• 대한토목학회논문집
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• 제26권2C호
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• pp.89-98
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• 2006

본 연구에서는 해성점토의 전단강도를 증진시킬 목적으로 철과 알루미늄 전극을 직접 삽입한 후 전극을 분해하여 지반 고결화 효과를 유발하였다. 이를 위해 남해안에서 채취한 실제 해성점토에 대해 실내 토조를 이용한 파일럿 실험을 실시하였고, 각각 철과 알루미늄을 삽입한 후 일정 고전류(2.5A)를 적용시켰다. 고결화에 의한 영향을 파악하고자 실험 종료 후에는 콘관입시험기를 이용하여 비배수 전단강도를 측정하였으며, 위치별 함수비와 pH 및 전기전도도를 측정하여 철과 알루미늄의 전극분해에 의한 고결화 효과를 간접적으로 판단하였다. 철 전극 전기분해 실험 결과, 양(+)극부 근처에서의 함수비는 초기에 비해 35% 감소하였고, 음극부 근처에서는 13% 증가하였으나, 양극부에서 용출된 철 이온과 흙 입자의 고결화 작용에 의해 전체적으로 측정된 전단강도는 초기에 비해 상당히 증가하였다. 또한 알루미늄 전극을 이용하였을 경우, 철에 비해 비교적 균일한 전단강도 증진효과가 나타났으며, 그 개량정도 역시 더 크게 나타났다.

• 한국산학기술학회논문지
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• 제19권1호
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• pp.56-62
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• 2018

일반적으로 지반의 강도가 강한 지반은 입도분포가 양호하다고 예상할 수 있다. 그러나 Gap입도로 이루어진 지반으로 입도분포가 불량하더라도 지반의 강도가 강한 경우가 있다. 본 연구에서는 이와 같은 사실에 근거하여 인위적으로 조성한 Gap 입도시료와 입도분포가 균일한 시료, 양호한 시료를 직접전단시험을 통하여 지반의 강도정수를 구하고 이를 비교 분석하였다. 또한 13mm 골재와 19mm 골재를 이용한 평판재하시험으로 확대 적용하여 현장 적용성과 입도에 따른 강도 변화의 재현성을 확인하였다. 실험 결과 입자크기비와 내부마찰각이 상관관계가 있음을 확인 할 수 있었고, 특정한 입자 크기비의 범위에서 전단저항각이 상당히 커지는 것을 알 수 있었다. 또한 평판재하시험으로 극한지지력을 산정한 결과 입도조정법이 강도증가율에 크게 영향을 미치는 것을 알 수 있다. 따라서 위의 직접전단 시험을 통한 시험적 검증과 평판재하시험을 통한 재현성 확인을 통해 입도분포가 좋지 않음에도 간단한 입도 조정만으로 지반의 강도 증진을 유도할 수 있었다.

• 한국의류산업학회지
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• 제8권5호
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• pp.591-596
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• 2006

In order to analyze the tailorbility of different fabrics for men's suit, FAST system has been used for measuring the distribution of mechanical properties in this study. As results, cashmere mixed woolen fabrics showed the minimum degree in relaxation shrinkage, formability, and shear rigidity than any other fabrics, and also showed more than 6% as maximum level of extensibility. Thus, cashmere mixed woolen fabrics requires careful tailoring in lay-out, marking, and cutting. It is necessary to establish new tailoring criteria for automatic sewing with cashmere mixed woolen fabrics than any other fabrics, because they show more failure rate of tailorbility. There have been noticeably more variation of shrinkage and extension for woolen fabrics with cashmere mixed than 100% woolen fabrics by evaluating the formability of the suits when these are completed to suits through cutting and tailoring from fabrics. Especially nylon mixed woolen fabrics showed shrinkage overall, but polyester mixed woolen fabrics showed extension at waist area. Thus, it is necessary to adjust the appropriate overfeed rate considering the amount of shrinkage and extension while tailoring.

• 한국정밀공학회지
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• 제10권2호
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• pp.146-153
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• 1993

Thd specimens were melited in high frequency induction furnace. The samples for measurements were prepared by machining cylinder of 9.5mm diameter and 15mm height. These samples were then hot-pressed according to strain rate ( .epsilon. ). These samples were decanned and cut out, and subsequently heat treated at 1000 .deg. C for 4hours. These were investigated for the change of microstructure, domain pattern, X-ray diffraction and magnetic properties. The stress distributions in the specimens during compressing process were calculated by a finite element method program(SPID). The calculated stresses were effective stress( .sigma. $_{eff}$), compressive direction stress( .sigma. $_{z}$), and shear stress( .tau. $_{rz}$ ). These stresses were compared with the experimental data.a.a.

• Korea-Australia Rheology Journal
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• 제20권4호
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• pp.189-196
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• 2008

The pulsatile flow of blood through a stenosed artery under the influence of external periodic body acceleration is studied. The effect of non-Newtonian nature of blood in small blood vessels has been taken into account by modeling blood as a Casson fluid. The non-linear coupled equations governing the flow are solved using perturbation analysis assuming that the Womersley frequency parameter is small which is valid for physiological situations in small blood vessels. The effect of pulsatility, stenosis, body acceleration, yield stress of the fluid and pressure gradient on the yield plane locations, velocity distribution, flow rate, shear stress and frictional resistance are investigated. It is noticed that the effect of yield stress and stenosis is to reduce flow rate and increase flow resistance. The impact of body acceleration is to enhance the flow rate and reduces resistance to flow.

