• Journal of the Society of Naval Architects of Korea
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• v.30 no.1
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• pp.104-114
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• 1993

In this paper, effects of free surface on viscous flow is investigated. Continuity equation coupled with Navier-Stokes equations are solved numerically by using an artificial compressibility method[1, 2]. The body-fitted generalized curvilinear coordinate system is employed to deal with arbitrary body shape. The IAF scheme with finite difference method is used to solve the equations, and a diagonal algorithm is applied to time-varying Jacobian matrices for the computational economics. Free surface shape is obtained by applying zero pressure condition to still water surface at each time step. A numerical test is made for larminar flow around a circular cylinder vertically piercing the free surface. Computed flow patterns are largely affected by the existance of free surface in low Reynolds number flows treated in this paper. Free surface causes viscous pressure drag to vary much in depth direction in accordance with the variations of flow pattern.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.262-263
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• 2011

Flexible electronics, a future technology of electronics, require a low cost integrated circuit that can be built on various types of the flexible substrates. As a potential candidate for this application, a single walled carbon nanotube network is studied as an active device with a scheme of thin film transistor. Transistors are formed on a plastic foil by the Roll-to-Roll (R2R) and the Roll-to-Device (R2D) printing method. For both printing methods, electrical transports for the transistors are presented with the temperature dependence of threshold voltage (V_Th) and mobility from the measured transfer curves at temperatures ranging from 10 K to 300 K. It is observed that ${\mu}=0.044cm^2/V{\cdot}sec$ and V_Th=7.28V for R2R and ${\mu}=0.025cm^2/V{\cdot}sec$ and V_Th=3.10V for R2D, both for the temperature at 300K. Temperature dependence of mobility and V_Th is observed. However for R2R, the temperature dependence of V_Th is constant. It is the difference between, R2R and R2D.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.13 no.4
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• pp.485-500
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• 2000

In this paper the adaptive crack propagation analysis based on the estimated local and global error in the element-free Galerkin (EFG) method is presented. It is possible to keep consistency and accuracy of analysis in each propagation step by adaptive analysis. The adaptivity analysis in crack propagation is achieved by adding and removing the node along the background integration cell that are refined or recovered as estimated error. These errors are obtained by calculating the difference between the values of the projected stresses and original EFG stresses. To evaluate the performance of proposed adaptive procedure, the convergence behavior is investigated lot several examples. The results of these examples show the efficiency of proposed scheme in crack propagation analysis.

• Journal of the Society of Naval Architects of Korea
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• v.45 no.4
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• pp.345-352
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• 2008

The motion of a projectile initiated by the release of highly pressurized air is simulated presuming the flow field as a two dimensional one. The effects of water compressibility on projectile movements are investigated, comparing results based on the Fluent VOF model where water is treated as an incompressible medium with those from the presently developed VOF scheme. The present model considers compressibility of both air and water. The Fluent results show that the body moves farther and at higher speeds than the present ones. As time proceeds, the relative difference of speed and displacement between the two results drops substantially, after acoustic waves in water traverse and return the full length of the tube several times. To estimate instantaneous accelerations, however, requires implementation of the water compressibility effect as discrepancies between them do not decrease even after several pressure wave cycles.

• Journal of the Korean Solar Energy Society
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• v.31 no.5
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• pp.140-145
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• 2011

In this study, the performance and behavior of solar heating system according to the system control scheme, variable flow control (proportional control) and constant flow control (on-off control) was carried out by experiment. The on-off control is used generally for solar thermal system by now. But the proportional control is used for the solar district heating system which is supplied the higher temperature of water than that of desired. The proportional control logic that pump speed is varied in an attempt to maintain a specified outlet temperature of solar heating system was developed and tested for the use widely for the small and medium solar thermal system. The results are as following. First, the proportional controller which is made here could be adopted the characteristics for setting temperature control. Second, the proportional control is better than the on-off control in the side of the performance of thermal stratification in storage tank. Third, the operating energy(electricity consumption by pump) of solar thermal system can be saved more than 60% using the proportional control comparing to the on-off control.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.5
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• pp.1244-1253
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• 1990

Time-Marching methods solving Euler equations are used for calculation of two-dimensional, steady, inviscid flow through a stationary compressor cascade. Calculation method is based on the Denton`s opposed difference scheme. A smoothing in the axial direction is used to increase the stability of solution. The computational grid consists of quadrilateral elements, one of which has four nodes at each corner and the grid points on the upper periodic boundaries are located one pitch away from those on the lower boundaries to satisfy the periodicity condition. Results of calculation show good agreement with other computational and experimental results, proving that the present method of calculation should be applied with confidence for the cascade flow with shock wave.

