• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2005년도 제24회 춘계학술대회논문집
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• pp.343-346
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• 2005

전산 해석과 병렬처리를 이용하여 정사각 관 내부를 전파하는 데토네이션파의 삼차원 구조를 살펴보았다. 가변 비열비 공식과 간략화 된 일단계 Arrhenius 반응 모델과 연계된 비점성 유체 방정식을 MUSCL 기반 TVD 해법과 4단계 Runge-Kutta 적분 방법을 이용하여 해석하였다. 삼차원에서의 비정상 해석 결과로부터 그을음 막 기록(smoked-foil record)에서 같은 길이와 다른 폭을 가지는 수평 및 대각 방향 불안정에 의한 상세한 파면 구조를 파악할 수 있었다.

• 한국추진공학회지
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• 제11권1호
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• pp.71-84
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• 2007

액체추진제 로켓 엔진에서 발생되는 연소불안정 현상에 대해 논의하였다. 지난 1930년대에 고체 및 액체 로켓에서 발견되었던 연소불안정 현상은 연소현상을 이용하는 가스터빈, 램 및 스크램젯, 로켓 등 모든 기관에서 문제가 대두되었고, 이러한 기관들의 안정적인 운용을 위해서는 연소 불안정성에 대한 연구가 필요하게 되었다. 그러나 엔진을 파괴하는 심각한 현상을 초래하는 이 현상을 아직까지 완전히 제어하고 있지 못하다. 따라서 연소불안정 현상이 발생되는 원인과 메커니즘을 알아보고, 액체추진제 로켓에 대한 각국의 개발사를 알아보았다.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2000년도 춘계학술발표대회 논문집
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• pp.126-130
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• 2000

In this study, flutter characteristics of a composite wing have been studied for the variation of laminate angles in the subsonic, transonic and supersonic flow regime. The laminate angles are selected by the aspect of engineering practice such as 0, $\pm$45 and 90 degrees. To calculate the unsteady aerodynamics for flutter analysis, the Doublet Lattice Method(DLM) in subsonic flow and the Doublet Point Method(DPM) in supersonic flow are applied in the frequency domain. In transonic flow, transonic small disturbance(TSD) code is used to calculate the nonlinear unsteady aerodynamics in the time domain. Aeroelastic governing equation has been solved by v-g method in the frequency domain and also by Coupled Time-Integration Method(CTIM) in the time domain. from the results of present study, characteristics of free vibration responses and aeroelastic instabilities of a composite wing are presented for the set of various lamination angles in the all flow range.

• 대한족부족관절학회지
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• 제16권2호
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• pp.73-78
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• 2012

Severe ankle sprain secondarily leads to chronic lateral ankle instability in 20-30%. Many surgical procedures have been presented for reconstruction of the lateral ankle instability, but controversy still remains for the ideal surgical option. Br$\ddot{o}$strom procedure or its modifications have been widely used but they have some limitations for the instabilities for the over-weight, physically high demanding patients and especially for significantly deficient or attenuated ligaments. Moreover the tenodesis procedures using peroneus brevis tendon are non-anatomical and sacrifice important lateral stabilizing tendon. Therefore recently, many reconstructive procedures for lateral ankle instability utilizing free allograft or autograft tendon have been introduced to anatomically stabilize the lateral ligaments to various degrees.

• 한국유체기계학회 논문집
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• 제1권1호
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• pp.72-80
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• 1998

Computational analysis of incompressible flows by numerically solving Navier-Stokes equations using multi-block finite volume method is conducted on a parallel computing system. Numerical algorithms adopted in this study $include^{(1)}$ QUICK upwinding scheme for convective $terms,^{(2)}$ central differencing for other terms $and^{(3)}$ the second-order Euler differencing for time-marching procedure. Structured grids are used on the body-fitted coordinate with multi-block concept which uses overlaid grids on the block-interfacing boundaries. Computational code is parallelized on the MPI environment. Numerical accuracy of the computational method is verified by solving a benchmark test case of the flow inside two-dimensional rectangular cavity. Computation in the axial compressor cascade is conducted by using 4 PE's md, as results, no numerical instabilities are observed and it is expected that the present computational method can be applied to the turbomachinery flow problems without major difficulties.

