• Title/Summary/Keyword: Cross-Coupling

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Numerical calculation of Laminar flow in a Square Duct of 90° Bend (정사각형 단면을 갖는 90° 곡관의 층류유동 계산)

  • Kim H. T.;Kim J. J.
    • Journal of computational fluids engineering
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    • v.2 no.1
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    • pp.1-7
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    • 1997
  • A FA-FD hybrid method, developed for solving three-dimensional incompressible Navier-Stokes equations, is applied to calculate three-dimensional laminar flows through a square duct with a 90° bend. The method discretizes the convective terms in the primary flow direction with 3rd-order upwind finite-differences and the convective and diffusive terms in the transverse directions with the two-dimensional finite analytic method. The non-staggered grid system is used and the pressure-velocity coupling is achieved by a global iteration procedure based on the PISO algorithm. Detailed comparisons between the computed solutions and the available experimental data are given mainly for the velocity distributions at cross-sections in a 90° bend of a square duct with both fully developed and developing entry flows. Although the computational result shows generally a good agreement with the experimental data, there are some significant discrepancies underlining the necessity of more accurate numerical methods as well as reliable experimental data for their validation.

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Multi-Physics Simulations of Fluidelastic Instability for Tube Bundles in Cross-Flow (유체-구조 상호작용을 적용한 튜브다발의 유체탄성불안정성 과도적 전산해석)

  • Lee, Min-Hyung;Kim, Yong-Chan
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.28 no.2
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    • pp.174-180
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    • 2004
  • Failure of tube bundles due to excessive flow-induced vibrations continues to affect the performance of nuclear power plant Early experimental studies concentrated on rigid structures and later investigators dealt with elastic structures because of their importance in many engineering fields. On the other hand, much less numerical work has been carried out, because of the numerical complexity associated with the problem. Conventional approaches usually decoupled the flow solution from the structural problem. The present numerical study proposes the methodology in analyzing the fluidelastic instability occurring in tube bundles by coupling the Computational fluid Dynamics (C%) with the tube equation of motions. The motion of the structures is modeled by a spring-damper-mass system that allows transnational motion in two directions (a two-degree-of-freedom system). The fluid motion and the cylinder response are solved in an iterative way, so that the interaction between the fluid and the structure can be accounted for property. The aim of the present work is to predict the fluidelstic instability of tube bundles and the associated phenomena, such as the response of the cylinder, the unsteady lift and drag on the cylinder, the vortex shedding frequency.

Identification of flutter derivatives from full-scale ambient vibration measurements of the Clifton Suspension Bridge

  • Nikitas, Nikolaos;Macdonald, John H.G.;Jakobsen, Jasna B.
    • Wind and Structures
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    • v.14 no.3
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    • pp.221-238
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    • 2011
  • The estimated response of large-scale engineering structures to severe wind loads is prone to modelling uncertainties that can only ultimately be assessed by full-scale testing. To this end ambient vibration data from full-scale monitoring of the historic Clifton Suspension Bridge has been analysed using a combination of a frequency domain system identification method and a more elaborate stochastic identification technique. There is evidence of incipient coupling action between the first vertical and torsional modes in strong winds, providing unique full-scale data and making this an interesting case study. Flutter derivative estimation, which has rarely previously been attempted on full-scale data, was performed to provide deeper insight into the bridge aerodynamic behaviour, identifying trends towards flutter at higher wind speeds. It is shown that, as for other early suspension bridges with bluff cross-sections, single-degree-of-freedom flutter could potentially occur at wind speeds somewhat below requirements for modern designs. The analysis also demonstrates the viability of system identification techniques for extracting valuable results from full-scale data.

A Study on the Acousto-Optical Wavelength Tunable Filters Utilizing Tapered Directional Coupler SAW Guides (Tapered 방향성 가중 결합 음향파 도파로 구조를 이용한 음향광학형 파장가변 광 필터에 관한 연구)

  • Jeong, Gi-Jo;Kim, Jeong-Hui;Jeong, Hong-Sik
    • Journal of the Institute of Electronics Engineers of Korea SD
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    • v.39 no.1
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    • pp.58-66
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    • 2002
  • Acousto-optical wavelength tunable optical filters in LiNbO$_3$ have been demonstrated using taperd directional weighted coupling acoustic waveguides and Ti double diffusion technique. Conversion efficiency in excess of 61%, 86% and sidelobe intensity of -14.29㏈, -14.99㏈ were measured at a wavelength of 1551.1nm RF frequency of 173.58MHz and RF power of 35㎽ for both TE and TM input polarizations, respectivelv. A spectral width of ~l.8nm and linear tuning late of 8.6nm/MHz were demonstrated. A 2.82$mutextrm{s}$ switching time has been measured. With two channels with 2.5nmseparation, channel cross-talk was lower than -l4㏈ for single wavelength filtering due to sidelobe.

Comparison of Phase Noise Characteristics of Three Quadrature Voltage Controlled Oscillators (3가지 직교신호 발생 전압제어 발진기의 위상 잡음 특성비교)

  • Moon Seong-Mo;Cho Il-Hyun;Lee Moon-Que
    • The Journal of The Korea Institute of Intelligent Transport Systems
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    • v.4 no.2 s.7
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    • pp.73-79
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    • 2005
  • Various CMOS quadrature-voltage-controlled oscillators(QVCOS) are designed and fabricated for the comparison of the phase noise characteristic. The first one is that the QVCO is composed of two Colpitts oscillators cross-coupled with PMOS coupling transistors. The second and third ones are the conventional LC VCO and the balanced Colpitts VCO followed by the frequency-divide-by-two, respectively. The simulation result demonstrate that Colpitts schemes show better phase noise performance by 6 dB than that of a conventional stheme in which LC VCO is followed by the frequency-divide-by-two.

