• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2009년도 추계학술대회 논문집
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• pp.403-407
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• 2009

In this work, finite element investigations were carried out to manufacture a seamless aluminum liner without crack generation using four-stage deep drawing followed by two-stage ironing process. In order to predict the crack generation during the liner manufacturing process, the Normalize Cockroft-Latham(NCL) which is one of ductile fracture criteria was adopted. In addition, the tensile tests were carried out to obtain the critical value of NCL by comparing the experimental and FE simulation results. From this, various case studies based on FE simulation were carried to obtain the optimum die designs which can prevent the crack generation during ironing processes. Finally, the aluminum liner was successfully made using obtained die designs so that requirements were met in terms of thickness and height of the liner.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2005년도 전력전자학술대회 논문집
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• pp.507-510
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• 2005

High voltage pulse power supply using Marx generator and solid-state switches is proposed in this study. The Marx generator is composed of 12 stages and each stage is made of IGBT stack, two diode stacks, and capacitor. To charge the capacitors of each stage in parallel, inductive charging method is used and this method results in high efficiency and high repetition rates. It can generate the pulse voltage with the following parameters: Voltage: up to 120kv Rising time: sub ${\mu}S$ Pulse width: up to $10{\mu}S$, Pulse repetition rate: 1000pps The proposed pulsed power generator uses IGBT stack with a simple driver and has modular design. So this system structure gives compactness and easiness to implement total system. Some experimental results are included to verify the system performances in this paper.

• 수산해양기술연구
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• 제30권4호
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• pp.341-349
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• 1994

From the results of model tests, statistical regression analysis for EHP estimation based on hull form parameters is adopted in this study. From this result, the method for estimation of EHP and optimization of hull form parameters at the initial design stage of fishing boats is developed. This method is applied to two standard fishing boats with chine lines. The EHP s are estimated and compared to experimental results. From the optimization of four principal hull form parameters of these fishing boats, approximately 19% of resistance reduction at the design speed is achieved and thus certifies that this method can be used efficiently for the initial design of hull forms of fishing boats.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2003년도 추계 학술대회논문집
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• pp.132-138
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• 2003

The optimal design for a leading car considering the aerodynamic resistance is required on the high-speed train due to increasing of ratio of drag force with proportion for the square of velocity. The aerodynamic analysis using CFD in the stage of concept design offers more economical analysis method which is used to estimate the influence of flow and pressure around the leading car than the experimental method using the Mock-up. In this study, we want to assist the artistic design with aerodynamics analysis in order to get the optimal design for leading car with the operation speed of 180km/h. The results of aerodynamic analysis for two leading car models which one is expressed with lineal beauty and the other is with curvaceous beauty are compared with each other and they offer the proposal of modification for two models in order to decrease the drag force. The shape of curvaceous model is better for the pressure force but slightly worse for the viscous force than the other. The Fluent software is used for the calculation of flow profile in this study.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2004년도 춘계학술발표대회 논문집
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• pp.38-42
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• 2004

The optimal design for a leading car considering the aerodynamic resistance is required on the high-speed train due to increasing of ratio of drag force with proportion for the square of velocity. The aerodynamic analysis using CFD in the stage of concept design offers more economical analysis method which is used to estimate the influence of flow and pressure around the leading car than the experimental method using the Mock-up. In this study, we want to assist the artistic design with aerodynamics analysis in order to get the optimal design for leading car made of composite material. The results of aerodynamic analysis for two leading car models, which one is expressed with lineal beauty and the other is with curvaceous beauty, are compared with each other and offer the proposal of modification for two models in order to decrease be drag force. The shape of curvaceous model is better for the pressure force but slightly worse for the viscous force than the other. The Fluent software is used for the calculation of flow profile in this study.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2003년도 추계학술대회 논문집(III)
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• pp.351-357
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• 2003

The optimal design for a leading car considering the aerodynamic resistance is required on the high-speed train due to increasing of ratio of drag force with proportion for the square of velocity. The aerodynamic analysis using CFD in the stage of concept design offers more economical analysis method which is used to estimate the influence of flow and pressure around the leading car than the experimental method using the Mock-up. In this study, we want to assist the artistic design with aerodynamics analysis in order to get the optimal design for leading car with the operation speed at 180km/h. The results of aerodynamic analysis for two leading car models which one is expressed with lineal beauty and the other is with curvaceous beauty are compared with each other and they offer the proposal of modification for two models in order to decrease the drag force. The shape of curvaceous model is better for the pressure force but slightly worse for the viscous force than the other. The Fluent software is used for the calculation of flow profile in this study.

