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풍력터빈의 가동 풍속범위 내에서 뒷전 두께비를 갖는 NACA64-418 익형의 공력성능에 관한 연구
유홍석,이장창 한국항공우주학회 2014 한국항공우주학회 학술발표회 논문집 Vol.2014 No.11
IEA wind사의 풍력터빈 로터 블레이드인 Mexico model은 팁 블레이드로 NACA64-418 익형을 채택하고 있다. 풍력터빈의 팁 블레이드는 장기간 운용으로 인해 종종 균열이 생기고 수리과정을 거쳐 계속 사용되고 있다. 수리된 익형을 모방하기 위해 adding thickness 방법을 이용하여 NACA64-418 익형을 수정하고 풍력터빈의 가동풍속 범위 내에서 수정된 익형의 공력성능을 조사하였다. 수치해석 결과, 모든 풍속에서 뒷전 두께비가 증가할수록 항력은 증가하였으나 양력에는 아무런 변화가 없었으며 피칭 모멘트는 실속영역 전까지 받음각이 증가할수록 풍속 10m/s에서는 불안정하게 증가하였으나 풍속이 증가하면서 피칭 모멘트는 선형적으로 증가하였다. The Mexico model, the rotor blade of wind turbine, of IEA wind adopts NACA64-418 airfoil as the tip blade. The tip blades of wind turbine become cracked due to a long employment period and are repaired through maintenance in order to allow their continuous use. To imitate the repaired airfoil, the NACA64-418 airfoil is modified by the adding thickness method. The aerodynamic performance of the modified airfoil is investigated within operating velocity of wind turbine. The numerical results show that for all wind velocity the drag increases but the lift doesn"t change as the blunt thickness ratios are increased and pitching moment at wind speed 10m/s increases unstably as the angle of attack is increased before the stall region. However the pitching moment increases linearly as the wind speed is increased.
Numerical Analysis of NACA64-418 Airfoil with Blunt Trailing Edge
유홍석,이장창 한국항공우주학회 2015 International Journal of Aeronautical and Space Sc Vol.16 No.4
The aerodynamic performance of blunt trailing edge airfoils was investigated. The flow fields around the modified NACA64- 418, which consists of the tip blade of the wind turbine and Mexico model of IEA wind, were analyzed. To imitate the repaired airfoil, the original NACA64-418 airfoil, a cambered airfoil, is modified by the adding thickness method, which is accomplished by adding the thickness symmetrically to both sides of the camber line. The thickness ratio of the blunt trailing edge of the modified airfoil, tTE /tmax, is newly defined to analyze the effects of the blunt trailing edge. The shape functions describing the upper and lower surfaces of the modified NACA64-418 with blunt trailing edge are obtained from the curve fitting of the least square method. To verify the accuracy of the present numerical analysis, the results are first compared with the experimental data of NACA64-418 with high Reynolds number, Re=6×106, measured in the Langley low-turbulence pressure tunnel. Then, the aerodynamic performance of the modified NACA64-418 is analyzed. The numerical results show that the drag increases, but the lift increases insignificantly, as the trailing edge of the airfoil is thickened. Re-circulation bubbles also develop and increase gradually in size as the thickness ratio of the trailing edge is increased. These re-circulations result in an increase in the drag of the airfoil. The pressure distributions around the modified NACA64-418 are similar, regardless of the thickness ratio of the blunt trailing edge.
Wi-Fi Direct 망을 위한 부하량 예측 기반의 전력 절감 기법
유홍석,박양우,이채수,윤태진,Yoo, Hongseok,Park, Yang-Woo,Lee, Chae-Soo,Yun, Tae-Jin 대한임베디드공학회 2015 대한임베디드공학회논문지 Vol.10 No.4
Wi-Fi Direct allows battery powered mobile devices to form a wireless ad hoc network. Since one member of the network called Group Owner (GO) takes the role of managing the network, the network lifetime is mainly affected by the energy efficiency of GO. Hence, Wi-Fi Direct defines power saving schemes that allow GO to save the energy by turning off its radio interface during the periods called absence periods. However, the Wi-Fi Direct specification does not specify how to set parameters (denoted by PS parameters) determining the schedule of the absence periods. In this paper, we therefore propose a novel traffic-aware power saving scheme for Wi-Fi Direct networks. In particular, the proposed scheme estimates the application-level traffic load and adaptively tunes the PS parameters according to the estimated value.
