• Journal of Korean Society on Water Environment
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• v.31 no.5
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• pp.491-506
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• 2015

Distributed models represent watersheds using a network of numerous, uniform calculation units to provide spatially detailed and consistent evaluations across the watershed. However, these models have a disadvantage in general requiring a high computing cost. Semi-distributed models, on the other hand, delineate watersheds using a simplified network of non-uniform calculation units requiring a much lower computing cost than distributed models. Employing a simplified network of non-uniform units, however, semi-distributed models cannot but have limitations in spatially-consistent simulations of hydrogeochemical processes and are often not favoured for such a task as identifying critical source areas within a watershed. Aiming to overcome these shortcomings of both groups of models, a hybrid watershed model STREAM (Spatio-Temporal River-basin Ecohydrology Analysis Model) was developed in this study. Like a distributed model, STREAM divides a watershed into square grid cells of a same size each of which may have a different set of hydrogeochemical parameters reflecting the spatial heterogeneity. Like many semi-distributed models, STREAM groups individual cells of similar hydrogeochemical properties into representative cells for which real computations of the model are carried out. With this hybrid structure, STREAM requires a relatively small computational cost although it still keeps the critical advantage of distributed models.

• Journal of the Korea Institute of Military Science and Technology
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• v.7 no.1
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• pp.34-46
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• 2004

Copper films were prepared by using ECR-MOCVD(Electron Cyclotron Resonance Metal Organic Chemical Vapor Deposition) coupled with a DC bias system. The DC bias is connected to the electrode which placed 1∼3cm above the polymer substrate. The pulse electrical field around the electrode attracts the positive charged copper ions generated from the dissociation of copper precursor, $Cu(hfac)_2$, under ECR plasma. Condensation of supersaturated copper ions in the space between the electrode and substrate, makes it possible to deposit copper film on the polymer substrate even at room temperature. In this study, optimization of the electrode configuration was carried out in order to obtain the uniform films. The uniformity of the deposited films were closely related to the parameters of electrode geometry such as electrode shape, thickness, grid size and the spacing between electrodes. The most uniform copper film was observed with the electrode that enabled uniform electrical field distribution across the whole dimension of electrode.

• 한국전산유체공학회:학술대회논문집
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• 2000.05a
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• pp.45-50
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• 2000

We study a conceptual numerical model on shock-vortex interaction setting an impulsive shock in a compressible vertex. Navier-Stokes equations are solved for the investigation of interactive structure and acoustic wave propagation. The rotationally symmetric vortex enforces two compression-expansion pairs resultantly forming a quadrupolar shape. These compressive and expansive waves cylindrically propagate to the far field and turn to acoustic waves. Using a fine uniform Cartesian grid system and a TVD-high resolution method, the flow data irl: precisely obtained to extend our interest to the sound source.

• Journal of applied mathematics & informatics
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• v.19 no.1_2
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• pp.33-55
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• 2005

The temporal discretisation of a moderate semilinear parabolic problem in an abstract setting by the two-step backward differentiation formula with variable step sizes is analysed. Stability as well as optimal smooth data error estimates are derived if the ratios of adjacent step sizes are bounded from above by 1.91.

• Journal of Ocean Engineering and Technology
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• v.1 no.2
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• pp.39-51
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• 1987

석유시추 보호관의 비선형 운동을 시뮬레이트하는 유효한 해법이 non-uniform grid 유한차분법과 implicit time 적분법에 근거하여 제시되었다. 극한 상태에 있는 지지 플랫폼의 상승 가속도에 의해 생기는 보호관의 동적 좌굴형 반응에 관하여 상세히 연구되었고, 이 반응에 미치는 중요 변수가 규명되었다. 운동의 현저한 감소와 이에 따른 응력들이 컴플라이언트 행오프(hang-off)를 적용시킴으로써 얻어졌다.

• The KIPS Transactions:PartC
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• v.17C no.1
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• pp.61-68
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• 2010

As the mobile technology advances, file searching among the mobile device users becomes more important. In this paper, we propose the uniform grid, greedy, and MIS P2P systems that have double-layered topology to search files efficiently for mobile ad-hoc networks. In these systems, peers are classified into two groups, super-peers and sub-peers, and each super-peer manages its neighboring sub-peers. In the proposed systems, each super-peer maintains the appropriate information of its sub-peers so that when a peer requests a file, the request is sent to its super-peers and then to neighboring super-peers. Hence the proposed systems could avoid multi-broadcasting and reduce network overheads. The experimental results show that the proposed systems outperform a single-layered P2P system in terms of the average number of messages to find target files. Especially the MISsystem improves by reducing the average number of messages by 48.9% while maintaining the same search accuracy.

