• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.3
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• pp.275-282
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• 2014

Particle-reinforced metal matrix composites exhibit a strengthening effect due to the particle size-dependent length scale that arises from the strain gradient, and thus from the geometrically necessary dislocations between the particles and matrix that result from their CTE(Coefficient of Thermal Expansion) and elastic-plastic mismatches. In this study, the influence of the size-dependent length scale on the particle-matrix interface failure and ductile failure in the matrix was examined using finite-element punch zone modeling whereby an augmented strength was assigned around the particle. The failure behavior was observed by a parametric study, while varying the interface failure properties such as the interface strength and debonding energy with different particle sizes and volume fractions. It is shown that the two failure modes (interface failure and ductile failure in the matrix) interact with each other and are closely related to the particle size-dependent length scale; in other words, the composite with the smaller particles, which is surrounded by a denser dislocation than that with the larger particles, retards the initiation and growth of the interface and matrix failures, and also leads to a smaller amount of decrease in the flow stress during failure.

• Journal of Institute of Control, Robotics and Systems
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• v.7 no.9
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• pp.749-757
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• 2001

We present a simple artificial landmark model and robust landmark tracking algorithm for mobile robot localization. The landmark model, consisting of symmetric and repetitive color patches, produces color histograms that are invariant under the geometric and photometric distortions. A stochastic approach based on the CONDENSATION tracks the landmark model robustly even under the varying illumination conditions. After the landmark detection, relative position of the mobile robot to the landmark is calculated. Experimental results show that the proposed landmark model is effective and can be detected and tracked in a clustered scene robustly. With the tracked single landmark, we extract geometrical information than achieve accurate localization.

• Journal of the Korean Vacuum Society
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• v.22 no.6
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• pp.277-284
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• 2013

Carbon coils could be synthesized using $C_2H_2/H_2$ as source gases and $SF_6$ as an incorporated additive gas under thermal chemical vapor deposition system. The Ni layer on the $SiO_2$ substrate was used as a catalyst for the formation of the carbon coils. The characteristics (formation densities, morphologies, and geometries) of the as-grown carbon coils on the substrate with or without the $H_2$ plasma pretreatment process were investigated. By the relatively short time (1 minute) $H_2$ plasma pretreatment on the Ni catalyst layered-substrate prior to the carbon coils synthesis reaction, the dominant formation of the carbon microcoils on the substrate could be achieved. After the relatively long time (30 minutes) $H_2$ plasma pretreatment process, on the other hand, we could obtain the noble-shaped geometrical nanostructures, namely the formation of the numerous carbon nanocoils along the growth of the carbon microcoils. This noble-shaped geometrical nanostructure seemed to play a promising role as the good catalyst support for holding the very tiny Ni catalyst grains.

• Journal of Korea Water Resources Association
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• v.54 no.8
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• pp.607-616
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• 2021

The purpose of this study is to simulate the transport of nonuniform sediment considering the hiding-exposure effect numerically. In order to calculate the transport of multi-disperse suspended sediment mixtures, the set of advection-diffusion equations for each particle class is solved. The applicability of the numerical model is examined by comparing the simulation results with experimental data. In this study, we calculate the vertical distribution of total concentration of sediment particles using two approaches: (1) by considering the mixture as represented by a single size; and (2) by combining the concentration of the sediment corresponding to several particle size classes; From the simulation results, it is shown that both approaches calculate reasonable results due to the narrow range of size distribution. Under the condition of nonuniform sediment, the critical shear stress of the sediment particle is influenced by the size-selective entrainment, i.e., hiding-exposure effect. It is shown in this study that the effect of hiding-exposure effect on the erosion rates of fine sand is negligibly small.

• Proceedings of the Korean Geotechical Society Conference
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• 2000.03b
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• pp.365-372
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• 2000

현장상황에 대한 불충분한 자료와 파괴 메커니즘에 대한 불완전한 이해로 인해 발생하는 가변성(variability)과 불확실성(uncertainty)은 암반사면공학뿐만 아니라 지반공학에서 흔히 접하게 되는 문제점이다. 특히 암반사면공학에서는 이러한 가변성과 불확실성이 불연속면의 방향 및 기하학적 특성, 그리고 실내실험 결과의 분산으로 나타난다. 그러나 안전율(factor of safety)의 개념을 기초로 하는 전통적인 결정론적 해석방법(deterministic analysis)은 이러한 분산을 고려하지 않은 채 단일 대표 값만을 이용하여 구조물의 안정성을 판단하여 왔다. 확률론적 해석방법(probabilistic analysis)은 이러한 가변성과 불확실성을 효과적으로 정량화하여 해석에 이용할 수 있는 방법 중의 하나로 제안되었다. 이러한 해석방법은 불연속면의 기하학적 특성과 강도 특성을 확률변수(random variable)로 취급하여 신뢰성이론(reliability theory)과 확률이론(probability theory)을 근거로 분석하였으며 이를 기초로 하여 Monte Carlo Simulation과 같은 해석법을 이용, 구조물의 붕괴가능성을 확률로 표현하였다. 확률론적 해석 방법은 기존의 안전율을 대체하여 구조물의 안정성을 붕괴확률(probability of failure)로 제안하였으며 이 붕괴확률은 안전율의 확률분포함수 (probability density function)에서 안전율이 1보다 작을 가능성을 확률로 나타낸 수치이다. 본 논문에서는 확률론적 해석방법을 이용하여 불연속면 특성들의 확률특성을 고찰하였으며 이를 기초로 하여 암반사면의 안정성 해석에 응용했다.

