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듀얼노즐에서 나오는 기체 제트유동과 물줄기와의 상호작용
최대현(Daehyun Choi),이주호(Juho Lee),박은수(Eunsoo Park),변정원(Jungwon Byun),박형민(Hyungmin Park) 대한기계학회 2018 대한기계학회 춘추학술대회 Vol.2018 No.12
The liquid atomization through a gas-phase jet has various applications of coating, cooling, and material processing. Previously, most studies used a single-nozzle, but multi-stage configuration is considered to overcome its limitations. In this study, we experimentally study jet flows through two annular nozzles (upper and lower). To optimize the jet flow, we vary parameters like the pressure of each nozzle, the angle of the lower nozzle, distance between upper and lower nozzles, and so on. For each configuration, the single-phase gas jet flow is measured with a particle image velocimetry, which is classified depending on the turbulent kinetic energy, and the mean streamwise momentum. Also, we perform the tests of water-glycerin mixture atomization and measure the size distribution of atomized droplets, while varying the mass flow rate and the viscosity of liquid. It is found that the higher upper nozzle pressure is required to suppress the back flow, and the atomized droplet size can be controlled. Finally, we try to propose a model for predicting the size of atomized particles according to dual-nozzle configurations.
최대현(Daehyun Choi),박형민(Hyungmin Park) 대한기계학회 2017 대한기계학회 춘추학술대회 Vol.2017 No.11
In this study, flow around an in-line array of spheres has been investigated, focusing on the interaction between the sphere wakes. In a circulating water tunnel, 12.7 mm-diameter steel balls have been aligned along the direction of flow, with each sphere held by a thin steel wire. Considered Reynolds number for a single sphere is 1,000 and the number of spheres is increased up to five with varying the distance between them, as well. PIV and dye visualization has been used in order to measure the velocity fields and vortex shedding frequency. It is found that hairpin vortices are periodically detached from each sphere, move to downstream and undergo active interaction with other sphere’s wake. For the case of an array with two spheres, three distinctive flow structures have been identified depending on the distance between spheres. When the number of the spheres added, we find that there exists a specific trend on the Strouhal number. Also, the time-averaged velocity field and turbulence intensity in the wake will be discussed depending on the considered conditions.
초고속 광통신을 위한 고성능 저면적 Iterative BCH 복호기 구조
최대현(Dae-Hyun Choi),이한호(Hanho Lee) 대한전자공학회 2019 전자공학회논문지 Vol.56 No.1
본 논문은 100Gbps 이상의 데이터 처리율을 갖는 차세대 광통신 시스템을 위한 20% 오버헤드 기반 반복적인 Bose-Chaudhuri-Hocquenghem (BCH) 부호와 고성능 Iterative BCH (I-BCH) 복호기 구조의 설계 방법을 제안한다. 제안된 I-BCH 구조는 고속 데이터 처리율뿐만 아니라 뛰어난 오류정정능력을 보여준다. 제안된 I-BCH 복호기는 메모리 기반의 인터리빙 기술을 적용하였으며 7번의 반복 복호시 10<SUP>-15</SUP> post-FEC Bit Error Rate (BER) 기준 10.25 dB의 Net Coding Gain (NCG) 성능을 제공한다. 제안된 고성능 I-BCH 복호기의 구조는 90-nm CMOS 공정을 사용하여 합성되었으며, 성능 분석 결과 2-병렬 구조로 설계하였을 때 430 MHz의 동작 속도와 165 Gbps의 데이터 처리율을 갖는다. 따라서 제안한 구조는 100Gbps 이상의 데이터 처리율을 갖는 차세대 BCH 기반 순방향 오류정정 구조에 적용하여 사용할 수 있다. This paper shows a 20% overhead-based iterative Bose-Chaudhuri-hocquenghem (BCH) code and a high-performance iterative BCH (I-BCH) decoder architecture for next generation optical communication systems with data rates of 100 Gbps or higher. The proposed I-BCH decoder architecture shows high error correction capability as well as high data throughput. The proposed 7-iterative I-BCH decoder adopts a memory-based interleaving technique and provides a net coding gain (NCG) performance of 10.25 dB based on 10<SUP>-15</SUP> post-FEC Bit Error Rate (BER) in 7 iterative decoding. The proposed high-performance I-BCH decoder architecture is synthesized using a 90-nm CMOS process. The performance of the proposed I-BCH decoder is 430 MHz and data rate of 165 Gbps in case of two parallel designs. Therefore, the proposed architecture can be applied to the next generation BCH-based forward error correction architecture with data throughput rate of 100Gbps or more.
화재시뮬레이션에 의한 보 인접 스프링클러헤드의 동작시간 분석에 관한 연구
최대현(Choi, Daehyun),이재문(Lee, Jaemoon),민세홍(Min, Sehong) 한국방재학회 2020 한국방재학회논문집 Vol.20 No.1
본 연구에서는 국가화재정보시스템의 화재통계 분석을 통해 차량화재의 위험성에 대하여 파악하였으며, 화재발생시 초기소화의가장 중요한 역할을 하는 스프링클러 소화설비의 동작에 대한 분석을 수행했다. 시뮬레이션은 NFSC 103에서 보와 가까운스프링클러헤드 설치기준에 대하여 현행기준과 개정지침을 구분하여 시나리오를 구성하였으며, 추가적으로 주차장 화재발생시FAN을 기동할 경우 스프링클러헤드의 동작시간에 대해 분석했다. 시뮬레이션 프로그램으로 FDS를 사용하였으며, 시뮬레이션결과 개정지침을 적용할 경우 화원 직상부의 스프링클러헤드가 현행기준에 대한 결과와 비교하여 약 1분 먼저 동작하여개정지침의 적용이 적절함을 확인하였다. 화재발생시 감지기에 의해 FAN을 동작시킬 경우 직상부 스프링클러헤드는 FAN이동작하지 않았을 때의 시뮬레이션 결과와 비교하여 2분 이상 동작이 지연됨을 확인하였다. If the revised guidelines were applied to thesimulation, the sprinkler head located directly above the fire source was activated approximately 1 minin advance compared to the sprinkler head operating under current standards. Therefore, it was found that the revised guidelines were suitable and aided in early fire extinguishing attempts. In the case where a fan was operated along with the detector, during the outbreak of a fire, it was found that the operation of the sprinkler head located directly above the fire was delayed by two or more minutes compared to the simulated case where no fan was operated.