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권래언,Kwon, Laeun 한국군사과학기술학회 2016 한국군사과학기술학회지 Vol.19 No.3
Autonomy of unmanned systems is important because the unmanned system with high level of autonomy is able to perform desired tasks in unstructured environments without continuous human guidance. Evaluation of their autonomy is vital to realize the autonomous operation ability of unmanned system. Compared to the methods of evaluating the level of autonomy(LOA) for an unmanned ground vehicle(UGV) and unmanned aerial vehicle(UAV), the method of expressing the LOA of unmanned maritime system(UMS) is not established yet. Since UMS has a unique characteristics in terms of operational area, mission complexity and required technologies, compared to the UGV and UAV, it is required to establish for expressing the LOA for UMS. This paper reviews the current approaches to assess the LOA of unmanned system and proposes potential metrics for UMS in order to determine the autonomy levels of UMS.
원형 실린더 주위의 유동해석을 통한 URANS 난류 모델 성능 비교
김민재,신지환,권래언,이건철,Kim, Minjae,Shin, Jihwan,Kwon, Laeun,Lee, Kurnchul 한국군사과학기술학회 2014 한국군사과학기술학회지 Vol.17 No.6
In the present study, the flow around a circular cylinder at $Re=3.6{\time}10^6$ is numerically simulated using URANS approach. The objective of this study is to evaluate the turbulence models(Realizable k-${\varepsilon}$, RNG k-${\varepsilon}$) through the prediction of the unsteady flow characteristics around the cylinder. The time-averaged drag coefficients and vortex shedding phenomenon in the wake region are compared to available experimental data and other numerical results. The simulation with Realizable k-${\varepsilon}$ model is found to be more dissipative due to large eddy viscosity predicted in the wake region while the simulation with RNG k-${\varepsilon}$ model predicts a complex vortex shedding phenomenon with more coherent structures realistically.
고속기동 조건에서의 수중 음향 카메라 영상의 도플러 왜곡 보정 연구
배호석,김우식,권래언,정우근 한국마린엔지니어링학회 2019 한국마린엔지니어링학회지 Vol.43 No.4
Recently, acoustic cameras have become increasingly important with developments in autonomous underwater vehicle (AUV) technology. An acoustic camera is a device that visualizes nearby underwater targets and plays a major role in the autonomous operation of AUVs. For acoustic cameras that use multi-frequencies, the Doppler effect inevitably occurs during the operation of the platform. This Doppler effect causes a transition in the frequency component of the received signals, resulting in a locational distortion in the underwater target image. This study describes the image distortion caused by the Doppler effect of an acoustic camera using multi-frequencies and performs correction of the acquired images using numerical datasets. The study confirms that the position distortion of the acquired image using the acoustic camera is quantitatively generated through numerical tests. In addition, the applicability of the proposed technique to compensate the Doppler effect is verified. 최근 자율형 무인잠수정 기술의 발전과 함께 무인잠수정에 탑재되는 음향 카메라의 중요성이 대두되고 있다. 음향 카메라는 수중에 위치하는 근접 수중물체를 가시화하는 장비로 자율형 무인잠수정에 있어 매우 중요한 역할을 한다. 다중주파수를 사용하는 음향 카메라의 경우 수중플랫폼 운용 중에 도플러 효과가 필연적으로 발생하는데, 이러한 도플러 효과는 수신 음향신호의 주파수 성분의 천이를 발생시키므로, 결과적으로 수중물체 영상의 위치적 왜곡을 야기시킨다. 본 연구는 다중주파수를 사용하는 음향 카메라의 도플러 효과에 의해 발생되는 영상 왜곡에 대하여 설명하고, 가상모의 자료를 이용하여 획득영상의 보정을 수행한다. 수치모델링 결과로부터 음향카메라를 이용한 획득영상의 위치상의 왜곡이 정량적으로 발생하는 것을 확인할 수 있었으며, 도플러 천이를 이용한 도플러 보상 기법의 적용성을 확인하였다.
하이브리드 제상 방식을 적용한 냉장고용 핀-관 열교환기의 제상 성능 평가
이수원(Suwon Lee),박용주(Yongjoo Park),권래언(Laeun Kweon),정영만(Youngman Jeong),이재근(Jaekeun Lee) 대한설비공학회 2011 설비공학 논문집 Vol.23 No.1
The hybrid defrost process combined with hot-gas bypass defrost and electric heater defrost was experimentally evaluated about its defrost performance in the fin-tube evaporators of household refrigerators. Also the hybrid defrost process was compared with only electric heater defrost process. The defrost efficiency of the hybrid defrost process was shown two times higher than electric heater defrost process. The defrost time of the hybrid defrost process was shorten about 10%∼50% than electric heater defrost process. Thermal shock after defrost process was decreased about 50% for the case of the hybrid defrost. It was found that energy consumption ratio of defrost process was reduced up to 7.4% compared with 22.4% of electric heater defrost at the condition of 25℃ ambient temperature.