• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2010년 춘계학술대회논문집
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• pp.551-555
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• 2010

Electrowetting is a versatile tool to handle tiny droplets and forms a backbone of digital microfluidics. Numerical analysis is necessary to fully understand the dynamics of electrowetting, especially in designing electrowetting-based devices, such as liquid lenses and reflective displays. We developed a numerical method to analyze the general contact-line problems, incorporating dynamic contact angle models. The method is based on the conservative level set method to capture the interface of two fluids without loss of mass. We applied the method to the analysis of spreading process of a sessile droplet for step input voltages and oscillation of the droplet for alternating input voltages in electrowetting. The result was compared with experimental data. It is shown that contact line friction significantly affects the contact line motion and the oscillation amplitude. The pinning process of contact line was well represented by including the hysteresis effect in the contact angle models. In level set method, in the mean time, material properties are made to change smoothly across an interface of two materials with different properties by introducing an interpolation or smoothing scheme. So far, the weighted arithmetic mean (WAM) method has been exclusively adopted in level set method, without complete assessment for its validity. We viscosity, thermal conductivity, electrical conductivity, and permittivity, can be an alternative. I.e., the WHM gives more accurate results than the WAM method in certain circumstances. The interpolation scheme should be selected considering various characteristics including type of property, ratio of property of two fluids, geometry of interface, and so on.

• International Journal of Concrete Structures and Materials
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• 제18권1E호
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• pp.3-9
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• 2006

Five slab specimens with predefined cracks are examined to evaluate the corrosion behavior of epoxy-coated bars in chloride contaminated concrete, using linear polarization method. The test specimens were subjected to alternating weekly cycles of ponding in a salt solution and drying for 48 weeks. Test results show that the current density of the specimen of normal steel bars becomes 0.715 ${\mu}A/cm^2$ indicating that the steel bars are in moderate or high corrosion condition. However, the corrosion rates of the specimens with damaged epoxy-coated bars are significantly below 0.1 ${\mu}A/cm^2$ and the bars appears to be in passive condition. The damaged epoxy-coated bars with a corrosion inhibitor of calcium nitrite showed a corrosion rate of 0.110 ${\mu}m/year$ or 56 percents of the corrosion rate of damaged epoxy-coated specimen without such an inhibitor, 0.195 ${\mu}m/year$. However, the corrosion rates of specimens containing the other two corrosion inhibitors, a combination of amines and esters or mixtures of organic alkenyl dicarboxyl acid salts are quite equivalent to the control specimen. The research technique of linear polarization resistance method has proven itself to be useful in measuring corrosion rates of reinforcement in concrete.

• Journal of Biosystems Engineering
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• 제37권4호
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• pp.265-270
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• 2012

Purpose: An analytic method to design excitation and emission filters of a multispectral fluorescence imaging system is proposed and was demonstrated in an application to poultry fecal inspection Methods: A mathematical model of a multispectral imaging system is proposed and its system parameters, such as excitation and emission filters, were optimally determined by linear discriminant analysis (LDA). An alternating scheme was proposed for numerical implementation. Fluorescence characteristics of organic materials and feces of poultry carcasses are analyzed by LDA to design the optimal excitation and emission filters for poultry fecal inspection. Results: The most appropriate excitation filter was UV-A (about 360 nm) and blue light source (about 460 nm) and band-pass filter was 660-670 nm. The classification accuracy and false positive are 98.4% and 2.5%, respectively. Conclusions: The proposed method is applicable to other agricultural products which are distinguishable by their spectral properties.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제14권9호
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• pp.3745-3761
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• 2020

Low-rank representation methods already achieve many applications in the image reconstruction. However, for high-gradient image patches with rich texture details and strong edge information, it is difficult to find sufficient similar patches. Existing low-rank representation methods usually destroy image critical details and fail to preserve edge structure. In order to promote the performance, a new representation-based image super-resolution reconstruction method is proposed, which combines gradient domain guided image filter with the structure-constrained low-rank representation so as to enhance image details as well as reveal the intrinsic structure of an input image. Firstly, we extract the gradient domain guided filter of each atom in high resolution dictionary in order to acquire high-frequency prior information. Secondly, this prior information is taken as a structure constraint and introduced into the low-rank representation framework to develop a new model so as to maintain the edges of reconstructed image. Thirdly, the approximate optimal solution of the model is solved through alternating direction method of multipliers. After that, experiments are performed and results show that the proposed algorithm has higher performances than conventional state-of-the-art algorithms in both quantitative and qualitative aspects.

• 한국전자파학회논문지
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• 제21권6호
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• pp.690-697
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• 2010

본 논문에서는 부호 교차 위상 개념이 적용된 유전 알고리즘을 이용한 널링 안테나(nulling antenna)의 연구 결과를 제시하였다. 기존 국내 및 국외에서 제안되었던 유전 알고리즘을 이용한 널 합성 방법들은 다수의 배열 소자를 갖는 경우에 빠르고 정확한 널 합성이 용이하지 않았다. 유전 알고리즘의 특성상 이진 부호로 표현된 위상 값들의 교배 및 변이를 통해 널을 합성하게 되므로 배열 소자의 개수가 늘어날수록 빠르고 정확한 널 합성이 힘들게 된다. 따라서 본 논문에서는 100개 이상의 배열 소자를 갖는 널링 안테나에서 널 합성에 사용되는 위상 값들이 전체 배열 소자들의 중심을 기점으로 대칭되는 값을 갖도록 하고, 인접 소자 간에 인가되는 위상값의 부호를 반대가 되도록 하는 개념이 적용된 유전 알고리즘을 제안하였으며, 기존 연구되었던 논문들에 비해 절반의 위상 값만을 구해 널을 합성하므로 수렴 속도를 크게 개선하였고, 또한 -70 dB 이상의 깊은 널을 정확한 위치에 합성해 내었다.

