• 한국신재생에너지학회:학술대회논문집
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• 2005.06a
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• pp.196-200
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• 2005

In this work, we investigated simple Aㅣ/TCO/a-Si:H(n)/c-Si(p)/Al hetero-junction solar cells prepared by low temperature processes, unlike conventional thermal diffused c-Si solar cells. a-Si:H/c-Si hetero-junction solar cells are processed by low temperature deposition of n-type hydrogenated amorphous silicon (a-Si:H) films by plasma-enhanced chemical vapor deposition on textured and flat p-type silicon substrate. A detailed investigation was carried out to acquire optimization and compatibility of amorphous layer, TCO (ZnO:Al) layer depositions by changing the plasma process parameters. As front TCO and back contact, ZnO:Al and AI were deposited by rf magnetron sputtering and e-beam evaporation, respectively. The photovoltaic conversion efficiency under AMI.5 and the quantum efficiency on $1cm^2$ sample have been reported. An efficiency of $12.5\%$ is achieved on hetero-structure solar cells based on p-type crystalline silicon.

• Journal of the Korean Society for Nondestructive Testing
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• v.26 no.6
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• pp.403-410
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• 2006

Eddy current testing (ECT) signals produced by a differential bobbin coil probe vary according to probe design parameters such as the number of turns, geometry and coil gap size. In the present study, the characteristics of a differential bobbin coil probe signals are investigated by numerical simulation in order to determine the optimum coil gap. For verification of numerical simulation accuracy, a specially designed bobbin probe of which the coil gap can be adjusted is fabricated and a series of experiments to acquire signals from two kinds of standard tubes with the variation in coil gap is performed. Then, the experimental signals are compared to the simulation results. Based on this investigation, a decision on the optimum range of coil gap is made. The theoretically predicted signals agree very well to the experimental signals. In fact, this excellent agreement demonstrates a high potential of the simulation as a design optimization tool for ECT bobbin probes.

• Journal of the Korean Society for Precision Engineering
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• v.23 no.1 s.178
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• pp.72-79
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• 2006

The objective of this work is to simulate the etching characteristics for the optimization on the etching process of Lead-Frame. The etching characteristics such as etching factor, etching uniformity were investigated under different the actual operating conditions. The correlation between the etching characteristics and the spray ones were analyzed to simulate the etching characteristics in the etching process. To improve the etching characteristics in the etching process, effects of the various operating conditions such as pressure, distance from nozzle tip, pipe pitch, and feed speed should be understood in detail. The spray characteristics obtained by experiment using PDA system were simulated by the Monte-Carlo simulation. The etching process model was coded by Java language. It was found that the spray characteristics were correlated with the etching ones and simulation results generally agreed well with the measured results of etching characteristics in the etching process of Lead-Frame. The optimal operating parameters were successfully found under variable conditions.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.1682-1685
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• 2005

System algorithms estimated by deterministic input may occur the error between predicted and actual output. Especially, actual system can't predict the exact outputs due to uncertainty and tolerance of input parameters. A single output to a set of inputs has a limited value without the variation. Hence, we should consider various scatters caused by the load assessment, material characteristics, stress analysis and manufacturing methods in order to perform the robust design or estimate the reliability of structure. The system design with uncertainty should perform the probabilistic structural optimization with the statistical response and the reliability. This method calculated the probability distributions of the characteristics such as stress by combining stress analysis, response surface methodology and Monte-Carlo Method and got the probabilistic sensitivity. The sensitivity of structural response with respect to inconstant design variables was estimated by fracture probability. Therefore, this paper proposed the probabilistic reliability design method for fracture of uncorved freight end beam and the design criteria by fracture probability.

• Transactions of Materials Processing
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• v.20 no.2
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• pp.160-166
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• 2011

Weight reduction while maintaining functional requirements is one of the major goals in the automotive industry. The use of lightweight magnesium alloys offers great potential for reducing weight because of the low density of these alloys. However, the formability and the surface quality of the final magnesium alloy product for auto-body structures are not acceptable without a careful optimization of the design parameters. In order to overcome some of the main formability limitations in the stamping of magnesium alloys, a new approach, the so-called "hybrid technology", has been recently proposed for body-in-white structural components. Within this approach, necessary level of mechanical joining can be obtained through the use of lightweight material-steel adhesion promoters. This paper presents the development process of an automotive hybrid hood assembly using magnesium alloy sheets. In the first set of material pairs, the selected materials are magnesium alloy AZ31B alloy and steel(SGCEN) as inner and outer panels, respectively. In order to optimize the design of the inner panel, the stamping process was analyzed with the finite element method (FEM). Laser welding by CW Nd:YAG were used to join the magnesium alloy sheets. Based on the simulation results and mechanical test results of the joints, the determination of die design variables and their influence on formability were discussed. Furthermore, a prototype based on the proposed design was manufactured and the static stiffness test was carried out. The results demonstrate the feasibility of the proposed hybrid hood with a weight reduction of 25.7%.

