• 한국전산유체공학회:학술대회논문집
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• 2007.10a
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• pp.92-99
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• 2007

In this paper, optimization of the vaned centrifugal compressor was carried out at a given mass flow rate condition. Firstly, impeller optimization was conducted using response surface method (RSM) which is one of optimization methods. After the optimization of the impeller was completed, diffuser optimization was performed with the optimized impeller. In these processes, Navier-Stokes solver was used to calculate the flow inside the centrifugal compressor. And the optimization is performed with Box-Behnken design method which is efficient for fitting second-order response surfaces to reduce the number of calculations required. As a result, compared with the reference model, the efficiency and the pressure ratio of the optimized impeller and diffuser are found to be increased. The performance at off-design conditions is presented.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.845-850
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• 2003

Unsteady nature of a tip leakage vortex in an axial flow fan operating at a design and off-design operating conditions has been investigated by measuring the velocity fluctuation in a blade passage with a rotating hotwire probe sensor. Two hot-wire probe sensors rotating with the fan rotor were also introduced to obtain the cross-correlation coefficient between the two sensors located in the vortical flow as well as the fluctuating velocity. The results show that the vortical flow structure near the rotor tip can be clearly observed at the quasi-orthogonal planes to a tip leakage vortex. The leakage vortex is enlarged as the flow rate is decreased, thus resulting in the high blockage to main flow. The spectral peaks due to the fluctuating velocity near the rotor tip are mainly observed in the reverse flow region at higher flow rates than the peak pressure operating condition. However, no peak frequency presents near the rotor tip for near stall condition.

• Proceedings of the KIEE Conference
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• 2000.07d
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• pp.2837-2839
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• 2000

We design a stable controller for a mobile robot with variable gains and reference velocity in order to apply the proper gains and reference velocity, which are generated with fuzzy logic in on-line. The stability is guranteed by the Lyapunov theory. The fuzzy logic rules is found in off-line with GA strategy which drives each object function to be the least. The proposed controller is applied smooth path tracking due to the local path planing. Simulation results show robust performances under a different initial conditions.

• The Proceedings of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.8 no.1
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• pp.21-28
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• 1994

It is very important and necessary to predict luminous enviroment in an interior space. This paper has described about energy saving and evaluated interior visual environment in a office building having on/off turning control lighting system utilizing daylight. In order to predict the interior varior illumination distribution, the scale model was made and examined under various conditions, such ad difference of window glass, and color pattern of wall, floor, and also ceiling lighting system type. This paper suggests that basic fundamental data of lighting design performance in the concept and schematic stages of design.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2000.11a
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• pp.20-20
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• 2000

2개의 경사 충격파와 하나의 수직 충격파로 초음속 유동을 압축하는 초음속 공기 흡입구의 수치적 연구를 수행하였다. 지배방정식으로는 Navier-Stokes방정식을 사용하였고 난류모델로는 SST 모델을 사용하였다. 지배방정식의 점성항 계산에는 중심차분법을 사용하였고 대류항 계산에는 풍상차분법인 Roe의 FDS기법을 MUSCL기법과 결합하여 이용하였다. 유한 체적법을 이용하여 차분된 방정식은 LU분할 기법을 이용한 완전 내재적 방법으로 2차 정확도 시간 적분으로 비정상 과정의 연구를 수행하였다. 흡입구 배압을 정해주어야 하는 어려움을 해결하기 위해 흡입구 후면에 노즐을 달고 노즐의 면적을 조절하여 배압이 형성되도록 하였다.(중략)

• The Transactions of the Korean Institute of Power Electronics
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• v.7 no.5
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• pp.405-412
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• 2002

Since the switching device of current-fed bridge-type topology suffers from him-off voltage spikes associated with larger energy than that of voltage-fed topology, a high-efficiency non-dissipative snubber is considered essential. However, the complicated operation and the capricious performance according to various conditions make the design of the non-dissipative difficult. In this paper, the non-dissipative snubber employed in the current-fed half-bridge converter operating at a duty ratio above 0.5 is completely analyzed and the design considerations are discussed. Some design examples and the experimental results are provided to confirm the analysis and design presented in this paper.

