Deep Learning-Based, Passive Fault Tolerant Control Facilitated by a Taxonomy of Cyber-Attack Effects

In the interest of improving the resilience of cyber-physical control systems to better operate in the presence of various cyber-attacks and/or faults, this dissertation presents a novel controller design based on deep-learning networks. This research lays out a controller design that does not rely on fault or cyber-attack detection. Being passive, the controller’s routine operating process is to take in data from the various components of the physical system, holistically assess the state of the physical system using deep-learning networks and decide the subsequent round of commands from the controller. This use of deep-learning methods in passive fault tolerant control (FTC) is unique in the research literature. The proposed controller is applied to both linear and nonlinear systems. Additionally, the application and testing are accomplished with both actuators and sensors being affected by attacks and /or faults

CONTROL TECHNIQUES APPLIED TO INTEGRATED SHIP MOTION CONTROL

Fins stabilisers are devices which are fitted to the hull of a ship and utilised to ameliorate its rolling motions. They apply a regulated moment about the ship's axis of roll in order to oppose the sea induced disturbances. Recognising their unsurpassed performance, the Royal Navy, since the 1950's, equips all its vessels with fin stabilisers. It can be shown that the rudders, in vessels of appropriate size, also have the potential to be harnessed as roll stabilisers Rudder Roll Stabilisation (RRS) without degrading the ship's course-keeping. Thus creating a more stable platform for the human operators and equipment. The reported success of RRS imparted an impetus to the Royal Navy to initiate this study. The objectives are to ascertain whether RRS is possible without rudder modifications and to establish whether enhanced levels of stabilisation would accrue if the fins and RRS were operated in congress. The advantages in this novel approach being: avoidance of redesign and refit of rudders, three modes of operation (fins alone, RRS alone and combined RRS and fins), reduced fin activity and by implication self-generated noise, and amenability to be retrofitted by simple alteration of any existing ship's autopilot software. The study initially examined the mathematical models of the ship dynamics, defining deficiencies and evaluating sources of uncertainty. It was postulated that the dual purpose of the rudder can be separated into non-interacting frequency channels for controller design purposes. An integrated design methodology is adopted to the roll stabilisation problem. Investigating the capabilities of the rudder servomechanism, a new scheme, the Anti-Saturation Algorithm (ASA) was proposed which can eliminate slew rate saturation. Application of the ASA is generic to any servomechanism. The effects of lateral accelerations of the ship on human operators was examined. This resulted in an unique contribution to the Lateral Force Estimator problem in terms of generating time domain models and defining the limitations of the applicability of a control design strategy. Linear Quadratic Guassian and two types of classical controllers were constructed for the RRS and fins. A novel application of linear robust control theory to the ship roll stabilisation problem resulted in H . controllers whose performance was superior to the other design methods. This required the development of weight functions and the identification and quantification of possible sources of uncertainty. The structured singular value utilised this information to give comparable measures of robustness. The sea trials conducted represent the first experience of the integrated ship roll stabilisation approach. Experimental results are detailed. These afforded an invaluable opportunity to validate the software employed to predict ship motion. The data generated from the sea trials concurs with the simulations data in predicting that enhanced levels of roll stabilisation are possible without any modification to the rudder system. They also confirm that when the RRS is acting in congress with the fin stabilisers the activity of both actuators diminishes

Dynamic power management: from portable devices to high performance computing

Electronic applications are nowadays converging under the umbrella of the cloud computing vision. The future ecosystem of information and communication technology is going to integrate clouds of portable clients and embedded devices exchanging information, through the internet layer, with processing clusters of servers, data-centers and high performance computing systems. Even thus the whole society is waiting to embrace this revolution, there is a backside of the story. Portable devices require battery to work far from the power plugs and their storage capacity does not scale as the increasing power requirement does. At the other end processing clusters, such as data-centers and server farms, are build upon the integration of thousands multiprocessors. For each of them during the last decade the technology scaling has produced a dramatic increase in power density with significant spatial and temporal variability. This leads to power and temperature hot-spots, which may cause non-uniform ageing and accelerated chip failure. Nonetheless all the heat removed from the silicon translates in high cooling costs. Moreover trend in ICT carbon footprint shows that run-time power consumption of the all spectrum of devices accounts for a significant slice of entire world carbon emissions. This thesis work embrace the full ICT ecosystem and dynamic power consumption concerns by describing a set of new and promising system levels resource management techniques to reduce the power consumption and related issues for two corner cases: Mobile Devices and High Performance Computing

