• Journal of the Korean Society of Propulsion Engineers
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• v.20 no.4
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• pp.68-76
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• 2016

This research is carried out for the performance evaluation of the injector that is one of the critical components of bipropellant-rocket-engine. Spray characteristics are investigated in detail according to the recess length and injection pressure on the swirl-coaxial-injector using gaseous methane and liquid oxygen as propellants. A visualization is conducted by the Schlieren photography that is composed of a light source, concave mirrors, knife, and high-speed-camera. A hollow-cone-shape is identified in the liquid spray that is spread only by inner injector and the spray angle is decreased due to the diminution of swirl strength in accordance with the increase of the length of injector orifice. When the injector sprays the liquid through the inner injector with the aid of gas through the outer injector, the spray angle in external mixing region tends to increase with rise of the recess length, while in internal mixing region, it is decreased. It is also confirmed that the same tendency of the spray angle with recess length appears irrespective of the injection pressure of liquid spray.

• The KIPS Transactions:PartB
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• v.16B no.2
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• pp.131-140
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• 2009

This paper presents a new algorithm to the segmentation of the FISH images. First, for segmentation of the cell nuclei from background, a threshold is estimated by using the gaussian mixture model and maximizing the likelihood function of gray value of cell images. After nuclei segmentation, overlapped nuclei and isolated nuclei need to be classified for exact nuclei analysis. For nuclei classification, this paper extracted the morphological features of the nuclei such as compactness, smoothness and moments from training data. Three probability density functions are generated from these features and they are applied to the proposed Bayesian networks as evidences. After nuclei classification, segmenting of overlapped nuclei into isolated nuclei is necessary. This paper first performs intensity gradient transform and watershed algorithm to segment overlapped nuclei. Then proposed stepwise merging strategy is applied to merge several fragments in major nucleus. The experimental results using FISH images show that our system can indeed improve segmentation performance compared to previous researches, since we performed nuclei classification before separating overlapped nuclei.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.9B
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• pp.947-954
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• 2009

In mobile ad hoc networks, service discovery to search for an available service is an important issue. In this paper, we propose an efficient service discovery protocol that is combined a dht-based service discovery scheme and a P2P caching-based information spreading scheme. Proposed scheme store key information in hashed zone and search services using it's information. To search quickly a service, it use its physical neighbors information which collected by 1-hop hello message between a node and its physical neighbors. We do not use a central look up server and do not rely on flooding. Hence, it uniquely balanced all node's load in mobile ad hoc networks and reduced the number of messages exchanged, network load and response time. The simulation results show that our protocol outperforms DHT-based and flooding protocols.

• Journal of Soil and Groundwater Environment
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• v.11 no.6
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• pp.76-82
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• 2006

Fenton's reaction are difficult to apply in the field due to the low pH requirements for the reaction and the loss of reactivity caused by the precipitation of iron (II) at neutral pH. Moreover, Fenton-like reactions using iron mineral instead of injection of iron ion as a catalyst are operated to get high removal result at low pH. Because hydroxyl radical can generate at the surface of iron mineral, there are competition with a lot of hydroxide at around neutral pH. On the other side, to operate Fenton's reaction series at neutral pH, modified Fenton reaction is suggested. The complexes, composed by iron ions (ferrous ion or ferric ion)-chelating agent, could be acted as a catalyst and presented in the solution at neutral pH. However, modified Fenton reaction requires a lot of hydrogen peroxide. Accordingly, the purpose of this experiment was to effectively combine Fenton-like reaction and modified Fenton reaction for extending application of Fenton's reaction. i.e., injecting chelating agents in Fenton-like reaction at around neutral pH is increasing the concentration of dissolved iron ion and highly promoting the oxidation effect. 2,4,6-trinitrotoluene (TNT) was used as a probe compound for comparing reaction efficiencies in this study. If the concentration of dissolved iron ion in combined Fenton process were existed more than 0.1 mM, the total TNT removal were increased. Magnetite-NTA system showed the best TNT removal (76%) and Magnetite-EDTA system indicated about 56% of TNT removal. The results of these experiments proved more promoted 40-60% of TNT removal than Fenton-like reaction's.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.8
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• pp.589-595
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• 2020

Large eddy simulation (LES) of a partially premixed gas turbine combustor is conducted. Four different hydrogen compositions are considered to investigate the fuel composition effects on the flow field inside the combustor. The comparison with the experimental flame structure and velocity profile is conducted to verify the LES results, revealing that the partially premixed flame structure is altered when hydrogen composition is changed. The flame structure becomes shorter and thicker as the hydrogen composition is increased, and therefore, the flame effect in the rigid wall is minimized. The change in the recirculation zone at the combustor wall with hydrogen addition is further investigated. Overall, the LES with combustion model is quite promising for accurately predicting the reactive flow characteristics in connection with the fuel composition.

