• Journal of Korea Water Resources Association
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• v.31 no.5
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• pp.539-552
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• 1998

When the pier is constructed in the cohesive be, the accuracy maynot be obtained because the equation for calculating the scour at piers is based upon the results which are analyzed through the experiments in the non-cohesive bed. In this paper, the variation of the depth of the pier scour occurred by constructing 5 types of pier in the channel having the cohesive material is examined. The experimental results are analyzed based upon Froude numbers and non-dimensional numbers which are indicated as the flow depths compared to the pier width. The results are also compared with the results obtained using the existing pier scour equations. In this paper, the shape factors, which can be used for calculating the scour depth of the pier in the cohesive channel bed, are suggested. The shape factors are indicated through the ratios between the scour depth at the circular pier and the scour depths at the different types of pier, and are suggested as two stages. In the first stage, in which the water depth compared to the pier width is less than 1.2, the shape factors are given as the equations. However, in the second stage the shape factors are given as the constant values. It is understood that the shape factors suggested in this paper can be properly usd for calculating local scour at piers in the bridges which are constructed in the cohesive channel bed having the characteristics of the bed material which is used in these experiments. Keywords : local scour, maximum scour depth, cohesive bed material, pier shape, pier, shape factor.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• v.29 no.1
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• pp.35-40
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• 2005

Maneuverability of ships has been receiving a great deal of attention both concerning navigation safety and the prediction of ship maneuvering characteristics, to improve it. high-lift device could be applied to design of rudder at design stage. Now, we carried out the flow visualization and investigation of flow field around a flap rudder(trailing-edge flap). Flow visualization results of flap defection shown as the flow around a NACA0020 Flap Rudder will be conducted in a Circulating Water Channel. The purpose of this investigation will be to investigate the development of the separation region on the flap rudder with the variation of the angle of attack and determine the angle of attack at which the flow separates and reattaches.

• Journal of Information Processing Systems
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• v.10 no.4
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• pp.602-617
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• 2014

The performance of a cognitive radio network (CRN) solely depends on how precisely the secondary users can sense the presence or absence of primary users. The incorporation of a spatial false alarm makes deriving the probability of a correct decision a cumbersome task. Previous literature performed this task for the case of a received signal under a Normal probability density function case. In this paper we enhance the previous work, including the impact of carrier frequency, the gain of antennas on both sides, and antenna heights so as to observe the robustness against noise and interference and to make the correct decision of detection. Three small scale fading channels: Rayleigh, Normal, and Weibull were considered to get the real scenario of a CRN in an urban area. The incorporation of a maximal-ratio combining and selection combing with a variation of the number of received antennas have also been studied in order to achieve the correct decision of spectral sensing, so as to serve the cognitive users. Finally, we applied the above concept to a traffic model of the CRN, which we based on a two-dimensional state transition chain.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.13 no.9
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• pp.4408-4428
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• 2019

Due to the rapid advancement in smart phones, numerous new specifications are developed for variety of applications ranging from health monitoring to navigations and tracking. The word indoor navigation means location identification, however, where GPS signals are not available, accurate indoor localization is a challenging task due to variation in the received signals which directly affect distance estimation process. This paper proposes a hybrid approach which integrates fingerprinting based K-Nearest Neighbors (K-NN) and lateration based MinMax position estimation technique. The novel idea behind this hybrid approach is to use Euclidian distance formulation for distance estimates instead of indoor radio channel modeling which is used to convert the received signal to distance estimates. Due to unpredictable behavior of the received signal, modeling indoor environment for distance estimates is a challenging task which ultimately results in distance estimation error and hence affects position estimation process. Our proposed idea is indoor position estimation technique using Bluetooth enabled smart phones which is independent of the radio channels. Experimental results conclude that, our proposed hybrid approach performs better in terms of mean error compared to Trilateration, MinMax, K-NN, and existing Hybrid approach.

• Proceedings of the Korean Society of Fisheries Technology Conference
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• 2005.05a
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• pp.62-69
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• 2005

Maneuverability of ships has been receiving a great deal of attention both concerning navigation safety and the prediction of ship maneuvering characteristics, to improve it. High-lift device could be applied to design of rudder at design stage. Now, we carried out the flow visualization and inversitgation of flow around a flap rudder (trailing-edge flap). Flow visualization results of flap defection shown as the flow around a NACA0020 Flap Rudder will be conducted in a Circulating Water Channel. The purpose of this investigation will be to investigate the development of the separation region on the flap rudder with the variation of angle of attack and determine the angle of attack at which the flow separates and reattaches.

