No description available.

Wireless Sensor Networks (WSNs) are composed of a large number of battery-powered sensor nodes that have the ability to sense the physical environment, compute the obtained information and communicate using the radio interfaces. Because sensor nodes are generally deployed on a large and wild area, they are powered by embedded battery. And it is difficult to change or recharge the battery, thus to reduce the energy consumption when sensors and protocols are designed is very important and can extend the lifetime of WSNs. So sensor nodes transmit packets with a lower transmission power (e.g. OdBm). With this transmission power, a packet can only be transmitted dozens of meters away. Therefore, when a sensor detects an event, a packet is sent in a multi-hop, ad-hoc manner (without fixed infrastructure and each sensor is able to relay the packet) to the sink (specific node which gathers information and reacts to the network situation). In this thesis, we first give an elaborate state of the art of WSNs. Then the impacts of duty-cycle and unreliable links or the performances of routing layer are analyzed. Based on the analytical results, we then propose three new simple yet effective methods to construct virtual coordinates under unreliable links in WSNs. By further taking the duty-cycle and real-time constraints into consideration we propose two cross-layer forwarding protocols which can have a greater delivery ratio and satisfy the deadline requirements. In order to have protocols for the WSNs that have dynamic topology, we then propose a robust forwarding protocol which can adapt its parameters when the topology changes. At last, we conclude this thesis and give some perspectives.

The size of the IoT network is expanding due to advancements in the IoT field, leading to increased interest in the multi-sink mechanism. The IPv6 Routing Protocol for Low-Power and Lossy Networks (RPL) is a representative IoT protocol that focuses on the Low-Power and Lossy Networks. However, research on comparing multi-sink strategies within the RPL network is limited. Therefore, this project aims to compare three common strategies: multiple-DODAG in one instance, virtual root, and multiple-instance. Using these strategies, we design and implement RPL networks and conduct simulations in various scenarios. Five different topologies are utilized in the experiments, considering different packet loss rates. Performance evaluation of each strategy is conducted using the Cooja simulator and Contiki-NG system, with a focus on the number of RPL control packets, Packet Delivery Ratio (PDR), and energy consumption. The results indicate that both the virtual root and multiple-DODAG strategies perform well with low packet loss, while the virtual root strategy outperforms the multiple-DODAG strategy with high packet loss. Additionally, the virtual root strategy incurs slightly higher energy costs than the multiple-DODAG strategy. Furthermore, the multiple-instance strategy demonstrates poor performance in most scenarios, except for the packet delivery ratio under high packet loss conditions. Besides the analysis, potential areas for future research on the RPL’s multi-sink mechanism are finally identified. / Storleken på IoT-nätverket expanderar på grund av framsteg inom IoT-området, vilket leder till ökat intresse för multi-sink-mekanismen. IPv6 Routing Protocol for Low-Power and Lossy Networks (RPL) är ett representativt IoT-protokoll som fokuserar på Nät med låg effekt och förluster. Forskningen om jämförelse av multi-sink-strategier inom RPL-nätverket är dock begränsad. Därför syftar detta projekt till att jämföra tre vanliga strategier: multiple - DODAG i en instans, virtuell rot och multi-instans. Med hjälp av dessa strategier designar och implementerar vi RPL-nätverk och genomför simuleringar i olika scenarier. Fem olika topologier används i experimenten, med olika packet loss rate. Prestationsutvärdering av varje strategi utförs med hjälp av Cooja-simulatorn och Contiki-NG-systemet, med fokus på antalet RPL control packets, Packet Delivery Ratio (PDR) och energiförbrukning. Resultaten indikerar att både virtuell rot och multiple-DODAG strategier fungerar bra vid låg datapaketförlust, medan den virtuella rotstrategin överträffar multiple-DODAG strategin vid hög datapaketförlust. Dessutom medför den virtuella rotstrategin något högre energikostnader än flera DODAG-strategin. Dessutom visar multi-instans-strategin dålig prestanda i de flesta scenarier, förutom när det gäller datapaketleveransförhållandet under höga datapaketförlustförhållanden. Utöver analysen identifieras slutligen potentiella områden för framtida forskning om RPL-protokollets multi-sink-mekanism.

