Acoustic Emission

Structural testing and assessment, process monitoring, and material characterization are three broad application areas of acoustic emission (AE) techniques. Quantitative and qualitative characteristics of AE waves have been studied widely in the literature. This book reviews major research developments in the application of AE in numerous engineering fields. It brings together important contributions from renowned international researchers to provide an excellent survey of new perspectives and paradigms of AE. In particular, this book presents applications of AE in cracking and damage assessment in metal beams, asphalt pavements, and composite materials as well as studying noise mitigation in wind turbines and cylindrical shells

Diagnosis and Fault detection in Electrical Machines and Drives based on Advanced Signal Processing Techniques

In the present thesis, a new methodology of diagnosis based on advanced use of time-frequency technique analysis is presented. More precisely, a new fault index that allows tracking individual fault components in a single frequency band is defined. More in detail, a frequency sliding is applied to the signals being analyzed (currents, voltages, vibration signals), so that each single fault frequency component is shifted into a prefixed single frequency band. Then, the discrete Wavelet Transform is applied to the resulting signal to extract the fault signature in the frequency band that has been chosen. Once the state of the machine has been qualitatively diagnosed, a quantitative evaluation of the fault degree is necessary. For this purpose, a fault index based on the energy calculation of approximation and/or detail signals resulting from wavelet decomposition has been introduced to quantify the fault extend. The main advantages of the developed new method over existing Diagnosis techniques are the following: - Capability of monitoring the fault evolution continuously over time under any transient operating condition; - Speed/slip measurement or estimation is not required; - Higher accuracy in filtering frequency components around the fundamental in case of rotor faults; - Reduction in the likelihood of false indications by avoiding confusion with other fault harmonics (the contribution of the most relevant fault frequency components under speed-varying conditions are clamped in a single frequency band); - Low memory requirement due to low sampling frequency; - Reduction in the latency of time processing (no requirement of repeated sampling operation)

The efffect of elastomeric bearing degradation on bridge dynamic response

The dynamic response of highway bridges is a topic that has been thoroughly researched over many years. However, understanding of how the dynamic response of bridges is affected by the performance of their bearings over an extended period of time is, at present, not clearly defined. Although health monitoring of bridge structures is relatively advanced, the scope for further research is wide. The study presented in this thesis contains research on plate structures; ranging from a simple Euler-Bernoulli method to determine natural frequencies; modal analysis of a plate structure in the laboratory; FEA of the plate structure; modal analysis on a full-scale structure subjected to vehicle loading; and FEA of a simplified model representing the full-scale structure. A combination of these methods has allowed the conclusions presented herein to be drawn with respect to the effects of support degradation, and the consequent effect on structural performance. In the laboratory, modal analysis of a small-scale, thin rectangular plate of Perspex' has been completed. A series of boundary conditions have been investigated through altering the support offered to the plate by a series of springs, each with a different stiffness, to simulate bearings with different stiffnesses. Vibrations of varying frequency have also been forced upon the plate, and its response recorded. Displacement values provided the clearest indication of the effect of bearing stiffness, with the least stiff spring resulting in the largest displacement. Alteration of support stiffness in the model can have a marked effect on the resonant frequency of the plate (approx. 23 % frequency change between spring 1 (1.22 Nmm 1) and 5 (15.62 Nmm 1)). Full-scale testing on a highway bridge at Berwick-upon-Tweed on the Al, over the River Tweed, was completed in May 2005. These data form the baseline for future dynamic testing and condition monitoring of the structure. To describe the dynamic properties of the structure, the force generated by each type of vehicle traversing the structure was determined using instrumentation already in place on the bridge. Statistics drawn from the data are presented, which indicate that the bearings are functioning as expected, but are subjected to forces of a much larger magnitude due to overloaded HGVs than in current design specifications. Larger HGVs made up a small percentage of overall vehicles recorded, but contribute a much higher proportion of damage caused to the bridge. Displacement and frequency were both valid measures of bearing performance and therefore state of degradation. The method is offered as a condition monitoring test for bridges and their bearings.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