• Proceedings of the Korea Water Resources Association Conference
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• 2005.05b
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• pp.699-704
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• 2005

합리식(rational formula)은 일정한 강우강도를 갖는 호우로 인한 소유역의 첨두홍수량을 결정할 때 대표적으로 사용되고 있다. 기존의 합리식 틀 안에서 유역의 기하학적인 형상이 타원의 형태와 비슷하다면 유역의 형상을 고려한 수정된 합리식으로 첨두홍수량을 결정할 수 있다. 수정된 합리식에서는 강우가 전체 지속시간 동안 유역에 균등하게 분포한다는 기존의 합리식의 가정과는 달리 강우가 유효우량주상도의 각 시간간격에 균등하게 분포한다고 가정한다. 이러한 가정은 강우 지속시간이 도달시간 보다 작은 경우에도 합리식을 적용할 수 있음을 나타낸다. 따라서 본 연구에서는 유역의 기하학적인 형상이 타원형에 가까운 예곡천 유역에 합리식과 수정합리식을 적용 한 후 그 결과를 비교 분석하였다. 그 결과 수정합리식에의한 첨두유량이 합리식보다 상당히 적게 산정되었다. 이는 합리식이 식생이 발달한 투수유역에서 첨두유량을 과다 산정한다는 기존 연구결과와 일치하는 것이다. 따라서 수정합리식은 합리식 가정의 한계를 보완하면서 비교적 단순한 프로세스를 유지하고 있어 조건이 부합되는 소유역에서 유용할 것으로 판단되었다.

• Composites Research
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• v.18 no.2
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• pp.30-37
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• 2005

In this paper, geometrically non-linear finite element analyses were performed to study the mechanical behavior of the material system of the envelope of stratospheric airships. The microstructure of the load-bearing plain weave layer was identified and modeled. The Updated Lagrangian formulation was employed to consider the geometric non-linearity as well as the induced structural non-linearity for the fiber tows. The stress-strain behavior was predicted and the effective elastic modulus was calculated by numerical experiments. It was found the non-linear stress-strain curves were largely different from those by linear analysis. And non-linear elastic moduli were much higher than linear elastic moduli. The difference was more distinguishable when the tow waviness ratio was smaller.

• School Mathematics
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• v.15 no.4
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• pp.957-973
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• 2013

This study analyzed Secondary Mathematically Gifted' mathematical thinking processes demonstrated from the activities. They configured regular triangle tessellations in the Non-Euclidean hyperbolic disk model. The students constructed the figure and transformation to construct the tessellation in the poincare disk. gsp file which is the dynamic geometric environmen, The students were to explore the characteristics of the hyperbolic segments, construct an equilateral triangle and inversion. In this process, a variety of strategic thinking process appeared and they recognized to the Non-Euclidean geometric system.

• Computational Structural Engineering
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• v.10 no.1
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• pp.213-223
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• 1997

In the analysis of the behavior of a complex structure, it requires much time and cost to analyze its behavior by using shell elements at the early design concept. For the purpose of the decrease of time and cost, many researches have been performed with the intention to analyze its behavior through replacing a shell model by a simple beam model. In the present study, a method is proposed for determining a bending spring stiffness which means the flexibility for applying into the joints of the simple beam model. Geometrically nonlinear analysis is performed through the application of the determined flexibility into joints of the simple beam model. The nonlinear behavior of thin-walled tube shell structure can be described within a little error through the simple beam model with flexible joints.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.3C
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• pp.264-270
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• 2010

Non-planar screens such as cylinder and sphere shaped screens are widely used for high-resolution immersive visualization environments. An existing method employs quadric matrix that maps an image onto a curved screen. However if the shape of the screen changes or moves, the quadric matrix will not be valid. In this paper, we assume that the screen is a quadric shape and the screen movement or change are relatively small. Then we propose to use a piecewise planar approximations for the screen to compensate for the geometric distortion on a non-planar screen. We demonstrate the effectiveness and efficiency of the proposed method through experiments.