• Proceedings of the KIPE Conference
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• 2017.07a
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• pp.256-257
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• 2017

최근 산업 및 에너지 관련 분야에서의 전력변환기술 및 제어기술의 중요성이 계속 화두가 되어 왔다. 전통적인 전력변환 토폴로지는 2레벨 시스템이 일반적이었다. 하지만 고압 시스템 분야에서는 2레벨, 3레벨 혹은 그 이상의 멀티레벨 토폴로지가 적용되고 있다. 이런 멀티레벨 토폴로지를 사용함으로써 출력 전류의 고조파 저감등의 이점들을 가질 수 있다. 특히, 양방향 케스케이드 NPC 토폴로지는 케스케이드 하프브리지 토폴로지에 비해 몇가지 이점들을 가지는데 파워 셀 혹은 서브모듈의 개수를 줄일 수 있고 트랜스포머의 사이즈를 줄 일수 있다. 이 논문에서는 이러한 모듈러타입의 고압 케스케이드 NPC 토폴로지 인버터의 파워 스택 개발에 대한 내용을 담고 있다.

• Proceedings of the KIPE Conference
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• 2014.11a
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• pp.135-136
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• 2014

본 논문은 계통연계형 인버터를 위한 비례공진제어 기반의 케스케이드전류-전압 제어기 설계에 대해 다루고있다. 인버터가 계통연계모드로 동작할 때 인버터는 계통의 보조 전력원으로서의 역할을 하기 때문에 전류원으로 정의된다. 이때 LCL 필터가 연결된 계통연계형 인버터의 출력 LC 단에 비선형 지역적 부하가 연결될 경우 기존의 단일 전류 제어기만으로는 비선형 부하로 인한 고조파 왜곡에 대처하기 힘들고 독립운전모드와의 모드절환시 매끄러운 과도 특성을 보장하기 힘들다. 따라서 본 논문에서는 비례다중공진제어기를 활용한 내부 출력 전압, 외부 출력 전류 루프로 구성된 케스케이드 전류-전압 제어기를 제안하였고 제안된 방식이 고조파 보상과 모드 절환시의 매끄러운 과도 특성에 효력을 보임을 PSIM 시뮬레이션을 통해 검증하였다.

• 한국신재생에너지학회:학술대회논문집
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• 2009.11a
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• pp.170-170
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• 2009

AIP(Air Independent Propulsion)시스템에 적용되는 연료전지 스택의 경우 연료의 이용율을 극대화시키는 것이 매우 중요하다. 일반적인 연료전지 스택은 물배출과 성능의 안정화를 위해 이론적 요구량보다 양론적으로 많은 양을 공급하여, 반응에 사용되지 않고 배출되는 연료 가스가 많아 이용율이 낮다. 여러 단으로 구성되어 전 단에서 사용하고 남은 연료 가스를 다음 단에 재공급하여 사용하는 케스케이드 구조의 연료전지 스택을 적용하게 되면 연료이용율을 90% 이상으로 높일 수 있다. 그러나 연료전지 스택에서 반응에 의해 발생한 물과 응축된 가습수가 재공급되면 연료전지 스택의 성능과 내구성에 악영향을 주는 플러딩현상이 발생하게 된다. 반면 반응수와 응축수를 제거할 때 스택에 재공급되는 연료 가스의 가습수가 같이 제거되면 낮은 가습도로 스택에 공급되는 문제점도 있다. 따라서 연료 가스의 가습도를 잘 유지하면서 액화된 물만 원활하게 제거할 수 있는 기액분리기의 개발이 필요하다. 본 연구에서는 CFD(Computational Fluid Dynamics)해석을 활용하여 다양한 디자인의 기액분리기를 설계하고 실험을 통해 각 디자인의 장단점을 분석하였다. 결과를 바탕으로 최적의 기액분리기를 개발하고 제작 및 평가를 통해 성능을 검증하였다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.12
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• pp.3148-3165
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• 1993

A cascade wind tunnel test for a turbine nozzle, which was designed for a small turbo jet engine in a previous study, has been conducted to evaluate its aerodynamic performance and losses. The large-scale blades were based on the mid-span profile of the nozzle. Oil film flow structure, and then 3-dimensional velocity components were measured in the flow passage with a 5-hold pressure probe, in addition to turbulent intensities at mid-span of cascade exit using a hot-wire anemometer. From this study, 3-dimensional growth of horseshoe and passage vortices in the downstream direction was clearly understood with near-wall flow phenomena. In addition, secondary flow and losses associated with the blade configuration were obtained in detail.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.148-151
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• 2008

In a double-passage cascade apparatus, only two blades are installed in order to increase the accuracy of experimental result by applying bigger blade than the size of multi-blades on the same apparatus. However, this causes difficulties to make correct periodic condition. In this study, sidewalls are designed to meet periodic condition without removing the operating fluid or adjusting tail boards. Surface Mach number on the blade surface is applied to a responsible variable, and 12 design variables which are related with sidewall profile control are selected. A gradient based optimization is adopted for wall design and CFX-11 is used for the internal flow computation. The computed result shows that it could obtain the same flow structure by modifying only the sidewalls of the double-passage cascade apparatus.

