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MLS기반 변절점 유한요소 및 레벨셋 방법을 이용한 고체-유체 경계의 전산모사
임재혁(Jae Hyuk Lim),조영삼(Young-Sam Cho),임세영(Seyoung Im) 대한기계학회 2004 대한기계학회 춘추학술대회 Vol.2004 No.11
Tracking of evolving solid-fluid interfaces is treated using level set method and MLS-based finite element with variable nodes. Several applications will be illustrated to demonstrate the effectiveness of the present scheme
임재혁(Jae Hyuk Lim),한만희(Man-Hee Han),이준연(Jun-Youn Lee),박정순(Jeong Soon Park),엄윤용(Youn Young Earmme),임세영(Seyoung Im) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.11
Prediction of warpage and residual stress in semiconductor chip devices play an important role in chip design. However, there are a few uncertainties in warpage prediction due to unknown patterning material properties, and moisture effect on polymer film. To estimate patterning material properties, we adopt a composite plate analysis and experimental techniques. and measure the warpage of chip after drying at about 250℃ for 30min to remove moisture. In 100㎛, 80㎛ chip cases, finite element analysis result shows a good agreement with measured values, but for 50㎛ and 60㎛ chip cases, there exist a substantial deviation from the measured values due to local deformation from imperfection and defects inherently embedded in the patterning layer and nonuniform bonding between PIcoating and silicon.
국부적 비주기성을 갖는 이종재료의 해석을 위한 다절점 유한요소를 이용한 다중스케일 해석기법
임재혁(Jae Hyuk Lim),손동우(Dongwoo Sohn),임세영(Seyoung Im) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.10
We present a new multiscale method for locally-nonperiodic heterogeneous materials. By decomposing them into periodic part and nonperiodic part, multiscale finite element model is constructed in a straightforward manner. The periodic part is appropriately coarse-grained through homogenization process and the nonperiodic part is retained to capture the localizing phenomena of materials. For seamless transition from coarse scale meshes to fine scale meshes, we replace some elements consisting of the periodic part, in the vicinity of the nonperiodic part, by homogenized variable-node finite elements. To demonstrate the performance of the proposed method, several examples involving defects embedded in composite materials are given. It is shown that the proposed method have outstanding advantages over fully fine scale analysis in terms of computational costs without losing its accuracy.
이동최소제곱 다절점 유한요소를 이용한 새로운 전역-국부해석
임재혁,임세영,Lim, Jae-Hyuk,Im, Se-Young 한국전산구조공학회 2007 한국전산구조공학회논문집 Vol.20 No.3
본 연구에서는 이동최소제곱 다절점 유한요소를 이용한 새로운 전역-국부해석기법을 제시하였다. 다절점 유한요소는 요소의 변에 임의의 수 절점을 가질 수 있으므로, 여러 개의 유한요소를 요소망의 재구성 없이 동시적으로 결합시킬 수 있다. 이는 응력구배가 집중되는 곳에 유한요소망을 구성하는 데에 있어 큰 편의를 제공한다. 또한 기존의 전역-국부해석기법처럼 중첩된 요소망을 사용하거나, 지배방정식을 두 번 해석할 필요가 없기 때문에 매우 간편하고 정확하다. 제시된 방법론의 성능을 검증하기 위해 응력 집중과 관련된 다양한 다중스케일 문제를 해석하였다. We present a new global-local analysis with the aid of MLS(Moving Least Square) variable-node finite elements which can possess an arbitrary number of nodes on element master domain. It enables us to connect one finite element with a few finite elements without complex remeshing. Compared to other type global-local analysis, it does not require any superimposed mesh or need not solve the equilibrium equation twice. To demonstrate the performance of the proposed scheme, we will show several examples in relation to capturing highly local stress field using global-local analysis.
