• Journal of Advanced Marine Engineering and Technology
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• v.41 no.2
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• pp.146-149
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• 2017

Si clusters generated during the plasma chemical vapor deposition (CVD) process have a great influence on the quality of the fabricated films. In particular, in hydrogenated amorphous silicon thin films (a-Si:H) used for thin film solar cells, Si clusters are mainly responsible for light-induced degradation. In this study, we investigated the amount of clusters incorporated into thin films using a quartz crystal microbalance (QCM) and specially designed cluster eliminating filters, and investigated the effect of the DC grid mesh in preventing cluster incorporation. Experimental results showed that as the applied voltage of the grid mesh, which is placed between the electrode and the QCM, decreased, the number of clusters incorporated into the film decreased. This is due to the electrostatic force from the grid mesh bias, and this method is expected to contribute to the fabrication of high-quality thin films by preventing Si cluster incorporation.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.411-412
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• 2013

최근 UV LED는 생화학 및 의료 산업에서 많은 각광을 받고 있다. 특히, 360nm 이하의 파장대를 갖는 UV LED는 치료 기술, 센서, 물이나 공기 등의 정화와 같은 목적으로 특별한 관심이 쏠리고 있다 [1]. 이러한 지속적인 연구를 통하여 현재까지 UV LED는 거대한 성장을 이루어 왔다. 하지만 이러한 노력에도 불구하고, 360 nm 이하의 UV LED는 여전히 오믹 접촉과 전류 분산이 원활하지 못하다는 문제점을 가지고 있다. 이것은 UV LED의 외부 양자 효율을 감소시키고, 더 나아가 극도로 낮은 광 추출 효율을 초래한다. 최근 이러한 문제를 해결하고자, 투명 전도성 산화물(TCO)을 금속 전극과 p-AlGaN 사이에 삽입해주는데, 현재 가장 널리 사용되는 TCO 물질은 ITO 이다 [2]. 하지만 ITO 물질은 상대적으로 작은 밴드갭(3.3~4.3 eV)과 단파장 빛이 가지는 큰 에너지로 인하여 deep-UV 영역에서는 빛이 투과하지 못하고 대부분 흡수된다 [3]. 따라서 본 연구에서는 기존의 박막형 ITO 투명 전극에 비해 투과도 손실을 최소화할 수 있는 mesh, grid 기반의 투명전극을 연구하였다. Fig. 1과 같이 $5{\mu}m$, $10{\mu}m$, $20{\mu}m$ 간격으로 이루어진 mesh, grid 구조의 투명전극을 구현하여 투과도 손실을 최소화하면서 우수한 전기적 특성을 확보하기 위한 구조 최적화 연구를 진행하였다. 본 연구를 위해 mesh, grid 구조의 ITO 전극 패턴을 photolitho 공정으로 형성하였으며, e-beam 증착법으로 60 nm 두께의 ITO 전극을 형성 후 질소 분위기/$650^{\circ}$에서 30초 동안 RTA 공정을 진행하였다. Fig. 1에서 볼 수 있듯이 mesh, grid의 간격이 증가할수록 투명 전극이 차지하는 면적이 감소하여 투과도는 향상되는 반면, 투명 전극과 p-GaN과의 접촉 면적 또한 감소하므로 오믹 특성이 저하된다. 따라서 투과도 손실을 최소화하면서 우수한 전기적 특성을 확보하기 위해 mesh는 $20{\mu}m$, grid는 $10{\mu}m$ 간격의 구조로 각각 최적화하였다. 그 결과 박막 기반의 ITO 투명전극 대비 최대 약 10% 향상된 투과도를 확보하였으며, I-V Curve 결과를 통하여 p-GaN 기판과 mesh 구조의 ITO 전극 사이에 박막 기반의 투명 전극과 비슷한 수준인 $0.35{\mu}A(@5V)$의 전기적 특성을 확보하였다. 결과적으로 mesh, grid 기반 투명전극의 구조 최적화를 통하여 p-GaN과 원활한 오믹 접촉을 형성하는 동시에 기존 박막형 ITO 투명 전극 구조보다 높은 투과도를 확보할 수 있었다.

• Wind and Structures
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• v.24 no.3
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• pp.223-247
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• 2017

By using numerical simulation, vast and detailed information and observation of the physics of flow over a train model can be obtained. However, the accuracy of the numerical results is questionable as it is affected by grid convergence error. This paper describes a systematic method of computational grid refinement for the Unsteady Reynolds Navier-Stokes (URANS) of flow around a generic model of trains using the OpenFOAM software. The sensitivity of the computed flow field on different mesh resolutions is investigated in this paper. This involves solutions on three different grid refinements, namely fine, medium, and coarse grids to investigate the effect of grid dependency. The level of grid independence is evaluated using a form of Richardson extrapolation and Grid Convergence Index (GCI). This is done by comparing the GCI results of various parameters between different levels of mesh resolutions. In this study, monotonic convergence criteria were achieved, indicating that the grid convergence error was progressively reduced. The fine grid resolution's GCI value was less than 1%. The results from a simulation of the finest grid resolution, which includes pressure coefficient, drag coefficient and flow visualization, are presented and compared to previous available data.