내과계 중환자실 전담의에 의해 시행된 경피적 확장 기관절개술의 안정성 및 유용성
유홍석,임소연,박치민,박치민,전경만 대한중환자의학회 2011 Acute and Critical Care Vol.26 No.4
Background: Tracheostomy is one of the most commonly performed surgical procedures in the intensive care unit (ICU). After its introduction, percutaneous dilatational tracheostomy (PDT) has been recognized in western countries as a reliable alternative to surgical tracheostomy. However, data on the safety and feasibility of PDT performed by medical intensivists are limited in Korea. Methods: To evaluate the safety and feasibility of PDT performed by medical intensivists and to compare with those of surgical tracheostomy (ST), we retrospectively analyzed the clinical characteristics of all prospectively registered patients who underwent either PDT or ST in medical ICU from December 2010 to July 2011. Results: A total of 81 patients underwent tracheostomy over the study period: PDT in 56 (69%) and ST in 25 (31%). One patient in whom major bleeding developed during PDT underwent ST as a substitute for PDT. There were no differences in the demographics, laboratory findings, and parameters of mechanical ventilation between the two groups. Procedure time was significantly shorter in the PDT group (20 [IQR 18−30] min) than that in the ST group (38 [27.5−57.5] min) (p < 0.001). The major complication observed in 24 hours after PDT was bleeding in 6 (11%) patients of the PDT group and 4 (16%) patients of the ST group (p = 0.489). However, surgical interventions for major bleeding were required in 2 patients who underwent. Conclusions: PDT performed by medical intensivists was safe and feasible. However, immediate surgical assistance should be available when required.
A Case of Acute Pulmonary Embolism Associated with Dysplasminogenemia
유홍석,김희진,이진아,조윤영,정지영,정혜민,전경만 대한의학회 2013 Journal of Korean medical science Vol.28 No.6
The incidence of pulmonary embolism (PE) rises markedly with age, and only a few cases have been reported in younger adults. Thrombophilia has been reported as one of the predisposing factors for PE in younger adults. Here we report an extraordinary case of PE complicated with dysplasminogenemia, a rare genetic disorder resulting in hypercoagulability, in a young male. An 18-yr-old male visited an emergency room in the United States complaining chest discomfort. He was diagnosed as PE with deep vein thrombosis without apparent risk factors. Anticoagulation therapy with warfarin had been initiated and discontinued after 6 months of treatment. After returning to Korea he was tested for thrombophilia which revealed decreased activity of plasminogen and subsequent analysis of PLG gene showed heterozygous Ala620Thr mutation. He was diagnosed with PE complicated with dysplasminogenemia. Life-long anticoagulation therapy was initiated. He is currently under follow-up without clinical events for 2 yr.
Verapamil [anticalcium agent]의 심근 보호작용Langendorff씨 장치하의 심근 보호 작용
유홍석,정정기,이동준,Yu, Hong-Seok,Jeong, Jeong-Gi,Lee, Dong-Jun 대한흉부심장혈관외과학회 1990 Journal of Chest Surgery (J Chest Surg) Vol.23 No.6
This study was evaluated the metabolic, physiologic and histologic effects of myocardial protection of verapamil[isoveratril]on isolated rat hearts to 90 minutes of ischemic arrest. Heart was perfused with a modified Kreb’s Henseleit bicarbonate buffer with glucose and arrested with retrograde coronary perfusion by glucose insulin[GI], potassium and verapamil. Mean aortic systolic pressure, heart rate, coronary flows were measured and morphologic changes were examined during working heart perfusion. Perfusion and arrest were controlled four groups subjected 60 isolated rat hearts. Four groups hearts reperfused during 40 minutes after 90 minutes global ischemia for physiologic recovery. 15 hearts of four groups were assayed to histological morphologic changes. GI treated hearts recovered less than 28% of function and changed more than 80% of mitochondria of control group. Verapamil hearts[0.2, 0.1 gm/kg] recovered more than 88% of function and permitted the maintenance of continuous cellular level of Serum Glutamic Oxalaxetate Transaminase[SGOT], but declined 28% of Phosphate Kinase[CP], GI treated heart showed widespread evidence of extensive damage of mitochondria. The damage was that interstitial huge edema are present and there was contraction band formation within the swollen cells. The verapamil and potassium group were not found morphologic change compared with control group. Their functions were shown that metabolic and physiologic action of verapamil-group lasted 20 minutes longer than potassium group.