• Journal of the Korean Society of Propulsion Engineers
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• v.4 no.4
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• pp.42-49
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• 2000

A computation using the mass-averaged implicit Wavier-Stokes equations has been applied to solve the flow fields of the supersonic jets normally injected into supersonic freestreams and several types of turbulence model has been employed to close the governing equations. The ratio of the freestream to injection flow total pressures has been varied to elucidate the major characteristics of the mixing flow of the two streams. The freestream Mach number has been varied to investigate some change in the injection flow field. The results show that the positions of the separation and reattachment, locating upstream and downstream of the injection hole respectively, are strongly dependent on the ratio of total pressures and the freestream Mach number.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.1
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• pp.97-103
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• 1993

This paper presents a quasi-analytical method using integral equations to obtain head distributions in unsaturated porous media with different hydrogeologic properties. One-dimensional soultion algorithms were developed for two cases of boundary conditions at the top: 1) constant head and 2) constant flux. Water table elevation at the bottom was assumed known for both cases. The methodology was applied to a fly ash disposal facility in an alluvium area. The results showed that the pressure head distributions had high nonlinearity with large gradients slightly above the interface of two media which made preliminary numerical solutions implausible. The developed method helped to structure finite element grids for improving convergence and accuracy.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.11
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• pp.989-997
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• 2017

We study opening transient responses of a self-sustainable poppet valve, which is usually used for the main oxidizer shut-off valve of liquid rocket engines. In order to perform numerical analysis, a pneumatic supply system was simulated as an orifice with a diameter of 3.2 mm and the equations of motion of valve moving part were derived. For the validation of the study, a comparison of numerical predictions and experimental results has been done. As one of the practical applications of this study, the employment of an orifice in a high pneumatic pressure has been presented to control the valve opening time.

• Nuclear Engineering and Technology
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• v.23 no.3
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• pp.306-315
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• 1991

This paper considered the out-of-plane motion of the piping system conveying fluid through the elbow connecting two straight pipes. The extended Hamilton's principle is used to derive equations of motion. It is found that dynamic instability does not exist for the clamped-clamped, clamped-pinned and pinned-pinned boundary conditions. The frequency equations for each boundary conditions are solved numerically to find the natural frequencies. The effects of fluid velocity and Coriolis force on the natural frequencies of piping system are investigated. It is shown that buckling-type instability may occur at certain critical velocities and fluid pressures. Equivalent critical velocity, which is defined as a function of flow velocity and fluid pressure, are calculated for various boundary conditions.

• Nuclear industry
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• v.20 no.6 s.208
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• pp.31-44
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• 2000

본 연구에서 액체금속로의 노심용융(core meltdown)으로 인한 초 즉발 임계(super-prompt critical)의 출력 폭주 사고시, 노심의 반응도 및 열수력 특성 변화와 에너지 방출량등을 계산하기 위하여, Bethe-Tait 방버론을 수정, 보완한 분석 모델이 개발되었다. 주요 보완 내용으로서는, 금속 연료 노심의 단상 액체 영역에서의 선형의(Linear) threshold 형태의 상태 방정식뿐만 아니라 포화 증기(saturated fuel vapor) 영역에서의 상태 방정식이 개발되었고, 이에 따른 노심 붕괴 반응도(disassembly reactivity)의 분석 모델이 개발되었다. 또한 도플러 반응도 효과를 고려하기 위한 분석모델도 아울러 개발되었다. 상기 보완 모델을 실행할 수 있는 수치 해석 프로그램이 개발되었고, 이를 활용하여 KALIMER에서 HCDA가 발생하였을 경우 노심에서의 에너지 방출량 계산이 수행되었다. 분석결과 도플러 효과와 포화 증기 영역에서의 압력 증가 및 노심팽창의 중요성이 확인되었다. 도플러 효과가 고려되지 않을 경우 HCDA는 분석된 모든 반응도 삽입률에 대하여 폭발적인 에너지 방출과 함께 사고가 종결되는 것으로 평가되었다. 그러나 도플러 상수가 최적 평가치인 -0.002인 경우 50$/s이하의 반응도 삽입률에서는 노심은 비등점(0.8KJ/g)에 도달치 않았으며, 설계 기준 사고인 100$/s의 경우에도 노심은 포화 증기 영역에 머물고 압력이 급격히 증가하는 단상(single phase)액체 영역의 threshold 값에 미치지 않기 때문에 사고는 핵연료 증기(vapor)의 점진적인 분산과 함께 종결되는 것으로 분석되며, 총 에너지 발생량은 약 1,800MJ로서 기계적 손상 에너지로 전환되는 분율을 고려할 때 KALIMER 원자로 용기의 구조 설계 기준치에 비해 상당한 여유도를 갖는 것으로 평가되었다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.8
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• pp.8-17
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• 2005

It is well known that preconditioning methods are efficient for convergence acceleration in the compressible low Mach number flows. In this study, the original Euler equations and three differently nondimensionalized preconditioning methods are implemented in two dimensional inviscid bump flows using the 3rd order MUSCL and DADI schemes as numerical flux discretization and time integration, respectively. The multigrid and local time stepping methods are also used to accelerate the convergence. The test case indicates that a properly modified local preconditioning technique involving concepts of a global preconditioning allows Mach number independent convergence. Besides, an asymptotic analysis for properties of preconditioning methods is added.

