• Title/Summary/Keyword: 중앙차분법

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Dynamic Analysis of MLS Difference Method using First Order Differential Approximation (1차 미분 근사를 이용한 MLS차분법의 동적해석)

  • Kim, Kyeong-Hwan;Yoon, Young-Cheol;Lee, Sang-Ho
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.31 no.6
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    • pp.331-337
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    • 2018
  • This paper presents dynamic algorithm of the MLS(moving least squares) difference method using first order differential Approximation. The governing equations are only discretized by the first order MLS derivative approximation. The system equation consists of an assembly of the approximate function, so the shape of system equation is similar to FEM(finite element method). The CDM(central difference method) is used for time integration of dynamic equilibrium equation. The natural frequency analyses of the MLS difference method and FEM are performed, and two analysis results are compared. Also, the accuracy of the proposed numerical method is verified by displaying the dynamic analysis results together with the results by the existing second order differential approximation. In the process of assembling the first order MLS derivative approximation, the oscillation error was suppressed and the stress distribution was interpreted as relatively uniform.

Analysis of Simple Supported Anisotropic Symmetric Laminated Cylindrical Shells (단순지지된 비등방성 대칭 적층 원통형 쉘의 해석)

  • Chai, Sang Youn;Yhim, Sung Soon;Chang, Suk Yoon
    • Journal of Korean Society of Steel Construction
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    • v.11 no.2 s.39
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    • pp.117-129
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    • 1999
  • The objective of this study is to identify the advantages of composite materials and to investigate the behavior of the anisotropic symmetric laminated cylindrical shell structures. To analyze the anisotropic symmetric laminated cylindrical shell structures, the finite difference technique. that consists of forward, central and backward difference, is introduced. In this study, the degree of freedom consists of three displacements and, especially, two moments except twisting moment. It has the advantage of improving the accuracy for calculating the moments. All four edges are assumed to be simply supported. From the numerical results, it is proved that the finite difference technique can be used efficiently to analyze the anisotropic symmetric laminated cylindrical shells and gives a guide in deciding how to make use of the fiber angle the anisotropic symmetric laminated cylindrical shells.

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A Study of Rayleigh Damping Effect on Dynamic Crack Propagation Analysis using MLS Difference Method (MLS 차분법을 활용한 동적 균열전파해석의 Rayleigh 감쇠영향 분석)

  • Kim, Kyeong-Hwan;Lee, Sang-Ho;Yoon, Young-Cheol
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.29 no.6
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    • pp.583-590
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    • 2016
  • This paper presents a dynamic crack propagation algorithm with Rayleigh damping effect based on the MLS(Moving Least Squares) Difference Method. Dynamic equilibrium equation and constitutive equation are derived by considering Rayliegh damping and governing equations are discretized by the MLS derivative approximation; the proportional damping, which has not been properly treated in the conventional strong formulations, was implemented in both the equilibrium equation and constitutive equation. Dynamic equilibrium equation including time relevant terms is integrated by the Central Difference Method and the discrete equations are simplified by lagging the velocity one step behind. A geometrical feature of crack is modeled by imposing the traction-free condition onto the nodes placed at crack surfaces and the effect of movement and addition of the nodes at every time step due to crack growth is appropriately reflected on the construction of total system. The robustness of the proposed numerical algorithm was proved by simulating single and multiple crack growth problems and the effect of proportional damping on the dynamic crack propagation analysis was effectively demonstrated.

A Stable MOT Scheme with Combined Field Integral Equation for the Analysis of Transient Scattering from Conducting Structure (도체 구조물의 과도 산란 해석을 위한 결합 적분방정식의 안정된 MOT 기법)

  • Lee, Chang-Hwa;An, Ok-Kyu;Kwon, Woo-Hyen;Jung, Baek-Ho
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
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    • v.19 no.4
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    • pp.427-435
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    • 2008
  • In this paper, a stable marching-on in time(MOT) method with a time domain combined field integral equation(CFIE) is presented to obtain the transient scattering response from arbitrarily shaped three-dimensional conducting bodies. This formulation is based on a linear combination of the time domain electric field integral equation(EFIE) with the magnetic field integral equation(MFIE). The time derivatives in the EFIE and MFIE are approximated using a central finite difference scheme and other terms are averaged over time. This time domain CFIE approach produces results that are accurate and stable when solving for transient scattering responses from conducting objects. Numerical results with the proposed MOT scheme are presented and compared with those obtained from the conventional method and the inverse discrete Fourier transform(IDFT) of the frequency domain CFIE solution.

Calculation of characteristic Impedance of the U-Type Transmission Line by the Moment Method (모먼트법에 의한 U형 부송선의 특성임피던스 계산)

  • 이상설
    • Journal of the Korean Institute of Telematics and Electronics
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    • v.19 no.1
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    • pp.29-34
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    • 1982
  • We can find the characteristic impedances of the U-type transmission lines by finite d ifference method. In this paper, the characteristic impedances of the lines are computed by the moment method. There are 10% differences between the results of the finite difference method and those of the moment method. But when the interior conductor of the line is located at the center of the exterior conductor, the results of the moment method approache to that of analytical result when the length of outer conductor becomes in finite.

