• Nuclear Engineering and Technology
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• v.41 no.6
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• pp.841-848
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• 2009

A simple model to analyze non-linear density-wave instability in a sodium-cooled helically coiled steam generator is developed. The model is formulated with three regions with moving boundaries. The homogeneous equilibrium flow model is used for the two-phase region and the shell-side energy conservation is also considered for the heat flux variation in each region. The proposed model is applied to the analysis of two-phase instability in a JAEA (Japan Atomic Energy Agency) 50MWt No.2 steam generator. The steady state results show that the proposed model accurately predicts the six cases of operating temperatures on the primary and secondary sides. The sizes of three regions, the secondary side pressure drop according to the flow rate, and the temperature variation in the vertical direction are also predicted well. The temporal variations of the inlet flow rate according to the throttling coefficient, the boiling and superheating boundaries and the pressure drop in the two-phase and superheating regions are obtained from the unsteady analysis.

• Journal of the Society of Naval Architects of Korea
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• v.49 no.5
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• pp.384-390
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• 2012

Power Flow Analysis (PFA) is introduced for solving the noise and vibration analysis of structures in medium-to-high frequency ranges. The vibration analysis software, $PFADS_{C{+}{+}}$ R4 based on Power Flow Finite Element Method (PFFEM) and the noise prediction software, $NASPFA_{C{+}{+}}$ R1 based on Power Flow Boundary Element Method (PFBEM) are developed. In this paper, the coupling equation which represents relation between structural energy and acoustic energy is developed for vibro-acoustic coupling analysis. And vibro-acoustic coupling analysis software based on PFA and coupling equation is developed. Developed software is composed of translator, cavity-finder, solver and post-processor over all. Translator can translate FE model into PFADS FE model and cavity-finder can automatically make NASPFA BE model from PFADS FE model for noise analysis. The solver module calculates the structural energy density, intensity of structures, the fictitious source on the boundary and the acoustic energy density at the field in acoustic cavities. Some applications of vibro-acoustic coupling analysis software to various structures and cruise ship are shown with reliable results.

• Korean Journal of Hydrosciences
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• v.3
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• pp.1-9
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• 1992

The effects of fractures in rock masses on the groundwater flow and the groundwater flow system in the volcanic rocks are analyzed by GFFP-WT model, which allows more realistic analysis of groundwater system by considering the fractures in rock masses. The evaluation of the effects of fractures in rock masses on the groundwater flow has been carried out in the 2nd Yeonwha and resulted in that the fractures mostly influence flow time because of hydraulic head distribution change. The results of the groundwater flow system analysis in the volcanic rocks are as follows. Most of groundwater once flowed in Lapilli tuff flowed out through Lappilli tuff layer. But only a small fraction of water flowed out through crystal tuff layer.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.13 no.4
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• pp.36-43
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• 2014

Recently, research has been conducted to develop the ORC (organic Rankine cycle), to recover waste heat from facilities such as industrial plants ultimately to create mechanical or electrical energy. The ORC system consists of a heat exchange, a condenser, a pump and a boiler. In this paper, 84 flow analyses were conducted with 21 cases and three variables, i.e., a number of large wings, a number of small wings, and RPMs. R245fa was used as a refrigerant. The flow cavitation phenomenon was investigated through a flow analysis, and a flow stream analysis was conducted.

• Proceedings of the Korea Water Resources Association Conference
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• 2008.05a
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• pp.1732-1736
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• 2008

The characteristics of a river flow analysis are significant for river maintenance plan. At the present time, HEC-RAS, 1-Dimensional Numerical Analysis Model, is mainly applied to analyze the character of a river flow. The shape of a river is somewhat in longitudinal linear form. It was suspected that the usage of 1-dimensional numerical analysis model is more economical. Development of numerical analysis models and computers are possible to calculate large volume. Hence, it is possible to adapt the analysis of the key stations by 2-dimensional numerical analysis model. The limitation of 1-Dimensional Numerical Analysis Model is that it is hard to evaluate structure affection of numerical simulation by energy loss coefficient at river structure analyzing. When adaptation of the 2-dimensional numerical analysis model in river structure ensues, it takes more objective analyzing than 1-dimensional numerical analysis model for flow affection by river structure. 2-dimensional numerical analysis model consults with the different structure position of hydraulic characteristics and different water depth of shape and scope in vertical flow. 1-dimensional numerical analysis model is possible to simulate with only energy loss coefficient for sudden river section changing, sudden waterway changing by curved. 2-dimensional numerical analysis model use original geographical features. So the model removes technical subjectivity of faulty judgment. It is an objective analysis.