• Journal of Korean Society on Water Environment
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• v.24 no.2
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• pp.239-246
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• 2008

In this study, an optimized deterministic water-quality model was constructed to estimate water quality of a river and lake in the upstream basin of a dam. A stochastic water-quality analysis using reliability analysis technique was applied to the model. The model was tested in the 13.9 km reach from Maeil stage station of Kyechun to Hoengsung Dam of Sum River. After finding hydraulic characteristics from nonuniform flow analysis, Broyden-Fletcher-Goldfarb-Shanno (BFGS) optimization technique for model calibration was applied to determine optimum reaction parameters, and model verification was performed based on these. The stochastic model, using Mean First­Order Second­-Moment (MFOSM) and Monte-Carlo methods, was applied to the same reach as the deterministic study. Variations of discharge and water quality in headwater were considered, as well as variations of hydraulic coefficients and reaction coefficients. The statistical results of output variables from MFOSM were similar to those from the Monte-Carlo method. Risk analysis using MFOSM and Monte-Carlo methods presented the probabilities of some locations in the Hoengsung Lake violating existing water-quality standards in terms of DO and BOD.

• Proceedings of the Korea Water Resources Association Conference
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• 2009.05a
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• pp.2215-2219
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• 2009

For model calibration in rainfall-runoff modeling, streamflow data at a specific outlet is obviously required but is not sufficient to identify parameters of a model since numerous parameter combinations can result in very similar model performance measures (i.e. objective functions) and indistinguishable simulated hydrographs. This phenomenon has been called 'equifinality' due to inherent parameter uncertainty involved in rainfall-runoff modeling. This study aims to investigate catchment responses in time and space to various uncertain parameter sets in distributed rainfall-runoff modeling. Seven plausible (or behavioral) parameter sets, which guarantee identically-good model performances, were sampled using deterministic and stochastic optimization methods entitled SCE and SCEM, respectively. Then, we applied them to a computational tracer method linked with a distributed rainfall-runoff model in order to trace and visualize potential origins of streamflow at a catchment outlet. The results showed that all hydrograph simulations based on the plausible parameter sets were performed equally well while internal catchment responses to them showed totally different aspects; different parameter values led to different distributions with respect to the streamflow origins in space and time despite identical simulated hydrographs. Additional information provided by the computational tracer method may be utilized as a complementary constraint for filtering out non-physical parameter set(s) (or reducing parameter uncertainty) in distributed rainfall-runoff modeling.

• Journal of Energy Engineering
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• v.14 no.3 s.43
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• pp.194-202
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• 2005

The present study was analytically and experimentally carried out to predict the absorption characteristics on combined heat and mass transfer process in a vertical falling film of variable absorbers. Heat and mass transfer enhancements were analytically investigated. Effects of geometric parameters by insert device (spring) and corrugate, flow pattern on absorption performances has been also investigated. Especially, the optimal values of absorber geometry (ID=22.8mm, L=1150m) and kinetic variables (solution flow rate, flow pattern) for maximum absorption performance has been predicted by the numerical analysis. The maximum absorption performance in a numerical analysis and experiment was shown at the wavy-flow by insert device (spring).

• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.991-992
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• 2011

This study was designed to satisfy induced voltage limits considering drive's specifications and optimize design reducing usage of permanent magnet, by increasing salient poles ratio, when designing 150kW IPMSM. In order to achieve these objectives, design plans were determined, based on Ld and Lq parameters of a basic design model, according to changes in salient poles ratio and flux linkage using IPMSM's voltage equation and torque equation and then, required torque and induced voltage were analyzed using Sensitivity Analysis. Based on analysis data, the optimum design was performed and basic model's characteristics were compared to final model's through Gradient-Based Optimization Technique.

• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.1430-1431
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• 2011

To develope the transparent conducting oxide(TCO) films is one of the essential technologies to improve various properties of electro-optical devices such as dye-sensitized solar cells(DSCs). ITiO thin film is considered one of the candidates as TCO electrodes of DSCs because it shows many advantages such as the high transparency in long wavelength range above 700nm and excellent properties of electrical necking between nanoporous TiO2 and ITiO transparent electrode. This paper presents the effect of sputtering processes on the structural, electrical and optical properties of ITiO thin film deposited by r.f. magnetron sputtering. The effect of doping concentration of Ti on the chemical compounds and C axis-orientation properties of were mainly studied experimentally. The morphology and electrical properties were greatly influenced by deposition processes, especially by the doping concentration of Ti. The $3.8{\times}10^{-4}{\Omega}{\cdot}cm$ of minimum volume resistivity were obtained under the experimental conditions of gas pressure 7mTorr, substrate temperature $300^{\circ}C$, and 2.5% of Ti doping concentration.