• Title, Summary, Keyword: 시간 적분법

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The Derivation of Error Estimates with Various Shape Functions for Time Integration Using Finite Element Approach (유한요소 기법을 적용한 시간적분법에서 형상함수에 따른 오차추정치 유도)

  • 장인식;맹주원;김동호
    • Computational Structural Engineering
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    • v.11 no.4
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    • pp.187-196
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    • 1998
  • 불연속 갤러킨 정식화에 기초를 둔 시간적분법에 대하여 시간을 변수로 한 유한요소적 접근법을 시도하였다. 단일 형상함수와 두 형상함수 정식화에 대해 각각 선형, 이차 형상함수를 적용하여 모두 네 종류의 시간적분법을 유도하였으며, 각 방법에 대하여 시간시텝의 증가에 따른 변위와 속도의 관계를 나타내는 증폭행렬을 계산하였다. 유도된 방법들의 성능을 평가하기 위하여 부하가 갑자기 변화는 진동 문제를 해석하고 변위의 오차를 비교하였다. 네 가지의 방법에 대하여 국부 오차 추정치를 개발하였으며, 오차 추정치의 정확도를 수치예를 이용하여 평가하였다. 단일 형상함수 정식화에서 이차 형상함수를 이용한 오차 추정치가 실제 국부오차를 잘 나타내었으며 유도된 오차 추정치는 시간간격제어 기법에서 시간간격의 크기를 결정하는 척도로 이용 가능하다.

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금속 성형 공정의 준정적 변형 예측을 위한 외연적 시간 적분 유한 요소법의 적용성 연구

  • 유요한;양동열
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • pp.192-197
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    • 1995
  • 소재의 손실을 최소한 줄이면서 원하는 형상의 제품을 가공하는 가장 기본적인 금속 가공 방법은 금형을 이용하는 금속 성형(metal forming)이다. 본 논문에서는 준정적 금속 성형 문제 해석 에대한 외연적 시간 적분 유한 요소법의 적용성을 평가 하기 위하여 변형모드가 복잡한 박판튜브 (thin-walled tube)의 좌굴문제를 해석하여 변형과정이 이론 및 실험결과와 비교적 잘 일치하는지 살펴보기로 한다. 또한 준정적 금속 성형 문제 해석에 외연적 시간 적분 유한 요소법을 사용할 때 계산 시간을 줄이기 위하여 많이 사용되는 가압속도 조절법(loading velocity control technique) 의 타당성을 평가하기 위하여 박판 튜브와 중실 실린더(solid cylinder)의 변형 속도에 따른 변형 모드의 변화를 비교 관찰하여 기하학적 형상에따른 가압속도 조절법의 적용 가능 여부를 분석하여 보겠다.

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Numerical Characteristics of Hypersonic Air Chemistry and Application of Partially Implicit Time Integration Method (극초음속 공기반응의 수치해석적 특성과 부분 내재적 적분법 적용)

  • Kim, Seong-Lyong;Ok, Ho-Nam;Ra, Seung-Ho;Kim, In-Sun
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.31 no.7
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    • pp.1-8
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    • 2003
  • Numerical characteristics of air chemistry associated with hypersonic flows are described and are compared with those of hydrogen oxygen combustion, applying the partially implicit time integration method to air chemistry. This paper reveals that the time integration of air chemistry needs a chemical Jacobian for stable calculations. However the positive real eigenvalues in air chemistry are relatively smaller than those of hydrogen combustion, and the numerical integration is less sensitive than that with combustion. lt is also found that the application of the partia1ly irnplicit method reduces the computing time without numerical instabilities.

An Accelerated Iterative Method for the Dynamic Analysis of Multibody Systems (반복 계산법 및 계산 가속기법에 의한 다물체 동역학 해법)

  • 이기수;임철호
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.16 no.5
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    • pp.899-909
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    • 1992
  • An iterative solution technique is presented to analyze the dynamic systems of rigid bodies subjected to kinematic constraints. Lagrange multipliers associated with the constraints are iteratively computed by monotonically reducing an appropriately defined constraint error vector, and the resulting equation of motion is solved by a well-established ODE technique. Constraints on the velocity and acceleration as well as the position are made to be satisfied at joints at each time step. Time integration is efficiently performed because decomposition or orthonormalization of the large matrix is not required at all. An acceleration technique is suggested for the faster convergence of the iterative scheme.

Spectroscopy of Visible Light Emitted from Plasma Occurred by Pulse Discharge (펄스형 방전플라스마에서 발생하는 가시광선의 분광특성 연구)

  • Choi, Woon Sang
    • Journal of Korean Ophthalmic Optics Society
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    • v.3 no.1
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    • pp.27-31
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    • 1998
  • We investigated visible light radiated from Plasma focus device by time-resolved analyzed method and time-integrated analyzed method. Plasma focus consisted of two coaxial electrodes is a device that translated from electric energy of maximum 40 kV/20 kJ in capacitor banks into visible light by electric discharge. Spectral analysis is using Monochromator(f =0.5m). Time-resolved spectrum is analyzed with a oscilloscope the light pulse of constant wavelength and time-integrated spectrum does with densitometer the film which developed a constant range of wavelength. The optimum condition of visible emission was that the discharging voltage was 17kV and the gas pressure 0.5 torr Ar.

