Local spectral analysis using wavelet packets

Wavelet packets are a useful extension of wavelets, which are of wide potential use in a statistical context. In this paper, an approach to the local spectral analysis of a stationary time series based on wavelet packet decomposition is developed. This involves extensions to the wavelet context of standard time series ideas such as the periodogram and spectrum. Some asymptotic properties of the new estimate are provided. The technique is illustrated by simulated signals and its application to physiological data, and its potential use in studies of time-dependent spectral analysis is discussed.     

铣刀切入切出阶段声发射信号特征的研究

铣刀切入切出过程的研究对于有效监测刀具状态以及改善铣削加工具有重要的意义。研究了铣刀切入切出阶段声发射信号的特征。在正交试验的基础上,通过小波变换提取各频段信号的能量比作为特征量,分析了切削速度、进给速度和铣削深度对切入切出阶段声发射信号的影响。     

Radioisotope Techniques Applied to the Investigation of Surface Contact in Rolling Element Bearings

A radiotracer method of investigation was developed to study metallic contact phenomena in rolling contacts. It consists of activating one rolling element and running it against inactive parts onto Which active material is deposited during operation. The transferred activity is Quantitatively determined by calibrated autoradiography. Exploratory tests on cylindrical roller bearings show the location of high pressure areas in the contacts in agreement with elasticity theory. The tests performed so far do not permit the definite determination that the deposited activity is transferred by micro-welding in direct metallic contact. (The possibility exists that it is deposited out of contaminated lubricant.) A simple modification of the method is outlined to overcome this ambiguity.     

Thrust bearing groove race defect measurement by wavelet decomposition of pre-processed vibration signal

Nature of vibration signal from a ball bearing system reveals location of fault and its severity. A proper signal processing technique is required to extract relevant information from a vibration signal. In this work measurement of groove race defect width in thrust bearing is presented by processing vibration signal using wavelet based technique. In the first step, pre-processing of vibration signal is done by multiplying the signal amplitude with its own absolute values. It helps to overcome the problem of detection of weak burst in normal vibration signal retaining sign of the original signal. In the second step, Symlet5 wavelet based decomposition is applied to the pre-processed signal to measure the size of seeded defect in outer groove race of thrust bearing. The decomposition based on Symlet wavelet is preferred because it reduces the ambiguity in detecting the entry point and exit point of the defect as it is having linear phase in nature. Measurement has been done for the groove defect width over the range of 0.4399–1.4854 mm. Measurement of defect has been also verified using image examination. Maximum deviation in result has been found in the cases which have minimum axial load (48 N) for every size of defect. With increase in axial load to 73 N and further to 98 N the bearing system gets properly stressed, which increases the accuracy of measurement. With further increase in axial load to 126 N and above, it has been observed that the burst disappears due to prevailing over-stressed condition of the loading disk and additional stiffness and damping of the flexible shaft at increased load.     

Stochastic seismic response of single-degree-of-freedom systems through wavelets

This paper proposes a wavelet-based approach for estimation of the stochastic response of a single-degree-of-freedom (SDOF) system which is subjected to an earthquake ground motion process modelled by its wavelet coefficients. Expressions have been derived for (i) the representation of the excitation process through wavelets, (ii) relationship between the wavelet coefficients of the excitation and response processes, and (iii) instantaneous mean-square value and power spectral density function (PSDF) of the response process. The proposed formulation considers both amplitude and frequency non-stationarities in the ground motion process, and is thus more generalized than the earlier methods based on the use of frequency-independent modulating functions. Compared with an alternative wavelet-based formulation (Basu B, Gupta VK. Seismic response of SDOF systems by wavelet modelling of non-stationary processes. J Eng Mech (ASCE) 1998;124(10):1142–50), this formulation does not require the wavelet bases to be mutually orthogonal and energy bands corresponding to different scales to be non-overlapping, for computing the instantaneous mean-square value of the response process. This is also applicable for very short excitations where the sudden application of excitation may be of crucial importance. The proposed formulation has been validated through statistical simulation in the case of an example ground motion process and oscillators of different periods.     