• Journal of Ocean Engineering and Technology
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• v.27 no.6
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• pp.32-42
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• 2013

In this paper, a wave-induced swirl water chamber (SWC) for breakwater and wave power generation is introduced and its applicability to wave power generation in the coastal waters of Korea is investigated. The SWC type of wave power generation is a way to drive a turbine using the unidirectional swirl flow that is induced in the back of a curtain wall of a breakwater due to incident waves. The typical wave characteristics are obtained by analyzing the annual statistical wave data from KHOA (Korea Hydrographic and Oceanographic Administration). A numerical analysis is carried out on the variations in the SWC entrance height, wave height, and different installation conditions. For the numerical analysis, a commercial code, Fluent based on FVM, is used. As the entrance height decreases, the mass flow rate through the entrance is rarely changed, whereas the magnitude of the flow velocity of the smaller entrance height is greater than the other ones, which is better for the formation of an SWC swirl flow inside and the flow kinetic energy at the entrance. In cases of installation conditions where a wall is place behind and under SWC, it has been shown that the mass flow rate through the entrance is greater than that in the open condition, and sufficient flow kinetic energy is generated in the entrance for wave power generation. However, the swirl flow kinetic energy is relatively small. Thus, in the future, it is necessary to study the swirl flow generation, which is affected by the SWC shape.

• Proceedings of the Korean Nuclear Society Conference
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• 1996.05b
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• pp.598-603
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• 1996

When locked rotor event. occurs, instantaneously affected loop and core flow were quickly reduced, which resulted in an increase in coolant temperature and system pressure. Analysis method of this event was that constant core inlet temperature and system pressure as well as change in core flow calculated from COAST code were statically used as an input variable to HERMITE code, because of no tools to simulate NSSS behavior and 1-D core neutronics transient coincidently. With employing TASS code revised with 1-D neutronics model, this event was analyzed in point of DNBR. By doing so, analysis procedure could be simplified and unreasonable conservatism might be removed in DNBR calculation by consideration of pressure increase.

• Journal of Energy Engineering
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• v.22 no.1
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• pp.28-37
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• 2013

Stirred tank is widely used in various industries for mixing operations and chemical reactions for single- or multi-phase fluid systems. For designing agitator of high performance, quantity data of internal flow characteristics influenced by mixing performance are definitely confirmed but quantity analysis about the transient flow characteristics of complicate structure is recognized as difficult problem in the present. In this study, two models of commercial CFD code Fluent 6.3 used to propose suitable for the tank analysis. Agitation of Stirred tank is analyzed using a mixed model and the flow in the stirred tank is analyzed using a standard k-${\varepsilon}$ model. Multiple reference frame(MRF) and Sliding mesh(SM), the analysis techniques were used For compare a result of CFD with a visualization experiment result, to grasp internal flow and mixing characteristic in stirred tank and to present fundamental analysis method.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.16 no.12
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• pp.1227-1233
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• 2004

Air handling unit (AHU)'s air filter pressure difference is important for energy consumption and indoor air quality. Both energy Performance data and air filter differential pressure of AHU in real office buildings were monitored and analyzed to investigate quantitatively energy impact as dust buildup level on air filter grows. We also modeled and simulated CAV system using HVACSIM＋ program to examine the energy effect of dust buildup on filters. Through analysis of time series pressure drop data, the filter pressure difference rate has been increased due to cumulative supply air flow rate increase. As filter pressure drop increased to 1 inch water column, it is found that the supply air flow rate was decreased by 10%, the chilled water flow rate was increased by 5.9% and the pump energy consumption was increased to 5.9%.

• Journal of Hydrogen and New Energy
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• v.26 no.4
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• pp.386-392
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• 2015

Flow characteristics inside a 10 inch ball valve have been analyzed using three-dimensional numerical analysis and experiments. Continuity and three-dimensional Reynolds-averaged Navier-Stokes equations have been used as governing equations for the numerical analysis. The numerical model has been constructed through the grid dependency test and validation with the results of experiments to ensure reliability and numerical effectiveness. The shear stress transport (SST) model has been used as the turbulence closure. The experimental test-rig has been constructed to measure pressure, temperature and flow rate along the pipeline. Some valve opening angles have been tested to evaluate the flow characteristics inside the ball valve and pipeline. The results show that the rapid pressure variations is observed while the valve opening angle decreases, which caused by flow separation at the downstream of the ball valve.