• Magazine of the Korean Society of Agricultural Engineers
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• v.43 no.1
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• pp.75-86
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• 2001

North Korea reported that tideland reclamation projects had been successfully constructed and/or under construction during the period of the third development scheme(1987∼1993), which were 28,400ha in 9 project areas: 8 projects along the western coast and one in the eastern coast. In this study eight projects located in western coast were investigated in order to confirm the detail of works, construction stages and difference from our project formulation methods using the topographic maps published in different years and the recent sattelite image data especially Lansat TM and SPOT PN. Intensity-hue-saturation (IHS) method was adopted to merge two sattelite data for the image enhancement of remote sensing. Construction stages of sea-dikes, land consolidation for paddy and salt pan, reservoir for irrigation and desalinization and the present land use were investigated and estimated the acreage of the development areas. The total gross project areas of 38,105 ha: 16,555 ha completed for paddy or salt pan, 16,826 ha under construction, and 4,724 ha under planning were confirmed, although the area of 27,100 ha in 8 projects were reported to be completed or ongoing on the bimonthly journal of N. Korean Trend published in 1994.

• Korean Journal of Agricultural and Forest Meteorology
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• v.6 no.3
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• pp.164-169
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• 2004

A spatial interpolation scheme incorporating local geographic potential for cold air accumulation (TOPSIM) was used to test the feasibility of operational frost warning in Chatancheon basin in Yeoncheon County, where the introduction of new crops including temperate zone fruits is planned. Air temperature from April to June 2003 was measured at one-minute intervals at four locations within the basin. Cold-air accumulation potentials (CAP) at 4 sites were calculated for 3 different catchment scales: a rectangular area of 65 x 55 km which covers the whole county, the KOWACO (Korea Water Corporation) hydrologic unit which includes all 4 sites, and the sub-basins delineated by a stream network analysis of the digital elevation model. Daily minimum temperatures at 4 sites were calculated by interpolating the perfect prognosis (i.e., synoptic observations at KMA Dongducheon station) based on TOPSIM with 3 different CAPs. Mean error, mean absolute error, and root mean square error were calculated for 45 days with no precipitation to test the model performance. For the 3 flat locations, little difference was detected in model performance among 3 catchment areas, but the best performance was found with the CAPs calculated for sub-basins at one site (Oksan) on complex terrain. When TOPSIM loaded with sub-basin CAPs was applied to Oksan to predict frost events during the fruit flowering period in 2004, the goodness of fit was sufficient for making an operational frost warning system for mountainous areas.

• Journal of the Korean Society for information Management
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• v.13 no.1
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• pp.173-185
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• 1996

In this paper, we propose four optimizing methods for effectively processing queries in the Booleam information retrieval system ; (i) the short-circuit evaluation scheme used for optimizing logical expressions in programming lan-guages is applied to Boolean queries.(II) use the difference of the number of index word frequencies appearing in the related documents. (IIi) reduce the number of operators in the queries by applying the distribution law in the set theory. (iv) evaluate only once for the repeated expressions in the query. These methods have been implemented and tested in KRISTAL-II system on the UNIX workstation environment.

• ETRI Journal
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• v.26 no.2
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• pp.101-111
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• 2004

This paper presents a near-optimum blind decision feedback equalizer (DFE) for the receivers of Advanced Television Systems Committee (ATSC) digital television. By adopting a modified trellis decoder (MTD) with a trace- back depth of 1 for the decision device in the DFE, we obtain a hardware-efficient, blind DFE approaching the performance of an optimum DFE which has no error propagation. In the MTD, the absolute distance is used rather than the squared Euclidean distance for the computation of the branch metrics. This results in a reduction of the computational complexity over the original trellis decoding scheme. Compared to the conventional slicer, the MTD shows an outstanding performance improvement in decision error probability and is comparable to the original trellis decoder using the Euclidean distance. Reducing error propagation by use of the MTD in the DFE leads to the improvement of convergence performance in terms of convergence speed and residual error. Simulation results show that the proposed blind DFE performs much better than the blind DFE with the slicer, and the difference is prominent at the trellis decoder following the blind DFE.