• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.479-482
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• 2008

In order to more closely examine the vacuum arc phenomena, it is necessary to predict the magnetohydrodynamic (MHD) characteristics by the multidisciplinary numerical modeling, which is coupled with the electromagnetic and hydrodynamic fields, simultaneously. In this study, the thermal-fluid characteristics of high current vacuum arcs were calculated by a commercial multiphysics package, ANSYS, in order to obtain Joule heat, Lorentz force and the interactions with flow variables. We assumed the diffused-mode arc within an AMF vacuum interrupter. It was found with four different currents that the temperature distributions on the anode surface are diffused uniformly without concentration in 7kA for both types (cup and coil-type). But the arc plasma transition and an increase of thermal flux density for increasing the applied current have caused the change of temperature distributions on the anode surface. We should need further studies on the two-way coupling method and radiation model for arc plasmas in order to accomplish the advanced analysis method for multiphysics.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.7
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• pp.976-982
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• 2002

In this study, smoke movement in tunnel fire with natural ventilation shaft has been investigated with various size of fire source. Gasoline pool fire with different size of diameter - 73mm, 100mm, 125mm and 154mm - was used to describe fire source. Experimental data is obtained with 1/20 model tunnel test and its results are compared with numerical results. The computation were carried out using FDS 1.0 which is a field model of fire-driven now. Temperature profiles between measured and predicted data are compared along ceiling and near the ventilation shaft. Both results are in good agreement with each other. In order to evaluating a safe egress time in tunnel fire, horizontal smoke front velocity was measured in model tunnel fire tests and those are compared with numerical results. According to the presence or absence of natural ventilation shaft, ventilation effect are estimated quantitatively. Finally, this paper shows that computational fluid dynamics(CFD) is applicable to predict fire-induced flow in tunnel.

• 한국전산유체공학회:학술대회논문집
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• 2007.04a
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• pp.103-107
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• 2007

Computational Fluid Dynamics (CFD in short) approach is now playing an important role in the engineering process recently. Generating proper grid system for the region of interest in time is prerequisite for the efficient numerical calculation of flow physics using CFD approach. Grid generation is, however, usually considered as a major obstacle for a routine and successful application of numerical approaches in the engineering process. CFD approach based on the unstructured grid system is gaining popularity due to its simplicity and efficiency for generating grid system compared to the structured grid approaches. In this paper an automated triangular surface grid generation using CAD surface data is proposed According to the present method, the CAD surface data imported in the STL format is processed to identify feature edges defining the topology and geometry of the surface shape first. When the feature edges are identified, node points along the edges are distributed. The initial fronts which connect those feature edge nodes are constructed and then they are advanced along the CAD surface data inward until the surface is fully covered by triangular surface grid cells using Advancing Front Method. It is found that this approach can be implemented in an automated way successfully saving man-hours and reducing human-errors in generating triangular surface grid system.

• 유체기계공업학회:학술대회논문집
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• 2005.12a
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• pp.302-307
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• 2005

The discharge coefficient in segmental wedge having ninety degrees vertex angle for the five kinds of opening ratio with differential pressure taps located at both upstream and downstream of one diameter of pipe was measured main purpose of this work is placed on developing the proper form of an equation for the discharge coefficient of a segmental wedge used as a primary element of flow metering devices, and from thata six-term equation which can express the variability of opening ratios was developed. The same assumption and hypotheses were used and tested for all procedures as conventional differential producers; however, the range of the opening ratio over this work is more expanded than previous studies. The opening ratios of segmental wedge, namely 0.3, 0.4, 0.5, 0.6 and 0.7 were investigated the Reynolds number based on the spool inside diameter ranges from 12,000 to 380,000, the resulting equation for the discharge coefficient is relatively simple; it contains only one variable-opening ratio because the characteristic of discharge coefficient of segmental wedge has little connection with the Reynolds number as shown by previous studies.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.9 s.252
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• pp.834-841
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• 2006

In the present wort the Laser-induced Fluorescence (LIF) technique and Confocal Laser Scanning Microscopy (CLSM) have been combined to measure the temperature distribution across a micro-scale liquid layer as a direct and non-invasive method. Only the fluorescent light emitted from a very thin volume around a focal plane can be selectively detected, and it enables us to measure the liquid temperatures even at the close vicinity of the walls. As an experimental verification, a test section consists of two flat plates (for heating and cooling, respectively) separated by about 240 microns was made, and the methanol mixed with a temperature-sensitive dye, Rhodamine B, was filled in the gap between them. The measured temperature distribution across the gap showed good linearity, which is a typical characteristic of conduction heat transfer through a thin liquid layer. In result, the CLSM-LIF technique proposed in the present study was found to be a promising method to measure the local temperatures in the liquid flow field in microfluidic devices.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1997.04a
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• pp.627-635
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• 1997

