• 한국안전학회지
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• 제7권4호
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• pp.45-53
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• 1992

Sponataneous ignition characteristics for granulated activated carbon were observed by performing experiments at constant ambient temperature and varying the ambient temperature sinusoidally. In case of varying the ambient temperature sinusoidally, the amplitudes of temperature were 5$^{\circ}C$, 1$0^{\circ}C$ and 15$^{\circ}C$ respectively, and the period in each amplitude was varied at an interval of 30minutes from zero to 3hours. As the results of experiments at a constant ambient temperature, the critical spontaneous ignition temperature of the sample decreased as the sample vessel size increased. Apparent activation energy of the sample calculated from the Frank-Kamenetskii's thermal Ignition theory was 38.82［kca1/mo1］ In case of varying the ambient temperature sinusoidally, the critical spontaneous ignition tempera-ture was lower than that at the constant ambient temperature, and the minimum critical spontaneous ignition temperature decreased with the amplitude of heating sinusoidal curve. At the same amplitude, the critical spontaneous ignition temperature decreased until it reached the minimum point and then in-creased as the period increased.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• 제5B권1호
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• pp.50-56
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• 2005

This paper develops a sensorless BLDCM drive for frequently startup. The position information is based on detecting the zero-crossing point of the BEMF that can be directly obtained from the terminal voltage of the floating phase without voltage-dividing and filtering. As a result, this approach makes it possible to detect the rotor position over a wide speed range, especially at a lower speed. A fast startup procedure is also discussed because the induced BEMF signals are not present when motor is at rest. Experimental results shows that the schemes implemented are feasible and the performance achieved are satisfactory.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2005년도 제36회 하계학술대회 논문집 A
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• pp.274-276
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• 2005

Stability is an important constraint in powr system operation. A new methodology that reduces the need for repeated simulation to determine a transiently secure operating point is presented. at cntingency, critical generator is limited generation to prevent rotor accelation until system is secured. when energh margin is zero, generation is degermined Implementation issues and simulation results are discussed in th context of a 10-bus system.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2004년도 하계학술대회 논문집 A
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• pp.245-247
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• 2004

Stability is an important constraint in powr system operation. A new methodolgy that reduces the need for repeated simulation to determine a transiently secure operating point is presented. at cntingency , critical generator is limited generation to prevent rotor accelation until system is secured. when energy margin is zero, generation is degermined Implementation issues and simulation results are discussed in th context of a 23-bus system

• 대한전기학회:학술대회논문집
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• 대한전기학회 1988년도 전기.전자공학 학술대회 논문집
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• pp.33-36
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• 1988

In this paper, the starting point of affricate is detected from the first predictor coefficient of a 12-pole linear predictive coding (LPC) analysis and phonemic segmentation is done through measuring short time energy and zero crossing rate. By this segmentation method, the duration of an aspirate can be mearsured in order to detect an aspirate or not.

• 전력전자학회논문지
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• 제17권1호
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• pp.21-26
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• 2012

In recent years, DC distribution systems are becoming hot issue due to the increase in digital loads and DC generation systems according to the expansion of renewable energy technologies. However, removing the fault current in DC grids is comparably difficult since the current in DC grids has no zero-crossing point like in AC grids. Thus, developing dedicated DC circuit breakers for DC grids is necessary to get safety for people and electrical facilities. This paper proposes magnet arc extinguishing method to develop a 300[$V_{DC}$]/10[A] DC circuit breaker. The performance of the proposed DC circuit breaker was verified by an experimental circuit breaker test system built in this research.

