• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.2
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• pp.145-152
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• 2011

The performance of flat-tube radiators with louvered fins was numerically investigated for different tube insertion lengths. The results of numerical analysis using CFX-11 were compared with experimental results. In this study, three types of flat-tube radiators with louvered fins were considered. An experiment was conducted to validate the numerical results. Flow rate ratio (FR) and Stotal were introduced to understand the uniformity of flow distribution easily. The results of numerical analysis revealed that the heat transfer rate and pressure drop increased as the mass flow rate increased. Further, the results showed that the heat transfer rate of sample 3 with h/D = 0.5 was higher than that of the other samples. The pressure drop increased as the insertion length toward the header part increased, and the pressure drop in the case of sample 3 appeared to be the highest. The factor Stotal showed that the uniformity of the flow distribution in the case of sample 1 with h/D = 0 was higher than that in the case of the other samples.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.8
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• pp.537-544
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• 2017

The purpose of this study is to analyze the flow characteristics when a staggered hollow fiber membrane module is modeled as a porous medium. The pressure-velocity equation was used for modeling the porous medium, using pressure drop data. In terms of flow characteristics, we compared the case of the "porous medium" when the membrane module was modeled as a porous medium with the case of the "membrane module" when considering the original shape of the membrane module. The difference in pressure drop between the "porous medium" and "membrane module" was less than 0.6%. However, the maximum flow velocity and mean turbulent kinetic energy of the "porous medium" were 2.5 and 95 times larger than those of the "membrane module," respectively. Our results indicate that modeling the hollow fiber module as a porous medium is useful for predicting pressure drop, but not sufficient for predicting the maximum flow velocity and mean turbulent kinetic energy.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.29 no.6
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• pp.521-527
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• 2016

This paper is concerned with the numerical analysis of dynamic response of floating offshore wind turbine subject to underwater explosion using an effective non-reflecting technique. An infinite sea water domain was truncated into a finite domain, and the non-reflecting technique called the perfectly matched layer(PML) was applied to the boundary of truncated finite domain to absorb the inherent reflection of out-going impact wave at the boundary. The generalized transport equations that govern the inviscid compressible water flow was split into three PML equations by introducing the direction-wise absorption coefficients and state variables. The fluid-structure interaction problem that is composed of the wind turbine and the sea water flow was solved by the iterative coupled Eulerian FVM and Largangian FEM. And, the explosion-induced hydrodynamic pressure was calculated by JWL(Jones-Wilkins-Lee) equation of state. Through the numerical experiment, the hydrodynamic pressure and the structural dynamic response were investigated. It has been confirmed that the case using PML technique provides more reliable numerical results than the case without using PML technique.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.10
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• pp.618-627
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• 2016

This study numerically analyzes the characteristics of the velocity distribution for each location of a square-sectional $180^{\circ}$ bent duct using a Reynolds Stress Turbulent model. The flow parameters were varied, including the working fluids, inlet velocity, surface roughness, radius of curvature, and hydraulic diameter. The boundary conditions for computational fluid dynamics analysis were inlet temperatures of air and water of 288 K and 293 K, inlet air velocity of 3-15 m/s, inner surface roughness of 0-0.001 mm, radius of curvature of 2.5-4.5 D, and hydraulic diameter of 70-100 mm. The working fluid characteristics were highly affected by changes in the viscous force. The maximum velocity profiles in the bent duct were indicated when the $90^{\circ}$ section was in the region of X/D=0.8 and the $180^{\circ}$ section was in the region of Y/D=0.8. Lower surface roughness and higher radius of curvature resulted in a higher rate of velocity change. Also, an efficient measuring location downstream of the bent duct is suggested since the flow deviations were the most stable when the straight duct length was in the region of L/D=30. The minimum deviations at the same velocity conditions according to the hydraulic diameter were mostly indicated in the range of L/D=15-30 based on the standard deviation characteristics.

• The Journal of the Petrological Society of Korea
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• v.13 no.4
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• pp.224-237
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• 2004

The anorthositic rocks of the study area are divided into the northern Sancheong and southern Hadong anorthositic rocks depending on the different distribution patterns and lithologies. In order to evaluate the characteristics of the hydrothermal systems developed in the study area, oxygen and hydrogen isotopic compositions of the anorthositic rocks were measured. Oxygen isotopic values of the plagioclase exhibit an interesting spatial distribution. Plagioclase collected from the Sancheong anorthositic rocks in the northern part tends to have a relatively restricted range of $\delta$$^{18/0}$ values between 7.3 and 8.8$\textperthousand$, which are heavier than 'normal' $\delta$$^{18/O}$ value (6-6.5$\textperthousand$) typical for plagioclase of the fresh mantle-derived anorthosite, whereas plagioclase from the southern part is characterized by a wide range of $\delta$$^{18/O}$ values between -4.4 and 8.2$\textperthousand$ and much lighter values than 'normal' value for plagioclase of the fresh mantle-derived anorthosite. Plagioclase from the middle part has $\delta$$^{18/O}$ values heavier than the plagioclase from the southern part, but lighter than that from the northern part. The spatial distribution of $\delta$$^{18/O}$ values suggests that the decoupled hydrothermal flow systems might have been developed in the study area. Meteoric water dominated in the hydrothermal flow systems developed in the southern area, whereas magmatic fluid dominated in the northern area. The relationship between water content and hydrogen isotopic composition of anorthosites shows a positive correlation. The positive correlation indicates that fluids exsolved from magma during magmatic differentiation caused deuteric alteration of anorthositic rocks involving replacement of pyroxenes to amphiboles. After the deuteric alteration, hydrothermal system developed by meteoric water dominated the southern area, and erased record of the hydrothermal system developed by magmatic fluid at earlier stage. However, the development of meteoric hydrothermal system has been limited in the southern area only, and could not affect the Sancheong anorthositic rocks in the northern area. The abundant occurrences of secondary alteration minerals such as sericite, calcite, and chlorite in the southern Hadong anorthosite relative to the northern Sancheong anorthositc seem to be related to the overlapping of two distinct hydrothermal systems in the southern area.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.6
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• pp.713-725
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• 2004

