Academic literature on the topic 'Commutateur virtuel'

Let [Formula: see text], respectively [Formula: see text] denote the virtual, respectively welded, braid group on [Formula: see text]-strands. We study their commutator subgroups [Formula: see text] and, [Formula: see text], respectively. We obtain a set of generators and defining relations for these commutator subgroups. In particular, we prove that [Formula: see text] is finitely generated if and only if [Formula: see text], and [Formula: see text] is finitely generated for [Formula: see text]. Also, we prove that [Formula: see text] and for [Formula: see text] the commutator subgroups [Formula: see text] and [Formula: see text] are perfect, i.e. the commutator subgroup is equal to the second commutator subgroup.

The mathematical description of the wear processes of brushes of brush-type motors is described. The actions directed on increase of the lifetime of brushes are offered. The proposed mathematical model of the wear processes of brushes considers the highest number of parameters of a sliding contact, including sparking energy of windings switching and the mechanical condition of a commutator and bearings. The approach for evaluating the optimum pressure on the brush in order to increase its resource is offered. The real and the virtual lifetime tests of the universal motor considering changing of the mechanical state of the commutator and bearings during lifetime were carried-out. The constant force value acting on the brush which provides its lifetime increase by 11% is proposed.

In recent years, with the continuous growth in China’s economy, the continuous advancement of urbanization and industrialization, the contradiction between rapid economic development and the continuous reduction in traditional fossil energy reserves such as coal, oil, and natural gas, the continuous aggravation of environmental pollution has become increasingly prominent. In this era, clean energy power generation technologies such as hydropower, wind power, and solar power generation, which have the advantages of renewability, environmental protection, and economy, have developed rapidly. However, wind and photovoltaic power plants are often located in remote areas, which means significant losses in the transmission process. High-voltage direct current (HVDC) transmission technology becomes the best choice to solve this problem. The HVDC transmission system based on a grid commutator is widely used in China’s AC-DC hybrid power grid. When an AC fault occurs on the inverter side, the line-commutated converter high-voltage direct current (LCC-HVDC) system is more prone to continuous commutation failure, which brings serious harm to system operation. To better suppress the problem of continuous commutation failure on the contravariant side, this paper analyzes the mechanism of continuous commutation failure from multiple angles. The DC current command sensitivity of a voltage-dependent current order limiter (VDCOL) in the LCC-HVDC system is low, which will lead to different degrees of continuous commutation failure. In addition, the rapid rise in DC current and the drop in commutation voltage during the fault will cause the turn-off angle to drop, and the probability of continuous commutation failure of the system will increase significantly. Based on the above theoretical analysis, a new control strategy combining the dynamic compensation of the turn-off angle of a virtual inductor and the suppression of continuous commutation failure by dynamic nonlinear VDCOL is proposed. A dynamic nonlinear VDCOL control strategy is proposed for the low sensitivity of current command adjustment under conventional VDCOL control. Secondly, two concepts of virtual inductance and DC current change rate are introduced, and a control strategy based on virtual inductance is proposed to comprehensively ensure that the switching angle has sufficient commutation margin during fault recovery. Finally, based on the CIGRE standard test model in PSCAD/EMTDC, the accuracy of the correlation mechanism analysis and the effectiveness of the suppression method are verified.

The number of ways an element of a finite group can be expressed as a square, a commutator, or more generally in the form w(x1, …, xr), where w is a word in the free group, defines a natural class function. We investigate some properties of these class functions, in particular their tendency to be characters or virtual characters of the underlying group. Generalizing classical results of Frobenius and others, we prove that generalized commutators yield characters in this manner, and use this to exhibit a criterion for nilpotency based on a certain equation associated with the irreducible characters.

This paper has proposed a phase controlled and PWM controlled power current source converter (CSC) for transmission line de-icing. The proposed system consists of a high-power thyristor-based line commutated converter to contribute a majority of the dc de-icing current and a low power PWM CSC to provide a part of the dc de-icing current and to compensate the low order harmonic ac current from the TCR. Thus, the grid current can be highly sinusoidal. In order to avoid the resonance caused by the interaction between TCR and PWM CSC, a virtual impedance control is implemented in the PWM CSC without using any additional sensors. Comprehensive verification results have been obtained to validate the correctness of the proposed approach.

