• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07b
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• pp.714-718
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• 2003

Usually for the commercial preparation of barium titanate films or ceramics the reaction atmosphere must be preferably in air. However, normally air is not used because it contains carbon dioxide, which can easily react with barium to form the undesired product barium carbonate, leading to unwanted second-phase formation in the (mal stages of the process. In the present work a series of perovskite barium titanate films was prepared by the sol-gel method, using a metal alkoxide solutions in the electrophoretic deposition (EPD). The influence of several process parameters, like sintering temperature of sol preparation before EPD and heat-treatment temperature and non-oxidized atmosphere, on the film properties is described.

• Journal of Positioning, Navigation, and Timing
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• v.7 no.3
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• pp.175-181
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• 2018

The use of dual-frequency measurements from the Global Navigation Satellite System (GNSS) enables us to observe precise ionospheric total electron content (TEC). Currently, many GNSS reference stations in South Korea provide both GPS and GLONASS data. In the present study, we estimated the grid-based TEC values and relative receiver differential code biases (DCB) from a GNSS network operated by the Korea Astronomy and Space Science Institute. In addition, we compared the diurnal variations in a TEC time series from solutions of the GPS only, the GLONASS only, and combined GPS/GLONASS processing. A significant difference between the GPS only TEC and combined GPS/GLONASS TEC at a specific grid point over South Korea appeared near the solar terminator. It is noted that GLONASS measurements can contribute to observing a variation in ionospheric TEC over high latitude regions.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.9
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• pp.2322-2330
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• 1994

The torsion problem in a cylindrical rod is usually formulated in terms of either the warping function or the Prandtl stress function. In a rod whose cross-section is bounded by circles and rectangles, we develop an analytic solution approach based on the warping function, which satisfies Laplace's equation. The present formulation employs polynomials and The Fourier series-type solutions, both of which satisfy exactly the governing differential equation. Using the present method, the maximum shear stress and torsional rigidity are efficiently and accurately calculated and the present results are compared with those by other methods. The specific numerical examples include the case with eccentric holes which was investigated earlier. The finite element results are also compared with the present results.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.11
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• pp.1802-1812
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• 2001

The theoretical method is developed to investigate the effects of ring stiffeners on free vibration characteristics and transient response for the ring stiffened composite cylindrical shells subjected to the impulse pressure Loading. In the theoretical procedure, the Love's thin shell theory combined with the discrete stiffener theory to consider the ring stiffening effect is adopted to formulate the theoretical model. The concentric or eccentric ring stiffeners are laminated with composite and have the uniform rectangular cross section. The modal analysis technique is used to develop the analytical solutions of the transient problem. The analysis is based on an expansion of the loads, displacements in the double Fourier series that satisfy the boundary conditions. The effect of stiffener's eccentricity, number, size, and position on transient response of the shells is examined. The results are verified by comparison with FEM results.

• Proceedings of the KSME Conference
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• 2001.11a
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• pp.234-239
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• 2001

The stress intensity factors have been widely used in numerical studies of crack growth direction. However in many cases, omissive terms of the series expansion are quantitatively significant, so we consider the computation of such terms. For this purpose, we used the finite element method with isometric quadratic quarter-point elements. For examples, infinite square plate with a slant crack subjected to a uniaxial load is analyzed. The numerical analysis were performed for the wide range of crack tip element lengths and inclined angles. The numerical results obtained are compared with the theoretical solutions. Also they were accurate and efficient.

• Transactions of the Korean Society of Mechanical Engineers
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• v.8 no.5
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• pp.408-415
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• 1984

The stress state of orthotropic cylindrical shells subjected to localized loads is considered. The governing equations for orthotropic cylindrical shells are derived on the basis of the Morley-Koiter's isotropic shell theory. It is assumed here that the material has a special orthotropy. Solutions are obtained by the Bijlaard's method in the from of double Fourier series. Numerical examples are presented for cylindrical shells having various orthotropic material properties and shell geometries.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 2006.05a
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• pp.1133-1138
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• 2006

This paper considers a hybrid flow shop scheduling problem for the objective of minimizing the number of tardy jobs. The hybrid flow shop consists of two stages in series, each of which has multiple identical parallel machines, and the problem is to determine the allocation and sequence of jobs at each stage. A branch and bound algorithm that gives the optimal solutions is suggested that incorporates the methods to obtain the lower and upper bounds. Dominance properties are also derived to reduce the search space. To show the performance of the algorithm, computational experiments are done on randomly generated problems, and the results are reported.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1996.04a
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• pp.761-765
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• 1996

This paper describes the forging of circular tooth profiled gears as a series of development of simulator for non-axisymmetric parts that being used at the pump pulley, timing belt pulley etc. in automobiles. The half pitch of gear is divided into 6 deformation regious and kinematically admissible velocity fields for those regions are proposed. The neutral surface is introduced torepresent inner flow of material during forging operation with flat punch and, for each step, it is assumed as a circle. The upper bound solutions obtained from the suggested kinematically admissible velocity fields are in good agreement with experimental results and they are useful to predict the capacity of forging press for forging of circular gears.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.25 no.6
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• pp.420-425
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• 2015

In this paper a transfer matrix method is developed to solve for bending vibration of beam with linearly reduced width, and subsequently used to determine the exact natural frequencies for such problems. The differential equation, shear force, and bending moment are derived from Hamilton's principle, and the roots of the differential equation are computed using the power series solution of the Frobenius method. The effect of various taper ratio for bending vibration of beam with linearly reduced width is investigated in detail, and to validate the accuracy of the proposed method the results computed are compared with those given from commercial software(ANSYS).

• Laser Solutions
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• v.2 no.1
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• pp.22-29
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• 1999

This work was carried out as a fundamental experiment to fabricate a Graded-Boundary Ni/Steel material using a laser beam. A Ni sheet was placed on a steel substrate, and then a series of high power $CO_2$ laser beams were irradiated on the surface in order to produce a homogeneous alloyed layer. The processing parameters were : 4 ㎾ laser power, 2m/min traverse speeds, -2mm defocuing, 17 l/min sheiding gas flow rates. The sequential repetition of the laser surface alloying treatment up to 4 times, resulted in about 5mm thick of fair compositional gradient systems. In order to determine the microstructure, phase and compositional profiles in this material, optical microscopy, XRD and EDS were used. The compositions varied from 66% to 0% for Ni and 34% to 100% for Fe in this material The microstructures were typical morphologies of rapid solidification and solid-state cooling. Since compressive stress was formed in the heat affected region due to martensitic transformation, while relative tensile stress was developed in the alloyed region, cracks were formed between the alloyed region and the substrate region.