• Journal of the Korean earth science society
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• v.27 no.5
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• pp.539-547
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• 2006

The activity of the seismic wave propagation around the cavity is investigated for the exact inversion of the crosshole tomography data, in order to understand the possibility of the existence inside the underground cavity. It is found that the adequate frequency range for the tunnel investigation is about 2 kHz to 5 kHz, and the grid space should be set up to 1/10 of the wavelength. The propagation of the seismic wave near the cavity may go through or detour the cavity according to the seismic velocity inside the cavity. The detouring wave propagates with the seismic velocity of mother rock in spite of the velocity of inside of the cavity. The smaller the velocity difference is between the mother rock and cavity, the more frequent penetration of the seismic wave through the cavity appears.

• Journal of the Korean Geophysical Society
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• v.4 no.2
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• pp.113-120
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• 2001

The discrete wavelet transform(DWT) has potential as a tool for supplying discriminatory attributes with which to distinguish seismic events. The wavelet transform has the great advantage over the Fourier transform in being able to localize changes. In this study, a discrete wavelet transform is applied to seismic traces for identifying seismic events and picking of arrival times for first breaks and S-wave arrivals. The precise determination of arrival times can greatly improve the quality of a number of geophysical studies, such as velocity analysis, refraction seismic survey, seismic tomography, down-hole and cross-hole survey, and sonic logging, etc. provide precise determination of seismic velocities. Tests for picking of P- and S- wave arrival times with the wavelet transform method is conducted with synthetic seismic traces which have or do not have noises. The results show that this picking algorithm can be successfully applied to noisy traces. The first arrival can be precisely determined with the field data, too.

• Journal of the Korean Geophysical Society
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• v.5 no.3
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• pp.233-245
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• 2002

The spectral-analysis-of-surface-waves (SASW) method is a nondestructive testing method based upon generation and detection of elastic stress waves. SASW is widely used as one of the techniques to determine stiffness profile in engineering geophysics. The essential steps involved are construction of an experimental dispersion curve from data collected in situ, and inversion of the dispersion curve to determine the stiffness profile. The main object of this study is to derive an analytical Jacobian for the inversion. If we set the subsurface to N homogeneous layer, it could save 2N times Jacobian calculation compared to numerical jacobian calculation during inversion. To reconstruct a stiffness profile, constrained damped least square method was applied for the inversion. The algorithm was tested for the numerical data and for the real asphalt and tunnel data, which were able to verify the stiffness profile. The stiffness profile reconstructed by the algorithm showed the possibility to appraise the soundness of tunnel with applications SASW.

• 한국지구물리탐사학회:학술대회논문집
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• 2006.06a
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• pp.291-296
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• 2006

The aspect of wave propagation around cavity was investigated for the exact inversion of crosshole tomography data in order to understand the possibility of the existence of underground cavity. We found that the adequate frequency range for the tunnel investigation was about 2kHz to 5kHz, and the grid space was set up to 1/10 length of wavelength. The propagation of the seismic wave near the cavity may go through or detour the cavity according to the seismic velocity of inside of cavity. The detouring wave propagates with the seismic velocity of mother rock in spite of the velocity of inside of cavity. The smaller the velocity difference between the mother rock and cavity, the more frequent penetration of the seismic wave through the cavity was appeared.

• Science of Emotion and Sensibility
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• v.5 no.1
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• pp.9-16
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• 2002

This study was designed to cluster the preferred sensibilities of college students, and to distinguish the most preferred sensibility according to gender and their inter-subject differences. 98 of sensibility adjectives were composed into questionnaire with SD method and the data of 176 students were analyzed in ANOVA, Cluster and Correspondence analysis using SAS package. College students were divided into 10-sensibility clusters: the Casual(no-decoration casual, cool-dynamic casual and elaborate-clean casual), the Romantic Modem, the Simple Natural, the Classic(craft-romantic classic and monotonous classic), the Expressionless, the Gorgeous, and the Traditional Folklore. The adjectives and the sensibility clusters of students were visualized together into 2-D with two axis of static vs. dynamic and light vs. heavy.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.25 no.4
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• pp.244-254
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• 2013

In this study, a method has been developed for estimating the change of nearshore random waves in response to sea-level rise, by extending the method proposed for regular waves by Townend in 1994. The relative changes in wavelength, refraction coefficient, shoaling coefficient, and wave height for random waves are presented as functions of relative change in water depth. The changes in wavelength and refraction coefficient are calculated by using the significant wave period and principal wave direction in the regular-wave formulas. On the other hand, the changes in shoaling coefficient and wave height are calculated by using the formulas proposed for shoaling and transformation of random waves in the nearshore area including surf zone. The results are proposed in the form of both formulas and graphs. In particular, the relative change in wave height is compared with the result for regular waves.