The efffect of elastomeric bearing degradation on bridge dynamic response

The dynamic response of highway bridges is a topic that has been thoroughly researched over many years. However, understanding of how the dynamic response of bridges is affected by the performance of their bearings over an extended period of time is, at present, not clearly defined. Although health monitoring of bridge structures is relatively advanced, the scope for further research is wide. The study presented in this thesis contains research on plate structures; ranging from a simple Euler-Bernoulli method to determine natural frequencies; modal analysis of a plate structure in the laboratory; FEA of the plate structure; modal analysis on a full-scale structure subjected to vehicle loading; and FEA of a simplified model representing the full-scale structure. A combination of these methods has allowed the conclusions presented herein to be drawn with respect to the effects of support degradation, and the consequent effect on structural performance. In the laboratory, modal analysis of a small-scale, thin rectangular plate of Perspex' has been completed. A series of boundary conditions have been investigated through altering the support offered to the plate by a series of springs, each with a different stiffness, to simulate bearings with different stiffnesses. Vibrations of varying frequency have also been forced upon the plate, and its response recorded. Displacement values provided the clearest indication of the effect of bearing stiffness, with the least stiff spring resulting in the largest displacement. Alteration of support stiffness in the model can have a marked effect on the resonant frequency of the plate (approx. 23 % frequency change between spring 1 (1.22 Nmm 1) and 5 (15.62 Nmm 1)). Full-scale testing on a highway bridge at Berwick-upon-Tweed on the Al, over the River Tweed, was completed in May 2005. These data form the baseline for future dynamic testing and condition monitoring of the structure. To describe the dynamic properties of the structure, the force generated by each type of vehicle traversing the structure was determined using instrumentation already in place on the bridge. Statistics drawn from the data are presented, which indicate that the bearings are functioning as expected, but are subjected to forces of a much larger magnitude due to overloaded HGVs than in current design specifications. Larger HGVs made up a small percentage of overall vehicles recorded, but contribute a much higher proportion of damage caused to the bridge. Displacement and frequency were both valid measures of bearing performance and therefore state of degradation. The method is offered as a condition monitoring test for bridges and their bearings.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Vibration-based damage identification in beam structures through wavelet analysis

Nowadays the topic of damage identification in structures is of primary interest in the field of civil, aerospace, mechanical engineering research. Indeed, due to the increasing use of advanced structural systems (e.g. airplanes, space shuttles, wind turbines, etc.) and to the aging of old structures (e.g. buildings, towers, bridges, etc.), the safety and reliability of structures have to be guaranteed to avoid catastrophic events and loss of human lives. The present thesis is focused on vibration-based damage identification in beam structures through wavelet analysis. The dissertation is arranged in six chapters. Chapter 1 introduces the topic of the thesis through a broad presentation of the state of the art of damage identification methods for structural health monitoring and control, with particular attention to vibration-based structural damage identification methods. In Chapter 2, the time-frequency technique, named wavelet analysis, is firstly theoretically presented and its application, available in the literature particularly for beam-like structures, as a damage detection tool both in time and in space domains is discussed. In Chapter 3, the mechanical models of homogeneous and fiber-reinforced cracked beams are presented. The models are used to simulate the real static and dynamic responses of beam structures for successive damage detection through wavelet analysis. The last three chapters of the thesis are devoted to the original findings of the present research. Chapter 4 focuses on the issue of border distortions in damage detection by continuous wavelet transform. To tackle the problem, a new polynomial padding method is proposed and compared with the most effective padding methods commonly used in the literature. In Chapter 5 the effect of spatial sampling in damage detection of cracked beams by continuous wavelet transform is thoroughly investigated through a parametric study. From the outcomes, some general indications on the optimal number of sampling intervals for an effective damage detection are obtained. Finally in Chapter 6, a new health structural monitoring method based on time-spatial wavelet analysis is presented to control the static and dynamic, elastic-plastic behaviour of a cracked fiber-reinforced beam. The capability of the method is discussed particularly with respect to scale of the analysing wavelet, the noise level and the spatial sampling interval, considering a small crack

Prognostic Algorithms for Condition Monitoring and Remaining Useful Life Estimation

