• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.490.2-490.2
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• 2014

Since the general solar cells accept sun light at the front side, excluding the electrode area, electrons move from the emitter to the front electrode and start to collect at the grid edge. Thus the edge of gridline can be important for electrical properties of screen-printed silicon solar cells. In this study, the improvement of electrical properties in screen-printed crystalline silicon solar cells by contact treatment of grid edge was investigated. The samples with $60{\Omega}/{\square}$ and $70{\Omega}/{\square}$ emitter were prepared. After front side of samples was deposited by SiNx commercial Ag paste and Al paste were printed at front side and rear side respectively. Each sample was co-fired between $670^{\circ}C$ and $780^{\circ}C$ in the rapid thermal processing (RTP). After the firing process, the cells were dipped in 2.5% hydrofluoric acid (HF) at room temperature for various times under 60 seconds and then rinsed in deionized water. (This is called "contact treatment") After dipping in HF for a certain period, the samples from each firing condition were compared by measurement. Cell performances were measured by Suns-Voc, solar simulator, the transfer length method and a field emission scanning electron microscope. According to HF treatment, once the thin glass layer at the grid edge was etched, the current transport was changed from tunneling via Ag colloids in the glass layer to direct transport via Ag colloids between the Ag bulk and the emitter. Thus, the transfer length as well as the specific contact resistance decreased. For more details a model of the current path was proposed to explain the effect of HF treatment at the edge of the Ag grid. It is expected that HF treatment may help to improve the contact of high sheet-resistance emitter as well as the contact of a high specific contact resistance.

• Nuclear Engineering and Technology
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• v.45 no.7
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• pp.895-910
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• 2013

The reflood test data from the rod bundle heat transfer (RBHT) test facility showed that the grids in the upper portion of the rod bundle could become wet well before the arrival of the quench front and that the sizes of liquid droplets downstream of a wet grid could not be predicted by the droplet breakup models for a dry grid. To investigate the water droplet generation from a wet grid spacer, a viscous linear temporal instability model of the water sheet issuing from the trailing edge of the grid with the surrounding steam up-flow is developed in this study. The Orr-Sommerfeld equations along with appropriate boundary conditions for the flow are solved using Chebyshev series expansions and the Tau-Galerkin projection method. The effects of several physical parameters on the water sheet oscillation are studied by determining the variation of the temporal growth rate with the wavenumber. It is found that a larger relative steam velocity to water velocity has a tendency to destabilize the water sheet with increased dynamic pressure. On the other hand, a larger ratio of steam boundary layer to the half water sheet thickness has a stabilizing effect on the water sheet oscillation. Droplet diameters downstream of the spacer grid predicted by the present model are found to compare reasonably well with the data obtained at the RBHT test facility as well as with other data recently reported in the literature.

• Journal of computational fluids engineering
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• v.21 no.4
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• pp.85-89
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• 2016

Wing is the most important part of aircraft which produces lift. In general when aircraft takes off or lands, high lift is required and additional devices are adopted in front and aft-side of wing, which constitute so-called multi element airfoils. The objective of this research is to develop a specialized grid generation program to help engineers in reducing human labor and eliminating time-consuming process for mesh regeneration by deforming the initially-given grid system with efficient deforming method. This paper describes briefly about the mesh deformation methods, and provides some results to verify the quality of deformed mesh and eventually correctness of current approach.

• Journal of The Korean Astronomical Society
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• v.34 no.4
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• pp.237-241
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• 2001

Our goal is to present a simple volume-of-fluid type interface-tracking algorithm to compressible two-phase flow in two space dimensions. The algorithm uses a uniform underlying Cartesian grid with some cells cut by the tracked interfaces into two subcells. A volume-moving procedure that consists of two basic steps: (1) the update of volume fractions in each grid cell at the end of the time step, and (2) the reconstruction of interfaces from discrete set of volume fractions, is employed to follow the dynamical behavior of the interface motion. As in the previous work with a surface-tracking procedure for general front tracking (LeVeque & Shyue 1995, 1996), a high resolution finite volume method is then applied on the resulting slightly nonuniform grid to update all the cell values, while the stability of the method is maintained by using a large time step wave propagation approach even in the presence of small cells and the use of a time step with respect to the uniform grid cells. A sample preliminary numerical result for an underwater explosion problem is shown to demonstrate the feasibility of the algorithm for practical problems.

• Journal of the Korea Society of Computer and Information
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• v.14 no.12
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• pp.1-8
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• 2009

Grid services offer SSO(single sign-on) mechanism using GSI(grid security infrastructure) based on X.509. However. portal applications in web environment use ID and password model for single sign-on. Grid portals means a system which provides grid services by integrating portlet contents on single web interface. In existing research such as GAMA and PURSE, SSO for a whole grid portal is figured out in the way that user is authenticated by ID and password in front and call grid service via GSI at back-end. Other types of web applications outside of portlet framework cannot unfortunately access grid service in SSO way in the existing researches, because the SSO mechanism is developed for portlet framework only. In this paper, we suggest a SSO mechanism based on ID and password model, which forwards authentication information and a GSI token for grid access among portlets and grid-enabled web applications. This mechanism is applied to MGrid for SSO, which consists of applications of java web start, applet, servlet, and etc. as also as portlets.

