• The Transactions of the Korean Institute of Electrical Engineers C
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• v.51 no.3
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• pp.115-120
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• 2002

This Paper describes an algorithm for the design of axi-symmetrical spacer under specified field conditions. The electric field alas been calculated by combination method of Integral Equation Method(IEM) and Charge Simulation Method(CSM). The contour of spacer is represented with NURB(Non-Uniform Rational B-spline) curve of which effectiveness has been proved. This algorithm introduces a design process in the aspect of electrical field, when a spacer in airtight cylinder is designed. Also various field conditions for obtaining optical shapes have been proposed. Due to the algorithm, the entire process shows a stable convergence. Both tangential and total electrical field are taken into consideration as specified field criteria.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.3 s.174
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• pp.676-684
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• 2000

In this study, behavior of $C_t$ which is a well-known fracture parameter characterizing creep crack growth rate, is investigated for weld interface cracks. Finite element analyses were per formed for a C(T) specimen under constant loading condition for elastic-plastic-creeping materials. In modeling C(T) geometry, an interface was employed along the crack plane which simulated the interface between weld and base metals. The $C_t$ versus time relations were obtained under various creep constant combinations and plastic constant combinations for weld and base metals, respectively. A unified $C_t$ versus time curve is obtained by normalizing $C_t$ with $C^*$ and t with $t_T$ for all the cases of material constant variations.

• Journal of the Korean Mathematical Society
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• v.36 no.4
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• pp.707-723
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• 1999

Since the modular curve $X(4)=\Gamma(4)/{\mathfrak{}}^*$ has genus 0, we have a field isomorphism K(X(4)){\approx}\mathcal{C}(j_{4})$ where $j_{4}(z)={\theta}_{3}(\frac{z}{2})/{\theta}_{4}(\frac{z}{2})$ is a quotient of Jacobi theta series ([9]). We derive recursion formulas for the Fourier coefficients of $j_4$ and $N(j_{4})$ (=the normalized generator), respectively. And we apply these modular functions to Thompson series and the construction of class fields.

• Proceedings of the KSME Conference
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• 2000.11a
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• pp.328-332
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• 2000

Following the method described in ASTM E1737, J resistance curves are measured for Cr-Mo steel SA387, and Cr steel A240 which are used as piping materials in nuclear industry. Crack driving force diagrams are generated in order to find out instability points in crack growth. The $J_{appl}$ curves, which are used in the crack driving force diagram, are obtained from EPRI J estimation method and the finite element analysis. Crack growth instability points are plotted in load-crack length plane and the results are discussed.

• Proceedings of the KIEE Conference
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• 2001.07a
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• pp.206-209
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• 2001

This paper illustrates a new method for reliability evaluation at load points in a composite power system. The algorithm includes uncertainties of generators and transmission lines as well as main transformers at substations. The CMELDC based on the new effective load model at HLII has been developed also. The CMELDC can be obtain from convolution integral processing of the outage capacity probabilistic distribution function of the fictitious generator and the original load duration curve given at the load point. The CMELDC based on the new model at HLII will extend the application areas of nodal probabilistic production cost simulation, outage cost assessment and reliability evaluation etc. at load points. The characteristics and effectiveness of this new model are illustrated by a case study of a small test system.

• Proceedings of the KIEE Conference
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• 1998.07b
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• pp.509-511
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• 1998

Design of fuzzy logic controllers encounters difficulties in the selection of optimized membership function and fuzzy rule base, which is traditionally achieved by tedious trial-and-error process. In this paper We proposed a new method to generate fuzzy logic controllers throught genetic algorithm(GA). The controller design space is coded in base-7 strings chromosomes, where each bit gene matches the 7 discrete fuzzy value. The developed approach is subsequently applied to the design of proportional plus integral type fuzzy controller for a do-servo motor control system. It was presented in discrete fuzzy linguistic value, and used a membership function with Gaussian curve. The performance of this control system is demonstrated higher than that of a conventional PID controller and fuzzy logic controller(FLC).

• Elastomers and Composites
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• v.30 no.2
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• pp.105-111
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• 1995

The thermal decomposition of the paper sludge with poly (acrylonitrile-butadiene-styrene) was using a thermal analysis techniques in the stream of nitrogen gas of 30ml/min at various heating rates from 4 to $20^{\circ}C/min$. The mathmatical, derivative and integral method were used to obtain values of activation energy of decomposition reaction. 1. The values of activation energy evaluated by derivative and Intergral method were consistent with each other very well. 2. The maximum value of heat of decomposition evaluated by DSC method was 10.120cal/g at weight ratio of paper sludge/ABS=20/80. 3. The thermogravimetric trace curve agreed with the theoretical equation.

• Elastomers and Composites
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• v.31 no.2
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• pp.122-129
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• 1996

The Thermal decomposition of the ${\alpha}-Cellulose$ and NaCl was studied using a thermal analysis technique in the steam of nitrogen gas with 30ml/min at various heating ranges from 4 to $20^{\circ}C/min$. The Derivative and Integral method used to be obtained values of activation energy of decomposition reaction. 1. The values of activation energy evaluated by Derivative and Intergral method were consistent with each other very well. 2. The maximum value of heat of decomposition evalated by DSC method was ${\alpha}-Cellulose/NaCl= 90/10$. 3. The thermogravimetric trace curve agreed with the theoretical equation.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.8
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• pp.1447-1453
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• 2008

In this paper, we proposed to improve performance of the design of a cascade controller with the smith-predictor structure. The parameters of controller in the inner loop are determined to minimize the integral of time multiplied by the absolute value of error (ITAE) value of performance Index. The controller of outer loop and parameters of Smith-Predictor can be obtain using reduction model. The model reduction is considered that it is the transient response and the steady-state response through the use of nyquist curve. Simulation examples are given to show the better performance of the proposed method than conventional methods.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.4
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• pp.2752-2759
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• 1996

This paper presents crack growth analysis approach on the basis of neural networks, a branch of cognitive science to high temperature low cycle fatigue that shows strong nonlinearity in material behavior. As the number of data patterns on crack growth increase, pattern classification occurs well and two point representation scheme with gradient of crack growth curve simulates crack growth rate better than one point representation scheme. Optimal number of learning data exists and excessive number of learning data increases estimated mean error with remarkable learning time J-da/dt relation predicted by neural networks shows that test condition with unlearned data is simulated well within estimated mean error(5%).