Sets and Constraints in the Analysis Of Uncertain Systems

This thesis is concerned with the analysis of dynamical systems in the presence of model uncertainty. The approach of robust control theory has been to describe uncertainty in terms of a structured set of models, and has proven successful for questions, like stability, which call for a worst-case evaluation over this set. In this respect, a first contribution of this thesis is to provide robust stability tests for the situation of combined time varying, time invariant and parametric uncertainties. The worst-case setting has not been so attractive for questions of disturbance rejection, since the resulting performance criteria (e.g., ℋ∞,) treat the disturbance as an adversary and ignore important spectral structure, usually better characterized by the theory of stochastic processes. The main contribution of this thesis is to show that the set-based methodology can indeed be extended to the modeling of white noise, by employing standard statistical tests in order to identify a typical set, and performing subsequent analysis in a worst-case setting. Particularly attractive sets are those described by quadratic signal constraints, which have proven to be very powerful for the characterization of unmodeled dynamics. The combination of white noise and unmodeled dynamics constitutes the Robust ℋ2 performance problem, which is rooted in the origins of robust control theory. By extending the scope of the quadratic constraint methodology we obtain a solution to this problem in terms of a convex condition for robustness analysis, which for the first time places it on an equal footing with the ℋ∞ performance measure. A separate contribution of this thesis is the development of a framework for analysis of uncertain systems in implicit form, in terms of equations rather than input-output maps. This formulation is motivated from first principles modeling, and provides an extension of the standard input-output robustness theory. In particular, we obtain in this way a standard form for robustness analysis problems with constraints, which also provides a common setting for robustness analysis and questions of model validation and system identification

Flexible and Adaptive Real-Time Task Scheduling in Cyber-Physical Control Systems

In a Cyber-Physical Control System (CPCS), there is often a hybrid of hard real-time tasks which have stringent timing requirements and soft real-time tasks that are computationally intensive. The task scheduling of such systems is challenging and requires flexible schemes that can meet the timing requirements without being over-conservative. Fixed-priority scheduling (FPS) is a scheduling policy that has been widely used in industry. However, as an open-loop scheduler, FPS has low system dynamics and no feedback from historic operation. As the working conditions of a CPCS will change due to both internal and external factors, an improved scheduling scheme is required which can adapt to changes without a costly system redesign. In recent years, there is a large research interest in the co-design of control and scheduling systems that explicitly considers task scheduling during the design of a controller. Many of these works reveal the possibility of adapting control periods at run-time in order to accommodate varying resource requirements and to optimise CPU utilization. It is also shown that control quality can be traded off for resource usages. In this thesis, an adaptive real-time scheduling framework for CPCS is presented. The adaptive scheduler has a hierarchical structure and it is built on top of a traditional FPS scheduler. The idea of dynamic worst-case execution time is introduced and its cause and methods to identify the existence of a trend are discussed. An adaptation method that uses monitored statistical information to update control task periods is then introduced. Finally, this method is extended by proposing a dual-period model that can switch between multiple operational modes at run-time. The proposed framework can be potentially extended in many aspects and some of these are discussed in the future work. All proposals of this thesis are supported by extensive analysis and evaluations

AFIT School of Engineering Contributions to Air Force Research and Technology Calendar Year 1973

This report contains abstracts of Master of Science Theses, Doctoral dissertations, and selected faculty publications completed during the 1973 calendar year at the School of Engineering, Air Force Institute of Technology, at Wright-Patterson Air Force Base, Ohio

AFIT School of Engineering Contributions to Air Force Research and Technology Calendar Year 1973

This report contains abstracts of Master of Science Theses, Doctoral dissertations, and selected faculty publications completed during the 1973 calendar year at the School of Engineering, Air Force Institute of Technology, at Wright-Patterson Air Force Base, Ohio