6 research outputs found

    Fault tolerant flight control system design for unmanned aerial vehicles

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    Safety and reliability of air vehicles is of the utmost importance. This is particularly true for large civil transport aircraft where a large number of human lives depend on safety critical design. With the increase in the use of unmanned aerial vehicles (UAVs) in our airspace it is essential that UAV safety is also given attention to prevent devastating failures which could ultimately lead to loss of human lives. While civil aircraft have human operators, the pilot, to counteract any unforeseen faults, autonomous UAVs are only as good as the on board flight computer. Large civil aircraft also have the luxury of weight hence redundant actuators (control surfaces) can be installed and in the event of a faulty set of actuators the redundant actuators can be brought into action to negate the effects of any faults. Again weight is a luxury that UAVs do not have. The main objective of this research is to study the design of a fault tolerant flight controller that can exploit the mathematical redundancies in the flight dynamic equations as opposed to adding hardware redundancies that would result in significant weight increase. This thesis presents new research into fault tolerant control for flight vehicles. Upon examining the flight dynamic equations it can be seen, for example, that an aileron, which is primarily used to perform a roll manoeuvre, can be used to execute a limited pitch moment. Hence a control method is required that moves away from the traditional fixed structure model where control surface roles are clearly defined. For this reason, in this thesis, I have chosen to study the application of model predictive control (MPC) to fault tolerant control systems. MPC is a model based method where a model of the plant forms an integral part of the controller. An optimisation is performed based on model estimations of the plant and the inputs are chosen via an optimisation process. One of the main contributions of this thesis is the development of a nonlinear model predictive controller for fault tolerant flight control. An aircraft is a highly nonlinear system hence if a nonlinear model can be integrated into the control process the cross-coupling effects of the control surface contributions can be easily exploited. An active fault tolerant control system comprises not only of the fault tolerant controller but also a fault detection and isolation subsystem. A common fault detection method is based on parameter estimation using filtering techniques. The solution proposed in this thesis uses an unscented Kalman filter (UKF) for parameter estimation and controller updates. In summary the main contribution of this thesis is the development of a new active fault tolerant flight control system. This new innovative controller exploits the idea of analytical redundancy as opposed to hardware redundancy. It comprises of a nonlinear model predictive based controller using pseudospectral discretisation to solve the nonlinear optimal control problem. Furthermore a UKF is incorporated into the design of the active fault tolerant flight control system

    Fault Diagnosis and Performance Recovery Based on the Dynamic Safety Margin

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    The complexity of modern industrial processes makes high dependability an essential demand for reducing production loss, avoiding equipment damage, and increasing human safety. A more dependable system is a system that has the ability to: 1) detect faults as fast as possible; 2) diagnose them accurately; 3) recover the system to the nominal performance as much as possible. Therefore, a robust Fault Detection and Isolation (FDI) and a Fault Tolerant Control (FTC) system design have attained increased attention during the last decades. This thesis focuses on the design of a robust model-based FDI system and a performance recovery controller based on a new performance index called Dynamic Safety Margin (DSM). The DSM index is used to measure the distance between a predefined safety boundary in the state space and the system state trajectory as it evolves. The DSM concept, its computation methods, and its relationship to the state constraints are addressed. The DSM can be used in different control system applications; some of them are highlighted in this work. Controller design based on DSM is especially useful for safety-critical systems to maintain a predefined margin of safety during the transient and in the presence of large disturbances. As a result, the application of DSM to controller design and adaptation is discussed in particular for model predictive control (MPC) and PID controller. Moreover, an FDI scheme based on the analysis of the DSM is proposed. Since it is difficult to isolate different types of faults using a single model, a multi-model approach is employed in this FDI scheme. The proposed FDI scheme is not restricted to a special type of fault. In some faulty situations, recovering the system performance to the nominal one cannot be fulfilled. As a result, reducing the output performance is necessary in order to increase the system availability. A framework of FTC system is proposed that combines the proposed FDI and the controllers design based on DSM, in particular MPC, with accepted degraded performance in order to generate a reliable FTC system. The DSM concept and its applications are illustrated using simulation examples. Finally, these applications are implemented in real-time for an experimental two-tank system. The results demonstrate the fruitfulness of the introduced approaches

