• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.1
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• pp.1-7
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• 2011

Active power control scheme for distributed generation in microgrid consists of feeder flow control and unit power control. Feeder flow control is more useful than the unit power control for demand-side management, because microgrid can be treated as a dispatchable load at the point of common coupling(PCC). This paper presents detailed descriptions of the feeder flow control scheme for the hybrid system in microgrid. It is divided into three parts, namely, the setting of feeder flow reference range for stable hybrid system operation, feeder flow control algorithm depending on load change in microgrid and hysteresis control. Simulation results using the PSCAD/EMTDC are presented to validate the inverter control method for a feeder flow control mode. As a result, the feeder flow control algorithm for the hybrid system in microgrid is efficient for supplying continuously active power to customers without interruption.

• Journal of Dental Anesthesia and Pain Medicine
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• v.18 no.2
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• pp.105-110
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• 2018

Background: A stellate ganglion block (SGB) causes increased blood flow in the maxillofacial region, exhibiting the potential for regenerative effects in damaged tissue. The focus of this study was to understand the efficacy of SGB for regenerative effects against nerve damage. A rat model of the superior cervical ganglion block (SCGB) was created instead of SGB, and facial blood flow, as well as sympathetic nervous system function, were measured. Methods: A vertical incision was made on the left side of the neck of a Wistar rat, and a 5-mm resection of the superior cervical ganglion was performed at the back of the bifurcation of the internal and external branches of the left common carotid artery. Blood flow in the skin at the mandibular angle and mean facial temperature were measured using a laser-Doppler blood flow meter and a thermographic camera, respectively, over a 5-week period after the block. In addition, the degree of ptosis and miosis were assessed over a period of 6 months. Results: The SCGB rat showed significantly higher blood flow at the mandibular angle on the block side (P < 0.05) for 3 weeks, and significantly higher skin temperature (P < 0.05) for 1 week after the block. In the SCGB rat, ptosis and miosis occurred immediately after the block, and persisted even 6 months later. Conclusions: SCGB in rats can cause an increase in the blood flow that persists over 3 weeks.

• Journal of Environmental Science International
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• v.12 no.12
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• pp.1245-1254
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• 2003

A numerical simulation for 11 February 1996 has been done to grasp main mechanisms of the occurrence of strong downslope winds near Gangnung area. The simulation performed by using ARPS (Advanced Regional Prediction System) showed that enhanced surface winds were not related with a reflection of vertically propagating gravity waves. Froude numbers were about 1.0, 0.4 and 0.6 for the atmosphere above Daekwanryoung and above a place located 220km upstream, and above another place located 230km downstream from the Taebak mountains, respectively. This suggested that as a subcritical flow ascended the upslope side of the Taebak mountains, Froude numbers would tend to increase according to the increase in wind speed, and near the crest the flow would become supercritical and continue to accelerate as it went down the downslope side until it was adapted back to the ambient subcritical conditions in a turbulent hydraulic jump. Simulated Froude numbers corroborated the hydraulic jump nature of the strong downslope wind. In addition, the inversion was found near the mountain top height upstream of the mountains, and it was favorable for the occurrence of strong downslope winds.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.36 no.1
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• pp.25-32
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• 2018

Namdae-cheon in Gangwon-do Province, Korea, is a valuable well-preserved lagoon. The estuary of Namdae-cheon Stream is closed because of the surrounding natural sand shoal. Thus, during the dry season, river water cannot easily flow to the ocean and therefore stagnates. River water congestion causes environmental deterioration of estuaries, often by eutrophication. In this study, we examined wall disintegration in the estuary area and used it to determine appropriate measures for the conservation of estuary water quality in the future. A total of 24 sites were selected, with 13 sites on the west side and 11 sites on the east side of the estuary study area. Samples were collected and analyzed for particle size and moisture content both vertically and horizontally. Sedimentary deposition rate was measured, and subsidence analysis was performed. Particle size, water content, sedimentary deposition, and subsidence analyses indicated that flow shifted to the west during the study period. In conjunction with other variables that may affect changes in flow, these parameters can be used in future research to predict shoal breaches and associated changes in water flow direction.

• Transactions of the Korean Society of Automotive Engineers
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• v.16 no.4
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• pp.88-96
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• 2008

Effects of the duct inlet guide vane on the flowrate distribution characteristics of the defroster nozzle exit in a defrost duct system were investigated experimentally to design the optimum heating, ventilation and air conditioning (HVAC) system applied in an automotive compartment. A 3-dimensional hot-wire anemometer system was used to measure the velocity field in the vicinity of the defroster nozzle jet flow and the velocity distributions near the windshield interior surface. At first, two cases of with- and without-duct inlet guide vanes were considered as the test condition, and then three cases of the duct inlet guide vane were tested to determine the optimum guide vane shape and their positions. The arrangement of the duct inlet guide vanes has an effect on the improved flowrate distribution at the defroster nozzle exit and near the windshield interior surface. However, the application of the lots of guide vane to control the flow direction leads to increase the flow resistance, resulting in the decreased flowrate issuing from the defroster nozzle. The shape of the duct inlet guide vane affects not only the flowrate distribution between the driver side and the assistant driver side but also the reduction of the flow resistance in the defrost duct system.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.11a
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• pp.116-121
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• 2011

