No description available.

We consider the problem of estimating the failure stresses of bundles (i.e. the tensile forces that destroy the bundles), constructed of several statisti-cally similar fibres, given a particular kind of censored data. Each bundle consists of several fibres which have their own independent identically dis-tributed failure stresses, and where the force applied on a bundle at any moment is distributed equally between the unbroken fibres in the bundle. A bundle with these properties is an example of an equal load-sharing sys-tem, often referred to as the Daniels failure model. The testing of several bundles generates a special kind of censored data, which is complexly struc-tured. Strongly consistent non-parametric estimators of the distribution laws of bundles are obtained by applying the theory of martingales, and by using the observed data. It is proved that random sampling, with replace-ment from the statistical data related to each tested bundle, can be used to obtain asymptotically correct estimators for the distribution functions of deviations of non-parametric estimators from true values. In the case when the failure stresses of the fibres are described by a Weibull distribution, we obtain strongly consistent parametric maximum likelihood estimators of the distribution functions of failure stresses of bundles, by using the complexly structured data. Numerical examples illustrate the behavior of the obtained estimators.

No description available.

Load distribution problems in distributed computing networks have attracted much attention in the literature. A major objective in these studies is to distribute the processing load so as to minimize the time of processing of the entire load. In general, the processing load can be indivisible or divisible. An indivisible load has to be processed in its entirety on a single processor. On the other hand, a divisible load can be partitioned and processed on more than one processor. Divisible loads are either modularly divisible or arbitrarily divisible. Modularly divisible loads can be divided into pre-defined modules and cannot be further sub-divided. Further, precedence relations between modules may exist. Arbitrarily divisible loads can be divided into several fractions of arbitrary lengths which usually do not have any precedence relations. Such type of loads are characterized by their large volume and the property that each data element requires an identical and independent processing. One of the important problems here is to obtain an optimal load distribution, which minimizes the processing time when the distribution is subject to communication delays in the interconnecting links. A specific application in which such loads are encountered is in edge-detection of images. Here the given image frame can be arbitrarily divided into many sub-frames and each of these can be independently processed. Other applications include processing of massive experimental data. The problems associated with the distribution of such arbitrarily divisible loads are usually analysed in the framework of what is known as divisible job theory. The research work reported in this thesis is a contribution in the area of distributing arbitrarily divisible loads in distributed computing systems subject to communication delays. The main objective in this work is to design and analyseload distribution strategies to minimize the processing time of the entire load in a given network. Two types of networks are considered, namely (i) single-level tree (or star) network and (ii) linear network. In both the networks we assume that there is a non-zero delay associated with load transfer. Further, the processors in the network may or may not be equipped with front-ends (Le., communication co-processors). The main contributions in this thesis are summarized below. First, a mathematical formulation of the load distribution problem in single-level tree and linear networks is presented. In both the networks, it is assumed that there are (m +1) processors and m communication links. In the case of single-level tree networks, the load to be processed is assumed to originate at the root processor, which divides the load into (m +1) fractions, keeps its own share of the load for processing, and distributes the rest to the child processors one at a time and in a fixed sequence. In all the earlier studies in the literature, it had been assumed that for a load distribution to be optimal, it should be such that all the processors must stop computing at the same time. In this thesis, it is shown that this assumption is in general not true, and holds only for a restricted class of single-level tree networks which satisfy a certain condition. The concept of an equivalent network is introduced to obtain a precise formulation of this condition in terms of the processor and link speed parameters. It is shown that this condition can be used to identify processor-link pairs which can be eliminated from a given network (i.e., these processors need not be given any computational load) without degrading its time performance. It is proved that the resultant reduced network (a network from which these inefficient processor-link pairs have been removed) gives the optimal time performance if and only if the load distribution is such that all the processors stop computing at the same time instant. These results are first proved for the case when the root processor is equipped with a front-end and then extended to the case when it is not. In the latter case, an additional condition, between the speed of the root processor and the speed of each of the links, to be satisfied by the network is specified. An optimal sequence for applying these conditions is also obtained. In the case of linear networks the processing load is assumed to originate at the processor situated at one end of the network. Each processor in the network keeps its own load fraction for computing and transmits the rest to its successor. Here too, in all the earlier studies in the literature, it has been assumed that for the processing time to be a minimum, the load distribution must be such that all the processors must stop computing at the same instant in time. Though this condition has been proved by others to be both necessary and sufficient, a different and more rigorous proof, similar to the case of single-level tree network, is presented here. Finally, the effect of inaccurate modelling on the processing time and on the above conditions are discussed through an illustrative example and it is shown that the model adopted in this thesis gives reasonably accurate results. In the case of single-level tree networks, so far it has been assumed that the root processor distributes the processing load in a fixed sequence. However, since there are m child processors, a total of m! different sequences of load distribution are possible. Using the closed-form derived for the processing time, it is proved here that the optimal sequence of load distribution follows the decreasing order of link speeds. Further, if physical rearrangement of processors and links is allowed, then it is shown that the optimal arrangement follows a decreasing order of link and processor speeds with the fastest processor at the root. The entire analysis is first done for the case when the root processor is equipped with a front-end, and then extended to the case when it is not. In the without front-end case, it is shown that the same optimal sequencing result holds. However, in an optimal arrangement, the root processor need not be the fastest. In this case an algorithm has been proposed for obtaining optimal arrangement. Illustrative examples are given for all the cases considered. Next, a new strategy of load distribution is proposed by which the processing time obtained in earlier studies can be further minimized. Here the load is distributed by the root processor to a child processor in more than one installment (instead of in a single installment) such that the processing time is further minimized. First; the case in which all the processors are equipped :tn front-ends is considered. Recursive equations are obtained for a heterogeneous network and these are solved for the special case of a homogeneous network (having identical processors and identical links). Using this closed-form solution, the ultimate limits of performance are explored through an asymptotic analysis with respect to the number of installments and number of processors in the network. Trade-off relationships between the number of installments and the number of processors in the network are also presented. These results are then extended to the case when the processors are not equipped with front-ends. Finally, the efficiency of this new strategy of load distribution is demonstrated by comparing it with the existing single-installment strategy in the literature. The multi-installment strategy explained above is then applied to linear net-As. Here, .the processing load is assumed to originate at one extreme end of the network, First the case when all the processors are equipped with front-ends is considered. Recursive equations for a heterogeneous network are obtained and these are solved for the special case of a homogeneous network. Using this closed form solution, an asymptotic analysis is performed with respect to the number of installments. However, the asymptotic results with respect to the number of processors was obtained computationally since analytical results could not be obtained. It is found that for a given network, once the number of installments is fixed, there is an optimum number of processors to be used in the network, beyond which the time performance degrades. Trade-off relationships between the number of installments and the number of processors is obtained. These results are then extended to the case when the processors are not equipped with front-ends. Comparisions with the existing single-installment strategy is also done. The single-installment strategy discussed in the literature has the disadvantage that the front-ends of the processors are not utilized efficiently in a linear network. This is due to the fact that a processor starts computing its own load fraction only after the entire load to be communicated through its front-end has been received. In this thesis, a new strategy is proposed in which a processor starts computing as soon as it receives its load fraction, simultaneously allowing its front-end to receive and transmit load to its successors. Recursive equations are developed and solved for the special case of a heterogeneous network in which the processors and links are arranged in the decreasing order of speeds. Further, it is shown that in this strategy, if the processing load originates in the interior of the network, the sequence of load distribution should- be such that the load should be first distributed to the side with a lesser number of processors. An expression for the optimal load origination point in the network is derived. A comparative study of this strategy with an earlier strategy is also presented. Finally, it is shown that even though the analysis is carried out for a special case of a heterogeneous network, this load distribution strategy can also be applied to a linear network in which the processors and links are arbitrarily arranged and still obtain a significant improvement in the time performance.

