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H υποβάθμιση της δομικής ακεραιότητας των γηρασμένων κατασκευών αποτελεί ένα από τα σημαντικότερα σύγχρονα τεχνολογικά προβλήματα, και ειδικότερα το πρόβλημα του ‘γηράσκοντος’ Αεροσκάφους αποτελεί ένα από τα σημαντικότερα προβλήματα της Αεροπορικής Βιομηχανίας. Τεχνολογικά το πρόβλημα της γήρανσης της δομής του αεροσκάφους είναι ένα πρόβλημα κόπωσης. Οι περιοχές των συνδέσεων στην άτρακτο ενός αεροσκάφους αποτελούν υψηλά καταπονούμενες περιοχές της δομής, με αποτέλεσμα τη δημιουργία πολλών μικρών ρωγμών στα ελάσματα του περιβλήματος της ατράκτου γύρω από τις οπές (ευρείας έκτασης βλάβη κόπωσης – wide spread fatigue damage). Με το χρόνο λειτουργίας οι ρωγμές αυτές εξελίσσονται και αλληλεπιδρούν. Η κατάσταση αυτή, που ονομάζεται κατάσταση πολλαπλής βλάβης (Multi-Side-Damage) υποβαθμίζει σημαντικά τη φέρουσα ικανότητα του κατασκευαστικού μέρους και μπορεί να οδηγήσει σε απώλεια της δομικής του ακεραιότητας. Η ύπαρξη διάβρωσης επιτείνει σημαντικά το πρόβλημα της δομικής ακεραιότητας του γηράσκοντος αεροσκάφους. Στις υψηλά καταπονούμενες περιοχές της δομής η ύπαρξη διάβρωσης με την ταυτόχρονη παρουσία ρωγμών κόπωσης μπορεί να οδηγήσει σε απώλεια της δομικής ακεραιότητας με καταστροφικές συνέπειες. Πρόσφατες έρευνες [3,4] έδειξαν, ότι η διάβρωση τυπικών αεροπορικών κραμάτων των σειρών 2xxx (π.χ. 2024) 6xxx (π.χ. 6013) και 7xxx (π.χ.7075) σε διαβρωτικό περιβάλλον αποφλοίωσης (EXCO) αλλά και σε φυσική διάβρωση, οδηγεί σε υποβάθμιση του ορίου διαρροής και του ορίου θραύσης των υλικών, κυρίως όμως υποβαθμίζει δραματικά την παραμόρφωση θραύσης και τη ικανότητα των υλικών να αποταμιεύουν μηχανική ενέργεια πριν την θραύση, δηλαδή την αναμενόμενη ανοχή τους στη βλάβη κόπωσης. Η υποβάθμιση αυτή των ιδιοτήτων αποδόθηκε σε ψαθυροποίηση των κραμάτων αλουμινίου που προκαλείται από τη διάβρωση λόγω προσρόφησης και παγίδευσης υδρογόνου σε συγκεκριμένες παγίδες στην μικροδομή του υλικού που εξαρτώνται από το κραματικό σύστημα [56,59,62,68]. Στην παρούσα διατριβή πραγματοποιήθηκε πειραματική και θεωρητική διερεύνηση της επίδρασης της διάβρωσης στα χαρακτηριστικά κόπωσης και θραύσης του κράματος αλουμινίου 2024. / Loss of structural integrity is one of the most significant threats for ageing structures. The occurrence of Multiple Site Damage (MSD), that implies the simultaneous existence of several interacting fatigue cracks at various locations of a structural element can degrade the structural strength and service life of a structure. The occurrence of MSD in older airplanes was highlighted by the “Aloha accident” [49] at 1988, when a Boeing 737 of Aloha Airlines with a service life of nearly 90000 flights suffered an in-flight failure of a portion of the fuselage. The occurrence of corrosion presents an additional significant cause of structural degradation. As the service time for an aircraft structure increases, there is an increasing probability that corrosion will interact with other forms of damage, such as single fatigue cracks or MSD in the form of widespread cracking at regions of high stress gradients; it can result to loss of structural integrity and may lead to fatal consequences. Thus, the effect of corrosion on the damage tolerance ability of advanced aluminum alloys calls for a very diligent consideration to problems associated with the combined effect of corrosion and MSD mechanisms. Extensive experimental data referring to accelerated laboratory corrosion tests, have shown a significant reduction of material mechanical properties, leading to a decrease of the load bearing capacity of the corroded structural member. It has been recognized that, this decrease is associated with hydrogen embrittlement, as hydrogen produced during the corrosion process may diffuse into the material and be trapped at different trapping sites depending on the alloy system [56,62,68]. In the present thesis, experimental and numerical investigations have been carried out in the Laboratory of Technology and Strength of Materials of the University of Patras to study the influence of corrosion on the damage tolerance and fracture toughness characteristics of the high strength aluminum alloy 2024.

