Adaptive filtering applications to satellite navigation

PhDDifferential Global Navigation Satellite Systems employ the extended Kalman filter to estimate the reference position error. High accuracy integrated navigation systems have the ability to mix traditional inertial sensor outputs with navigation satellite based position information and can be used to develop high accuracy landing systems for aircraft. This thesis considers a host of estimation problems associated with aircraft navigation systems that currently rely on the extended Kalman filter and proposes to use a nonlinear estimation algorithm, the unscented Kalman filter (UKF) that does not rely on Jacobian linearisation. The objective is to develop high accuracy positioning algorithms to facilitate the use of GNSS or DGNSS for aircraft landing. Firstly, the position error in a typical satellite navigation problem depends on the accuracy of the orbital ephemeris. The thesis presents results for the prediction of the orbital ephemeris from a customised navigation satellite receiver's data message. The SDP4/SDP8 algorithms and suitable noise models are used to establish the measured data. Secondly, the differential station common mode position error not including the contribution due to errors in the ephemeris is usually estimated by employing an EKF. The thesis then considers the application of the UKF to the mixing problem, so as to facilitate the mixing of measurements made by either a GNSS or a DGNSS and a variety of low cost or high-precision INS sensors. Precise, adaptive UKFs and a suitable nonlinear propagation method are used to estimate the orbit ephemeris and the differential position and the navigation filter mixing errors. The results indicate the method is particularly suitable for estimating the orbit ephemeris of navigation satellites and the differential position and navigation filter mixing errors, thus facilitating interoperable DGNSS operation for aircraft landing

Fault-Tolerant Flight Control Using One Aerodynamic Control Surface

University of Minnesota Ph.D. dissertation. June 2018. Major: Aerospace Engineering and Mechanics. Advisor: Peter Seiler. 1 computer file (PDF); xiii, 291 pages.Small unmanned aircraft systems (UAS) have recently found increasing civilian and commercial applications. On-board fault management is one of several technical challenges facing their widespread use. The aerodynamic control surfaces of a fixed-wing UAS perform the safety-critical functions of stabilizing and controlling the aircraft. Failures in one or more of these surfaces, or the actuators controlling them, may be managed by repurposing the other control surfaces and/or propulsive devices. A natural question arises in this context: What is the minimum number of control surfaces required to adequately control a handicapped aircraft? The answer, in general, depends on the control surface layout of the aircraft under consideration. For some aircraft, however, the answer is one. If the UAS is equipped with only two control surfaces, such as the one considered in this thesis, then this limiting case is reached with a single control surface failure. This thesis demonstrates, via multiple flight tests, the autonomous landing of a UAS using only one aerodynamic control surface and the throttle. In seeking to arrive at these demonstrations, this thesis makes advances in the areas of model-based fault diagnosis and fault-tolerant control. Specifically, a new convex method is developed for synthesizing robust output estimators for continuous-time, uncertain, gridded, linear parameter-varying systems. This method is subsequently used to design the fault diagnosis algorithm. The detection time requirement of this algorithm is established using concepts from loss-of-control. The fault-tolerant controller is designed to operate the single control surface for lateral control and the throttle for total energy control. The fault diagnosis algorithm and the fault-tolerant controller are both designed using a model of the aircraft. This model is first developed using physics-based first-principles and then updated using system identification experiments. Since this aircraft does not have a rudder, the identification of the lateral-directional dynamics requires some novelty

Nature of the learning algorithms for feedforward neural networks

The neural network model (NN) comprised of relatively simple computing elements, operating in parallel, offers an attractive and versatile framework for exploring a variety of learning structures and processes for intelligent systems. Due to the amount of research developed in the area many types of networks have been defined. The one of interest here is the multi-layer perceptron as it is one of the simplest and it is considered a powerful representation tool whose complete potential has not been adequately exploited and whose limitations need yet to be specified in a formal and coherent framework. This dissertation addresses the theory of generalisation performance and architecture selection for the multi-layer perceptron; a subsidiary aim is to compare and integrate this model with existing data analysis techniques and exploit its potential by combining it with certain constructs from computational geometry creating a reliable, coherent network design process which conforms to the characteristics of a generative learning algorithm, ie. one including mechanisms for manipulating the connections and/or units that comprise the architecture in addition to the procedure for updating the weights of the connections. This means that it is unnecessary to provide an initial network as input to the complete training process.After discussing in general terms the motivation for this study, the multi-layer perceptron model is introduced and reviewed, along with the relevant supervised training algorithm, ie. backpropagation. More particularly, it is argued that a network developed employing this model can in general be trained and designed in a much better way by extracting more information about the domains of interest through the application of certain geometric constructs in a preprocessing stage, specifically by generating the Voronoi Diagram and Delaunav Triangulation [Okabe et al. 92] of the set of points comprising the training set and once a final architecture which performs appropriately on it has been obtained, Principal Component Analysis [Jolliffe 86] is applied to the outputs produced by the units in the network's hidden layer to eliminate the redundant dimensions of this space

The resistance of laminated glass to blast pressure loading and the coefficients for single degree of freedom analysis of laminated glass