No description available.

No description available.

This dissertation studies modeling and control issues of parallel three-phase pulse-width modulated (PWM) converters. The converters include three-phase boost rectifiers, voltage source inverters, buck rectifiers and current source inverters. The averaging of the parallel converters is performed based on a generic functional switching unit, which is called a phase leg in boost rectifiers and voltage source inverters, and a rail arm in buck rectifiers and current source inverters. Based on phase-leg and rail-arm averaging, the developed models are not only equivalent to the conventional three-phase converter models that are based on phase-to-phase averaging, but they also preserve common-mode information, which is critical in the analysis of the parallel converters. The models reveal such parallel dynamics as reactive power circulation and small-signal interaction. A unique feature of the parallel three-phase converters is a zero-sequence circulating current. This work proposes a novel zero-sequence control concept that uses variable zero-vectors in the space-vector modulation (SVM) of the converters. The control can be implemented within an individual converter and is independent from the other control loops for the converter. Therefore, it greatly facilitates the design and expansion of a parallel system. Proper operation of the parallel converters requires an explicit load-sharing mechanism. In order to have a modular design, a droop method is recommended. Traditionally, however, a droop method has to compromise between voltage regulation and load sharing. After parametric analysis, a novel droop method using a gain-scheduling technique is proposed. The numeric analysis shows that the proposed droop method can achieve both good voltage regulation and good load sharing. An interleaving technique is often used in parallel converter systems in order to reduce current ripples. Because of its symmetrical circuit structure, the parallel three-phase converter system can reduce both differential-mode and common-mode noise with a center-aligned symmetrical SVM. Based on the concept that a symmetrical circuit can reduce common-mode dv/dt noise, a conventional three-phase, four-leg inverter is modified so that its fourth leg is symmetrical to the other three legs. The common-mode dv/dt noise can be practically eliminated with a new modulation strategy. Meanwhile, with a modified control design, the new four-leg inverter still can handle low-frequency common-mode components that occur due to unbalanced and nonlinear load. / Ph. D.

