• Journal of the Computational Structural Engineering Institute of Korea
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• v.14 no.4
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• pp.413-422
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• 2001

In this study, the effect of hydrodynamic masses is investigated in the dynamic characteristics and earthquake response analyses of the submerged HANARO flow tubes. First, the consistent hydrodynamic masses of the surrounding water are obtained by finite element method. Then, modal analyses and response spectrum analyses are performed and verified by comparing the results with those measured from an experiment. Arbitrary cross-sections of submerged structures and boundary conditions of the surrounding fluid can be considered by using the general benefits of a finite element method comparing with the conventional analytical methods. Practical criteria based on parametric studies are proposed to evaluate the dynamic characteristics of HANARO flow tubes including the hydrodynamic masses.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.6
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• pp.1128-1146
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• 1989

본 논문에서는 2상 횡유동의 진동 메카니즘을 규명하기 위한 실험계획의 일환으로 실시된 실험으로 부터 튜브집합체의 추가질량(hydrodynamic mass)과 감쇠 (damping)에 대해 고찰하였다. 실험은 튜브배열과 피치 대 직경비(pitch-over-di- ameter:.rho./ｄ)가 상이한 튜브집합체에 대해 2상 유체를 모의한 공기-물(air-water) 혼합물에서 수행하였다. 액체상태로부터 99%의 보이드율까지 변화된 2상 유체의 유량은 튜브가 유체탄성 불안정성 (fluidelastic instability)에 도달할 때까지 점진적으로 증가하였다.

• Journal of the Korean Society of Propulsion Engineers
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• v.2 no.2
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• pp.83-87
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• 1998

To reduce the supersonic jet noise from the liquid rocket engine, water injetion silencers were designed and tested. Test variables were the mass flow rate of water jet, the length of primary pipe and the diameter of expansion pipe. Followings are the results of this study. 1. From the same mass flow rate of water, longer primary pipe was more effective to reduce the noise. 2. Noise level was significantly reduced with increasingly water flow rate. 3. The optimum water flow rate was 10～12 times of the propellant flow rate. 4. By installing expansion pipe, noise level was reduced approximately 30㏈ compared to without expansion pipe

• Bulletin of the Society of Naval Architects of Korea
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• v.27 no.3
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• pp.107-116
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• 1990

The liquid sloshing in an elastic tank is a fluid-structure interaction problem. It requires nonlinear analysis to solve the complicated physics involved in the large interaction of fluid-structure, the variation of dynamic characteristics of structure due to hydrodynamic loading, and the distorsion of fluid flow due to structural vibration. In this paper a Lagrangian FEM is introduced to analyze the liquid sloshing in an elastic tank assuming that the elastic wall is one degree of freedom rigid wall. Numerical integration is performed using an implicit-explicit algorithm, which is formed by mixing the predictor-corrector method and the Runge-Kutta 4th order method. The influence of dynamic characteristics of the sloshing tank on the fluid flow is discussed. The numerical method is also applied for the simulation of the wall generated wave in the tank.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.3
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• pp.171-181
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• 2017

Two-phase cross flow exists in many shell-and-tube heat exchangers such as condensers, evaporators, and nuclear steam generators. The drag force acting on a tube bundle subjected to air/water flow is evaluated experimentally. The cylinders subjected to two-phase flow are arranged in a normal square array. The ratio of pitch to diameter is 1.35, and the diameter of the cylinder is 18 mm. The drag force along the flow direction on the tube bundles is measured to calculate the drag coefficient and the two-phase damping ratio. The two-phase damping ratios, given by the analytical model for a homogeneous two-phase flow, are compared with experimental results. The correlation factor between the frictional pressure drop and the hydraulic drag coefficient is determined from the experimental results. The factor is used to calculate the drag force analytically. It is found that with an increase in the mass flux, the drag force, and the drag coefficients are close to the results given by the homogeneous model. The result shows that the damping ratio can be calculated using the homogeneous model for bubbly flow of sufficiently large mass flux.

