• Transactions of the Korean Society of Automotive Engineers
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• v.24 no.2
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• pp.198-204
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• 2016

In this study, a wind tunnel test was conducted to measure the aerodynamic characteristics of a streamline-designed high-speed bus with the change of wind direction and speed and the result is compared with the aerodynamic performance of a commercialized high-speed bus model (Model-0) manufactured by Zyle Daewoo Bus Corp. Aerodynamic performance of the existing rear-spoiler was tested to prove its aerodynamic effect on the test model bus. From the study, it was found that 24.6 % of the total drag of the original bus model (Model-0) was reduced on the streamline-designed model bus(model-1) without the rear-spoiler but only 14.3 % of the total drag was reduced with the spoiler on the streamlined model bus. It means that the rear spoiler does not work properly with the streamlined model bus (model-1) and should be noted that an optimum design of a rear-spoiler of a vehicle is important to reduce the induced pressure drag and increase the driving stability of a vehicle against yaw motion. The experimental outcome was also compared to the previous numerical research result to evaluate the reliability of the numerical algorithm of the aerodynamic performance analysis of a vehicle. The error rate (%) of the numerical result to the experimental output is about 5.4 % and it is due to the simplified body configuration of the numerical model bus. The drag increases at the higher yaw angle because the transparent frontal area of the model vehicle increases and the downward force increases with the yaw angle as well. It has a positive effect to the driving stability of the vehicle but the moderated downward force should be kept for the fuel economy of a vehicle.

• Transactions of the Korean Society of Automotive Engineers
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• v.18 no.5
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• pp.100-107
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• 2010

This paper gives new conceptual descriptions of drag reduction mechanism owing to rotating wheel and moving ground condition when dealing with automotive aerodynamics. Using Computational Fluid Dynamics (CFD), flow simulation of three dimensional automobile configuration made by Vehicle Modeling Function (VMF) is performed and the influence of wheel arch, wheels, rotating wheel & moving ground condition to the automotive aerodynamic performance is analyzed. Finally, it is shown that rotating wheel & moving ground condition decreases automotive aerodynamic drag owing to the reduction of the induced drag led by the decrease of COANDA flow intensity of the rear trunk flow.

• Journal of Energy Engineering
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• v.15 no.1 s.45
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• pp.8-13
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• 2006

The oxidation behavior of $UO_2$, pellet was studied using an XRD and a thermogravimetric analyzer in the temperature range from 573 to 873 K and in the density range from 94.64 to 99.10% of theoretical density in air. It was found from the XRD study that $UO_2$ was completely converted to $U_3O_8$ in this experimental temperature range. The formation of $U_3O_8$ displays sigmoidal reaction kinetics. The oxidation rate was reduced with density. Induction time for the oxidation of $UO_2$ was delayed with density because of open pore formed in surface of $UO_2$ pellet. The activation energy for oxidation of $UO_2$ was determined to be 89.54 kJ/mol and 34.40 kJ/mol in the temperature range from 573 to 723 K and from 723 to 873 K, respectively.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.2
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• pp.163-170
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• 2008

The aeroelastic stability analysis of a soft-in-plane, composite hingeless rotor blade in hover and in forward flight has been performed by combining the mixed beam method and the aeroelastic analysis system that is based on a moderate deflection beam approach. The aerodynamic forces and moments acting on the blade are obtained using the Leishman-Beddoes unsteady aerodynamic model. Hamilton's principle is used to derive the governing equations of composite helicopter blades undergoing extension, lag and flap bending, and torsion deflections. The influence of key structural modeling issues on the aeroelastic stability behavior of helicopter blades is studied. The issues include the shell wall thickness, elastic couplings and the correct treatment of constitutive assumptions in the section wall of the blade. It is found that the structural modeling effects are largely dependent on the layup geometries adopted in the section of the blade and these affect on the stability behavior in a large scale.

• Korean Journal of Food Science and Technology
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• v.24 no.5
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• pp.428-439
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• 1992

Drying process in a fixed bed red pepper dryer was modeled and simulated. Drying efficiency describing the effectiveness of energy usage in red pepper drying was defined as a ratio of energy used for moisture evaporation to total energy consumption, and expressed in combination of measurable temperature variables. The efficiency was compared with real evaporative efficiency and tested in the simulated and experimental drying. An overall drying efficiency was derived, and analyzed for various control variables consisting of drying temperature, air recycle ratio and air flow rate. Optimal operation conditions of drying was then searched by Box's complex method by using it as an objective function. Carotenoids retention was simulated and put as a constraint of product quality in the optimization. The optimization results gave that two staged drying operation could improve the ding efficiency compared with single staged drying. As a technique for further energy saving automatic termination of drying appeared feasible by monitoring an exit air temperature from dryer.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.9 no.1
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• pp.59-69
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• 2001

The rotor blade is modeled using a composite box beam with arbitrary wall. The active constrained damping layers are bonded to the upper and lower surfaces of the box beam to provide active and passive damping. A finite element model, based on a hybrid displacement theory, is used in the structural analysis. The theory is capable of accurately capturing the transverse shear effects in the composite primary structure, the viscoelastic and the piezoelectric layers within the ACLs. A reduced order model is derived based on the Hankel singular value. A linear quadratic Gaussian (LQG) controller is designed based on the reduced order model and the available measurement output. However, the LQG control system fails to stabilize the perturbed system although it shows good control performance at the nominal operating condition. To improve the robust stability of LQG controller, the loop transfer recovery (LTR) method is applied. Numerical results show that the proposed controller significantly improves rotor aeromechanical stability and suppresses rotor response over large variations in rotating speed by increasing lead-lag modal damping in the coupled rotor-body system.

