• Proceedings of the KSME Conference
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• 2004.04a
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• pp.2146-2150
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• 2004

To evaluate the variation of spring stiffness in nuclear plant operating condition, load-displacement tests ($P-{\delta}$ test) were performed using two kinds of space grid springs in high temperature and high pressure water. With increasing temperature, stiffness of each spring gradually decreased except $100{\sim}150^{\circ}C$. It is apparently showed that spring with convex shape had a relatively high stability of spring stiffness at high temperature compared with I-shaped spring. It is suggested that the variation of spring stiffness with temperature and spring shape should be considered as an important variable in the design and analysis of the fuel assembly.

• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.431-432
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• 2007

It is necessary for the stabilized operation of the power system even if a severe condition in system operation takes place. There is the need to develop the intelligent Power grid Monitoring System. In this system, the PMU(Phasor Measurement Unit) measures the synchrophasor and transmits it to the PIDS(Power Infrastructure Defense System). The IEEE PC37.118 protocol defines the message format to implement the communication both the PMU and the PIDS. In this paper, We measure and analyze the network traffic from simulated the PMU to simulated the PIDS according to network routing. And, We present the finest network routing in developing the intelligent Power grid Monitoring System.

• Journal of Positioning, Navigation, and Timing
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• v.3 no.1
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• pp.17-23
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• 2014

Satellite Based Augmentation Systems (SBAS) provide ionospheric corrections at geographically five degree-spaced Ionospheric Grid Points (IGPs) and confidence bounds, called Grid Ionospheric Vertical Errors (GIVEs), on the error of those corrections. Since the ionosphere is one of the largest error sources which may threaten the safety of a single frequency Global Navigation Satellite System (GNSS) user, the ionospheric correction and integrity bound algorithm is essential for the development of SBAS. The current single frequency based SBAS, already deployed or being developed, implement the ionospheric correction and error bounding algorithm of the Wide Area Augmentation System (WAAS) developed for use in the United States. However, the ionospheric condition is different for each region and it could greatly degrade the performance of SBAS if its regional characteristics are not properly treated. Therefore, this paper discusses key factors that should be taken into consideration in the development of the ionospheric correction and integrity bound algorithm optimized for the Korean SBAS. The main elements of the conventional GIVE monitor algorithm are firstly reviewed. Then, this paper suggests several areas which should be investigated to improve the availability of the Korean SBAS by decreasing the GIVE value.

• The Transactions of the Korean Institute of Power Electronics
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• v.17 no.6
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• pp.546-552
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• 2012

This paper presents an active anti-islanding detection method using negative sequence voltage injection to the grid through a three-phase photovoltaic inverters. Because islanding operation mode can cause a variety of problems, the islanding detection of grid-connected photovoltaic inverter is the mandatory feature. The islanding mode is detected by measuring the magnitude of negative sequence impedance calculated by the negative sequence voltage and current at the point of common coupling. Simulation and experimental test are performed to verify the effectiveness of the proposed method which can detect the islanding mode in the specified time. The test has been done in accordance with the condition on IEEE Std 929-2000.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.6
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• pp.14-20
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• 2002

The aerodynamic heating at a nose cone is predicted under the KSR-III flight conditions. An equilibrium reacting gas condition is applied. The parametric study is performed with Mach number of 4.9, 10.2 and 15 and for the following nose shapes of hemisphere, cut cylinder and parabola. AUSMPW+ and shock aligned grid technique are used to provide the best aerodynamic solutions. In addition, the composite material of a nose cone is discussed in the viewpoint of a thermal safety.

• The Transactions of the Korean Institute of Power Electronics
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• v.19 no.4
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• pp.312-319
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• 2014

When distributed generation such as a wind power system is connected to the grid, it should meet grid requirements like IEEE Std. 1547, which regulates the anti-islanding method. Since the islanding may cause damage on electrical equipments or safety hazards for utility line worker, a distributed generation should detect it as soon as possible. This paper proposes a hybrid anti-islanding method coupled with the active and passive detection methods. To enhance the harmonic extraction capability for an active harmonic injection method, cascaded second-order band-pass filter and signal processing scheme are employed. Simulation and experiments are carried out under the islanding test condition specified in IEEE Std. 1547. Passive over/under voltage and over/under frequency methods are combined with the active method to improve the detection speed under certain condition. The simulation and experimental results are presented to verify that the proposed hybrid anti-islanding method can effectively detect the islanding.

• Journal of Korea Multimedia Society
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• v.10 no.2
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• pp.187-199
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• 2007

The purpose of painterly rendering is to express real painting work from input image. For expression of real pain ting impression, drawing condition is one of main element. In this paper, we propose new algorithm for using density of edges. Drawing condition of new algorithm uses color difference and density of edges. And for finding next position from current position, we used dynamic grid. We did direction interpolation for coherence direction. Also using various texture brush, we express the feel of a material effective. We show results of images rendered more realistic oil painting effect, and discuss long-term goals for more effective result.

• Journal of radiological science and technology
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• v.21 no.2
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• pp.19-25
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• 1998

By analyzing each part of expsure condition and the status of an entrance dose which is exposed to patients, this study reached the following conclusion. Since there is no standard in setting up an exposure condition, the technology practiced in each facility varies tremendously, and the entrance dose increased especially due to the improper selection of screen and grid and the shortage of a total amount of filtration in leaching the standard filtration amount. Entrance dose was, generally, turned out to be $2{\sim}3$ times as much as that of advanced countries, and there was big difference between facilities ; approximately 52 times inlateral of cervical vertebrae, 35 times in A-P of femur, 33 times in chest A-P, and 11 times in lumber A-P. Therefore, to minimize the entrance dose of a patient with thegreatest amount of image information, acquirement of technological know-how necessary for standardization of exposure condition for each part can be an important research task.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.1
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• pp.122-130
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• 1998

The present work analyzes the pressure drop and heat transfer characteristics of the plate heat exchanger with staggered dimples. The flow is assumed to be constant property, three dimensional and laminar. A thermal boundary condition is uniform wall temperature and it is assumed that the flow is periodically fully developed. Elliptic grid generation is used for proper modelling of the internal tube geometry with dimples. Computations have been carried out for a variety of geometric parameters, Reynolds number, and Prandtl number. The friction factor ratio and the ratio of a module average Nusselt number are presented for the cases considered in this study. It is found that the distance between dimples has a substantial effect on the pressure drop and heat transfer.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.62 no.5
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• pp.632-638
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• 2013

In this study, we described voltage fluctuation characteristics of distribution line during starting and normal operation condition of the small hydro generators. Based on these theories, we scrutinized the starting and operating characteristics of induction generators installed in two small hydro power plants that is connected to the distribution line and researched necessary factors when selecting the generator type. The type of turbines and capacity of generators are different. One is below 1,000kW and the other is above 1,000kW. Two generators are tested during starting, and it acts as motor not generator at the instant that the machine is connected to the grid. After connecting to the grid, the machine rotates above synchronous speed before converting to the generator mode. Therefore the characteristic of the generator during starting is same as it of motor.