• Journal of the Society of Naval Architects of Korea
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• v.39 no.3
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• pp.8-17
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• 2002

In this paper, the computational analysis of open-water characteristics for three model propellers(P4119, P4842 and 3 podded propeller of KRISO) is done by using a viscous-flow method based on Reynolds-Averaged Navier-Stokes equations. The results are presented for open-water performances, blade-section pressures, and circumferentially-averaged velocity profiles for the all three propeller models. Overall close agreements with available experimental data are shown. However, some discrepancies are also found in the pressure near the leading edge of the propeller blade and the open-water performance of the podded propellers.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.163.1-163.1
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• 2013

플라즈마 시뮬레이션을 수행하기 전에 현 컴퓨터의 계산 능력범위 내에서 물리적으로 타당하게 설명할 수 있는 수치 해석 방법을 먼저 정한다. 예를 들면, 가스 반응이 많고 각 가스 반응 중에 중요가스 반응을 빠르고 선택적으로 선별하고자 할 때, 혹은 외부 입력 변화에 따른 플라즈마 종의 온도 또는 밀도를 대략적으로 파악하고자 할 때는 공간적인 분포를 고려하지 않는 0차원 global 모델링을 이용한다. 압력이 높고 충돌이 빈번한 경우에는 플라즈마를 유체적인 관점에서 기술이 가능하므로, 볼츠만 방정식에서 속도에 관한 0차, 1차, 2차 모멘텀을 이용하여 유도된 유체 방정식을 이용한다. 반대로 압력이 낮고 충돌이 거의 없는 경우에는 플라즈마 입자를 개별적으로 추적하는 입자 전산 모사 방법을 이용한다. 지금까지는 앞에서 언급한 예와 같이, 개별 플라즈마 상태에 맞는 시뮬레이션 코드를 각각 만들어야 했고, 각 코드를 개별적으로 유지 보수해야 했다. 하지만, 개별적으로 코드를 유지 보수를 해야 할 경우에는, 동일한 기능을 하는 함수를 반복적으로 각 코드에 입력해야 하는 불편함이 따르고, 각 수치해석 방법의 장점을 모은 하이브리드 방법과 같은 전사모사를 개발할 때 각 기능을 통합해야 하는 어려움이 따른다. 또한 지금까지 개발된 대부분의 플라즈마 코드는 외부 입력에 대해 유연하지 못한 대처로 새로운 가스 반응을 추가하거나 새로운 수치해석 방법을 추가할 경우에는 코드를 전체적으로 수정해야 하는 어려움이 있었다. 따라서 코드를 통합적으로 관리할 수 있고, 외부 입력에 대해 유연하게 대처할 수 있는 시뮬레이터가 필요했다. 여기에서는 객체 지향 언어인 C++ 언어를 이용하여, 사용자 입력에 대해 유연하게 대처할 수 있고, 복잡한 화학 반응을 특정 수치 해석 방법에 상관없이 통합적으로 관리할 수 있는 코드를 개발하였다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.04a
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• pp.103-108
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• 2011

The turbulent mixing of a kerosene/liquid oxygen coaxial swirl injector under supercritical pressures have been numerically investigated. Kerosene surrogate models are proposed for the kerosene thermodynamic properties. Turbulent numerical model is based on LES(Large Eddy Simulation) with real-fluid transport and thermodynamics over the entire pressure range; Soave modification of Redlich-Kwong equation of state, Chung's model for viscosity/conductivity, and Fuller's theorem for diffusivity to take account Takahashi's compressible effect. The effect of operating pressure on thermodynamic properties and mixing dynamics inside an injector and a combustion chamber are investigated. Power spectral densities of pressure fluctuations in the injector under various chamber pressure are analyzed.

• Journal of the Korean Chemical Society
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• v.18 no.5
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• pp.320-328
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• 1974

It is unable to derive the standard emf ($E^{\circ}$) of the cell at high pressure from the conventional method. However, when the concept of the complete equilibrium constant($K{\circ})$) is available to the conventional Nernst equation, it is possible to get the standard emf of the cell at high pressure(complete Nernst equation). Moreover, the other thermodynamic properties, such as the net change of solvation number(k), the compressibility of solvent(${\beta}$), ionization constant(K), the standard free energy change(${\Delta}G^{\circ}$), the standard enthalpy change(${\Delta}H^{\circ}$) and the standard entropy change (${\Delta}S^{\circ}$) of the cell reaction at equilibrium state have been also obtained. In this experiment, the emf of the cell; 12.5 % Cd(Hg)│$CdSO_4(3.105{\times}10^{-3}M),\;Hg_2SO_4│Hg$ have bee measured at temperature from 20 to $35^{\circ}C$ and at pressures from 1 to 2500 atms. The emf of the cell increased with increasing pressure at constant temperature, and did with increasing temperature at constant pressure. The net change of solvation number(k) of the cell reaction was 41.96 at $25^{\circ}C$, and kept constant value with pressure, while, K and ${\Delta}S^{\circ}$ increased with pressure, but whereas ${\Delta}G^{\circ}$ and ${\Delta}H^{\circ}$ decreased. Since the standard emf of the cell at high pressure can be calculated from the complete Nernst equation, the theory of chemical equilibrium could be developed with at high pressure as well as at the atmosphere.