In general, the booming noise intensity at tunnel exit is strongly related to the gradient of the compression wave front created by high speed train entering the tunnel. This paper presents some results in relation with the compression wave front produced when the high speed train enters a tunnel. Four kinds of tunnel entrance shape with real dimensions were studied to investigate the formation of compression wave front inside tunnel by train entering tunnel. Computations were carried out using three-dimensional compressible Euler equation with vanishing viscosity and conductivity of fluid. According to the reslts, the flow disturbance occured at tunnel entrance were eliminated by tunnel hood with same cross sectional area. The compression wave front is formed completely at 30-40m from tunnel entrance. The maximum pressure gradient of compression wave front is reduced by 29.8% for the inclined tunnel hood and reduced by 21.5% for the tunnel hood with holes at the top face with tunnel without hood. The length of the inclined hood is 15m and the length of the hood with holes is 20m.

• 한국신재생에너지학회:학술대회논문집
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• 2011.11a
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• pp.159.1-159.1
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• 2011

Due to the global warming, the need to secure the alternative resources has become more important worldwide. Having very strong current on the west coast with up to 10 m tidal range, there are many suitable sites for the application of TCP(Tidal current power) in Korea. Not only from the current produced from the high tidal range, but also it can be widely applied to the offshore jetties and piers. The VAT(Vertical axis turbine) system could be very effective tidal device to extract the energies from the attacking flow to the structures. For the relatively slow current speed, the VAT system could be more effective application than HAT(Horizontal axis turbine) device. The performance of VAT can be evaluated by various parameters including number of blades, shape, sectional size, diameters and etc. The paper introduces the multi-layer vertical axis tidal current power system with savonius turbine. The turbine was designed with consideration of optimal blade numbers and the performance was simulated by CFD analysis.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.28 no.2
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• pp.190-199
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• 2018

Objectives: The purpose of this case study is to assess the current airflow and find the ideal ventilation conditions in tank reactors for minimizing the possibility of exposure respiratory dusts(size of $2.5{\mu}m$, $10{\mu}m$) when workers exchange catalysts in the tank reactors. Methods: A Numerical study was performed to determine ideal ventilation conditions, We considered two sizes of airborne respiratory particles($2.5{\mu}m$, $10{\mu}m$) at 12points from the bottom of tank reactor. We changed input & output ventilation conditions and analyzed the particle motion in the tank reactor. The star-ccm+, computational fluid dynamics tool was used to predict air & particle flow patterns in the tank reactor and a numerical simulation was achieved by applying the realized ${\kappa}-{\varepsilon}$ turbulence model and the Lagrangian particle tracking method. Results: From the results, the increase of recirculation air had a significant impact on removing dusts because they are removed by HEPA filter. To the contrary, Increasing the clean air quantity or changing the input position of clean air is not good for workers because it causes the exit of respiratory dusts through workers' entrance or cause it to remail suspended in the air in the workplace tank.

• 유체기계공업학회:학술대회논문집
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• 2004.12a
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• pp.572-577
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• 2004

This paper presents numerical study on the performance improvement of the sirocco fan in a range hood. The performance of sirocco fan means a higher flowrate, a higher static pressure and a lower required motor power in a fixed geometry constraint. Various impeller geometric parameters, such as blade profile, blade diameter, blade thickness profile and blade exit angle, were investigated by numerically and the results were compared with each other to know the effects on the performance. In this approach, the volute geometry were fixed with the original shape. The numerical results show that the blade profile with airfoil shape and small exit blade thickness increases the performance. The blade exit angle shows optimum angle within a varied range. The efficiency of the optimized exit angle was about $10\%$ higher than the base blade exit angle and the static pressure was about $28\%$ higher at the flow coefficient 0.22.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2007.04a
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• pp.276-280
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• 2007

In this paper, heat transfer changes due to the shock/boundary layer interaction were investigated on surfaces where protruding bodies such as a cylinder and a secondary jet are mounted. With an infra-red thermography, surface temperature was measured and the measured data was used to obtain the convective heat transfer. Heat transfer phenomena around these two solid and fluid bodies were appeared to be very comparable each other. The inclination of a cylinder and the jet injection ratio were the important factors for the change of heat transfer on the effective surfaces.