• Title/Summary/Keyword: variational characteristics

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Design of Directional Couplers in Bilevel Microstrip Using the Least Squares Residual Method (최소자승법을 이용한 이중층 마이크로스트립 방향성 결합기의 설계)

  • 양기덕;김원기;이용민;나극환;신철재
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
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    • v.9 no.2
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    • pp.253-264
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    • 1998
  • In this paper, a design method for directional couplers using bilevel microstrip substrates is proposed. This kind of broadside-coupled coupler provides large coupling factors and broadband characteristics which can not be provided by conventional edge-coupled couplers. Physical dimensions needed for design are obtained by numerical analysis of characteristic parameters of the coupler using the least squares residual method, a kind of variational method, and an eigenvalue problem analysis method. A 3[dB] directional coupler is designed by the proposed method at the center frequency of 1 GHz, built, and tested. The validation and accuracy of the method are confirmed by comparing the numerical results with the experimental results.

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Limit analysis of seismic collapse for shallow tunnel in inhomogeneous ground

  • Guo, Zihong;Liu, Xinrong;Zhu, Zhanyuan
    • Geomechanics and Engineering
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    • v.24 no.5
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    • pp.491-503
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    • 2021
  • Shallow tunnels are vulnerable to earthquakes, and shallow ground is usually inhomogeneous. Based on the limit equilibrium method and variational principle, a solution for the seismic collapse mechanism of shallow tunnel in inhomogeneous ground is presented. And the finite difference method is employed to compare with the analytical solution. It shows that the analytical results are conservative when the horizontal and vertical stresses equal the static earth pressure and zero at vault section, respectively. The safety factor of shallow tunnel changes greatly during an earthquake. Hence, the cyclic loading characteristics should be considered to evaluate tunnel stability. And the curve sliding surface agrees with the numerical simulation and previous studies. To save time and ensure accuracy, the curve sliding surface with 2 undetermined constants is a good choice to analyze shallow tunnel stability. Parameter analysis demonstrates that the horizontal semiaxis, acceleration, ground cohesion and homogeneity affect tunnel stability greatly, and the horizontal semiaxis, vertical semiaxis, tunnel depth and ground homogeneity have obvious influence on tunnel sliding surface. It concludes that the most applicable approaches to enhance tunnel stability are reducing the horizontal semiaxis, strengthening cohesion and setting the tunnel into good ground.

Analytical evaluation of the influence of vertical bridge deformation on HSR longitudinal continuous track geometry

  • Lai, Zhipeng;Jiang, Lizhong;Liu, Xiang;Zhang, Yuntai;Zhou, Tuo
    • Steel and Composite Structures
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    • v.44 no.4
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    • pp.473-488
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    • 2022
  • A high-speed railway (HSR) bridge may undergo long-term deformation due to the degradation of material stiffness, or foundation settlement during its service cycle. In this study, an analytical model is set up to evaluate the influence of this long-term vertical bridge deformation on the track geometry. By analyzing the structural characteristics of the HSR track-bridge system, the energy variational principle is applied to build the energy functionals for major components of the track-bridge system. By further taking into account the interlayer's force balancing requirements, the mapping relationship between the deformation of the track and the one of the bridge is established. In order to consider the different behaviors of the interlayers in compression and tension, an iterative method is introduced to update the mapping relationship. As for the validation of the proposed mapping model, a finite element model is created to compare the numerical results with the analytical results, which show a good agreement. Thereafter, the effects of the interlayer's different properties of tension and compression on the mapping deformations are further evaluated and discussed.

Spectral Element modeling for the one-dimensional blood flow analysis (일차원 혈류해석을 위한 스펙트럴 요소 모델링)

  • Jang, In-Joon;Lee, U-Sik
    • Proceedings of the Computational Structural Engineering Institute Conference
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    • 2008.04a
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    • pp.152-155
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    • 2008
  • The blood flow characteristics have been closely related to various cardiovascular diseases, it is very important to predict them accurate enough in an efficient way. Thus, this paper proposes a one-dimensional spectral element model for the blood flow through blood vessels. The spectral element model is formulated by using the variational method. The nonlinear terms in spectral element model are all treated as the pseudo-force and an iterative solution method is applied in the frequency domain.

