• Structural Engineering and Mechanics
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• v.40 no.6
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• pp.745-762
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• 2011

Damage detection methodologies based on the direct examination of the nonlinear-nonstationary characteristics of the structure dynamic response may play an important role in online structural health monitoring applications. Different signal processing based damage detection methodologies have been proposed based on the uncovering of spikes in the high frequency component of the structural response obtained via Discrete Wavelet transforms, Hilbert-Huang transforms or high pass filtering. The performance of these approaches in systems subjected to different types of excitation is evaluated in this paper. It is found that in the case of random excitations, like earthquake accelerations, the effectiveness of such methodologies is limited. An alternative damage detection approach using the Continuous Wavelet Transform (CWT) is also evaluated to overcome this limitation. Using the CWT has the advantage that the central frequencies at which it operates can be defined by the user while the frequency bands of the detail functions obtained via DWT are predetermined by the sampling period of the signal.

• Proceedings of the KIEE Conference
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• 2003.11c
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• pp.920-923
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• 2003

An wearable electrocardiogram (ECG) monitoring system is a widely used non-invasive diagnostic tool for ambulatory patient who may be at risk from latent life-threatening cardiac abnormalities. In this paper, we have a portable ECG monitoring system with conductive fiber which was characterized by the small-size and the low power consumption. The system consists of conductive fibers, one-chip microcontroller, ECG preprocessing circuit, and monitoring software to be able to record and analyze in PC. ECG preprocessing circuit is made of pre-amplifier with gain of 10, band-pass filter with bandwidth of 0.5-120Hz and 2.5V offset circuit for A/D conversion. ECG signals obtained by sensor are included with corrupted noises such as a baseline wandering, 60 Hz power noise and interference noise by body movement. For cancellation corrupted noises in signals obtained by conductive fiber, we used the wavelet decomposition of wavelet transforms in MATLAB toolbox.

• Proceedings of the IEEK Conference
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• 2001.06d
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• pp.49-52
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• 2001

This paper presents a FPGA Implementation of wavelet-based CODEC, which can compress 2-dimensional image. For real-time processing, a scheduling method of input image data is proposed and a new structure of MAC(multiplier-accumulator) is proposed for wavelet transforms. Also this study proposes global pipelining structure of wavelet CODEC and efficient buffering method at interfaces between each module with different clock frequency.

• Bulletin of the Korean Mathematical Society
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• v.37 no.3
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• pp.507-517
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• 2000

Existence of Gibbs' phenomenon has been well known in wavelet expansions. But the estimation of its size is another problem. Because of the oscillation of wavelets, it is not easy to estimate the Gibbs size of wavelet expansions. For wavelets defined via Fourier transforms, we give a new formula to calculate the size of overshoot. But using this we compute the size of Gibbs effect for Barttle-Lemarier wavelets.

• Kyungpook Mathematical Journal
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• v.51 no.3
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• pp.293-300
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• 2011

In this paper, we obtain that the space $\mathcal{W}_2$ of minimally supported frequency wavelets, the supports of whose Fourier transforms consist of two intervals, is path-connected.

• Structural Engineering and Mechanics
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• v.58 no.6
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• pp.1087-1107
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• 2016

A method of damage detection based on the moving harmonic excitation and continuous wavelet transforms is presented. The applied excitation is used as a moving actuator and its frequency and speed parameters can be adjusted for an amplified response. The continuous wavelet transforms, CWT, is used for cracks detection based on the resulting amplified signal. It is demonstrated that this identification procedure is largely better than the classical ones based on eigenfrequencies or on the eigenmodes wavelet transformed. For vibration responses, free and forced vibration analyses of multi-cracked beams are investigated based on both analytical and numerical methodological approaches. Cracks are modeled through rotational springs whose compliances are evaluated using linear elastic fracture mechanics. Based on the obtained forced responses, multi-cracks positions are accurately identified and the CWT identification can be highly improved by adjusting the frequency and the speed excitation parameters.

• Earthquakes and Structures
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• v.9 no.6
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• pp.1221-1232
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• 2015

In recent decades, wavelet transforms as a strong signal processing tool have attracted attention of researchers for damage identification. Apart from the wide application of wavelet transforms for damage identification, influence of higher order modes on the quality of damage detection has been a challenging matter for researchers. In this study, influence of higher order modes and different mass configurations on the quality of damage detection through Discrete Wavelet Transform (DWT) was studied. Nine different damage scenarios were imposed to four cantilever structures having different mass configurations. The first four mode shapes of the cantilever structures were measured experimentally and analyzed by DWT. A damage index was defined in order to study the influence of higher order modes. Results of this study showed that change in the mass configuration had a great impact on the quality of damage detection even when the changes altered natural frequencies slightly. It was observed that for successful damage detection all available mode shapes should be taken into account and measured mode shapes had no significant priority for damage detection over each other.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• v.3 no.1
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• pp.107-114
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• 1999

In many applications (e,g., identification of non-destructive testing signal and biomedical signal and multiscale analysis of image), it is of interest to analyze and identify phenomena occurring at the different scales. The recently introduced wave let transforms provide a time-scale decomposition of signals that offers the possibility of such signals. However, there is no corresponding statistical properties to development of multiscale statistical signal processing. In this paper, we derive such properties of random signals in wavelet domain.

• Proceedings of the IEEK Conference
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• 1999.06a
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• pp.223-226
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• 1999

We study the propagation property of the transient signals along the microstrip using the wavelet transform. Wavelet transform can offer the time-frequency windows. It makes the resolution of time high in high frequency range and the resolution of frequency high in low frequency range. So It is useful to analyze the signals which have both low and high frequency components.

• Computers and Concrete
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• v.2 no.6
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• pp.481-498
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• 2005

A wavelet based approach is proposed for structural damage detection in beams, plate and delamination of composite plates. Wavelet theory is applied here for crack identification of a beam element with a transverse on edge non-propagating open crack. Finite difference method was used for generating a general displacement equation for the cracked beam in the first example. In the second and third example, damage is detected from the deformed shape of a loaded simply supported plate applying the wavelet theory. Delamination in composite plate is identified using wavelet theory in the fourth example. The main concept used is the breaking down of the dynamic signal of a structural response into a series of local basis function called wavelets, so as to detect the special characteristics of the structure by scaling and transformation property of wavelets. In the light of the results obtained, limitations of the proposed method as well as suggestions for future work are presented. Results show great promise of wavelet approach for damage detection and structural health monitoring.