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Design of Microstrip Patch Array Antenna for ISM Band (ISM대역용 마이크로스트립 패치 배열 안테나 설계)

  • 이현진;임영석
    • Journal of the Institute of Electronics Engineers of Korea TC
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    • v.41 no.8
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    • pp.119-124
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    • 2004
  • In this paper, we are designed and fabricated circular polarization microstrip patch antenna of 5[GH]z bandwidth for the wireless LAN and the ISM. We are proposed new structure that removed the section which intersected at a right angle and were composed to four separated slots. The antenna of proposed structure could solve parasitic elements from intersected in a right angle and weak coupling efficiency from asymmetry between feed line and a slot. The proposed cross slots antenna is easily impedance matching and increased impedance bandwidth. Also this is increased efficiency and a bandwidth of antenna and reduce back lobe of radiation pattern. We designed 2${\times}$2 array antenna of 5[GHz] band. It took impedance bandwidth 280[MHz](VSWR < 1.5) and gam 12.5[dBi]

A Simple and Accurate Analysis of Two Dimensional Concrete Slab for a Railroad Bridge by the Composite Laminates Plate Theory (복합적층판 이론에 의한 2차원 콘크리트 슬래브 철도교량의 정확하고 간단한 해석)

  • Han, Bong-Koo;Bang, Bae-San
    • Journal of the Korean Society for Advanced Composite Structures
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    • v.2 no.2
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    • pp.20-25
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    • 2011
  • In this paper, two dimensional concrete slabs for a railroad bridge were analyzed by the specially orthotropic laminates theory. Both the geometrical and material property of the cross section of the slab was considered symmetrically with respect to the neutral surface so that the bending extension coupling stiffness, $B_{ij}$ = 0, and $D_{16}=D_{26}=0$ Bridge deck behaves as specially orthotropic plates. In general, the analytical solution for such complex systems is very difficult to obtain. Thus, finite difference method was used for analysis of the problem. In this paper, the finite difference method and the beam theory were used for analysis.

A Numerical Analysis of H Shape Rolling (H 형강압연의 수치해석)

  • Park, Jong-Jin;Jeong, Nak-Joon;Kim, Jae-Joo
    • Transactions of Materials Processing
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    • v.4 no.4
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    • pp.375-389
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    • 1995
  • In H shape rolling, accurate predictions of deformation and temperature distribution in a billet are quite important because they are the main factors in determining roll calibers and roll pass schedules. Many researches have been performed to achieve the predictions, but most of them are limited to single pass or isothermal assumptions. In the present investigation, it is attempted to develop a method to predict the deformation and temperature distributions which is applicable to a complete rolling process that usually consists of several rollings under different rolls for a period of time. The method works by coupling two analyses : one is an approximate analysis for temperature distribution prediction and the other is the slab-FEM hybrid analysis for deformation prediction. The method is applied to analyze a "H" shape rolling process consisting of nine passes under four different rolls. In the present paper, basic ideas of the method are presented. Also, shapes of cross sections, strain and temperature distributions, roll separating force and roll torque predicted by the method are discussed.

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All-Optical AND Gate Using XPM Wavelength Converter

  • Kim, Jae-Hun;Kang, Byoung-Kwon;Park, Yoon-Ho;Byun, Young-Tae;Lee, Seok;Woo, Deok-Ha;Kim, Sun-Ho
    • Journal of the Optical Society of Korea
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    • v.5 no.1
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    • pp.25-28
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    • 2001
  • By using an XPM (Cross Phase Modulation) wavelength converter, an all-optical AND gate, which is one of six fundamental logic gates, has been demonstrated. The wavelengths for probe and pump signals are 1553.8 and 1545 nm, respectively. First, characteristics of the XPM wavelength converter have been studied. When both probe and pump signals are driven by high power, the output power of the XPM wavelength is high. Based on this fact and the experiment, the all-optical AND gate has been porved. Probe and pump signals are transformed to pulse signals by using Mach-Zehnder modulator, which is induced by a pulse generator. Square pulse signals that are similar to the format of NRZ signals have been generated. By coupling two pulse signals into the XPM wavelength converter, AND characteristics in substantiated.

Fabrication of High Speed Optical Matrix Wwitch by Ti:Ti:LiNbO3 (Ti:Ti:LiNbO3를 이용한 초고속 광 매트릭스 스위치 제조)

  • Yang, U-Seok;Kwak, Yong-Seok;Kim, Je-Min;Yoon, Hyeong-Do;Lee, Han-Yeong;Yoon, Dae-Ho
    • Korean Journal of Materials Research
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    • v.12 no.4
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    • pp.254-258
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    • 2002
  • To realize channel cross-connecting in optical communications systems, a high speed optical matrix switch was fabricated using z-cut $LiNbO_3$. For switch fabrication was design bending structure and coupling length and four $2{\times}2$ directional couplers were integrated on one substrate far construction of a $4{\times}4$ switch. Single-mode optical waveguides were formed by Ti-diffusion at a wet $O_2$ atmosphere. Ti-diffusion profile, refractive index variation and waveguide morphology were analyzed by Prism coupler and optical microscopy, respectively.