• International Journal of Vascular Biomedical Engineering
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• 제1권1호
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• pp.24-31
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• 2003

As endothelial cells are subject to flow shear stress, it is important to determine the detailed velocity distribution in microvessels in the study of mechanical interactions between blood and endothelium. This paper describes a velocity field of the arteriole in the rat mesentery using an intravital microscope and high-speed digital video system obtained by a highly accurate PIV technique. Red blood cells (RBCs) velocity distributions with spatial resolutions of $0.8{\times}0.8{\mu}m$ were obtained even near the wall in the center plane of the arteriole. By making ensemble-averaged time-series of velocity distributions, velocity profiles over different cross-sections were calculated for comparison. The shear rate at the vascular wall also evaluated on the basis of the ensemble-averaged profiles. It was shown that the velocity profiles were blunt in the center region of the vessel cross-section while they were steep in the near wall region. The wall shear rates were significantly small, compared with those estimated from the Poiseuille profiles.

• Korea-Australia Rheology Journal
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• 제21권3호
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• pp.193-200
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• 2009

We present a direct simulation technique for two-dimensional mold-filling simulations of fluids filled with a large number of circular disk-like rigid particles. It is a direct simulation in that the hydrodynamic interaction between particles and fluid is fully considered. We employ a pseudo-concentration method for the evolution of the flow front and the DLM (distributed Lagrangian multipliers)-like fictitious domain method for the implicit treatment of the hydrodynamic interaction. Both methods allow the use of a fixed regular discretization during the entire computation. The discontinuous Galerkin method has been used to solve the concentration evolution equation and the rigid-ring description has been introduced for freely suspended particles. A buffer zone, the gate region of a finite area subject to the uniform velocity profile, has been introduced to put discrete particles into the computational domain avoiding any artificial discontinuity. From example problems of 450 particles, we investigated the particle motion and effects of particles on the flow for both Newtonian and shear-thinning fluid media. We report the prolonged particle movement toward the wall in case of a shear-thinning fluid, which has been interpreted with the shear rate distribution.

• 한국주조공학회지
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• 제28권6호
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• pp.261-267
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• 2008

In-situ quasicrystalline icosahedral (I) phase reinforced Ti-based bulk metallic glass (BMG) matrix composites have been successfully fabricated by using two distinct thermal histories for BMG forming alloy. The BMG composite containing micron-scale Iphase has been introduced by controlling cooling rate during solidification, whereas nano-scale I-phase reinforced BMG composite has been produced by partial crystallization of BMG. For mechanical properties, micron-scale I-phase distributed BMG composite exhibited lower strength and plasticity compared to the monolithic BMG. On the other hand, nano-scale icosahedral phase embedded BMG composite showed enhanced strength and plasticity. These improved mechanical properties were attributed to the multiplication of shear bands and blocking of the shear band propagation in terms of isolation and homogeneous distribution of nanosize icosahdral phases in the glassy matrix, followed by stabilizing the mechanical and deformation instabilities.

• 한국가시화정보학회지
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• 제18권3호
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• pp.103-108
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• 2020

RBC (red blood cell) deformability is one of factors inducing blood shear thinning effect. Reduction of RBC deformability increases blood viscosity in high shear region. In this study, 3D printed chip with proper distribution of wall shear rate (WSR) was proposed to measure RBC deformability of blood samples. To fabricate 3D printed chip, the design of 3D printed chip determined through numerical simulation was modified based on the resolution of the 3D printer. For the estimation of pressure drop in the 3D printed chip, two bypass outlets with low and high WSR are exposed to atmospheric pressure through the needles. By positioning the outlet of needles in the gravity direction, the formation of droplets at bypass outlets can be captured by smartphone. Through image processing and fast Fourier transform (FFT) analysis, the frequency of droplet formation was analyzed. Since the frequency of droplet formation is related with the pressure at bypass, high pressure drop caused by reduction of RBC deformability can be estimated by monitoring the formation of blood droplets using the smartphone.

• 대한토목학회논문집
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• 제34권4호
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• pp.1317-1325
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• 2014

본 연구의 목적은 공간적 또는 지리적 데이터인 도시구조특성 요소의 공간자기상관성을 최소화 시킬 수 있는 공간샘플링 기법에 대해 제시하고자 한다. 연구의 주요결과와 시사점은 다음과 같다. 첫째, 공간적 또는 지리적 자료가 지니고 있는 공간자기상관성을 제거하기 위해서는 적절한 공간샘플링 방법을 사용하여야 한다는 점이다. 서울시 전체 행정구역별 대중교통 분담률에 관한 공간자기상관성을 측정한 결과 간 의존성이 상당히 높은 것으로 분석되었다. 하지만 적정한 거리(400m)이상을 이격 시켜 공간샘플링을 실시한 후 공간자기상관성이 제거됨을 확인하였다. 공간샘플링을 실시하지 않으면, 공간적 자료의 왜곡으로 인한 잘못된 결과가 도출되며, 이를 해결하기 위해서는 공간샘플링을 하여 표본을 추출하는 과정이 필수불가결 하다는 점이다. 둘째, 공간샘플링 전후의 대중교통 분담률에 영향을 미치는 도시공간구조 특성 요인이 달라진다는 점이다. 그러나 이는 공간적 자료에 존재하는 공간자기상관성을 통제하지 못한 왜곡된 결과이다.