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이한솔(Hansol Yi),김우진(Woojin Kim),최해천(Haecheon Choi),이정일(Jungil Lee) 대한기계학회 2015 대한기계학회 춘추학술대회 Vol.2015 No.11
Control of the ski jumper’s posture is essential to achieve a longer flight distance. For this purpose, we conduct a large eddy simulation (LES) of turbulent flow past a model of a ski jumper which is obtained by 3D scanning the ski jumper’s body (Mr. Chil-Ku Kang, a member of the Korean national ski jump team). The angle of attack of the jump ski is 30° and the Reynolds number based on the length of the jump ski and the flight velocity is 540,000. The flow statistics including the drag and lift coefficients during the flight are in good agreements with our own experimental data. We investigate the flow characteristics such as the stagnation region, flow separation, and three-dimensional vortical structures and their effects on the drag, lift, and lift/drag. To find the optimal posture of the ski jumper, we build a simple geometric model of a ski jumper based on the result of LES where each part of the ski jumper’s body is modeled as a canonical bluff body such as a sphere, cylinder and flat plate. The drag and lift obtained from this approach are in good agreements with those from LES. Also, using this approach, the optimal posture for the best aerodynamic performance is to be found.
목표물 신호 모니터링 및 SPGD 알고리즘 기반 3 채널 타일형 결맞음 빔결합 시스템 연구
김영찬,윤영선,김한솔,장한별,박재덕,최윤진,나정균,이주한,강현구,여민수,최규홍,노영철,정윤찬,이혁재,유봉안,염동일,전창수,Kim, Youngchan,Yun, Youngsun,Kim, Hansol,Chang, Hanbyul,Park, Jaedeok,Choe, Yunjin,Na, Jeongkyun,Yi, Joohan,Kang, Hyungu,Yeo, Minsu 한국광학회 2021 한국광학회지 Vol.32 No.1
단일 레이저의 출력 한계를 뛰어넘기 위한 빔결합 방법으로서, 보강간섭 원리를 이용한 타일형 결맞음 빔결합 시스템에 대해 연구하였다. 와트급 출력의 3 채널 결맞음 광섬유 레이저 및 삼각형 배치의 팁-틸트(tip-tilt) 기능을 갖춘 3 채널 출력단을 자체제작 하였다. 모니터링 시스템, 위상제어기, 3 채널 위상변조기 간의 궤환 제어 시스템(closed-loop system)을 구성하고 SPGD 알고리즘을 적용하여, 위상잠금 속도 5~67 kHz, 이상적인 계산값 대비 중심부 광세기 효율 53.3%의 성공적인 3 채널 위상잠금을 구현하였다. 빔결합 소자가 필요 없고, 가장 고출력 가능성을 가진 타일형 결맞음 빔결합을 위한 요소기술 개발이 완료되어, 향후 다채널, 고출력, 고속 제어 연구로 이어질 수 있을 것으로 기대된다. We have studied a tiled-aperture coherent-beam-combining system based on constructive interference, as a way to overcome the power limitation of a single laser. A 1-watt-level, 3-channel coherent fiber laser and a 3-channel fiber array of triangular tiling with tip-tilt function were developed. A monitoring system, phase controller, and 3-channel phase modulator formed a closed-loop control system, and the SPGD algorithm was applied. Eventually, phase-locking with a rate of 5-67 kHz and peak-intensity efficiency comparable to the ideal case of 53.3% was successfully realized. We were able to develop the essential elements for a tiled-aperture coherent-beam-combining system that had the potential for highest output power without any beam-combining components, and a multichannel coherent-beam-combining system with higher output power and high speed is anticipated in the future.