• Journal of the Institute of Convergence Signal Processing
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• v.3 no.4
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• pp.1-6
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• 2002

Generally, most significant information of images is included in the object regions. Thus, this paper proposes the object regions prior transmission method using the bidirectional round filter. The proposed method extracts the object regions, and then transmits the wavelet coefficients of the object regions, prior to others, in the encoding procedure using SPIHT So, it makes significant image information be restored faster than others for a short time. Consequently, through the proposed method the significant information of images is able to be recognized at a low bit rate and the condition of the continuous transmission is decidable by recognizing significant information fast, so that the searching time and efficiency can be improved.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.23 no.6
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• pp.69-74
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• 2023

In this paper we review techniques for building and analyzing wavelets on irregular point sets in one and two dimensions. In particular we focus on subdivision schemes and commutation. Subdivision means the skill that approximates the initial lines or mesh into a tender curve or a curved surface by continuous partitioning operation. The key to generalizing wavelet constructions to non-traditional settings is the use of generalized subdivision. The first generation setting is already connected with subdivision schemes, but they become even more important in the construction of second generation wavelets. Subdivision schemes provide fast algorithms, create a natural multi-resolution structure, and yield the underlying scaling functions and wavelets we seek.

• Wind and Structures
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• v.12 no.5
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• pp.441-455
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• 2009

Studying the spatial distribution in coherent fields such as turbulence and turbulence-induced force is important to model and evaluate turbulence-induced forces and response of structures in the turbulent flows. Turbulence field-based coherence function is commonly used for the spatial distribution characteristic of the turbulence-induced forces in the frequency domain so far. This paper will focus to study spectral coherent structure of the turbulence and induced forces in not only the frequency domain using conventional Fourier transform-based coherence, but also temporo-spectral coherence one in the time-frequency plane thanks to wavelet transform-based coherence for better understanding of the turbulence and force coherences and their spatial distributions. Effects of spanwise separations, bluff body flow, flow conditions and Karman vortex on coherent structures of the turbulence and induced pressure, comparison between turbulence and pressure coherences as well as intermittency of the coherent structure in the time-frequency plane will be investigated here. Some new findings are that not only the force coherence is higher than the turbulence coherence, the coherences of turbulence and forces depend on the spanwise separation as previous studies, but also the coherent structures of turbulence and forces relate to the ongoing turbulence flow and bluff body flow, moreover, intermittency in the time domain and low spectral band is considered as the nature of the coherent structure. Simultaneous measurements of the surface pressure and turbulence have been carried out on some typical rectangular cylinders with slenderness ratios B/D=1 (without and with splitter plate) and B/D=5 under the artificial turbulent flows in the wind tunnel.

• Earthquakes and Structures
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• v.8 no.6
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• pp.1463-1480
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• 2015

This research aims to develop an empirical model for simulation of time-varying frequency in earthquake ground motion so as to be used easily in engineering applications. Briefly, 10545 recordings of the Next Generation Attenuation (NGA) global database of accelerograms from shallow crustal earthquakes are selected and binned by magnitude, distance and site condition. Then the wavelet spectrum of each acceleration record is calculated by using one-dimensional continuous wavelet transform, and the frequencies corresponding to the maximum values of the wavelet spectrum at a series of sampling time, named predominant frequencies, are extracted to analyze the variation of frequency content of seismic ground motions in time. And the time-variation of the predominant frequencies of 178 magnitude-distance-site bins for different directions are obtained by calculating the mean square root of predominant frequencies within a bin. The exponential trigonometric function is then use to fit the data, which describes the predominant frequency of ground-motion as a function of time with model parameters given in tables for different magnitude, distance, site conditions and direction. Finally, a practical frequency-dependent amplitude envelope function is developed based on the time-varying frequency derived in this paper, which has clear statistical parameters and can emphasize the effect of low-frequency components on later seismic action. The results illustrate that the time-varying predominant frequency can preferably reflect the non-stationarity of the frequency content in earthquake ground motions and that empirical models given in this paper facilitates the simulation of ground motions.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.11
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• pp.1555-1565
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• 2010

