• Journal of the Korean Society for Nondestructive Testing
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• v.24 no.4
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• pp.331-340
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• 2004

Deployment of an advanced on-line monitoring of the component integrity offers a prospect of improved performance, enhanced safety, and reduced overall cost for nuclear power plants. Ultrasonic guided waves have been known as one of the promising techniques that could be utilized for on-line monitoring. The present work is aimed at developing a new method for on-line monitoring of the pipes during the operation period of nuclear power plants. For this purpose, the steam generator (S/G) tube was selected as an object of tile experiment. Dispersion corves and the incident angles corresponding to the specific modes were calculated for the S/G tube. The modes of guided waves were identified by the time-frequency diagrams obtained by the short time Fourier transform. It was experimentally confirmed that there was no mode conversion when the ultrasonic guided waves passed over the curved region of the S/G tube. An optimum mode of guided wave for the S/G tube was suggested and verified by the experiment.

• Journal of the Korean Society for Nondestructive Testing
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• v.29 no.2
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• pp.114-121
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• 2009

Ultrasonic guided waves have been widely utilized for long range inspection of structures. Especially, development of array guided waves techniques and its application for long range gas pipe lines(length of from hundreds meters to few km) were getting increased. In this study, focusing algorithm for array guided waves was developed in order to improve long range inspectability and accuracy of the array guided waves techniques for long range inspection of gas pipes, and performance of the developed techniques was verified by experiments using the developed array guided wave system. As a result, S/N ratio of array guided wave signals obtained with the focusing algorithm was increased higher than that of signals without focusing algorithm.

• Journal of the Korean Society of Marine Environment & Safety
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• v.28 no.5
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• pp.700-711
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• 2022

In this study, deepwater design waves were estimated for 16 wave directions and various return periods based on statistical analysis of extreme waves observed for more than 20 years at three stations (Chilbal-do, Geomun-do, Donghae). These values were compared with design waves estimated based on the omni-directional wave data. The Weibull distribution was used as the probability distribution function whose parameters were determined by the least square method. The Kolmogorov-Smirnov test was applied for the goodness of fit test. Notably, the directional design waves were smaller than the omni-directional design wave for every wave direction. The maximum 50-year wave heights for directional sectors were 7.46 m (NNE), 12.05 m (S), and 9,59 m (SSW) at Chilbal-do, Geomun-do and Donghae whereas those for uni-directional wave data were 7.91 m, 13.82 m and 10.38 m, respectively. This implied possible under-estimation of the deepwater design waves for 16 wave directions being currently used in the design of offshore and coastal structures.

• Science of Emotion and Sensibility
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• v.26 no.4
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• pp.125-132
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• 2023

This study investigated the effects of continuous Singing Bowl healing on brainwaves and autonomic nervous system responses. The variations in brainwaves were measured during 45-minute sessions in eight participants, before and after Singing Bowl healing sessions to assess the changes in brainwaves before and after five weeks of Singing Bowl healing treatment. BioBrain BIOS-S8 was used to obtain brainwave measurements. Electrodes were placed on six channels: F3, F4, T3, T4, P3, and P4. A standard limb lead I with electrodes was used for electrocardiogram (ECG) measurements. Using the collected brainwave data, changes in brain waves were observed before and after five weeks of Singing Bowl healing. Beta waves, alpha waves, and sensorimotor rhythm were found to have reduced, while theta waves, delta waves, and the standard deviation of normal-to-normal intervals in heart rate variability had increased. These results indicate that continuous Singing Bowl healing over five weeks can stabilize brainwaves, activate the autonomic nervous system, and increase the relaxation-inducing effects of the parasympathetic nervous system.

• The Bulletin of The Korean Astronomical Society
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• v.25 no.1
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• pp.33-33
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• 2000

• The Journal of the Acoustical Society of Korea
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• v.30 no.7
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• pp.361-367
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• 2011

Propagating waves (flexural, longitudinal and shear waves) travelling with constant amplitudes and evanescent waves decaying exponentially are generated on a cylindrical shell. Evanescent waves are generally generated in the vicinity of an vibration excitation point and near ends of the shell. But the evanescent waves can generates strong axial vibration at the ends of the cylindrical shell. The strong end axial vibration due to those evanescent waves has been observed in an author's previous paper dealing with measurements of the in-plane axial vibration of a finite cylindrical shell. In this paper the strong end axial vibration due to the evanescent waves has been theoretically analyzed. In order to analyze the vibration of the cylindrical shell, wave propagation approach has been implemented. Comparison between theoretical and experimental results for the axial vibration of the shell showed that the strong evanescent wave can be generated due to mode conversion (conversion from flexural wave to evanescent wave) at the ends of cylindrical shell. It also showed that the evanescent wave can generate the strong axial vibration near the ends of the cylindrical shell and that it can have effect even on 1/3 of the total length of the shell.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.53 no.10
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• pp.530-538
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• 2004

A electromagnetic waves are used for sensing in insulation diagnosis at electric machine or equipment. When it a method, waves are transformed into the FFT(Fast Fourier Transform); a kind of the process for data transformation. In a general way, a scientist use frequncy band 30[㎒]～l[㎓] to applied field. If we are measured high frequency band, we will need to a high capacity hardware. Also a antenna has a fault on atmospheric phenomena, outside environment and the like. In this paper We proposed new method for detecting electric equipment faulty state using only electric voltage which is generally measured in the electric and electronic field. It is called the Partition-FFT The analytic method is this first divide measured voltage waves into equal parts, second each deal with give effect to the FFT, finally each results deal with a graphic method and gather graphic. We are compare Partition-FFT with discharge form by tracking tester. As the result it demonstrated that the Partition-FFT is applicable.

• Journal of the Society of Naval Architects of Korea
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• v.37 no.1
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• pp.50-59
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• 2000

This paper presents a brief outline of dynamic stability of a damaged ship at final stage of flooding in rough beam wind and waves. One degree-of-freedom, roll equation is adopted with effects of flooding water and external forces due to wind and waves, but without effect of sloshing. We discuss the dynamic stability of the damaged ship in terms of capsizing probability based on risk analysis, the method of which was firstly proposed by Umeda et al.[6] to high speed craft in intact condition. As a result, we can evaluate the dynamic stability of the damaged ship in probabilistic manner according to sea state, operating condition and damage situation.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2003.10a
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• pp.187-191
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• 2003

The motion and time-mean drift force of a 2-D floating BBDB in waves are studied with and without taking account of fluctuating air pressure in the air chamber. It has been found numerically that the drift for a of the BBDB is in the reverse direction of propagation of the incident waves over specific frequency ranges as found by McCormick through his experiment work. The drift force is calculated by Pinkster's near-field method. Since Maruo's formula method for the drift force is always positive, Maruo's formula is only approximate and should be replaced by the correct near-field method.

• Proceedings of the KIEE Conference
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• 2002.07c
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• pp.1878-1880
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• 2002

In this paper, electromagnetic waves radiated from discharge at three-type electrodes (needle-plane, plane-plane and sphere-plane electrode) using DC power source in air measured and the peculiar patterns of their spectra are reported. The radiated electrodmagnetic waves were measured in bandwidth of VHF($30{\sim}230$[MHz]) using a biconcal antenna and a spectrum analyzer. Frequency spectrum distribution of radiated electromagnetic wave was revealed under 50[MHz] at positive DC, and high electric field was shown at 45[MHz] frequency band. But, it was revealed under 70[MHz] frequency band at negative DC under plane-plane electrodes and sphere-plane electrodes, and high electric field was shown at 55 [MHz] frequency band.