Joints are the most critical elements in a steel framed structure. In most design guides or codes, the joints are assumed to a have higher fire resistance than the connected structural members because of the lower temperatures in the joints. However, in severe fire conditions, a connected beam's temperature may be higher than its limiting temperature and the beam may develop catenary action when the beam’s axial shortening from large deflections becomes greater than the beam’s thermal expansion. This beam catenary action force could fracture the joints, increasing the risk of progressive collapse. This research focuses on the interaction between joints and the connected steel beams and columns in steel framed structures in fire, including how the behaviour of a joint-beam assembly may be efficiently analyzed and how the joints may be constructed to achieve high degrees of catenary action. Three methods of simulating the joint behaviour in fire have been developed and implemented in the commercial finite element software ABAQUS. In the first modelling method, all structural members, including the connections, were simulated using detailed solid elements to enable detailed behaviour of the structure to be faithfully represented. In the second method, the columns were represented by conventional line (beam) elements, the joints were represented using springs (Connector Elements) based on the component based method, and the beam was modelled using solid elements. In the third method, the joints were modelled using springs as in the second method and the beam and columns were simulated using line (beam) elements. As expected, the detailed simulation method was extremely time-consuming, but was able to produce detailed and accurate results. The simulation results from the second and third methods contained some inaccuracies, but depending on the simulation objective, their simulation results may be acceptable. In particular, the third simulation method was very efficient, suitable for simulating complete frame structures under very large deflections in fire. The first method (detailed finite element method) was then used to investigate how to change the joint details to increase the survivability of restrained steel beams and beam-column assemblies at high temperatures since it enables detailed behaviour of the structure to be faithfully represented. It is found that by improving joint deformation capacity, in particular, using extended endplate connection with fire resistant bolts, very high temperatures can be resisted. The frame robustness in fire was investigated using the third simulation method to save computation time. The simulation structure was three-bay by three-floor and different scenarios of fire location, fire spread and initial structural damage were considered. The simulation results show that once failure of a column occurs, progressive collapse of the structure could be easily triggered and it would be rather futile to only enhance the joint capacity. Therefore, in addition to the measures of improving joint capacities (both rotation and strength), design of the affected columns should include consideration of the additional catenary forces from the connected beams and the increased effective lengths. Furthermore, the lateral bracing system should be ensured to provide the structure with lateral restraint.

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Dans cette thèse, nous nous intéressons à un problème de fiabilité dans les réseaux multicouches IP-sur-WDM. Etant donné un ensemble de demandes pour lesquelles on connaît une topologie fiable dans la couche IP, le problème consiste à sécuriser la couche optique WDM en y cherchant une topologie fiable. Nous montrons que le problème est NP-complet même dans le cas d'une seule demande. Ensuite, nous proposons quatre formulations en termes de programmes linéaires en nombres entiers pour le problème. La première est basée sur les contraintes de coupes. Nous considérons le polyèdre associé. Nous identifions de nouvelles familles de contraintes valides et étudions leur aspect facial. Nous proposons également des algorithmes de séparation pour ces contraintes. En utilisant ces résultats, nous développons un algorithme de coupes et branchements pour le problème et présentons une étude expérimentale. La deuxième formulation utilise comme variables des chemins entre des terminaux dans le graphe sous-jacent. Un algorithme de branchements et génération de colonnes est proposé pour cette formulation. Par la suite, nous discutons d'une formulation dite naturelle utilisant uniquement les variables de design. Enfin, nous présentons une formulation étendue compacte qui, en plus des variables naturelles, utilise des variables de routage. Nous montrons que cette formulation fournit une meilleure borne inférieure. / This thesis deals with a problem related to survivability issues in multilayer IP-over-WDM networks. Given a set of traffic demands for which we know a survivable logical routing in the IP layer, the aim is determine the corresponding survivable topology in the WDM layer. We show that the problem is NP-hard even for a single demand. Moreover, we propose four integer linear programming formulations for the problem. The first one is based on the so-called cut inequalities. We consider the polyhedron associated with the formulation. We identify several families of valid inequalities and discuss their facial aspect. We also develop separation routines. Using this, we devise a Branch-and-Cut algorithm and present experimental results. The second formulation uses paths between terminals of the underlying graph as variables. We devise a Branch-and-Price algorithm based on that formulation. In addition, we investigate a natural formulation for the problem which uses only the design variables.  Finally, we propose an extended compact formulation which, in addition to the design variables, uses routing variables. We show that this formulation provides a tighter bound for the problem.