임재혁(Jae Hyuk Lim),조영삼(Young-Sam Cho),임세영(Seyoung Im) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.5
Our major concern is to develop a new efficient methodology for finite element analysis of welding processes. Level set method and a new finite element called MLS-based variable-node element are included in the method to deal with the evolving solid-fluid interface, generated from melting or solidification in the course of welding. This method is capable of solving a variety of multi-physics problems with evolving solid-fluid interfaces, only with the minimal adjustment of finite element meshes without a large scale remeshing. An accurate the sizes of HAZ(Heat Affected Zone) and MZ(Melting Zone) are now well predictable with new methodology when applied to welding processes. Several numerical examples are included to demonstrate the effectiveness and accuracy of the present scheme.
달착륙선 충격흡수장치용 알루미늄 허니콤의 Crush Strength에 관한 연구
김신,이혁희,김현덕,박정선,임재혁,황도순,Kim, Shin,Lee, Hyuk-Hee,Kim, Hyun-Duk,Park, Jung-Sun,Im, Jae-Hyuk,Hwang, Do-Soon 항공우주시스템공학회 2010 항공우주시스템공학회지 Vol.4 No.3
Understanding the crushing behaviour of aluminum honeycombs under dynamic loading is useful for crash simulations of vehicles and for design of impacting energy absorbers. In the study of honeycomb crushing under quasi-static, dynamic loading, the most important parameter is crush strength. Crush strength is indicated to energy absorption characteristic of aluminum honeycomb. In this study, Using Finite Element Analysis carried out crush strength of hexagonal aluminum honeycomb then the results was compared with Quasi-static test. Consequently, Crush strength is different in quasi-static loading and dynamic loading about 16%.
전자기식 충격흡수구조의 설계를 위한 동특성 해석 및 실험
이미선,배재성,황재혁,임재혁,Yi, Mi-Seon,Bae, Jae-Sung,Hwang, Jae-Hyuk,Im, Jae-Hyuk 항공우주시스템공학회 2012 항공우주시스템공학회지 Vol.6 No.1
A shock absorber with magnetic effects is suggested for a lunar space-ship expected to launch in 2025. The device consists of a copper steel combined tube, two magnets, and a piston. The piston is designed to move a magnet through the tube when it is pushed by an external impact. While the magnet is moving in the tube, it generates the eddy current force with the copper part of the tube and it also makes the large friction force with the steel part of the tube. Beside, it gets resistive forces against its movement such as the magnetic force with a steel-ring at the first time of the movement and the repulsive force with a same pole opposed magnet at the end time of the movement. In this thesis, results of analyses and experiments of each force are represented and the expected performance of the electromagnetic shock absorber is drawn from the results.
불일치 격자망의 효율적인 연결을 위한 3 차원 변절점 요소
손동우(Dongwoo Sohn),임재혁(Jae Hyuk Lim),임세영(Seyoung Im) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.11
A novel type of variable-node finite element is proposed to connect nonmatching meshes with two or three different resolutions. The shape functions of variable-node finite elements are derived through point interpolation. By introducing additional nodes on nonmatching interface, the only elements that are located on the interface can be converted into variable-node finite elements. Therefore, the proposed elements make it possible to connect nonmatching interface between the different-scale meshes in a seamless way. Throughout numerical examples, the performance of the three-dimensional variable-node finite elements is examined in terms of accuracy. Furthermore, it is shown that complex structures are modeled efficiently with the aid of three-dimensional variable-node finite elements.
다절점 유한요소를 이용한 비균질 재료의 다중스케일 균열 진전
손동우(Dongwoo Sohn),임재혁(Jae Hyuk Lim),임세영(Seyoung Im) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.10
An efficient algorithm for multi-scale crack propagation, with the aid of variable-node finite elements, is described in this paper. We split the domain into global(coarse) mesh zone far from the crack tip and local(fine) mesh zone containing crack tip. A homogenization scheme is employed for representing the majority of the global zone in which the periodicity of RVE (Represent Volume Element) is valid. To capture the highly localized features around defects, we simply refine the local region involving cracks, and its neighboring elements are replaced with variable-node elements, which connect the zones of different mesh resolution in a seamless way, meeting the nodal connectivity across the interface of the two mesh zones. To demonstrate the simplicity and effectiveness of the scheme proposed, we will show numerical examples in relation to multiscale crack propagation.