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Three-dimensional Elastic Green's Solution by Formal Time-integration Method (시간적분을 이용한 3차원 탄성파 임펄스 반응 해의 계산)

  • Park Kwon Gyu;Shin Changsoo;Yoon Kwangjin;Suh Jung Hee
    • Geophysics and Geophysical Exploration
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    • v.3 no.4
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    • pp.125-128
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    • 2000
  • An ad hoc method of deriving three-dimensional elastic Greens solution for displacements is proposed in this study; Instead of direct evaluation of four-dimensional Fourier integral that is usual in spectral approaches, we first derived the expression for particle acceleration using the calculus of residues, and then, derived the expression for particle displacement by direct formal integration with respect to time. As a result, we can detour the disconcertion related to causality due to directly evaluating the integral with respect to angular frequency in conventional spectral approach.

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신속한 3차원 전자탐사 모델링

  • Jo, In-Gi;Kim, Ha-Rim
    • Journal of the Korean Geophysical Society
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    • v.5 no.1
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    • pp.63-71
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    • 2002
  • The integral equation method is a powerful tool for electromagnetic numerical modeling. But the difficulty of this technique is the size of their linear equations, which demands excessive memory and calculation time to invert. This limitation of the integral equation method becomes critical in inverse problem. To overcome this limitation, a lot of approximation and series methods, such as conventional Born, modifed Born and extended Born, were developed. But all the methods need volume integration of Green tensor, which is very time consuming. In electromagnetic theory, Green tensor rapidly decreases as the distance between source and field cell increases. Therefore, the source cell which are far away from the field cell does not make an effect on the electric field of the field cell. Consequently, by ignoring the effect of Green tensor due to far away source cells, computing time for electromagnetic numerical modeling can be reduced dramatically. Comparisons of this new method against a full integral equation, extended Born approximation and series code show that the method is accurate enough much less time consuming.

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Accuracy Analysis of GLONASS Orbit Determination Strategies for GLONASS Positioning (GLONASS 측위를 위한 위성좌표 산출 정확도 향상 방안)

  • Lee, Ho-Seok;Park, Kwan-Dong;Kim, Hye-In
    • Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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    • v.28 no.6
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    • pp.573-578
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    • 2010
  • Precise determination of satellite positions is necessary to improve positioning accuracy in GNSS. In this study, GLONASS orbits were predicted from broadcast ephemeris using the 4th-order Runge-Kutta numerical integration method and their accuracy dependence on the integration step and the integration time was analyzed. The 3D RMS (Root Mean Square) differences between the results from I-second integration step and 300-second integration step was about 3 cm, but the processing time was one hundred times less for the I-second integration time case. For trials of different integration times, the 3D RMS errors were 8.3 m, 187.3 m, and 661.5 m for 30-, 150-, and 300-minutes of integration time, respectively. Though this integration-time analysis, we concluded that the accuracy gets higher with a shorter integration time. Thus we suggest forward and backward integration methods to improve GLONASS positioning accuracy, and with this method we can achieve a 5-meter level of 3-D orbit accuracy.

Numerical Simulation of Incipient Breaking Waves (초기 쇄파의 수치모사)

  • 김용직;김선기
    • Journal of the Society of Naval Architects of Korea
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    • v.39 no.4
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    • pp.1-10
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    • 2002
  • For the time-domain simulation of incipient breaking waves, usually the boundary integral method has been used so far, and it seems to be successful except a problem of too much computation time. The present paper shows a new computation technique for the simulation of breaking wave experiment. This technique uses the high-order spectral/boundary element method and the boundary integral method in sequence, and reduces the computation time remarkably. The wave generation and energy focusing process is efficiently simulated by the high-order spectral/boundary element method. Only the wave over-turning process is simulated by the boundary integral method. In the example calculation result, salient features of breaking waves such as high particle velocities and accelerations are shown.

Predictions of Heat and Mass Transfer Rates to a Spray Droplet Experiencing Condensation (응축을 수반하는 분무수적으로의 열 및 질량전달률 예측)

  • 이상균;조종철;신원기;조진호;서정일
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.15 no.5
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    • pp.1763-1773
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    • 1991
  • 본 연구에서는 포화수증기와 공기의 혼합기내에서 분무수적으로의 열 및 질량 전달률을 계산하기 위하여 수적의 부분혼합모형과 비혼합모형에 대하여 수적내 과도온 도분포의 해석해를 적용성이 보장되면서도 계산상의 어려움이 수반되지 않는 형태로 구하기 위하여 수적내부의 열전도해석에 있어서 적분법을 적용하였다. 적분법으로 얻어지는 과도온도분포의 해는 유한차의 다항식으로 표시되어 비혼합모형인 경우 각시 간 구간의 경계에서의 온도분포가 연속성을 유지하면서 물성치들의 온도에 대한 종속 성이 쉽게 고려되고 계산도 용이한 형태이다. 본 보에서 제시하는 해석결과의 적용 성을 조사하기 위하여 완전혼합모형을 포함하는 세가지 수적모형들에 대한 계산결과들 로부터 얻어진 시간변화에 따른 수적의 무차원 체적평균온도변동을 유효한 실험결과들 과 비교, 검토하였으며, 부분혼합모형에 대하여 혼합기의 압력, 수적의 초기온도, 혼 합기 속에 포함되어 있는 수증기의 체적분율, 수적의 초기크기, 수적의 초기속도 및 분사각도가 주위혼합기로부터 수적으로 전달되는 열 및 질량전달에 미치는 영향을 조] 사하고 도출된 대표적인 검토 결과를 제시하였다.