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최홍석(Hongseok Choi),김병민(Byungmin Kim),강충길(Chunggil Kang),하세윤(Seyun Ha),이동휘(Donghui Lee) 한국자동차공학회 2009 한국자동차공학회 학술대회 및 전시회 Vol.2009 No.11
Automotive companies are pursuing to use the ultra advanced high strength steels(UAHSS) for improving fuel efficiency and crashworthiness in body panels and structures. Hot stamping process using martensitic phase transformation of austenized blank has been developed to obtain the strength above 1.5GPa with high dimensional accuracy and formability. In this study, the optimization of blank shape for hot stamping has been performed to reduce trial-and error method in development the center pillar of the automotive structural panel. In order to optimize blank shape which is one of the most important factors in hot stamping process, inverse analysis was performed to obtain initial blank shape for center pillar by the conventional stamping code, J-Stamp.Optimal blank shape has been determined by thermo-mechanical simulation considered to friction, holding force and tool shape using compensation the error between deformed path and target contour. furthermore, wrinkle at bottom region of center pillar, assembled with sill side, were significantly reduced by applying optimized drawbead. In this study, it can be established that blank optimization method for hot stamping of center pillar, an automotive structural part, in order to reduce shape error, wrinkle and fracture.
Ad hoc 네트워크에서 전달지연을 고려한 전력인지 라우팅 프로토콜
최홍석(Hongseok Choi),서경룡(Kyungryong Seo) 한국멀티미디어학회 2010 한국멀티미디어학회 학술발표논문집 Vol.2010 No.2
??MANET 에서의 전력인지 라우팅 프로토콜은 각 노드의 전력소비를 최소화 하여 네트워크의 수명을 연장할 수 있도록 하지만 프로토콜의 특성상 전달지연을 증가시키는 경향이 있어 전달지연이 중요한 멀티미디어 전송에는 적용하기 어렵다. 본 논문에서는 ad hoc 네트워크에 적용할 수 있는 전달지연을 고려한 전력인지 라우팅 프로토콜을 제안하였다. 제안된 프로토콜은 전달지연과 전력소비 두 가지의 상충된 지표를 동시에 고려하는데 전달지연을 일정한 수준으로 유지하면서 소비전력을 최소화 하는 방식을 사용한다. 전달지연을 고려하기 때문에 경로구성에 필요한 제어패킷의 수는 증가하지만 적절한 휴리스틱을 사용하여 패킷의 수가 크게 증가하지 않도록 하였다. 시뮬레이션 결과 기존의 전달지연을 고려하지 않은 방식에 비하여 전달지연은 30% 정도로 크게 감소한 반면 전력소비는 10%미만의 증가에 그쳤다.
DP980 트리밍 시 전단 각도에 따른 금형 수명에 관한 연구
최홍석(Hongseok Choi),고대철(Daecheol Ko),김병민(Byungmin Kim) 한국자동차공학회 2012 한국자동차공학회 지부 학술대회 논문집 Vol.2012 No.5-1
Ultra high strength steels such as DP980 are widely used in automotive industry for the light weight body. However, cutting tool life decreases due to their extremely high strength when trimming or blanking these steels. Trimming angle is importance parameter for the reduction of contact pressure on tool edge resulting in premature tool failure. In this study, the effect of trimming angle on the burr formation and sheared edge in trimming of DP980 sheet Trimming load and sheared edge with respect to the trimming angle are investigated using finite element analysis. Furthermore, tool life on the basis of burr height of 0.1mm is estimated using burr height diagram during 30,000 strokes by trimming experiment As a result of FE-analysis and experiment, trimming angle of -10° provide better influence on sheared edge, trimming load and trimming tool life.
초소수성 표면이 프로펠러 후류 유동에 미치는 영향에 대한 PIV기법을 사용한 실험적 연구
최홍석(Hongseok Choi),이정진(Jungjin Lee),박형민(Hyungmin Park) 대한기계학회 2016 대한기계학회 춘추학술대회 Vol.2016 No.12
The effect of superhydrophobic surface (with random textures) on the flow behind the rotating propeller has been investigated experimentally using stereo PIV (particle image velocimetry) in a still water tank. Stereo PIV is used to measure the out-of-plane velocity component of the propeller wake. More than 6,000 instantaneous velocity fields were measured at two different rotating speeds and two different surface conditions (i.e., smooth and superhydrophobic surfaces). It is found that due to the slip, even on the rotating surface, the applied superhydrophobic surfaces lead to the decrease of thrust generation but also the reduction of turbulence intensity in the wake.
최홍석(Hongseok Choi),한욱민(Ukmin Han),이호성(Hoseong Lee) 대한기계학회 2021 대한기계학회 춘추학술대회 Vol.2021 No.11
In this paper, the effects of the diverging channel design cooling plate for improving temperature uniformity of high energy density lithium-ion battery (LIBs) are examined. A large capacity NMC (Nickel Manganese Cobalt: LiNiMnCoO2) battery with 355Wh/L is used. To verify the cooling simulation model, the battery module cooling experiments is discharged with 0.33 current-rate (C-rate) are proceeded using cooling plates with straight channels and diverging channels. With the verified cooling model, the thermal effects of the diverging channel cooling plate with oblique fins are examined especially in perspective to the uniformity of battery temperature. In addition, scale-up and simulations of the cooling plate for battery pack are progressed. As a result, the diverging channel cooling plate with oblique fins shows more enhanced effects on the battery temperature distribution than the straight channel cooling plate for the battery pack.