The two-dimensional motion of a freely falling circular cylinder in an infinite fluid is investigated numerically using combined formulation. The effect of vortex shedding on the motion of a freely falling cylinder is clearly seen: as the streamwise velocity of the cylinder increases due to gravity, the periodic vortex shedding induces a periodic motion of the cylinder. This motion in turn affects the flow field, which is manifested by the generation of the angular velocity vector of the cylinder parallel to the cross product of the gravitational acceleration vector and the transverse velocity vector of the cylinder. A correlation of St-Re relationship for a freely falling circular cylinder is drawn from the present results. The Strouhal number for a freely falling circular cylinder is found to be smaller than that for a fixed circular cylinder when the two Reynolds numbers based on the streamwise terminal velocity of a freely failing circular cylinder and the free stream velocity of a fixed one are the same. From "thought experiments", it is shown that the transverse motion of the cylinder plays a crucial role in reducing the Strouhal number and has an effect of reducing the Reynolds number from the viewpoint of the pressure coefficient. The mechanism of this reduction in the Strouhal number is revealed by the fact that the freely falling cylinder experiences a smaller lift force than the fixed one due to the transverse motion resulting in the retardation of the vortex shedding.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.9
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• pp.937-944
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• 2012

The thermodynamic characteristics of a trilateral cycle with water as a working fluid have been theoretically investigated for an electric generation system to recover the waste heat of the exhaust gas from a diesel engine used for the propulsion of a large ship. As a result, when a heat source was given, the efficiencies of energy and exergy were maximized by the specific conditions of the pressure and mass flow rate for the working fluid at the turbine(expander) inlet. In this case, as the condensation temperature increased, the volume expansion ratio of the turbine could be reduced properly; however, the exergy loss of the heat source and exergy destruction of the condenser increased. Therefore, in order to recover the waste exergy from the topping cycle, the combined cycle with a bottoming cycle such as an organic Rankine cycle, which is utilized at relatively low temperatures, was found to be useful.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.13 no.2
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• pp.124-130
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• 2014

In a mass manufacturing system of optical fibers, the sufficient cooling of glass fibers freshly drawn from a draw furnace is essential, asinadequately cooled glass fibers can lead to poor resin coating on the fiber surface and possibly fiber breakage during the process. In order to improve fiber cooling at a high drawing speed, it is common to use a helium injection into a glass fiber cooling unit in spite of the high cost of the helium supply. The present numerical analysis carried out three-dimensional thermo-fluid computations of the cooling gas flow and heat transfer on moving glass fiber to determine the cooling performance of glass fiber cooling depending on the method of helium injection. The results showed that afront injection of helium is most effective compared to a uniform or rear injection for reducing air entrainment into the unit and thus cooling the glass fibers at a high fiber drawing speed. However, above a certain amount of injected helium, there was no more increase of the cooling effect regardless of the helium injection method.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.3
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• pp.1040-1044
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• 2013

The present paper has been accomplished to elucidate the characteristics of temperature change in a car washer heater system for removal of frost formed at the surface of a car. The previous studies had used a simplified mathematical modeling to analyse the temperature change characteristics for a car washer heater system. In the present study, an unsteady computational fluid flow and heat transfer analysis for a washer heater system has been done by using computational fluid dynamic analysis method. From the present CFD analysis, the time dependent temperature change in a car washer heater system has been analysed and derived the heating time and ejection temperature of the washer liquid to establish the optimal design basis for a washer heater system.

• Journal of the Society of Naval Architects of Korea
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• v.53 no.6
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• pp.494-502
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• 2016

The accurate assessment of hull-appendage interaction in the early design stage is important to control the inflow to the propeller plane, which can cause undesirable hydrodynamic effects in terms of cavitation phenomenon. This paper describes a numerical analysis for the flow around a fully appended surface ship model for which KRISO has carried out a model test in the Large Cavitation Tunnel(LCT). This numerical study was performed with the LCT model test in a complementary manner for a good reproduction of the wake distribution of surface ships. A second order accurate finite volume method provided by a commercial computational fluid dynamics(CFD) program was used to solve the governing Reynolds Averaged Navier-Stokes(RANS) equations, where the SST $k-{\omega}$ model was used for turbulence closure. The numerical results were compared to available LCT experimental data for validation. The calculations gave good predictions for the boundary layer profiles on the walls of the empty cavitation tunnel and the wake at the propeller plane of the fully appended hull model in the LCT.