• The KIPS Transactions:PartA
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• v.14A no.1 s.105
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• pp.1-14
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• 2007

MPICH-G2 is an MPI implementation to solve complex computational problems by utilizing geographically dispersed computing resources in grid environments. However, the computation nodes in MPICH-G2 are exposed to the external network due to the lack of supporting the private IP clusters, which raises the possibility of malicious security attacks. In order to address this problem, we propose MPICH-GP with a new relay scheme combining NAT(Network Address Translation) service and an user-level proxy. The proxy running on the front-end system of private IP clusters forwards the incoming connection requests to the systems inside the clusters. The outgoing connection requests out of the cluster are forwarded through the NAT service on the front-end system. Through the connection path between the pair of processes, the requested MPI jobs can be successfully executed in grid environments with various clusters including private IP clusters. By simulations, we show that the performance of MPICH-GP reaches over 80% of the performance of MPICH-G2, and over 95% in ease of using RANK management method.

• Journal of the Korean Society of Groundwater Environment
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• v.6 no.1
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• pp.23-32
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• 1999

A new numerical method using solution-adaptive grids (SAG) is developed to solve the Richards' equation (RE) for unsaturated flow in porous media. Using a grid generation technique, the SAG method automatically redistributes a fixed number of grid points during the flow process, so that more grid points are clustered in regions of large solution gradients. The method uses the coordinate transformation technique to employ a new transformed RE, which is solved with the standard finite difference method. The movement of grid points is incorporated into the transformed RE, and therefore all computation is performed on fixed grid points of the transformed domain without using any interpolation techniques. Thus, numerical difficulties arising from the movement of the wetting front during the infiltration process have been substantially overcome by the new method. Numerical experiments for an one-dimensional infiltration problem are presented to compare the SAG method to the modified Picard method using a fixed grid. Results show that accuracy of a SAG solution using 41 nodes is comparable with the solution of the fixed grid method using 201 nodes, while it requires only 50% of the CPU time. The global mass balance and the convergence of SAG solutions are strongly affected by the time step size (Δt) and the weighting parameter (${\gamma}$) used for generating solution-adaptive grids. Thus, the method requires automated readjustment of Δt and ${\gamma}$ to yield mass-conservative and convergent solutions, although it may increase computational costs. The method can be effective especially for simulating unsaturated flow and other transport problems involving the propagation of a sharp-front.

• Journal of computational fluids engineering
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• v.21 no.1
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• pp.30-35
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• 2016

In order to investigate effects of grid resolution on large-eddy simulation of flow over a heavy vehicle, large-eddy simulations over the vehicle with coarse grid and fine grid are conducted. In addition, comparison of drag coefficients with the experimental data obtained by a wind tunnel experiment is conducted. Both of the drag coefficients of coarse grid and fine grid large-eddy simulation show good agreement with the experimental data. Flow fields obtained by the coarse and the fine grid large-eddy simulation are compared in the vehicle frontal-face region, the vehicle rear wheel region, and the vehicle base region. Coarse grid large-eddy simulation shows good agreement with the fine grid large-eddy simulation in the vehicle front face region and the vehicle rear wheel region, since the flow over the present vehicle is dominated by flow separation which is geometrically pre-determined, not by the skin friction which is known to be sensitive to grid resolution.

• Journal of the Korean Society for Precision Engineering
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• v.17 no.6
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• pp.210-217
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• 2000

Noncontact measuring methodology of 3-dimensional profile using CCD camera are very attractive because of it's high measuring speed and it's high sensitivity. Especially when projecting a grid pattern over the object, the captured image have 3 dimensional information of the object. Projection moire extract 3-D information with another grid pattern in front of CCD camera. However phase measuring profilometry(PMP) obtain similar results without additional grid pattern. In this paper, the projection moire are compared with the PMP mathematically, and it is shown that PMP can generate moire image with simple mathematical computations. Experimental works are also carried out showing the same results. It is shown that using a single gird pattern, moire image can be obtained directly without any mathematical operation when some conditions are satisfied.

• Journal of Mechanical Science and Technology
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• v.15 no.6
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• pp.796-803
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• 2001

Numerical solutions for the convection-dominated melting in a rectangular cavity are presented. The enthalpy-porosity model is employed as the mathematical model. This model is applied in conjunction with the EIT method to detect boundary movement in a phase changing environment. The absorption and evolution of latent heat during the phase change is dealt with by the enthalpy-based energy equation. This seems to be more efficient than resolving the temperature-based energy equation. The velocity switch-off, which is required when solid changes into liquid, is modeled by the porous medium assumption. For efficiency and simplicity of the solutions procedure, this paper proposes a simple algorithm, which iterates the temperature and the liquid fraction of the cells comprising the front layer. The numerical results agree reasonably well with the experimental data and other previous works using the transformed-grid system.