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최가람(Ka-Ram Choi),장춘만(Choon-Man Jang),탁봉열(Bong Yul Tak),김찬규(Chan Kyu Kim) 대한설비공학회 2011 대한설비공학회 학술발표대회논문집 Vol.2011 No.7
Unsteady behavior of an internal flow has been performed for the diaphragm blower of a 1kW fuel cell. To analyze three-dimensional flow field in the diaphragm blower, general analysis code, CFX, is employed in the present work. SST turbulence model with scalable wall function is employed to estimate the eddy viscosity. Unstructured grids are used to represent a composite grid system. Throughout the numerical simulation, unsteady nature of an internal flow is successively analyzed by appling a moving mesh to the cavity region of diaphragm blower. Force variations on the lower plate of the cavity, which can analyze the motor torque, are also obtained in time. Detailed flow characteristics inside the cavity are analyzed and discussed.
최가람(Choi, Ka-Ram),장춘만(Jang, Choon-Man) 한국신재생에너지학회 2011 신재생에너지 Vol.7 No.3
This paper describes an internal flow characteristics of a fuel pressurized blower, used for 1kW domestic fuel cell system. To analyze the flow field inside the diaphragm cavity, compressible unsteady numerical simulation is introduced. SST model with scalable wall function is employed to estimate the eddy viscosity. Moving mesh system is applied to the numerical analysis for describing the volume change of a diaphragm cavity in time. Throughout numerical simulation with the modeling of the inlet and outlet valves in a diaphragm cavity, unsteady nature of an internal flow is successfully analyzed. Force variations on the lower plate of a diaphragm cavity are evaluated in time. It is found that the driving force at the suction stage of a diaphragm cavity is more necessary than that at the discharging stage.
최가람(Ka-Ram Choi),구원철(Weon-Cheol Koo) 한국해양공학회 2010 韓國海洋工學會誌 Vol.24 No.6
Bragg reflection of nonlinear waves is simulated by a 2D fully nonlinear numerical wave tank (NWT). The developed MWT was based on the Boundary Element Method (BEM) with potential theory and the mixed Eulerian-Lagrangian (MEL) time marching scheme with Runge-Kutta 4th-order time integration. A spatial variation of wave elevations and their Fourier amplitudes of each component are compared to investigate the effect of sea bottom ripples and their relative heights. The incident waves over an undulated sea bottom are partially reflected and changed to partial standing waves due to Bragg reflection. The present results are verified with linear calculations and experimental data. It is found that the 1st-order wave component is mainly affected by Bragg reflection and its spatial modulation is significant in front of the bottom ripples.
수치 파동 수조를 이용한 비선형파의 파형변화와 속도분포 해석
구원철(Weon-Cheol Koo),최가람(Ka-Ram Choi) 한국해양공학회 2009 韓國海洋工學會誌 Vol.23 No.6
In this study, the wave profiles and kinematics of highly nonlinear waves at various water depths were calculated using a 2D fully nonlinear Numerical Wave Tank (NWT). The NWT was developed based on the Boundary Element Method (BEM) with the potential theory and the mixed Eulerian-Lagrangian (MEL) time marching scheme by 4th-order Runge-Kutta time integration. The spatial variation of intermediate-depth waves along the direction of wave propagation was caused by the unintended generation of 2nd-order free waves, which were originally investigated both theoretically and experimentally by Goda (1998). These free waves were induced by the mismatch between the linear motion of wave maker and nonlinear displacement of water particles adjacent to the maker. When the 2nd-order wave maker motion was applied, the spatial modulation of the waves caused by the free waves was not observed. The respective magnitudes of the nonlinear wave components for various water depths were compared. It was found that the high-order wave components greatly increase as the water depth decreases. The wave kinematics at various locations were calculated and compared with the linear and the Stokes 2nd-order theories.
장춘만(Choon-Man Jang),최가람(Ka-Ram Choi),김진혁(Jin-Hyuk Kim),차경훈(Kyung-Hun Cha),김광용(Kwang-Yong Kim) 대한설비공학회 2011 대한설비공학회 학술발표대회논문집 Vol.2011 No.7
This paper describes the performance of centrifugal fan used for refuse collection system according to the number of splitters. To analyze the effect of blade numbers on fan performance, splitters installed between blades are introduced. The chord length of splitters is determined by 90 percent blade chord using the results of preliminary research. The fan performance is analyzed by three-dimensional Navier-Stokes analysis, and also compared to the results obtained by experiments. Throughout the experimental measurements and numerical simulation, fan performance can be increased by reducing the flow loss region mainly observed on the blade suction side. Pressure and efficiency are successfully increased by 3.6% and 4.4% compared to reference, respectively. Detailed flow pattern is also analyzed by the results of numerical simulation.
