• Journal of Mechanical Science and Technology
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• 제20권12호
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• pp.2230-2241
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• 2006

This paper presents a sole application of boundary element method to the conjugate heat transfer problem of thermally developing laminar flow in a thick walled pipe when the fluid velocities are fully developed. Due to the coupled mechanism of heat conduction in the solid region and heat convection in the fluid region, two separate solutions in the solid and fluid regions are sought to match the solid-fluid interface continuity condition. In this method, the dual reciprocity boundary element method (DRBEM) with the axial direction marching scheme is used to solve the heat convection problem and the conventional boundary element method (BEM) of axisymmetric model is applied to solve the heat conduction problem. An iterative and numerically stable BEM solution algorithm is presented, which uses the coupled interface conditions explicitly instead of uncoupled conditions. Both the local convective heat transfer coefficient at solid-fluid interface and the local mean fluid temperature are initially guessed and updated as the unknown interface thermal conditions in the iterative solution procedure. Two examples imposing uniform temperature and heat flux boundary conditions are tested in thermally developing region and compared with analytic solutions where available. The benchmark test results are shown to be in good agreement with the analytic solutions for both examples with different boundary conditions.

• Coupled systems mechanics
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• 제9권1호
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• pp.5-28
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• 2020

Despite a widely-held belief that the finite element method is the method for the solution of solid mechanics problems, which has for 30 years dissuaded solid mechanics scientists from paying any attention to the finite volume method, it is argued that finite volume methods can be a viable alternative. It is shown that it is simple to understand and implement, strongly conservative, memory efficient, and directly applicable to nonlinear problems. A number of examples are presented and, when available, comparison with finite element methods is made, showing that finite volume methods can be not only equal to, but outperform finite element methods for many applications.

• Advances in Computational Design
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• 제9권2호
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• pp.81-96
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• 2024

Modeling and analyzing the dynamic behavior of fluid-soil-structure interaction problems are crucial in structural engineering. The solution to such coupled engineering systems is often not achievable through analytical modeling alone, and a numerical solution is necessary. Generally, the Finite Element Method (FEM) is commonly used to address such problems. However, when dealing with coupled problems with complex geometry, the finite element method may not precisely represent the geometry, leading to errors that impact solution quality. Recently, Isogeometric Analysis (IGA) has emerged as a preferred method for modeling and analyzing complex systems. In this study, IGA based on Non-Uniform Rational B-Splines (NURBS) is employed to analyze the seismic behavior of concrete gravity dams, considering fluid-structure-foundation interaction. The performance of IGA is then compared with the classical finite element solution. The computational efficiency of IGA is demonstrated through case studies involving simulations of the reservoir-foundation-dam system under seismic loading.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회A
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• pp.442-447
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• 2008

This paper presents a new approach to simulate fluid-solid interaction problems involving non-matching interfaces. The coupling between fluid and solid domains with dissimilar finite element meshes consisting of 4-node quadrilateral elements is achieved by using the interface element method (IEM). Conditions of compatibility between fluid and solid meshes are satisfied exactly by introducing the interface elements defined on interfacing regions. Importantly, a consistent transfer of loads through matching interface element meshes guarantees the present method to be an efficient approach of the solution strategy to fluid-solid interaction problems. An arbitrary Lagrangian-Eulerian (ALE) description is adopted for the fluid domain, while for the solid domain an updated Lagrangian formulation is considered to accommodate finite deformations of an elastic structure. The stabilized equal order velocity-pressure elements for incompressible flows are used in the motion of fluids. Fully coupled equations are solved simultaneously in a single computational domain. Numerical results are presented for fluid-solid interaction problems involving nonmatching interfaces to demonstrate the effectiveness of the methodology.

• 한국공간구조학회논문집
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• 제8권4호
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• pp.81-90
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• 2008

이 논문에서는 적분형 르장드르 다항식을 사용한 3차원 계층적 고체요소의 유한요소 정식화를 보여준다. 제안하는 육면체 고체요소는 절점, 변, 면, 그리고 내부모우드를 포함한은 4개의 서로 다른 모우드로 구성되어 있다. 영에너지 모우드와 일정변형률 조건을 확인하기 위해 고유치 시험과 조각시험이 수행되었다. 여기에 추가되어, 적응적 p-유한요소해석을 위해 유한요소해석으로부터 구한 후처리 응력값의 평활화에 기초를 둔 사후오차평가 기법이 연구된다. 자유도가 증가함에 따라 수렴속도측면에서 균등 p-분배와 불균등 p-분배에 의한 유한요소해의 차이점이 비교된다. 제안된 요소의 성능을 보이기 위해 간단한 캔틸레버보가 테스트되었다.

• Structural Engineering and Mechanics
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• 제76권3호
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• pp.379-393
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• 2020

In this paper, we propose an automatic procedure to improve the accuracy of finite element solutions using enriched 2D solid finite elements (4-node quadrilateral and 3-node triangular elements). The enriched elements can improve solution accuracy without mesh refinement by adding cover functions to the displacement interpolation of the standard elements. The enrichment scheme is more effective when used adaptively for areas with insufficient accuracy rather than the entire model. For given meshes, an error for each node is estimated, and then proper degrees of cover functions are applied to the selected nodes. A new error estimation method and cover function selection scheme are devised for the proposed adaptive enrichment scheme. Herein, we demonstrate the proposed enrichment scheme through several 2D problems.

