Theoretical research on structural damage alarming of long-span bridges using wavelet packet analysis

The state equation and observation equation of the structural dynamic systems under various analysis scales are derived based on wavelet packet analysis. The time-frequency properties of structural dynamic response under various scales are further formulated. The theoretical analysis results reveal that the wavelet packet energy spectrum （WPES） obtained from wavelet packet decomposition of structural dynamic response will detect the presence of structural damage. The sensitivity analysis of the WPES to structural damage and measurement noise is also performed. The transfer properties of the structural system matrix and the observation noise under various analysis scales are formulated, which verify the damage alarming reliability using the proposed WPES with preferable damage sensitivity and noise robusticity.

Structural health monitoring of long-span suspension bridges using wavelet packet analysis

During the service life of civil engineering structures such as long-span bridges, local damage at key positions may continually accumulate, and may finally result in their sudden failure. One core issue of global vibration-based health monitoring methods is to seek some damage indices that are sensitive to structural damage, This paper proposes an online structural health monitoring method for long-span suspension bridges using wavelet packet transform （WPT）. The WPT- based method is based on the energy variations of structural ambient vibration responses decomposed using wavelet packet analysis. The main feature of this method is that the proposed wavelet packet energy spectrum （WPES） has the ability to detect structural damage from ambient vibration tests of a long-span suspension bridge. As an example application, the WPES-based health monitoring system is used on the Runyang Suspension Bridge under daily environmental conditions. The analysis reveals that changes in environmental temperature have a long-term influence on the WPES, while the effect of traffic loadings on the measured WPES of the bridge presents instantaneous changes because of the nonstationary properties of the loadings. The condition indication indices VD reflect the influences of environmental temperature on the dynamic properties of the Runyang Suspension Bridge. The field tests demonstrate that the proposed WPES-based condition indication index VD is a good candidate index for health monitoring of long-span suspension bridges under ambient excitations.

HYBRID WAVELET PACKET-TEAGER ENERGY OPERATOR ANALYSIS AND ITS APPLICATION FOR GEARBOX FAULT DIAGNOSIS

Based on wavelet packet decomposition （WPD） algorithm and Teager energy operator （TEO）, a novel gearbox fault detection and diagnosis method is proposed. Its process is expatiated after the principles of WPD and TEO modulation are introduced respectively. The preprocessed sigaaal is interpolated with the cubic spline function, then expanded over the selected basis wavelets. Grouping its wavelet packet components of the signal based on the minimum entropy criterion, the interpolated signal can be decomposed into its dominant components with nearly distinct fault frequency contents. To extract the demodulation information of each dominant component, TEO is used. The performance of the proposed method is assessed by means of several tests on vibration signals collected from the gearbox mounted on a heavy truck. It is proved that hybrid WPD-TEO method is effective and robust for detecting and diagnosing localized gearbox faults.

A NOVEL METHOD FOR NETWORK WORM DETECTION BASED ON WAVELET PACKET ANALYSIS

Objective To detect unknown network worm at its early propagation stage. Methods On the basis of characteristics of network worm attack, the concept of failed connection flow (FCT) was defined. Based on wavelet packet analysis of FCT time series, this method computed the energy associated with each wavelet packet of FCT time series, transformed the FCT time series into a series of energy distribution vector on frequency domain, then a trained K-nearest neighbor (KNN) classifier was applied to identify the worm. Results The experiment showed that the method could identify network worm when the worm started to scan. Compared to theoretic value, the identification error ratio was 5.69%. Conclusion The method can detect unknown network worm at its early propagation stage effectively.

Influence of explosion parameters on wavelet packet frequency band energy distribution of blast vibration

Blast vibration analysis is one of the important foundations for studying the control technology of blast vibration damage. According to blast vibration live data that have been collected and the characteristics of short-time non-stationary random signals, the wavelet packet energy spectrum analysis for blast vibration signal has made by wavelet packet analysis technology and the signals were measured under different explosion parameters （the maximal section dose, the distance of blast source to measuring point and the section number of millisecond detonator）. The results show that more than 95% frequency band energy of the signals sl-s8 concentrates at 0-200 Hz and the main vibration frequency bands of the signals sl-s8 are 70.313-125, 46.875-93.75, 15.625-93.75, 0-62.5, 42.969-125, 15.625-82.031, 7.813-62.5 and 0-62.5 Hz. Energy distributions for different frequency bands of blast vibration signal are obtained and the characteristics of energy distributions for blast vibration signal measured under different explosion parameters are analyzed. From blast vibration signal energy, the decreasing law of blast seismic waves measured under different explosion parameters was studied and the wavelet packet analysis is an effective means for studying seismic effect induced by blast.

