• Aerospace Engineering and Technology
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• v.1 no.2
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• pp.51-56
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• 2002

Satellite propulsion system is employed for orbit transfer, orbit correction, and attitude control. The monopropellant feeding system in the low-earth-orbit satellite blowdowns fuel to the thrust chamber. The thrust produced by the thruster depends on fuel amount flowed into the combustion chamber. If the thruster valve be given on-off signal from on-board commander in the satellite, valve will be opened or closed. When the thrusters fire fuel flows through opened thruster valve, instantaneous stoppage of flow in according to valve actuation produces transient pressure due to pressure wave. This paper describes transient pressure predictions of the KOMPSAT-2 propulsion system resulting from latching valve and thrust control valve operations. The time-dependent set of the fluid mass and momentum equations are calculated by MOC.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.9
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• pp.899-905
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• 2009

Most supersonic-flow test facility has axisymmetric nozzles or two-dimensional symmetric nozzles. Compared to these nozzles, a two-dimensional asymmetric nozzle has advantages of reducing low cost for various Mach number testing and undesirable flow structure such as shock wave reflection because the nozzle part can be directly connected to the test section part in this type of nozzle. The two-dimensional asymmetric nozzle, which was Mach number 2, was designed for supersonic combustion experiment. And it was verified with the numerical analysis and visualization of Mach wave. This study suggested the practical method for design and verification of supersonic two dimensional asymmetric nozzles.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.22 no.1
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• pp.1-13
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• 2009

A study for the nonlinear solution strategies to predict the ultimate behavior of a curved PSC cable-stayed bridge with complex geometry and highly nonlinear characteristics is presented. The load and displacement control strategies are used and found to be stable for the nonlinear solution of the PSC bridge up to the moderately excessive load. The ultimate analysis of curved PSC cable-stayed bridge using these solution strategies is not converged due to the propagation of the cracks in the wide range of the concrete elements and excessive variation of the stresses in the concrete elements and cables according to the complex geometry. The load control strategy using scale-down of the unbalanced loads is proposed as an alternative method for the case that the solution is not converged due to the severe nonlinearities involved in the PSC structures like a curved PSC cable-stayed bridge. Through the ultimate analysis of the PSC girder, the accuracy and the stability of the proposed solution strategies are evaluated. Finally, the numerical results for the ultimate analysis of the curved PSC cable-stayed bridge using scale-down of the unbalanced loads are compared with those obtained from other investigator. The validity of the proposed nonlinear solution strategy is demonstrated fairly well.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.2 no.3
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• pp.57-66
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• 1982

This study is directed toward the statical analysis of the curved girder bridge having irregular supports, This paper is specifically intended to propose an analytical methods in order to obtain the forces and displacements a section of girder bridges for mini-computer design. Transfer matrix, one of the efficient and widly used techniques in the structual analysis for mini-computer, is applied for characteristics of the section of curved girder bridges considering practical applicability of the solution method. Also, by eliminating the terms which contain the central angle of the member, in their denominators it has shown that this solution may also be used for the girder bridges whose axes become straight.

• Proceedings of the Korea Water Resources Association Conference
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• 2005.05b
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• pp.1088-1092
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• 2005