• Journal of the Korean Institute of Gas
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• v.26 no.5
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• pp.49-57
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• 2022

If the hydrogen industry is activated in the future, the LH2 receiving terminal with membrane storage tank is a major way to store and send large capacity hydrogen. Since such a LH2 receiving terminal does not currently exist, the process simulation model of it was completed by referring to the design data on existing LNG receiving terminal with same typed storage tank. Based on this model, the amount of BOG generation according to change of design conditions, which is a very important factor in the operation of LH2 receiving terminal, was predicted. Through this, it was attempted to review the appropriate operating conditions to minimize the amount of BOG generated during unloading in LH2 receiving terminal with membrane storage tank.

• Journal of Korean Society of Steel Construction
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• v.19 no.1
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• pp.15-27
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• 2007

Over the past decade, labor costs have increased relative to the cost of material hardware according to analysts in the construction industry. Therefore, the minimum weight design, which has been widely adopted in the literature for the optimal design of steel structures, is no longer the most economical construction approach. Presently, although connection- related costs is crucial in determining the most cost-effective steel structures, most studies on this subject focused on minimum-weight design or engaged in higher analysis. Therefore, in this study, we proposed a fabrication scheme for the most cost-effective moment-resisting steel frame structures that resist lateral loads without compromising overall stability. The proposed approach considers the cost of steel products, fabrication, and connections within the design process. The optimal design considered construction realities, with the optimal trade-off between the number of moment connections and total cost was achieved by reducing the number of moment connections and rearranging them using the combination of analysis that includes shear, displacement and interaction value based on the LRFD code and optimization scheme based on genetic algorithms. In this study, we have shown the applicability and efficiency in the examples that considered actual loading conditions.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.30 no.1
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• pp.16-30
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• 1997

Application of digital filter to the wave analysis is studied using the observed data by wave gauge. Sea wave data obtained from wave gauge always include long wave frequency components. In order to estimate the sea wave parameters, we must re-analyzed wave data by using a digital filter and the concept of mean sea level correction method. By the wave by wave analysis and spectral methods, sea wave parameters on the basis of wave data obtained by the conventional method and digital filter are compared. The best-fitted design filter determined by the necessary conditions of frequency responses, can be obtained by calculating various transfer functions. Thus, to get the best the digital filter design, both Butterworth filter and Savitzky-Golay filter of digital filter are used in the frequency and time domain, respectively. Three cases of observation wave data are calculated by applying digital filter. The components of different frequency bands in the surf zone are coexisted in three cases. The wave data for wind wave components is computed using the digital filter the surf zone and off-surf zone, and based on the filtered data, wave parameters are calculated by the spectral analysis and wave by wave analysis methods, respectively. As a results, when sea wave data observed by wave gauge are analyzed, the Savitzky-Golay method is recommended which can well appear cut-off frequency by experimental choosing filter length in the time domain. The better mean sea level correction method is the Butterworth filter in the frequency domain.

• Transactions of the Korean hydrogen and new energy society
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• v.29 no.2
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• pp.139-147
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• 2018

Korea Electric Power Research Institute (KEPCO RI) had developed molten carbonate fuel cell (MCFC) system since 1993. Finally, KEPCO RI developed and operated a 125 kW MCFC system in 2010. To make MCFC system compact, it is indispensable to install an ejector in this system where the anode off gas, the cathode off gas, and fresh air are mixed before flowing to the catalytic burner. KEPCO RI had developed various ejectors for MCFC system since 2006. The 125 kW MCFC system built with the developed ejector was operated successfully in Boryeong Thermal Power Plant in 2010. This 125 kW MCFC ejector was designed on the basis of the experimental results of 5 kW and 75 kW MCFC ejectors. The main goal of ejector design in our MCFC system is to maintain the entrainment ratio and the pressure between fuel cell stack and catalytic burner within the operating range. In this paper, the design results of the ejector are presented based on the 125 kW MCFC system operating conditions. In addition, a designed ejector was manufactured and installed in the MCFC system. As the fuel cell is under load operation, the pressure surrounding the ejector was measured to ensure that the fuel cell system is operating smoothly.