• Plant Journal
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• v.16 no.4
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• pp.40-44
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• 2020

In this study, after supplying a pulse wave to the 2 V Industrial Lead-Acid Battery electrode plate and repeating the charging and discharging, the discharging time per voltage was analyzed. According to the result of experiment, while the lead-acid Battery that a pulse wave is not supplied decreased about 18 % of discharging capacity than the beginning, the lead-acid Battery that a pulse wave is supplied decreased a little amount much lower than 18 %, of discharging capacity and recorded the 0.56 % decrease, at a minimum, from discharging capacity at the 20 kHz frequency. This means that the sulfate on electrode plate is detached and the positive and negative charge transfer is highly activated at the 20 kHz frequency

• Journal of IKEEE
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• v.23 no.2
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• pp.495-501
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• 2019

This paper proposes a variable passive harmonic filter for reduction and improvement of harmonics and power factor of single-phase uninterruptible power supply(UPS) with full bridge rectifier. Recently, UPSs have excellent harmonic and power factor operation characteristics by applying 2-level or more levels of power conversion methods. On the other hand, the single-phase UPS of the full bridge rectifier seriously causes the third, fifth, and seventh harmonics, and the power factor reduction on the grid side. Therefore, we present a variable passive harmonic filter for eliminating (2n+1) order harmonics and improving the power factor generated by the full bridge rectifier operation. In order to evaluate the performance of the proposed variable harmonic filter, the its validity is verified by various simulations and experiments.

• Journal of Ocean Engineering and Technology
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• v.12 no.1
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• pp.99-106
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• 1998

3차원 파수조에서 완전 비선형파를 시뮬레이션하기 위하여 우선 랜킨 소스를 기저로한 적분방정식을 고차경계요소법을 이용하여 이산화하였다. 그리고 방사경계조건은 파흡수 비치와 포텐셜 스트레칭 기법을 이용하여 모델링하였으며, 비선형 자유표면과 경계조건식은 고차 예측 및 보정 기법을 이용하여 시간 적분하였다. 파흡수 비치는 파의 진행방향 특성에 따라 수조내에 다양하게 배치할 수 있으며 비칭서 흡수가 덜된 파는 수조의 길이 방향 끝단에서 포텐셜 스트레칭 기법에 의하여 반사없이 진행하도록 하였다. 수치실험 결과 일-에너지 보존법칙과 모멘텀-임펄스 보존 법칙이 만족됨으로써 본 수치기법의 효용성이 검증되었다.

• The Proceeding of the Korean Institute of Electromagnetic Engineering and Science
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• v.2 no.2
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• pp.39-53
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• 1991

디지탈 기기를 포함한 일반적인 전기전자기기로 부터 발생하는 방해전자파는, 낮은 주파수 대역(MF, HF 대역)에서는 전원성 등의 도선을 따라서 전달(전도성 방해파)되고, 높은 주파수 대역(VHF, UHF 대역)에서는 직접 공간에 방사(방사성 방해파)된다. 이러한 전도성 및 방사성 방해파의 측정은 IEC, CISPR, FCC, VDE 등의 규격이 정하고 있는 규정에 따라서 실시된다. 이들 규격은 방해파 측정법을 규정하고 있을 뿐만 아니라, 재현성이 좋은 측정을 실현시키기 위해 측정용 시설에 대해서도 자세하게 규정하고 있다. 방사성 방해파의 측정에 사용하는 측정시설로서는, 기본적으로 야외시험장(Open Area Test Site, OATS)을 사용하도록 규정하고 있는데, 측정치의 상호연관성을 위해서는 규약에 정해진 적합성이 평 가되고 확인되어 있어야만 한다. 여기서는 방사성 방해파 측정용 시설중에서 가장 기본적이고도 중요한 야외시험장의 적합성 평가 파 라미터 - 두 지점간의 전송손실, 이를 시험장감쇠량 이라함 - 에 대하여 기술하기로 한다.