• 대한조선학회논문집
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• 제41권4호
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• pp.30-37
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• 2004

Flow characteristics of the inflow ahead of a rotating propeller attached to a container ship model were investigated using a two-frame PIV (Particle Image Velocimetry) technique. Ensemble-averaged mean velocity fields were measured at four different blade phases. The mean velocity fields show the acceleration of inflow due to the rotating propeller and the velocity deficit in the near-wake region. The axial velocity distribution of inflow in the upper plane of propeller is quite different from that in the lower plane due to the thick hull boundary layer. The propeller inflow also shows asymmetric axial velocity distribution in the port and starboard side. As the inflow moves toward the propeller, the effect of phase angle variation of propeller blade on the inflow becomes dominant. In the upper plane above the propeller axis the inflow has very low axial velocity and large turbulent kinetic energy, compared with the lower plane. The boundary layer developed along the bottom surface of stern hull forms a strong shear layer affecting vortex structure of the propeller near-wake.

• 대한조선학회논문집
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• 제45권6호
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• pp.620-630
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• 2008

The characteristics of complicated propeller wake influenced by hull wake are investigated by using a two-frame PIV (Particle Image Velocimetry) technique. As the propeller is significantly affected by the hull wake in a real marine vessel, the measurements of propeller wake under the hull wake would be certainly necessary for more reliable validation and the prediction of numerical simulation with wake modeling. Velocity field measurements have been conducted in a medium-size cavitation tunnel with a hull wake. Generally, the hull wake generated by the boundary layer of ship's hull produces the different loading distribution on the propeller blade in both upper and lower propeller planes. The difference of the propeller wake behaviors caused by the hull wake is discussed in terms of axial velocity, vorticity and turbulence kinetic energy distribution in the present study.

• International Journal of Fluid Machinery and Systems
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• 제9권4호
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• pp.287-299
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• 2016

In China, agricultural irrigation water often contains a lot of suspended sediment which may cause the nozzle wear. In this study, a new numerical simulation combing the Discrete Phase Model and a remeshing algorithm was conducted. The geometric boundary deformation caused by the erosion wear, was considered. The weight loss of the nozzle, the node displacement and the flow field were investigated and discussed. The timestep sensitivity analysis showed that the timestep is very critical in the erosion modeling due to the randomness and the discreteness of the erosion behavior. Based on the simulation results, the major deformation of the boundary wall due to the erosion was found at the corners between outlet portion and contraction portion. Based on this remeshing algorithm, the simulated erosion weight loss of the nozzle is 4.62% less compared with the case without boundary deformation. The boundary deformation changes the pressure and velocity distribution, and eventually changes the sediment distribution inside the nozzle. The average turbulence kinetic energy at the outlet orifice is found to decrease with the erosion time, which is believed to change the nozzle's spray performance eventually.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2009년도 제38회 동계학술대회 초록집
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• pp.438-438
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• 2010

The abnormal behavior of the argon metastable density during the E-H mode transition in argon ICP discharge was investigated. Lots of investigations including global models expected that during and after the mode transition of ICP discharge, the density of metastable increases with applied rf power (i.e. electron density). However, recent direct measurement of metastable density revealed that the metastable density of argon decreases with the applied power during and after the mode transition. This result may not be explained by the previous global model which is based on the assumption of the Maxwellian electron energy distribution function (EEDF). In this paper, to explain this abnormal behavior with simple manners, a simple global model taking account of the effect of the non-Maxwellian EEDFs incorporating into a set of coupled rate equations is proposed. The result showed that the calculated metastable density taking account of non-Maxwellian EEDF and its evolution during the transition has an abnormal behavior with electron density and is in good agreement with the previous measurement results, indicating the close coupling of electron kinetics and the behavior of metastable density. The proposed simple model is expected to provide qualitative kinetic insight to understand the behavior of the metastable density in various plasma discharges which typically exhibit non-Maxwellian distribution.

• 한국기계가공학회지
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• 제21권7호
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• pp.64-70
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• 2022

The aim of this study is to improve the purification efficiency of odor gas by increasing the contact area between an odor gas and adsorbent. To analyze the flow in the adsorption tower, the flow characteristics in the hollow activated carbon-adsorption tower are identified by applying the loss model, which is a porous flow analysis model. The flow characteristics are investigated for pressure loss, velocity distribution, turbulent kinetic energy, and residence time distribution. The results show that the hollow adsorption tower performs better than the solid adsorption tower in terms of pressure loss and performance. The inner diameter of the hollow region inside the adsorption tower is 0.64 m (Di/Do = 0.37). Furthermore, the adsorbent performance is unaffected even when adsorbent stages are installed to replace the adsorbent.

• 천문학회보
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• 제44권2호
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• pp.47.2-47.2
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• 2019

Observations indicate that turbulence in molecular clouds of the interstellar medium (ISM) is highly supersonic (M >> 1) and strongly magnetized (β ≈ 0.1), while in the intracluster medium (ICM) it is subsonic (M <~1) and weakly magnetized (β ≈ 100). Here, M is the turbulent Mach number and β is the ratio of the gas to magnetic pressures. Although magnetohydrodynamic (MHD) turbulence in such environments has been previously studied through numerical simulations, some of its properties as well as its consequences are not yet fully described. In this talk, we report a study of MHD turbulence in molecular clouds and the ICM using a newly developed code based the high-order accurate, WENO (Weighted Essentially Non-Oscillatory) scheme. The simulation results using the WENO code are generally in agreement with those presented in the previous studies with, for instance, a TVD code (Porter et al. 2015 &, Park & Ryu 2019), but reveal more detailed structures on small scales. We here present and compare the properties of simulated turbulences with WENO and TVD codes, such as the spatial distribution of density, the density probability distribution functions, and the power spectra of kinetic and magnetic energies. We also describe the populations of MHD shocks and the energy dissipation at the shocks. Finally, we discuss the implications of this study on star formation processes in the ISM and shock dissipation in the ICM.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제40회 동계학술대회 초록집
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• pp.433-433
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• 2011

