• Tribology and Lubricants
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• 제2권2호
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• pp.52-58
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• 1986

The contact problem of a rigid smooth plane and computer-slmuiated elastic rough surfaces is studied by divided the sampling intervals into three groups. An iso-parametric element ,is used to calculate the contact pressure-separation relationship accurately. It is obtained that: 1) the more asperity shows the higher contact pressure, 2) the smaller element gives the better results but the effect is negligible.

• 대한기계학회논문집
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• 제18권8호
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• pp.2113-2122
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• 1994

The 3-D FEM analysis for simulating the stamping operation of planar anisotropic sheet metals with arbitrarily-shaped tools is introduced. An implicit, incremental, updated Lagrangian formulation with a rigid-viscoplastic constitutive equation is employed. Contact and friction are considered through the mesh-normal, which compatibly describes arbitrary tool surfaces and FEM meshes without depending on the explicit spatial derivatives of tool surfaces. The consistent full set of governing relations, comprising equilibrium equation and mesh-normal geometric constraints, is appropriately linearized. The linear triangular elements are used for depicting the formed sheet, based on membrane approximation. Barlat's non-quadratic anisotropic yield criterion(strain-rate potential) is employed, whose in-plane anisotropic properties are taken into account with anisotropic coefficients and non-quadratic function parameter. The planar anisotropic finite element formulation is tested with the numerical simulations of the stamping of an automotive hood inner panel and the drawing of a hemispherical punch. The in-plane anisotropic effects on the formability of both mild steel and aluminum alloy sheet metals are examined.

• Nuclear Engineering and Technology
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• 제41권3호
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• pp.335-346
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• 2009

This paper deals with a hydroelastic vibration analysis of two rectangular plates partially coupled with a liquid, which is bounded by two plates and two rigid side walls. The wet displacement of each plate is assumed to be a combination of the modal functions of a dry uniform beam with a clamped boundary condition. As the liquid is assumed to be an ideal liquid, the displacement potential satisfying the Laplace equation is determined so that the liquid boundary conditions can meet the requirements at the rigid surfaces and the free liquid surface. The wet dynamic modal functions of each plate are expanded by using the finite Fourier transform to obtain an appropriate form of the compatibility requirement along the contacting surfaces between the plates and the liquid. The liquid-coupled natural frequencies of the plates are derived by using the Rayleigh-Ritz method. Finite element analyses using commercial software are carried out to verify the proposed theory. It is observed that the theoretical method agrees excellently with the three-dimensional finite element analyses results. The effects of the liquid depth and the liquid thickness on the normalized natural frequencies are investigated to identify the dynamic characteristics of the liquid coupled system.

• International Journal of Aeronautical and Space Sciences
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• 제14권4호
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• pp.356-368
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• 2013

The Korea Aerospace Research Institute plans to launch a lunar module by 2025, and so is carrying out a preliminary study. Landing stability on the lunar surface is a key design factor of a lunar module. In this paper, a 1/6 scale model of a lunar module is investigated, for its landing stability on non-level surfaces. The lunar module has four tripod legs, with aluminum honeycomb shock absorbers in each leg strut. ADAMS$^{TM}$, the most widely used multi-body dynamics and motion analysis software, is used to simulate the module's lunar landing. Three types of dampers in the struts (rigid, viscous, and aluminum honeycomb dampers), and two types of lunar surfaces (rigid and elastic) are considered. The Sforce function is adopted, to model the aluminum honeycomb dampers. Details on the modeling and analysis of the landing stability of the 1/6 scale lunar module and the simulation results are provided in this paper.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2009년도 추계학술대회 논문집
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• pp.33-37
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• 2009

Finite-element methods are used to study non-adhesive, frictionless rough contact of elastic and plastic solids. Roughness on spherical surfaces is realized by self-affine fractal. True contact area between the rough surfaces and flat rigid surfaces increases with power law under external normal loads. The power exponent is sensitive to surface roughness as well as the curvature of spherical geometry. Surface contact pressures are analyzed and compared for the elastic and plastic solids. Distributions of local contact pressure are shown dependent on the surface roughness and the yield stress of plastic solids.