Thesis (MScEng)-- Stellenbosch University, 2013. / ENGLISH ABSTRACT: In this thesis the design, analysis, implementation, and verification of a fault-tolerant unmanned aerial vehicle (UAV) flight control system which is robust to structural damage causing the natural flight dynamics of the vehicle to become asymmetric, is presented. The main purpose of the robust control architecture is to maintain flight stability after damage has occurred. The control system must be able to handle an abrupt change from an undamaged to a damaged state, and must also not depend on explicit knowledge of the damage. A robust control approach is therefore preferred above an adaptive control approach. As a secondary objective, the system must provide robust flight performance to ensure adequate response times and acceptable transients’ behaviour, both in normal flight, and after damage has occurred. An asymmetric six degrees of freedom equations of motion model is derived. The model accounts for the changes in the aerodynamic model of the aircraft as well as changes in the centre of gravity location. Vortex lattice techniques are used to determine the aerodynamic coefficients of the aircraft for damage to the main wing resulting in 0% to 40% spanwise lifting surface loss. A sequential quadratic programming optimisation algorithm is applied to the force and moment equations to find the trim flight state and actuator deflections of the asymmetric aircraft for constant airspeed and altitude. The trim flight state can be further constrained to force zero bank angle, zero sideslip angle or a desired relative weighting of nonzero bank angle and nonzero sideslip angle. The calculated trim actuator deflections are compared to the physical deflection limits to determine the feasibility of maintaining trim flight for different percentages of wing loss. Assuming that a valid trim condition exists, the relative stability of the aircraft’s natural modes is analysed as a function of percentage wing loss by tracing the locus of the open-loop poles. An acceleration-based flight control architecture is designed and implemented, and the robustness of the flight control stability and performance is analysed as a function of percentage wing loss. The robustness and performance of the flight control system is verified with a nonlinear simulation for spanwise wing loss from 0 to 40%. Practical flight tests are performed to verify the robustness and performance of the flight control systems to in-flight damage. A detachable wing with release mechanism is designed and manufactured to simulate 20% wing loss. The flight control system is implemented on a practical UAV and a successful flight test shows that it performs fully autonomous flight control, and is able to accommodate an in-flight partial wing loss. / AFRIKAANSE OPSOMMING: In hierdie tesis word die ontwerp, analise, implementasie en verifikasie van ’n fout-verdraende onbemande vliegtuig beheerstelsel wat robuust is tot strukturele skade wat die natuurlike vlug dinamika van die voertuig asimmetries maak, voorgestel. Die hoofdoel van hierdie robuuste beheer argitektuur is om stabiliteit te verseker na die skade aangerig is. Die beheerstelsel moet die skielike verandering van normale na beskadigde vlug hanteer sonder enige eksplisiete kennis daarvan. Dus word ’n robuuste beheer aanslag verkies bo ’n aanpassende beheer struktuur. Tweedens moet die vlugbeheerstelsel robuust genoeg wees om steeds die gewenste reaksietyd en aanvaarbare oorgangsverskynsels te kan hanteer, tydens beide normale en beskadigde vlug. ’n Asimmetriese ses grade van vryheid beweginsvergelykings model word afgelei. Die model het die vermoë om veranderinge in die aerodinamiese model van die vliegtuig, sowel as massamiddelpunt verskuiwing, voor te stel. “Vortex Lattice” metodes is gebruik om die aerodinamiese koëffisiënte van die beskadigde vlerk voor te stel tussen 0% en 40% verlies. ’n Sekwensiële kwadratiese programmering optimiserings algorithme is aangewend op die krag en moment vergelykings om die ekwilibrium vlug toestand en aktueerder defleksies te vind vir ’n asimmetriese vliegtuig met konstante lugspoed en hoogte. Die ekwilibrium vlug toestand word verder beperk deur ’n nul rolhoek, ’n nul sygliphoek of ’n relatiewe weging van die twee. Die bepaalde ekwilibrium defleksies word dan vergelyk met die fisiese limiete om hulle geldigheid te bepaal vir ekwilibrium vlug. As ’n geldige ekwilibrium toestand bestaan, kan die relatiewe stabiliteit van die vliegtuig se natuurlike modusse ontleed word as ’n persentasie van vlerkverlies deur die wortellokusse van die ooplus pole na te gaan. ’n Versnellings-gebaseerde vlug beheerstelsel argitektuur is ontwerp en geïmplementeer. Daarna is die robuustheid ontleed as ’n funksie van die persentasie vlerkverlies. Die robuustheid en gedrag van hierdie vlugbeheerstelsel is geverifieer met ’n nie-linêre simulasie vir 0 tot 40% vlerkverlies. Praktiese vlugtoetse is onderneem om die robuustheid en gedrag tydens/na skade gedurende ’n vlug, te verifeer. ’n Vlerkverlies meganisme is ontwerp en vervaardig om 20% vlerkverlies te simuleer. Die vlugbeheerstelsel is geïmplementeer op ’n onbemande vliegtuig en die daaropvolgende suksesvolle vlug lewer bewys dat die vlugbeheerstelsel wel skade, in die vorm van gedeeltelike vlerkverlies, tydens vlug kan hanteer.