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The Study of Finite Element Method for Analyses of Travelling Magnetic Field Problem (운동자계 문제의 해석을 위한 유한요소법에 관한 연구)

  • Chang Ho-Sung
    • Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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    • v.19 no.4
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    • pp.108-116
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    • 2005
  • This paper presents finite element analyses solution in the travelling magnetic field problem. The travelling magnetic field problem is subject to convective-diffusion equation. Therefore, the solution derived from Galerkin-FEM with linear interpolation function may oscillate between the adjacent nodes. A simple model with Dirichlet, Neumann and Periodic boundary condition respectively, have been analyzed to investigate stabilities of solutions. It is concluded that the solution of Galerkin-FEM may oscillate according to boundary condition and element type, but that of Upwind-FFM is stable regardless boundary condition.

Effect of Gradient Vector Calculation Method On Adaptive Beamforming using LMS Algorithm (기울기 벡터 계산법이 LMS 알고리즘을 이용한 적응 빔포밍에 미치는 영향)

  • Kwang-Chol Chae;Ki-Ryang Cho
    • The Journal of the Korea institute of electronic communication sciences
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    • v.18 no.3
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    • pp.535-544
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    • 2023
  • In this paper, we study the effect of gradient vector calculation method(analytical method, central finite difference method) on adaptive beamforming to control weight distribution during iterated calculation when LMS algorithm (repeating method) is used to realize desired beam pattern. To this end, a quasi-ideal beam having an arbitrarily set beam width, a rotating beam, and a multi-beam were reviewed as examples. Numerical experiments applied the step parameters of the appropriate values to the adaptive beamforming system through trial and error equally to the two calculations, and compared the convergence characteristics of objective functions that evaluate adaptability and error using two methods for calculating gradient vectors.

Effective Simulation Technology for Near Shore Current Flow (연안해수유동에 관한 효율적인 수치계산기법)

  • Yoon, B.S.;Rho, J.H.;Fujino, M.;Hamada, T.
    • Journal of the Society of Naval Architects of Korea
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    • v.32 no.4
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    • pp.38-47
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    • 1995
  • The three-dimensional multi-layer computer simulation technology for tidal current developed in the previous study is updated to a new version. many improvements are achieved by following changes : (1) No-reflection condition is adopted instead of no-gradient condition as an open boundary condition. (2) Time marching algorithm is changed so that velocity and pressure(surface movement) might be salved in turn at different time step (3) Convection term in equation of motion is estimated by upwind differencing scheme instead of central differencing. The stability is improved considerably and the steady state is achieved within 2 tidal periods which is about 3 times shorter than that of the old version. Moreover, fluctuations in time disappeared by introducing the new time marching technique. An application to the real near shore area(near Inchon harbor) is performed by the new version. Simulated results are compared with those by the simulation total developed in the University of Tokyo. Validity and effectiveness of the two simulation technologies are chocked through the comparative research works.

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Analysis of Characteristics of Cohesive Sediment Settling (점착성 퇴적물의 침전 특성 분석)

  • Kim, Jong-Woo;Yoon, Sei-Eui;Lee, Jong-Tae
    • Journal of Korea Water Resources Association
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    • v.38 no.2
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    • pp.133-142
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    • 2005
  • The settling concentration of fine suspended solid particles(alumina(Al$_2$O$_3$) and quartz(SiO$_2$)) is investigated with the physico-chemical effects(initial concentration, pH and NaCl). Laboratory tests have confirmed the significant influence of increasing initial concentration and salinity which can lead to flocculation due to the intermolecular attraction. Furthermore, the influence of the pH value on the concentration-time corves of alumina has been on firmed. Besides a numerical model to predict the behaviour of cohesive deposit under still water is analyzed by solving the unsteady one-dimensional diffusion-advection equation with a explicit, implicit, Crank-Nicolson and finite difference scheme. The model predicts the existence of an equilibrium concentration. Application of the model with implicit centered difference to data from settling experiments shows a similar distribution.

Natural Convection about a Vertical Flat Plate Immersed in a Thermal Plume (자유 열상승류 중앙에 놓인 수직평판에 관한 자연대류)

  • Chang, K. S.
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.10 no.5
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    • pp.798-805
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    • 1986
  • 단열 혹은 등온 경계조건 하의 수직평판과, 선열원으로부터 형성되는 열상승류 간의 열적 상호작용을 조사형ㅆ다. 경계층 방정식은 Patankar-Spalding의 유한차분법을 사용하여 계산하였다. 단열평판의 경우에 자유 열상승류로부터 벽 경계층으로 부터의 점진적인 발달 단계를 설명하였다. 등온평판의 경우에는 평판주위에 새롭게 형성되는 열경계층에서의 열전달현상을 자세히 고찰하였다.