• 전력전자학회논문지
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• 제14권6호
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• pp.449-456
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• 2009

본 논문에서는 PFC단 링크 캐패시터의 실효 전류를 크게 저감 할 수 있는 링크 캐패시터 전류 스트레스 저감기법을 제안한다. 링크 캐패시터 선정 기준에는 여러 가지가 있으나 가장 큰 비중을 차지하는 것이 캐패시터 실효전류이다. 제안된 C-L 필터는 PFC단 출력 전류를 필터링하여 링크 캐패시터의 실효 전류를 크게 줄일 수 있고, 제안된 C-L-L-C 필터는 C-L 필터의 출력 전류 필터링 효과와 함께 L-C 필터가 DC/DC단 입력 전류를 필터링 함으로써 링크 캐패시터의 실효 전류를 더욱 크게 줄일 수 있다. 제안된 필터는 설계가 간단하고 PFC단의 Crossover frequency가 매우 낮아 C-L 필터 및 C-L-L-C 필터의 Cut-off frequency가 PFC단의 제어기 루프에 영향을 주지 않으므로 적은 소자를 가지고 손쉬운 방법으로 링크 캐패시터의 실효전류를 크게 줄일 수 있다. 제안된 필터의 이론적 해석과 설계 방법을 제시하며, 실험을 통하여 그 우수성을 검증한다.

• 설비공학논문집
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• 제6권3호
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• pp.237-246
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• 1994

Experimental data are reported for charging and collection of NaCl aerosols in the 0.03- to $0.2{\mu}m$-geometric-mean-diameter range in 2-stage parallel-plate electrostatic precipitators. The NaCl aerosols are generated with geometric standard deviation of about 1.74 and particle generation rate of about 10^9 particles/see by the constant output atomizer and injected into the air flow in the clean wind-tunnel. The 2-stage parallel-plate electrostatic precipitator installed in the test section of the wind-tunnel is operated with a positive corona discharge. The NaCl aerosols in the channel flow are sampled and transported to the aerosol particle number concentration measurement system by using the isoaxial sampling and transport system constructed based on the Okazaki and Willeke design. The aerosol particle number concentration measurement system measures the size distribution of submicrometer aerosols by an electrical mobility detection technique. It is confirmed from comparing the measured collection efficiencies in this study and the predicted ones by our previous theoretical analysis that the predicted collection efficiencies agree well with the experimental ones. It is also found from the comparison that below about $0.02{\mu}m$ all particles are not charged and the uncharged particles are not collected, and consequently 2-stage parallel-plate electrostatic precipitators are not suitable for that particle size range.

• 한국주조공학회지
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• 제11권3호
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• pp.245-253
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• 1991

It is known that the analysis of thermal stresses is substantially important in optimal design of casting mould. In this paper unsteady state thermal stresses generated in ingot and mould during the solidification process are analyzed by the two dimensional thermal elasto-plastic analysis. Distribution of temperature and stress of the mould is calculated using the finite element method and compared with experimental result. The significant results obtained in this study are as follows. At the early stage of the casting process, abrupt temperature change was shown in the vicinity of the inner surface of the mould. The largest temperature gradient is occurred at the corner of the mould. In the thermal stress analysis, compressible stress occurred in the inside wall of the mould where as tensile stress on outside wall. Smaller thermal stress is observed at the rounded corner. It is also observed that the shown is influenced by the thickness of the wall. A fairly good coincidence is found between analytical and experimental results, showing that the proposed analytical methodology is reliable.

• 소성∙가공
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• 제22권3호
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• pp.171-177
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• 2013

Vacuum-assisted thermoforming is one of the critical steps for successful application of film insert molding (FIM) to make parts of complex shape. If the thickness distribution of the formed film is non-uniform, then cracking, deformation, warpage, and wrinkling can easily occur at the injection molding stage. In this study, the simulation of thermoforming was performed to predict the film thickness distribution, and the results were compared with experiments. Uniaxial tensile tests with a constant crosshead speed for various high temperatures were conducted to investigate the stress-strain behavior. An instance of yielding occurred at the film temperature of $90^{\circ}C$, and the film stiffness increased with increasing crosshead speed. Two types of viscoelastic models, G'Sell model, K-BKZ model, were used to describe the measured stress-strain relationship. The predicted film thickness distributions were in good agreement with the experimental results.