• Journal of Mechanical Science and Technology
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• 제18권8호
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• pp.1338-1348
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• 2004

A simplified method that models the deflagration process occurring in closed or vented vessels is described. When combustion occurs within the spherical or cylindrical vessels, the flame moves spherically or segmentally to the vessel periphery. The volume and area of each element along the propagating flame front are calculated by using simple geometrical rules. For instabilities and turbulence resulting in enhanced burning rates, a simple analysis results in reasonable agreement with the experimental pressure transients when two burning rates (a laminar burning rate prior to the onset of instability and an enhanced burning rate) were used. Pressure reduction caused by a vent opening at predetermined pressure was modeled. Parameters examined in the modeling include ignition location, mixture concentration, vented area, and vent opening pressure. It was found that venting was effective in reducing the peak pressure experienced in vessels. The model can be expected to estimate reasonable peak pressures and flame front distances by modeling the enhanced burning rates, that is, turbulent enhancement factor.

• International Journal of Aeronautical and Space Sciences
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• 제13권2호
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• pp.210-220
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• 2012

The model-free control of aeroelastic vibrations of a non-linear 2-D wing-flap system operating in supersonic flight speed regimes is discussed in this paper. A novel continuous robust controller design yields asymptotically stable vibration suppression in both the pitching and plunging degrees of freedom using the flap deflection as a control input. The controller also ensures that all system states remain bounded at all times during closed-loop operation. A Lyapunov method is used to obtain the global asymptotic stability result. The unsteady aerodynamic load is considered by resourcing to the non-linear Piston Theory Aerodynamics (PTA) modified to account for the effect of the flap deflection. Simulation results demonstrate the performance of the robust control strategy in suppressing dynamic aeroelastic instabilities, such as non-linear flutter and limit cycle oscillations.

• 한국자동차공학회논문집
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• 제6권5호
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• pp.37-44
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• 1998

Lean burn combustion is an important concept for improving the fuel consumption and exhaust emissions. However, the lean burning is associated with increased cycle-to-cycle combustion variations due to the ignition instabilities and redu- ced flame propagation rates. Engine stability under lean mixture conditions could be improved by increasing flame speed through enhanced flow characteristics and by securing ignitability with improvement of ignition systems. The effects of flow motion and ignition characteristics on the combustion performances were investigated in a 4-valve SI engine. Flow motions of tumble-swirl were varied with a swirl control valve attached at the inlet ports, while ignition energy and its distribution were controlled in a high -frequency ignition system by changing spark duration and spark frequency. The improvement of lean burn performance by the optimum flow motion and ignition characteristics is discussed.

• 한국항공운항학회지
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• 제13권1호
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• pp.20-31
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• 2005

In this study, subsonic flutter analyses have been conducted for a composite smart UAV with T-tail configuration at the critical flight condition. Detailed three-dimensional finite element model for dynamic analysis is constructed including its nonstructural elements corresponding to installed electronic equipments and fuels. Computational structural dynamics and aeroelastic techniques are conducted using MSC/NASTRAN and originally developed in-house codes. The results for fundamental vibration characteristics and flutter instabilities are presented and compared to each other for different fuel conditions.

• 한국항공운항학회지
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• 제22권1호
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• pp.76-84
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• 2014

Heavy Rainfall event accompanying with Mesoscale Convective Systems(MCSs) inducing flash flooding and Kimpo and Inchon International Airport closing over Seoul metropolitan area was investigated this study. This heavy rainfall event was occurred through the synoptic scale boundary of North Pacific Subtropical high, Typhoon and also can predicted by proper analysis of various forecasting parameters such as abundant moisture, instabilities, and synoptic/mesoscale forcing.