Signalverarbeitungsverfahren und virtuelle Instrumente zur Messung von elektrischen Signalen und zur Fehlerdiagnose an Maschinen

Es wird in dieser Arbeit gezeigt, dass sich die Chirp-z-Transformation (CZT) und das Zeropadding-Verfahren (ZP), kombiniert mit der Anwendung geeigneter Fensterfunktionen, zur Bestimmung der Größen von Spannungs- und Stromsignalen bezüglich der Zuverlässigkeit bei kurzen Messzeiten eignen. Die allgemeinen Bedingungen für die Anwendung der CZT bzw. des ZP bei reellen Multifrequenz-Signalen unter dem Einsatz der Fensterfunktionen dargestellt. Der Einfluß eines reellen weißen Rauschsignals auf die geschätzten Größen eines reellen Multifrequenz-Signals wurde untersucht. Das TDA-Verfahren wird zur Verarbeitung der harmonischen Komponenten der Ausgangssignale eines Frequenzumformers untersucht. Zur Detektion und Messung der interharmonischen Komponenten wird ein digitales Differenz-Filter vorgestellt. Die Anwendbarkeit des TDA-Verfahrens und des digitalen Differenz-Filters wird durch die Ergebnisse aus Simulationen und praktischen Anwendungen gezeigt. Virtuelle Instrumente wurden zur Fehldiagnose und Schwingungsanalyse an Planetengetrieben entwickelt. Die praktischen Anwendungen zeigen, dass das Spektrum der demodulierten hochfrequenten mechanischen Schwingungen – Hüllkurvenspektrum – eine spektrale Struktur bei den Frequenzen enthält, die mit den Fehlern auf Innenring- oder Außenringlaufbahn in Verbindung stehen.It will be shown that the chirp-z-transform and zero-padding, combined with a appropriate window, are suitable for the estimation of the parameters of the voltage and current signals with moderate computational complexity. Through the analysis of the spectral interference in the discrete time Fourier transform the conditions for the simultaneous use of the windows and the chirp-z-transform or zero-padding will be presented. The statistical errors of the estimations will be discussed. The time domain averaging will be here investigated to process harmonic components in the output signals of frequency converters. For the detection and measurement of interharmonics a digital difference-filter will be proposed. Simulations and field test results are provided to illustrate the utility of the time domain averaging and the difference-filter. Based on the analysis of the faults of gears and rolling bearings the virtual instruments for the fault diagnosis and vibration analysis in epicyclic gearboxes are developed. The practical applications show that the spectrum of the demodulated high-frequency vibration – envelope spectrum – contains a pattern of spectral lines at frequencies which can be related to the faults on the inner or outer race of rolling bearings

Existence Theorem for Periodic Solutions of Higher Order Nonlinear Differential Equations

AbstractWe study the existence of periodic solutions to differential equations of the formL(x)+g(t,x,x′,…,x(m))=f(t) withL(x)=x(m)+am−1x(m−1)+···+a1x′

Towards the Tradeoff Between Service Performance and Information Freshness

The last decade has witnessed an unprecedented growth in the demand for data-driven real-time services. These services are fueled by emerging applications that require rapidly injecting data streams and computing updated analytics results in real-time. In many of such applications, the computing resources are often shared for processing both updates from information sources and queries from end users. This requires joint scheduling of updates and queries because the service provider needs to make a critical decision upon receiving a user query: either it responds immediately with currently available but possibly stale information, or it first processes new updates and then responds with fresher information. Hence, the tradeoff between service performance and information freshness naturally arises in this context. To that end, we propose a simple single-server two-queue model that captures the coupled scheduling of updates and queries and aim to design scheduling policies that can properly address the important tradeoff between performance and freshness. Specifically, we consider the response time as a performance metric and the Age of Information (AoI) as a freshness metric. After demonstrating the limitations of the simplest FCFS policy, we propose two threshold-based policies: the Query-k policy that prioritizes queries and the Update-k policy that prioritizes updates. Then, we rigorously analyze both the response time and the Peak AoI (PAoI) of the threshold-based policies. Further, we propose the Joint-(M,N) policy, which allows flexibly prioritizing updates or queries through choosing different values of two thresholds M and N. Finally, we conduct simulations to evaluate the response time and the PAoI of the proposed policies. The results show that our proposed threshold-based policies can effectively control the balance between performance and freshness.Comment: Submitted to 2019 IEEE International Conference on Communications (ICC

Chinese women in white : a study of nurses in Taiwan.

The work started when I first registered as a part time Postgraduate student at Warwick, after finishing my MSc degree in medical sociology at Bedford College, London University in October 1982. Some preliminary investment had been done and a few essays written while I was in Taiwan teaching in a medical school. But it was only after April 1985, when I secured a grant from the Chinese Central Government in Taiwan to come over to England again and switched to full time study that the real work could really start. Since then, many parts of the work have been changed, such as the target problems and the methodology to tackle them. The whole working process was dynamic. Ideas exchanged, floating to and fro between my supervisor, Professor Margaret Stacey and me over years to find out results, as well as problems and methods. Only the original purpose of the study (Chinese women) and the sample group (nurses) have remained the same and still fascinate me. The problems were focussed gradually. The process of emergence of the problems and the conceptual framework used in the study will be described in part 1: introduction. The methodology changed in response to the focusing of the problems. Both the original plan and the evolving current design will be presented in Part 2: the research process. The field work and data analysis will be also dealt with in the same part. Some further but small alterations away from the research pIan were made to adjust to the situation of the field work as it happened in practice. Part 3 will be the results of the historical and literature review. The literature review gave me a more clear and closer look at my sample against their background of Chinese women's life in the past (chapter 8) and at the present day in Taiwan (chapter 10). Also traditional Chinese women healers and carers and the modern nursing history (chapter 9) were brought to light to elucidate the problems in nursing today. Part 4 will be the emergent themes which were attained through analysis of the field work. From these themes, a general profile of the life of these women in our sample in present day Taiwan gradually emerged. In part 5 conclusions are drawn concerning 'the new patriarchy', in which our respondents' lives are formed, as always around their menfolk – father, husband and son - although with certain differences from the situation in the past