• 대한토목학회논문집
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• 제12권4호
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• pp.1-10
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• 1992

프리스트레스트 콘크리트 교량을 압출공법으로 가설하는 과정에서는 구조계가 계속하여 변하므로 교량의 주형에는 사용하중 상태에서와는 상이한 교번 단면력이 발생하게 된다. 이러한 단면력의 크기는 경간 길이, 추진코의 길이 및 강성등에 영향을 받게 된다. 본 논문에서는 많은 예제를 해석하여 이러한 요소들이 주형에 발생하는 최대 단면력에 미치는 영향을 연구하였다. 주프로그램의 복잡한 입력작업을 쉽게 처리할 수 있는 선처리 프로그램과 더불어 주형압출시 변화되는 구조계의 다단계 해석을 수행하여 최종적인 결과를 종합 출력할 수 있는 전산프로그램을 개발하였다. 압출공법으로 시공되는 박스거더교를 대상으로 하여 여러 가지 경간길이에 대한 구조해석을 수행한 결과로부터 경간 길이에 따른 최적 추진코길이와 강성비의 상호 관계를 제안하였다.

• Journal of Power Electronics
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• 제18권2호
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• pp.615-626
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• 2018

To ensure a DC current path and avoid large voltage overshoot of the DC-link inductor, alternating PWM pulses in the current-source rectifier should be supplemented by overlap time, which generates an overlap current and causes input current distortion. In this study, the influence of overlap time is illustrated by comparing the AC-side current before and after overlap time is added. The overlap current distribution caused by overlap time is discussed under different modulation carriers, including triangle carrier, positive-going carrier, and negative-going carrier. The quantitative relationship between the extra harmonics of the AC-side current and overlap time is based on the Fourier analysis. Based on the commutation analysis, a new carrier modulation scheme that can restrain overlap current is proposed. A 3 kW prototype is established to verify the effectiveness of the influence of overlap time and the proposed restraining modulation scheme.

• Macromolecular Research
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• 제17권12호
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• pp.1003-1009
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• 2009

Copolymers of N-vinylpyrrolidone (NVP) comonomer with styrene (St), hydroxypropyl methacrylate (HPMA) and carboxyphenyl maleimide (CPMI) were synthesized by free radical polymerization using 2,2'-azobisisobutyronitrile (AIBN) initiator in 1,4-dioxane solvent. The copolymers formed were characterized by FTIR, $^1H$ NMR and $^{13}C$ NMR techniques and their thermal properties were studied by DSC and TGA. Copolymer composition was determined by $^1H$ NMR and/or by elemental analysis and monomer reactivity ratios (MRR) were estimated by the linear methods of Kelen-Tudos (K-T) and extended Kelen-Tudos (EK-T) and the non-linear approach. Copolymers of St and HPMA with NVP formed blocks of one of the monomer units, whereas alternating copolymers were obtained in CPMI-NVP, depending upon the side chain substitution. The MRR values are discussed in terms of monomer structural properties such as electronegativity and electron delocalization. The sequence distribution of monomers in the copolymers was studied by statistical method based on the average reactivity ratios obtained by EK-T method.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1996년도 한국자동제어학술회의논문집(국내학술편); 포항공과대학교, 포항; 24-26 Oct. 1996
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• pp.612-615
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• 1996

In the continuous casting process, molten metal contacts the mold wall and the molten metal surface is subject to the mold oscillation. The mold oscillation results in the oscillation marks on the surface of solidified steel, which has undesirable effects on the quality of slabs. In order to reduce the oscillation marks by achieving soft contact of molten metal with the mold surface, alternating magnetic field is applied to the surface of molten metal. However, if the magnetic field strength becomes too strong, the melt flow induced by the magnetic field. causes the instability of the molten metal surface, which has also the bad influence on the slab quality. Therefore, it is very important to choose the optimal position of the inductor coil and the optimal level of electric power to minimize the surface defects. In the present work, as a first step toward the optimization problem of the process, numerical studies are performed to investigate the effects of coil position and the electric power level on the meniscus shape and the flow field. As numerical tools, the boundary integral equation method(BIEM) is used for the magnetic field analysis and the finite difference method (FDM) with orthogonal grid generation is used for the flow analysis.

• 한국게임학회 논문지
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• 제17권1호
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• pp.89-98
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• 2017

본 논문에서는 물리기반 동적 변형을 실시간에 안정적으로 시뮬레이션하는 새로운 ARAP(as-rigid-as-possible) 방법을 제안한다. 1, 2, 3차원 물체의 변형을 안정적이며, 빠르고, 일관성 있게 다루기 위하여 방향성 입자로 이루어진 변형 그래프를 도입하고 그에 따른 ARAP 변형에너지를 공식화한다. 방향성 입자의 안정적인 시간 적분을 위해서는 변분 공식화에 기반을 둔 내재적 시간 적분 기법을 개발한다. 또한 국지적/전역적 최적화를 교대로 반복 적용하여 방향성 입자의 최적 위치 및 회전을 구한다. 제안된 방법은 구현이 쉽고 복잡한 변형을 실시간에 시뮬레이션할 수 있을 정도로 빠르다.