• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2003.03a
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• pp.3-11
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• 2003

We analysed phases recorded by the M$_{L}$ 3.6 Cheolwon, Korea, earthquake occurred on the 10th of December, 2002 and computed source parameters such as hypocenter, origin time, earthquake magnitude and focal solutions. We used PmP and SmS phases to increase the accuracy in determinations of the hypocenter and origin time in addition to the phases such as Pg, Pn, Sg and Sn which are generally used in routine processes. The epicenter, depth, and origin time of the Cheolwon earthquake determined based on data of 11 stations within 200 km from the epicenter are 38.8108$^{\circ}$N, N, 127.2214'E, 11.955 km, and on 7:42:51.436. The earthquake magnitude obtained from all the stations is 3.6 M$_{L}$. The fault plane solution calculated based on data from 19 stations indicates slip process of a normal fault including strike-slip motion. The direction of compressional stress field has a large vertical component and a ESE-WNW direction of horizontal component, which is different from the mainly horizontal direction of main compressional stress field in the Korean Peninsula (ENE-WSW) obtained by previous studies.ies.s.

• Proceedings of the KIEE Conference
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• 1992.07b
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• pp.1077-1080
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• 1992

In this paper suggested methods for current control in active filter are using the triangular carriers which were composed of independently generated threefold carriers and controllable current source which compensates the harmonics generated independently from the types of the load with instantaneous amplitude adjusting from the maximum magnitude of the compensating currents. And the 2-nd order high pass passive filter connected to the source finally supplies pure sinusoidal waves by suppressing the residual harmonics which cannot removed by the active filter. As the typical load which generates the harmonics, a rectifier was set and the system was also designed by simulations and implementations.

• Journal of Korea Multimedia Society
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• v.8 no.6
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• pp.753-760
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• 2005

This paper introduces a variable step-size adaptive algorithm for blind source separation. From the frequency characteristics of mixed input signals, we need to adjust the convergence speed regularly in each frequency bin. This algorithm varies a step-size according to the magnitude of input at each frequency bin. This guarantee of the regular convergence in each frequency bin would become more efficient in separation performances than conventional fixed step-size FDICA. Computer simulation results show the improvement of about 5 dB in signal to interference ratio (SIR) and the better separation quality.

• Proceedings of the KIPE Conference
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• 2008.06a
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• pp.449-451
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• 2008

This paper studies the instability between homopolar generator and constant power load with negative impedance characteristics, provides the design method of homopolar generator system which overcomes the instability. In case of magnitude and phase of impedance of source and load mismatch, control instability of source can occur. For the safety of phase of load impedance, the gain of P, I controller with sufficient phase margin is applied through analysis on the simulation model of generator system, and the gain limit of load impedance is ensured by limitation of the gain margin of generator system. The stability of power system can be increased by considering and analyzing the impedance of source and load.

• Journal of Electrical Engineering and Technology
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• v.6 no.3
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• pp.334-341
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• 2011

This paper presents accurate solutions for nonlinear transcendental equations of the selective harmonic elimination technique used in three-phase PWM inverters feeding the induction motor by particle swarm optimization (PSO). With the proposed approach, the required switching angles are computed efficiently to eliminate low order harmonics up to the $23^{rd}$ from the inverter voltage waveform, whereas the magnitude of the fundamental component is controlled to the desired value. A set of solutions and the evaluation of the proposed method are presented. The obtained results prove that the algorithm converges to a precise solution after several iterations. The salient contribution of the paper is the application of the particle swarm algorithm to attenuate successfully any undesired loworder harmonics from the inverter output voltage. The current paper demonstrates that the PSO is a promising approach to control the operation of a three-phase voltage source inverter with a selective harmonic elimination strategy to be applied in induction motor drives.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2524-2529
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• 2008

The thermal system like a combustion chamber is believed to experience a significant instability problem with vibration in case that the thermal energy or the acoustic energy are transformed into a different form through a relevant path. This study deals with a numerically- predicted, Thermoacoustic instability in a Rijke tube by using a non-linear model for a heat source. The heating part where the energy transformation occurs actively is modeled after simulating two-dimensional cylinder case with constant surface temperature, and a nonlinear model that accounts for the transfer function of magnitude- and phase-characteristics is properly implemented so as to be dependent on the pulsation strength in the tube. The heat source model is observed to result in equivalent Thermoacoustic instabilities in the Rijke tube except low flow-rate cases in which the natural convection is dominant.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.18 no.2
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• pp.61-68
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• 2022

Accurate evaluation of residual stress is important for stress corrosion cracking assessment. In this paper, electron beam welding experiment is simulated via finite element analysis and the sensitivity of the parameters related to the combined heat source model is investigated. Predicted residual stresses arecompared with measured residual stresses. It is found that the welding efficiency affects the size of the tensile residual stress area and the magnitude of maximum longitudinal residual stress. It is also found that the parameter related to the ratio of energy distributed to the two-dimensional heat source has little effect on the size of tthe tensile residual stress area, but affects the size of the longitudinal residual stress in the center of the weld.