• Journal of Advanced Marine Engineering and Technology
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• v.11 no.1
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• pp.72-79
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• 1987

When the wall temperature is very high, a stable vapor film covers the heat transfer surface. The vapor film creates a strong thermal resistance when heat is transferred to the liquid though it. This phenomenon, called "film boiling" is very important in the heat treatment of metals, the design of cryogenic heat exchangers, and the emergency cooling of nuclear reactors. In the practical engineering problems of the transient cooling process of a high temperature wall, the wall temperature history, the variation of the heat transfer coefficients, and the wall superheat at the rewetting points, are the main areas of concern. These three areas are influenced in a complex fashion such factors as the initial wall temperature, the physical properties of both the wall and the coolant, the fluid temperature, and the flow state. Therefore many kinds of specialized experiments are necessary in the creation of precise thermal design. The object of this study is to investigate the heat transfer characteristics in the transient cooling process of a high temperature wall. The slow transient cooling experiment was carried out with a copper block of high thermal capacity. The block was 240 mm high and 79 mm O.D.. The coolant flowed throuogh the center of a 10 mm diameter channel in the copper block. In the copper block, three sheathed thermocouples were placed in a line perpendicular to the flow. These thermocouples were used to take measurements of the temperature histories of the copper block.

• Journal of Korean Society on Water Environment
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• v.31 no.3
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• pp.313-318
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• 2015

To study the influence of changes in river discharge on water quality of the main stem of the Geum River, we investigated variation of inflow load from tributaries with river discharge. We also studied the mixing behavior of pollutants during mixing of waters of the main stem and Gap Stream. For this study, we collected water quality data such as suspended solids (SS), biochemical oxygen demand (BOD), chemical oxygen demand (COD), total organic carbon (TOC), total nitrogen (TN) and total phosphorus (TP) representing pre-monsoon, monsoon, and post-monsoon events of 2013 from a website of Water Information System. Based on inflow load, the Gap and Miho streams may be ones of tributaries which may largely influence water quality of main stem in upper river region. The Suksung and Nonsan Streams seemed to further affect water quality downstream. Results of modified EMMA indicated SS and TP may have another source(besides Gap Stream) at pre-monsoon, monsoon, and post-monsoon period. In contrast, TN and organic matter (BOD, COD, TOC) were conservative at pre-monsoon and post-monsoon. However, when river discharge increased, these pollutants may also came from unspecified non-point sources. Therefore, we need to attempt to find non-point sources for the pollutants in the main channel of upper Geum River region.

• Current Optics and Photonics
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• v.4 no.6
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• pp.472-476
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• 2020

We have investigated the impact of optical filter bandwidth on the performance of all-optical automatic gain-controlled (AGC) erbium-doped fiber amplifiers (EDFAs). In principle, an optical bandpass filter (OBPF) should be placed within the feedback gain-clamping loop to set the lasing wavelength as well as the passband of the feedback amplified spontaneous emission (ASE) in all-optical AGC EDFA. From our measurement results, we found that the power level of feedback ASE with 0.1 nm passband of the optical filter was smaller than the ones with >0.2 nm passband cases. Therefore, the peak-to-peak power variation of the surviving channel with 0.1 nm passband was much larger than the ones with >0.2 nm passband. In addition, no significant difference in the power level of the feedback ASE was observed when the passband of the optical filter was ranging from 0.2 nm to 4.5 nm in our measurements. From these results, we have concluded that the passband of the optical filter should be slightly larger than 0.2 nm by taking into account the effect of feedback ASE power and the efficient use of the EDFA gain spectrum for the lasing ASE peak.

• The KSFM Journal of Fluid Machinery
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• v.4 no.1 s.10
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• pp.30-37
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• 2001

The experimental study on the effect of axial clearance between the tip of impeller blades and stationary shroud has been performed. The investigated compressor, which is a part of a small auxiliary power unit engine, consists of a curved inlet, a centrifugal impeller, a channel diffuser and a plenum chamber. It was designed for a total pressure ratio of 4.3 and an efficiency of $77\%$ at design speed of 60,000 rpm. The experiments are carried out in an open-loop centrifugal compressor test rig driven by a turbine. For the four different clearance ratios Cr(clearance/impeller tip width) of 6.25, 10.93, 15.60 and 20.30 percent, the overall performance data are obtained at $97\%,\;90\%$ and $80\%$ of the design speed. The results show the overall pressure ratio decrease of $7.7\%$ and the efficiency loss of $8.7\%$ across the variation of clearance ratio near the design speed. It also indicates that the influence of tip clearance became weaker as the flow rate is reduced and the stable operating range is not significantly influenced by the change of clearance ratio.

• 한국정보디스플레이학회:학술대회논문집
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• 2009.10a
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• pp.389-392
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• 2009

Metal oxides have been proposed as an alternative channel material to hydrogenated amorphous silicon in thin film transistors (TFTs) because their higher mobility and stability make them suitable for transistor active layers. Thin films of indium zinc oxide (IZO) were deposited using a High Target Utilization Sputtering (HiTUS) system on various dielectrics, some of which were also deposited with the HiTUS. Investigations into bottom-gated IZO TFTs have found mobilities of 8 $cm^2V\;^1s^{-1}$ and switching ratios of $10^6$. There is a variation in the threshold voltage dependent on both oxygen concentration, and dielectric choice. Silica, alumina and silicon nitride produced stable TFTs, whilst hafnia was found to break down as a result of the IZO.