Application of wavelet packet in gravity anomaly processing

Based on the advantages of the wavelet to separate regional field and local anomalies in MATLAB environment,a high-precision regional-residual separation was finally realized. Analytical continuation and trend surface analysis are conventional methods for gravity anomaly separation. But the wavelet packet analysis in analyzing gravity data can make the gravity anomaly to be computed at a higher precision. In this paper,wavelet packet method is used to process gravity anomaly data obtained in Laos,and the separation result is good. Daubechies wavelet series has a higher precision in the wavelet packet.

Characteristics of acoustic emission signals in damp cracking coal rocks

A uniaxial load experiment on coal rocks at different stress rates was carried out, based on the characteristics of acoustic emission (AE) signals in cracking coal rocks, decomposition, de-noising and reconstruction for the AE signals through wavelet packet transform for solving the current problems created by the presence of noise in AE signals and the existing problems in AE signal processing. The results show that the various characteristics of AE signals in coal rocks cracking under different situations can be clearly reflected, after the AE signals are de-noised by the wavelet packet. Compared to dry coal rocks, the number of AE occurrences in damp coal rocks was significantly reduced, as well as the average amplitude. The number of AE occurrences in damp and dry coal rocks clearly increased with increases in the loading rate, but the largest amplitude of the AE signals in damp coal rocks has been reduced. There is no clear evidence of change in dry coal rocks.

Influence of maximum decking charge on intensity of blasting vibration

Based on the character of short-time non-stationary random signal, the relationship between the maximum decking charge and energy distribution of blasting vibration signals was investigated by means of the wavelet packet method. Firstly, the characteristics of wavelet transform and wavelet packet analysis were described. Secondly, the blasting vibration signals were analyzed by wavelet packet based on software MATLAB, and the change of energy distribution curve at different frequency bands were obtained. Finally, the law of energy distribution of blasting vibration signals changing with the maximum decking charge was analyzed. The results show that with the increase of decking charge, the ratio of the energy of high frequency to total energy decreases, the dominant frequency hands of blasting vibration signals tend towards low frequency and hlasting vibration does not depend on the maximum decking charge.

Diagnosis of Vocal Cord Paralysis in Anaesthesia

Vocal cord paralysis can occur as a complication o surgery or anaesthesia,if permanent is a significant clinica problem.Early detection is important to optimize the chance o repair,and avoid complications associated with an impaired swallow.An algorithm to detect altered vocal cord function was presented based on wavelet packet analysis(WPA) and suppor vector machines(SVM),and compared with the Hoarseness Diagram method(HDm),which was reported as an objective voice quality evaluation approach and could be used for pathological voice discrimination.Experiments using voice signals recorded from subjects before and after the procedure show high classification accuracy with the new algorithm,whereas HDm fails in the detection of a hoarse voice.This finding would help to develop a screening tool to detect the vocal structure damage during surgery.

Orthogonal Wavelet Packet Analysis Based Chaos Recognition Method

The chaotic motion characteristics are expounded by taking the Duffing equation system as an example.The frequency band segmentation ability and the frequency resolution of the orthogonal multiresolution analysis and the orthogonal wavelet packet analysis are compared.A new orthogonal wavelet packet analysis-based chaos recognition method for chaotic motion characteristics is put forward.The chaotic,random,and periodic motions are identified effectively by use of the subfrequency band energy distribution in the signal spectrum.The characteristic frequency of chaotic motion is thus extracted.

Dynamic response analysis of ship-bridge collisions experiment

Over the past decades, there has been continual construction of sea-crossing bridges as the technology of transportation improves. The probability of bridge pier being subjected to more vehicular impact is also growing. This study performed scale model tests and analyzed a collision mechanism considering the non-navigable span of a sea-crossing bridge in East China Sea as an engineering background. Comparing the test results with the finite element calculations, the dynamic response of the sample bridge and local damages of the fragile components under impact force were evaluated. Subsequently, the time-frequency characteristics of the vibration signal were analyzed based on wavelet packet analysis, and the multi-resolution characteristics as well as energy distribution of the vibration signal were discussed. It was observed that the impact energy transferred from ship to pier during the period of collision distributed different frequency bands with varying characteristics. The main frequency band(0–62.5 Hz) contains more than 75% of the vibration energy. The analysis can provide a basis for structural damage identification after the collision and anti-collision design of bridges.