• 한국터널지하공간학회 논문집
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• 제4권3호
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• pp.207-216
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• 2002

기존 국내 터널 시공 시 터널의 갱구부는 터널 천단부의 안전성을 고려하여 충분한 아칭효과를 획득할 수 있는 위치를 선정해왔고 그 토피 두께는 평균 터널지름의 약 1.5배에서 2.0배 정도를 요구한다. 이러한 안정된 지층에 갱구부를 위치하도록 하기 위하여, 많은 환경훼손을 감수하며 대규모의 절토를 수행하였다. 그러나 최근에 이런 환경적인 문제를 해결하기 위한 저토피 터널 공법인 Pipe Roof 공법의 일종으로 AT-casing system이 개발되었다. 본 공법은 기존에 알려진 터널 보강공법에 비하여 기술적인 편이성과 정밀성은 물론이고 구조적으로도 매우 안정적이며, 3~5m의 토피 두께에서도 터널의 갱구부를 시공할 수 있어서 환경친화적인 터널을 형성할 수 있다고 판단된다.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2008년도 하계학술발표대회 논문집
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• pp.1134-1138
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• 2008

Electret filter media are used in general ventilation filters, disposable respirators, vehicle cabin filters, vacuum cleaners and room air cleaners. There are basic mechanisms of interception, inertial impaction, diffusion, gravitational settling, electrostatic attraction by which an aerosol particle can be deposited onto a fiber in a filter. The ability of fine particle removal strongly depends on the electrostatic forces between particles and polarized fibers. Thus, the stability of the fiber polarization is a major factor in the reliability of electret filters. In this study, electrical properties and filtration performance of electrospun filter media are quantitatively investigated. Electrical properties of electrospun filters have been studied on surface charge potential and surface charge density. Also the filtration performance of the electret filters are evaluated on collection efficiency. Electrospun filters show same collection efficiency with low pressure drop compare to commercialized HEPA filters. Surface charge potential and surface charge density of electrospun filters are increased with increasing applied voltage. Also collection efficiency of electrospun filters is increased with increasing surface charge potential and surface charge density.

• 에너지공학
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• 제24권2호
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• pp.144-153
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• 2015

저온에서 경유의 파라핀 왁스 생성 및 침전현상은 차량의 저온성능에 악영향을 준다. 본 연구에서는 경유에 바이오디젤, 등유, 저온특성첨가제를 혼합한 연료에 대해 연료조성에 따른 담점, 필터막힘점, 유동점 변화를 분석하였고, 경유의 저온특성에 따른 차량의 저온성능에 대해 평가하였다. 경유는 유동성향상 첨가제(WAFI)와 등유유분의 혼합량이 증가할수록 저온특성이 개선되었으며, 바이오디젤 혼합량이 증가할수록 저온특성이 악화되었다. WAFI는 필터막힘점 개선에, 등유유분은 담점 개선에 효과적이었다. 차량의 저온성능에 대하여 필터막힘점과 유동점의 영향성은 확인하였으나, 담점은 큰 영향이 없었다. 필터막힘점은 차량에 대해 저온에서의 운행가능 한계를 반영하였다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2008년도 춘계 학술발표회 초청강연 및 논문집
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• pp.938-946
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• 2008

This study is on sealing leakage holes where are in landfills to make clay cakes with clay particles, which have a negative surface charge using the method of electrophoresis. Generally, electrophoresis is the motion of charged particles in a colloid under the influence of an electric field; particles with a positive charge go to the cathode and negative to the anode. In this study in order to develop the prevention system of leakages of the leachate in landfills, one-dimensional electrophoresis tests were conducted for determining the properties of the motion of the electrophoresis and cutoff using the method of electrophoresis depending on various the effect factors such as types of clays, concentrations of the clays, and applied electric field. In case of the experiments of determining the optimum clays, Na and Ca-Bentonite, Na and Ca-Montmorillonite, which have greater zeta-potential, cation, exchange capacity as well as ability of cutoff, and Micro-cement inducing cementation were chosen and then the effect of those clays was investigated. Moreover, the properties of the motion and settling of the clays were investigated following electric field varied from 0 to 1V/cm at different concentration of the clays in order to determine both the properties of the motion of the clays and the efficiency of electric field when applying different direct current. Ultimately, the ability of cutoff was examined through measuring the permeability of the clay cakes derived from the one-dimensional electrophoresis tests.

• 공업화학
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• 제1권1호
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• pp.63-72
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• 1990

결정성 실리카의 표면을 아민(TEA, CTMAB, BETAC) 및 과산화물(BPO) 촉매를 사용하여 실란(A 187), 액상고무(CTBNx8), 비닐단량체(AA, MMA, 2-HEA, GMA) 등으로 차례로 반응시켜 새로운 표면처리 실리카를 제조하였다. 표면처리 효과를 검토하기 위하여 실리카를 에폭시 수지에 전체 혼합물 중 0~36%(부피 %)의 범위로 혼합하여 혼합 점도 및 침전율의 변화를 시험하였다. 실험 결과 표면 피복량은 반응 촉매의 양과 종류에 의존하였으며, 촉매량 0.1~20%에서 실리카에 대한 피복량은 2.5~5.8% 범위의 값을 표시하였고, 실리카의 표면이 실란/고무, 실란/고무/비닐로 점차 처리됨에 따라서 무처리물이나 실란처리물에 비하여 점도가 저하되었으며, 침전율도 낮은 값을 표시하였다. 표면처리 상태는 처리제의 종류에 따라서 각기 다른 특성을 나타내었다.

