• 제목/요약/키워드: Local equilibrium

검색결과 225건 처리시간 0.019초

Bypass, homotopy path and local iteration to compute the stability point

  • Fujii, Fumio;Okazawa, Shigenobu
    • Structural Engineering and Mechanics
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    • 제5권5호
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    • pp.577-586
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    • 1997
  • In nonlinear finite element stability analysis of structures, the foremost necessary procedure is the computation to precisely locate a singular equilibrium point, at which the instability occurs. The present study describes global and local procedures for the computation of stability points including bifurcation points and limit points. The starting point, at which the procedure will be initiated, may be close to or arbitrarily far away from the target point. It may also be an equilibrium point or non-equilibrium point. Apart from the usual equilibrium path, bypass and homotopy path are proposed as the global path to the stability point. A local iterative method is necessary, when it is inspected that the computed path point is sufficiently close to the stability point.

다공성 물질 안에서의 자연대류 현상에 대한 열역학적 국소평형상태 가정의 고찰 (An Investigation on Local Thermodynamic Equilibrium Assumption of Natural Convection in a Porous Medium)

  • 김인선;남진현;김찬중
    • 대한기계학회:학술대회논문집
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    • 대한기계학회 2000년도 추계학술대회논문집B
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    • pp.112-117
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    • 2000
  • A numerical study on natural convection in a vertical square cavity filled with a porous medium is carried out with Brinkman-Forchheimer-extended Darcy flow model, and the validity of local thermodynamic equilibrium assumption is studied. The local thermodynamic equilibrium refers to the state in which a single temperature can be used to describe a heat transfer process in a multiphase system. With this assumption, the analysis is greatly simplified because only one equation is needed to describe the heat transfer process. But prior to using this assumption, it is necessary to know in what conditions the assumption can be used. The numerical results of this study reveal that large temperature difference between fluid phase and solid phase exists near wall region, paticularily when the convection becomes dominant over conduction. And the influence of flow parameters such as fluid Rayleigh number, fluid Prandtl number, dimensionless particle diameter and conductivity ratio are investigated.

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다공성 매질에서 Local Thermal Equilibrium에 관한 연구 (Study on Local Thermal Equilibrium in a Porous Medium)

  • 장석필;김성진
    • 대한기계학회논문집B
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    • 제26권8호
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    • pp.1172-1182
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    • 2002
  • In the present study a general criterion for local thermal equilibrium is presented in terms of parameters of engineering importance which include the Darcy number, the effective Prandtl number of fluid, and the Reynolds number. For this, an order of magnitude analysis is performed for the case when the effect of convection heat transfer is dominant in a porous structure. The criterion proposed in this study is more general than the previous criterion suggested by Carbonell and Whitaker, because the latter is applicable only when conduction is the dominant heat transfer mode in a porous medium while the former can be applied even when convection heat transfer prevails. In order to check the validity of the proposed criterion for local thermal equilibrium, the forced convection phenomena in a porous medium with a microchanneled structure subject to an impinging jet are studied using a similarity transformation. The proposed criterion is also validated with the existing experimental and numerical results for convection heat transfer in various porous materials that include some of the parameters used in the criterion such as a microchannel heat sink with a parallel flow, a packed bed, a cellular ceramic, and a sintered metal. It is shown that the criterion presented in this work well-predicts the validity of the assumption of local thermal equilibrium in a porous medium.

Local Thermal Equilibrium 모델에 의한 이차이온 질량분석의 정량화 방법

  • 곽병화;권오준
    • ETRI Journal
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    • 제10권2호
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    • pp.63-69
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    • 1988
  • SIMS(Secondary Ion Mass Spectrometry) 분석 데이터의 정량화 방법으로 이온주입에 의한 실험적 접근법과 LTE(Local Thermal Equilibrium) 모델을 사용한 준이론적 접근법 2가지가 주로 논의되고 있다. 본 고에서는 LTE 모델을 사용, SIMS data를 정량화하는 방법에 대하여 기술하였으며 아울러 BASIC language로 된 간단한 LTE 프로그램을 제시하였다.

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미소 변형 및 회전 단위 벡터를 이용한 판의 대변형 해석 (Large Deflection Analysis of Plates By Using Small Local Deflections And Rotational Unit Vectors)

  • 이기수
    • 한국정밀공학회지
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    • 제17권2호
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    • pp.201-210
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    • 2000
  • The large deflection of plate is analyzed by co-rotational formulations using small local displacements and rotating unit vectors on the nodal points. The rotational degrees of the freedom are represent ed by the unit vectors1 In the nodal points, and the equilibrium equations are formulated by using small deflection theories of the plates by assuming that the directions of the unit vectors of the nodal points are known apriori. The translational degrees of freedom are independently solved from the rotational degrees of freedom in the equilibrium equations, and the correct directions of the unit vectors are computed by the iterative scheme by imposing the moment equilibrium constraint. The equilibrium equations and the associated solution procedure are explained, and the verification problems are solved.