Les réseaux de capteurs sans fils (WSN) sont composés d'un très grand nombre de capteurs, capables de mesurer des paramètres physiques de l'environnement, de mettre en forme l'information obtenue et de la communiquer aux autres capteurs grâce à une interface radio. Les capteurs étant en général déployés sur de très grandes étendues géographiques, l'énergie nécessaire pour les faire fonctionner est fournie par une batterie embarquée sur le capteur. En général, il est difficile de recharger les batteries une fois les capteurs déployés. Economiser l'énergie est donc une préoccupation constante lors de la conception des capteurs et des protocoles de communication utilisés, de manière à prolonger la durée de vie du réseau. Dans ce but, les capteurs transmettent leurs données avec des puissances d'émission très faibles. Avec de telles puissances d'émission, un message ne peut être transmis que sur quelques dizaine de mètres. De ce fait, lorsqu'un capteur détecte un événement, le message est transmis en mode ad-hoc multisauts jusqu'au puits, un nœud spécifique du réseau, qui récolte toutes les informations et est capable de réagir de manière adéquate. Dans cette thèse, nous donnons d'abord un état de l'art avancé sur les WSN. Ensuite nous analysons l'impact du cycle d'endormissement et des liens non fiable sur la couche de routage. A partir des résultats analytiques, nous proposons trois méthodes originales, simples et efficaces pour construire des coordonnées virtuelles en prenant en compte la non fiabilité des liens dans les WSN. En prenant en compte le cycle d'endormissement et les contraintes temps-réel, nous proposons deux protocoles cross-layer qui ont de bons taux de livraison et qui permettent de respecter des contraintes temporelles. Pour pallier à la dynamicité des réseaux de capteurs sans fil, nous proposons un protocole de routage robuste qui adapte ses paramètres quand la topologie change. Enfin, nous concluons et donnons quelques perspectives. / Wireless Sensor Networks (WSNs) are composed of a large number of battery-powered sensor nodes that have the ability to sense the physical environment, compute the obtained information and communicate using the radio interfaces. Because sensor nodes are generally deployed on a large and wild area, they are powered by embedded battery. And it is difficult to change or recharge the battery, thus to reduce the energy consumption when sensors and protocols are designed is very important and can extend the lifetime of WSNs. So sensor nodes transmit packets with a lower transmission power (e.g. OdBm). With this transmission power, a packet can only be transmitted dozens of meters away. Therefore, when a sensor detects an event, a packet is sent in a multi-hop, ad-hoc manner (without fixed infrastructure and each sensor is able to relay the packet) to the sink (specific node which gathers information and reacts to the network situation). In this thesis, we first give an elaborate state of the art of WSNs. Then the impacts of duty-cycle and unreliable links or the performances of routing layer are analyzed. Based on the analytical results, we then propose three new simple yet effective methods to construct virtual coordinates under unreliable links in WSNs. By further taking the duty-cycle and real-time constraints into consideration we propose two cross-layer forwarding protocols which can have a greater delivery ratio and satisfy the deadline requirements. In order to have protocols for the WSNs that have dynamic topology, we then propose a robust forwarding protocol which can adapt its parameters when the topology changes. At last, we conclude this thesis and give some perspectives.

Orientador: Carlos Alberto Carrasco Altemani / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-08-06T09:32:44Z (GMT). No. of bitstreams: 1 Souza_ValterCesarde_D.pdf: 4532174 bytes, checksum: 07cf885bb91505cb080fc4a067621191 (MD5) Previous issue date: 2005 / Resumo: Os dissipadores térmicos de placas paralelas com entrada de topo e saída lateral constituem uma alternativa para intensificar a remoção da potência elétrica dissipada em microprocessadores. Neste trabalho, três dissipadores térmicos de placas paralelas foram construídos e testados com escoamento variável de ar sob condições de entrada de topo e saída lateral. Os resultados experimentais foram comparados com correlações da literatura e com resultados de simulações numéricas tridimensionais. Após a validação com os resultados experimentais, o modelo numérico foi utilizado num procedimento para obter o número de aletas do dissipador para a máxima troca térmica convectiva. Dois casos foram considerados, um deles baseado numa velocidade média do ar constante na entrada do dissipador, e o outro, numa relação linear da curva de operação de um ventilador / Abstract: The parallel plates heat sinks with top inlet and side exit constitute an enhanced heat transfer alternative for the local removal of electric power dissipation in microprocessors. In the present work, three parallel plates heat sinks were built and tested with variable airflow under the conditions of top inlet and side exit. The experimental results were compared with correlations from the literature and with results from three-dimensional numerical simulations. After the validation with the experimental results, the numeric model was used in an optimization procedure to obtain the heat sink number of fins for the maximum convective heat transfer. Two cases were considered, one based on a constant average inlet air velocity, and the other, on an assumed linear fan curve / Doutorado / Termica e Fluidos / Doutor em Engenharia Mecânica