하도에서의 홍수추적시 유역내의 지류 혹은 지표 및 지하수등은 추적대상이 되는 하도구간내에서 측방유입량의 되어 유출수문곡선의 첨두유량, 첨두시간, 수문곡선의 형태등에 영향을 주므로 정확한 산정이 필요하며, 직접유출수문곡선에서 측방유입량은 지표유출에 의해 발생하므로 강우발생시 유역에서 하도까지 걸리는 도달시간의 산정이나 측방유입속도의 결정이 필요하다. 기존의 강우-유출 수문모형은 지표수흐름의 복잡한 메카니즘 및 수리특성을 규명하는데 어려움이 있다. 본 연구에서는 관측유입수문곡선 및 유출수문곡선을 이용하여 측방유입량을 산정하고, 하도구간으로 유입되는 기지의 측방유입량으로부터 수리학적 홍수추적을 위한 지배방정식인 Saint-Venant방정식의 수치해법중 하나인 양해법에 diffusing scheme을 적용하였다. 또한 하도 전구간에 동일한 측방유입속도로 유입될 경우와 하도중심을 기점으로 상류부와 하류부로 구분하여 두 구간의 측방유입속도가 다른 두가지 경우에 대해 측방유입속도를 역추정하였으며, 계산 유출 수문곡선과 관측 유출수문곡선을 비교$\cdot$분석함으로써 구성한 홍수추적모형에 대한 정확성과 타당성, 적용 가능성등을 검증하고자 하였다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.42 no.12
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• pp.1028-1036
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• 2014

A design procedure is established for hypersonic nozzles by using MOC(Method of Characteristics) and CFD. The inviscid nozzle contour is designed by MOC, then BLC(Boundary Layer Correction) is made by evaluating the boundary layer thickness from viscous CFD analysis. By comparing various definitions of the boundary layer thicknesses, it seems that the boundary layer thickness of 95% speed of the maximum value at the cross section satisfies best the design Mach number. Design procedure is as follow; MOC design, grid generation, inviscid analysis, viscous analysis, BLC and viscous analysis for confirmation and post-processing. All procedures are made automatically by using the batch processing.

• Transactions of the Korean Society of Mechanical Engineers
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• v.9 no.5
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• pp.638-646
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• 1985

Water hammering in nuclear or thermal power plant condenser cooling water systems in mathematically modeled and numerically analyzed based on the method of characteristics. Effects of variations of the discharge valve operating condition and the system geometry on the hydraulic transients are investigated for the cases when all or one of four pumps are tripped accidently due to loss of offisite power. Effects of ocean waves and tides on the steady-state and the transient operations are also studied. Water column separation in taken into account whenever necessary by means of a simplified physical model.

• Computational Structural Engineering
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• v.9 no.3
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• pp.107-114
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• 1996

The performance for the algorithm of the arc length method has been examined in terms of the choice of the tangential stiffness matrix through the analysis for the snap buckling phenomenon of the arch beam. The curved beam element with 2 nodes including shear effect has been formed by strain element technique and then it has been used in this nonlinear analysis. Snap-through characteristics has been examined with respect to the ratios of the arch beam length to hight.

• Water for future
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• v.23 no.2
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• pp.251-263
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• 1990

For surcharge flow in a sewer, the slot technique simulates surcharge flow as open - channel flow using a hypothetical narrow open piezometric slot at the sewer crown. The flow in a sewer is described mathematically using the unsteady open - channel Saint-Venant equations. In this study, the computer simulation model(USS-slot) using slot techniques is develeped to simulate the inlet hydrographs to manholes and the flow under pressure as well as free - surface flow in tree - type sewer networks of circular conduits. The inlet hydrographs are simulated by using the rational method or the ILSD progrm. The Saint-Venant equations for unsteady open - channel flow in seweres are solved by using a four - point implicit difference scheme. The flow equations of the sewers and the junction flow equations are solved simulaneously using a sparse matrix solution technique.

• Journal of the Korean Geotechnical Society
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• v.25 no.6
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• pp.59-72
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• 2009

The load distribution and deflection of offshore piles are investigated by lateral load-transfer curve method (p-y curve). Special attention is given to the soil-pile interaction and soil resistance of 3D wedge failure mode. A framework for determining a hyperbolic p-y curve is proposed based on theoretical analysis and experimental load test results. The methods for determining appropriate material parameters needed for constructing the proposed p-y curves are presented in this paper. Through comparisons with field case studies, it was found that the proposed method in the present study estimates reasonably the load transfer behavior of pile, and thus, the computed pile responses, such as bending moment and lateral displacement, agree well with the actual measured responses.