A Causal-Based Consistent Update Approach for Software-Defined Networks

Software-Defined Network (SDN) is a network paradigm that has been recently introduced. Unlike traditional networks, e.g. IP networks, SDNs separate the network control logic from forwarding devices, and delegate network management tasks to a logically-centralized entity called the controller. However, SDN is still a distributed and asynchronous system. In fact, during forwarding policy updates, any network entity may trigger update events at any time, e.g. the sending of messages or data packets, while they are prone to arbitrary and unpredictable transmission delays. Moreover, the absence of an agreed and common temporal reference results in a broad combinatorial range space of event order. An out-of-order execution of events may lead to invariant violations, e.g. forwarding loops and forwarding blackholes, referred to as inconsistent updates. Some works tackle the issue of inconsistent updates by imposing global time references; however, they do not compromise consistency during updates as clocks of entities cannot be perfectly synchronized. Other solutions lie on performing updates on different rounds, i.e. steps, while each update step guarantees consistency. These solutions compromise consistency during updates; however, performing updates over different steps may congest the communication canals between the controller and the forwarding devices, leading to bandwidth overhead. In this dissertation, we propose a causal-based consistent update approach that ensures the connectivity update properties: transient forwarding loop-free and transient forwarding blackhole-free. This is achieved by defining a formal model of the two connectivity invariant violations as a specification of the Happened-Before relation of Lamport. Based on this model, network update policies are introduced by establishing causal dependencies between relevant update events. These update policies are reflected by an update mechanism oriented towards transient connectivity inconsistency-free SDN updates. To prove the correctness of the update mechanism, it was demonstrated that it is sufficient to ensure the transient forwarding loop-free and the transient forwarding blackhole-free properties. In terms of findings, the formal modelisation of the two connectivity update properties defines the root cause of their triggering and capture the conditions under which they may occur

Analyse des conditions de rupture des conduites d’adduction d’eau potable en polyéthylène, sous l’effet d’écoulement transitoire, en présence d’un défaut

The efficiency of potable water distribution systems has been recently the subject of much research. Leakages or a ruptures, occurring in pipes, are quite a frequent phenomenon in urban areas. In order to minimize long-term risks of leakage, about 60% of potable water networks are built or renewed with the third generation of polyethylene pipe, PE100. It is a material with various features, which makes it a widely used material in the water supply networks. However, under transient conditions and with a surficial defect in the pipe, a failure occurs. To investigate this issue, our study is divided into two main parts. The first part is studying the dynamic effect of the viscoelastic material under transient flow conditions using a developed mathematical model. We have demonstrated that the viscoelastic behavior of PE100 plays a primordial role in the damping of water hammer and resonance phenomenon. In case of presence of coupling junction, a study of the fluid structure interaction is mandatory to correctly define the natural frequencies of a piping system. In the second part, we have investigated the crack behavior of PE100 pipes with defects. Using the experimental tests and finite elements results, we have demonstrated that the concept of elastic-plastic fracture mechanics, the J-Integral, define with reasonable accuracy the behavior of cracked PE100-pipe. At the end, we sought to determine the J-Integral with a semi-empirical model in order to define a relationship between the crack initiation pressure, the dimension of semi-elliptical surface cracks and the geometry of the pipeLe problème du rendement de la distribution des eaux potables a récemment fait l’objet de nombreux travaux de recherche. En effet, les ruptures des canalisations et les fuites sont des phénomènes assez fréquents en milieu urbain. Afin de réduire au maximum les risques de fuite à long terme, près de 60 % des réseaux d’eau potable sont construits ou renouvelés avec des conduites en polyéthylène de troisième génération, PE100. De par ses caractéristiques, c’est un matériau de choix pour les réseaux d’adduction d’eau. Mais la présence d’un défaut superficiel peut générer la rupture de la conduite sous l’effet d’écoulement transitoire. Afin d’étudier ce problème, notre étude est décomposée en deux parties. La première est consacrée à l’étude de l’effet dynamique du comportement viscoélastique du matériau sur l’écoulement transitoire à l’aide d’un modèle mathématique que nous avons développé dans cette thèse. Nous avons démontré que le comportement viscoélastique du PE100 joue un rôle primordial dans l’amortissement du phénomène du coup de bélier et de résonance. En cas de présence de couplage de jonction, l’étude de l’interaction fluide-structure est nécessaire pour définir correctement les fréquences propres d’un système de conduites. Ensuite, dans la seconde partie, nous avons étudié le comportement à la fissuration des conduites en PE100 présentant un défaut. A l’aide d’essais expérimentaux et de modélisations par éléments finis, nous avons démontré que le concept de la mécanique élasto-plastique de rupture, l’intégrale J, peut définir avec une précision acceptable le comportement à la fissuration d’une conduite en PE100. Nous avons cherché à déterminer l’intégrale J à l’aide d’un modèle semi-empirique afin de définir une relation entre la pression d’amorçage de fissure, la taille de défaut (fissure semi-elliptique) et la géométrie de la conduit

Failure analysis of drinking water polyethylene pipe under the effect of transient flow in the presence of a defect