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충격 압축에 의한 제논 가스의 이온화 특성 연구 (A Study of the Ionization Characteristics of Xenon Gas by Shock Compression)

  • 이대성;신재렬;최정열;최윤수;김형원
    • 한국군사과학기술학회지
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    • 제13권3호
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    • pp.493-502
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    • 2010
  • In this paper, the ionization characteristics of noble gases are studied numerically behind strong shock waves. As a first step, the equilibrium ionization mechanism of noble gases is modeled in wide ranges of temperature and pressure. As a next step the equilibrium ionization model is coupled with fluid dynamic equations to analyze the local thermodynamic equilibrium(LTE) ionization process at high temperature and pressure conditions behind the strong imploding shock waves. The ionization characteristics of xenon gas is studied in a wide range of test conditions with thermal radiation effects. Hence, the results give optimal conditions of maximum ionization and radiation behind the imploding shock waves.

직교이방성 I형 단면 압축재의 국부좌굴 주도요소판별 (Identification of Dominant Plate Component for Local Buckling of Orthotropic I-Shape Compression Member)

  • 김학군;채수하;정상균;윤순종
    • 한국복합재료학회:학술대회논문집
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    • 한국복합재료학회 2000년도 춘계학술발표대회 논문집
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    • pp.9-14
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    • 2000
  • This paper presents the analytical results of local buckling of orthotropic I-shape compression members. Employing the equilibrium approach, the characteristic equation for local buckling of I-shape compression member is derived. Using the derived equation, the minimum buckling coefficients with respect to the ratio of width to thickness for the I-shape column are suggested as a graphical form. In addition, the dominant plate component initiating the local buckling of I-shape column is also identified by using the approximate solution and the results are plotted with dotted line on the minimum bucking coefficient curve.

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GLOBAL STABILITY OF A NONLINEAR DIFFERENCE EQUATION

  • Wang, Yanqin
    • Journal of applied mathematics & informatics
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    • 제29권3_4호
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    • pp.879-889
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    • 2011
  • In this paper, we investigate the local asymptotic stability, the invariant intervals, the global attractivity of the equilibrium points, and the asymptotic behavior of the solutions of the difference equation $x_{n+1}=\frac{a+bx_nx_{n-k}}{A+Bx_n+Cx_{n-k}}$, n = 0, 1,${\ldots}$, where the parameters a, b, A, B, C and the initial conditions $x_{-k}$, ${\ldots}$, $x_{-1}$, $x_0$ are positive real numbers.

LTNE 모델을 이용한 다공성 채널 입구영역에서의 열전달 특성 해석 (Analysis of Heat Transfer Characteristics in the Thermally Developing Region of a Porous Channel by LTNE Model)

  • 이상태;이관수;김서영
    • 대한기계학회논문집B
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    • 제26권7호
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    • pp.983-990
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    • 2002
  • A numerical analysis has been carried out on forced convection heat transfer in the developing region of a porous channel. The channel is filled with an isotropic porous medium. At the channel walls, a uniform heat flux is given. Comprehensive numerical solutions are acquired to the Brinkman-Forchheimer extended Darcy equation and the LTNE model which does not employ the assumption of local thermal equilibrium between solid and fluid phases. Details of thermal fields in the developing region are examined over wide ranges of the thermal parameters. The numerical solutions at the fully developed region are compared with the previous analytical solutions. The correlation for predicting local Nusselt number in a porous channel is proposed.

토양 내 철의 이동특성에 관한 연구 (A Study on Transport Characteristics of Fe in Soil)

  • 조기철;이경호;정영헌;조상원;오광중
    • 대한환경공학회지
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    • 제27권10호
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    • pp.1043-1051
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    • 2005
  • 이류-확산 국부적 평형흡착모델(convection-dispersion local equilibrium sorption model)과 Two-site 비평형 흡착모델(non-equilibrium sorption model)을 이용하여 철(Fe)의 토양 내 흡착 및 이동특성을 살펴보았다. 회분실험에서는 철의 주입농도를 변화시키면서 시간에 따른 농도변화를 측정함으로써 철의 흡착특성을 선형흡착등온선과 Freundlich 흡착등온선으로 살펴보았으며, 칼럼실험에서는 주입유속, 유기물함량, 철의 농도를 변화시키면서 주입액과 유출액의 철의 농도를 측정하고, CXTFIT 프로그램을 이용하여 two-site 비평형 흡착 모델에 사용된 매개변수(D, R, ${\beta}$, ${\omega}$)를 구하였다. CXTFIT 프로그램에 의해 구하여진 매개변수들을 이용하여 철의 토양 내 이동특성을 살펴보았으며, 철과 같은 흡착성 물질의 이동특성은 two-site 비평형 흡착모델에 의해 예측할 수 있음을 알 수 있었다.