• Proceedings of the Korean Society of Coastal and Ocean Engineers Conference
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• 1997.10a
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• pp.53-57
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• 1997

해양파는 해양구조물에 작용하는 주된 외력이고, 쇄파와 물질의 확산등 해양의 역학적 현상을 유발하며, 표사와 누유의 이동등 물질유동의 원인이 된다. 이러한 이유 때문에 정확한 해양파의 역학적 특성 및 재현기법에 대한 연구가 활발히 이루어져 왔다. Longet-Hggins(1975)와 Barber(1963)가 파의 방향분산성을 나타내는 방향스텍트럼 해석법을 제안한 이래 Mtsuyasu(1970)는 실해역 측정을 통해 Mitsuyasu형 방향분포함수 및 주파수 스펙트럼을 얻는 등 많은 심해역 파랑의 해석기법에 대한 연구가 꾸준히 진행되고 있다. (중략)

• Journal of Ocean Engineering and Technology
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• v.3 no.2
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• pp.17-25
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• 1989

해양에서 바람에 의해 생성된 파도를 예측하는 모델을 제시하고 이 모델의 성질을 무한 해면에서 나타내 보이고 마지막으로 파의 이송과 깊이의 영향에 관한 결과를 유한폭의 해상에서 계산해서 비교 가능한 자료와 비교해 보았다.

• Journal of Ocean Engineering and Technology
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• v.2 no.1
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• pp.36-45
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• 1988

해양에서 바람에 의해 생성된 파도를 예측하는 모델을 제시하고 이 모델에 대한 개략적인 설명과 아울러 분류에 의한 기존 모델들을 소개하고 마지막으로 이 모델을 유한폭의 해양에 대하여 적용한 결과를 기존의 다른 모델들과 비교하였다.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2004.05b
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• pp.500-504
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• 2004

This research is about the result of leakage current waveform about the situation of surface leakage current and environmental changes(Salt fog, clean fog and rain) by EPDM polymer insulators' amount of salt. The researcher presents the result of changing about fundamental harmonic, 3rd harmonic and 5th harmonic from starting point of supplying power to flashover. In this study, researched environmental affects (clean fog, salt fog and .am) about surface aging of polymer insulators and used frequency spectrum of leakage current waveform to develop the diagnostic technique of surface aging. When amount of salt contents changed, surface aging stage and the degree of aging (distortion factor) about 3rd and 5th harmonir waveform on low frequency harmonic wave. The distortion factor which is harmonic percentage about basic harmonic is important pointer to evaluate the surface condition of polymer insulators.

• The Journal of the Korea Contents Association
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• v.13 no.1
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• pp.48-54
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• 2013

With the development of IT convergence technology and the construction of infrastructure for water leakage detection, the detection technology of damaged pileline's location and size is being spotlighted. The exhaustion of water resource due to the leakage of water supply facilities renders it urgent to detect water leakage effectively. In this paper, we proposed the water leakage detection monitoring simulation using the power spectrum analysis. We measured the reflected wave signal by the proposed water leakage detection monitoring simulation. The rate variability is calculated form the acquired reflected wave signal. And the power spectrum analysis using the Fast Fourier Transform is evaluated the correlation between the water leakage's size and the reflected wave. Ultimately, this paper suggests empirical simulation to verify the adequacy and the validity. Accordingly, the satisfaction and the quality of services will be improved the efficient management by supporting the real-time water leakage detection.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.34 no.6
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• pp.705-712
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• 2001

It is of great importance to represent the directional ocean waves in a laboratory basin for hydraulic model tests. The directional ocean waves can be expressed as a linear superposition of a large number of component waves with different frequencies and propagating directions. The aim of the study is to check the wave generating characteristics by serpent-type wave generating system in PKNU (Pukyong National University) which is composed of 10 piston-type wave generators. In the experiment, spatial variation of irregular wave heights and propagating angles are measured in the multi-directional wave maker basin. Target wave directional spectrum is reproduced in the area of multi-directional wave maker basin. The directional spreading of the generated waves varied spacially in the basin. They differed from target spectrum as the measurement point becomes far from the center line normal to the generator face, The effective generation area where that target can be reproduced is limited to the triangular area attached the generator face. According to the results, it is emphasized that the effective experiment area in the basin considered wave generator characteristics should be determined in consideration of experimental conditions including structural shapes, water depth, wave directionality etc.