A influência da fuselagem sobre a posição do centro aerodinâmico da asa é complexa e deve ser considerada nos cálculos de equilíbrio e estabilidade estática longitudinal da aeronave. Este trabalho apresenta uma análise comparativa para indicar o mais preciso dentre sete métodos teóricos para prever esta influência, em condições de baixa velocidade, utilizando seis configurações de modelos de asa mais fuselagem em escala reduzida, com proporções dimensionais características da aviação leve. Mediram-se os coeficientes de momento e sustentação para cada configuração, através de ensaios em túnel de vento de baixa velocidade, circuito aberto e seção de testes fechada. Calcularam-se as posições experimentais do centro aerodinâmico através da distância do eixo de rotação da balança ao bordo de ataque da asa e derivadas do coeficiente de momento em relação ao coeficiente de sustentação. Aplicaram-se os métodos teóricos às configurações. Os resultados demonstram que a maioria dos métodos prevê comportamentos na variação da posição do centro aerodinâmico semelhantes aos obtidos experimentalmente e apontados na revisão da literatura. A análise dos resultados teóricos ante os experimentais aponta o método descrito em Engineering Sciences Data Unit (1996a) como o mais preciso. / The fuselage influence on the wing aerodynamic center is complex and must be considered within longitudinal static stability and equilibrium calculations of the airplane. This work presents a comparative analysis to indicate the most accurate between seven theoretical methods that predict this influence, at low speed conditions, using six configurations of wing-fuselage reduced scale models, with the dimensional proportions found in light aviation. The moment and lift coefficients have been measured by experiments in a low speed open circuit wind tunnel with a closed test section. The experimental aerodynamic center positions have been found by the distance of the balance trunnion to wing leading edge and the derivation of the moment coefficient relative to the lift coefficient. The theoretical methods have been applied to all configurations. The results show that most of the methods predict variations in aerodynamic center position in the same way as those obtained in experimental results and shown in the literature review. The analysis between theoretical and experimental results indicates the method from Engineering Sciences Data Unit (1996a) as the most accurate.

Cabines de aeronaves vêm sendo desenvolvidas de modo a tornar o ambiente a bordo mais aceitável e confortável para os seus usuários. No presente trabalho, a influência de sistema de ventilação personalizada instalado na poltrona na dispersão de partículas expiratórias foi estudada em um mock-up de 12 lugares, que reproduz o interior de uma aeronave comercial com quatro poltronas por fileira. Os ensaios foram realizados com temperatura do ar insuflado na cabine a 18°C, correspondendo a uma leve sensação de frio, e temperatura do ar insuflado pelo sistema personalizado a 24°C com vazão de 3,0 l/s. As partículas simulando uma pessoa espirrando foram injetadas em dois pontos no fundo da cabine, respectivamente, na poltrona próxima da fuselagem e naquela perto do corredor, a 1,10m do piso, que corresponde à região de respiração. A contagem de partículas foi realizada nos assentos da fileira imediatamente à frente do ponto de injeção das partículas, ou seja, na fileira do meio do mock-up, onde se encontra instalado o sistema de ventilação personalizada, respectivamente, na poltrona próxima da fuselagem e naquela perto do corredor. Medições para o mapeamento dos perfis de temperaturas e de velocidades do ar também foram realizadas. Os resultados mostraram que a dispersão de partículas sofre forte influência do sistema de ventilação personalizada e do ponto de injeção de partículas. A quantidade de partículas expiratórias na cabine sempre foi maior quando a injeção foi feita pelo assento junto ao corredor. Isto ocorre devido ao sistema de ventilação por mistura da cabine, com exaustão do ar pela parte inferior próximo da fuselagem. O sistema personalizado avaliado no assento próximo da fuselagem e junto do corredor foi capaz de reduzir, respectivamente, em 40% e 65% a quantidade de partículas expiratórias na zona de respiração dos ocupantes destas poltronas. Adicionalmente, quando o sistema personalizado está funcionando junto ao corredor, a redução das partículas em toda a fileira é de quase 60% em comparação ao sistema personalizado desligado. / Aircraft cabins have been developed in order to make the onboard environment more acceptable and comfortable for their users. In the present work, the influence of a personalized ventilation system installed on the armchair in the dispersion of expiratory particles was studied in a 12-seat mock-up, which reproduces the interior of a commercial aircraft with four seats per row. The tests were performed with inlet air temperature into the cabin at 18°C, corresponding to a slight cold sensation, and inlet air