• Journal of the Korean Society of Marine Environment & Safety
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• v.23 no.7
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• pp.791-800
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• 2017

For fires in ship accommodation areas, if it is possible to predict the pattern in which fire will spread and suggest proper countermeasures according to a situation using a fire simulation tool, fire damage may be reduced. However, fire simulations have a practical limit: a significant amount of time is required to analyze the results due to the size of the computational domain and the number of grids. Therefore, in this study, applicable grid size for fire simulations to predict fire patterns in ship accommodation areas was analyzed, and a generation method was conducted to predict fire behavior in real time. As a result, a value within 0.25[m] was judged appropriate as an applicable grid size for ship accommodation areas. Also, in comparison with studies using a single mesh generation method, the visibility value was similar, within 4.3 %, as was the temperature value, within 8.3 %, when a multi mesh generation method was used, showing a decline of 80 % in analysis time. Therefore, it was confirmed that composing a grid using multi mesh was effective for reducing analysis time.

• Korean Journal of Computational Design and Engineering
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• v.14 no.3
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• pp.197-206
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• 2009

In a finite element analysis of the metal forming processes having large plastic deformation, largely distorted elements are unstable and hence they influence upon the result toward negative way so that adaptive remeshing is required to avoid a failure in the numerical computation. Therefore automatic mesh generation and regeneration is very important to avoid a numerical failure in a finite element analysis. In case of generating quadrilateral mesh, the automation is more difficult than that of triangular mesh because of its geometric complexity. However its demand is very high due to the precision of analysis. Thus, in this study, an automatic quadrilateral mesh generation and regeneration method using grid-based approach is developed. The developed method contains decision of grid size to generate initial mesh inside a two dimensional domain, classification of boundary angles and inner boundary nodes to improve element qualities in case of concave domains, and boundary projection to construct the final mesh.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.9B
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• pp.1390-1398
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• 2010

We present the concept of applying Wireless Mesh Networking (WMN) technology into Smart Grid, which is recently rising as a potential technology in various areas thanks to its advantages such as low installation costs, high scalability, and high flexibility. Smart Grid is an intelligent, next-generation electrical power network that can maximize energy efficiency by monitoring utility information in real-time and controlling the flow of electricity with IT communications technology converged to the existing power grid. WMNs must be designed for Smart Grid communication systems considering not only the high level of reliability, QoS support and mass-data treatment but also the properties of the traditional power grid. In addition, it is essential to design techniques based on international standards to support interoperability and scalability. In this paper, we evaluate the performance of IEEE 802.11s based Smart Grid Mesh Networks by conducting preliminary simulation studies with the ns-3 simulator. We also outline some challenging issues that should be reviewed when considering WMNs as the candidate for Smart Grid communication infrastructure.

• Journal of computational fluids engineering
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• v.16 no.1
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• pp.30-35
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• 2011

In this paper, our effort to apply 3-D Virtual Reality system for stereoscopic visualization of mesh data on the web is briefly described. This study is an extension of our previous and on-going research efforts to develop an automatic grid generation program specialized for wing mesh, named as eGWing. The program is developed by using JAVA programming language, and it can be used either as an application program on a local computer or as an applet in the network environment. In this research advancing layer method(ALM) augmented by elliptic smoothing method is used for the structured grid generation. And to achieve a stereoscopic viewing capability, two graphic windows are used to render its own viewing image for the left and right eye respectively. These two windows are merged into one image using 3D monitor and the viewers can see the mesh data visualization results with stereoscopic depth effects by using polarizing glasses. In this paper three dimensional mesh data visualization with stereoscopic technique combined with 3D monitor is demonstrated, and the current achievement would be a good start-up for further development of low-cost high-quality stereoscopic mesh data visualization system which can be shared by many users through the web.

• Korean Journal of Computational Design and Engineering
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• v.8 no.1
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• pp.41-47
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• 2003

In this paper, a tetrahedral mesh generation algorithm which uses a grid based method for interior region and an advancing front method for outer surface region is proposed. In order to apply an advancing front method for outer region of an object, a new operator so called a hole operator has been developed to handle multiple shells. With this grid based approach in the interior region, more stable and uniform meshes can be constructed especially in the interior region.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.20 no.5
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• pp.116-124
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• 2006

No matter how the equally spaced grounding grid is designed there are many problem. The best-fitted design for unequally spaced grounding grid is a part that must be considered. This paper Suggest a new way of calculation for grounding grid space of ground conductor by an algebraic function control(The first-order function, Root function, Polynomial function etc.) and on the optimal spaced grounding conductor that make the under 2[%] between maximum potential and minimum potential.

• International Journal of Aeronautical and Space Sciences
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• v.14 no.2
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• pp.122-132
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• 2013

In this research the development of unstructured grid discretization solution techniques is presented. The purpose is to describe such a conservative discretization scheme applied for experimental validation work. The objective of this paper is to better establish the effects of mesh generation techniques on velocity fields and particle deposition patterns to determine the optimal aerodynamic characteristics. In order to achieve the objective, the mesh surface discretization approaches used the VLA prototype manufacturing tolerance zone of the outer surface. There were 3 schemes for this discretization study implementation. They are solver validation, grid convergence study and surface tolerance study. A solver validation work was implemented for the simple 2D and 3D model to get the optimum solver for the VLA model. A grid convergence study was also conducted with a different growth factor and cell spacing, the amount of mesh can be controlled. With several amount of mesh we can get the converged amount of mesh compared to experimental data. The density around surface model can be calculated by controlling the number of element in every important and sensitive surface area of the model. The solver validation work result provided the optimum solver to employ in the VLA model analysis calculation. The convergence study approach result indicated that the aerodynamic trend characteristic was captured smooth enough compared with the experimental data. During the surface tolerance scheme, it could catch the aerodynamics data of the experiment data. The discretization studies made the validation work more efficient way to achieve the purpose of this paper.