To enable the benets of a truly condition-based maintenance philosophy to be realised, robust, accurate and reliable algorithms, which provide maintenance personnel with the necessary information to make informed maintenance decisions, will be key. This thesis focuses on the development of such algorithms, with a focus on semiconductor manufacturing and wind turbines. An introduction to condition-based maintenance is presented which reviews dierent types of maintenance philosophies and describes the potential benets which a condition- based maintenance philosophy will deliver to operators of critical plant and machinery. The issues and challenges involved in developing condition-based maintenance solutions are discussed and a review of previous approaches and techniques in fault diagnostics and prognostics is presented. The development of a condition monitoring system for dry vacuum pumps used in semi- conductor manufacturing is presented. A notable feature is that upstream process mea- surements from the wafer processing chamber were incorporated in the development of a solution. In general, semiconductor manufacturers do not make such information avail- able and this study identies the benets of information sharing in the development of condition monitoring solutions, within the semiconductor manufacturing domain. The developed solution provides maintenance personnel with the ability to identify, quantify, track and predict the remaining useful life of pumps suering from degradation caused by pumping large volumes of corrosive uorine gas. A comprehensive condition monitoring solution for thermal abatement systems is also presented. As part of this work, a multiple model particle ltering algorithm for prog- nostics is developed and tested. The capabilities of the proposed prognostic solution for addressing the uncertainty challenges in predicting the remaining useful life of abatement systems, subject to uncertain future operating loads and conditions, is demonstrated. Finally, a condition monitoring algorithm for the main bearing on large utility scale wind turbines is developed. The developed solution exploits data collected by onboard supervisory control and data acquisition (SCADA) systems in wind turbines. As a result, the developed solution can be integrated into existing monitoring systems, at no additional cost. The potential for the application of multiple model particle ltering algorithm to wind turbine prognostics is also demonstrated

Überwachung von Gasemissionen aktiver Vulkane: Identifizierung von natürlichen Entgasungsvariationen und Kombination von Vulkanüberwachungstechniken

This thesis is a contribution to the interdisciplinary field of applied volcanology and focuses on the study of volcanic gas emissions by means of ground-based spectroscopic remote sensing techniques. Furthermore it aims at fostering the routine use and integration of such measurements into existing multi-parameter volcano surveillance networks of the involved local volcano observatories. For this purpose continuous long-term monitoring of sulphur dioxide (SO2) emission rates was performed using permanent networks of fully-automated scanning ultraviolet (UV) spectrometers at some of the most active and persistently degassing stratovolcanoes in the volcanic arcs of Chile, Costa Rica and Nicaragua. These measurements yielded detailed time series of SO2 emission rates, which were calculated using differential optical absorption spectroscopy (DOAS) in conjunction with wind transport directions and velocities derived from weather hindcasts of the Global Forecast System (GFS), and delivered insights into the degassing behaviour of the monitored volcanoes.Diese Dissertation ist ein Beitrag zum weitläufigen interdisziplinären Feld der angewandten Vulkanologie und der Studie von vulkanischen Gasemissionen unter der Verwendung von bodengebundenen spektroskopischen Fernerkundungstechniken. Desweiteren zielt sie darauf ab, die routinierte Benutzung und die Integrierung solcher Messungen in die bereits existierenden Multi-Parameter Vulkanüberwachungsnetzwerke der involvierten Vulkanobservatorien zu fördern. Für diese Zwecke wurde an einigen der aktivsten und dauerhaft entgasenden Stratovulkane in Chile, Costa Rica und Nicaragua eine kontinuierliche Langzeitüberwachung von Schwefeldioxid (SO2) -Emissionsraten mittels permanent installierter Netzwerke aus voll-automatischen ultraviolett (UV) –Spektrometer Stationen mit eingebauter Abtastvorrichtung durchgeführt. Diese Messungen lieferten detaillierte Zeitreihen von SO2 –Emissionsraten, die mittels differentieller optischer Absorptionsspektroskopie (DOAS) in Verbindung mit Windrichtungen und Windgeschwindigkeiten aus Rückberechnungen des Global Forecast Systems (GFS) berechnet wurden, und gaben somit Einblicke in das Entgasungsverhalten der überwachten Vulkane und ermöglichten darüber hinaus die gemeinsame Analyse mit komplementären seismischen Überwachungsdaten

Monitoring gas emissions of active volcanoes: Identification of natural degassing variations and combination of volcano monitoring techniques

This thesis is a contribution to the interdisciplinary field of applied volcanology and focuses on the study of volcanic gas emissions by means of ground-based spectroscopic remote sensing techniques. Furthermore it aims at fostering the routine use and integration of such measurements into existing multi-parameter volcano surveillance networks of the involved local volcano observatories. For this purpose continuous long-term monitoring of sulphur dioxide (SO2) emission rates was performed using permanent networks of fully-automated scanning ultraviolet (UV) spectrometers at some of the most active and persistently degassing stratovolcanoes in the volcanic arcs of Chile, Costa Rica and Nicaragua. These measurements yielded detailed time series of SO2 emission rates, which were calculated using differential optical absorption spectroscopy (DOAS) in conjunction with wind transport directions and velocities derived from weather hindcasts of the Global Forecast System (GFS), and delivered insights into the degassing behaviour of the monitored volcanoes