인장 하중을 받는 무한 고체에 포함된 다수의 다이아몬드 형 함유체 문제 해석을 위한 체적 적분방정식법

이정기(Jung-Ki Lee) 대한기계학회 2012 大韓機械學會論文集A Vol.36 No.1

체적 적분방정식법(Volume Integral Equation Method)이라는 새로운 수치해석 방법을 이용하여, 서로 상호작용을 하는 등방성 또는 이방성 다이아몬드 형 함유체를 포함하는 등방성 무한고체가 정적 인장하중을 받을 때 무한고체 내부에 발생하는 응력분포 해석을 매우 효과적으로 수행하였다. 즉, 등방성 기지에 다수의 등방성 또는 이방성 다이아몬드 형 함유체의 중심이 1) 정사각형 배열 형태 또는 2) 정육각형 배열 형태로 포함되어 있는 경우에, 다양한 다이아몬드 형을 포함하는 원형 실린더 함유체의 체적비에 대하여, 중앙에 위치한 다이아몬드 형 함유체와 등방성 기지의 경계면에서의 인장응력 분포의 변화를 구체적으로 조사하였다. 또한, 체적 적분방정식법을 이용하여 구한 해의 정확도를 검증하기 위하여, 체적 적분방정식법을 이용한 해를 유한요소법을 이용한 해와 비교해 보았다. A volume integral equation method (VIEM) is introduced for the solution of elastostatic problems in unbounded isotropic elastic solids containing multiple interacting isotropic or anisotropic diamond-shaped inclusions subject to remote uniaxial tension. The method is applied to two-dimensional problems involving long parallel diamond-shaped cylindrical inclusions. A detailed analysis of the stress field at the interface between the matrix and the central inclusion is carried out for square and hexagonal packing of the inclusions. The effects of the number of isotropic or anisotropic diamond-shaped inclusions and of the various fiber volume fractions for the circular inclusions circumscribing its respective diamond-shaped inclusion on the stress field at the interface between the matrix and the central inclusion are also investigated in detail. The accuracy and efficiency of the method are examined through comparison with results obtained using the finite element method.

인장 하중을 받는 무한 고체에 포함된 다수의 등방성 함유체 문제 해석을 위한 체적 적분방정식법

이정기(Jung-Ki Lee) 대한기계학회 2010 大韓機械學會論文集A Vol.34 No.7

체적 적분방정식법(Volume Integral Equation Method)이라는 새로운 수치해석 방법을 이용하여, 서로 상호작용을 하는 등방성 함유체를 포함하는 등방성 무한고체가 정적 인장하중을 받을 때 무한고체 내부에 발생하는 응력분포 해석을 매우 효과적으로 수행하였다. 즉, 등방성 기지에 다수의 등방성 함유체가 1) 정사각형 배열 형태 또는 2) 정육각형 배열 형태로 포함되어 있는 경우에, 다양한 함유체의 체적비에 대하여, 중앙에 위치한 등방성 함유체와 등방성 기지의 경계면에서의 인장응력 분포의 변화를 구체적으로 조사하였다. 또한, 체적 적분방정식법을 이용한 해를 해석해 또는 유한요소법을 이용한 해와 비교해 봄으로서, 체적 적분방정식 법을 이용하여 구한 해의 정확도를 검증하였다. A volume integral equation method (VIEM) is introduced for solving the elastostatic problems related to an unbounded isotropic elastic solid; this solid is subjected to remote uniaxial tension, and it contains multiple interacting isotropic inclusions. The method is applied to two-dimensional problems involving long parallel cylindrical inclusions. A detailed analysis of the stress field at the interface between the matrix and the central inclusion is carried out; square and hexagonal packing of the inclusions are considered. The effects of the number of isotropic inclusions and different fiber volume fractions on the stress field at the interface between the matrix and the central inclusion are also investigated in detail. The accuracy and efficiency of the method are clarified by comparing the results obtained by analytical and finite element methods. The VIEM is shown to be very accurate and effective for investigating the local stresses in composites containing isotropic fibers.

