Fault tolerant embedded systems design by multi-objective optimization

The design of fault tolerant systems is gaining importance in large domains of embedded applications where design constrains are as important as reliability. New software techniques, based on selective application of redundancy, have shown remarkable fault coverage with reduced costs and overheads. However, the large number of different solutions provided by these techniques, and the costly process to assess their reliability, make the design space exploration a very difficult and time-consuming task. This paper proposes the integration of a multi-objective optimization tool with a software hardening environment to perform an automatic design space exploration in the search for the best trade-offs between reliability, cost, and performance. The first tool is commanded by a genetic algorithm which can simultaneously fulfill many design goals thanks to the use of the NSGA-II multi-objective algorithm. The second is a compiler-based infrastructure that automatically produces selective protected (hardened) versions of the software and generates accurate overhead reports and fault coverage estimations. The advantages of our proposal are illustrated by means of a complex and detailed case study involving a typical embedded application, the AES (Advanced Encryption Standard).

S-SETA: Selective Software-Only Error-Detection Technique Using Assertions

Software-based techniques offer several advantages to increase the reliability of processor-based systems at very low cost, but they cause performance degradation and an increase of the code size. To meet constraints in performance and memory, we propose SETA, a new control-flow software-only technique that uses assertions to detect errors affecting the program flow. SETA is an independent technique, but it was conceived to work together with previously proposed data-flow techniques that aim at reducing performance and memory overheads. Thus, SETA is combined with such data-flow techniques and submitted to a fault injection campaign. Simulation and neutron induced SEE tests show high fault coverage at performance and memory overheads inferior to the state-of-the-art.

Relevance of microstructural influences in the short crack regime to overall fatigue resistance

The behaviour of short fatigue cracks is shown to be relevant only to a limited number of engineering situations. Within these situations, further restrictions on the extent to which metallurgical control can be exerted to improve fatigue crack growth behaviour are identified. The degree of control remaining is discussed in terms of two separate regimes which are described as intrinsic and extrinsic crack growth resistance. These separate effects are highlighted by comparisons both within and between a wide range of alloy systems. The implications of such an analysis are discussed in terms of aerospace applications.

Three-port DC-DC converter for stand-alone photovoltaic systems

System efficiency and cost effectiveness are of critical importance for photovoltaic (PV) systems. This paper addresses the two issues by developing a novel three-port dc-dc converter for stand-alone PV systems, based on an improved Flyback-Forward topology. It provides a compact single-unit solution with a combined feature of optimized maximum power point tracking (MPPT), high step-up ratio, galvanic isolation, and multiple operating modes for domestic and aerospace applications. A theoretical analysis is conducted to analyze the operating modes followed by simulation and experimental work. This paper is focused on a comprehensive modulation strategy utilizing both PWM and phase-shifted control that satisfies the requirement of PV power systems to achieve MPPT and output voltage regulation. A 250-W converter was designed and prototyped to provide experimental verification in term of system integration and high conversion efficiency.

Desarrollo de un dispositivo de liberación para la industria aeroespacial basado en una aleación con memoria de forma de NiTi.

Los dispositivos liberadores son utilizados en los satélites para desplegar los paneles solares, antenas y otros apéndices en las etapas iniciales de su puesta en órbita. En la actualidad, muchos de estos dispositivos tienen actuadores activados con cargas pirotécnicas. Esto trae algunas desventajas: niveles de shock elevados sobre los componentes cercanos, no son reutilizables y no son seguros de manipular. Por ello, es que desde hace unos años se están realizando importantes esfuerzos para desarrollar dispositivos no-pirotécnicos. En este trabajo se realiza el desarrollo de un dispositivo liberador que utiliza como actuador un cilindro tubular de una Aleación de Memoria de Forma (SMA, del inglés Shape Memory Alloys) de NiTi. Las SMAs tienen la posibilidad de deformarse por debajo de determinada temperatura y luego al calentarse, recuperar su forma original. Al restringir mecánicamente la trayectoria de recuperación, la aleación genera un esfuerzo mecánico. En el presente trabajo se caracteriza esta aleación, recurriendo a diversos tratamientos térmicos para obtener las propiedades deseadas. La liberación del conjunto se produce cuando el elemento de unión entre las piezas, el cual consiste en un bulón con una entalla circunferencial, se fractura debido al estiramiento de un actuador de NiTi previamente comprimido. Dada la importancia del bulón, se estudiaron diversos materiales para el mismo. Además se analizó el efecto de la geometría de la entalla y la profundidad de la misma. Finalmente, se realizaron pruebas de integración entre el actuador de SMA, el bulón y otros elementos auxiliares. Se pudo probar el funcionamiento del conjunto con éxito.