• Journal of Power Electronics
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• 제5권1호
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• pp.67-75
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• 2005

A high efficiency ZVS PWM asymmetrical half bridge converter for a plasma display panel (PDP) sustaining power modules is proposed in this paper. To achieve the ZVS of power switches for the wide load range, a small additional inductor L/sub 1kg/, which also acts as an output filter inductor, is serially inserted into the transformer's primary side. At that point, to solve the problem of ringing in the secondary rectifier caused by L/sub 1kg/, the proposed circuit employs a structure without the output filter inductor, which helps the voltages across rectifier diodes to be clamped at the output voltage. Therefore, no dissipative RC (resistor capacitor) snubber for rectifier diodes is needed and a high efficiency as well as low noise output voltage can be realized. In addition, since it has no large output inductor filter, the asymmetrical half bridge converter features a simpler structure, lower cost, less mass, and lighter weight. In addition, since all energy stored in L/sub 1kg/ is transferred to the output side, the circulating energy problem can be effectively solved. The operational principle, theoretical analysis, and design considerations are presented. To confirm the operation, validity, and features of the proposed circuit, experimental results from a 425W, 385Vdc/170Vdc prototype are presented.

• 한국정밀공학회지
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• 제23권4호
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• pp.75-82
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• 2006

In this paper, we propose an optimal trajectory for biped robots to move up-and-down stairs using a genetic algorithm and a computed-torque control for biped robots to be dynamically stable. First, a Real-Coded Genetic Algorithm (RCGA) which of operators are composed of reproduction, crossover and mutation is used to minimize the total energy. Constraints are divided into equalities and inequalities: Equality constraints consist of a position condition at the start and end of a step period and repeatability conditions related to each joint angle and angular velocity. Inequality constraints include collision avoidance conditions of a swing leg at the face and edge of a stair, knee joint conditions with respect to the avoidance of the kinematic singularity, and the zero moment point condition with respect to the stability into the going direction. In order to approximate a gait, each joint angle trajectory is defined as a 4-th order polynomial of which coefficients are chromosomes. The effectiveness of the proposed optimal trajectory is shown in computer simulations with a 6-dof biped robot that consists of seven links in the sagittal plane. The trajectory is more efficient than that generated by the modified GCIPM. And various trajectories generated by the proposed GA method are analyzed in a viewpoint of the consumption energy: walking on even ground, ascending stairs, and descending stairs.

• 대한기계학회논문집
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• 제12권1호
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• pp.137-151
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• 1988

본 논문에서는 아래 평판은 높은 온도 $T_{h}$로 유지되고, 위의 평판은 낮은 온도 $T_{i}$로 유지되어 있을 때 온도차에 의하여 발생하는 난류 열대류 문제를 난류모델 방정식을 사용하여 수치적으로 해석하고자 한다.다.다.

• 한국지구과학회지
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• 제40권4호
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• pp.353-381
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• 2019

The general world model for homogeneous and isotropic universe has been proposed. For this purpose, we introduce a global and fiducial system of reference (world reference frame) constructed on a (4+1)-dimensional space-time, and assume that the universe is spatially a 3-dimensional hypersurface embedded in the 4-dimensional space. The simultaneity for the entire universe has been specified by the global time coordinate. We define the line element as the separation between two neighboring events on the expanding universe that are distinct in space and time, as viewed in the world reference frame. The information that determines the kinematics of the geometry of the universe such as size and expansion rate has been included in the new metric. The Einstein's field equations with the new metric imply that closed, flat, and open universes are filled with positive, zero, and negative energy, respectively. The curvature of the universe is determined by the sign of mean energy density. We have demonstrated that the flat universe is empty and stationary, equivalent to the Minkowski space-time, and that the universe with positive energy density is always spatially closed and finite. In the closed universe, the proper time of a comoving observer does not elapse uniformly as judged in the world reference frame, in which both cosmic expansion and time-varying light speeds cannot exceed the limiting speed of the special relativity. We have also reconstructed cosmic evolution histories of the closed world models that are consistent with recent astronomical observations, and derived useful formulas such as energy-momentum relation of particles, redshift, total energy in the universe, cosmic distance and time scales, and so forth. The notable feature of the spatially closed universe is that the universe started from a non-singular point in the sense that physical quantities have finite values at the initial time as judged in the world reference frame. It has also been shown that the inflation with positive acceleration at the earliest epoch is improbable.