Le problème du rendement de la distribution des eaux potables a récemment fait l’objet de nombreux travaux de recherche. En effet, les ruptures des canalisations et les fuites sont des phénomènes assez fréquents en milieu urbain. Afin de réduire au maximum les risques de fuite à long terme, près de 60 % des réseaux d’eau potable sont construits ou renouvelés avec des conduites en polyéthylène de troisième génération, PE100. De par ses caractéristiques, c’est un matériau de choix pour les réseaux d’adduction d’eau. Mais la présence d’un défaut superficiel peut générer la rupture de la conduite sous l’effet d’écoulement transitoire. Afin d’étudier ce problème, notre étude est décomposée en deux parties. La première est consacrée à l’étude de l’effet dynamique du comportement viscoélastique du matériau sur l’écoulement transitoire à l’aide d’un modèle mathématique que nous avons développé dans cette thèse. Nous avons démontré que le comportement viscoélastique du PE100 joue un rôle primordial dans l’amortissement du phénomène du coup de bélier et de résonance. En cas de présence de couplage de jonction, l’étude de l’interaction fluide-structure est nécessaire pour définir correctement les fréquences propres d’un système de conduites. Ensuite, dans la seconde partie, nous avons étudié le comportement à la fissuration des conduites en PE100 présentant un défaut. A l’aide d’essais expérimentaux et de modélisations par éléments finis, nous avons démontré que le concept de la mécanique élasto-plastique de rupture, l’intégrale J, peut définir avec une précision acceptable le comportement à la fissuration d’une conduite en PE100. Nous avons cherché à déterminer l’intégrale J à l’aide d’un modèle semi-empirique afin de définir une relation entre la pression d’amorçage de fissure, la taille de défaut (fissure semi-elliptique) et la géométrie de la conduiteThe efficiency of potable water distribution systems has been recently the subject of much research. Leakages or a ruptures, occurring in pipes, are quite a frequent phenomenon in urban areas. In order to minimize long-term risks of leakage, about 60% of potable water networks are built or renewed with the third generation of polyethylene pipe, PE100. It is a material with various features, which makes it a widely used material in the water supply networks. However, under transient conditions and with a surficial defect in the pipe, a failure occurs. To investigate this issue, our study is divided into two main parts. The first part is studying the dynamic effect of the viscoelastic material under transient flow conditions using a developed mathematical model. We have demonstrated that the viscoelastic behavior of PE100 plays a primordial role in the damping of water hammer and resonance phenomenon. In case of presence of coupling junction, a study of the fluid structure interaction is mandatory to correctly define the natural frequencies of a piping system. In the second part, we have investigated the crack behavior of PE100 pipes with defects. Using the experimental tests and finite elements results, we have demonstrated that the concept of elastic-plastic fracture mechanics, the J-Integral, define with reasonable accuracy the behavior of cracked PE100-pipe. At the end, we sought to determine the J-Integral with a semi-empirical model in order to define a relationship between the crack initiation pressure, the dimension of semi-elliptical surface cracks and the geometry of the pip

Effect of integrating polymeric pipes on the pressure evolution and failure assessment in cast iron branched networks

International audiencePressure response and structural integrity assessment of cast iron and HDPE pipes were investigated in this study. The failure analysis of pipes in a branched network was considered taking into consideration the maximum stress generated by hydraulic transient events and the presence of an initial external semi-elliptical defect. The numerical study was conducted based on a developed non-conventional transient solver that incorporates the viscoelasticity of polymeric pipes. Considering the replacement of pipes located in sensitive zones with high-density polyethylene (HDPE) pipes, the pressure evolution of the network was evaluated for different network states at different locations. The integration of polymeric pipes in the originally cast-iron network provided remarkable pressure wave damping and dispersing in some locations. Since the failure of pipes with a corrosion crater is likely to occur when the admissible stress is reached, a structural integrity analysis was conducted. Failure Assessment Diagram (FAD) using the SINTAP code was considered to calculate the safety factors for cast iron pipes with different metallic-plastic combinations, whereas a semi-empirical model that calculates the J-integral is used for HDPE pipes. The results of this study conclude that high attention should be paid when a longitudinal crack is located in the pipelines. It may be possible for integrated polymeric pipes to alleviate the risk of failure in the network. However, under large crack geometries, additional measures should be taken

Structural integrity assessment of defected high density poly-ethylene pipe: Burst test and finite element analysis based on J-integral criterion

International audienceThe main objective of this study was to analyze the integrity of a defective high density poly-ethylene (HDPE) pipe by computing the J-integral. To this end, an experimental test was performed to measure the toughness and to determine the mechanical behavior of the HDPE. Many burst tests were achieved on longitudinally notched pipe specimens subjected to internal pressure. The defect was machined by a disc cutter with 0.5 mm thickness. So the notch geometry was given by the disc cutter penetration in the pipe wall. Numerical simulations based on the computation of the J-integral were used to analyze the fracture behavior of these structures (notched pipe and pre-cracked pipe). The numerical results were discussed and compared with the experimental tests. Using the critical value of J-integral, the numerical simulations allowed determining the crack initiation pressure and the opening stress in the vicinity of the defect root. Numerical results show that there is a gap between the crack initiation pressures of pre-cracked pipe and those of the notched pipe. This gap increases when the defect is deeper than half of the wall thickness. These pressures decrease parabolically with the defect depth

Investigation of viscoelastic effects on transient flow in a relatively long PE100 pipe

International audienceIn this paper, the dynamic effect of the viscoelastic behavior of PE100 material, on the transient flow in a relatively long pipe, has been studied. At first, to study the transient flow in pipes with fluid structure interaction (FSI), two mathematical models, i.e., fully coupled four equation model and simplified two equation model, have been developed. The method of characteristics has been used to solve the model. Then, we have demonstrated that the viscoelastic behavior of PE100 plays a primordial role in the damping of the water hammer phenomenon. It has a dynamic effect to cause the decrease of pressure wave velocity with increase of pressure along the wave front. At the end of the paper, It has been shown that the coupled model with FSI does not introduce many changes from the simplified viscoelastic model