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최호연(Choi, Ho-Yeon),이상민(Lee, Sang-Min),이구연(Lee, Goo-Yeon) 강원대학교 산업기술연구소 2011 産業技術硏究 Vol.31 No.1
Recently, smartphones have been widely used in wireless communications which caused severe data overload in cellular networks. Cellular companies consider increasing wireless data capacity in overloaded areas. Determining overloaded areas is mainly made from user reports which are currently collected by calling or simple apps by some active users experiencing overloads. Since the current reporting method is inconvenient and does not contain detail information about the overload conditions, and therefore is used by only some active users, the overloaded areas determined from the reports are not likely to be accurate. Therefore, we need a new reporting method which is convenient enough for even inactive users to willingly report the overload condition and which delivers detail information about the overloads. In this paper, we design and implement a measurement function of smartphone s WCDMA communication quality including overload condition and management system of mobile wireless communication networks about smartphones communication quality.
스윙 모션을 동반한 4-way 카세트 천장형 에어컨 기류의 냉방성능 및 열쾌적성 분석 및 평가
최호연(Ho Yeon Choi),오재현,박용갑(Yong Gap Park),하만영(Man Yong Ha) 대한기계학회 2018 대한기계학회 춘추학술대회 Vol.2018 No.12
A numerical simulation would be carried out using CFD to compare the cooling performance and Thermal comfort of 4-way cassette Air-conditioner when its vane is maintained to constant angle or moving. To evaluate the flow from indoor unit, cooling speed, Draft rate and ADPI calculation is used as well as distribution of air temperature and velocity. The CFD simulation was carried out using commercial CFD code, Fluent, based on Finite Volume Method(FVM). To validate CFD results, comparison with experiment was conducted. The CFD result show the good agreement with experimental result within 2%. The results in this paper indicate that the swing motion of vane increase the cooling speed due to the wide discharge airflow compared with fixed vane. And it improve thermal comfort felt by occupants.
최호연(Ho-Yeon Choi),김기현(Ki-Hyun Kim),신형섭(Hyung-Seop Shin),박종서(Jong-Seo Park),이해무(Hae-Moo Lee) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.3
The toughness data obtained from Charpy impact tests are presented by a temperature-energy relationship. Data fitting for quantitative comparing of transition temperature with upper shelf energy, ductile-brittle transition, in other words, the representation with general mathematical model equation for energy variation according to the temperature is necessary. In this study, the Charpy impact tests to two kinds of the representative steel were carried out as a work for the material property standardization technique development. The fitting procedure of the scattering in data according to materials and temperature in the transition region was described. The data fitting procedure was established through the variances treatment in the transition region using the tangent hyperbolic function.
최호연(Ho-Yeon Choi),김기현(Ki-hyun Kim),정영진(Young-Jin Jeong),신형섭(Hyung-Seop Shin) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.6
The friction welding of Cu-based similar and dissimilar BMGs has been tried utilizing the superplastic-like deformation behavior of BMG in the supercooled liquid region. The apparatus for friction welding of BMGs adopting a pneumatic cylinder and gripper based on a conventional lathe was constructed. The friction pressure and the friction time were in the range of 100~200 ㎫ and 0.4~1.0 sec, respectively. The rotation speed was constant as 1800 RPM. The friction welding of a similar Cu₄?Zr₄?Ag?Al?/Cu₄?Zr₄?Ag?Al? BMG alloy and a dissimilar Cu₄?Zr₄?Ag?Al?/Zr??Al₁?Ni?Cu₃? BMG alloy has been tried. In order to characterize the properties after friction welding, various crystallographic techniques and property evaluation procedures were adopted. Finally, the residual strength after friction welding was evaluated by the tensile testing.
항공용 가스터빈엔진 오일쿨러의 설치 위치에 따른 열-수력학적 성능에 관한 수치적 연구
최호연(Ho Yeon Choi),김민성(Minsung Kim),하만영(Man Yeong Ha),민준기(June Kee Min) 대한기계학회 2017 대한기계학회 춘추학술대회 Vol.2017 No.11
In an aero gas-turbine engine, the heat exchanger is needed to cool the oil system for the gearboxes and electric devices. Among the various type of heat exchanger, Surface air-oil heat exchanger with plate-fin is used for enhanced heat transfer characteristics. The plate-fin type SAOHE was modeled using two-dimensional porous approximation for the fin region to evaluate the aero-thermal performance of SAOHE. Governing equations of mass, momentum, and energy equations for compressible turbulent flow were solved using ideal-gas assumption for the air flow. The six mounting locations were considered on the engine core and casing sides. Using the porous media model, the pressure drop and heat transfer performance of the heat exchanger were predicted, and the results were compared with three-dimensional computational fluid dynamics results and experiment data for validation.