• Journal of the Earthquake Engineering Society of Korea
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• v.28 no.3
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• pp.159-164
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• 2024

Recent earthquakes in Korea, like Gyeongju and Pohang, have highlighted the need for accurate seismic hazard assessment. The lack of substantial ground motion data necessitates stochastic simulation methods, traditionally used with a simplistic point-source assumption. However, as earthquake magnitude increases, the influence of finite faults grows, demanding the adoption of finite faults in simulations for accurate ground motion estimates. We analyzed variations in simulated ground motions with and without the finite fault method for earthquakes with magnitude (Mw) ranging from 5.0 to 7.0, comparing pseudo-spectral acceleration. We also studied how slip distribution and hypocenter location affect simulations for a virtual earthquake that mimics the Gyeongju earthquake with Mw 5.4. Our findings reveal that finite fault effects become significant at magnitudes above Mw 5.8, particularly at high frequencies. Notably, near the hypocenter, the virtual earthquake's ground motion significantly changes using a finite fault model, especially with heterogeneous slip distribution. Therefore, applying finite fault models is crucial for simulating ground motions of large earthquakes (Mw ≥ 5.8 magnitude). Moreover, for accurate simulations of actual earthquakes with complex rupture processes having strong localized slips, incorporating finite faults is essential even for more minor earthquakes.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.58 no.10
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• pp.1916-1922
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• 2009

Introducing distributed generators(DGs) to utility distribution system can cause malfunction of relay on the grid when ground faults or severe load unbalances are occurred on the system. Because DGs interconnected to the grid can contribute fault currents and make bidirectional power flows on the system, fault currents from DGs can cause an interference of relay operation. A directional over current relay(DOCR) can determine the direction of power flow whether a fault occurs at the source side or load side through detecting the phases of voltage and current simultaneously. However, it is identified in this paper that the contributed fault current(Ifdg) from the ground source when was occurred to contribute single-line-to-ground(SLG) fault current, has various phases according to the distances from the ground source. It means that the directionality of Ifdg may not be determined by simply detecting the phases of voltage and current in some fault conditions. The magnitude of Ifdg can be estimated approximately as high as 3 times of a phase current and its maximum is up to 2,000 A depending on the capacity of generation facilities. In order to prevent malfunction of relay and damage of DG facilities from the contribution of ground fault currents, Ifdg should be limited within a proper range. Installation of neutral ground reactor (NGR) at a primary neutral of interconnection transformer was suggested in the paper. Capacity of the proposed NGR can be adjusted easily by controlling taps of the NGR. An algorithm for unidirectional relay was also proposed to prevent the malfunction of relay due to the fault current, Ifdg. By the algorithm, it is possible to determine the directionality of fault from measuring only the magnitude of fault current. It also implies that the directionality of fault can be detected by unidirectional relay without replacement of relay with the bidirectional relay.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.19 no.10
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• pp.942-946
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• 2006

We simulated insulation defects of stator winding wire on high voltage generator by 5 types. 4 types have one discharge source and other one has multi discharge source by simulation. For accurate decision, measurements used to PRPD pattern to occurred partial discharge source of various types. In this research, when PRPD pattern carried out or analyzed pattern recognition of discharge source, it used to powerful tools. In this result, PRPD Pattern defined to have single discharge source of 4 types by insulation defect. When insulation defect simulated, all the defected winding have not the same result. Errors for a little different can make mistakes from a subtle distinction. The difference between internal and void discharge have magnitude of pulse amplitude of inner discharge bigger than void discharge and have a shape of bisymmetry. But void discharge has a shape of bisymmetry against maximum value on polarity respectively. In cases of slot and surface discharge, we confirmed to show similar results those other researchers. In case of multi-discharge, as a result of we could classify not perfect match with occurred patterns in single discharge eachother. In the future, we will have to recognize and classify with results of multi-discharge.