• Journal of Power Electronics
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• v.2 no.4
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• pp.297-304
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• 2002

The paper identifies a severe form of core saturation instability in a DC/AC interaction system. It then seeks solutions to the problem by HVDC control means. This is achieved by a proper design of the Voltage Dependent Current Order Limiter (VDCOL), the Current Regulate. and Timing Pulse generator. Supplementary control loops have also been introduced to result in a satisfactory performance as compared to that obtained one with the use of uncharacteristic harmonic filter on the AC side. All the options have been demonstrated through recovery performance of the DC link in response to both 1-phase and 3-phase 5 cycle faults on both rectifier and inverter commutating buses.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.38 no.2
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• pp.137-143
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• 1989

System modeling from input-output data is generally carried out in two steps. The first step is to determine the form of the model. In the second step, the parameters of the model in an appropriate form are estimated from input-output data. This paper presents a method, via single term Walsh functions, for simultaneous estimation of the order and the parameters of linear systems from input-output data. The estimation of the model order is based on minimizing an error function, which is defined by Desai and Fairman. Unknown system parameters are recursively estimated by the least square method.

• Electrical & Electronic Materials
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• v.8 no.6
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• pp.774-779
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• 1995

Process optimization experiments based on the Taguchi method were performed in order to set up the optimal process conditions for the contact oxide etching process module which was built in order to be attached to the cluster system of multi-processing purpose. In order to compare with Taguchi method, the contact oxide etching process carried out with different process parameters(CHF$_{3}$/CF$_{4}$ gas flow rate, chamber pressure, RF power and magnetic field intensity). Optimal etching characteristics were evaluated in terms of etch rate, selectivity, uniformity and etched profile. In this paper, as a final analysis of experimental results the optimal etching characteristics were obtained at the process conditions of CHF3/CF4 gas flow rate = 72/8 sccm, chamber pressure = 50 mTorr, RF power = 500 watts, and magnetic field intensity = 90 gauss.

• International Journal of Naval Architecture and Ocean Engineering
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• v.12 no.1
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• pp.711-722
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• 2020

An optimization framework using genetic algorithms has been developed towards an automated parametric optimization of the Octabuoy semi-submersible design. Compared with deep draft production units, the design of the shallow draught Octabuoy semi-submersible provides a floating system with improved motion characteristics, being less susceptible to vortex induced motions in loop currents. The relatively large water plane area results in a decreased natural heave period, which locates the floater in the wave period range with more wave energy. Considering this, the hull design of Octabuoy semi-submersible has been optimized to improve the floater's motion performance. The optimization has been conducted with optimized parameters of the pontoon's rectangular cross section area, the cone shaped section's height and diameter. Through numerical evaluations of both the 1st-order and 2nd-order hydrodynamics, the optimization through genetic algorithms has been proven to provide improved hydrodynamic performance, in terms of heave and pitch motions. This work presents a meaningful framework as a reference in the process of floating system's design.

• Journal of KSNVE
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• v.8 no.6
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• pp.1144-1149
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• 1998

A two degree-of-freedom model of suspended cables is studied for forced resonant response. The method of averaging is used to obtain first-order approximations to the response of the system. A bifurcation analysis of the averaged system is performed in the case of 2-to-1 internal resonance. Nonlinear coupled-mode motions are found to bifurcate from single-mode responses and further bifurcate to limit cycle motions via Hopf bifurcations. The limit cycle solutions undergo period doubling bifurcations to chaos.

