• Journal of the Korean Society for Nondestructive Testing
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• v.17 no.3
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• pp.156-161
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• 1997

The eddy current probe was designed for the test of fin tubes that have uneven outer and inner surfaces to enhance the efficiency of heat emission. Because of the surface roughness of the fin tube, it needs much care to detect flaws in the tube employing eddy current test(ECT). We made ECT probes with different coil lengths and performed eddy current test using these probes for artificially flawed specimens. By the fast Fourier transform and digital filtering, signals from these probes were processed to characterize frequency spectra. From the analysis of eddy current signals and their frequency spectra, we concluded that, for the effective testing of the tubes with the fins of 1mm pitch, 4mm coil length gave the highest S/N ratio.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.17 no.5
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• pp.43-50
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• 2003

This presents a fault detecting method for a power transformer based upon a neural network. To maintain a normal relay operating conditions, external winding faults of a power transformer and magnetic inrush have been tested under consideration of the EMTP/ATP software and internal faults of power transformer have been tested by the EMTP/BCTRAN software. The neural network has been evaluated by the proposed fault. Input variables of the neural network for the proposed model can be obtained from fundamental currents, restraining and operating currents. This algorithm uses back-propagation and the ratio of a restraining current and an operating current as relay input parameters. The ratio may enhance the fault detection since the restraining currents increase rapidly at external faults. The proposed detecting method has been applied to the practical relay systems for transformer protection. As a result, the proposed detecting method based on the neural network has been shown to have better characteristics.

• The Journal of the Acoustical Society of Korea
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• v.19 no.3
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• pp.26-34
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• 2000

In this paper, we propose a 4kbps speech coder that combines the harmonic vector excitation coding with time-separated transition coding. The harmonic vector excitation coding uses the harmonic excitation coding in the voiced frame and uses the vector excitation coding with the structure of analysis-by-synthesis in the unvoiced frame, respectively. But two mode coding method is not effective for transition frame mixed in voiced and unvoiced signal and a new method beyond using unvoiced/voiced mode coding is needed. Thus, we designed a time-separated transition coding method for transition frame in which a voiced/unvoiced decision algorithm separates unvoiced and voiced duration in a frame, and harmonic-harmonic excitation coding and vector-harmonic excitation coding method is selectively used depending on the previous frame U/V decision. In the decoder, the voiced excitation signals are generated efficiently through the inverse FFT of harmonic magnitudes and the unvoiced excitation signals are made by the inverse vector quantization. The reconstructed speech signal are synthesized by the Overlap/Add method.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2007.04a
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• pp.295-298
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• 2007

The effectiveness of passive control techniques for reducing the pressure oscillation generated in a supersonic cavity flow was investigated numerically and experimentally, respectively. The control device includes a sub-cavity installed in the upstream edge of a rectangular cavity. Time-dependent supersonic cavity flow characteristics with turbulent features were examined by using the three-dimensional, mass-averaged Navier-Stokes computation based on a finite volume scheme and large eddy simulation. The results show that the pressure oscillation near the trailing edge dominates overall time-dependent cavity pressure variations. Such an oscillation can be attenuated more significantly in the presence of the sub-cavity compared with the cavity without sub-cavity, and a larger sub-cavity leads to better control performance.

• Journal of the Earthquake Engineering Society of Korea
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• v.20 no.7_spc
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• pp.527-536
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• 2016

This paper investigates seismic damage potential of recent September 12 M5.8 Gyeongju earthquake from diverse earthquake engineering perspectives using the accelerograms recorded at three stations near the epicenter. In time domain, strong motion durations are evaluated based on the accelerograms and compared with statistical averages of the ground motions with similar magnitude, epicentral distance and soil conditions, while Fourier analysis using FFT is performed to identify damaging frequency contents contained in the earthquake. Effective peak ground accelerations are evaluated from the calculated response spectra and compared with apparent peak ground accelerations and the design spectrum in KBC 2016. All these results are used to consistently explain the reason why most of seismic damage in the earthquake was concentrated on low-rise stiff buildings but not quite significant. In order to comparatively appraise the damage potential, the constant ductility spectrum constructed from the Gyeongju earthquake is compared with that of the well-known 1940 El Centro earthquake. Deconvolution analysis by using one accelerogram speculated to be recorded at a stiff soil site is also performed to estimate the soil profile conforming to the response spectrum characteristics. Finally, response history analysis for 39- and 61-story tall buildings is performed as a case study to explain significant building vibration felt on the upper floors of some tall buildings in Busan area during the Gyeongju earthquake. Seismic design and retrofit implications of M5.8 Gyeongju earthquake are summarized for further research efforts and improvements of relevant practice.

