• The Transactions of the Korean Institute of Electrical Engineers B
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• v.52 no.2
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• pp.68-79
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• 2003

We estimated harmonics on power system of AC railway based on quantitatively measured harmonics and investigated the need of facilities for harmonics reduction. In order to analysis harmonics which inflow into power system due to increase in collector voltages and harmonic currents generated from the train when the railway is in operation, the railway system Is sectioned into power supply, railway line, AT, sectioning Post and subsectioning post. For analysis of extension of currents resulting from the railway loads, PWM converter, VVVF inverter and the feeder system are modeled based on the dynamic node technique(DNT). In order to test the usefulness of the DNT for analysis of harmonic effects, the measured harmonic currents and harmonic magnification ratios at the S/K substation are compared with simulation results using DNT modelling, which include the results for two cases with and without filters for suppression of harmonic currents. When 8 cars(4M4T) are in operation, the total sum of harmonic currents resulting from the train at M and T phases, which inflow into the substation along with the railway line, is calculated. Using the harmonics analysis program for railway feeder system with these data, the total harmonic distortion factor(710) at the outgoing point of KEPCO substation is computed. The calculation shows that when the maximum THD at the receiving point of H/K substation was 0.0443% which is much lower than 1.5% which is the allowable value of KEPCO at 154kV as well as IEEE-519 above 132kV This result indicates that any measure for harmonics reduction in Incheon International Airport Railway is not needed.

• Journal of Internet Computing and Services
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• v.11 no.2
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• pp.1-15
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• 2010

The damage of safety accidents at home can be minimized by preventing accidents in advance as well as by coping with the accidents promptly through the help of safety management system. In this paper, we identify several services to prevent and cope with the accidents that may occur at home by leveraging sensors and wireless network technology available at home network environments. In order to provide these services, we propose a context-aware system for safety management at home. The proposed system awares the dangerous situations through the information collected by the sensors in home network environment. The proposed system tries to not only prevent the accidents but also to cope with the situations using the information of rescue targets and the location where the accident occurs. We evaluate the appropriateness of sensors by implementing the proposed environments. Through OPNET simulation experiments, we also measure the amount of network traffic in order to confirm that the bandwidth of IEEE 802.15.4 is enough for the proposed system. Finally, we determine more appropriate wireless data transmission mechanism with respect to the end-to-end delay and battery consumption for the proposed system.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.2
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• pp.276-285
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• 2008

These days the automobile industry, which has rapidly progressed, has been an indispensable part in social and economic activities as well as its research and development have been activated in response to various needs of consumers and markets. The second and third generation control system, getting count on safety and convenience differently than early circuits, cause the hypertrophy of wire harness. The J/Box(Junction Box), which distributes power and wires, was developed to solve the problem. As vehicles have been better in quantity and intelligence, however, environment-friendly electric apparatus system has continuously increased and ITS(Intelligent Transport System) has been introduced in earnest. In result, wires got complicated and multilateral and also there has been a stronger probability that vehicles are out of order due to various problems including mechanical failure. In this study, ISJB(Intelligent Smart Junction Box) was introduced to solve the problem. The diagnosis system was applied to prevent the overload and short of ISJE. Also, the state of vehicles displayed so that drivers monitor it in motion. Likewise error data are saved in the memory so that such data can be analyzed retrospectively. The busbar was adopted in to the main power terminal and the part of power pattern was coverd by lead. Because ISJB is more sensitive to heat in comparison to the busbar type J/Box. With regard the circuits related with safe, alternative circuits were set up in order that electronic devices may be normally operated even when an error arises. ISJB is expected to improve the safety and quality of vehicles.

• Nuclear Engineering and Technology
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• v.56 no.5
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• pp.1712-1724
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• 2024

Spiral tubes are used in a wide range of applications and it is significant to understand the vibration introduced by two-phase flow in spiral tubes. In this paper, the numerical method is used to study the vibration induced by the gas-liquid two-phase flow in a spiral tube with different flow regimes. The pressure fluctuation characteristics at the pipe wall and the solid vibration response characteristics are obtained. The results show that the motion of small bubbles in bubbly flow leads to small pressure fluctuations with low-frequency broadband (0-50 Hz). The motion of the gas plug in the plug flow causes small amplitude periodic pressure fluctuation with a shortened low-frequency broadband (0-15 Hz) compared to the bubbly flow. The motion of the gas slug in the slug flow causes large periodic fluctuations in pressure with a significant dominant frequency (6-7 Hz). The wavy flow is very stable and has a distinct main frequency (1-2 Hz). The vibration regime in the bubbly flow and wave flow are close to the first-order mode, and the vertical vibrating component is dominant. The plug flow and slug flow excite higher-order vibration modes, and the lateral vibration component plays more important part in the vibration response.