타원 섬유가 포함된 복합재료에서의 탄성 해석

이정기 ( Jung Ki Lee ) 한국복합재료학회 2011 Composites research Vol.24 No.6

체적 적분방정식법(Volume Integral Equation Method)이라는 새로운 수치해석 방법을 이용하여, 서로 상호작용을 하는 등방성 또는 이방성 타원 함유체를 포함하는 등방성 무한고체가 정적 인장하중을 받을 때 무한고체 내부에 발생하는 응력분포 해석을 매우 효과적으로 수행하였다. 즉, 등방성 기지에 다수의 등방성 또는 이방성 타원 함유체의 중심이 1) 정사각형 배열 형태 또는 2) 정육각형 배열 형태로 포함되어 있는 경우에, 다양한 타원을 포함하는 원형 실린더 함유체의 체적비에 대하여, 중앙에 위치한 타원 함유체와 등방성 기지의 경계면에서의 인장응력 분포의 변화를 구체적으로 조사하였다. 또한, 체적 적분 방정식법을 이용한 해를 유한요소법을 이용한 해 및 해석해와 비교해 봄으로서, 체적 적분방정식법을 이용하여 구한 해의 정확도를 검증하였다 A volume integral equation method (VIEM) is introduced for the solution of elastostatic problems in an unbounded isotropic elastic solids containing interacting multiple isotropic or anisotropic elliptical inclusions subject to remote uniaxial tension. The method is applied to two-dimensional problems involving Long parallel elliptical cylindrical inclusions. A detailed analysis of stress field at the interface between the matrix and the central inclusion is carried out for square and hexagonal packing of the inclusions. Effects of the number of isotropic or anisotropic elliptical inclusions and various fiber volume fractions for the circular inclusion circumscribing its respective elliptical inclusion on the stress field at the interface between the matrix and the central inclusion are also investigated in detail. The accuracy and efficiency of the method are examined through comparison with results obtained from analytical and finite element methods. The method is shown to be very accurate and effective for investigating the Local stresses in composites containing isotropic or anisotropic elliptical fibers.

Lattice Boltzmann 방법을 사용한 층류 및 난류 해석

최석기(Seok-Ki Choi),김성오(Seong-O Kim) 한국전산유체공학회 2010 한국전산유체공학회 학술대회논문집 Vol.2010 No.11

A finite volume formulation commonly employed in the well-known SIMPLE family algorithms is used to discretize the lattice Boltzmann euqations on a cell-centered, non-uniform grid. The convection terms are treated by a higher-order bounded scheme to ensure accuracy and stability of solutions, especially in the simulation of turbulent flows. The source terms are linearized by a convetional method, and the resulted algebraic equations are solved by a strongly implicit procedure. The method is applied to the a laminar flow and atubulent flow. The predicted solutions are compared with the experimental data, benchmark solution and the solutions by the conventional finite volume method. The results of these numerical experiments for laminar flow show that the present formulation of the lattice Bolzmann method is slightly more diffusive than finite volume method when the same numerical grid and convection scheme are used. For a turbulent flow the finite volume lattice Boltzmann method slightly under-predicts the reattachment length in a separated flow. In general the finite volume lattice Boltzmann method is as acurate as the conventional finite volume method in predicting the mean velocity and the pressure at the wall. These observations show that the present method is stable and accurate enough to be used in the practical simulations of laminar and tubulent flows.

분할격자체계를 이용한 천수흐름수치모형의 개발

김형준,이승오,조용식 한국방재학회 2008 한국방재학회논문집 Vol.08 No.04

Numerical implementation with a Cartesian cut-cell method is conducted in this study. A Cartesian cut-cell method is an easy and efficient mesh generation methodology for complex geometries. In this method, a background Cartesian grid is employed for most of computational domain and a cut-cell grid is applied for the peculiar grids where the flow characteristics are changed such as solid boundary to enhance the accuracy, applicability and efficiency. Accurate representation of complex geometries can be obtained by using the cut-cell method. The cut-cell grids are constructed with irregular meshes which have various shape and size. Therefore, the finite volume method is applied to numerical discretization on a irregular domain. The HLLC approximate Riemann solver, a Godunov-type finite volume method, is employed to discretize the advection terms in the governing equations. The weighted average flux method applied on the Cartesian cut cell grid for stabilization of the numerical results. To validate the numerical model using the Cartesian cut-cell grids, the model is applied to the rectangular tank problem of which the exact solutions exist. As a comparison of numerical results with the analytical solutions, the numerical scheme well represents flow characteristics such as free surface elevation and velocities in x-and y-directions in a rectangular tank with the Cartesian and cut-cell grids. 본 연구는 Cartesian 격자망을 기본으로 하여 복잡한 지형을 위한 격자를 간편하고 효율적으로 생성할 수 있는 기법인 분할격자체계를 제안하고자 한다. 분할격자기법은 전반적인 흐름영역의 격자는 균일한 크기의 Cartesian 격자로 표현하지만 수치모형의 정확성, 적용성 및 효율성을 증대시키기 위하여 흐름의 특성이 변하는 격자를 분할하여 처리하는 기법이다. 분할격자체계에 의한 격자망은 다양한 크기 및 형상을 지니게 되므로, 유한체적기법을 적용하여 복잡한 흐름영역을 위한 수치모형을 구성한다. HLLC Riemann 근사해법을 이용하여 지배방정식을 이산화하였으며, 수치해의 안정성을 기하기 위하여 TVD-WAF기법을 적용하였다. 분할격자체계를 이용한 수치모형을 검증하기 위하여 해석해가 존재하는 사각형수조의 자유진동흐름을 모의하였다. 해석해와 수치모의 결과를 비교하여 본 연구에서 제안된 기법이 균일격자 및 분할격자체계에서 자유수면변위 및 x-축 및 y-축 방향의 유속을 정확히 모의함을 확인하였다.