• Korean Journal of Veterinary Research
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• v.45 no.1
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• pp.131-137
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• 2005

To assess anesthetic depth using quantitative electroencephalography (q-EEG), we recorded processed EEG (raw EEG) till 100 minutes in beagle dogs anesthetized for 60 minutes with tiletamine/zolazepam (n=5, TZ group), xylazine/ketamine (n=5, XK group) and propofol (n=5, PI group) by intermittent bolus injection. Raw EEG was converted into 95% spectral edge frequency (SEF) and median frequency (MF) through fast fourier transformation (FFT) method. 95% SEF value of TZ group was significantly higher (p<0.05) than the XK group from 10 minutes to 100 minutes. 95% SEF value of PI group was significantly higher (p<0.05) than the XK group from 10 minutes to 40 minutes, and significantly low (p<0.05) than XK group at 90 and 100 minutes. MF was significantly higher (p<0.05) in TZ group from 60 minutes to 100 minutes. Based on these results, using dissociative agent with ${\alpha}_2$-adrenergic agent is more potent in CNS depressed than using dissociative agent alone, and low doses of propofol has a disinhibitory effect on CNS.

• Journal of IKEEE
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• v.24 no.1
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• pp.200-207
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• 2020

In this paper, an area-efficient feature extractor was proposed for security surveillance radar systems and FPGA-based implementation results were presented. In order to reduce the memory requirements, features extracted from Doppler profile for FFT window-size are used, while those extracted from total spectrogram for frame-size are excluded. The proposed feature extractor was design using Verilog-HDL and implemented with Xilinx Zynq-7000 FPGA device. Implementation results show that the proposed design can reduce the logic slice and memory requirements by 58.3% and 98.3%, respectively, compared with the existing research. In addition, security surveillance radar system with the proposed feature extractor was implemented and experiments to classify car, bicycle, human and kickboard were performed. It is confirmed from these experiments that the accuracy of classification is 93.4%.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.4
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• pp.27-34
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• 2016

A new algorithm for determining optimal accelerometer locations is proposed by using a frequency-domain Hankel matrix which is much simpler to construct than a time-domain Hankel matrix. The algorithm was examined through simulation studies by comparing the outcomes with those from other available methods. To compare and analyze the results from different methods, a dynamic analysis was carried out under seismic excitation and acceleration data were obtained at the selected optimal sensor locations. Vibrational amplitudes at the selected sensor locations were determined and those of all the other degrees of freedom were determined by using a spline function. MAC index of each method was calculated and compared to look at which method could determine more effective locations of accelerometers. The proposed frequency-domain Hankel matrix could determine reasonable selection of accelerometer locations compared with the others.

• Korean Journal of Optics and Photonics
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• v.12 no.2
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• pp.83-90
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• 2001

The Talbot effect for periodic objects with the spatial period p illuminated by expanded coherent light is analyzed by Fresnel diffraction theory, and the Talbot distance (Zr) at which we can observe 1: 1 imaging without any lenses can be defined. We confmned experimentally the Talbot imaging of line, circular, X -type and '||'&'||'copy;-type 2 dimensional alTay gratings at ZT. At the same time, we observed phase reversed Talbot imaging at Zr/2 and Talbot subimage with p/2 at Zr/4 and 3Zr/4. The visibility of Talbot images as a function of the number of slits of the input grating was measured by the FFf (Fast Fourier Transform) results of these images. As a result stationary maximum visibility of V = 0.25 was obtained from grating numbers with more than 15 slit pairs.

• Journal of Advanced Navigation Technology
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• v.27 no.1
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• pp.111-118
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• 2023

For the implementation of a smart factory, it is necessary to collect data by connecting various sensors and devices in the manufacturing environment and to diagnose or predict failures in production facilities through data analysis. In this paper, to predict the residual useful lifetime of milling insert used for machining products in CNC machine, weight k-NN algorithm, Decision Tree, SVR, XGBoost, Random forest, 1D-CNN, and frequency spectrum based on vibration signal are investigated. As the results of the paper, the frequency spectrum does not provide a reliable criterion for an accurate prediction of the residual useful lifetime of an insert. And the weighted k-nearest neighbor algorithm performed best with an MAE of 0.0013, MSE of 0.004, and RMSE of 0.0192. This is an error of 0.001 seconds of the remaining useful lifetime of the insert predicted by the weighted-nearest neighbor algorithm, and it is considered to be a level that can be applied to actual industrial sites.