This paper presents a new method for indentifying the location of impact source in a buried duct. In a gas pipeline, the problem of leakage occurs due to the mechanical load exerted by construction equipment. Such leakage can cause catastrophic disasters in gas supply industries. Generally, the cross-correlation method has been used for indentifying the location of impact source in a pipeline. Since this method involves the use of the dispersive acoustic wave, it derives an amount of error in process of estimating the time delay between acoustic sensors. The object of this paper is to estimate the time delay in the arrival of the direct wave by using the wavelet transform instead of the dispersive wave. The wavelet transform based method gives more accurate estimates of the impact location than the cross-correlation method does. This method is successfully used to identify the location of impact force in an actual buried gas duct.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.4A
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• pp.295-302
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• 2011

The setting time which is the important element for the determination of slip-up speed of Slip-Form system is the hardening time of early-age concrete when the in place concrete has minimum compressive strength before the concrete appears out of Slip-Form system. But it is very difficult to predict the setting time because it depends on not only the composition ratio of concrete but also various conditions of construction fields. Thus, the technique to estimate accurately and continuously the hardening time of early-age in place concrete during operating Slip-Form system is necessary to guarantee the safety of Slip-Form system and the maintenance of the shape of concrete. Ultrasonic wave-based nondestructive testing methods have the advantages which are accurate and continuous in estimating concrete compressive strength. Of such methods, the method using surface wave which propagates along the surface of material is effective for thick member such as a pylon. Thus, in this paper a study on the determination of slip-up speed for Slip-Form system using surface wave velocity is performed. The relation between the slip-up speed of Slip-Form system and the setting time is formulated, and the surface wave velocity is estimated from continuous wavelet transform of the numerical results for surface wave propagation. Finally, the accuracy of this method according to the distance between the wave source and receivers and the relation between the estimated surface wave velocity and the elastic modulus are investigated.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.895-902
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• 2007

Rotating machinery has two typical faults with clearance, one is partial rub and the other is looseness. Due to these faults, non-linear and non-stationary signals are occurred. Therefore, time-frequency analysis is necessary for exact fault diagnosis of rotating machinery. In this paper newly developed time-frequency analysis method, HHT(Hilbert-Huang Transform) is applied to fault diagnosis and compared with other method of FFT, SFFT and CWT. The results show that HHT can represent better resolution than any other method. Consequently, the faults of rotating machinery are diagnosed efficiently by using HHT.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11a
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• pp.107-111
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• 2005

It has been reviewed whether it would be suitable that the application of the time-frequency signal analysis techniques to estimate the location of the impact source in plate structure. The STFT(Short Time Fourier Transform), WVD(Wigner-Ville distribution) and CWT(Continuous Wavelet Transform) methods are introduced and the advantages and disadvantages of those methods are described by using a simulated signal component. The essential of the above proposed techniques is to separate the traveling waves in both time and frequency domains using the dispersion characteristics of the structural waves. These time-frequency methods are expected to be more useful than the conventional time domain analyses fer the impact localization problem on a plate type structure. Also it has been concluded that the smoothed WVD can give more reliable means than the other methodologies for the location estimation in a noisy environment.

• The Journal of Korea Robotics Society
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• v.18 no.3
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• pp.271-280
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• 2023

FMCW (Frequency Modulated Continuous Wave) radar system is widely used in autonomous driving and navigation applications due to its high detection capabilities independent of weather conditions and environments. However, radar signals can be easily contaminated by various noises such as speckle noise, receiver saturation, and multipath reflection, which can worsen sensing performance. To handle this problem, we propose a learning-free noise removal technique for radar to enhance detection performance. The proposed method leverages adaptive thresholding to remove speckle noise and receiver saturation, and wavelet transform to detect multipath reflection. After noise removal, the radar image is reconstructed with the geometric structure of the surrounding environments. We verify that our method effectively eliminated noise and can be applied to autonomous driving by improving the accuracy of odometry and place recognition.

• Annual Conference of KIPS
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• 2024.10a
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• pp.670-671
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• 2024

본 연구는 ECG 기반 사용자 인식 시스템에서 MobileNet-V2, SqueezeNet과 기존 전이 학습 모델들의 성능을 비교하였다. PTB-ECG 데이터베이스를 사용하여 각 모델의 계산 효율성과 인식 정확도를 분석하였다. MobileNet-V2는 98.88% 의 검증 정확도와 8분 59초로 빠른 훈련 속도를 기록하였으며, SqueezeNet은 95.75%의 검증 정확도를 보이며 3분 12초의 훈련 속도로 메모리 효율성 면에서 뛰어난 성능을 나타냈다. 실험 결과, 두 모델은 ECG 신호 분석에 적합한 경량화 모델임을 확인할 수 있었다.