• 항공우주시스템공학회지
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• 제12권2호
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• pp.15-22
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• 2018

7개의 방정식으로 구성된 DIM을 사용하여 압축성 다상 유동에 대해 연구하였다. 액체와 기체의 상세한 경계면 유동 구조를 얻기 위해 5 차의 MLP와 변형된 HLLC 근사 리만 해법을 포함하는 고차 수치기법이 구현되었다. 수치 방법의 유효성 검증을 위해 물과 공기로 구성된 다양한 1차원 충격관 문제를 해석하였고, 불연속면에 대해 뛰어난 해상도를 얻을 수 있었다. 마하수 1.22의 충격파 조건에서의 2차원 공기-헬륨 기포에 대한 충격파 상호 작용을 수치 해석하였고, 충격파 현상들을 잘 모사하였으며 실험결과와 비교 검증하였다.

• 한국전산유체공학회지
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• 제17권3호
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• pp.99-107
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• 2012

In this paper, the shock waves in compressible solids and liquids are simulated using a six-equation diffuse interface multiphase flow model that is extended to the Cochran and Chan equation of state. A pressure relaxation method based on a volume fraction function and a pressure-correction equation are newly implemented to the six-equation model. The developed code has been validated by a shock tube problem with liquid nitromethane and an impact problem of a copper plate on a solid explosive. In addition, a new problem, an impact of a copper plate on liquid nitromethane, has been solved. The present code well shows the wave structures in compressible solids and liquids without any numerical oscillations and overshoots. After the impact of a solid copper plate on liquid, two shock waves (one propagates into liquid and the other into solid) are generated and a material interface moves to the impacting direction. The computational results show that the shock velocity inside the liquid linearly increases with the impact velocity.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2006년도 정기 학술대회 논문집
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• pp.365-372
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• 2006

A new meshfree formulation is developed for material discontinuity problems. A local interfacial jump function which is defined as hyperplane function is embedded in the meshless approximation and the approximation accurately models functions with jumps in the displacement and the derivative fields. Diffuse derivative technique copes with difficulty due to complexity of derivative computation of meshfree approximation. Collocation method with diffuse derivative accelerates computing speed for numerical solution. By solving inclusion and composite material problems, the robustness and effectiveness of the method are verified.

• International Journal of Naval Architecture and Ocean Engineering
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• 제3권4호
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• pp.263-273
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• 2011

The diffuse interface model of Saurel et al. (2008) is used for the computation of compressible cavitating flows around underwater missiles. Such systems use gas injection and natural cavitation to reduce drag effects. Consequently material interfaces appear separating liquid and gas. These interfaces may have a really complex dynamics such that only a few formulations are able to predict their evolution. Contrarily to front tracking or interface reconstruction method the interfaces are computed as diffused numerical zones, that are captured in a routinely manner, as is done usually with gas dynamics solvers for shocks and contact discontinuity. With the present approach, a single set of partial differential equations is solved everywhere, with a single numerical scheme. This leads to very efficient solvers. The algorithm derived in Saurel et al. (2009) is used to compute cavitation pockets around solid bodies. It is first validated against experiments done in cavitation tunnel at CNU. Then it is used to compute flows around high speed underwater systems (Shkval-like missile). Performance data are then computed showing method ability to predict forces acting on the system.

• 대한전자공학회논문지SP
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• 제48권3호
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• pp.1-12
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• 2011

대형 멀티터치스크린의 구현은 기존의 저항막, 정전용량, 초음파 방식으로는 기술 제약 및 비용 등의 문제로 구현에 어려움이 있어 주로 적외선을 이용하는 방식을 많이 사용한다. 적외선을 사용한 멀티터치스크린은 대형스크린을 구현하기 용이하지만 멀티터치에 기술적인 제한을 갖고 있는 경우가 많다. 이러한 단점을 보완하기 위해 적외선 카메라를 이용한 FTIR(Frustrated Total Internal Reflection), DI(Diffuse Illumination)방식들이 Microsoft의 차세대 유저인터페이스인 Surface를 통해 제안되었다. FTIR이나 DI 방식은 대형스크린의 구현이 쉽고 멀티터치의 개수에 제한을 받지 않는다. 하지만 FTIR은 터치 포인트의 검출은 쉬운 반면에 스크린의 크기와 재질, 적외선 LED 배열을 위한 모듈, 많은 소비전력 등의 단점을 가지고 있고 DI 방식은 구조상의 문제로 터치 검출이 어려운 반면 FTIR이 가지고 있는 단점을 해결할 수 있다. 본 논문에서는 기존에 제안된 DI 방식의 터치 포인트 검출시의 문제점을 해결하기 위해 손가락 외곽선을 이용한 영상처리 알고리즘, 광학 렌즈 왜곡 현상을 효과적으로 보정하기 위한 알고리즘에 대해 연구하였다. 또한 멀티터치의 터치 정확도를 높이기 위한 Calibration 알고리즘과 정확한 제스처 및 정확한 이동을 위한 Tracking 기법을 고안하였다. 연구 결과 DI 방식을 위해 본 논문에서 제안한 영상처리 알고리즘들은 간단하면서 쉽게 대형 멀티터치스크린 구현을 위한 효과적인 방법이 될 수 있을 것으로 판단된다.