• 한국염색가공학회지
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• 제16권5호
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• pp.35-41
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• 2004

Poly(ethylene terephthalate), polyimide(Kapton), and polypropylene surfaces were modified with argon low temperature plasma by RF glow discharge at 240m Torr, 40W to investigate the surface morphological changes due to the plasma treatment using atomic force microscopy(AFM). Analysis of the AFM images and Ra(average roughness) revealed that the plasma treatment resulted in significant ablation on the surfaces. The morphological changes and surface roughness, however, were different depending on material characteristics such as heat stability, presence of amorphous region, swelling phenomenon, and molecular structure of repeating unit. It was assumed that polypropylene due to its tertiary hydrogen was ablated easily compared to poly(ethylene terephthalate), and that polyimide was more resistant to the ablation than PET due to rigid skeleton of imide and stable phenyl ring structure.

• 정보처리학회논문지A
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• 제9A권1호
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• pp.99-104
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• 2002

본 논문에서는 벡터공간 $R_n$에서 정의된 Bezier곡선과 Bezier곡면을 Lie군(Lie group)에서 확장하는 일반적인 새로운 생성방법을 제시한다. 이 방법에 의해서 생성된 Bezier곡선과 Bezier곡면은 Lie군의 성질에 의해서 미분 가능한 구조를 갖는다. 이 방법은 공간상에서 움직이는 물체에 대한 부드러운 움직임을 묘사하거나 궤도생성에 사용할 수 있다.

• 대한수학회지
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• 제53권5호
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• pp.1077-1100
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• 2016

We develop an invariant local theory of Lorentz surfaces in pseudo-Euclidean 4-space by use of a linear map of Weingarten type. We find a geometrically determined moving frame field at each point of the surface and obtain a system of geometric functions. We prove a fundamental existence and uniqueness theorem in terms of these functions. On any Lorentz surface with parallel normalized mean curvature vector field we introduce special geometric (canonical) parameters and prove that any such surface is determined up to a rigid motion by three invariant functions satisfying three natural partial differential equations. In this way we minimize the number of functions and the number of partial differential equations determining the surface, which solves the Lund-Regge problem for this class of surfaces.

• 한국멀티미디어학회논문지
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• 제16권6호
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• pp.700-707
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• 2013

본 논문에서는 시간차 흉부 CT 영상의 폐 실질 비강체 정합을 위하여 영역 이진화 모델링과 지역적 변형 모델을 이용한 정합 기법을 제안한다. 제안 기법은 먼저 폐 혈관과 실질을 분할하고, 영역 이진화 모델링을 수행하여 두 영상 사이의 밝기값의 차이에 따른 정합 오차를 최소화 한다. 다음으로 초기 정합 기법으로 두 폐 표면을 전역적으로 정렬하고, 지역적 변형 변환 모델을 제안하여 비강체 정합을 수행한다. 또한, 정합 후 감산된 시간에 따른 밝기값 차이가 미리 정의된 칼라 맵을 이용하여 가시화 된다. 실험 결과는 제안기법이 10명의 환자에 대하여 최대호흡과 최소호흡 CT 영상에서 폐 실질을 정확하게 정합하였음을 보여주었다. 제안된 비강체 정합 기법은 폐 실질에 대한 정량적 분석 결과의 직관적인 칼라 매핑을 통하여 다양한 폐 질환의 정량적 분석에 유용하게 사용될 수 있다.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1988년도 한국자동제어학술회의논문집(국제학술편); 한국전력공사연수원, 서울; 21-22 Oct. 1988
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• pp.826-831
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• 1988

This paper presents an approach to segment an image into areas of surfaces, and to compute the surface properties from a gray-scale image in order to describe the surfaces for reconstruction of the 3-D shape of the objects. In general, an rigid body has several surfaces and many edges. But if it is not polyhedoron, it is necessary not only to describe the relation between surfaces, i.e. its line drawings but also to represent the surfaces' equations itself. In order to compute the surfaces' equation we use a probability of edge distribution. At first it is extracted edges from a gray-level image as much as possible. These are not only the points that maximize the change of an image intensuty but candidates which can be seemed to be edges. Next, other character of a surface (color, coordinates and image intensity) are extracted. In our study, we call the all feature of a surface as "texture", for example color, intensity level, orientation of an edge, shape of a surface and so on. These features of a surface on a pixel of an image plane are mapped to a point of the feature space, and segmented to each groups by cluster analysis on this space. These groups are considered to represent object surface in an image plane. Finally, the states of object surface in 3-D space are computed from distributional probability of local and overall statistical features of a surface, and from shape of a surface.a surface.