Spacecraft fulfill a myriad of critical functions on orbit, from defense and intelligence to science, navigation, and telecommunication. Spacecraft can also cost several hundred millions of dollars to design and launch, and given that physical access for maintenance remains difficult if not impossible to date, designing high reliability and survivability into these systems is an engineering and financial imperative. While reliability is recognized as an essential attribute for spacecraft, little analysis has been done pertaining to actual field reliability of spacecraft and their subsystems. This thesis consists of two parts. The first part fills the gap in the current understanding of spacecraft failure behavior on orbit through extensive statistical analysis and modeling of anomaly and failure data of Earth-orbiting spacecraft. The second part builds on these results to develop a novel theoretical basis (interdependent multi-layer network approach) and algorithmic tools for the analysis of survivability of spacecraft and space-based networks. Space-based networks (SBNs) allow the sharing of on-orbit resources, such as data storage, processing, and downlink. Results indicate and quantify the incremental survivability improvement of the SBN over the traditional monolith architecture. A trade-space analysis is then conducted using non-descriptive networkable subsystems/technologies to explore survivability characteristics of space-based networks and help guide design choices.

Multiprotocol Label Switching (MPLS) fuses the intelligence of routing with the performance of switching and provides significant benefits to networks with a pure IP architecture as well as those with IP and ATM or a mix of ther Layer 2 technologies. MPLS technology is key to scalable virtual private networks (VPNs) and end-to-end quality of service (QoS), enabling efficient utilization of existing networks to meet future growth. The technology also helps to deliver highly scalable, differentiated end-to-end IP services with simpler configuration, management, and provisioning for both Internet providers and end-users. However, MPLS is a connection-oriented architecture. In case of failure MPLS first has to establish a new label switched path (LSP) and then forward the packets to the newly established LSP. For this reason MPLS has a slow restoration response to a link or node failure on the LSP.The thesis provides a description of MPLS-based architecture as a preferred technology for integrating ATM and IP technologies, followed by a discussion of the motivation for the fast and reliable restoration mechanism in an MPLS network. In this thesis first we address the fast rerouting mechanisms for MPLS networks and then we focus on the problem of packet loss, packet reordering and packet delay for protected LSP in MPLS-based network for a single node/link failure. In order to deliver true service assurance for guaranteed traffic on a protected LSP we use the fast rerouting mechanism with a preplanned alternative LSP. We propose enhancements to current proposals described in extant literature. Our fast rerouting mechanism avoids packet disorder and significantly reduces packet delay during the restoration period.An extension of the Fast Rerouting proposal, called Reliable and Fast Rerouting (RFR), provides some preventive actions for the protected LSP against packet loss during a failure. RFR maintains the same advantages of Fast Rerouting while eliminating packet losses, including those packet losses due to link or node failure (circulating on the failed links), which were considered to be "inevitable" up to now.For the purpose of validating and evaluating the behavior of these proposals a simulation tool was developed. It is based on the NS, a well-known network simulator that is being used extensively in research work. An extension featuring the basic functionality of MPLS (MNS) is also available for the NS, and this is the basis of the developed simulation tool.Simulation results allow the comparison of Fast Rerouting and RFR with previous rerouting proposals.In addition to this we propose a mechanism for multiple failure recovery in an LSP. This proposal combines the path protection, segment protection and local repair methods. In addition to the multiple link/node failure protection, the multiple fault tolerance proposal provides a significant reduction of delay that the rerouted traffic can experience after a link failure, because the repair action is taken close to the point of failure.Then we proceed to address an inherent problem of the preplanned alternative LSP. As alternative LSPs are established together with the protected LSP it may happen that the alternative is not the optimal LSP at the time the failure occurs. To overcome this undesired behavior, we propose the Optimal and Guaranteed Alternative Path (OGAP). The proposal uses a hybrid of fast-rerouting and a dynamic approach to establish the optimal alternative LSP while rerouting the affected traffic using the preplanned alternative LSP. This hybrid approach provides the best of the fast rerouting and the dynamic approaches.At the same time we observed that the protection path becomes in fact unprotected from additional failures after the traffic is rerouted onto it.To address this we propose a guarantee mechanism for protection of the new protected LSP carrying the affected traffic, by establishing an alternative LSP for the rerouted traffic after a failure, avoiding the vulnerability problem for the protected traffic.Finally, we present a further optimization mechanism, adaptive LSP, to enhance the existing traffic engineering for Quality of Services (QoS)provision and improve network resource utilization. The adaptive LSP proposal allows more flexibility in network resource allocation and utilization by adapting the LSP to variations in all network loads,resulting in an enhancement of existing MPLS traffic engineering.