• Proceedings of the KSAR Conference
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• 2003.06a
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• pp.60-60
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• 2003

소의 난포란과 난구세포의 체외배양시 plasminogen activators(PAs)의 생산을 보고하였다 (Choi 등, 1998). 따라서 본 연구는 돼지 난포란 및 난구세포의 체외성숙시 PAs의 생산을 SDS-PAGE와 Zymogram을 이용하여 조사하였다. PCOCs는 도축암퇘지의 난소로부터 채취하여, 난구세포가 충실한 것만 선별하였으며, 실험구에 사용될 난구세포는 pipetting에 의해 분리하여 이용하였다. 돼지 신선정액은 D-PBS로 1,500 rpm, 5분간 2회 원심분리하여 정장물질을 제거하고, 3회째는 5mM caffein이 함유된 BO(Brackett과 Oliphant, 1985) 배양액으로 세정하였다. 처리한 돼지 정액은 1$\times$$10^{8}$ cells/$m\ell$로 조정하여 20${\mu}\ell$씩 분주하고 0, 1, 2, 3 또는 4시간 동안 39$^{\circ}C$ 5% $CO_2$, 95% 공기인 배양기에서 수정능획득을 유도하였다. 배양이 완료된 정액은 20${\mu}\ell$의 sample buffer(5% SDS, 20% glycerol, 0.0025% bromophenol blue 그리고 0.125M Tris HC1 buffer)에 넣어 -7$0^{\circ}C$ 동결기에 보관하였다. 전기영동은 4% stacking gel과 10% separating gel로 분리하였으며, 20 mA에서 90분간 실시하였다. Zymogram은 Choi 등(1988)의 방법에 따라 실시하여 PAs의 생산을 확인하였으며, 이상의 실험은 3반복을 실시하였다. 시험구 전체에서 urokinase type plasminogen activator(uPA)가 확인되었으며, 체외수정능 획득시간에는 차이가 없었다. 두 종류의 고분자량의 uPA의존성 영역이 나타났으며, 분자량은 65kD과 62 kD이었다. 이러한 결과로 볼 때 Hart 등(1986)이 uPA의 경우 다양한 영역의 분자량 변이를 확인할 수 있었다고 한 것과 동일하였으며, 돼지 정자가 체외수정능 획득시 uPA를 생산하는 것을 확인할 수 있었다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.6
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• pp.4024-4031
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• 2014

Nanofibers have attracted significant interest in many industrial fields because their high surface area and porosity. In addition, the continued use of petrochemical based polymers has caused the depletion of oil resources and accelerated the greenhouse effect by the emission of carbon dioxide. Therefore, biomass-based polymer has become a very important environmentally friendly alternative. In this study, nanofibers were fabricated by an electrospinning process using biomass based PEF(polyethylene furoate) prepared by the polymerization of 2,5-furandicaboxylic acid and ethylene glycol. Furthermore, the electrospun nanofiber was strongly affected by various parameters, such as the solvent, polymer concentration and electric field. In conclusion, nanofibers with an average fiber diameters of 200 - 700 nm could be prepared at polymer concentration of 15 wt% using HFIP, and their fiber diameter increased with increasing electric field.

• Membrane Journal
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• v.25 no.1
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• pp.32-41
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• 2015

High performance polysulfone microfiltration membranes with a high were successfully prepared by vapor induced phase separation (VIPS) coupled with non-solvent induced phase separation (NIPS) process. Asymmetric Membranes were prepared with PSF/DMF/PVP/PEG/DMSO/water mixed solutions and water/IPA coagulant. PSF, DMF, PVP, PEG, DMSO, water was used as a membrane polymer, a solvent, a hydrophilic polymer additive, a polar protic liquid polymer, a polar aprotic nonsolvent, and a polar protic nonsolvent in the casting solution, respectively. The addition of polar aprotic nonsolvents, and polar protic nonsolvents is a convenient and effective method to control membrane structure. In order to control the morphology of polymeric membranes, the spontaneous emulsification induced by drawing water vapor into the exposed casting solution surface has been used. Control of the internal morphology of polymeric membranes by using mixed coagulation solution such as water and IPA is discussed in the present work. The pure water permeability, pore size distribution, surface hydrophilicity and membrane morphology were investigated. Due to the addition of DMSO to casting solution, the mean pore size increased almost $0.2{\mu}m$ and the water flux increased about 1000-1800 LMH.

• Journal of the Korean Geotechnical Society
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• v.27 no.3
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• pp.75-83
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• 2011

Emerging issues related with fully coupled Thermo-Hydro-Mechanical (THM) behavior of unsaturated soil demand the development of a numerical tool in diverse geo-mechanical and geo-environmental areas. This paper presents general governing equations for coupled THM processes in unsaturated porous media. Coupled partial differential equations are derived from three mass balances equations (solid, water, and air), energy balance equation, and force equilibrium equation. With Galerkin formulation and time integration of these governing equations, finite element code is developed to find nonlinear solution of four main variables (displacement-u, gas pressure-$P_g$), liquid pressure-$P_1$), and temperature-T) using Newton's iterative scheme. Three cases of numerical simulations are conducted and discussed: one-dimensional drainage experiments (u-$P_g-P_1$), thermal consolidation (u-$P_1$-T), and effect of pile on surrounding soil due to surface temperature variation (u-$P_1$-T).