Since the concept of graphene was established, it has been intensively investigated by researchers. The unique characteristics of graphene have been reported, the graphene attracted a lot of attention for material overcomes the limitations of existing semiconductor materials. Because of these trends, economical fabrication technique is becoming more and more important topic. Especially, the epitaxial growth method by sublimating the silicon atoms on Silicon carbide (SiC) substrate have been reported on the mass production of high quality graphene sheets. Although SiC exists in a variety of polytypes, the 3C-SiC polytypes is the only polytype that grows directly on Si substrate. To practical use of graphene for electronic devices, the technique, forming the graphene on 3C-SiC(111)/Si structure, is much helpful technique. In this paper, we report on the growth of graphene on 3C-SiC(111) surface. To investigate the morphology of formed graphene on the 3C-SiC(111) surface, the radial distribution function (RDF) was calculated using molecular dynamics (MD) simulation. Through the comparison between the kinetic energies and the diffusion energy barrier of surface carbon atoms, we successfully determined that the graphitization strongly depends on temperature. This graphitization occurs above the annealing temperature of 1500K, and is also closely related to the behavior of carbon atoms on SiC surface. By analyzing the results, we found that the diffusion energy barrier is the key parameter of graphene growth on SiC surface.

• 한국자동차공학회논문집
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• 제22권7호
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• pp.63-69
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• 2014

Domestic automobile companies have adopted drum type brake system for commercial vehicles. However recently those companies have been applying disc-brake system to solve vehicle control-instability and inefficient heat discharge performance of conventional drum brake system for a medium commercial vehicle. Because the kinetic energy of a running commercial vehicle is relatively high, the brake system should discharge lots of heat energy while braking. A ventilated type brake disc has been used to increase heat discharge performance of a brake system. The vent structure of a disc highly affects cooling efficiency. This paper compares thermal characteristics of three types of vent structure in JASO C421 braking condition. It is found that the slant bend type disc has the lowest temperature and thermal stress distributions in the braking condition.

• 한국자동차공학회논문집
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• 제22권7호
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• pp.48-56
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• 2014

Engine oil is an oil used for lubrication of various internal combustion engines. The main function is to reduce wear on moving parts; it also cleans, inhibits corrosion, improves sealing, and cools the engine by carrying heat away from moving parts. In engines, there are parts which move against each other. Otherwise, the friction wastes the useful power by converting the kinetic energy to heat. Those parts were worn away, which could lead to lower efficiency and degradation of the engine. It increases fuel consumption, decreases power output, and can induce the engine failure. This study was conducted to evaluate the relation between engine oil property changes and engine performance for the diesel engine. This test was performed by using 12L, 6 cylinder, heavy duty engines. Low SAPS 10W30 engine oil (two type engine oils) was used. Test procedure and method was in accordance with the modified CEC L-57-T97 (OM441LA) method. In this study, TAN, TBN, KV and metal components, engine power, blowby gas, A_F were presented to evaluate the relation with engine oil property changes and engine performance. TAN, TBN, KV and metal We found that the components were generally increased but engine performance did not change. This results mean that property changes did not affect on engine performance because those were not enough to affect engine performance.

• 청정기술
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• 제25권3호
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• pp.198-205
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• 2019

야자계 입상활성탄에 대한 Brilliant Green의 흡착 평형과 동역학 및 열역학 파라미터들을 다양한 초기농도($300{\sim}500mg\;L^{-1}$), 접촉시간(1 ~ 12 h) 및 흡착온도(303 ~ 323 K)를 변수로 하여 회분식 실험을 통하여 연구하였다. 흡착평형 값들은 Langmuir, Freundlich, Temkin, Harkins-Jura 및 Elovich 식으로 해석하였다. 그 결과는 Langmuir 식에 가장 잘 맞았으며, 평가된 Langmuir 무차원 분리계수 값($R_L=0.018{\sim}0.040$)과 Freundlich 상수값(1/n = 0.176 ~ 0.206)은 활성탄에 의한 Brilliant Green의 흡착이 효과적인 공정임을 보여주었다. Temkin 식에 의해 평가된 흡착열 관련상수($B=12.43{\sim}17.15J\;mol^{-1}$)는 물리흡착에 해당하였다. Harkins-Jura 식에 의한 등온선 매개변수($A_{HJ}$)는 온도가 증가할수록 이종 기공 분포도 증가함을 나타내었고, Elovich 식에 의한 최대흡착용량은 실험값보다 매우 적은 것으로 나타났다. 흡착공정은 유사이차반응속도식에 더 잘 맞았으며, 흡착과정은 입자내 확산이 율속단계였다. 입자내 확산속도 상수는 초기 농도가 커질수록 염료의 운동이 활발해졌기 때문에 증가하였다. 그리고 초기농도가 커질수록 경계층의 영향이 커졌다. Gibbs 자유에너지($-3.46{\sim}-11.35kJ\;mol^{-1}$), 엔탈피($18.63kJ\;mol^{-1}$) 및 활성화에너지($26.28kJ\;mol^{-1}$)는 흡착공정이 자발적이고, 흡열 및 물리흡착임을 나타냈다.