• Wind and Structures
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• v.30 no.1
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• pp.55-67
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• 2020

Wind tunnel test is one of the most important means to study the flutter performance of bridges, but there are blockage effects in flutter test due to the size limitation of the wind tunnel. On the other hand, the size of computational domain can be defined by users in the numerical simulation. This paper presents a study on blockage effects of a simplified box girder by computation fluid dynamics (CFD) simulation, the blockage effects on the aerodynamic characteristics and flutter performance of a long-span suspension bridge are studied. The results show that the aerodynamic coefficients and the absolute value of mean pressure coefficient increase with the increase of the blockage ratio. And the aerodynamic coefficients can be corrected by the mean wind speed in the plane of leading edge of model. At each angle of attack, the critical flutter wind speed decreases as the blockage ratio increases, but the difference is that bending-torsion coupled flutter and torsional flutter occur at lower and larger angles of attack respectively. Finally, the correction formula of critical wind speed at 0° angle of attack is given, which can provide reference for wind resistance design of streamlined box girders in practical engineering.

• Proceedings of the KIEE Conference
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• 1994.07b
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• pp.1559-1561
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• 1994

At present, the principle of puffer action in high current interruption is adopted in almost of the EHV(Extra High Voltage) and UHV(Ultra High Voltage) GCB(Gas Circuit Breakers). The thermal interruption capability of these GCBs critically depends on the pressure rise in the puffer cylinder at current zero. The pressure rise in the puffer cylinder depends on the puffer cylinder volume, flow passage and leakage area in the interrupter, stroke curve etc. Recently commercial CFD(Computational Fluid Dynamics ) packages have been widely adopted to calculate the pressure distribution in the interrupter. However, there are still several problems with it, e.g. very expensive price, moving boundary problem, computation time, difficulty in using the package etc. Thus, the calculation of the puffer cylinder pressure in simple and relatively correct method is essential in early stage of GCB design. In these paper, the model ing technique and computed results for EHV class GCB (HICO, 145kV 40kA and 362kV 40kA GCB) are presented and compared with available measured results.

• Journal of Navigation and Port Research
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• v.40 no.4
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• pp.173-181
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• 2016

From 2016, controls on reduction of NOx and SOx emissions from the vessels that are operated in the emission control area were tightened. The selectivity catalytic reduction system of the denitrification equipment which NOx among the above controlled materials is very effective and used commercially very much. But it has the disadvantage that CSR is activated at high temperatures. Therefore, the SCR and SCR activation instrument that can react even at low temperatures by using micro-nano bubbles so that the above problems can be minimized were developed. And the computational fluid dynamics technique was used by ANSYS-CFX package to prepare the plan that improves the SCR system's efficiency. Simulation for the viscous flow analysis of the SCR system was executed by applying the Navier-Stokes equation to it as a governing equation. For the SCR system's shape, 3D modeling was done by using CATIA V5. SCR jet nozzle's position was checked by changing it to the intervals of 1/3, 1/2, and 2/3 from the inlet of the vent pipe to compare the SCR system's efficiency. And the number of nozzles was compared and analyzed by simulating 4, 6, and 8 holes to check an effect of the number on the SCR system's efficiency. The simulation result has found that the closer nozzles are to the inlet of the vent pipe and the more nozzles are, the more efficiency is improved.

• Wind and Structures
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• v.22 no.4
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• pp.477-501
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• 2016

Though hilly topography influences both wind speeds and directions aloft, only the influence on wind speeds, i.e. the speed-up effect, has been thoroughly investigated. Due to the importance of a model showing the spatial variations of wind directions above hilly terrains, it is worthwhile to systematically assess the applicability and limitations of the model describing the influence of hilly topographies on wind directions. Based on wind-tunnel test results, a model, which describes the horizontal and vertical variations of the wind directions separately, has been proposed in a companion paper. CFD (Computational Fluid Dynamics) techniques were employed in the present paper to evaluate the applicability of the proposed model. From the investigation, it has been found that the model is acceptable for describing the vertical variation of wind directions by a shallow hill whose primary-to-secondary axis ratio (aspect ratio) is larger than 1. When the overall hill slope exceeds $20^{\circ}$, the proposed model should be used with caution. When the aspect ratio is less than 1, the proposed model is less accurate in predicting the spatial variation of wind directions in the wake zone in a separated flow. In addition, it has been found that local slope of a hill has significant impact on the applicability of the proposed model. Specifically, the proposed model is only applicable when local slope of a hill varies gradually from 0 (at the hill foot) to the maximum value (at the mid-slope point) and then to 0 (at the hill top).

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.7
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• pp.652-659
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• 2011

A computational system to predict flowfield and infrared signature in aircraft exhaust system is developed. As the first step, a virtual mission profile is considered and an engine is selected through a performance analysis. Then a nozzle that meets the requirement of each mission is designed. The internal flow in the exhaustion nozzle at the maximum thrust is analyzed using a state-of-the-art CFD code. In addition, a system to combine information of the skin temperature distribution of the nozzle and after-body surface with an infrared prediction code is developed. Finally, qualitative results for the infrared signature reduction design are obtained by investigating the infrared signature level under various conditions.