Carbon dioxide from biogas production is currently considered to be without value and isbecause of this released into the atmosphere in the biogas upgrading process. The residualgas is a potential carbon source and can create value in the biogas manufacturing process.By finding a suitable value-creating process that utilizes carbon dioxide, it can be possibleto provide both economic and environmental incentives for companies to develop theiroperations. This project explored the possibility to create value from this CO2. Through anevaluation of the technical maturity of CCU technologies, a recommendation could be givenat the end of the project. An analysis of technical barriers, such as pollutants in the gas, aswell as barriers in the form of competence and corporate culture were examined in orderto provide a reasoned recommendation. The project mapped which value-creating systemswould be suitable for biogas producers in a Swedish context. This included established methaneand carbon dioxide upgrading techniques currently in use and suitable CCU techniquesthat can interact with the selected upgrading processes and serve as value creators. Based onthis survey, it was then possible to identify common, critical variables for these systems. Thereafter,a recommendation of an appropriate CCU technology could be given depending onthe CO2 composition produced. One conclusion from the study was that carbon dioxide concentrationsfrom the residual gas was often high (approx. 97-98 %) and did not contain anycorrosive or toxic components, and that this largely depends on how the digestion reactor ishandled in the production process. Thus, questions were raised about what the actual limitationsof the CCU are, as they did not seem to be technical. CCU techniques that proved to beof particular interest were pH regulation of sewage plants, CO2 as a nutrient substrate for thecultivation of microalgae, and manufacturing of dry-ice for refrigerated transports. All of thesetechnologies currently have a sufficiently high degree of technical maturity to be installedalready today. Other CCU techniques, such as "’Power to gas”, require a high CO2 concentrationand were discarded as the literature review did not suggest the economic potential forthem as they require additional CO2 upgrading steps. Instead, CCU techniques were chosenthat could be implemented directly with the existing CO2 quality. Furthermore, it was concludedthat one reason why CCU technologies have not been widely implemented is internalbarriers between distributors and manufacturers (or users) of CCU technologies. Thus, theuse of carbon dioxide from biogas production and implementation of CCU technologies canbe promoted by eliminating barriers in companies, such as a lack of both knowledge andfinancial incentives. / Koldioxid från biogasproduktion betraktas i dagsläget som utan värde och släpps ut i atmosfärenvid uppgradering av biogas. Restgasen är en potentiell kolkälla och kan vara värdeskapandeför biogasprocessen. Genom att finna en lämplig värdeskapande process som utnyttjarkoldioxid går det att ge både ekonomiska och miljömässiga incitament till företag att utvecklasin verksamhet. I detta projekt undersöktes möjligheten att skapa värde av denna CO2.Genom en utvärdering av den tekniska mognadsgraden hos CCU-tekniker kunde en rekommendationges vid projektets slut. En analys av tekniska hinder, såsom föroreningar i gassammansättningen,såväl som hinder i form av kompetens och företagskultur undersöktes för attkunna ge en motiverad rekommendation. I projektet kartlades vilka värdeskapande systemsom skulle passa för biogasproducenter i en svensk kontext. Detta inkluderade etableradeuppgraderingstekniker för metan- och koldioxid som används i dagsläget. I projektet undersöktesäven lämpliga CCU-tekniker som kan samverka med de valda uppgraderingsprocessernaoch och agera värdeskapande. Utifrån denna kartläggning kunde det sedan anges vilkagemensamma, kritiska variabler som finns för dessa system. Därefter kunde en rekommendationav lämplig CCU-teknik ges beroende på den producerade CO2 sammansättningen. Enslutsats i projektet var att koldioxid från restgasen ofta var av hög koncentration (ca. 97-98 %)och ej innehöll några korrosiva eller toxiska komponenter, och att detta till stor del beror påhur rötkammaren är hanterad i produktionsprocessen. Således väcktes frågor kring vilka defaktiska begränsningarna för CCU är, då de inte torde vara tekniska. CCU-tekniker som visadesig vara av särskilt intresse var pH-reglering av avloppsverk, CO2 som näringssubstratför odling av mikroalger, samt tillverkning av kolsyreis för kyltransporter. Samtliga dessatekniker har tillräckligt hög teknisk mognadsgrad för att kunna installeras i dagsläget. AndraCCU-tekniker, såsom ”Power to gas”, kräver en hög CO2-koncentration och avfärdades dålitteraturstudien inte talade för den ekonomiska potentialen i dessa eftersom de kräver ytterligareuppgraderingssteg för CO2. Således valdes istället CCU-tekniker som skulle gå attimplementera direkt med den befintliga CO2 kvalitén. Vidare drogs slutsatsen att en anledningtill att CCU-tekniker inte har blivit vida implementerade till stor del är interna hindermellan distributörer och tillverkare (eller utnyttjare) av CCU-tekniker. Således kan användandetav koldioxid från biogasproduktion och implementering av CCU-tekniker främjasgenom att eliminera hinder hos företag. I projektet yttrade sig detta som bristande ekonomiskaincitament och okunskap. Ett ökat användande av CCU-tekniker kan också uppnås genomatt införa lagar och regler som begränsar användandet av föråldrade tekniker som drivs avfossila bränslen, och som kan ersättas av klimatvänliga CCU-tekniker.

No description available.