• 한국군사과학기술학회지
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• 제7권3호
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• pp.69-76
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• 2004

In this paper, an efficient inverse design method for nose shape of submerged body based on the MGM(Modified Garabedian-McFadden) design method has been developed. The MGM design method is a residual-correction technique, in which the residuals are differences between the desired and the computed pressure distributions. 3-D incompressible Wavier-Stokes equation was adopted for obtaining the surface pressure distribution and combined with the MGM design method to perform the inverse design of nose shape of submerged body. The design method was verified by applying to several airfoil shapes. Improved design shapes could be obtained when the method was applied to nose shapes of submerged body.

• Korean Journal of Mathematics
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• 제21권2호
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• pp.125-150
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• 2013

The stabilized Gauge-Uzawa method (SGUM), which is a second order projection type algorithm to solve the time-dependent Navier-Stokes equations, has been newly constructed in 2013 Pyo's paper. The accuracy of SGUM has been proved only for time discrete scheme in the same paper, but it is crucial to study for fully discrete scheme, because the numerical errors depend on discretizations for both space and time, and because discrete spaces between velocity and pressure can not be chosen arbitrary. In this paper, we find out properties of the fully discrete SGUM and estimate its errors and stability to solve the evolution Navier-Stokes equations. The main difficulty in this estimation arises from losing some cancellation laws due to failing divergence free condition of the discrete velocity function. This result will be extended to Boussinesq equations in the continuous research (part II) and is essential in the study of part II.

• 대한조선학회논문집
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• 제36권4호
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• pp.28-36
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• 1999

본 연구에서는 MGM(Modified Grrabedian-McFadden)방법에 기초한 효율적인 역설계 방법을 개발하였다. 표면압력 분포를 얻기 위해 2-D Navier-Stokes 방정식을 풀었고, 역설계를 수행하기 위해 MGM방법을 사용하였다. MGM 방법은 설계 목적 압력분포와 Navier-Stokes 방정식에서 계산된 압력분포의 차인 잔여량을 보정하는 잔여-보정 기법이다. 코드 개발을 위하여 몇몇 익형과 프로펠러 형상설계에 적용하였다. 이들 모두 목표하는 형상에 잘 수렴해 갔다.

• Journal of Advanced Marine Engineering and Technology
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• 제30권1호
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• pp.73-80
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• 2006

In order to compute the radiated sound from a vibrating structure, the Rayleigh's integral equation has to be derived from the Helmholtz equation using Green's function. Generally, the surface velocity in the Rayleigh's integral equation uses the root mean square(rms) velocity. The calculation value is too large, because it's not considered cancelation. On the other hand. using the complex velocity, the sound pressure is calculated too small, because it considers that sound is perfectly canceled out. Therefore, this thesis proposes a correction factor(CF) which considers vibration modes and the method by which to calculate the radiating sound pressure. The theoretical results are compared with the experimental values, and the proposed method can be verified with confluence.

• Nuclear Engineering and Technology
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• 제21권2호
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• pp.73-88
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• 1989

5개의 기존모델과 상관관계식에 기초한 10가지의 2상류 전체 압력강하 예측방법을 그 정확도와 가압경수로 운전 조건하에서의 적용도를 함께 검증하였다. 이 10가지 방법을 209개의 국부 및 전체비등 조건하의 실험치에 대해서 검증하였다. 각 상관관계식을 다른 범위의 압력과 질량속도 및 건조도에 대해서 평가하여 각각의 적은 데이터 군(Subsets)에 가장 잘 맞는 모델을 찾아냈다. 주어진 상태량(Property) 범위에 대해 가장 잘 맞는 기존 상관관계식과 그 상관관계식이 가진 예측오차를 보정하기 위한 수정계수를 사용하여 2상류 전체 압력강하를 계산하는 'K-TWOPD'라고 명명한 전산코드를 개발하였다. 이 전산코드의 평가 결과를 보면 기존 상관관계식의 실험치와의 오차범위는 대체로 $\pm$25%이상인데 비하여, 본 연구에서 제시한 방법은 사용한 모든 데이터를 95%의 확신도에서 $\pm$11% 범위이내로 실험치와 일치하고 있다.