Desarrollo de un dispositivo de liberación para la industria aeroespacial basado en una aleación con memoria de forma de NiTi.

Los dispositivos liberadores son utilizados en los satélites para desplegar los paneles solares, antenas y otros apéndices en las etapas iniciales de su puesta en órbita. En la actualidad, muchos de estos dispositivos tienen actuadores activados con cargas pirotécnicas. Esto trae algunas desventajas: niveles de shock elevados sobre los componentes cercanos, no son reutilizables y no son seguros de manipular. Por ello, es que desde hace unos años se están realizando importantes esfuerzos para desarrollar dispositivos no-pirotécnicos. En este trabajo se realiza el desarrollo de un dispositivo liberador que utiliza como actuador un cilindro tubular de una Aleación de Memoria de Forma (SMA, del inglés Shape Memory Alloys) de NiTi. Las SMAs tienen la posibilidad de deformarse por debajo de determinada temperatura y luego al calentarse, recuperar su forma original. Al restringir mecánicamente la trayectoria de recuperación, la aleación genera un esfuerzo mecánico. En el presente trabajo se caracteriza esta aleación, recurriendo a diversos tratamientos térmicos para obtener las propiedades deseadas. La liberación del conjunto se produce cuando el elemento de unión entre las piezas, el cual consiste en un bulón con una entalla circunferencial, se fractura debido al estiramiento de un actuador de NiTi previamente comprimido. Dada la importancia del bulón, se estudiaron diversos materiales para el mismo. Además se analizó el efecto de la geometría de la entalla y la profundidad de la misma. Finalmente, se realizaron pruebas de integración entre el actuador de SMA, el bulón y otros elementos auxiliares. Se pudo probar el funcionamiento del conjunto con éxito.

Self-sealing of thermal fatigue and mechanical damage in fiber-reinforced composite materials

Fiber reinforced composite tanks provide a promising method of storage for liquid oxygen and hydrogen for aerospace applications. The inherent thermal fatigue of these vessels leads to the formation of microcracks, which allow gas phase leakage across the tank walls. In this dissertation, self-healing functionality is imparted to a structural composite to effectively seal microcracks induced by both mechanical and thermal loading cycles. Two different microencapsulated healing chemistries are investigated in woven glass fiber/epoxy and uni-weave carbon fiber/epoxy composites. Self-healing of mechanically induced damage was first studied in a room temperature cured plain weave E-glass/epoxy composite with encapsulated dicyclopentadiene (DCPD) monomer and wax protected Grubbs' catalyst healing components. A controlled amount of microcracking was introduced through cyclic indentation of opposing surfaces of the composite. The resulting damage zone was proportional to the indentation load. Healing was assessed through the use of a pressure cell apparatus to detect nitrogen flow through the thickness direction of the damaged composite. Successful healing resulted in a perfect seal, with no measurable gas flow. The effect of DCPD microcapsule size (51 um and 18 um) and concentration (0 - 12.2 wt%) on the self-sealing ability was investigated. Composite specimens with 6.5 wt% 51 um capsules sealed 67% of the time, compared to 13% for the control panels without healing components. A thermally stable, dual microcapsule healing chemistry comprised of silanol terminated poly(dimethyl siloxane) plus a crosslinking agent and a tin catalyst was employed to allow higher composite processing temperatures. The microcapsules were incorporated into a satin weave E-glass fiber/epoxy composite processed at 120C to yield a glass transition temperature of 127C. Self-sealing ability after mechanical damage was assessed for different microcapsule sizes (25 um and 42 um) and concentrations (0 - 11 vol%). Incorporating 9 vol% 42 um capsules or 11 vol% 25 um capsules into the composite matrix leads to 100% of the samples sealing. The effect of microcapsule concentration on the short beam strength, storage modulus, and glass transition temperature of the composite specimens was also investigated. The thermally stable tin catalyzed poly(dimethyl siloxane) healing chemistry was then integrated into a [0/90]s uniweave carbon fiber/epoxy composite. Thermal cycling (-196C to 35C) of these specimens lead to the formation of microcracks, over time, formed a percolating crack network from one side of the composite to the other, resulting in a gas permeable specimen. Crack damage accumulation and sample permeability was monitored with number of cycles for both self-healing and traditional non-healing composites. Crack accumulation occurred at a similar rate for all sample types tested. A 63% increase in lifetime extension was achieved for the self-healing specimens over traditional non-healing composites.

High-order hp-adaptive discontinuous Galerkin finite element methods for compressible fluid flows

This article is concerned with the construction of general isotropic and anisotropic adaptive strategies, as well as hp-mesh refinement techniques, in combination with dual-weighted-residual a posteriori error indicators for the discontinuous Galerkin finite element discretization of compressible fluid flow problems.

