• Transactions of Materials Processing
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• v.16 no.3 s.93
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• pp.172-177
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• 2007

The process design for large-scale ring rolling of Ti-6Al-4V alloy was performed by calculation method, processing map approach and FEM simulation. The ring rolling design includes geometry design and optimization of process variables. The calculation method was used to make geometry design such as initial billet and blank sizes, and final rolled ring shape. A commercial FEM code, SHAPE-RR was used to simulate the effect of process variables in ring rolling on the distribution of the internal state variables such as strain, strain rate and temperature. In order to predict the forming defects during ring rolling and the formation of over-heating above $\beta$-transus temperature due to deformation heating, the process-map approach based on Ziegler's instability criterion was used with FEM simulation. Finally, an optimum process design to obtain sound Ti-6Al-4V rings without forming defects was suggested through combined approach of Ziegler's instability map and FEM simulation results.

• 유체기계공업학회:학술대회논문집
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• 2004.12a
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• pp.572-577
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• 2004

This paper presents numerical study on the performance improvement of the sirocco fan in a range hood. The performance of sirocco fan means a higher flowrate, a higher static pressure and a lower required motor power in a fixed geometry constraint. Various impeller geometric parameters, such as blade profile, blade diameter, blade thickness profile and blade exit angle, were investigated by numerically and the results were compared with each other to know the effects on the performance. In this approach, the volute geometry were fixed with the original shape. The numerical results show that the blade profile with airfoil shape and small exit blade thickness increases the performance. The blade exit angle shows optimum angle within a varied range. The efficiency of the optimized exit angle was about $10\%$ higher than the base blade exit angle and the static pressure was about $28\%$ higher at the flow coefficient 0.22.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.32A no.2
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• pp.57-65
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• 1995

The effects of device geometry and layout on high speed performance such as current gain outoff frequency(f$_{T}$) and maximum oscillation frequency(f$_{max}$) are of very improtant for the scaling-down of geterojunction bipolar transistors(HBT$_{s}$). In this paper AlGaAs/GaAs HBTs are fabricated by MBE epitaxial growth and conventional mesa process, and the experimental data of emitter-base geometru dependency of HBT performance are presented in order to provide the quantitative information for optimum device structure design. It is shown that f$_{T}$ and f$_{max}$ are inversely proportional to the emiter stripe width, while the low emitter perimeter/area ratio is better to f$_{T}$ and worse ot f$_{max}$. It is also demonstrated the f$_{T}$ and f$_{max}$ are highly improved by the emitter-base spacing reduction resulting in less parsitic effects. As the result f$_{T}$ of 42GHz and f$_{max}$ of 23GHz are obtained for fabricated HBT with emitter area of 3${\times}20^{\mu}m^{2}$ and E-B spacing of 0.2$\mu$m.m.m.

• Nuclear Engineering and Technology
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• v.53 no.10
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• pp.3438-3448
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• 2021

Dynamic seals are one of the critical components of Absorber Rod Drive Mechanism of Fast Breeder Reactors, requiring separate experimental development. Their significance can't be overemphasized considering that the availability and re-usability of Control Rod Drive Mechanisms of Fast Breeder Test Reactor is governed by the failure rate of dynamic seals (bellows). For prototype and subsequent Fast Breeder Reactors in India, choice of the dynamic seal is changed to an in-house designed & developed labyrinth type V-ring seal. The present work is related to the numerical investigations carried out to gain insights into the sealing mechanism and the thermal behaviour of these seals. The results indicate that the seal geometry is very important for obtaining optimum performance. By changing the geometry of the present seal, performance enhancement by more than 50% in important indices is obtained. Further, the results point out that caution shall be exercised when the seal material & its operating temperature are changed. Also, the numerical model developed in this study will be useful for developing more robust dynamic seals in future.

• Journal of the Korean Geotechnical Society
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• v.25 no.12
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• pp.131-142
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• 2009

Geosynthetic reinforced soil walls are well recognized alternatives to conventional retaining walls due to many advantages in terms of ease of construction, economy, and aesthetics, among others. In recent years, the use of back-to-back (BTB) geosynthetic reinforced soil walls has been increasing for roadway and railway construction. However, there are insufficient studies concerning the behavior of BTB type geosynthetic reinforced soil walls. In this study a series of finite element analysis were performed for BTB walls with various wall geometry and reinforcement distribution. The results were then analyzed to relate the wall geometry and reinforcement distribution and the performance of BTB walls. Optimum reinforcement pattern was also investigated.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.1845-1848
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• 2005