The subject of this research is the new methods for improving the efficiency of Zabbix monitoring systems for the computational infrastructure of the universal infocommunication commutator, built upon the principle of globally distributed computational complex using the information cloud technologies. The object of this research is the globally distributed computational system of RingCentral corporation (USA), which is based on the technology of hybrid information cloud deployed in over a hundred  data storage and processing centers in all large economic and geographical zones, which provides universal infocommunication services, including video and audio conferences, virtual stationary automated telephone, and organization of call centers. Design and improvement of infocommunication cloud platforms, which provide universal communication services is a complex scientific, technical and economic problem; without its solution it is impossible to create information infrastructure with the service quality indicators that meet the demands of the society. This problem is of particular relevance in the context of worldwide sanitary-epidemiological pandemic of coronavirus, since part of the production processes was switched to remote work, and is executed without physical presence of administrative and technical personnel at the enterprises of national economy. This entailed a decline in the efficiency of networks and quality of customer service in certain infocommunication companies due to excessive nominal loads on the information network, and this, the failure of crucial nodes of user traffic processing.

Le Cloud computing offre aux utilisateurs l’opportunité d’exploiter des services qui peuvent être des infrastructures, des plateformes, des applications,... Ceci représente un gain de temps et d’argent considérable puisque l’utilisateur n’a besoin ni d’investir dans une infrastructure onéreuse, ni de gérer sa maintenance, de plus il paye juste les ressources utilisées. Afin de prendre en charge des applications à grande échelle et stocker de gros volumes de données, les centres de données ont été largement déployés par des fournisseurs cloud. Cependant, les études ont montré une mauvaise utilisation des ressources qui ne sont pas exploitées pleinement. Les technologies de virtualisation ont permis d’améliorer la situation en déployant des centres de données virtualisés. Ces derniers sont des centres de données où tout ou une partie du matériel (par exemple, serveurs, routeurs, commutateurs et liens) est virtualisé à l’aide d’un logiciel appelé hyperviseur qui divise l’équipement en plusieurs instances virtuelles isolées et indépendantes (comme des machines virtuelles). Toutefois les performances des équipements peuvent être atténuées à cause de plusieurs phénomènes tels que le vieillissement logiciel. L’objectif de cette thèse est d’évaluer les performances de deux composants clés dans les centres de données qui sont le serveur virtualisé et le commutateur virtuel. Puisque, l’architecture de ces systèmes est complexe, on a opté pour utiliser les formalismes de modélisation avant de mettre en place des solutions pratiques. Notre première contribution concerne la modélisation et l’évaluation de la performabilité d’un serveur virtualisé qui implémente une politique de gestion de l’énergie et utilise le rajeunissement logiciel comme une technique proactive afin de prévenir les aléas de vieillissement logiciel. Cette modélisation est basée sur une approche modulaire utilisant le SRN (Stochastic Reward Nets) qui décrit les différents états du SVS ainsi que les transitions régissant le passage d’un état à l’autre. L’analyse numérique permet de capturer l’impact de la variation de la charge de travail et le trafic en rafale sur les métriques de performabilité, ce qui permet de bien définir les paramètres du système. La seconde contribution porte sur l’évaluation des performances d’un commutateur virtuel qui détermine les performances du réseau puisqu’il établit la communication entre des VMs. Le modèle analytique proposé représente l’architecture interne de cenoeud critique avec plusieurs cartes d’interface réseau (représentant des ports) et plusieurs cœurs de processeur (CPU). Chaque CPU sert un ensemble de ports. Le modèle est basé sur les files d’attente avec serveur en vacance et des arrivées groupées. Les résultats numériques montrent l’impact de la taille du groupe et la politique d’acceptation sur les performances du commutateur. Ces résultats peuvent être intéressants lors du dimensionnement des ressources d’un commutateur virtuel
Cloud computing allows users to exploit services such as infrastructures, platforms, applications, ...This allows a considerable cost and time saving since users do not need buying and managing of equipment. Moreover, they just pay the resources used (pay-as-you go). With the increasing large-scale applications and the need to store huge quantities of data, data centers have been widely deployed. However, studies have shown the under utilization of resources. Therefore, Cloud providers resort to virtualization technologies that are adopted by data center architectures and virtualized data centres have been deployed. A Virtualized Data Center is a data center where some or all of the hardware (e.g, servers, routers, switches, and links) are virtualized by using software called hypervisor that divides the equipment into multiple isolated and independent virtual instances (e.g virtual machines (VMs)). However, equipment performance can be mitigated due to several phenomena such as software aging. In this thesis, we focus on performance evaluation of two components in the data centers which are the virtualized server and the virtual switch, by usingmodeling formalisms. The first contribution concerns performability modeling and analysis of server virtualized systems subject to software aging, software rejuvenation and implements an energy management policy. A modular approach based on SRNs is proposed to investigate dependencies between several server virtualized modules. Numerical analysis shows how workload with bursty nature impacts performability metrics. This can handle decision making related to rejuvenation scheduling algorithms and to select the suitable rejuvenation mechanism. The second contribution concerns virtual switch (VS) which is considered as key element in data center networks since it achieves the communication between virtual machines. An analytical queueing model with batch arrivals and server vacations is proposed to evaluate VS performance with several network interface cards and several CPU cores. Performance metrics are obtained as a function of two proposed batch acceptance strategies and mean batch size. Numerical results aremeaningful when sizing virtual switch resources

