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New techniques for vibration condition monitoring: Volterra kernel and Kolmogorov-Smirnov
This thesis was submitted for the degree of Doctor of Philosophy and was awarded by Brunel University.This research presents a complete review of signal processing techniques used, today,
in vibration based industrial condition monitoring and diagnostics. It also introduces
two novel techniques to this field, namely: the Kolmogorov-Smirnov test and Volterra
series, which have not yet been applied to vibration based condition monitoring.
The first technique, the Kolmogorov-Smirnov test, relies on a statistical comparison
of the cumulative probability distribution functions (CDF) from two time series. It
must be emphasised that this is not a moment technique, and it uses the whole CDF,
in the comparison process.
The second tool suggested in this research is the Volterra series. This is a non-linear
signal processing technique, which can be used to model a time series. The
parameters of this model are used for condition monitoring applications.
Finally, this work also presents a comprehensive comparative study between these
new methods and the existing techniques. This study is based on results from
numerical and experimental applications of each technique here discussed.
The concluding remarks include suggestions on how the novel techniques proposed here can be improved.Brunel University Department of Mechanical Engineering and CAPES, Fundacao
Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior
Automatic Localization of Epileptic Spikes in EEGs of Children with Infantile Spasms
Infantile Spasms (ISS) characterized by electroencephalogram (EEG) recordings exhibiting hypsarrythmia (HYPS) are a severe form of epilepsy. Many clinicians have been trying to improve ISS outcomes; however, quantification of discharges from hypsarrythmic EEG readings remains challenging.
This thesis describes the development of a novel method that assists clinicians to successfully localize the epileptic discharges associated with ISS in HYPS. The approach includes: construct the time-frequency domain (TFD) of the EEG recording using matching pursuit TFD (MP-TFD), decompose the TFD matrix into two submatrices using nonnegative matrix factorizations (NMF), and employ the decomposed vectors to locate the spikes.
The proposed method was employed to an EEG dataset of five ISS individuals, and identification of spikes was compared with those which were identified by the epileptologists and those obtained using clinical software (Persyst). Performance evaluations showed results based on classification techniques: thresholdings, and support vector machine (SVM). Using the thresholdings, average true positive (TP) and false negative (FN) percentages of 86% and 14% were achieved, which represented a significant improvement over the use of Persyst, which only achieved average TP and FN percentages of 4% and 96%, respectively. Using SVM, the percentage of area under curve (AUC) of receiver operating characteristic (ROC) was significantly improved up to 98.56%.
In summary, the proposed novel algorithm based on MP-TFD and NMF was able to successfully detect the epileptic discharges from the dataset. The development of the proposed automated method can potentially assist clinicians to successfully localize the epileptic discharges associated with ISS in HYPS. The quantitative assessment of spike detection, as well as other features of HYPS, is expected to allow a more accurate assessment of the relevance of EEG to clinical outcomes, which is significant in therapy management of ISS
Towards the automated analysis of simple polyphonic music : a knowledge-based approach
PhDMusic understanding is a process closely related to the knowledge and experience
of the listener. The amount of knowledge required is relative to the
complexity of the task in hand.
This dissertation is concerned with the problem of automatically decomposing
musical signals into a score-like representation. It proposes that, as
with humans, an automatic system requires knowledge about the signal and
its expected behaviour to correctly analyse music.
The proposed system uses the blackboard architecture to combine the
use of knowledge with data provided by the bottom-up processing of the
signal's information. Methods are proposed for the estimation of pitches,
onset times and durations of notes in simple polyphonic music.
A method for onset detection is presented. It provides an alternative to
conventional energy-based algorithms by using phase information. Statistical
analysis is used to create a detection function that evaluates the expected
behaviour of the signal regarding onsets.
Two methods for multi-pitch estimation are introduced. The first concentrates
on the grouping of harmonic information in the frequency-domain.
Its performance and limitations emphasise the case for the use of high-level
knowledge.
This knowledge, in the form of the individual waveforms of a single
instrument, is used in the second proposed approach. The method is based
on a time-domain linear additive model and it presents an alternative to
common frequency-domain approaches.
Results are presented and discussed for all methods, showing that, if
reliably generated, the use of knowledge can significantly improve the quality
of the analysis.Joint Information Systems Committee (JISC) in the UK National Science Foundation (N.S.F.) in the United states. Fundacion Gran Mariscal Ayacucho in Venezuela
Time-Frequency Analysis of Systems with Changing Dynamic Properties
Time-frequency analysis methods transform a time series into a two-dimensional representation
of frequency content with respect to time. The Fourier Transform identifies
the frequency content of a signal (as a sum of weighted sinusoidal functions) but
does not give useful information regarding changes in the character of the signal, as all
temporal information is encoded in the phase of the transform. A time-frequency representation,
by expressing frequency content at different sections of a record, allows
for analysis of evolving signals. The time-frequency transformation most commonly
encountered in seismology and civil engineering is a windowed Fourier Transform, or
spectrogram; by comparing the frequency content of the first portion of a record with
the last portion of the record, it is straightforward to identify the changes between
the two segments. Extending this concept to a sliding window gives the spectrogram,
where the Fourier transforms of successive portions of the record are assembled into a
time-frequency representation of the signal. The spectrogram is subject to an inherent
resolution limitation, in accordance with the uncertainty principle, that precludes
a perfect representation of instantaneous frequency content. The wavelet transform
was introduced to overcome some of the shortcomings of Fourier analysis, though
wavelet methods are themselves unsuitable for many commonly encountered signals.
The Wigner-Ville Distribution, and related refinements, represent a class of advanced
time-frequency analysis tools that are distinguished from Fourier and wavelet
methods by an increase in resolution in the time-frequency plane. I introduce several
time-frequency representations and apply them to various synthetic signals as well as
signals from instrumented buildings.
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For systems of interest to engineers, investigating the changing properties of a
system is typically performed by analyzing vibration data from the system, rather
than direct inspection of each component. Nonlinear elastic behavior in the forcedisplacement
relationship can decrease the apparent natural frequencies of the system
- these changes typically occur over fractions of a second in moderate to strong excitation
and the system gradually recovers to pre-event levels. Structures can also suffer
permanent damage (e.g., plastic deformation or fracture), permanently decreasing the
observed natural frequencies as the system loses stiffness. Advanced time-frequency
representations provide a set of exploratory tools for analyzing changing frequency
content in a signal, which can then be correlated with damage patterns in a structure.
Modern building instrumentation allows for an unprecedented investigation into
the changing dynamic properties of structures: a framework for using time-frequency
analysis methods for instantaneous system identification is discussed
Diagnostic des machines dans le plan temps-frƩquence
Using short-time Fourier transform in machinery fault diagnosis -- Time-frequency distributions and their application to machinery fault detection -- Application of wavelet transform in machine fault detection -- Time-frequency algorithms and their applications
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