Performance of Secondary Injection Thrust Vector Control system is investigated under various secondary injection operating conditions. 3-dimensional converging-diverging nozzle having 8 secondary injection nozzles is used in this numerical study. Total pressure of flow inside the nozzle is about 70bars, and total temperature set to 300K for cold flow simulation. Effect of secondary injection flow rate and injection nozzle configuration is considered in this research. Simulation is conducted with commercial CFD code Ansys Fluent v13. Spalart-Allmaras(1-equation)model is used for turbulence modeling with AUSM+ scheme. Various performance factors as Axial thrust, side force, system specific impulse ratio are considered and explained for system performance evaluation.

• Journal of the Korean Society of Visualization
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• v.2 no.2
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• pp.52-57
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• 2004

The development and interaction of vortices over a delta wing with leading edge extension (LEX) was investigated through off-surface flow visualization using micro water droplets and a laser beam sheet. Angles of attack of $20^{\circ}$ and 24$^{\circ}$ were tested at sideslip angles of $0^{\circ}$, $-5^{\circ}$, and $-10^{\circ}$ The flow Reynolds number based on the main-wing root chord was $1.82{\times}10^{5}$. The wing vortex and the LEX vortex coiled around each other while maintaining comparable strength and identity at a zero sideslip. The increase of angle of attack intensified the coiling and shifted the cores of the wing and LEX vortices inboard and upward. By sideslip, the coiling, the merging and the diffusion of the wing and LEX vortices were increased on the windward side, whereas they were delayed significantly on the leeward side. The present study confirmed that the sideslip angle had a profound effect on the vortex structure and interaction of a delta wing with LEX, which characterized the vortex-induced aerodynamic load.

• Journal of Korean Society of Water and Wastewater
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• v.22 no.3
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• pp.367-372
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• 2008

This study configured the conventional $A^2O$ (Anaerobic-Anoxic-Aerobic bioreactor) system which the fixed media immersed into the anoxic reactor(Named PFR system : Plug Flow Reactor) for evaluating the removal efficiency of nitrogen in the wastewater. The experimental equipment was a cylinder which was consist of 4 pleated PE Pipes(Length 330M, Diameter 100mm) including 2 rope shape media. As a result, the average effluent T-N removal efficiency of the conventional $A^2O$ system was 17.9, 40.3, 50.6, 44.6% in each mode, but the average effluent T-N removal efficiency of the PFR system could achieve 38.8, 57.1, 71.8, 65.4% in each mode. It indicated that the PFR system caused to the increasing of C/N ratio that effected to the increasing of the denitrification efficiency. Not only the effective T-N removal efficiency but also the controllable install space will give advantages for retrofitting of the wastewater treatment plant with the conventional treatment system to the PFR system.

• Journal of Korean Society of Water and Wastewater
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• v.22 no.6
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• pp.619-625
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• 2008

Urban sewer systems are designed to operate in open-channel flow regime and energy loss at square manholes is usually not significant. However, the energy loss at surcharged manholes is considered as one of the major causes of inundation in urban area. Therefore, it is necessary to analyze the head loss associated with manholes, especially in surcharged flow. Hydraulic experimental apparatus which can change the manhole inner profile(CASE I, II, III, and IV) and the invert types(CASE A, B, C) were installed for this study. The experimental discharge was $16{\ell}/sec$. As the ratio of b/D(manhole width/inflow pipe diameter) increases, head loss coefficient increases due to strong horizontal swirl motion. The head loss coefficients for CASE I, II, III, and IV were 0.46, 0.38, 0.28 and 0.37, respectively. Side covers increase considerably drainage capacity at surcharged square manhole when the ratio of d/D(side cover diameter/inflow pipe diameter) was 1.0. The head loss coefficients for CASE A, B, and C were 0.45, 0.37, and 0.30, respectively. Accordingly, U-invert is the most effective for energy loss reduction at surcharged square manhole. This head loss coefficients could be available to evaluate the urban sewer system with surcharged flow.

• The KSFM Journal of Fluid Machinery
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• v.12 no.2
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• pp.39-45
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• 2009

Leakage flow through turbine blade tip gap causes strong leakage vortex near the blade suction side and induces large aerodynamic losses. In this study, the conventional plane tip and various squealer tip blades were tested in a linear cascade in order to measure the effect of the tip shape on the total pressure loss. Three tip gap clearances of 0.6%, 1.3%, and 2.0% of blade span were tested. Flow measurement was conducted at one chord downstream from the trailing edge with a five-hole probe. Results showed that the leakage vortex was stronger than passage vortex and the mass averaged overall total pressure loss through the cascade was the lowest for suction side blade tip case. For all tested cases, the area averaged overall total pressure loss was increased as the tip clearance increased.