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옥호남(Honam Ok) 한국전산유체공학회 2001 한국전산유체공학회 학술대회논문집 Vol.2001 No.-
The incompressible Reynolds-averaged Navier-Stokes equations are solved to predict the aerodynamic characteristics of an airship hull. The concept of pseudo-compressibility is employed to couple the pressure field with the velocity field. The upwind differencing method for spatial discretization and a line relaxation scheme for time integration are used. The flowfield around the low drag airship hull of fineness ratio 4 is solved for two Reynolds numbers with a wide range of angle of attack. The effect of Reynolds number and transition position is briefly examined together with the change in aerodynamic coefficients due to a gondola attached to the hull, and the results will be used as basic data for the design of a low drag airship hull.
옥호남(Honam Ok),김인선(Insun Kim) 한국항공우주연구원 2007 항공우주기술 Vol.6 No.1
로켓 노즐의 변위에 따라 추력 중심이 어떻게 이동되는지를 예측하기 위해 전산유동해석을 수행하였다. 노즐 변위각을 0/1/3도로 하여 3차원 계산을 수행하였으며, 축대칭 계산에서 보지 못했던 공력계수의 진동이 관찰되었다. 변위각 1도 및 3도 조건에 대하여 추력중심 위치가 -16 ㎜ 및 -4 ㎜로 나타났으며, 노즐 변위에 따른 추력 중시의 변화는 무시할 만한 정도라고 볼 수 있다. 이와 더불어 오해하기 쉬운 로켓 엔진의 추력 발생 원리를 간략히 수학적으로 기술하였으며, 로켓 외부 유동이나 노즐 변위와 같은 대칭 조건에서 압력 중심을 어떻게 정의해야 할 것인지에 대해서도 논하였다. A computation was made to predict the movement of the thrust center position due to the rocket nozzle deflection. Three dimensional computations were done for the nozzle deflection angles of 0/1/3 degrees, and the oscillation of aerodynamic coefficients, not observed for the axisymmetric cases, was encountered. The position of the thrust center was found to be at -16 ㎜ and -4 ㎜ for the deflection angles of 1 and 3 degrees, respectively, and it can be concluded that the thrust center movement due to nozzle deflection is negligible. In addition to the computational results, the mechanism of thrust generation in a rocket engine is described with a brief mathematical derivation as it is sometimes mistaken. Also presented are some descriptions on the problem of pressure center definition for symmetric cases such as a rocket external flow problem and the nozzle deflection case.
다중 Port로 연결된 다중 격실 Vent 해석 기법 개발
옥호남(Honam Ok),김인선(Insun Kim) 한국유체기계학회 2006 유체기계 연구개발 발표회 논문집 Vol.- No.-
An analysis method is developed for the prediction of venting in multiple compartments which are connected in series or parallel through multiple ports. The existing method by the authors is modified to remove the limitation in number of ports and compartments, and the more general polytropic relation or solution of the additional energy equation replaces the previous isentropic relation allowing the prediction of pressure rise in addition to pressure drop. The accuracy of the method is verified by comparison with the results by NASA Flap code for the problem of pressure drop in a payload in the Space Shuttle cargo bay. It is expected that this method will be a useful tool in prediction of the pressure variation in a payload or payload capsule without mentioning the payload fairing itself.
옥호남(Honam Ok),장병희(Byeong-Hee Chang),이융교(Yung-Gyo Lee),오수훈(Soo-Hun Oh) 한국전산유체공학회 2002 한국전산유체공학회 학술대회논문집 Vol.2002 No.-
Numerical analysis of the flowfield around a 50-meter class airship is performed to determine the optimal position for the airspeed probe installation. The turbulent flow around the hull with gondola is analyzed to examine the characteristics of the data measured by the probe attached to the gondola, and they turned out to show the nonlinear relation between the freestream and measured angles of attack and be influenced by the Reynolds number. New position of the hull nose was proposed and the effect of various factors on the flowfield around the nose was also examined. The analysis with a panel method showed that the effect of empennage was negligible, and the effect of gondola and boundary layer thickness had also little impact. It was shown that the freestream angle of attack would be the only independent variable for the probe position around the hull nose in constructing the calibration matrix.
혼합격자를 이용한 2차원 난류 유동장 해석 프로그램의 병렬화
옥호남(Honam Ok),박승오(Seung-O Park) 한국전산유체공학회 1999 한국전산유체공학회 학술대회논문집 Vol.1999 No.-
A two-dimensional Navier-Stokes solver using hybrid meshes is parallelized with 3 domain decomposition method. The focus of this paper is placed on minimizing the amount of effort in parallelizing the serial version of the solver, and this is achieved by adding an additional layer of cells to each decomposed domain. Most subroutines of the serial solver are used without modification, and the information exchange- between neighboring domains is achieved using MPI(Message Passing Interface) library. Load balancing among the processors and scheduling of the message passing are implemented to reduce the overhead of parallelization, and the speed-up achieved by parallelization is measured on the transonic - invisicd and turbulent flow problems. The parallelization efficiencies of the explicit Runge-Kutta scheme and the implicit point-SGS scheme are compared and the effects of various factors on the results are also studied.