• Transactions on Control, Automation and Systems Engineering
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• v.2 no.1
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• pp.47-55
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• 2000

In this paper, a vision-based roadway detection algorithm for an automated vehicle control system, based on roadway sign information on roads, is proposed. First, in order to detect roadway signs, the color scene image is enhanced under hue-invariance. Fuzzy logic is employed to simplify the enhanced color image into a binary image and the binary image is morphologically filtered. Then, an effective algorithm of locating signs based on binary rank order transform (BROT) is utilized to extract signs from the image. This algorithm performs better than those previously presented. Finally, the inner shapes of roadway signs with curving roadway direction information are recognized by neural networks. Experimental results show that the new detection algorithm is simple and robust, and performs well on real sign detection. The results also show that the neural networks used can exactly recognize the inner shapes of signs even for very noisy shapes.

• Journal of Korean Society for Quality Management
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• v.18 no.2
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• pp.9-17
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• 1990

This paper deals with a FOQ( ; fixed-order quantity) model for spare-part inventory control. In a spare-part inventory problem, stock depletion arises not from external market demand but from internal demand resulting from failures of parts in use. The problem differs from the classical inventory problem in that the demand for a failed part never arises more during stockout period, since the unit remains inoperative when stockout occurs until the failed part is replaced by new one. In the problem under consideration, n identical units are operating simultaneously and failed one is replaced immediately by new one if on-hand spares remain. In order to replenish spares, an order with quantity Q is placed whenever the number of on-hand spares falls to levels. The average annual cost of operating the spare-part inventory system is derived under the assumption that both lifetime of a part and replenishment lead-time distributions are exponential.

• Bulletin of the Korean Mathematical Society
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• v.55 no.3
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• pp.881-898
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• 2018

This article deals with implementation of a high-order finite difference scheme for numerical solution of the incompressible Navier-Stokes equations on curvilinear grids. The numerical scheme is based on pseudo-compressibility approach. A fifth-order upwind compact scheme is used to approximate the inviscid fluxes while the discretization of metric and viscous terms is accomplished using sixth-order central compact scheme. An implicit Euler method is used for discretization of the pseudo-time derivative to obtain the steady-state solution. The resulting block tridiagonal matrix system is solved by approximate factorization based alternating direction implicit scheme (AF-ADI) which consists of an alternate sweep in each direction for every pseudo-time step. The convergence and efficiency of the method are evaluated by solving some 2D benchmark problems. Finally, computed results are compared with numerical results in the literature and a good agreement is observed.

• Proceedings of the KSPS conference
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• 2005.04a
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• pp.91-94
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• 2005

The performance of speech recognition is degraded by the mismatch between training and test environments. Many methods have been presented to compensate for additive noise and channel effect in the cepstral domain, and Cepstral Mean Subtraction (CMS) is the representative method among them. Recently, high order cepstral moment normalization method has introduced to improve recognition accuracy. In this paper, we apply high order moment normalization method and smoothing filter for real-time processing. In experiments using Aurora2 DB, we obtained error rate reduction of 49.7% with the proposed algorithm in comparison with baseline system.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• v.13 no.2
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• pp.109-121
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• 2009

In this paper, we use He's polynomials for solving higher order integro differential equations (IDES) by converting them to an equivalent system of integral equations. The He's polynomials which are easier to calculate and are compatible to Adomian's polynomials are found by using homotopy perturbation method. The analytical results of the equations have been obtained in terms of convergent series with easily computable components. Several examples are given to verify the reliability and efficiency of the proposed method.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.11C
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• pp.1062-1069
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• 2003

This paper presents a new loop shaping technique for design of robust optimal PID controllers in order to satisfy the performance requirements. PID controller can be designed by selecting the suitable weighting factors Q and R. This technique is developed by pushing all two zeros formed by PID controller closely to a larger pole of the second order plant. As a result, a good loop shaping is achieved in the high frequencies region on the Bode plot. For the robust optimal tuning of PID controller for second order system, a new loop shaping procedure is developed via LQR approach.