• Journal of the Korean Geophysical Society
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• v.9 no.3
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• pp.231-240
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• 2006

The crustal structure of the Korean Peninsula was investigated by analyzing phase velocity dispersion data of Rayleigh waves. Earthquakes recorded by three component broad-band velocity seismographs during 1999-2004 in South Korea were used in this study. The fundamental mode Rayleigh waves were extracted from vertical components of seismograms by multiple filter technique and phase match filter method. Phase velocity dispersion curves of the fundamental mode signal pairs for 14 surface wave propagation paths on the great circle in the range 10 to 80 sec were computed by two-station method. Treating the shear velocity of each layer as an independent parameter, phase velocity data of Rayleigh wave were inverted. All the result models can be explained by a rather homogeneous crust of shear-wave velocity increasing from 2.8 to 3.25 km/sec from top to about 33 km depth without any distinctive crustal discontinuities and an uppermost mantle of shear-wave velocity between 4.55 and 4.67 km/sec. Our results turn out to agree well with recent study of Cho et al. (2006 b) based on the analysis of seismic background noises to recover short-period (0.5-20 sec) Rayleigh- and Love-wave group velocity dispersion characteristics.

• 한국지구물리탐사학회:학술대회논문집
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• 2005.05a
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• pp.29-36
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• 2005

The crustal structure of Korean Peninsula is investigated by analyzing phase velocity dispersion data of Rayleigh wave. Earthquakes recorded by three component seismographs during 1999 - 2004 in South Korea are used in this study. The fundamental mode signals of Rayleigh waves are obtained from vertical components of seismograms by multiple filter technique method and phase match filter method. Velocity dispersion curves of surface waves for 14 propagation paths on the great circle are computed from the fundamental mode signals on the great circle path by two-station method. Treating the shear velocity of each layer as an independent parameter, phase velocities of Rayleigh wave are inverted. The result models are regarded as average structure for surface wave propagation paths respectively. All the results can be explained by an earth model of the Korean Peninsula comprising crust of shear-wave velocity increasing from 2.8 to 3.25 km/sec from top to 33 km depth and uppermost mantle of shear-wave velocity between 4.55 and 4.67 km/sec.

• The Transactions of the Korean Institute of Power Electronics
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• v.23 no.2
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• pp.101-105
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• 2018

Shortage of electric power occurs frequently along with increased electric power demand. ESS is a precaution to solve this issue. Household ESS has a capacity of approximately 3 kW/7 kWh. Household ESS batteries are typically designed with nominal voltages between 40 and 50 V. To connect household ESS with a 220 V AC system, low battery voltages in power conditioning system (PCS) should be boosted. To boost low battery voltage and match it with AC grid voltage, the use of a transformer for a commercial frequency can be considered. To attenuate switching harmonics of the household single-phase ESS-PCS, LC filter can be installed in two positions: on the primary side or on the secondary side of a transformer. A method has been used generally in single-phase inverters for the ESS-PCS. In another method, however, the output efficiency of the ESS-PCS may be decreased. Parasitic components of the transformer can affect voltage losses, when the square wave with the switching frequency in the ESS-PCS is passed through the transformer windings. In this work, the characteristics of the transformer according to the position of an LC filter are investigated for household single-phase ESS-PCS.

• Geophysics and Geophysical Exploration
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• v.15 no.1
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• pp.23-32
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• 2012

The comparison between time-lapse seismic datasets is the most popular method in the reservoir monitoring. The method of extracting the changes only due to the change in the reservoir is the essential technique in the comparison of time-lapse seismic datasets. In the paper, the conventional cross-equalization approaches and an enhanced optimized approach have been tested and compared each other. As conventional approaches, the bandwidth equalization and phase rotation methods have been tested in frequency, time and mixed domains, respectively and their results were compared each other. In order to overcome the limit of the conventional approaches, which loses high frequency components, a new constrained optimum filtering method was proposed and experimented. The new constrained filtering method has shown the improvement in broadening the bandwidth of the components of reservoir changes by acquiring optimized match filter.

• The Transactions of the Korean Institute of Power Electronics
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• v.25 no.4
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• pp.329-332
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• 2020

A back-electromotive force (back-EMF) estimator for a permanent magnet synchronous motor (PMSM) uses the three-phase voltage references of a current controller to estimate rotor position. However, owing to voltage drops caused by the nonlinear characteristics of switches and passive components, the actual voltage in the motor and the three-phase voltage reference may not match. This study proposes a sensorless control method using a sine-wave output filter applied between the motor drive system and PMSM. The precise voltage in the motor can be measured with the sine-wave output filter and applied to the input of the estimator. Moreover, given that the voltage in the motor can be measured precisely at extremely low speeds, the stable operation range of the back-EMF estimator can be secured. Experimental results show that the proposed sensorless control method has stable operation at extremely low speeds compared with conventional sensorless control.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.8
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• pp.839-844
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• 2003

For mass and volume reduction, input demultiplxer and output multiplexer of satellite transponder widely adopt dual-mode waveguide filters fer channel filters. Generally, channel filters of the input demultiplexer are doubly terminated and channel filters of manifold output multiplexer should be singly terminated fur correct operation. This paper gives a tuning method using short-ended dummy cavity for dual-mode cavity filters. Tuning is based on the match of the computed and measured phase response of reflection coefficient. This proposed method is applied to 4-pole dual-mode doubly terminated elliptic response filter and 6-pole dual-mode singly terminated elliptic response filter for demonstration of this new tuning method. It is shown that this method shows good agreement between the experimental and computed results.

• Journal of ILASS-Korea
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• v.15 no.2
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• pp.53-60
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• 2010

This study presents development of digital particle holographic system and its application to spray field to measure three-dimensional velocities and sizes of spray droplets. A double exposure hologram recording system with synchronization system for time control was established and digital holograms can be recorded in a short time interval. To process recorded holograms, the correlation coefficient method was used for focal plane determination of particles. To remove noises and improve the quality of holograms and reconstructed images, the Wiener filter was adopted. The two-threshold and image segmentation methods were used in binary image transformation. For particle pairing, the match probability method was adopted. The developed system was applied to spray field and three-dimensional velocities and sizes of spray droplets were measured. The measurement results of digital holographic system were compared with those made by laser instruments, PDPA(Phase Doppler Particle Analyzer), which proved the feasibility of in-line digital particle holographic system as a good measurement tool for spray droplets.

• Journal of the Earthquake Engineering Society of Korea
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• v.3 no.4
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• pp.47-60
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• 1999

The stability and efficiency of structural control systems depend on the accuracy of mathematical model of the system to be controlled. In this study, state equation models of a small scale test structure and an AMD(active mass damper) are obtained separately using OKID(observer/Kalman filter identification) which is a time domain system identification method. The test structure with each floor acceleration as outputs is identified for two inputs - the ground acceleration and the acceleration of the moving mass of AMD relative to the installation floor - individually and the two identified state equation models are integrated into one by model reduction method. The AMD is identified with the motor control signal as an input and the relative acceleration of the moving mass as an output, and it is shown that the identified model has large damping ratio and phase shift. The transfer functions and the time histories reconstructed from the identified models of the test model and the AMD match well with those measured from the experiment.