• 소음진동
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• 제8권6호
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• pp.1043-1052
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• 1998

The noise sources in the outdoor unit of RAC are identified by the sound intensity method. The main noise sources are compressor noise and fluid noise which is caused by the fan. heat exchanger and shroud. First. the fluid noise is reduced through the design of new fan and shroud. reduction of the system resistance by rearrangement of heat exchanger. and optimization of the complex parameter between the fan and shroud. Next, in order to reduce the compressor noise, the new shape of compressor mount and sound-proof material was applied. As a result, the overall noise was reduced by 4∼5dB (A).

• Korea-Australia Rheology Journal
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• 제11권3호
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• pp.247-253
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• 1999

The growth of a spherical vapor bubble contained in a large body of upper convected Maxwell fluid is theoretically analyzed under the devolatilization condition of polymer by using a Galerkin FEM in the Lagrangian frame. Using the finite element technique, a fully explicit numerical scheme is developed both for the calculation of pressure distribution and for the tracking of bubble surface. Oscillatory behavior in bubble radius is observed during growth and the oscillatory behavior is found to be due to the interaction of mass transfer resistance and elasticity. It is found that the elasticity of fluid accelerates the growth and removal of volatile component. It is also found that the bubble growth in the devolatilization of polymers is affected by both mass transfer resistance and viscoelasticity of fluids.

• 한국유체기계학회 논문집
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• 제6권2호
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• pp.15-22
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• 2003

Comprehensive study on a centrifugal blower for air-purifier involving a few physical filters for percolation process has been accomplished for an optimal design of the air handling system. The filtering media causes a flow resistance for induced flows by a rotating impeller. The present methodology is to adopt PIV system for velocity measurements and wind tunnel connected with an anechoic chamber for total performance test of the blower. Trial prototypes for the blades of a rotor and casing are presented for satisfaction of both flow rate and noise level set by design objectives. Tapered blades with a special casing for a fan show good performance data. The results of velocity fields also explain the reason of improvements of the blower performance.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2010년도 추계 학술발표회 2차
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• pp.104-112
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• 2010

The thermal influential factor of energy pile system is investigated by considering the seasonal effect, saturation of ground, and fluid velocity based on the finite volume method. Analysis includes the evaluation of thermal resistance and corresponding heat exchange rate for each case. It is shown that the efficiency of heat exchange rate is more pronounced with higher fluid velocity due to the larger number of circulation for a given period. Through the parametric studies, it is also found that the degrees of saturation a little influenced thermal effect during 8 hours of operational scenario.

• 한국유체기계학회 논문집
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• 제20권2호
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• pp.11-16
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• 2017

The accurate prediction of leakage flow through the brush element of brush seal at the steam turbine is important to find optimum design parameters for increasing an efficiency. In this study, CFD analysis method using commercial software FLUENT is proposed to predict leakage through the brush element. Since the brush element has a complex three-dimensional shape with many bristle assemblies, it is difficult to analyze the flow field. Therefore, if the brush element is assumed to be porous medium region, the analysis time can be shortened. Two determination methods of resistance coefficients of the Darcian porous medium equation are suggested. By comparing the 2D and 3D CFD analysis results for the leakage of the brush element using the two resistance coefficient determination methods, the effectiveness of the analysis for the porous medium assumption is proved.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회B
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• pp.2788-2793
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• 2008

A numerical analysis has been conducted for flow characteristics and performance of a micropump with piezodisk and MHD(Magnetohydrodynamics) fluid. Various micro systems which could not be considered in the past have been recently growing with the development of MEMS(Micro Electro Mechanical System) and micro machining technology. Especially, micropumps, essential part of micro fluidic devices, are being lively studies by many researchers. In the present study, the piezo electric micropump with electromagnetic resistance for electrically conducting fluids is considered. The prescribed grid deformation method is used for the displacement of the membrane. The change of the performance of the micropump and flow characteristics of the electrically conducting fluid with the magnitude of the magnetic fields, duct size, the position of the inlet and outlet duct are investigated in the present study.