The automatic $CO_2$ welding is a manufacturing process to produce high quality joints for metal and it could provide a capability of full automation to enhance productivity. Despite the widespread use in the various manufacturing industries, the full automation of the robotic $CO_2$ welding has not yet been achieved partly because the mathematical model for the process parameters of a given welding task is not fully understood and quantified. Several mathematical models to control welding quality, productivity, microstructure and weld properties in arc welding processes have been studied. However, it is not an easy task to apply them to the various practical situations because the relationship between the process parameters and the bead geometry is non-linear and also they are usually dependent on the specific experimental results. Practically, it is difficult, but important to know how to establish a mathematical model that can predict the result of the actual welding process and how to select the optimum welding condition under a certain constraint. In this research, an attempt has been made to develop an intelligent algorithm to predict the weld geometry (top-bead width, top-bead height, back-bead width and back-bead height) as a function of key process parameters in the robotic $CO_2$welding. A sensitivity analysis has been conducted and compared the relative impact of three process parameters on bead geometry in order to verify the measurement errors on the values of the uncertainty in estimated parameters.

• Korean Journal of Optics and Photonics
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• v.3 no.4
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• pp.227-233
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• 1992

The simulation code was developed for the development of the split-disk geometry glass amplifier, which could design the laser apparatus and analyze the properties of the laser system. The flashlamp emission energy at the short wavelength region must be reduced, while maintaining a current density between 2000 and 4000 A/$\textrm{cm}^{2}$, in order to reduce the thermal loading in the laser glass and to raise the coupling efficiency between the emission spectrum of the flashlamps and the absorption spectrum of the laser glass. By cutting the laser glass into three equal pieces, the temperature rise in the laser glass dropped by 70% due to the efficient removal of the heat in the laser glass. It was found that the $Nd^{3+}$ doping rate of each laser glass should be properly selected and the optimum value of the product of the absorption coefficient $\alpha$ and the thickness d of the laser glass is about 0.26 in the split-disk geometry.

• Progress in Medical Physics
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• v.15 no.2
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• pp.84-93
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• 2004

Stereotactic radiosurgery (SRS) is a technique that delivers a high dose to a target legion and a low dose to a critical organ through only one or a few irradiations. For this purpose, many mathematical methods for optimization have been proposed. There are some limitations to using these methods: the long calculation time and difficulty in finding a unique solution due to different tumor shapes. In this study, many clinical target shapes were examined to find a typical pattern of tumor shapes from which some possible ideal geometrical shapes, such as spheres, cylinders, cones or a combination, are assumed to approximate real tumor shapes. Using the arrangement of multiple isocenters, optimum variables, such as isocenter positions or collimator size, were determined. A database was formed from these results. The optimization procedure consisted of the following steps: Any shape of tumor was first assumed to an ideal model through a geometry comparison algorithm, then optimum variables for ideal geometry chosen from the predetermined database, followed by a final adjustment of the optimum parameters using the real tumor shape. Although the result of applying the database to other patients was not superior to the result of optimization in each case, it can be acceptable as a plan starling point.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.3080-3085
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• 2007

Shape optimization of the 3-dimensional WIG airfoil with 3.0-aspect ratio has been performed by using the multi-objective genetic algorithm. The WIG ship effectively floating above the surface by the ram effect and the virtual additional aspect ratio by a ground is one of next-generation and cost-effective transportations. Unlike the airplane flying out of the ground effect, a WIG ship has possibility to capsize because of unsatisfying the static stability. The WIG ship should satisfy aerodynamic properties as well as a static stability. They tend to strong contradict and it is difficult to satisfy aerodynamic properties and static stability simultaneously. It is inevitable that lift force has to scarify to obtain a static stability. Multi-objective optimization technique that the individual objectives are considered separately instead of weighting can overcome the conflict. Due to handling individual objectives, the optimum cannot be unique but a set of nondominated potential solutions: pareto optimum. There are three objectives; lift coefficient, lift-to-drag ratio and static stability. After a few evolutions, the non-dominated pareto individuals can be obtained. Pareto sets are all the set of possible and excellent solution across the design space. At any selections of the pareto set, these are no better solutions in all design space

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.3050-3055
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• 2007

A wind turbine is one of the most popular energy conversion systems to generate electricity from the natural renewable energy source and an axial-flow type wind turbine is the most popular system for the electricity generation in the wind farm nowadays. In this study, a cross-flow type turbine has been studied for the application of wind turbine for electricity generation. The target capacity of electric power generation of the model wind turbine developing on the project is 12 volts, 130A/H (about 1.56kW). The important design parameters of the model turbine impeller are the inlet and exit angle of the turbine blade, number of blade, hub/tip ratio and the exit flow angle of the casing. In this study, the radial equilibrium theorem was used to decide the inlet and exit angle of the impller blade and CFD technique was used to have the performance analysis of the designed model power turbine to find out the optimum geometry of the CPT impeller and casing. The designed CPT with 24 impeller blades at ${\alpha}=82^{\circ}$, ${\beta}=40^{\circ}$ of turbine blade angle was estimated to generate 284.6 N.m of indicated torque and 2.14kW of indicated power.