• 대한조선학회논문집
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• 제47권3호
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• pp.388-397
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• 2010

A two-dimensional time-domain, potential-theory-based fully nonlinear numerical wave tank (NWT) was developed by using boundary element method and the mixed Eulerian-Lagrangian (MEL) approach for free-surface node treatment. The NWT was applied to prediction of primary wave energy conversion efficiency of a bottom-mounted oscillating water column (OWC) wave power device. The nonlinear free-surface condition inside the chamber was specially devised to represent the pneumatic pressure due to airflow velocity and viscous energy loss at the chamber entrance due to wave column motion. The newly developed NWT technique was verified through comparison with given experimental results. The maximum energy extraction was estimated with various chamber-air duct volume ratios.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2002년도 봄 학술발표회 논문집
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• pp.717-722
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• 2002

The results of an experiment on the water purification of the porous concrete and its influence on the compressive strength are reported in this paper. Two different sizes of coarse aggregate of 5-10, and 10-20mm, and three absolute volume ratios of paste to aggregate of 30, 40 and 50 percent for a given size of aggregate were used. For the compressive strength, the concrete with the aggregate size of 5-10mm showed much higher strength than that with the aggregate size of 10-20mm. But, the compressive strength is higher when the ratio of paste to aggregate is smaller. In the water purification experiment, the amount of attached an organism on the porous concrete surface indirectly is examined by measuring the consumption of the Dissolved Oxygen (DO). The ability of the water purification is evaluated by the removal amount of the Total Phosphorus(T-P) and Total Nitrogen(T-N). The ability of the removal of the T-N and T-P in the test water is superior to a porous concrete with a smaller size of aggregate and a higher void content. These results are owing to a large specific surface area of the specimen. As a result, porous concrete using by-products has sufficient performance of water purification.

• Carbon letters
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• 제10권3호
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• pp.217-220
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• 2009

In this study, porous electrospun carbon fibers were prepared by electrospinning with PAN and $MgCl_2$, as a MgO precursor. MgO was selected as a substrate because of its chemical and thermal stability, no reaction with carbon, and ease of removal after carbonization by dissolving out in acidic solutions. $MgCl_2$ was mixed with polyacrylonitrile (PAN) solution as a precursor of MgO with various weight ratios of $MgCl_2$/PAN. The average diameter of porous electrospun carbon fibers increased from 1.3 to 3 ${\mu}m$, as the $MgCl_2$ to PAN weight ratio increased. During the stabilization step, $MgCl_2$ was hydrolyzed to MgOHCl by heat treatment. At elevated temperature of 823 K for carbonization step, MgOHCl was decomposed to MgO. Specific surface area and pore structure of prepared electrospun carbon fibers were decided by weight ratio of $MgCl_2$/PAN. The amount of hydrogen storage increased with increase of specific surface area and micropore volume of prepared electrospun carbon fibers.

• 한국식품과학회지
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• 제35권1호
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• pp.33-37
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• 2003

잣죽의 제조조건이 죽의 기호도에 미치는 영향을 조사하였다. 잣죽의 제조조건인 주입액의 양(쌀 무게에 대한 물의 체적 비), 잣 첨가량(쌀 무게에 대한 잣의 무게 비) 및 호화를 위한 가열조리시간을 요인변수로 중심합성계획법에 의하여 실험을 설계하고 기호도를 반응변수로 하여 그 조사 결과에 대하여 반응표면분석을 진행하였다. 주입액의 양, 잣 첨가량 및 가열시간 모두가 색상에 대한 기호도에 크게 영향을 미치지 않았고 주입액의 양과 잣 첨가량은 10% 유의수준에서 향에 영향을 주었다. 점성과 전반적 기호도에 대하여 주입액의 양은 1% 유의수준에서, 가열조리시간은 5%의 유의수준에서 영향을 미쳤다. 잣죽에 대한 기호도 검사에서 전반적 기호도는 많이는 점성에 좌우되었고 색상의 영향을 가장 적게 받았다.