• Journal of Advanced Marine Engineering and Technology
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• v.34 no.1
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• pp.46-52
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• 2010

In this study, several types of natural gas liquefaction processes using two staged Inter-cooler are simulated and designed to secure a competitiveness in the industry of natural gas liquefaction plant. These processes are based on basic cascade process, and all of these are improved with two staged compressors type. One of types is applied Inter-cooler to each cycle such as propane, ethylene, methane, the other type is applied Inter-cooler to whole cycle. These processes are compared characteristics of performance with basic process. Cascade process with two staged Inter-cooler in the whole cycle is on the top ranked with increment ratio of COP about 13.7 ~ 20.5%, and yield efficiency of this process are improved comparing with the basic process by 23.8% ~ 35% lower specific power, respectively.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.1
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• pp.72-78
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• 2008

In this study, advanced (fluid-structure interaction (FSI)) analysis system has been developed in order to predict turbine cascade performance with blade deformation effect due to aerodynamic loads. Intereference effects due to the relative movement of the rotor cascade with respect to the stator cascade are also considered. Reynolds-averaged Navier-Stokes equations with one equation Spalart-Allmaras and two-equation k-ω SST turbulence models are solved to accurately predict fluid dynamic loads considering flow separation effects. A fully implicit time marching scheme based on the (coupled Newmark time-integration method) with high artificial damping is efficiently used to compute the complex fluid-structure interaction problem. Predicted aerodynamic performance considering structural deformation effect of the blade shows somewhat different results compared to the case of rigid blade model. Cascade performance evaluations for different elastic axis positions are importantly presented and its aeroelastic effects are investigated.

• KIPS Transactions on Software and Data Engineering
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• v.2 no.10
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• pp.713-722
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• 2013

This paper proposes a method of using depth information to detect the hand region in real-time based on the cascade method. In order to ensure stable and speedy detection of the hand region even under conditions of lighting changes in the test environment, this study uses only features based on depth information, and proposes a method of detecting the hand region by means of a classifier that uses boosting and cascading methods. First, in order to extract features using only depth information, we calculate the difference between the depth value at the center of the input image and the average of depth value within the segmented block, and to ensure that hand regions of all sizes will be detected, we use the central depth value and the second order linear model to predict the size of the hand region. The cascade method is applied to implement training and recognition by extracting features from the hand region. The classifier proposed in this paper maintains accuracy and enhances speed by composing each stage into a single weak classifier and obtaining the threshold value that satisfies the detection rate while exhibiting the lowest error rate to perform over-fitting training. The trained classifier is used to classify the hand region, and detects the final hand region in the final merger stage. Lastly, to verify performance, we perform quantitative and qualitative comparative analyses with various conventional AdaBoost algorithms to confirm the efficiency of the hand region detection algorithm proposed in this paper.

• Journal of Power System Engineering
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• v.14 no.2
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• pp.28-33
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• 2010

In this research, cascade liquefaction process was simulated using two-staged direct expansion with inter-cooler. Evaporated gaseous refrigerant which has low pressure and temperature from the inter-cooler is mixed with gaseous refrigerant from outlet of 1st compressor, and flows into 2nd compressor. Therefore this prevents superheating compression. Compressor work of process which includes inter-cooler to all cycles shows the lowest value of 338.68 MW and it is lower 16.34% than that of basic process. Refrigeration capacity shows decreasing tendency as applied inter-cooler and that of process which includes inter-cooler to all cycles shows the lowest value of 449 MW. COP was increased when the inter-cooler was applied, and process which includes inter-cooler to all cycles shows highest value of 1.33. It shows that COP was increased because decrement of compressor work by applying inter-cooler was higher than decrement of refrigeration capacity.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.11a
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• pp.519-522
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• 2010

Flow-induced vibration analyses have been conducted for a 3D compressor blade model. Advanced computational analysis system based on computational fluid dynamics(CFD) and computational structural dynamics has been developed in order to investigate detailed dynamic responses of designed compressor blades. A fully implicit time marching scheme based on the Newmark direct integration method is used for computing the coupled aeroelastic governing equations of the 3D compressor blade for fluid-structure interaction problems. Detailed dynamic responses and instantaneous pressure contours on the blade surfaces considering flow-separation effects are presented to show the multi-physical phenomenon of the rotating compressor blade.