• Journal of Advanced Marine Engineering and Technology
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• v.35 no.6
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• pp.750-756
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• 2011

An experimental study was carried out to measure the heat transfer coefficient in flow boiling to deionized water in a microchannel having a hydraulic diameter of $500{\mu}m$. Tests were performed in the ranges of heat fluxes from 100 to 400 kW/$m^2$, vapor qualities from 0 to 0.2 and mass fluxes of 200, 400 and 600 kg/$m^2s$. From the experimental results, it is found that the measured heat transfer coefficients is independent of mass flux and quality, and is somewhat dependent of heat flux. Measured data of heat transfer are compared to a few available correlations proposed for macroscale. The previous correlations for macroscale overpredicted the flow boiling heat transfer coefficient for the test conditions considered in this work.

• 한국전산유체공학회:학술대회논문집
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• 2005.04a
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• pp.223-227
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• 2005

최근 전산 유체의 발달로 이상 유동해석의 캐비테이션 모델 적용 방법이 발전되어 왔으나 다양한 수력학적 시스템에서 발생하는 캐비테이션 유동은 난류이며 물과 공기 사이에서의 복잡한 상호 작용을 가지고 있으므로 그 적용 예가 아직은 미흡한 상태이다. 본 연구에서는 수중에서의 캐비테이션 해석과 이상 유동 해석을 위한 코드 개발 및 검증을 목적으로 3차원 회전체 주위의 캐비테이션 유동을 여러 가지 조건들의 변화를 적용하여 해석하였다. 또한 캐비테이션 발생과 관련한 다른 난류 모델에 적용하여 비교 분석을 수행하였다. 해석을 위한 모델의 지배방정식은 이상유동 Wavier-Stokes 방정식, 질량$\cdot$모멘텀 방정식의 혼합된 형태로 구성되어 있으며 방정식의 해를 구하기 위한 방법으로 유한차분법을 이용하였다. 해석결과의 신뢰성을 고려하여 반구형 실린더 주위의 캐비테이션 유동의 실험치와 비교 분석하였다. 그 결과, 본 연구의 수치 해석 방법과 실험적 방법의 결과가 강한 양의 상관관계를 가짐을 알 수 있었으며, 이러한 수치적 뒷받침은 본 연구의 전산수치 해석 방법이 앞으로의 여러 유동 해석으로의 적용 가능성을 보여준다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.9 no.1
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• pp.56-63
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• 1985

Methods for evaluating the added masses of square and hexagonal structures with fluid gap are presented. For a sufficiently small fluid gap, an analytical expression for the added mass is found using the method of matched asymptotic expansion. Experimental data and numerical results using finite element method are also obtained for various sizes of fluid gap. It is shown that added masses increase in inverse proportion to the fluid gap as it becomes smaller. Experimental data, theoretical and numerical results are in good agreement.

• Journal of Power System Engineering
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• v.16 no.1
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• pp.30-37
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• 2012

공기 양수 펌프는 재생 에너지 분야, 부식 및 마모 특성의 유체의 활용 등 높은 신뢰성과 낮은 유지보수 비용을 필요로 하는 분야에서 그 사용이 증대되고 있다. 본 연구에서는 소형 공기 양수 펌프의 성능 평가 및 기초 데이터를 얻기 위한 연구로, D=0.012~0.019m, L=0.933m인 배관의 침수 깊이(${\beta}$=0.55,0.60,0.65,0.70)에 따른 수치해석을 수행하였다. 수치 해석 및 실험 결과는 유사성을 뛰었으며, 펌프의 사양과 효율은 공기의 질량 유속 비, 침수 깊이 비와 양수 배관의 길이에 관한 함수로 나타났다. 그리고 최대 물과 공기 질량 유속의 비는 각 배관에서 서로 다른 침수 깊이의 비로 나타났으며, 공기 양수 펌프의 최대 효율이 발생되는 운전조건은 슬러그(slug)와 슬러그 교반 정도(slug-churn flow regime)에 따라 나타남을 알 수 있었다.

• Journal of Energy Engineering
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• v.20 no.1
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• pp.30-35
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• 2011

To clarify the hydraulic and thermal characteristics of ice slurry which made from 6.5% ethylene glycol-water solution flow in the double tube and plate type heat exchanger, experimental studies were performed. The mass flux and ice fraction of ice slurry were varied from 800 to 3500 kg/$m^2s$(or 7 to 17 kg/min) and from 0 to 25%, respectively. Through the experiment, it was found that the measured pressure drop and heat transfer rate increase with the mass flux and ice fraction; however the effect of ice fraction appears not to be significant at high mass flux region. At the region of low mass flux, a sharp increase in the pressure drop and heat transfer rate were observed depends on mass flux.