• Title/Summary/Keyword: estimated natural frequency

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Analytical nonlocal elasticity solution and ANN approximate for free vibration response of layered carbon nanotube reinforced composite beams

  • Emrah Madenci;Saban Gulcu;Kada Draiche
    • Advances in nano research
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    • v.16 no.3
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    • pp.251-263
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    • 2024
  • This article investigates the free vibration behavior of carbon nanotube reinforced composite (CNTRC) beams embedded using variational analytical methods and artificial neural networks (ANN). The material properties of layered functionally graded CNTRC (FG-CNTRC) beams are estimated using nonlocal parameters modified power-law with different types of CNT distributions through the thickness direction of the beam. Adopting Eringen's nonlocal elasticity theory to capture the small size effects, the nonlocal governing equations are derived and solved using the analytical method. And also, the problem was analyzed using the ANN method. The architecture of the proposed ANN model is 3-9-1. In the experiments, we used 112 different data to predict the natural frequency using ANN. Based on the nonlocal differential constitutive relations of Eringen, the equations of motion as well as the boundary conditions of the beam are derived using Hamilton's principle. The classical beam theory is used to formulate a governing equation for predicting the free vibration of laminated CNTRC beams. According to the experimental results, the prediction ability of the ANN model is very good and the natural frequency can be predicted in ANN without attempting any experiments.

Effect of Observed Discharge Data on Regional Flood Frequency Analysis in the Han River Basin (한강유역 관측유출자료가 지역홍수빈도분석 결과에 미치는 영향)

  • Kim, Nam Won;Lee, Jeong Eun;Lee, Jeongwoo;Jung, Yong
    • Journal of Korea Water Resources Association
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    • v.48 no.6
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    • pp.511-522
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    • 2015
  • This study assessed the impact of uncertainties in flood data on the results of flood frequency analysis for Han river basin. To meet this aim, this study quantified assessment focused on the index flood and quantile by regional flood frequency analysis using the flood data from 17 water level gauges in Han river basin. We analysed the results categorized by three cases according to the characteristics of the measured data. Firstly, we analyzed the regional flood frequency for the water level gauge in the Pyungchang river basin to investigate the impact of water level data. The results has the error of 0.240 with respect to the mean flood. Secondly, we examined the impact of uncertainty in measurement data generated by the application of rating on the results of regional flood frequency analysis. We have compared the results by applying the rating estimated for each year to the one by the recently estimated rating. The results showed that the mean error has 0.246 in terms of the mean flood. Finally, we have inferred the regional flood frequency analysis results with the regulated flow in the downstream area of dams. The regulated specific discharge in the downstream area of dams controlled by dam operation showed a large difference to the estimated specific discharge in the downstream area of dams by extension of the natural specific discharge in the upstream area using the regionalization method.

A Sensitivity Analysis for Parameters Effection upon the Design Floods: Natural Watershed (설계홍수량에 영향을 미치는 매개변수의 민감도 분석: 자연유역을 중심으로)

  • Yun, Yeo-Jin
    • Journal of Korea Water Resources Association
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    • v.31 no.6
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    • pp.695-708
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    • 1998
  • Recently, it seems increasing trends that the design floods on the middle and small scale of urban regions and natural basins are evaluated with introducing to the concept of the critical storm duration. However the study of the critical storm duration is not sufficient and especially on the natural basins, it rarely performed. therefore in this study, estimated the critical storm duration and peak discharge according to the rainfall distribution type, the position of peak rainfall intensity, and the frequency on the natural basins were evaluated using Clark model and the influence of each factors on the design floods was analyzed with sensitivity analysis on the parameters of the model.

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A study on the vibration calculation method of portal frame structure with variable sections (변화하는 단면의 문형구조물의 진동계산에 관한 연구)

  • 조용수;전효중
    • Journal of Advanced Marine Engineering and Technology
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    • v.9 no.3
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    • pp.214-224
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    • 1985
  • In this paper, some theoretical equations are derived to calculate natural frequencies and their modes of a portal type derrick system and developed a computer program to carry out their calculations. The ship's structures, such as funnels, upper decks, engine structures, shaft systems suffer local vibrations of the ship. The exciting forces of vibrations are induced by the bearing force and the surface force of propeller or by the main engine. For solving the vibration problem of riggings like the derrick system the natural frequency of its system must be exactly estimated as far as possible and its resonance condition must be kept out of the normal engine operating speed range. When some severe resonances are encountered after the ship's launching, it may be required a tremendous cost to amend their condition. An experimental model of the portal type derrick is made, which is composed of two posts and a truss. This experimental model is excited by an electrical-magnet, and its vibration responses are found out. The calculating results of the model by the developed computer program are compared with those of measured values of model experiment, and they show fairly good agreements.

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Development of Cable Exciting Robot for Estimating Dynamic Properties of Stay Cables (사장교 케이블의 동특성 추정을 위한 케이블 가진 로봇의 개발)

  • Lee, Jong-Jae;Kim, Jae-Min;Ahn, Sang-Sup;Choi, Jun-Sung
    • Proceedings of the Computational Structural Engineering Institute Conference
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    • 2007.04a
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    • pp.39-42
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    • 2007
  • It is necessary to estimate the dynamic characteristics of stay cables ie., the natural frequencies and the damping ratios of the stay cables to design cable damper for appropriate mitigation of cable vibrations and/or to estimate the tension of cables in service. In this study, a cable exciting robot for evaluating dynamic characteristics of stay cables has been developed, and the feasibility of the developed system has been demonstrated through a field test on the stay cable installed at the test yard of Highway and Transportation Technology Institute (HTTI). The dynamic characteristics of the stay cable were estimated based on acceleration data as well as displacement measured by digital image processing technique.