• Journal of Technologic Dentistry
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• v.10 no.1
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• pp.25-41
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• 1988

In order to provide the National Dental Health Program with dasic data, and to implove the laborartory managent style, the author studied the operational situations of dental lads through questionaire. The results are as follows, 1. Unlicensured personnel should be replaced by the licensured(from present rate lf 49.2% licensured to more than80%) 2. Minimum wage guarantee system as well as well as oage raise should be established. 3. Monthly balancing accounts system and bepreciation reserve accounts system should be established for the reasonable management. 4. Manufacturing period should be elongated from presnt 2.8 days to 5-7 days for quality betterment of the processes. 5. Medical insurance system should be applied to the dental processes. 6. Manufacturing cost should be increased by 35%. 7. Retirement grants lr retirement annuity system, improvement of occupational environ-ment, and holidays incentives, and participation in medical insurance system should be adopted for the wellfare of the dental technicians. 8. Laboratory managers should operate the lads with pride and valuation. 9. Business Management course should be included in the curriculum of the dental labo-ratory school. 10. Good relationship between Korean Association of Dental Laboratory Technicians and local laboratories shorld be improved.

• Journal of the Korean Society for Precision Engineering
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• v.31 no.7
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• pp.597-604
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• 2014

High efficiency production requires the improved performance of CAD/CAM system. Although the CAD and CAM have been significantly developed over the last three decades, they must still study on the reuse of information during process. In this study, we developed a new integrated CAD/CAM system which can reuse the information generated in previous processes, in order to improve its performance. In addition, the developed system was verified by comparing with working-time, and system reproducibility was also examined with tolerance in the unmanned operation. Experimental results showed 58% reduction in working-time of 2D Auto-CAM module, 80% in case of 3D Auto-Exchange module, and 54.5% in case of Auto-Design module.

• Journal of Electrical Engineering and Technology
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• v.10 no.2
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• pp.487-495
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• 2015

This paper proposes a new robust decentralized power oscillation dampers (POD) design of doubly-fed induction generator (DFIG) wind turbine for damping of low frequency electromechanical oscillations in an interconnected power system. The POD structure is based on the practical $2^{nd}$-order lead/lag compensator with single input. Without exact mathematical model, the inverse output multiplicative perturbation is applied to represent system uncertainties such as system parameters variation, various loading conditions etc. The parameters optimization of decentralized PODs is carried out so that the stabilizing performance and robust stability margin against system uncertainties are guaranteed. The improved firefly algorithm is applied to tune the optimal POD parameters automatically. Simulation study in two-area four-machine interconnected system shows that the proposed robust POD is much superior to the conventional POD in terms of stabilizing effect and robustness.

• International Journal of Aeronautical and Space Sciences
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• v.7 no.2
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• pp.121-127
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• 2006

An analysis procedure for the combined problem of control algorithm and aeroelastic system which is based on the computational fluid dynamics(CFD) technique has been developed. The aerodynamic forces in the transonic region are calculated from the transonic small disturbance(TSD) theory. An linear quadratic regulator(LQR) controller is designed to suppress the transonic flutter. The optimal control gain is estimated by solving the discrete-time Riccati equation. The system identification technique rebuilds the CFD-based aeroelstic system in order to form an adequate system matrix which involved in the discrete-time Riccati equation. Finally the controller, that is constructed on the basis of system identification technique, is used to suppress the flutter phenomenon of the airfoil with attached store. This approach, that is, the CFD-based aeroservoelasticity design, can be utilized for the development of effective flutter controller design in the transonic region.

• International Journal of Fuzzy Logic and Intelligent Systems
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• v.5 no.2
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• pp.157-163
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• 2005

In this paper, we present the multimodal system based on the fusion of two user-friendly biometric modalities: Iris and Face. In order to reach robust identification and verification we are going to combine two different biometric features. we specifically apply 2-D discrete wavelet transform to extract the feature sets of low dimensionality from iris and face. And then to obtain Reduced Joint Feature Vector(RJFV) from these feature sets, Direct Linear Discriminant Analysis (DLDA) is used in our multimodal system. In addition, the Synergetic Neural Network(SNN) is used to obtain matching score of the preprocessed data. This system can operate in two modes: to identify a particular person or to verify a person's claimed identity. Our results for both cases show that the proposed method leads to a reliable person authentication system.