The predictable nature of the tides offers a regular, reliable source of renewable energy that can be harnessed using tidal stream turbines (TSTs). The UK's practically extractable tidal stream energy resource has the potential to supply around 7 % of the country's annual electricity demand. As of 2016, the world's first commercial scale arrays have been deployed around the UK and France. The harsh nature of the marine operating environment poses a number of engineering challenges, where the optimal turbine design solution remains under investigation. In this thesis, a numerical model is developed to assess the power production and hydrodynamic behaviour of horizontal axis tidal turbines. The developed model builds upon well established and computationally efficient Blade Element Momentum Theory (BEMT) method for modern three-bladed wind turbines. The main novel contribution of this thesis is extending the application to an alternative design of a ducted, high solidity and open centre TST. A validation study using measurements from multiple different scale model experimental tank tests has proven the applicability of the model and suitability of the imposed correction factors. The analytical modifications to account for ducted flow were subsequently indirectly verified, where predictions of turbine power and axial thrust forces under optimal operating speeds were within 2 % of those using more advanced computational fluid dynamics (CFD) methods. This thesis presents a commercial application case of two turbines designed by OpenHydro, examining the BEMT performance with a sophisticated blade resolved CFD study. A comparison of results finds that the model is capable of predicting the average peak power to within 12 %, however it under predicts thrust levels by an average of 35 %. This study concludes that the model is applicable to ducted turbine configurations, but is limited in capturing the complex flow interactions towards the open centre, which requires further investigation. The computational efficiency of the newly developed model allowed a structural analysis of the composite blades, thus demonstrating it is suitable to effectively evaluate engineering applications. Stresses are seen to be dominated by flap-wise bending moments, which peak at the mid-length of the blade. This tool will further enable EDF to perform third party assessments of the different turbine designs, to aid decision making for future projects.

This report is one of the first to examine how system methodology can be applied as a tool to facilitate a holistic view of fighter aircraft survivability. This is done through the application of a modified version of multi-agent influence diagrams (MAIDs), as an analytical tool of two generic one-on-one scenarios based on Robert E. Balls The Fundamentals of Aircraft Combat Survivability, Analysis and Design. The concept of survivability has been limited to susceptibility because this is where ECM, ECCM and ESM operate. The result: three influence diagrams for each scenario and a generic MAID developed for the first scenario. These should not be seen as an exact technical description of the interaction between threats and countermeasures, but as a pilot application of system methodology within the study area. Furthermore, the user validation indicates that the diagrams can convey the complexity of the interactions between threats and countermeasures through a graphical presentation. The diagrams led to a deeper discussion about which influences are important for survival. The conclusion is that MAID and systems methodology can serve as a tool to describe and help communicate the complex relationships between elements and influences that affect the aircraft's survivability between different actors, provided they are modelled correctly. / Denna rapport är en av de första som undersöker hur systemmetodik kan tillämpas som ett verktyg för att underlätta en holistisk syn på stridsflygplans överlevnadsförmåga. Detta görs genom tillämpningen av en modifierad version av multiagent influence diagrams (MAIDs) som ett analysverktyg av två generiska en-mot-en-scenarier baserade på Robert E. Balls The Fundamentals of Aircraft Combat Survivability, Analysis and Design. Begreppet överlevnadsförmåga har avgränsats till mottaglighet eftersom det är här ECM, ECCM och ESM verkar. Resultatet: tre influensdiagram för varje scenario och ett generisk MAID baserat på det första scenariot. Dessa ska inte ses som en exakt teknisk beskrivning av interaktionen mellan hot och motmedel, utan som en pilottillämpning av systemmetodik inom studieområdet. Vidare indikerar användarvalideringen att diagrammen kan förmedla komplexiteten i interaktionerna mellan hot och motmedel genom en grafisk presentation. Diagrammen ledde till en djupare diskussion om vilka influenser som är av vikt för överlevnad. Slutsatsen är att MAID och systemmetodik kan fungera som ett verktyg för att beskriva och hjälpa till att kommunicera de komplexa sambanden mellan element och influenser som påverkar flygplanens överlevnadsförmåga mellan olika aktörer. En förutsättning är dock att de modelleras på ett korrekt sätt.