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An Experimental Study on the Dynamic Characteristics of Onboard Machinery with Resilient Mounts (선내 탑재 마운팅 장비의 동특성에 관한 실험적 연구)

  • 김극수;최수현
    • Journal of the Society of Naval Architects of Korea
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    • v.40 no.2
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    • pp.28-33
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    • 2003
  • This study is performed to evaluate and design the dynamic characteristics of the onboard machinery with resilient mounts. To avoid resonance with onboard machinery and external force, it is necessary to calculate natural frequencies of the resilient mounting system more accurately. Natural frequencies of on board machinery are determined by rigid body properties(mass, moment of inertia, center of mass) of machinery and stiffness of mounts. But it is very difficult to calculate rigid body properties theoretically. And stiffness properties of rubber mounts vary with dynamic displacement, pre load, frequency and temperature, and so on. In this study, we have identified rigid body properties using experimental modal analysis and estimated dynamic stiffness of rubber mount for onboard machinery using measured vibration response during seatrial. We measured displacement excitation through deck under mounts and evaluated relationship between modes of resilient mounting system and main excitation sources of a ship.

Airbag Accelerometers Using Silicon Epitaxial Layers (실리콘 에피층을 이용한 자동차 에어백용 가속도계)

  • 고종수;김규현;이창렬;조영호;이귀로;곽병만
    • Transactions of the Korean Society of Automotive Engineers
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    • v.4 no.5
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    • pp.9-15
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    • 1996
  • A silicon microaccelerometer is designed and fabricated using silicon epitaxial layers for automotive electronic airbag applications. A cantilever structure is chosen for high sensitivity and piezoresistive detection method is adopted for circuit simplicity and low cost. An optimum design is used to find optimum microstructure sizes for maximum sensitivity subject to performance requirements and design constraints on natural frequency, damping ratio, maximum allowable stress and microfabrication limitations. The microaccelerometer is fabricated by micromachining processing steps, composed of material-selective and orientation-dependent chemical etching techniques. Fabricated prototype shows a sensitivity of 88.6$\mu\textrm{V}$/g within a resonant frequency of 1.75KHz. Estimated performance of the microaccelerometer is compared with measured one. Discrepancy between the theoretical values and the experimental values is discussed together with possible sources of the errors.

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Design and Evaluation of a Vibration Exciter for the Flow Resonance (유동공진을 위한 가진기 설계 및 평가)

  • Nam, Yoon-Su;Choi, Jae-Hyuck
    • Journal of the Korean Society for Precision Engineering
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    • v.18 no.6
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    • pp.141-147
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    • 2001
  • A heat dissipation technology using flow resonant phenomenon is a kind of new concept in heat transfer area. A vibration exciter is needed to generate an air turbulence which has the natural shedding frequency of a heat system. A mechanical vibrating device for the air flow oscillation is introduced, which is driven by a moving coil actuator. An analytical dynamic model for this mechanical vibration exciter is presented and its validity is verified by the comparison with experimental data. Values of some unko주 system parameters in the analytic model are estimated through the system identification approach. based on this mathematical model, a high bandwidth vibration exciter is designed using feedback control. During the experimental verification phased, it turns out the high frequency modal resonant characteristics of vibrating plate are the major barrier against obtaining a high bandwidth vibration exciter.

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Finite Element Model Updating and Vibration Analysis of PMDC Motor Rotor System (영구자석형 직류전동기 축계의 유한요소모델 개선과 진동해석)

  • Kim, Y.H.;Ha, J.Y.;Lee, J.G.;Kim, S.H.;Yang, B.S.
    • Journal of Power System Engineering
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    • v.11 no.1
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    • pp.20-27
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    • 2007
  • In this paper, finite element modeling was performed for vibration analysis of a rotor system installed in sunroof motor, and analysis process was developed for natural frequency and unbalance response analysis. At the same time, to reduce analysis modeling error caused by the difference between analysis and measured values, finite element model updating was conducted using an optimization algorithm, i.e. hybrid genetic algorithm and simulated annealing (HGASA) method. For this end experimental modal test was carried out and by using the measured frequency response function (FRF), model updating was performed considering both cases where core coil was removed and included. And acceptable result was obtained. Also, dynamic property coefficient of bush bearing which influences vibration response of the rotor system was estimated.

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Deep Learning Study of the 21cm Differential Brightness Temperature During the Epoch of Reionization

  • Kwon, Yungi;Hong, Sungwook E.
    • The Bulletin of The Korean Astronomical Society
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    • v.45 no.1
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    • pp.66.2-66.2
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    • 2020
  • We propose a deep learning analysis technique with a convolutional neural network (CNN) to predict the evolutionary track of the Epoch of Reionization (EoR) from the 21-cm differential brightness temperature tomography images. We use 21cmFAST, a fast semi-numerical cosmological 21-cm signal simulator, to produce mock 21-cm maps between z = 6 ~ 13. We then apply two observational effects, such as instrumental noise and limit of (spatial and depth) resolution somewhat suitable for realistic choices of the Square Kilometre Array (SKA), into the 21-cm maps. We design our deep learning model with CNN to predict the sliced-averaged neutral hydrogen fraction from the given 21-cm map. The estimated neutral fraction from our CNN model has great agreement with the true value even after coarsely smoothing with broad beam size and frequency bandwidth and heavily covered by noise with narrow beam size and frequency bandwidth. Our results show that the deep learning analyzing method has the potential to reconstruct the EoR history efficiently from the 21-cm tomography surveys in future.

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