency were compared with those of short tube orifices and capillary tubes. Generally, the bypass orifice showed the best flow trends among them, that will enhance the seasonal energy efficiency ratio of an inverter heat pump system. Based on experimental data, the semi-empirical flow model was developed to predict mass flow rate through bypass orifices. The maximum difference between measured data and model's prediction was within ${\pm}5%$.

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Analytical analysis for the forced vibration of CNT surrounding elastic medium including thermal effect using nonlocal Euler-Bernoulli theory

  • Bensattalah, Tayeb;Zidour, Mohamed;Daouadji, Tahar Hassaine
    • Advances in materials Research
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    • v.7 no.3
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    • pp.163-174
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    • 2018
  • This article studies the free and forced vibrations of the carbon nanotubes CNTs embedded in an elastic medium including thermal and dynamic load effects based on nonlocal Euler-Bernoulli beam. A Winkler type elastic foundation is employed to model the interaction of carbon nanotube and the surrounding elastic medium. Influence of all parameters such as nonlocal small-scale effects, high temperature change, Winkler modulus parameter, vibration mode and aspect ratio of short carbon nanotubes on the vibration frequency are analyzed and discussed. The non-local Euler-Bernoulli beam model predicts lower resonance frequencies. The research work reveals the significance of the small-scale coefficient, the vibrational mode number, the elastic medium and the temperature change on the non-dimensional natural frequency.

The Influence of Interphase Condition and Fiber Content on the Dynamic Properties of Short-fiber Reinforced Rubber (계면상 조건과 단섬유 함유량이 강화고무의 동적 특성에 미치는 영향)

  • 류상렬;이동주
    • Composites Research
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    • v.13 no.3
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    • pp.30-37
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    • 2000
  • The dynamic properties of short-fiber reinforced Chloroprene rubber have been studied as functions of interphase conditions and fiber content. The loss factor generally decreased with fiber content and showed different patterns according to interphase conditions. The better interphase condition showed the lower loss modulus, $E_2$. Also, the dynamic ratio decreased with fiber content and rapidly decreased in the case of double coatings, i.e., model C. Therefore, the short-fiber reinforced rubber could have the better isolation in frequency ratio($\sqrt{2}$ min.) compared to frequency ratio($\sqrt{2}$ max.). And we have investigate the possibility of applying short-fiber reinforced rubber to automotive engine mount.

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Optimal Design of Air-spring and Active Control of Vibration Isolation Table (공기스프링의 최적설계 및 방진 테이블의 능동 제어)

  • An, Chae-Hun;Kim, Ho-Sung;Yim, Kwang-Hyeok;Jin, Kyong-Bok;Rim, Kyung-Hwa
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2006.11a
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    • pp.909-914
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    • 2006
  • Vibration isolation tables are mostly required in precise measurement and manufacturing system. Among the vibration isolation tables, an air spring is the most favorable equipment because of low resonant frequency and high damping ratio. However, it is difficult to design the air spring with the required stiffness and damping ratio. Futhermore, whenever conventional active control methods are applied to the air spring, it may be difficult to obtain effective control performance due to high nonlinearity of air spring. In this paper, the optimal design of the air spring is performed using genetic algorithm to bring out low resonant frequency and high damping ratio. Also, active control of the vibration isolation table with 3-DOF model is proposed using the adaptive control method. Through experiments, optimal design is shown to be effective. And performance of the proposed control method is verified to be better than those of the passive control method and the conventional active control methods.

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Optimization of multiple tuned mass dampers for large-span roof structures subjected to wind loads

  • Zhou, Xuanyi;Lin, Yongjian;Gu, Ming
    • Wind and Structures
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    • v.20 no.3
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    • pp.363-388
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    • 2015
  • For controlling the vibration of specific building structure with large span, a practical method for the design of MTMD was developed according to the characteristics of structures subjected to wind loads. Based on the model of analyzing wind-induced response of large-span structure with MTMD, the optimization method of multiple tuned mass dampers for large-span roof structures subjected to wind loads was established, in which the applicable requirements for strength and fatigue life of TMD spring were considered. According to the method, the controlled modes and placements of TMDs in MTMD were determined through the quantitative analysis on modal contribution to the wind-induced dynamic response of structure. To explore the characteristics of MTMD, the parametric analysis on the effects of mass ratio, damping ratio, central tuning frequency ratio and frequency range of MTMD, was performed in the study. Then the parameters of MTMD were optimized through genetic algorithm and the optimized MTMD showed good dynamic characteristics. The robustness of the optimized MTMD was also investigated.