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Analysis of the shielded suspended substrate coplanar waveguide (차폐된 서스펜디드 섭스테레이트 코플래너 도파관 해석)

  • 안광은;이상설
    • Journal of the Korean Institute of Telematics and Electronics A
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    • v.32A no.4
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    • pp.40-46
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    • 1995
  • The characteristics of the shielded suspended substrate coplanar waveguide(SSCPW) are analyzed by applying the point matchning method to the quasi-TEM mode approximation. The characteristic impedances and the effective dielectric constants are also calculated by changing the height of air and dielectric layer, and the strip width of SSCPW. Approaching the side strip width of SSCPW to zero, values of characteristic impedances and effective dielectric constants are agreed well with the results obtained by the variational method.

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Analysis of the Shielded Suspended Substrate Strip Transmission Line (차폐된 서스펜디드 섭스트레이트 스트립 전송선 해석)

  • 황정섭;백경훈;이상설
    • Journal of the Korean Institute of Telematics and Electronics A
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    • v.31A no.2
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    • pp.53-59
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    • 1994
  • The characteristics of the shielded suspended substrate strip transmission line(SSSL) are analyzed by the point matching method and the variational method in Quasi-TEM mode. The accuracy of this solution is confirmed by analyzing and comparing this solution with the empirical solution obtained from the same dimension. The characteristic impedance and the effective dielectric constant are also studied by increasing the air-layer height of SSSL.

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Propagation Characteristics Analysis of Dielectric Waveguide Using a Finite-Element Method (유한요소법에 의한 유전체 광도파관의 전파특성 해석)

  • 강길범
    • Proceedings of the Optical Society of Korea Conference
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    • 1989.02a
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    • pp.157-160
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    • 1989
  • The most serious difficulty in using the finite element method is the appearance of the so-called spurious, nonphysical modes. We have proposed the finite element formulation of the variational expression in the three-component magnetic field based on Galerkin's method. In this approach, the divergence relation H is satisfied and spurious modes does not appear and finite-element solutions agree with the exact solutions.

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A Travel Time Prediction Model under Incidents (돌발상황하의 교통망 통행시간 예측모형)

  • Jang, Won-Jae
    • Journal of Korean Society of Transportation
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    • v.29 no.1
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    • pp.71-79
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    • 2011
  • Traditionally, a dynamic network model is considered as a tool for solving real-time traffic problems. One of useful and practical ways of using such models is to use it to produce and disseminate forecast travel time information so that the travelers can switch their routes from congested to less-congested or uncongested, which can enhance the performance of the network. This approach seems to be promising when the traffic congestion is severe, especially when sudden incidents happen. A consideration that should be given in implementing this method is that travel time information may affect the future traffic condition itself, creating undesirable side effects such as the over-reaction problem. Furthermore incorrect forecast travel time can make the information unreliable. In this paper, a network-wide travel time prediction model under incidents is developed. The model assumes that all drivers have access to detailed traffic information through personalized in-vehicle devices such as car navigation systems. Drivers are assumed to make their own travel choice based on the travel time information provided. A route-based stochastic variational inequality is formulated, which is used as a basic model for the travel time prediction. A diversion function is introduced to account for the motorists' willingness to divert. An inverse function of the diversion curve is derived to develop a variational inequality formulation for the travel time prediction model. Computational results illustrate the characteristics of the proposed model.

A Study about aerodynamic characteristics of High speed train by fore-body shape design (고속전철의 형상에 따른 공력특성 연구)

  • 진원재;이봉래
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 1997.10a
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    • pp.735-738
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    • 1997
  • The aerodynamic charateristics of high speed train can be improved by fore-body design. In this paper, the design a fore-body shape which has optimal aerodynamic charateristics, 6 models of fore-body shape are proposed and the change of aerodynamic characteristics is studied through calculations of flow field around high speed train fro each fore-body shape. The flow field around high speed trains are calculated using Navier-Stokes equation. The variational trends of aerodynamic characteristics are studied from the result of flow calculation around high speed trains for 6 fore-body shapes.

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Spectral Element Modeling for the Axially Moving Strings (축방향으로 이동하는 현에 대한 스펙트럴 요소 모델링)

  • Choi, Jung-Sik;Lee, U-Sik
    • Proceedings of the KSR Conference
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    • 2009.05a
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    • pp.1092-1096
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    • 2009
  • The spectral element modeling is known to provide very accurate structural dynamic characteristics, while reducing the number of degree-of-freedom to resolve the computational and cost problems. Thus, the spectral element model with variational method for an axially moving string subjected to axial tension is developed in the present paper. The high accuracy of the spectral element model is the verified by comparing its solutions with the conventional finite element solutions and exact analytical solutions. The effects of the moving speed and axial tension the vibration characteristics, wave characteristics, and the static and dynamic stabilities of a moving string are investigated.

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