• Proceedings of the Korea Water Resources Association Conference
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• 2022.05a
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• pp.18-18
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• 2022

하천 합류부에 있어 수체의 혼합양상을 분석은 고해상도의 자료가 필요하다. 반면에 수질환경 문제와 기존 모니터링 시스템이 고정된 측정 방식으로 이루어지기 때문에 하천 전체의 정보는 저해상도의 결과값은 나타낸다. 또한, 많은 수중 환경 문제가 1차원에서 3차원에 걸쳐 있지만, 대부분의 관측 시스템은 1차원에 머물러 있음을 확인할 수 있다. 이러한 문제를 해결하기 위해서는 보다 발전된 관찰 및 계측이 필요하다. 그에 따른 고해상도의 측정 자료를 얻기 위해서는 측정자가부담을 많이 가지며, 측정할 수 있는 영역이나 시간적으로 제한적이다. 해상도는 낮추되 광범위한 데이터를 취득하기 위해서는 적절한 보간법이 선정되어야 한다. 관련 논문을 검토한 결과, 측정 결과에 따른 2차원 횡단면 분포의 내용이 지배적이었고, 3차원 매핑 및 3차원 분석을 통한 수리학적 정보 획득에 관한 연구는 부족한 실정이였다. 특히 3차원 하천 수질 농도의 연구가 불충분했다. 그에 따라 저해상도 측정결과에서의 예측과 보간법에 대한 시각화를 통해 하천의 전체적인 수리·수질정보를 표기하였다. 각각의 보간법을 비교함으로써 하천 매핑에 있어 IDW, Natual Neighbor, Kriging 기법을 적용하여 시각화된 자료와 정량적 평가를 통해 하천매핑의 정밀성을 향상시켰다. 이를 통해 3차원화된 공간보간 자료를 이용한 하천합류부의 혼합양상을 해석하였다. 3차원 데이터를 활용하는 방법으로 측정 및 모니터링 기술의 중요한 데이터로 활용되며, 이러한 데이터는 유해물질 저감 기술 및 평가 예측 기술의 기초 데이터로 활용되고 있다. 유해화학물질 추정, 호수의 고위험 조류군 계층분석 등 다양한 수생건강 진단기술을 활용할 수 있다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.8C
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• pp.711-720
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• 2012

In this paper, we introduce the implementation of driver fatigue monitering system and its result. Input video device is selected commercially available web-cam camera. Haar transform is used to face detection and adopted illumination normalization is used for arbitrary illumination conditions. Facial image through illumination normalization is extracted using Haar face features easily. Eye candidate area through illumination normalization can be reduced by anthropometric measurement and eye detection is performed by PCA and Circle Mask mixture model. This methods achieve robust eye detection on arbitrary illumination changing conditions. Drowsiness state is determined by the level on illumination normalize eye images by a simple calculation. Our system alarms and operates seatbelt on vibration through controller area network(CAN) when the driver's doze level is detected. Our algorithm is implemented with low computation complexity and high recognition rate. We achieve 97% of correct detection rate through in-car environment experiments.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.04a
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• pp.445-452
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• 2011

The present work addresses structural characteristics of natural gas flames in a lean premixed swirl-stabilized combustor with an attention focused on the effect of the formation of recirculation zones on the combustion instability. It is known that the recirculation zone plays an important role in stabilizing a turbulent, premixed natural gas flames by providing a source of heat or radicals to the incoming premixed fuel and air. To improve our understanding of the role of recirculation zones, the flame structure was investigated for various mixture velocities, equivalence ratios and swirl numbers. The optically accessible combustor allowed for the application of laser diagnostics, and Particle Image Velocimetry(PIV) measurements was used to characterize the flame structure under both cold flow conditions and hot flow conditions. Dynamic pressures were also measured to investigate characteristics of combustion at the same time. The results indicates that the formation of recirculation zone is strongly related to the occurrence of thermo-acoustic instabilities.

• The Transactions of the Korean Institute of Power Electronics
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• v.4 no.4
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• pp.332-341
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• 1999

철도용 전동기는 작은 크기와 중량에 비해 큰 추진력(토크)을 필요로 하지만, 전철의 입력전원 시스템의 특유한 성질로 입력전압이 주기적으로 부족하다. 따라서 전압이용률을 최대화할 수 있는 과변조 PWM이 필요하다. 또 철도용 IGBT 인버터의 스위칭 주파수는 기존의 GTO인버터보다 2배 이상 크므로 철도용 IGBT 인버터 전용의 새로운 동기화 전략이 필요하다. 본 논문은 'Min/Max PWM'을 과변조 영역으로 선형 확장하는 과변조 PWM기법과 최적 동기화법을 혼합한 철도용 IGBT 인버터를 위한 최적 PWM 전략을 제안한다. 전동기-관성부하 모델을 대상으로 시뮬레이션한 결과와 축소모델 실험 결과는 본 전략이 타당함을 보여준다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1996.11a
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• pp.201-206
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• 1996

추진제 연소 기체의 연기도(degree of smoke)의 정량적 측정을 위하여 설계, 제작된 Smoke Chamber를 이용하여, 고체 추진제의 연소 기체에 대한 연기도의 측정 기법을 확립하였으며, 몇가지 유연성 및 무연성 혼합형 고체 추진제 조성들과 복기형 추진제의 연소 기체에 대하여 온·습도 조건의 변화에 따라 연기도를 측정하여 결과를 종합, 분석하였다. 그 결과, Smoke Chamber장비를 이용한 측정을 통하여 추진제 연소 기체중의 연기 생성도를 정량화 함으로써, 기후 조건과 추진제 조성에 따른 연기도의 차이를 구분할 수 있었으며, 일차 연기(primary smoke)와 이차연기(secondary smoke)의 생성 조건 및 이들의 분리 측정이 가능하다는 결론을 얻었다. 측정 파장 영역에 대한 확장을 통하여 측정 범위룰 보완한다면, Smoke Chamber System은 향후 고체 추진제의 연소 기체의 연기 특성의 파악 및 로켓 모터 plume 연구의 기초 자료 획득에 유용하게 이용될 수 있다고 판단된다.