Trehalose 인자 도입 수도 계통 현미가 화랑곡나방(나비목: 명나방과)과 어리쌀바구미(딱정벌레목: 바구미과)의 생활사에 미치는 영향
천용식,류기현,김성욱,고예강,최가람,남영우,류문일,Chun, Yong-Shik,Ryu, Ki-Hyun,Kim, Sung-Uk,Ko, Ye-Kang,Choi, Ka-Ram,Nam, Young-Woo,Ryoo, Mun-Il 한국응용곤충학회 2008 한국응용곤충학회지 Vol.47 No.1
The biology of indian meal moth and maize weevil on the trehalose gene introduced rice (var 'Nakdong') (T-Nakdong) was compared to that on the rice without gene introduction (Nakdong) at $28{\pm}1.0^{\circ}C$. Development of the both two insects was significantly delayed; on T-Nakdong, the developmental periods of female moth $({\pm}SE)$ and weevil were $38.46{\pm}0.42\;and\;36.38{\pm}0.28days$, respectively. Whereas those on Nakdong were $36.38{\pm}0.28\;and\;34.33{\pm}0.18$, respectively. Net reproduction rate of Indian meal moth on T-Nakdong $(3.0{\pm}0.14)$ was significantly lower than that on Nakdong $(9.25{\pm}0.13)$, due to the lower emergence rate $(21.08{\pm}0.04%\;vs\;48.30{\pm}0.06%)$. The life table statistics of maize weevil on T-Nakdong was estimated to be similar to those on Nakdong. The delayed development of T-Nakdong suggested that the factor for development of the insects could be changed by the introduction of trehalose gene into the rice variety. Trehalose 유전자를 삽입하여 내건성을 강화한 벼(품종 '낙동': T-낙동)에서 수확된 쌀이 주요저장 해충인 화랑곡나방(Plodia interpunctella Hubner)과 어리쌀바구미(Sitophilus zeamais Motschulsky)의 개체군 성장에 미치는 영향을 조사하였다. $28{\pm}1^{\circ}C$에서 T-낙동에서의 화랑곡나방 암컷의 발육$({\pm}SE)$ 일수는 $38.46{\pm}0.42$로 낙동에서의 발육일수 $36.38{\pm}028$일에 비해 유의하게 지연되었다. T-낙동에서의 화랑곡나방의 암컷 당 산란수는 $152.07{\pm}10.79$개로 낙동에서의 산란수$(141.6{\pm}14.56)$와 유사하였으나 우화율은 $21.08{\pm}0.04%$로 낙동에서의 $48.30{\pm}0.06%$에 비해 유의하게 낮았고 순증가율은 $3.0{\pm}0.14$로 낙동에서의 $9.25{\pm}0.13$에 비해 유의하게 낮았다. 어리쌀바구미의 발육일수는 T-낙동과 낙동에서 각각 $36.38{\pm}0.28$일과 $34.33{\pm}0.18$일로 유의한 차이를 보였으나 생명표 통계량에 영향을 미치지는 못하였다. 화랑곡나방과 어리쌀바구미 모두에서 발육이 지연된 현상은 형질전환으로 인해 발육에 관계된 인자에서의 변화가 있었음을 암시하는 것이다.
장춘만(Choon-Man Jang),최가람(Ka-Ram Choi),양상호(Sang-Ho Yang) 대한설비공학회 2011 대한설비공학회 학술발표대회논문집 Vol.2011 No.7
This paper describes structural characteristics of a centrifugal fan, which is mainly used for industrial plant. Structural analysis has been performed by finite element method using the results of pressure load obtained by computational fluid dynamics. The thickness distributions of impeller blade and plate are between 3.5 mm and 6 mm. Throughout the structural analysis of the fan, it is found that the positions of maximum stress and deformation are located at the junction of impeller blade and impeller plate and at the middle of impeller tip, respectively. Modal frequency is mainly affected by the thickness of impeller plate rather than impeller blade.
장춘만(Choon Man Jang),최가람(Ka Ram Choi),양상호(Sang Ho Yang) 대한기계학회 2011 대한기계학회 춘추학술대회 Vol.2011 No.4
본 연구에서는 생활폐기물 관로이송 설비에서 사용되고 있는 원심송풍기의 성능향상을 위해 임펠러 날개 압력면과 부압면 측에 스프리터를 각각 장착하고, 스프리터의 코드길이 변화에 따른 성능특성을 삼차원 나비어-스톡스 방정식을 통한 수치해석과 실험적인 방법을 적용하여 분석하였다. 스프리터에 의한 날개 수 증가를 고려하여 기존 송풍기의 11개 날개를 7개로 줄이고, 날개의 회전방향으로 2개의 스프리터를 균등하게 설치하였다. 실험 및 삼차원 수치해석에 의한 분석을 통하여 날개 부압면측에서 발생하는 역류현상을 억제할 수 있는 스프리터를 설치하고 코드길이를 변수로 설정하여 분석하였다. 이를 통해 스프리터의 코드길이가 길어질수록 원심송풍기 압력 및 효율특성이 설계유량 조건 뿐만 아니라 유량증가에 따라 향상됨을 확인하였다. 설계유량을 기준으로 스프리터 부착 원심송풍기에 의해 효율 및 압력은 기존대비 각각 4% 및 18% 향상됨을 알 수 있었다. This paper describes centrifugal fan performance, which is mainly used in refuse collection system, according to the splitters installed near the suction and pressure surface side. The flow characteristics inside the components are analyzed by three-dimensional Navier-Stokes analysis, and also compared to the results obtained by experiments. Throughout the experimental measurements and numerical simulation of the fan having splitters, it is found that the reverse flow region observed near the suction side of the blade can be reduced by installing a splitter. Fan performance is successfully increased by controlling the chord length of the splitter installed near the blade suction side. At the design flow condition, efficiency and pressure of the fan having splitters increase up to 4% and 18% compared to reference fan, respectively.