In the fast growing field of Telecommunications, the back up DC power supply plays a vital role in powering the telecom equipment. This DC power supply is a combination of AC-DC Rectifier coupled with a battery bank to support the load when AC input is not available. Figures 0.1 and 0.2 show the line diagram of the DC power supply. The power supply is the most critical element in a telecom installation and it should be highly reliable in order to have un-interrupted service. (Fig) Besides reliability, power density and cost are the driving forces behind the success of a power supply in the market. Off late, the reach of telecom in the society is very wide covering remote villages and major metros. Given this environment, the power supply is exposed to extreme input conditions. It is desirable to design the power supply capable of withstanding wide AC input conditions. Another advantage is that the rectifier unit will keep the battery charged so that the battery will have long life. This thesis is aimed at designing a 1400W (56V/25A) telecom power supply, keeping in view of the issues expressed above. The aim is to design a Switched Mode Rectifier (SMR) that tolerate wide input voltage variations (90Vac to 300Vac). In addition, the design covers unity input power factor, high efficiency (> 90%), high power density ( ), parallel operation and low cost ( ). Chapter 1 of this thesis covers the context and motivation of the work. Chapter 2 presents the design issues pertaining to power supplies. The normalized description of the power converters is presented. Such a description enables one to compare several circuit topologies in order to make effective design decisions. In a similar way the effectiveness of the switches and mgnetics are presented to enable design decisions in the output stage of the rectifier. Chapter 3 presents the design of the 1400W telecom power supply, keeping in view of the stated specifications. The performance results of the converter are presented in Chapter 4. All the design goals have been met. The design exercise has also given insights into possible further improvements. Contributions from this work and course of future development work are indicated in the concluding chapter.

Detta arbete var beställt av Sjöfartshögskolan i Kalmar. Skolan ville ha en enhet som kunde mäta aktiv-, reaktiv- och skenbar effekt, ström, spänning, frekvens och cosϕ på en generator och som kommunicerade vidare dessa värden till en PLC. Detta för att kunna lastfördela lasten mellan ett antal generatorer i kursen Tillämpad elteknik 15 hp där studenterna bygger en generatorinstallation med tre generatorer. Ett funktionsblock för lastfördelning skulle också programmeras. Prototypen som konstruerades baserades på en Arduino Ethernet och kommunikationen löstes med Modbus TCP/IP över Ethernet. Ett lastfördelningsprogram programmerades i form av ett funktionsblock som studenterna kunde importera till CoDeSys v2.3 och använda i sina installationer. Prototypen kunde läsa av värdena med ungefär samma noggrannhet som ett kommersiellt instrument som använder sig av samma mätteknik som prototypen. Uppdateringsfrekvensen var dock lägre än hos ett kommersiellt instrument. Kommunikationen med PLC:n fungerade utan problem. Då ingen undervisning hölls i arbetets slutskede kunde inte lastfördelningen testas på en fullskalig anläggning. Lastfördelningsprogrammet klarade dock av att hålla rätt frekvens på en ensam generator och fungerade som tänkt när programmet testades i en simulator. Prototypen gav fel mätvärden vid kapacitiv last. Vid jämförelse med en kommersiell tångamperemeter visade sig mätfelet bero på mätmetoden då båda gav liknande resultat. Som referens användes en professionell elkvalitetsanalysator. Alla uppdragsgivarens krav blev uppfyllda och arbetet kommer att kunna användas i undervisningen. / This thesis was ordered by Kalmar Maritime Academy. The request was for a device that could measure active, reactive and apparent power, as well as frequency, voltage, current and cosϕ on a generator. The measured values would be communicated to a PLC for use in a load sharing program between a number of generators in the course Tillämpad elteknik, 15 ECTS. In that course the students constructs a three-generator electric power grid. Included in the request was also to program a load sharing program. The prototype being constructed was based on the Arduino Ethernet, and the communication was enabled by means of the Modbus TCP/IP protocol over Ethernet. A load sharing program was created in the form of a function block which the student could import into the CoDeSys for use in the generator systems. The prototype could measure values with close to the same accuracy as a commercial available instrument that were using the same technique for measuring. The refresh rate was however lower than the commercial available instrument. Communication with the PLC worked without any issues. No full-scale testing could be done since no course was held during the final stages of the thesis, however the load sharing program could keep frequency on a single generator alone and worked in a simulated soft environment. Measuring errors occurred when measuring a capacitive load. When comparing to a commercial available clamp meter, the same errors occurred. As a reference a professional power and energy quality analyser was used. All the requests were fulfilled and the result of this thesis will be used in the educational programme at the Academy.