• 한국측량학회지
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• 제27권5호
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• pp.535-544
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• 2009

GPS 위성으로부터의 신호는 위성과 지상의 수신기 사이의 경로에 걸쳐서 누적된 양의 수증기나 가강수량으로 복원하기 위해 이용되고 있다. GPS 위성 신호의 대류권 지연으로부터 가강수량으로 복원하기 위해서는 대류권의 총 지연량으로부터 실제 습윤 지연량을 계산하기 위하여 표면 기압 관측을 통해 결정된 실제 건조 지연량의 계산이 필요하다. 그러나 기압 정보를 얻기 위한 기압계가 모든 GPS 상시관측소와 동일한 지점에 위치하고 있지 않기 때문에 지상 기상 관측소로부터 획득한 해면 경정된 기압 정보를 이용하곤 한다. 이러한 기압의 직접 이용은 GPS를 이용한 수증기 복원 능력을 저하시키는 원인이 된다. 본 연구에서는 우리나라에 적합한 기압의 역해면 경정 보정 방안을 제시하고 이를 이용한 GPS 수증기의 정확도를 레디오존데 PWV와 평가하고 GPS로 추정한 수증기의 복원 능력의 개선 방안을 제시하였다.

• 대한조선학회논문집
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• 제55권5호
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• pp.379-384
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• 2018

This study showed the development process of structural design method of BHB(Blast Hardened Bulkhead) which are applicable in preliminary design stage. In the previous 1st report, the simplified structural scantling equations of BHB were formulated theoretically using the modified plastic hinge method supplemented by considering the membrane effects due to large plastic deformation. And the scantling methodology of plate thickness and section area of stiffeners of the curtain plate type BHB was dealt with. In the present 2nd report, derivation process of the correction factors which can adjust the developed scantling equations considering the uncertainties contained in the design parameters was introduced. Considering the actual BHB structures of 3 warship, the correction factors for the developed scantling equations for curtain plate type BHB were derived. Finally the applicability, validity of them and the strategy of future improvement were considered.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집E
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• pp.294-298
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• 2001

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 KOMPSAT2 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 Method of Characteristics (MOC).

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2006년도 추계 학술대회논문집
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• pp.31-35
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• 2006

The delta-formulation of the Navier-Stokes equations has been popularly used in the aerodynamics area. Implicit algorithm can be easily implemented in that by using Taylor series expansion. This formulation is extended for an unsteady analysis by using a dual-time integration. In the meanwhile, the incompressible flows with heat transfers which occur in the area of thermo-hydraulics have been solved by a segregated algorithm such as the SIMPLE method, where each equation is discretised by using an under-relaxed deferred correction method and solved sequentially. In this study, the dual-time delta formulation is implemented in the segregated Navier-Stokes solver which is based on the collocated cell-centerd scheme with un unstructured mesh FVM. The pressure correction equation is derived by the SIMPLE method. From this study, it was found that the Euler dual-time method in the delta formulation can be combined with the SIMPLE method.

• Coupled systems mechanics
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• 제7권4호
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• pp.421-440
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• 2018

In this study, a computational method for wall shear stress combined with an implicit direct-forcing immersed boundary method is presented. Near the immersed boundaries, the sub-grid stress is determined by a wall model in which the wall shear stress is directly calculated from the Lagrangian force on the immersed boundary. A coupling mathematical model of the transition process for a model Francis turbine comprising turbulent flow and rotating rigid guide vanes is established. The spatiotemporal distributions of pressure, velocity, vorticity and turbulent quantity are gained with the transient process; the drag and lift coefficients as well as other forces (moments) are also obtained as functions of the attack angle. At the same time, analysis is conducted of the characteristics of pressure pulsation, velocity stripes and vortex structure at some key parts of flowing passage. The coupling relations among the turbulent flow, the dynamical force (moment) response of blade and the rotating of guide vane are also obtained.