Field Programmable Gate Array (FPGA) devices offer a suitable platform for survivable hardware architectures in mission-critical systems. In this dissertation, active dynamic redundancy-based fault-handling techniques are proposed which exploit the dynamic partial reconfiguration capability of SRAM-based FPGAs. Self-adaptation is realized by employing reconfiguration in detection, diagnosis, and recovery phases. To extend these concepts to semiconductor aging and process variation in the deep submicron era, resilient adaptable processing systems are sought to maintain quality and throughput requirements despite the vulnerabilities of the underlying computational devices. A new approach to autonomous fault-handling which addresses these goals is developed using only a uniplex hardware arrangement. It operates by observing a health metric to achieve Fault Demotion using Recon- figurable Slack (FaDReS). Here an autonomous fault isolation scheme is employed which neither requires test vectors nor suspends the computational throughput, but instead observes the value of a health metric based on runtime input. The deterministic flow of the fault isolation scheme guarantees success in a bounded number of reconfigurations of the FPGA fabric. FaDReS is then extended to the Priority Using Resource Escalation (PURE) online redundancy scheme which considers fault-isolation latency and throughput trade-offs under a dynamic spare arrangement. While deep-submicron designs introduce new challenges, use of adaptive techniques are seen to provide several promising avenues for improving resilience. The scheme developed is demonstrated by hardware design of various signal processing circuits and their implementation on a Xilinx Virtex-4 FPGA device. These include a Discrete Cosine Transform (DCT) core, Motion Estimation (ME) engine, Finite Impulse Response (FIR) Filter, Support Vector Machine (SVM), and Advanced Encryption Standard (AES) blocks in addition to MCNC benchmark circuits. A iii significant reduction in power consumption is achieved ranging from 83% for low motion-activity scenes to 12.5% for high motion activity video scenes in a novel ME engine configuration. For a typical benchmark video sequence, PURE is shown to maintain a PSNR baseline near 32dB. The diagnosability, reconfiguration latency, and resource overhead of each approach is analyzed. Compared to previous alternatives, PURE maintains a PSNR within a difference of 4.02dB to 6.67dB from the fault-free baseline by escalating healthy resources to higher-priority signal processing functions. The results indicate the benefits of priority-aware resiliency over conventional redundancy approaches in terms of fault-recovery, power consumption, and resource-area requirements. Together, these provide a broad range of strategies to achieve autonomous recovery of reconfigurable logic devices under a variety of constraints, operating conditions, and optimization criteria.

<p dir="ltr">A current engineering challenge is to understand and validate material systems capable of maintaining structural viability under the elevated temperature and environmental conditions of hypersonic flight. One aspect of this challenge is the joining of multiple materials with thermal expansion mismatch, which can lead to residual stress, resulting in debits in component lifetime under in-service loading. The focus of this work is a series of studies focused on a ceramic-metal composite (WC/Cu), a zirconia coating applied to a carboncarbon (C/C) composite, and a silicide (R512E) coating applied to a Nb-based alloy (C103). Each of these material systems are candidates for elevated temperature applications in which dissimilar constituents result in residual stress in the material. Each study leveraged experimental residual strain measurements, with the primary focus on the use of synchrotron X-ray diffraction, in conjunction with representative models, and microscopy to illuminate the active mechanisms in the development and evolution of residual stress in the bulk material. The combination of experimental and modeling predictions provides a framework to inform the viability and lifing of material systems exhibiting dissimilar expansion properties.</p>