• Wind and Structures
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• 제38권4호
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• pp.261-275
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• 2024

Before performing an experimental study on the downburst-generated wave, it is necessary to examine the scale effects and corresponding corrections or compensations. Analysis of similarity is conducted to conclude the non-dimensional force ratios that account for the dynamic similarity in the interaction of downburst with wave between the prototype and the scale model, along with the corresponding scale factors. The fractional volume of fluid (VOF) method in association with the impinging jet model is employed to explore the characteristics of the downburst-generated wave numerically, and the validity of the proposed scaling method is verified. The study shows that the location of the maximum radial wind velocity in a downburst-wave field is a little higher than that identified in a downburst over the land, which might be attributed to the presence of the wave which changes the roughness of the underlying surface of the downburst. The impinging airflow would generate a concavity in the free surface of the water around the stagnation point of the downburst, with a diameter of about two times the jet diameter (D_jet). The maximum wave height appears at the location of 1.5D_jet from the stagnation point. Reynolds number has an insignificant influence on the scale effects, in accordance with the numerical investigation of the 30 scale models with the Reynolds number varying from 3.85 × 10⁴ to 7.30 × 10⁹. The ratio of the inertial force of air to the gravitational force of water, which is denoted by G, is found to be the most significant factor that would affect the interaction of downburst with wave. For the correction or compensation of the scale effects, fitting curves for the measures of the downburst-wave field (e.g., wind profile, significant wave height), along with the corresponding equations, are presented as a function of the parameter G.

• 한국구조물진단유지관리공학회 논문집
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• 제13권1호통권53호
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• pp.161-168
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• 2009

본 연구에서는 강섬유보강 콘크리트의 시공성 및 품질향상 방안의 일환으로 고유동 자기충전 콘크리트(HSCC)에 형상비 및 길이를 달리한 강섬유(SF)를 혼입한 콘크리트를 제조하여 강섬유보강 일반콘크리트(CC)와 유동 및 강도 특성을 비교 검토하였다. 실험결과 SF를 혼입한 HSCC는 높은 유동성 및 점성의 영향으로 SF 자체의 뭉침현상이 발생하지 않아 강섬유보강 CC의 경우보다 유동성능 및 통과성능이 크게 향상 되었으며, 동일한 압축강도 범위에서 SF를 혼입하지 않은 HSCC의 경우보다 쪼갬 및 휨강도는 SF의 형상비와 관계없이 길이가 길어질수록 증가하는 경향이 나타났다. 이상의 실험결과를 통하여 강섬유를 혼입한 HSCC를 현장 적용할 경우 기존에 사용되고 있는 강섬유보강 CC의 경우보다 시공성 및 품질 향상이 가능할 것으로 판단된다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.94-94
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• 2013

The Cr-Zr-N films have much improved mechanical properties and very smooth surface roughness. However, in spite of their outstanding properties, the Cr-Zr-N coatings revealed their mechanical properties deteriorated severely with increasing Zr content at $500^{\circ}C$ ecause of very rapid oxidation. Recently oxynitride films have been widely studied due to their excellent unique mechanical properties and oxidation resistance. In this work, CrZr-O-N films with various O contents were synthesized by unbalanced magnetron sputtering with Cr-Zr segment targets (Cr:Zr volume ratios is 1：1) and all films were prepared in a nitrogen rich mixture of N2 and O2. Characteristics such as crystalline structure, hardness and chemical composition as a function of the O content were investigated by X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), microhardness testing system and energy dispersive spectroscopy (EDS). Results showed that the thin films had dense and compact microstructure as O content in the films increases. The microstructure of the thin films consisted of mainly crystalline Cr (Zr)N phase and Cr2O3 phase. The maximum hardness and elastic modulus of the films was measured to be approximately 33.2 GPa and 280.6 GPa from the films with low content of O elements. Detailed experimental results will be presented.