• Environmental Engineering Research
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• 제12권1호
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• pp.21-29
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• 2007

For this study, we polymerized polyacrylamide base flocculants (PAA) and tested their properties and settling efficiency as a treatment for potable water. The most common chemicals for potable water treatment in Korea are alum or PAC. However, due to various reasons (such as rainy season or algae), inorganic flocculants cannot be solely depended on to solve all the problems caused by the poor quality of inflow water. When PAA coupled with coagulants in a potable water purification process is used, the turbidity removal efficiency increases by a factor of three on a single chemical system using PAC (Raw water: 5.21 NTU; Treated PAA+PAC: 0.34 NTU; and, Treated PAC: 1.04 NTU). It is possible to offset the toxic effect of residual monomers in treated water using PAA, because the concentrations of residual acrylamide are less than 400 mg/L in the polymer itself and less than $0.04\;{\mu}g/L$ in the treated water base at a dosage of 0.1 mg/L. Therefore, PAAs may be a workable, and dependable, potable water treatment process for the high pollutant level of resource water.

• Journal of Microbiology and Biotechnology
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• 제13권3호
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• pp.378-384
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• 2003

Mesophilically-grown granular sludge seeded in thermophilic UASB reactor was monitored to better understand the start-up process of the reactor. The reactor was fed with a synthetic wastewater containing glucose. As COD loading rate increased stepwise, methane production rate increased. Maximum values of COD removal efficiency (95%) and methane production rate (5.3 l/day) were achieved by approximately day-80 and remained constant afterward. However, physicochemical and microbial properties of granules kept changing even after day-80. Specific methanogenic activity (SMA) was initially negligible, and increased continuously until day-153 and remained constant afterward, showing the maximum value of $1.51{\pm}0.13\;g\;CH_4-COD/g$ VSS/day. Deteriorated settling ability of granules recovered the initial value by day-98 and was maintained afterward, as determined by sludge volume index. Initially reduced granule size increased until day-126, reaching a plateau of 1.1 mm. Combined use of fluorescence in situ hybridization and confocal laser scanning microscopy (CLSM) allowed to localize families of Methanosaetaceae and Merhanosarcinaceae in granules with time Quantitative analyses of CLSM images of granule sections showed abundance patterns of the methanogens and numerical dominance of Methanosaeta spp. throughout the start-up period. The trend of SMA agreed well with abundance patterns of the methanogens.

• 대한기계학회논문집B
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• 제26권12호
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• pp.1715-1721
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• 2002

Numerical analysis was conducted to characterize the gas flow field and particle deposition on a horizontal freestanding semiconductor wafer under the laminar flow field at vacuum environment. In order to calculate the properties of gas, the gas was assumed to obey the ideal gas law. The particle transport mechanisms considered were convection, Brownian diffusion and gravitational settling. The averaged particle deposition velocities and their radial distributions fnr the upper surface of the wafer were calculated from the particle concentration equation in an Eulerian frame of reference for system pressures of 1 mbar~1 atm and particle sizes of 2nm~10$^4$ nm(10 ${\mu}{\textrm}{m}$). It was observed that as the system pressure decreases, the boundary layer of gas flow becomes thicker and the deposition velocities are increased over the whole range of particle size. One thing to be noted here is that the deposition velocities are increased in the diffusion dominant particle size range with decreasing system pressure, whereas the thickness of the boundary layer is larger. This contradiction is attributed to the increase of particle mechanical mobility and the consequent increase of Brownian diffusion with decreasing the system pressure. The present numerical results showed good agreement with the results of the approximate model and the available experimental data.

• Steel and Composite Structures
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• 제29권5호
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• pp.569-578
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• 2018

This paper aims to investigate the transient vibration behavior of functionally graded carbon nanotube (FG-CNT) reinforced nanocomposite plate resting on Pasternak foundation under pulse excitation. The plate is considered to be composed of matrix material and multi-walled carbon nanotubes (MWCNTs) with distribution as per the functional grading concept. The functionally graded distribution patterns in nanocomposite plate are explained more appropriately with the layer-wise variation of carbon nanotubes weight fraction in the thickness coordinate. The layers are stacked up in such a way that it yields uniform and three other types of distribution patterns. The effective material properties of each layer in nanocomposite plate are obtained by modified Halpin-Tsai model and rule of mixtures. The governing equations of an illustrative case of simply-supported nanocomposite plate resting on the Pasternak foundation are derived from third order shear deformation theory and Navier's solution technique. A converge transient response of nanocompiste plate under uniformly distributed load with triangular pulse is obtained by varying number of layer in thickness direction. The validity and accuracy of the present model is also checked by comparing the results with those available in literature for isotropic case. Then, numerical examples are presented to highlight the effects of distribution patterns, foundation stiffness, carbon nanotube parameters and plate aspect ratio on the central deflection response. The results are extended with the consideration of proportional damping in the system and found that nanocomposite plate with distribution III have minimum settling time as compared to the other distributions.

• 한국항만학회지
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• 제12권1호
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• pp.9-17
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• 1998

The evaluation structure of complex problems is composed of multi-attributes and hierarchy. A many studies were existed on this problems, but that based on the assumption that the evaluation elements were independent. The actual evaluation problems have the complexity, ambiguity and interlinkage among the elements. In this situation, the fuzzy evaluation process is very effective in settling the complex problems. For evaluation of large scale hierarchical MADM problem, the fuzzy evaluation algorithm is developed in this paper, and that is centering on the identification of fuzzy measures. In this study, we newly identified the weight and interaction among the evaluation attributes. The results of this study are as follows: we can identified the hierarchical structure of the evaluation problem which is composed of the evaluation structure, function and hierarchy; we improved the existed weighting method which could be accomplished by normalizing process, considering the uncertainty and new weight integrating method which come from Dempster-Shafer theory. And we take into account the interaction properties among more than 3 evaluation attributes, which can be compared with the existed studies in which only 2 evaluation attributes taked into account.