• 한국유체기계학회 논문집
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• 제13권2호
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• pp.5-11
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• 2010

The nanofluidics is characterized by a large surface-to-volume ratio, so that the surface properties strongly affect the flow resistance. We present here the results showing that the effect of wetting properties and the surface roughness may considerably reduce the friction of fluid past the boundaries. For a simple fluid flowing over hydrophilic and hydrophobic surfaces, the influences of surface roughness are investigated by the nonequilibrium molecular dynamics (NEMD) simulations. The fluid slip at near a solid surface highly depends on the wall-fluid interaction. For hydrophobic surfaces, apparent fluid slips are observed on smooth and rough surfaces. The solid wall is modeled as a rough atomic sinusoidal wall. The effects on the boundary condition of the roughness characteristics are given by the period and amplitude of the sinusoidal wall. It was found that the slip velocity for wetting conditions at interface decreases with increasing effects of surface roughness. The results show the surface rougheness and wettability determines the slip or no-slip boundary conditions. The surface roughness geometry shows significant effects on the boundary conditions at the interface.

• 대한조선학회논문집
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• 제49권2호
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• pp.174-181
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• 2012

In this paper, the Flow Control Fin(FCF) optimization has been carried out using computational fluid dynamics(CFD) techniques. This study focused on evaluation for the performance of the FCF attached in the stern part of the ship. The main advantage of FCF is to enhance the resistance performance through the lift generation with a forward force component on the foil section, and the propulsive performance by the uniformity of velocity distribution on the propeller plane. This study intended to evaluate these functions and to find optimized FCF form for minimizing viscous resistance and equalizing wake distribution. Four parameters of FCF are used in the study, which were angle and position of FCF, longitudinal location, transverse location, and span length in the optimization process. KRISO 300K VLCC2(KVLCC2) was chosen for an example ship to demonstrate FCF for optimization. The optimization procedure utilized genetic algorithms (GAs), a gradient-based optimizer for the refinement of the solution, and Non-dominated Sorting GA-II(NSGA-II) for Multiobjective Optimization. The results showed that the optimized FCF could enhance the uniformity of wake distribution at the expense of viscous resistance.

• 한국멀티미디어학회논문지
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• 제19권7호
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• pp.1146-1153
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• 2016

The bioelectrical impedance (BI) at the inner forearms was measured using bioelectrical impedance measurement system (BIMS), which employs the multi-frequency and the two-electrode method. Experiments were performed as follows. First, while applying a constant alternating current of 800A to the inner region of the forearms, BI (Z) was measured at nineteen frequencies ranging from 5 to 500 kHz. The prediction marker (PM) was calculated for right and left forearm. The resistance (R) and the reactance (X_c) were simultaneously measured during impedance measurement. Second, a Cole-Cole plot (relationship between reactance and resistance) was obtained for left and right forearm, indicating the different characteristic frequencies (f_c). Third, the phase angle was obtained, indicating strong dependence on the applied frequency.

• International Journal of Naval Architecture and Ocean Engineering
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• 제6권4호
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• pp.876-893
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• 2014

The resistance performance of an icebreaking cargo vessel according to the variation of waterline angles is investigated numerically and experimentally. A recently developed Finite Element (FE) model is used in our analysis. A resistance test with synthetic ice is performed in the towing tank at Pusan National University (PNU) to compare and validate the computed results. We demonstrate good agreement between the experimental and numerical results. Shipice interaction loads are numerically calculated based on the Fluid Structure Interaction (FSI) method in the commercial FE package LS-DYNA. Test results from model testing with synthetic ice at the PNU towing tank are used to compare and validate the numerical simulations. For each waterline angle, numerical and experimental comparisons were made for three concentrations (90%, 80%, and 60%) of pack ice. Ice was modeled as a rigid body, but the ice density was the same as that used in the experiments. A comparative study according to the variation of stem angles is expected to be conducted in the near future.