Studies on the Property and Application of Starch Sugar Ester Dodecenylsuccinic

In this study, we have prepared starch and Brown algae sugar ester dodecenylsuccinic, and by using infrared rays, scanning electron microscopy (SEM), and differential scanning calorimetry (DSC), we studied the structures and properties of the starch and Brown algae sugar ester dodecenylsuccinic. In addition, we studied the possibility of using this modified starch and Brown algae as emulsifier that can be used in ice cream

A Worst-Case Approximate Analysis of Peak Age-of-Information Via Robust Queueing Approach

A new timeliness metric, called Age-of-Information (AoI), has recently attracted a lot of research interests for real-time applications with information updates. It has been extensively studied for various queueing models based on the probabilistic approaches, where the analyses heavily depend on the properties of specific distributions (e.g., the memoryless property of the exponential distribution or the i.i.d. assumption). In this work, we take an alternative new approach, the robust queueing approach, to analyze the Peak Age-of-Information (PAoI). Specifically, we first model the uncertainty in the stochastic arrival and service processes using uncertainty sets. This enables us to approximate the expected PAoI performance for very general arrival and service processes, including those exhibiting heavy-tailed behaviors or correlations, where traditional probabilistic approaches cannot be applied. We then derive a new bound on the PAoI in the single-source single-server setting. Furthermore, we generalize our analysis to two-source single-server systems with symmetric arrivals, which involves new challenges (e.g., the service times of the updates from two sources are coupled in one single uncertainty set). Finally, through numerical experiments, we show that our new bounds provide a good approximation for the expected PAoI. Compared to some well-known bounds in the literature (e.g., one based on Kingman's bound under the i.i.d. assumption) that tends to be inaccurate under light load, our new approximation is accurate under both light and high loads, both of which are critical scenarios for the AoI performance.Comment: Published in IEEE INFOCOM 202

Random Fixed Point Theorems of Random Comparable Operators and an Application

We introduce the new concept of random comparable operators as a generalization of random monotone operators and prove several random fixed point theorems for such a class of operators in partially ordered Banach spaces. Part of the presented results generalize and extend some known results of random monotone operators. Finally, as an application, we consider the existence of the solution of a random Hammerstein integral equation

Electrical performance of ester liquids under impulse voltage for application in power transformers

Ester liquids including both natural ester and synthetic ester are being considered as potential alternatives to mineral oil, due to their better environmental performance and for some liquids their higher fire point. Although these liquids have been widely used in distribution and traction transformers, it is still a significant step to adopt ester liquids in high-voltage power transformers because the high cost and severe consequence of a factory test failure and the high level of safety and reliability required in service for these units, tend to lead to a cautious approach to any step change in technology. Lightning impulse strength as basic insulation level is of importance for insulation design of power transformers and lightning impulse test is commonly required in the factory routine tests for high-voltage power transformers, so this thesis is aimed to investigate the electrical performances including pre-breakdown and breakdown of natural ester and synthetic ester under impulse voltage. Two types of field geometry were considered in the study, one is sphere-sphere configuration which represents the quasi-uniform fields inside a transformer and another is strongly non-uniform point-plane configuration which represents the situation of a defect or a source of discharge. In quasi-uniform field study, standard breakdown tests were carried out under negative lightning and switching impulse voltages. Influence of various testing methods on the measured lightning breakdown voltage was studied and the 1% lightning withstand voltage was obtained based on Weibull distribution fitting on the cumulative probability plot built up using the approximately 1000 impulse shots. As for strongly non-uniform field study, streamer propagation and breakdown event in ester liquids either with or without pressboard interface were investigated at various gap distances under both positive and negative lightning impulse voltages. A relationship between the results under lightning impulse and previously published results under step voltage was built up to predict the lightning breakdown voltage of ester liquids at very large gaps. The results indicated that impulse strengths of ester liquids for both breakdown and withstand in a quasi-uniform field, are comparable to those of mineral oil. In a strongly non-uniform field, streamers in ester liquids propagate faster and further, than in mineral oil at the same voltage level. Thus breakdown voltages of ester liquids are generally lower than those of mineral oil, which could be as low as 40% at a large gap distance of approximately 1000 mm. Introduction of parallel pressboard interface has no influence on the streamer propagation and thus does not weaken the breakdown voltage, but it tends to reduce the acceleration voltage particularly for mineral oil under positive polarity. Last but not least, a unique phenomenon of secondary reverse streamer (SRS) was observed in ester liquids, which occurs subsequently and well after the extinction of the primary streamer (PS) propagation within a single shot of impulse voltage and has the reverse polarity to the PS. The formation mechanism of SRS is explained mainly due to the reverse electric field induced by the residual space charges left by the PS.EThOS - Electronic Theses Online ServiceI MaterialsNational GridScottish PowerTJH2b Analytical ServicesUK Power NetworksElectricity North WestGBUnited Kingdo