    Astronomy and Literature | Canon and Stylometrics

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    This eighth issue of Interfaces contains two thematic clusters: the first cluster, entitled The Astronomical Imagination in Literature through the Ages, is edited by Dale Kedwards; the second cluster, entitled Medieval Authorship and Canonicity in the Digital Age, is edited by Jeroen De Gussem and Jeroen Deploige

    Embedding the clinician-researcher pharmacist in healthcare

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    Nekrolog jako gatunek tekstu : analiza wydania internetowego The New York Times

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    The thesis presents an analysis of the death notice as a genre, which has been conducted by applying the research models of genre analysis designed by John Swales and Vijay K. Bhatia, and taxonomy of Polish death notices by Jacek Kolbuszewski. This in-depth structural analysis is based on a large corpus of texts (1843 texts consisting of 210,021 words), containing all death notices published in the online edition of The New York Times in a threemonth period (October 1st, 2012 – December 31st, 2012), and downloaded from Legacy.com (the leading global provider of online obituaries and death notices). The analysis involves identifying subgenres of the death notice and their communicative purposes, applying the Move and Steps analytical model to investigate the macrostructure of each subgenre of the death notice and its variants, and carrying out a register analysis, based on lexical and syntactic study with the aim of discovering patterns and lexemes characteristic of each move and/or step. Contrary to the well-researched staff-edited obituary, the genre of American death notice, written by non-professional authors (e.g. relatives, friends, employers or colleagues of the deceased) has not been thoroughly investigated; therefore, it is believed that the thesis will not only make a valuable contribution to the understanding of the genre in question, but it can be used as a reference manual helping prospective writers create a death notice in accordance with the American traditions and rules of the genre. The thesis consists of a theoretical part (Chapters One to Four) and a research part (Chapters Five to Eight). Chapter One revolves around the concepts of discourse, text and genre, and presents an overview of their theories. Chapter Two investigates the American discourse of death; it concentrates on the issue of death as a language taboo and various ways of coping with it, and provides a historical overview of numerous genres commemorating the dead. Chapter Three focuses on the both genres in question; it outlines their origin and evolution in the early British press, and summarizes contemporary research into them. Chapter Four introduces the research part as it discusses the corpus and principles of its division into subcorpora, the research model and applied methodology, and presents the discourse community and communicative purposes. Each of the four chapters constituting the research part deals with the Move and Step analysis of one of four subgenres of the death notice: informative (Chapter Five), farewell (Chapter Six), condolence (Chapter Seven), and anniversary (Chapter Eight); their lexico-structural analysis is illustrated with numerous excerpts from the respective sub-corpora. The Conclusion summarizes the research, and provides implications for future projects. The research has shown that the death notice is a highly conventionalized genre, deeply rooted in American culture and funeral tradition. While presenting biographies of the deceased (always in a positive way, according to the classical rule de mortuis nihil nisi bene), the American death notice emphasizes those specific periods and aspects of their lives (education, professional, political or military career, private life), accomplishments and traits that are valued and respected, and should be imitated by other members of the community. A notice usually contains a lengthy hierarchical list of relatives, both the predeceased and survivors. Each subgenre can be characterized by a specific set of communicative purposes, which are accomplished by a sequence of moves and steps. The commonest subgenre, the informative notice, continues the oldest traditions of the genre by informing the community about a person’s death (optionally its circumstances) and the date and place of the funeral and other services. The style and content of the farewell notice and the condolence notice depend on authorship: highly conventionalized formal institutional notices contrast with more original and intimate private ones. Their authors, whether representatives of an institution or relatives, friends, colleagues, etc., express their loss and grief, praise lives and deeds of the deceased, emphasize their importance for the authors or institution, and, in the case of the condolence notice, they offer their sympathy. The anniversary notice, the rarest subgenre, commemorates the anniversary of decedent’s birth or death, and frequently reminds the community about never-ending love and remembrance of its authors. A significant number of farewell and anniversary notices are addressed to the deceased themselves, the ‘virtual readers,’ which affects their structure and style. The register analysis displays a high level of intertextuality: non-professional obituarists tend to use conventional and stereotypical lexicon, phrases and structures, or even templates (they may copy or imitate other texts and study models provided in obituary manuals). There is no substantial evidence that the Internet has affected the genre: only few texts include hyperlinks that direct to the memorial sites at Legacy.com, where particular groups of the dead are commemorated (e.g. war veterans, university graduates, breast cancer victims)
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