A highly accurate ultrasonic ranging method based on onset extraction and phase shift detection

The opposite-type ultrasonic ranging application is widely used in spatial 3D coordinates measurement systems. The traditional phase shift (PS) estimation based on multi-frequency ultrasonic pulse is a highly accurate ranging method but has high requirement to the transducers and signal processing algorithm. This paper proposes a novel opposite-type ultrasonic ranging method with single frequency pulse. It can estimate the time of flight (TOF) roughly through extracting the signal’s onset based on self-correlation and correct the TOF accurately through detecting the phase shift between the transmission and reception signals. In order to reduce the noise disturbance to this algorithm, a new de-noising method based on wavelet decomposition is presented, and the de-noising effect is analyzed by MATLAB simulation. Finally, three separate ultrasonic ranging experiments were designed to validate the effects of wavelet de-noising, PS detection and temperature field compensation. The accuracy of distance measurement can achieve 0.5 mm for the distance up to 5000 mm.     

Wavelet analysis of experimental results for coupled structural–hydraulic behavior of the EURISOL target mock-up

During test runs of the The European Isotope Separation On-Line (EURISOL) target mock-up performed in December 2008, data were recorded for strain gages and for acceleration sensors. In this paper, the applicability of wavelet analysis for detecting the onset and the status of flow-induced cavitation is investigated for the first time. Even under noisy conditions, the detection of incipient cavitation was possible when combining measurements with data from structural and fluid dynamic simulations. The distribution of coefficients of suitably selected wavelets yields a quantitative measure for the extent of cavitation in the EURISOL target mock-up under representative flow conditions. Without cavitation, the distribution of the wavelet coefficients was Gaussian with a small standard deviation, whereas for developed cavitation the standard deviation was large and the probability density function (PDF) approached a uniform distribution.     

A fast computation method for time scale signal denoising

This paper presents a novel and fast scheme for signal denoising in the wavelet domain. It exploits the time scale structure of the wavelet coefficients by modeling them as superposition of simple atoms, whose spreading in the time scale plane formally is the solution of a couple of differential equations. In this paper, we will show how the numerical solution of such equations can be avoided leading to a speed up of the scale linking computation. This result is achieved through a suitable projection space of the wavelet local extrema, requiring just least squares and filtering operations. Intensive experimental results show the competitive performances of the proposed approach in terms of signal to noise ratio (SNR), visual quality and computing time.     

Wavelet analysis on fluctuating characteristics of airflow in building environments

This paper introduces the theory of the wavelet transform (WT) method and its application to the study of fluctuating characteristics of airflows in building environments. By applying wavelet analysis to the natural wind around buildings and to the free jet flow from a centrifugal fan, the differences and relations between natural and mechanical wind currents were found, and the results of the study indicate the unique features and advantages of wavelet analysis in the study of fluctuating characteristics of airflows.     

Recognition of wear mode using multi-variable synthesis approach based on wavelet packet and improved three-line method

Condition monitoring is an indispensable means of ensuring smooth running of key equipment, because it can improve machinery availability and performance, and also reduce damage and maintenance cost. One kind of condition monitoring is oil monitoring and it is applied extensively because of its capability to provide warning and to predict faults at early stages, with stronger pertinence. But the extraction and selection of features from oil data have always been the bottleneck of its effective application. In this study, prior to extraction and selection of features, denoising was implemented on the oil spectrometric data using 1D-DPT. For the purpose of mining more effective boundary features, we designed amelioration on classical three-line method based on statistics, and thus improved the three-line method. After the denoised signal was decomposed with WT, the three features, boundary, correlation degree and centroid were extracted, respectively, using the improved three-line method, correlation coefficients and K-means clustering. On the basis of these features, multi-variable synthesis analysis was advanced and the distance criterion parameter of synthesis analysis was proposed to classify and identify wear mode. Finally, through the comparison with examples applying the classical three-line method, we demonstrate the better the ability of the improved method to classify and recognize wear patterns with higher accuracy and precision.