• Journal of the Society of Naval Architects of Korea
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• v.55 no.6
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• pp.474-481
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• 2018

This paper is to compare by numerical analysis the flow characteristics and propulsion performance of stern with the shape change of K-duct, a pre-swirl duct developed by Korea Research Institute of Ships & Ocean Engineering (KRISO). First, the characteristics of the propeller and the resistance and self-propulsion before and after the attachment of the K-duct to the ship were verified and the validity of the calculation method was confirmed by comparing this result with the model test results. After that, resistance and self-propulsion calculations were performed by the same numerical method when the K-duct was changed into five different shapes. The efficiency of the other five cases was compared using the delivery horsepower in the model scale and the flow characteristics of the stern were analyzed as the velocity and pressure distributions in the area between the duct end and the propeller plane. For the computation, STAR-CCM +, a general-purpose flow analysis program, was used and the Reynolds Averaged Navier-Stokes (RANS) equations were applied. Rigid Body Motion (RBM) method was used for the propeller rotating motion and SST $k-{\omega}$ turbulence model was applied for the turbulence model. As a result, the tangential velocity of the propeller inflow changed according to the position angle change of the stator, and the pressure of the propeller hub and the cap changes. This regulated the propeller hub vortex. It was confirmed that the vortex of the portion where the fixed blade and the duct meet was reduced by blunt change.

• Korean Journal of Environmental Agriculture
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• v.27 no.2
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• pp.150-155
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• 2008

This study was carried out to determinate the location and the number of air inlet and outlet, optimum air inlet velocity for effective ventilation in windowless weaning piglet house($2.90(W){\times}9.90(L){\times}2.80(H)$ m) by CFD(Computation Fluid Dynamics) simulation. The weaning piglet house for this experiment was consisted of 11 air inlets and 9 outlets, modified and simulated using CFD code, FLUENT. The simulation result for the original weaning piglet house, which was not modified, showed ununiform ventilation for each room. Therefore, for uniform ventilation, 4 air inlets and 1 outlet were completely closed, and 2 air outlets were partially closed. The simulation result for the modified weaning piglet house showed uniform ventilation for each room and the optimum air inlet velocity of 0.5 $m\;sec^{-1}$.

• Journal of Korean Society of Environmental Engineers
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• v.32 no.9
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• pp.862-869
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• 2010

Numerical analysis was done to evaluate the gas flow distribution in small scale SCR system which has $2.4{\times}2.4{\times}3.1\;m^3$ in volume and 25,300 Sm3/hr in flue gas flow capacity. Various types of baffles proposed for controlling the flow uniformity were evaluated by the CFD analysis to find the optimal geometry of the baffle in the SCR system. By installing baffles in the SCR system, the RMS (%) value was raised up to 6.2% compared with the baffle-uninstalled state. The effect of baffle thicknesses on the RMS (%) value was not shown within 0 and 8 mm in thickness, but the RMS (%) value was raised by 2.5% in 10 mm of baffles thickness, which causes the unstability in flow. By comparison between the shape of baffles, it is known that the lattice type baffle has better performance in controlling the flow uniformity than the circular truncated cone type baffle or mixer type baffle. RMS (%) values have more that 10% difference according to the shape of baffle type.

• Korean Journal of Remote Sensing
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• v.36 no.6_3
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• pp.1653-1667
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• 2020

In this study, we coupled a computation fluid dynamics (CFD) model to the local data assimilation and prediction system (LDAPS), a current operational numerical weather prediction model of the Korea Meteorological Administration. We investigated the characteristics of fine particulate matter (PM2.5) distributions in a building-congested district. To analyze the effects of road emission on the PM2.5 concentrations, we calculated road emissions based on the monthly, daily, and hourly emission factors and the total amount of PM2.5 emissions established from the Clean Air Policy Support System (CAPSS) of the Ministry of Environment. We validated the simulated PM2.5 concentrations against those measured at the PKNU-AQ Sensor stations. In the cases of no road emission, the LDAPS-CFD model underestimated the PM2.5 concentrations measured at the PKNU-AQ Sensor stations. The LDAPS-CFD model improved the PM2.5 concentration predictions by considering road emission. At 07 and 19 LST on 22 June 2020, the southerly wind was dominant at the target area. The PM2.5 distribution at 07 LST were similar to that at 19 LST. The simulated PM2.5 concentrations were significantly affected by the road emissions at the roadside but not significantly at the building roof. In the road-emission case, the PM2.5 concentration was high at the north (wind speeds were weak) and west roads (a long street canyon). The PM2.5 concentration was low in the east road where the building density was relatively low.