• KIPS Transactions on Software and Data Engineering
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• v.3 no.10
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• pp.451-456
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• 2014

The correlations between electroencephalographic (EEG) spectral power and emotional responses during affective sound clip listening are important parameters. Hemispheric asymmetry in prefrontal activation have been proposed in two decades ago, as measured by power value, is related to reactivity to affectively pleasure audio stimuli. In this study, we designed an emotional audio stimulus experiment in order to verify frontal EEG asymmetry by analyzing Event-related Spectral Perturbation (ERSP) results. Thirty healthy college male students volunteered the stimulus experiment with the standard IADS(International Affective Digital Sounds) clips. These affective sound clips are classified in three emotion states, high pleasure-high arousal (happy), middle pleasure-low arousal (neutral) and low pleasure-high arousal (fear). The analysis of the data was performed in both theta (4-8Hz) and alpha (8-13Hz) bands. ERSP maps in the alpha band revealed that there are the stronger power responses of high pleasure (happy) in the right frontal lobe, while the stronger power responses of middle-low pleasure (neutral and fear) in the left frontal lobe. Moreover, ERSP maps in the theta band revealed that there are the stronger power responses of high arousal (fear and happy) in the left pre-frontal lobe, while the stronger responses of low arousal (neutral) in the right pre-frontal lobe. However, the high pleasure emotions (happy) can elicit greater relative right EEG activity, while the low and middle pleasure emotions (fear and neutral) can elicit the greater relative left EEG activity. Additionally, the most differences of theta band have been found out in the medial frontal lobe, which is proved as the frontal midline theta. And there are the strongest responses of happy sounds in the alpha band around the whole frontal regions. These results are well suited for emotion recognition, and provide the evidences that theta and alpha powers may have the more important role in the emotion processing than previously believed.

• The Journal of the Korea institute of electronic communication sciences
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• v.8 no.6
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• pp.949-954
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• 2013

We measured and analyzed the brain waves to observe the characteristics of human drowsiness. The basic method is to analyze the EEG(Electroencephalography) signals from subjects according to the frequency bands. It has been reported that alpha waves are related to a wakefulness state, an eye closure state and a state that begins to sleep. In this study, therefore, we restricted the frequency band for analyzing to between 8 and 13Hz called brain's alpha waves. We observed which components had a stronger influence on human drowsiness among the restricted frequency band and represented the experimental results to analyze using the power spectrum method.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2005.10a
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• pp.147-152
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• 2005

선형파 이론에 의한 파랑스펙트럼 분포에 의해서는 30m 크기의 파랑은 현실적으로 거의 발생 불가능하다고 인식되어 왔다. 그러나 최근의 위성 영상을 이용한 조사에 의해 3주간의 기간 통안 25m 이상의 거대파가 10개 이상 관측됨에 따라 실해역에서 빈번히 마주칠 수 있는 현상임이 입증되었으며 이에 따라 지금까지 이유 불명으로 치부되어 왔던 많은 해양 재난이 거대파에 의해 발생했던 것으로 추정되고 있다. 거대파의 발생원인은 파군 형성과 관련한 파고분포 특성의 변화, 전파하는 파군의 비선형 공명간섭 통이 제기되고 있으나, 그 출현의 복잡성과 자료의 부족 등으로 아직 명확하게 해명되지 못하고 있다. 본 연구에서는 실해역에서 발생하는 거대파의 특성 및 선형 및 비선형이론에 근거한 거대파 발생 기구를 고찰하고 비선형 파랑전파를 모사할 수 있는 수치모형을 개발하였다.

• Journal of the Korean Society for Nondestructive Testing
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• v.19 no.2
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• pp.85-92
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• 1999

The fact that material degradation can be evaluated by measuring nonlinear acoustic effect has been proposed by previous studies. The most conventional method to measure nonlinear acoustic effect is to measure the absolute magnitude of fundamental and $2^{nd}$ order harmonic frequency component in the propagated ultrasonic wave. For this aim, power spectral analysis technique has been used widely. However, the power spectral analysis has fatal disadvantage that the gaussian additive noise superimposed in the wave signal remains in the power spectrum domain. Moreover, the magnitude of $2^{nd}$ order harmonic frequency component generated by nonlinear effect is so small that it may be suppressed by the noise remained in the power spectrum. In order to overcome this problem, this paper proposes an alternative method using bispectrum analysis, which can reduce the effect of addictive gaussian noise and. the nonlinear parameter can be obtained more stably. Simulations showed that the proposed method can obtain the value of nonlinear parameter near to the true value in the case of low SNR signal. Also, in order to confirm the usefulness of our method in actual case, we compared the nonlinear parameter obtained by using both of power spectral and bispectral analysis for several specimen intentionally degraded by fatigue load.