Les engrenages en matériau polymère présentent de nombreux avantages par rapport aux aciers. Ils sont plus légers, résistants à la corrosion, fonctionne sans lubrifiant et leurs coûts de revient est moindre grâce au moulage par injection. Ils sont de plus en plus utilisés dans des domaines variés, mais se limitent à la transmission de mouvement. L’ajout de fibre de verre courte permet d’augmenter leur tenue mécanique et de diversifier leur domaine d’utilisation à des transmissions de petite à moyenne puissance. Le polyamide (Nylon) renforcé de fibres de verre est le composite le plus couramment utilisé dans le domaine des engrenages. Néanmoins, son comportement viscoélastique ainsi que la présence de fibres introduit une difficulté supplémentaire dans la modélisation. En outre, le comportement viscoélastique dépend de la température et pour le Polyamide, de l’humidité. Par conséquent, la viscoélasticité impacte directement la répartition des charges, l’erreur de transmission sous charge, la raideur d’engrènement. Dans cette thèse, une méthode numérique originale modélisant le comportement mécanique des engrenages en Polyamide 6 renforcé de fibre de verre est proposée. L’approche utilise le modèle rhéologique linéaire de Kelvin généralisé pour simuler le comportement viscoélastique du matériau et prendre en compte la température, l’humidité ainsi que le taux de fibre et leur anisotropie. Ensuite ce modèle rhéologique est intégré dans le modèle quasi-statique du partage des charges développé par le LaMCoS. Ce processus de calcul permet d’obtenir les résultats essentiels pour les engrenages (répartition des charges, pressions de contact, erreur de transmission sous charge, raideur d’engrènement) avec un temps de calcul assez court. Afin de de valider les modèles numériques développés, un banc d’essai a été mis en place, permettant la mesure de l'erreur de transmission et la visualisation de la température de l’engrenage pendant son fonctionnement. / Polymer gears present several advantages: they can be used without lubricant, their meshing is silencer, resistance to corrosion is better, weight is reduced. However they have a poor heat resistance and are limited to rotation transmission. In order to improve the gears performance, glass fibre reinforcement is being increasingly used, where their lower cost and higher strength, compared to unreinforced polyamide, offer a potential increase in gear performance. Mechanical behaviour of polymers materials is very complex; it depends on time, history of displacement, temperature and for several polymers, on humidity. Moreover, an addition of fibres can make the material properties heterogeneous and anisotropic. The particular case of Polyamide 6 + 30% glass fibres which is the most common fibre reinforced plastic is studied in this work. In the first part of this work, a mould was developed to better control the material choice and moulding conditions. Using tomographic observations, investigations were done to better understand the relation between moulding conditions, gears geometry and fibres orientation. Based on these observations and with the help of mechanical characterisation, a linear rheological generalized-Kelvin model was developed to simulate the viscoelastic behavior of the polymer material. In a second part, this model taking into account temperature, humidity and rotation speed is integrated in quasi-static load sharing computation developed by the LaMCoS laboratory. In the load sharing calculus, the displacements are obtained on a large meshing covering the entire surface of the tooth. This relation integrates the viscoelastic displacement, the fibre orientation and the geometrical influence coefficients. The method permits to obtain results such as the loaded transmission error, the instantaneous meshing stiffness, the load sharing and the root tooth stress at different temperature, humidity and rotation speeds within a reasonable computation time. Investigation have shown interesting results regarding the historic of displacements which represents up to 15% of the total displacement at the tip radius, the localization of the maximal tooth root stress, which is the same than metal gears, or the influence of the thermal expansion toward transmission error. On another hand, we have highlighted the low difference between a realistic description of the fibre orientation and an homogeneous anisotropic one. The last step concerns the validation of the numerical. The measurements are carried out on a test bench developed at the LaMCoS laboratory. It provides two experimental results: the temperature of the gear during operation, and the load transmission error using optical encoders to measure the angular positions of the pinion and the gear. This one is global enough to validate the three steps of the model: geometry, kinematics and load sharing.