temperature of the customized system at 24°C with a flow rate of 3.0 l/s. Particles simulating a person sneezing were injected at two points in the bottom of the cabin, respectively, in the seat near the fuselage and in the one near the corridor, 1.10m from the floor, which corresponds to the breathing zone. Particle counting was carried out in the row seats immediately in front of the particles\' injection point, i.e. in the middle row of the mock-up, where the custom ventilation system is installed, respectively, in the seat near the fuselage and in that one near the aisle. Measurements for the mapping of temperature and air velocities profiles were also performed. The results showed that the particle dispersion is strongly influenced by the custom ventilation system and the particle injection point. The amount of expiratory particles in the cabin was always greater when the injection was done by the seat near the aisle. This occurs due to the mixing ventilation system of cabin, with air exhaust located nearby the fuselage low part. The personalized ventilation evaluated on the fuselage seat and the aisle seat was able to reduce by 40% and 65%, respectively, the amount of expiratory particles in the breathing zone in these seats. Moreover, when the custom system is working along the corridor, the particle reduction across the row is nearly 60% less compared to the custom system, when it is off.

Resource allocation in control and communication systems constitutes the distribution of (finite) system resources in a way that achieves maximum system functionality and or cost effectiveness. Specific resource allocation problems in subband coding, Discrete Multi-tone modulation based systems and autonomous multi-agent control are addressed in this thesis. In subband coding, the number of bits used (out of a target bit budget) to code a sub- band signal are allocated in a way that minimizes the coding distortion. In Discrete Multi-tone modulation based systems, high bit rate streams are split into several parallel lower rate streams. These individual data streams are transmitted over different subchannels. Given a target bit rate, the goal of resource allocation is to distribute the bits among the different subchannels such that the total transmitted power is minimized. The last problem is achieving stable control of a fleet of autonomous agents by utilizing the available communication resources (such as transmitted Power and bandwidth) as effectively as possible. We present an efficient bit loading algorithm that applies to both subband coding and single-user multicarrier communication system. The goal is to effect an optimal distribution of B bits among N subchannels (subbands) to achieve a minimum transmitted power (distortion error variance) for multicarrier (subband coding) systems. All the algorithms in literature, except a few (which provides a suboptimal solution), have run times that increase with B. By contrast, we provide an algorithm that solves the aforementioned problems exactly and with a complexity (given by O(N log(N)),) which is dependent only on N. Bit loading in multi-user multicarrier systems not only involves the distribution of bit rates across the subchannels but also the assignment of these subchannels to different users. The motivation for studying suboptimal bit allocation is underscored by implicit and explicit claims made in some of the papers which present suboptimal bit loading algorithms, without a formal proof, that the underlying problem is NP-hard. Consequently, for no other reason than the sake of completeness, we present a proof for NP-hardness of the multiuser multicarrier bit loading problem, thereby formally justifying the search for suboptimal solutions. There has been a growing interest in the area of cooperative control of networks of mobile autonomous agents. Applications for such a set up include organization of large sensor networks, air traffic control, achieving and maintaining formations of unmanned vehicles operating under- water, air traffic control etc. As in Abel et al, our goal is to devise control laws that, require minimal information exchange between the agents and minimal knowledge on the part of each agent of the overall formation objective, are fault tolerant, scalable, and easily reconfigurable in the face of the loss or arrival of an agent, and the loss of a communication link. A major drawback of the control law proposed in Abel et al is that it assumes all agents can exchange information at will. This is fine if agents acquire each others state information through straightforward sensing. If however, state information is exchanged through broadcast commu- nication, this assumption is highly unrealistic. By modifying the control law presented in Abel et al, we devise a scheme that allows for a sharing of the resource, which is the communication channel, but also achieves the desired formation stably. Accordingly we modify the control law presented in [23] to be compatible with networks constrained by MAC protocols.