• 대한기계학회논문집A
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• 제33권1호
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• pp.56-63
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• 2009

Cell migration is one of the essential mechanisms responsible for complex biological processes. Intensive researches have begun to elucidate the mechanisms and search intriguing conditions for efficient control of cell migration. One general mechanism that is widely applicable for cells including Escherichia coli, amoebae and endothelial cell is chemotaxis. The single cell study for bacterial chemotaxis has an advantage over studies with the population of cells in providing a clearer observation of cell migration, which leads to more accurate assessments of chemotaxis. In this paper, we propose a three-dimensional model considering a single bacterium to study its chemotaxis. The semi-implicit Fourier spectral method is applied for high efficiency and numerical stability. The simulation results reveal rich dynamics of cell migration and provide quantitative assessments of bacterial chemotaxis with various chemoattractant gradient fields.

• 전자공학회논문지A
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• 제33A권6호
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• pp.151-157
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• 1996

We propose a mechanism for the formation of pinholes in the Si-buffer layer, through the observations with varying the process- and structure variables in the SEPOX (selective poly-oxidation) process, an isolation method for sub-u DRAMs. Pinholes are formed through the accumulation of Si vacancies generated by the oxidation of Si, in which Si atoms leave the sites (vacancies) at the Si/SiO$_{2}$ interfaces and diffuse into the oxide to be oxidized near interface. In the course of the accumulation of Si-vacancies, the stress induced in the Si-buffer layer affects the migration of vacancies to result in the final size and distribution of pinholes. This paper may be, to our knowledge, the first report about the oxidation-induced pinhole in the Si/SiO$_{2}$ system.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회A
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• pp.1638-1642
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• 2008

Cell migration is one of the essential mechanisms responsible for complex biological processes. Intensive researches have begun to elucidate the mechanisms and search intriguing conditions for efficient control of cell migration. One general mechanism which is widely applicable for cells including neutrophil, Escherichia coli and endothelial cell is chemotaxis. Especially, understanding the chemotactic mechanics of cell crawling has important implications for various medical and biological applications. The single cell study for chemotaxis has an advantage over studies with the population of cells in providing a clearer observation of cell migration, which leads to more accurate assessments of chemotaxis. In this paper, we propose a three-dimensional model considering a single crawling cell to study its chemotaxis. The semi-implicit Fourier spectral method is applied for high efficiency and numerical stability. The simulation results reveal rich dynamics of cell.

• 한국염색가공학회지
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• 제11권4호
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• pp.50-56
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• 1999

The adhesive properties of polyester cord in rubber matrix were investigated according to the surface modification. The polyester cord was oxidized in sodium hypochlorite solution, and graft-polymerized with acrylic acid under the irradiation with ultraviolet light, and then coated with resorcinol-formaldehyde latex (RFL). The modified surface was checked with scanning electron microscope. The adhesive properties were measured by the full-Out method, and evaluated with regard to the energy of adhesion and the maximum load. The polyester was not oxidized in sodium hypochlorite solution, so the surface was not able to etch to produce the coarse topology. As the concentration of acrylic acid and the reaction time were increased, the graft yields were also increased. It was considered that the acrylic acid would swell the polyester and diffuse easily to the inner side of substrate. The adhesive properties of polyeser to rubber matrix were affected by the surface condition. Namely, the maximum load was almost same, but the energy of adhesion was rather higher In the polyester grafted with acrylic acid than in control one. We concluded that the flexible aliphatic chains of polyacrylic acid situated in the interface of cord and rubber matrix were distributed well the stress and strain all over the filler resulting the high energy of adhesion.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2006년도 춘계학술대회 논문집
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• pp.341-343
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• 2006

The current spectral shape matching method (SSMM), developed by Ahn and Shanmugam (2004), relies on the assumption that the path radiance resulting from scattered photons due to air molecules and aerosols and possibly direct-reflected light from the air-sea interface is spatially homogeneous over the sub-scene of interest, enabling the retrieval of water-leaving radiances ($L_w$) from the satellite ocean color image data. This assumption remains valid for the clear atmospheric conditions, but when the distribution of aerosol loadings varies dramatically the above postulation of spatial homogeneity will be violated. In this study, we present the second version of SSMM which will take into account the horizontal variations of aerosol loading in the correction of atmospheric effects in SeaWiFS ocean color image data. The new version includes models for the correction of the effects of aerosols and Raleigh particles and a method fur computation of diffuse transmittance ($t_{os}$) as similar to SeaWiFS. We tested this method over the different optical environments and compared its effectiveness with the results of standard atmospheric correction (SAC) algorithm (Gordon and Wang, 1994) and those from in-situ observations. Findings revealed that the SAC algorithm appeared to distort the spectral shape of water-leaving radiance spectra in suspended sediments (SS) and algal bloom dominated-areas and frequently yielded underestimated or often negative values in the lower green and blue part of the electromagnetic spectrum. Retrieval of water-leaving radiances in coastal waters with very high sediments, for instance = > 8g $m^{-3}$, was not possible with the SAC algorithm. As the current SAC algorithm does not include models for the Asian aerosols, the water-leaving radiances over the aerosol-dominated areas could not be retrieved from the image and large errors often resulted from an inappropriate extrapolation of the estimated aerosol radiance from two IR bands to visible spectrum. In contrast to the above results, the new SSMM enabled accurate retrieval of water-leaving radiances in a various range of turbid waters with SS concentrations from 1 to 100 g $m^{-3}$ that closely matched with those from the in-situ observations. Regardless of the spectral band, the RMS error deviation was minimum of 0.003 and maximum of 0.46, in contrast with those of 0.26 and 0.81, respectively, for SAC algorithm. The new SSMM also remove all aerosol effects excluding areas for which the signal-to-noise ratio is much lower than the water signal.