For terrorist explosions or accidental explosions in urban areas, the greatest threat of death and serious injury comes from the effects of glass fragments. Laminated glazing has been proven by trials and experience of actual events to eliminate the risk of significant fragment injury to people behind the glazing, and also to provide substantial protection from blast injury effects, provided that after cracking it remains as a continuous membrane substantially attached to the supporting frame. However, design of laminated glazing is currently based on extrapolation from testing, with limited understanding of the material behaviour that underlies the behaviour under blast loading. This thesis presents an investigation into the application of a simplified method of dynamic analysis for laminated glass, the development of parameters derived from the properties of the materials in laminated glass and the behaviour of laminated glass systems that can be applied to the design of laminated glazing to resist blast loading. The development of the single degree of freedom method for analysis of dynamic response is reviewed from its inception use for analysis of glazing, through its adaptation for reinforced concrete analysis, to its modern use for analysis of glazing. Although the principles of the method are widely applicable, some procedures established for elastic-plastic reinforced concrete analysis in the 1950s are not appropriate for glazing, and should be treated with care. Coefficients for analysis of reinforced concrete date from approximate analyses in the 1950s and 60s and are not accurate. New calculations using advanced yield line models and finite element analysis have been used to provide alternative coefficients for rectangular panels supported on four edges. The elastic analyses for reinforced concrete are linear because they are based on small-deflection theory. Deflections of most uncracked glass panes exceed the limits of this theory. The development of practical non-linear large-deflection analyses in the 1980s was dependent on numerical methods and computer analysis, but they have previously only been applied to resistance and cracking. New non-linear finite element analyses refine the existing resistance data, and data from the same calculations has been used to derive large deflection single degree of freedom parameters for dynamic analysis and to assess the reaction distribution. The cracking of glass arises from small flaws in its surface, and can be very variable in its onset. In addition, the strength is sensitive to the loading rate. Statistical approaches have been based on quasi-static tests, either assuming a normal distribution, or using a more complex Weibull distribution. However, statistical refinement gains little, as strengths then need to be increased for the faster loading under blast. Back-analysis of extensive blast tests had been used to establish deterministic lower bound design cracking strengths for different types of glass. These have been applied in this thesis for design, and back-analysis of blast trials indicates that the design cracking strengths are lower bound. Formulae for a monolithic pane with equivalent behaviour to a laminated glass pane are proposed that would allow the large deflection analysis to be applied to laminated glass up to cracking of the final ply. The results of some blast trials of uncracked laminated glass are reported which are consistent with an equivalent monolithic analysis. They indicate that laminated glass under blast can be taken as fully composite to temperatures approaching 20ºC, but that it is not fully composite at 29ºC or above. Unfortunately, there is currently no data to indicate the performance in the critical temperature range between. After laminated glass cracks, the resistance is provided by an interlayer of the viscoelastic polymer, Polyvinyl Butyral. Though research is ongoing, non-linear viscoelastic material models for finite element analyses have not yet been developed to the point that they can reproduce the full range of behaviour observed in the tensile tests over the range of temperatures and elongation rates which are reported in the thesis. Instead, the results of the tensile tests are fitted to a simple bilinear material model by back-analysis of the tensile tests to give three stiffness and strength parameters that vary with temperature and strain rate. Non-linear finite element analyses of PVB membranes corresponding to two series of laminated glass blast trials are used to produce single degree of freedom parameters for membrane response. The blast trials are reported, and back-analysis of the deflection histories is used to estimate the ratio of the PVB material strain rates and the observed laminated glass strain rates for the best-fit calculated response. This ratio, found to have a mean value of 3.8, is expected to reflect the stiffening of PVB by attached glass fragments, together with other factors. However, the scatter in the data is large, so the reliability of this figure should be viewed with this in mind. Laminated glass providing blast protection is normally maintained close to room temperature, so a design based on a room temperature of 23ºC is proposed, using single degree of freedom data that is a composite of the uncracked data up to cracking and the membrane data after that point. For normal laminated glazing where the observed strain rate is expected to be about 10 /s, design membrane properties based on a PVB strain rate of 40 /s are proposed, but this may need to be modified for other cases. Typical design cases for marginal behaviour are analysed on this basis, and also for material properties at temperatures 6ºC higher and lower than 23ºC, to assess the sensitivity of the design to likely temperature variations. These indicate that a margin of 16-21% may be needed on deflection limits to allow for temperature increases, but that the calculated deflections would still be below the maximum deflections observed in the trials without PVB failure. The analyses indicate that the peak reactions are unlikely to be sensitive to temperature. However, they indicate that a margin of safety of 2.4 will need to be incorporated in the design anchorage strength to resist in-plane tension in the PVB membrane at reduced temperature. The thesis develops an improved design method under blast loading for laminated glass and double glazing incorporating laminated glass, although some of the values used in the method should be considered tentative. The thesis also indicates a level of anchorage strength sensitivity to temperature reductions that needs to be taken into account in practical glazing designs.EThOS - Electronic Theses Online ServiceGBUnited Kingdo