• International Journal of Naval Architecture and Ocean Engineering
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• 제7권3호
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• pp.580-594
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• 2015

Liquid sloshing in two-dimensional (2-D) and three-dimensional (3-D) rectangular tanks is simulated by using a level set method based on the finite volume method. In order to examine the effect of natural frequency modes on liquid sloshing, we considered a wide range of frequency ratios ($0.5{\leq}fr{\leq}3.2$). The frequency ratio is defined by the ratio of the excitation frequency to the natural frequency of the fluid, and covers natural frequency modes from 1 to 5. When fr = 1, which corresponds to the first mode of the natural frequency, strong liquid sloshing reveals roof impact, and significant forces are generated by the liquid in the tank. The liquid flows are mainly unidirectional. Thus, the strong bulk motion of the fluid contributes to a higher elevation of the free surface. However, at fr = 2, the sloshing is considerably suppressed, resulting in a calm wave with relatively lower elevation of the free surface, since the waves undergo destructive interference. At fr = 2, the lower peak of the free surface elevation occurs. At higher modes of $fr_3$, $fr_4$, and $fr_5$, the free surface reveals irregular deformation with nonlinear waves in every case. However, the deformation of the free surface becomes weaker at higher natural frequency modes. Finally, 3-D simulations confirm our 2-D results.

• 상하수도학회지
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• 제34권6호
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• pp.425-435
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• 2020

Numerous chemical modifications on activated carbon such as acidic conditioning, thermal treatment and metal impregnation have been investigated to enhance adsorption capacities of micropollutants in water treatment plants. In this study, chemical modification including acidic, alkaline treatment, and iron-impregnation was evaluated for adsorption of 2,4-dichlorophenol (2,4-DCP). For Fe-impregnation, three concentrations of ferric chloride solutions, i.e., 0.2 M, 0.4 M, and 0.8 M, were used and ion-exchange (MIX) of iron and subsequent thermal treatment (MTH) were also applied. Surface properties of the modified carbons were analyzed by active surface area, pore volume, three-dimensional images, and chemical characteristics. The acidic and alkaline treatment changed the pore structures but yielded little improvement of adsorption capacities. As Fe concentrations were increased during impregnation, the active adsorption areas were decreased and the compositional ratios of Fe were increased. Adsorption capacities of modified ACs were evaluated using Langmuir isotherm. The MIX modification was not efficient to enhance 2,4-DCP adsorption and the MES treatment showed increases in adsorption capacities of 2,4-DCP, compared to the original activated carbon. These results implied a possibility of chemical impregnation modification for improvement of adsorption of 2,4-DCP, if a proper modification procedure is sought.

• 폴리머
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• 제36권3호
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• pp.321-325
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• 2012

본 연구에서는 화학적으로 활성 흑연나노섬유를 제조하여 그에 따른 전기화학적 거동을 확인하였다. 활성화제로 KOH를 사용하였으며, KOH와 흑연나노섬유의 비를 무게비로 각각 0, 1, 2, 4, 및 5로 처리하여 표면과 기공특성을 연구하였고, 그에 따른 전기화학적 거동을 살펴보았다. 활성화된 흑연나노섬유의 결정구조와 표면특성은 각각 X-선 회절분석법(XRD), 주사전자현미경(SEM) 분석방법을 이용하여 확인하였으며, 기공 특성은 비표면적 장치(BET)를 이용하였으며 질소흡착 등온선에 의해 조사하였다. 전기화학적 특성은 10 mV/s의 주사속도로 순환전류전압(cyclic voltammetry)을 통한 곡선으로 고찰하였으며 정전류법(galvanostatic method)으로 측정된 충방전 곡선을 통해 비축전용량을 계산하였다. 실험 결과로부터, 활성 흑연나노섬유의 전기화학적 거동은 KOH 양이 증가함에 따라 향상되었으며, 4 배 처리된 활성 흑연나노섬유가 최대의 비축전용량을 가진 것으로 나타났다. 이것은 KOH 활성화에 의해 활성 흑연나노섬유의 비표면적과 기공부피가 증가하기 때문인 것으로 사료된다.