히트펌프 동적해석을 위한 이동경계법과 유한체적법의 비교

최준영(JunYoung Choi),이동찬(DongChan Lee),김용찬(Yongchan Kim) 대한설비공학회 2019 대한설비공학회 학술발표대회논문집 Vol.2019 No.-

Recently, various analysis methods have been developed to analyze transient behavior of a heat pump. Moving boundary method can analyze the dynamic behavior of a heat exchanger with short calculation time owing to simplification of lumped mass. However, there is a lack of research comparing which method is more appropriate between the advanced and the conventional methods. This study analyzes the dynamic behavior of the heat pump using the moving boundary method. In addition, the current study compares the result using the finite volume method and the result using the moving boundary method based on the experimental result. As a result, the finite volume method shows 4.2% higher accuracy in the condenser and the moving boundary method shows 7.6% higher accuracy in the evaporator. In terms of calculation time, the moving boundary method is 2.83 times faster than the finite volume method.

해석 기법 별 유체 슬로싱 현상에 대한 비교 분석

장유진(Y.J. Jang) 한국전산유체공학회 2020 한국전산유체공학회지 Vol.25 No.4

In a swaying tank partially filled with liquid, inertia of the liquid exerts body force on itself, causing a periodic motion of the free surface of the liquid. This might cause the tank sway, which leads to structural damages of it. This phenomenon is called “Liquid Sloshing.” Many researches on liquid sloshing including experiments were conducted through numerical methods like Finite Volume Method(FVM), Finite Element Method(FEM), and Smoothed Particle Hydrodynamics(SPH) Method and so on. Except for particle-based numerical methods, other numerical methods are required to simulate free surface shape of liquid. These grid-based methods use Volume of Fluid method(VOF) or Level-set method to imitate the free surface shape. In this Paper, It aims to simulate sloshing phenomena of 3-dimensional rectangular tank. FVM and VOF method, FEM and Level-set method, and a particle-based solver with SPH method are used for analyzing sloshing motions. The CFD results are compared with experimental data and other published computational data. The details of time history pressure data on the tank wall and the free surface shape are discussed to find characteristics of the numerical methods.

CIP법을 이용한 유체-고체 상호작용에 관한 수치해석

이정희(Jung Hee Lee),허남건(Namkeon Hur) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.11

An efficient co-simulation method for dynamic analysis of fluid-rigid body coupled systems is presented. The governing equation for fluid flow is formulated by a cubic interpolated propagation method which interpolates a spatial profile within each grid with a cubic polynomial. The multi-body dynamics system is formulated by differential algebraic equations with an implicit numerical integrator. In order to improve the solving speed, a semi-implicit coupling method is used in time domain, in which the position, velocity and force are communicated at pre-defined interface time step. The fluid solver gets the position, velocity, and angular velocity at the mass center point from the MBD solver. On return the MBD solver gets the force and torque from the CFD solver. A block grid index technique is proposed to efficiently search a grid to which a moving node belongs. Several examples are solved by the proposed method.

열전도 해석을 이용한 공기층의 유효열전도계수 추정

이현균(Lee, Hyeon-Kyun),손영우(Son, Young-Woo),이용준(Lee, Young-Jun),이상환(Lee, Sang-Hwan),이주희(Lee, Ju-Hee) 한국생태환경건축학회 2018 한국생태환경건축학회 논문집 Vol.18 No.6

FLUMEN 모형을 이용한 홍수범람모의

배용훈,고덕구,조용식 한국수자원학회 2005 한국수자원학회논문집 Vol.38 No.5

본 연구에서는 천수방정식을 지배방정식으로 하고, 유한체적법에 기반을 둔 FLUMEN 수치모형을 이용하여 홍수범람모의를 수행하였다. 실제 지형에서의 홍수범람모의 적용에 앞서 단순화된 문제들에 모형을 적용시켜 적용 타당성을 검증하였다. 수치계산 결과는 다른 기법을 통한 결과 및 수리모형실험 관측결과와 양호하게 일치하였다. 적용타당성의 검증 후, 실제 지형에서의 홍수범람을 모의하였다. 본 모형을 사용한 실제 지형에서의 홍수범람모의 결과는 향후 홍수범람지도 제 In this study, flood inundations have been simulated by using the numerical model FLUMEN solving the shallow-water equations with a finite volume method. Before applying to a real problem, the numerical model is first applied to simplified problems. Obtai