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Παρουσιάζονται υπολογιστικά μοντέλα τα οποία κατά το παρελθόν έχουν αναλυθεί από διάφορους μελετητές και τα οποία σχετίζονται άμεσα με θέματα δρομολόγησης αεροσκαφών, προγραμματισμού συντηρήσεων αεροσκαφών, καθώς και με τον ημερήσιο και τον μακροχρόνιο προγραμματισμό εργασιών σε στόλο αεροσκαφών αεροπορικών εταιρειών. Στο τέλος της εργασίας γίνεται μια επιλογή ενός εκ των παρουσιασθέντων υπολογιστικών μοντέλων λαμβάνοντας υπόψη τα θετικά και τα αρνητικά σημεία καθ’ ενός από αυτά. Και βέβαια πάντα με σημείο αναφοράς το εξεταζόμενο θέμα, της δρομολόγησης και του προγραμματισμού συντηρήσεων των αεροσκαφών μιας αεροπορικής εταιρείας. Και στο τελευταίο κεφάλαιο, έχοντας επιλέξει και αιτιολογήσει την επιλογή του καταλληλότερου, για την περίπτωσή μας, υπολογιστικού μοντέλου προχωρούμε στην εφαρμογή του με την χρήση του γνωστού υπολογιστικού πακέτου Premium Solver. / Presented computational models that previously have been analyzed by scholars and directly related to issues of aircraft routing, scheduling, aircraft maintenance, and daily and long term planning work on fleet of aircraft carriers. At the end of the work it is selected one of the presented computational models taking into account the positive and negative points of it. And at the last chapter,there are presented the reasons why we did that selection of the model and finally we proceed in the implementation of it using Premium Solver Platform and MS Excel.

Submitted by JANAINA ANDRÉA DA SILVA null (janaina.silva@embraer.com.br) on 2018-03-07T17:10:23Z No. of bitstreams: 1 Microsoft Word Viewer - DISSERTAÇÃO VERSÃO FINAL 06 MARÇO 2018.pdf: 1343678 bytes, checksum: 41cf1e1bcf5b5b653a5b3ea1b1a8e9fd (MD5) / Approved for entry into archive by Pamella Benevides Gonçalves null (pamella@feg.unesp.br) on 2018-03-07T17:46:16Z (GMT) No. of bitstreams: 1 silva_ja_me_guara.pdf: 1343678 bytes, checksum: 41cf1e1bcf5b5b653a5b3ea1b1a8e9fd (MD5) / Made available in DSpace on 2018-03-07T17:46:16Z (GMT). No. of bitstreams: 1 silva_ja_me_guara.pdf: 1343678 bytes, checksum: 41cf1e1bcf5b5b653a5b3ea1b1a8e9fd (MD5) Previous issue date: 2018-01-29 / O objetivo deste trabalho foi analisar a viabilidade de implantação de um sistema de captação de água de chuva para abastecer o processo de lavagem de aeronaves na EMBRAER, e este estudo pode ser estendido para aplicação aos centros de manutenção de companhias aéreas nacionais e aeroportos. O trabalho consiste em um estudo de caso. Em sua realização foram analisadas as condições locais para implantar o sistema de coleta de água de chuva, a quantidade de recurso pluvial disponível na região de São José dos Campos, a necessidade de armazenagem de água para suprir períodos de estiagem, a qualidade necessária da água para atender a esta finalidade, e as aplicações para o reuso do efluente da lavagem de aeronaves. Os resultados mostraram que o volume de água de chuva disponível na região é suficiente para abastecer o processo de lavagem das aeronaves e que a água tem qualidade suficiente para esta aplicação. O trabalho mostra ainda que com a reutilização do efluente gerado na lavagem de aeronaves torna a implantação do projeto viável e que além do retorno financeiro, a proposta traz benefício ambiental, preservando o recurso hídrico de boa qualidade. / The aim of this work was to verify the feasibility of introduce a rainwater harvesting system to supply the aircraft washing process at EMBRAER and this study may be extended to the airlines maintenance centers and airports. This work consists in a case study. To perform this work were studied the local conditions to introduce the rainwater harvesting system, the amount of rainfall available in São José dos Campos, the need to storage water to supply drought periods, the quality of the water to supply the process with security and the applications for reuse the effluent from aircraft washing process. The results showed that the amount of rainwater avaiable in the region is enough to supply the aircrafts washing process and the water is sufficient in quality for this application. The work also showed that the reuse of the effluent generated by the aircraft washing process makes feasible the project implementation. In addition to the financial return, the purpose brings environmental benefits preserving the good quality water resources.