• Proceedings of the KSME Conference
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• 2003.04a
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• pp.1742-1747
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• 2003

When a shock wave is discharged from the exit of a duct, complicated flow is formed near the duct exit. The flow field is much more complicated under the ground effects or any other objects near the exit of a duct, such as the circumstance near the exit of the high-speed railway tunnel. The resulting flow is essentially three-dimensional unsteady with the effects of strong compressibility. In the current study, three-dimensional flow fields of the weak shock wave which is discharged from the exit of a duct are numerically investigated using a CFD method. Computations are performed for the weak shock wave in the range below 1.5. The results obtained show that the directivity and magnitude of the weak shock discharged strongly depend upon the Mach number of initial shock wave and are significantly influenced by the ground effects.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.544-549
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• 2003

When a shock wave arrives at an open end of tube, an impulse wave is discharged from the tube exit and causes serious noise and vibration problems. In the current study, the effect of the cross-sectional area of tube on the impulse wave is numerically investigated using a CFD method. The Harten-Yee's total variation diminishing(TVD) scheme is used to solve the axisymmetric, two-dimensional, unsteady, compressible Euler equations. With three different cross-sectional areas of tube, the Mach number of the incident shock wave $M_{s}$ is varied between 1.01 and 1.5. The results obtained show that the directivity and magnitude of impulse wave strongly depend upon the Mach number of incident shock wave and are influenced by the tube area. It is also known that the tube cross-sectional area significantly affects the magnitude of impulse wave at or near the tube axis.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.1666-1671
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• 2003

Exact dynamic stiffness model for a uniform straight pipeline conveying unsteady fluid is formulated from a set of fully coupled pipe-dynamic equations of motion, in which the fluid pressure and velocity of internal flow as well as the transverse and axial displacements of the pipeline are all treated as dependent variables. The accuracy of the dynamic stiffness model formulated herein is first verified by comparing its solutions with those obtained by the conventional finite element model. The spectral element analysis based on the present dynamic stiffness model is then conducted to investigate the effects of fluid parameters on the dynamics and stability of an example pipeline problem.

• Journal of Energy Engineering
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• v.24 no.4
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• pp.211-216
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• 2015

Heat exchanger tube array in a heat recovery steam generator is exposed to the hot exhaust gas flow and it could cause the flow induced vibration, which could damage the heat exchanger tube array. It is needed for the structural safe operation of the heat exchanger to establish the characteristics of flow induced vibration in the tube array. The researches for the flow induced vibration of typical heat exchangers have been conducted by using single cicular tube or circular tube array and the nondimensional PSD(Power Spectral Density) function with the Strouhal number, fD/U, had been derived by experimental method. From the present study, the basis for the application of flow induced vibration to the heat recovery steam generator tube array would be prepared. For the previous mentioned purpose, the present CFD analysis introduced a single fin tube and calculated with the unsteady laminar flow over the single fin tube. The characteristics of vortex shedding and lift fluctuation over the fin tube was investigated. The derived nondimensional PSD was compared with the results of the previous experimental researches and the characteristics of lift PSD over a single fin tube was established from the present CFD study.

• Journal of the Korean Society of Marine Environment & Safety
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• v.22 no.1
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• pp.118-122
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• 2016

When a geometric size of moonpool and an inflow velocity are determined based on the similarity of Froude number, Reynolds number is depending on the scale ratio of moonpool geometry. It means that different characteristics of flow fluctuations in moonpool can be observed depending on the scale ratio of moonpool even though Froude number is the same. In the present study two dimensional numerical simulations were performed to investigate the influence of scale ratios on the flow characteristics inside the moonpool. The inflow velocity at several scale ratios was determined to keep Froude number constant. A periodic response was observed in a small size of moonpool while a large moonpool showed complicated fluctuations with various amplitudes and frequencies, which made it difficult to distinguish the statistical steady-state response from the temporal responses in the case of large moonpool. The similarity of Froude number gave rise to a spectral characteristic which was inversely proportional to the square root of scale ratios ($f_{0.5}{\approx}{\sqrt{2}}f_1{\approx}2f_{2.0}$) but a low frequent occurrence of strong vortex ($f_{2.0}=0.07$)which is observed inside the large moonpool was characterized depending on scale ratios.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.3
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• pp.933-944
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• 1996

