• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.55 no.1
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• pp.62-73
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• 2019

Recently, copper alloy netting has been proposed as a material for aquaculture facilities that can be set in harsh offshore environments. To design a cage made of copper alloy netting, it is necessary to calculate the flow of water through the netting and force of external sources on the netting. Therefore, this study measured and analyzed the current velocity reduction after passing through the netting and the hydrodynamic forces acting on the netting using copper alloy netting with nine solidity ratios. As a result of the reduction rate of the flow velocity through the netting, the flow reduction rate was increased as the solidity ratio of netting was increased. The flow reduction rate was also increased as the attack angle on the netting was decreased. In analyzing the resistance on the netting, we also discovered that resistance was increased with increase in the flow velocity and solidity ratio. An analysis of the hydrodynamic coefficient acting on the netting is shown that the drag coefficient tends to increase as the attack angle increases. We also analyzed the hydrodynamic coefficient according to the variation of the Reynolds number. When the drag coefficients acting on the netting were analyzed with the different Reynolds numbers, the Reynolds number increased from over 0.3 m/s to a relative constant. Finally, the copper alloy nettings had a smaller velocity reduction rate when comparing the flow velocity reduction rate between copper alloy nettings and nylon nettings.

• Journal of Korean Society on Water Environment
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• v.37 no.6
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• pp.469-482
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• 2021

The recent climate change and urbanization have seen an increase in runoff and pollutant loads, and consequently significant negative water pollution. The characteristics of the pollutant loads vary among the different flow regime depending on their source and transport mechanism, However, pollutant load reduction based on flow regime perspectives has not been investigated thoroughly. Therefore, it is necessary to analyze the effects of concentration on pollutant load characteristics and reductions from each flow regime to develop efficient pollution management. As non-point pollutants continuously increase due to the increase in impervious area, efficient management is necessary. Therefore, in this study, 1) the characteristics of pollutant sources were analyzed at the Dalcheon Basin, 2) reduction of nonpoint pollution, and 3) reduction efficiency for flow regimes were analyzed. By analyzing the characteristics of the Dalcheon Basin, a reduction efficiency scenario for each pollutant source was constructed. The efficiency analysis showed 0.06% to 5.62% for the living scenario, 0.09 to 24.62% for the livestock scenario, 0.17% to 12.81% for the industry scenario, 9.45% to 38.45% for the land scenario, and 9.8% to 39.2% for the composite scenario. Therefore, various pollution reduction scenarios, taking into account the characteristics of pollutants and flow regime characteristics, can contribute to the development of efficient measurements to improve water quality at various flow regime perspectives in the Dalcheon Basin.

• 유체기계공업학회:학술대회논문집
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• 2006.08a
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• pp.199-202
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• 2006

The objective of this study is to propose methods of controlling the wake behind a sphere for drag reduction using the suboptimal control theory and surrogate management framework, respectively. The Reynolds numbers considered is 300 at which the base flow is unsteady planar symmetric. Given the cost function defined as the square of the difference between the target pressure (potential-flow pressure) and real flow pressure on the sphere surface, the suboptimal control makes the flow steady axisymmetric and produces drag reduction. Based on the actuation profile from the suboptimal control, the optimal wavy actuation profile is obtained using the surrogate management framework and produces drag reduction.

• The KSFM Journal of Fluid Machinery
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• v.2 no.1 s.2
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• pp.73-80
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• 1999

Leakage vortices formed new blade tip causes an increase of total pressure loss near the casing endwall region and as a result, the efficiency of rotor decreases. The reduction of rotor efficiency is related to the size of the tip clearance. In this study, the three-dimensional flowfields in an axial flow rotor were calculated by varying the tip clearance under various flow rates, and the numerical results were compared with experimental ones. The effects of tip clearance and attack angle on the leakage vortex and overall performance, and the loss distributions were investigated through numerical calculations. In this study, tip leakage flow rate and total pressure loss by tip clearance were evaluated using numerical results and approximate equations were presented to evaluate the reduction of rotor efficiency by tip leakage flow.

• Journal of Advanced Marine Engineering and Technology
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• v.23 no.5
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• pp.679-686
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• 1999

This study is to investigate the effect of a substantial drag reduction caused by the polymer(A611P) when the working fluids flow to the vertical direction in the vertical cylindrical equipment of closed flow system. The drag reduction is associated with the mechanical degrada-tion thermal degradation and heat transfer. By ignore the heat fluxs within the closed system the pressure drop due to the polymer concentration the flow velocity and flow time have been mea-sured. By taking into account the mechanical and thermal degradation in the closed system an experiment has been focused on the determination of the condition which could improve the pump capacity in the heat union electric power plant. Under the condition of non-boiling it has been found out that the change of heat flux has little influence on the drag reduction.