Free vibration analysis of chiral double-walled carbon nanotube using non-local elasticity theory

  • Rakrak, Kaddour;Zidour, Mohamed;Heireche, Houari;Bousahla, Abdelmoumen Anis;Chemi, Awda
    • Advances in nano research
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    • v.4 no.1
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    • pp.31-44
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    • 2016
  • This article is concerned with the free vibration problem for chiral double-walled carbon nanotube (DWCNTs) modelled using the non-local elasticity theory and Euler Bernoulli beam model. According to the governing equations of non-local Euler Bernoulli beam theory and the boundary conditions, the analytical solution is derived and two branches of transverse wave propagating are obtained. The numerical results obtained provide better representations of the vibration behaviour of double-walled carbon nanotube, where the aspect ratio of the (DWCNTs), the vibrational mode number, the small-scale coefficient and chirality of double-walled carbon nanotube on the frequency ratio (${\chi}^N$) of the (DWCNTs) are significant. In this work, the numerical results obtained can be used to predict and prevent the phenomenon of resonance for the forced vibration analyses of double -walled carbon nanotubes.

Applying the Bi-level HMM for Robust Voice-activity Detection

  • Hwang, Yongwon;Jeong, Mun-Ho;Oh, Sang-Rok;Kim, Il-Hwan
    • Journal of Electrical Engineering and Technology
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    • v.12 no.1
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    • pp.373-377
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    • 2017
  • This paper presents a voice-activity detection (VAD) method for sound sequences with various SNRs. For real-time VAD applications, it is inadequate to employ a post-processing for the removal of burst clippings from the VAD output decision. To tackle this problem, building on the bi-level hidden Markov model, for which a state layer is inserted into a typical hidden Markov model (HMM), we formulated a robust method for VAD not requiring any additional post-processing. In the method, a forward-inference-ratio test was devised to detect the speech endpoints and Mel-frequency cepstral coefficients (MFCC) were used as the features. Our experiment results show that, regarding different SNRs, the performance of the proposed approach is more outstanding than those of the conventional methods.

Estimation of Slosh Model Parameters Using Experimental Test-bed (시험 장치를 이용한 슬로시 모델 파라미터 추정)

  • Oh, Choong-Seok;Sun, Byung-Chan;Park, Yong-Kyu;Roh, Woong-Rae
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.37 no.7
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    • pp.661-668
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    • 2009
  • The slosh natural frequencies, damping ratio, slosh mass and slosh force applying point of the liquid in cylindrical tank are estimated using the nonlinear least squares method in time domain. The estimated slosh model parameters are in good agreement with the results of the theoretical calculations for various liquid depths. Furthermore, this methodology will be applied to predict the sloshing parameters for a liquid propellant tank using ground experimental test-bed.

An Experimental Work on Cross Flow Induced Vibration of Staggered Array Pipe Bundles (어긋난 배열 을 갖는 파이프 집합체 의 횡유동 관련 진동 에 관한 실험적 연구)

  • 박윤식;이진희
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.9 no.1
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    • pp.24-30
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    • 1985
  • An experimental work to predict critical flow velocity to give whirling instability on staggered array tube banks model which is located in wind tunnel is presented. The critical flow velocity was obtained by measuring flow induced tube vibration on three tube array models having different pitch to diameter ratio as changing damping ratio and natural frequency of tube model. The obtained experimental results are directly compared with the numbers of other investigators and partly proved the truth of Blevin's new idea to predict critical flow velocity.