La complexité des microsystèmes, leur multidisciplinarité, l'hétérogénéité des matériaux utilisés et les interfaces avec l'environnement extérieur rendent difficiles l'évaluation et la maîtrise de leur fiabilité indispensables pour l'exploitation des nombreuses possibilités innovantes qu'ils offrent. L'approche que nous avons proposée dans ce travail, afin de prédire la fiabilité des microsystèmes, se fonde sur l'usage intensif de la modélisation et de la simulation, dans les conditions d'usage du microsystème (profil de mission), en associant donc l'évaluation de la fiabilité à la démarche de conception : avant d'entreprendre une modélisation fonctionnelle de type VHDL-AMS, les objectifs de fiabilité sont exprimés explicitement dans le cahier des charges du microsystème, au même titre que les objectifs plus habituels de performances. Afin de supporter nos travaux, nous avons appliqué cette démarche de prédiction de la fiabilité sur deux types de microsystèmes : - des micro-actionneurs électrothermiques. - des commutateurs RF capacitifs à actionnement électrostatique.

Cette thèse propose un schéma entièrement distribué de routage résilient pour les réseaux de switches. Dans cette approche une panne est traitée localement ; ainsi les autres nœuds du réseau n’ont pas besoin de prendre des mesures spécifiques. Contrairement aux systèmes classiques de routage IP qui se base uniquement sur la destination, le routage est fait en se basant sur l’arc de l’entrée et la destination. La contrainte qui en résulte est que les deux flux à la même destination entrant dans un nœud par un arc commun doivent fusionner après cet arc. Nous montrons que sous des faibles hypothèses (en supposant que le réseau est symétrique et bi-connexes au sens des liens), il existe un schéma de routage résilient pour toutes les situations de pannes simples de liens. Nous modélisons le problème de dimensionnement par un programme linéaire en nombres entiers qui peut être résolu exactement pour des réseaux de taille modeste. Nous proposons également plusieurs heuristiques pour traiter des instances de grande taille. Notre méthode généralise les méthodes de la littérature, en particulier celles de Xi et al. et de Nelakuditi et al. qui ont proposé des approches similaires. Notre approche permet d’obtenir de meilleurs résultats sur de nombreuses instances de test. Nous avons également étudié l’existence d’un schéma de routage résilient pour situation de panne de nœud dans le réseau basée sur les switches. Nous montrons que dans le cas des pannes de plusieurs liens, la condition de connexité n’est pas suffisante
This thesis presents a fully distributed resilient routing scheme for switch-based networks. A failure is treated locally, so other nodes in the network do not need to undertakespecial actions. In contrast to conventional IP routing schemes, each node routesthe traffic on the basis of the entering arc and of the destination. The resulting constraintis that two flows to the same destination entering in a node by a common archave to merge after this arc. We show that this is sufficient for dealing with all singlelink failure situations, assuming that the network is symmetric and two-link connected.We model the dimensioning problem with an Integer Linear Program which can besolved exactly for small networks. We also propose several heuristics for larger networks.Our method generalizes the methods of Xi et Chao and Li and of Nelakuditiet al. who have proposed similar schemes in the context of IP. Our methods are moreefficient than previous ones. We have also studied the existence of a resilient routingscheme for single node failure situation in switch-based network. We study also thecase of multi-link failure situations and show that requiring the network to be connectedafter any failure does not guarantee the existence of a resilent routing schemeas described above