• Structural Engineering and Mechanics
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• 제28권6호
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• pp.695-713
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• 2008

The aim of this contribution is to present a new link/beam finite element suitable for electrothermo-structural analysis of uni-axially graded materials. Continuous polynomial variation of geometry and material properties will be considered. The element matrix and relations for solution of Joule's heat (and its distribution to the element nodes) have been established in the sense of a sequence method of a coupled problem solution. The expression for the solution of nodal forces caused by a continuously distributed temperature field has also been derived. The theoretical part of this contribution is completed by numerical validation, which proves the high accuracy and effectiveness of the proposed element. The results of the performed experiments are compared with those obtained using the more expensive multiphysical link element and solid element of the FEM program Ansys. The proposed finite element could be used not only in the multiphysical analysis of the current paths and actuators but also in analysis of other 1D construction parts made of composite or uni-axially graded materials.

• 대한기계학회논문집
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• 제12권4호
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• pp.642-651
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• 1988

본 연구에서는 정적 혹은 동적인 하중을 받는 탄성체의 변위, 응력 등을 구할 수 있는 유한요소해석을 하였다. 이 경우에 얻어지는 대수적인 운동방정식은 비선형 적이지만 증분응력이 미소한 경우에는 선형화될 수 있다.따라서 유한요소식의 해법 도 선형적인 경우와 비선형적인 경우로 나누어 생각한다.선형문제에 대한 해법으로 는 (1) 정하중:Gauss소거법, (2) 동하중:모우드에 대한 해석 또는 Newmark의 직접적분 법을 사용했고, 비선형적인 문제에 대한 해법으로는 (1) 정하중:Newton-Raphson반복법, (2) 동하중 :Newton-Raphson 반복법에 의거한 Newmark의 직접적분법을 사용하였다. 비선형적인 문제의 풀이시에는 Newton-Raphson방법으로 반복하여 계산하면서 외력과 등가절점하중의 평형이 이루어지도록 하므로 상당히 많은 양의 계산이 필요한데, 이때 서로 종류가 다른 강성매트릭스의 수치적분시 각기 다른 차수의 Gauss-Legendre 적분 을 시도하여, 발생된 오차 및 계산시간의 변동 등을 고찰하므로써 계산량의 감소방안 을 찾아 보았다. 또한 초기응력이 균일한 경우, 선형해와 비선형해를 비교함으로써 증분응력의 영향을 무시하는 선형해석의 적용타당성을 검토하였다.

• Nuclear Engineering and Technology
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• 제54권8호
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• pp.2801-2808
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• 2022

The synergistic effect of ZrC nanoparticle pining and Re solution in W matrix on the thermal stability of tungsten was studied by investigating the evolution of the microstructure, hardness and tensile properties after annealing in a temperature range of 1000-1700 ℃. The results of metallography, electron backscatter diffraction pattern and Vickers micro-hardness indicate that the rolled W-1wt%Re-0.5 wt% ZrC alloy has a higher recrystallization temperature (1600 ℃-1700 ℃) than that of the rolled pure W (1200 ℃), W-0.5 wt%ZrC (1300 ℃), W-0.5 wt%HfC (1400-1500 ℃) and W-K-3wt%Re alloy fabricated by the same technology. The molecular dynamics simulation results indicated that solution Re atoms in W matrix can slow down the self-diffusion of W atoms and form dragging effect to delay the growth of W grain, moreover, the diffusion coefficient decrease with increasing Re content. In addition, the ZrC nanoparticles can pin the grain boundaries and dislocations effectively, preventing the recrystallization. Therefore, synergistic effect of solid solution Re element and dispersed ZrC nanoparticles significantly increase recrystallization temperature.

• 비파괴검사학회지
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• 제22권3호
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• pp.284-291
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• 2002

전기비저항법을 이용하여 2.25Cr-1Mo 강의 경년열화도를 평가하고자 하였다. 2.25Cr-1Mo 강이 $540^{\circ}C$에서 장시간 노출되었을 때 일어나는 미세조직 변화를 모사하기 위해 인공 열화를 실시하였으며 열화에 따른 미세조직 인자 (고용원소의 함량), 기계적 성질 (연성-취성 천이온도 ), 전기비저항을 측정하여 이들간의 상호관계를 구하고자 하였다. 열화재에서는 기지내의 고용 원소 (Mo 와 Cr)의 고갈이 나타났다. 연성-취성 천이온도는 열화 초반부에 급격히 증가 후 포화되는 경향을 보인 반면 전기비저항은 열화 초반부에 급격히 감소 후 포화되는 경향을 보였다. 즉, 열화 시간에 따른 연성-취성 천이온도의 변화 경향과 전기비저항의 변화는 서로 반대적으로 변화하는 관계를 나타내었다.