• Journal of ILASS-Korea
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• v.26 no.4
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• pp.163-170
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• 2021

Emergency generators normally use diesel engines. The generators need to conduct weekly no-load operation inspections to ensure stable performance at emergency situations. In particular, the generators with large diesel engines mainly use rectangle type filter substrates. In order to minimize hazardous emissions generated by generators, optimizing the reduction efficiency through CFD analysis of flow characteristics of PM/NO_X reduction system is important. In this study, we analyzed internal flow by CFD, which is difficult to confirm by experimental method. The main factors in our numerical study are the changes of flow uniformity and back pressure. Therefore, changes in flow characteristics were studied according to urea injector locations, selective catalyst reduction (SCR) diffuser angle, and filter porosity.

• Journal of the Korean Society of Visualization
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• v.21 no.2
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• pp.8-13
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• 2023

The primary challenge in improving fuel efficiency and reducing air pollution for commercial vehicles is reducing their aerodynamic drag. Various flow control devices, such as cab-roof fairing, gap fairing, cab extender, and side skirt have been introduced to reduce drag, however, the drag reduction effect and applicability are different depending on each commercial vehicle model. To evaluate the fuel consumption of heavy vehicles, a comprehensive research approach, including drag force measurement, flow field analysis is required. This study investigated the effect of a cab extender, which installed rear region of cab, on a drag coefficient of commercial vehicle through wind tunnel experiments and CFD. The results showed that the cab extender significantly modified the flow structure around the vehicle, leading to 8.2% reduction in drag coefficient compared to the original vehicle model. These results would provide practical application for enhancing the aerodynamic performance and fuel efficiency of heavy vehicle.

• Magazine of the Korean Society of Agricultural Engineers
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• v.43 no.4
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• pp.113-119
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• 2001

Ammonia emissions during composting of hog manure mixed with sawdust were studied in four runs comprising a total of 22 pilot-scale reactor vessels. These four runs extended previous work and both verified and extended the previous conclusions. The pilot-scale vessels were 205 L insulated stainless steel drums that were aerated either continuously (high/low thermostatically controlled fans) or intermittently (5 min high fan 55 min off). Temperature ammonia emissions air flow rates carbon dioxide production and oxygen utilization moisture and dry matter reduction initial and final chemical compositions were measured. Ammonia emissions from the intermittently aerated vessels were only about 50% as great as those from the continuously aerated ones but this was found to be a result more related to total air flow than to aeration technique. All of the data for total result more related to total air flow were fitted with a linear regression line y=0.139x+29.835 where y is ammonia expressed as g of N and x is air flow in kg with $R^2$=0.6808. this general trend indicates that about 50% reduction in ammonia emissions can be achieved with 75% reduction in air flow. For the aeration techniques used the minimum oxygen level in te exhaust gas from the vessels was 5% and this is probably a resonable lower limit constraining air flow reduction. However within this constraint lower air flow now appears to be a technique that can reduce odorous ammonia emissions.

• Journal of the Korean Society for Precision Engineering
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• v.15 no.1
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• pp.87-93
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• 1998

Pressure ripples of hydraulic vane pump results from flow ripples due to pump geometry and reverse flow through the discharge port due to compressibility of fluid and result in vibration and noise of connected hydraulic elements. In a balanced type vane pump, cam ring curve is important factor to influence the flow ripples. Therefore, to reduce the flow ripple, it has been required that optimal selection of seal region by proper design of cam ring and each port position, and notches for preventing the excessive reverse flow. This paper has been performed analytical study of compression characteristics with major design parameter in side plate and cam ring. and examined into the role of notch and radius reduction ratio.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.16 no.2 s.107
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• pp.107-114
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• 2006

The present experimental study deals with noise reduction and improvements in cooling performance in a plasma display panel (PDP) television (TV). The main ideas of the fan system noise reduction are maintenance of uniform inflow condition and reduction of the system loss, ${\Delta}P.$ The discrete noise is mainly related with the inflow condition therefore removing the structure which distorts inflow makes the discrete noise reduction. The broadband noise in PDP TV is related with the system losses which result from the presence of the fan downstream obstacle, PDP rear case. Through the modification of the distance and preventing the leakage flow between the fan and rear case, we can obtain the system loss and broadband noise reduction. Additionally we can reduce fan rotating speed because of increased flow rate which obtains from the reduction of system loss (resistance). Finally, 4.2 dB(A) noise reduction and $10\%$ increase in flow rate are achieved. From these results, we show that the reduction of system loss is the most effective way of the fan system noise reduction.