In this paper, two new techniques, the pattern filling and the refined flow field regeneration, based on the finite element method and Eulerian mesh advancement approach have been developed to analyze incompressible viscous flow with free surfaces. The gorerning equation for flow analysis is Navier-Stokes equation including inertia and gravity effects. The penalty and Newton-Raphson methods are used effectively for finite element formulation. The flow front surface and the volume inflow rate are calculated using the pattern filling technique to select an adequate pattern among five filling patterns at each quadrilateral control volume. By the refined flow field regeneration technique, the new flow field which renders better prediction in flow surface shape is generated and the velocity field at the flow front part is calculated more exactly. Using the new thchniques to be developed, the dam-breaking problem has been analyzed to predict flow phenomenon of fluid and the predicted front positions versus time have been compared with the reported experimental result.

• Proceedings of the Korean Institute of Industrial Safety Conference
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• 2003.10a
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• pp.86-91
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• 2003

원자력발전소의 설계는 다중방호의 개념에 의해 이루어져, 그 구조가 복잡하고 운전 형태도 다양하며, 이에 따라 사고의 전개 과정도 다양하게 나타난다. 이로 인해 원자력발전소의 운전원들은 발전소의 유동적인 상황에 대처할 수 있는 고도의 능력이 요구된다. 특히 주제어실 운전원들은 발전소의 기동 및 전출력 운전, 정지, 그리고 비정상 및 비상 상황 시의 적절한 대처에 대한 책임을 지고 있다. 발전소의 사고 분석 결과에 의하면, 사고에 대한 운전원의 대응이 사고의 전개에 직접적인 영향을 미치게 되며, 결과 적으로 사고에 대한 운전원들의 적절한 대응 능력은 발전소의 안전성에 중요한 부분임이 밝혀졌다.(중략)

• 한국전산유체공학회:학술대회논문집
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• 1998.11a
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• pp.191-196
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• 1998

A two-dimensional airfoil flying over a wavy wall is calculated by solving the unsteady Euler equation. Unsteady Transonic flow over an NACA00012 airfoil in pitching motion has been computed for code validation. Some numerical results for NACA6409 airfoil under different wave number, wave length, fly height are presented. The numerical results show the variation of lift and pitching moment coefficients are increased as wave length decrease.

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.1547-1548
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• 2008

본 논문에서는 유동적 비정상 시계열의 패턴과 규칙성을 잘 반영할 수 있는 최적의 차분 간격 후보군을 이용한 TS 퍼지 모델로 다중 퍼지 모델을 구현하였고, 각각의 모델들의 예측 특성을 반영하기 위하여 러프집합을 이용한 모델선택법을 제안하였다. 또한 TS퍼지 모델의 파라미터 식별에는 적절한 오차보정 메커니즘을 추가하여 더욱 예측 성능을 향상 시켰다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.3
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• pp.233-239
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• 2017

The CA (Control Assembly) of an SFR has a CRA(Control Rod Assembly) with an inner duct and control rod. During an emergency situation, the CRA falls into the duct of the CA for a rapid shut-down. The drop time and impact velocity of the CRA are important parameters with respect to the reactivity insertion time and the structural integrity of the CRA. The objective of this study was to investigate the dynamic behavior and integrity of the CRA owing to a drop impact. The impact analysis of the CRA under normal/abnormal drop conditions was carried out using the commercial FEM code LS-DYNA. Results of the drop impact analysis demonstrated that the CRA maintained structural integrity, and could be safely inserted into the flow hole of the damper under abnormal conditions.