• Journal of KIISE
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• v.44 no.6
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• pp.573-580
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• 2017

Despite the recent remarkable advances in the computing power of mobile devices, the heat and battery problems still restrict their performances, particularly compared to PCs. Therefore, in the application of the ray-tracing technique for high-quality rendering, the consideration of a method that traces only the secondary rays while the effects of the primary rays are generated through rasterization-based OpenGL ES rendering is worthwhile. Given that most of the rendering time is for the secondary-ray processing in such a method, a new volume-grid technique for dynamic scenes that enhances the tracing performance of the secondary rays with a low coherence is proposed here. The proposed method attempts to model all of the possible spatial secondary rays in a fixed number of sampling rays, thereby alleviating the visitation problem regarding all of the cells along the ray in a uniform grid. Also, a hybrid rendering pipeline that speeds up the overall rendering performance by exploiting the mobile-device CPU and GPU is presented.

• Journal of Electrochemical Science and Technology
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• v.11 no.4
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• pp.368-378
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• 2020

In the paper, corrosion behavior of T91 steel in different concentrations of NaHSO₃ solution was studied in combination with scanning electron microscope (SEM) and electrochemical measurements. The results showed that the steel exhibited active anodic dissolution characteristics in the solution, and NaHSO₃ concentration affected both cathodic and anodic behaviors. The steel surface was covered by intact corrosion products in the solutions, but the compactness and mechanical properties of the corrosion products degraded with the increase of NaHSO₃ concentration. In low-concentration NaHSO₃ solution the steel tended to undergo uniform corrosion with slight corrosion pits, but its corrosion mode gradually transited to localized corrosion as the NaHSO₃ concentration increased. The mechanical property degradation of the corrosion products caused by sulfur compounds and the pH decrease of the solution are the important factors to accelerating its corrosion process.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.12
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• pp.1555-1569
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• 2000

Numerical simulation of fluid flow with moving free surface has been carried out. For the free surface flow, a VOF(Volume of Fluid)-based algorithm utilizing a fixed grid system has been investigated. In order to reduce numerical smearing at the free surface represented on a fixed grid system, a new free surface tracking algorithm based on the donor-acceptor scheme has been presented. Novel features of the proposed algorithm are characterized as two numerical tools; the orientation vector to represent the free surface orientation in each cell and the baby-cell to determine the fluid volume flux at each cell boundary. The proposed algorithm can be easily implemented in any irregular non-uniform grid systems that are usual in finite element method (FEM). Moreover, the proposed algorithm can be extended and applied to the 3-D free surface flow problem without additional efforts. For computation of unsteady incompressible flow, a finite element approximation based on the explicit fractional step method has been adopted. In addition, the SUPG(streamline upwind/Petrov-Galerkin) method has been implemented to deal with convection dominated flows. Combination of the proposed free surface tracking scheme and explicit fractional step formulation resulted in an efficient solution algorithm. Validity of the present solution algorithm was demonstrated from its application to the broken dam and the solitary wave propagation problems.

• Fire Science and Engineering
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• v.29 no.1
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• pp.73-79
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• 2015

There are three kinds of design method of the fire sprinkler systems. Grid type is connected all branch as a trapezoid. Loop type is connected cross-mains like circle. The last one is a tree type most commonly used. Grid type needs computer program to calculate the friction loss and flow rate apart from very simple form. In loop type, manual calculation is possible. Design engineer can draw up and calculate the demands without computer program. Because water supplies two direction in loop type, friction loss is smaller than tree type. Water distribution in operation area is uniform because of the small differences of sprinklers discharge pressure. Loop type is superior to tree type in respect of total pressure and flow rate. Using the small diameter pipe, the labor and construction cost will be decreased in the end. Loop type sprinkler design is rarely laid out because design engineers don't know the method. This paper is intended to inform that the loop type is better than the tree type in performance and economic point of view. And also this paper intend to use the loop type easily and widely.