Design methodologies and architectures of hardware-based evolutionary algorithms for aerospace optimisation applications on FPGAS

This thesis is a study of new design methods for allowing evolutionary algorithms to be more effectively utilised in aerospace optimisation applications where computation needs are high and computation platform space may be restrictive. It examines the applicability of special hardware computational platforms known as field programmable gate arrays and shows that with the right implementation methods they can offer significant benefits. This research is a step forward towards the advancement of efficient and highly automated aircraft systems for meeting compact physical constraints in aerospace platforms and providing effective performance speedups over traditional methods.

Applications of Lean Ideas to the Aerospace Industry

• Lean Aerospace Initiative origin and mission • Functional lean successes • Successes through interaction between functions • Success through enterprise integration and value creation • Total enterprise integration of all stakeholders • Enterprise transformation insights

Optical fibre sensors and their applications in the industrial weighing and aerospace industries

This thesis presents the design, fabrication and testing of novel grating based Optical Fibre Sensor (OFS) systems being interrogated using “off the shelf” interrogation systems, with the eventual development of marketable commercial systems at the forefront of the research. Both in the industrial weighing and aerospace industries, there has been a drive to investigate the feasibility of using optical fibre sensors being deployed where traditionally their electrical or mechanical counterparts would traditionally have been. Already, in the industrial weighing industry, commercial operators are deploying OFS-based Weigh-In-Motion (WIM) systems. Likewise, in the aerospace industry, OFS have been deployed to monitor such parameters as load history, impact detection, structural damage, overload detection, centre of gravity and the determination of blade shape. Based on the intrinsic properties of fibre Bragg gratings (FBGs) and Long Period Fibre Gratings (LPFGs), a number of novel OFS-based systems have been realised. Experimental work has shown that in the case of static industrial weighing, FBGs can be integrated with current commercial products and used to detect applied loads. The work has also shown that embedding FBGs in e-glass, to form a sensing patch, can result in said patches being bonded to rail track, forming the basis of an FBG-based WIM system. The results obtained have been sufficiently encouraging to the industrial partner that this work will be progressed beyond the scope of the work presented in this thesis. Likewise, and to the best of the author’s knowledge, a novel Bragg grating based systems for aircraft fuel parameter sensing has been presented. FBG-based pressure sensors have been shown to demonstrate good sensitivity, linearity and repeatability, whilst LPFG-based systems have demonstrated a far greater sensitivity when compared to FBGs, as well the advantage of being potentially able to detect causes of fuel adulteration based on their sensitivity to refractive index (RI). In the case of the LPFG-based system, considerable work remains to be done on the mechanical strengthening to improve its survivability in a live aircraft fuel tank environment. The FBG system has already been developed to an aerospace compliant prototype and is due to be tested at the fuel testing facility based at Airbus, Filton, UK. It is envisaged by the author that in both application areas, continued research in this area will lead to the eventual development of marketable commercial products.

Study of acoustic emission data analysis tools for structural health monitoring applications

Acoustic emission (AE) technique is one of the popular diagnostic techniques used for structural health monitoring of mechanical, aerospace and civil structures. But several challenges still exist in successful application of AE technique. This paper explores various tools for analysis of recorded AE data to address two primary challenges: discriminating spurious signals from genuine signals and devising ways to quantify damage levels.

A hardware-based multi-disciplinary design optimization method for aeronautical applications

There are many applications in aeronautics where there exist strong couplings between disciplines. One practical example is within the context of Unmanned Aerial Vehicle(UAV) automation where there exists strong coupling between operation constraints, aerodynamics, vehicle dynamics, mission and path planning. UAV path planning can be done either online or offline. The current state of path planning optimisation online UAVs with high performance computation is not at the same level as its ground-based offline optimizer's counterpart, this is mainly due to the volume, power and weight limitations on the UAV; some small UAVs do not have the computational power needed for some optimisation and path planning task. In this paper, we describe an optimisation method which can be applied to Multi-disciplinary Design Optimisation problems and UAV path planning problems. Hardware-based design optimisation techniques are used. The power and physical limitations of UAV, which may not be a problem in PC-based solutions, can be approached by utilizing a Field Programmable Gate Array (FPGA) as an algorithm accelerator. The inevitable latency produced by the iterative process of an Evolutionary Algorithm (EA) is concealed by exploiting the parallelism component within the dataflow paradigm of the EA on an FPGA architecture. Results compare software PC-based solutions and the hardware-based solutions for benchmark mathematical problems as well as a simple real world engineering problem. Results also indicate the practicality of the method which can be used for more complex single and multi objective coupled problems in aeronautical applications.