Adaptive control: Myths and realities

It was found that all currently existing globally stable adaptive algorithms have three basic properties in common: positive realness of the error equation, square-integrability of the parameter adjustment law and, need for sufficient excitation for asymptotic parameter convergence. Of the three, the first property is of primary importance since it satisfies a sufficient condition for stabillity of the overall system, which is a baseline design objective. The second property has been instrumental in the proof of asymptotic error convergence to zero, while the third addresses the issue of parameter convergence. Positive-real error dynamics can be generated only if the relative degree (excess of poles over zeroes) of the process to be controlled is known exactly; this, in turn, implies perfect modeling. This and other assumptions, such as absence of nonminimum phase plant zeros on which the mathematical arguments are based, do not necessarily reflect properties of real systems. As a result, it is natural to inquire what happens to the designs under less than ideal assumptions. The issues arising from violation of the exact modeling assumption which is extremely restrictive in practice and impacts the most important system property, stability, are discussed

Integral MRAC with Minimal Controller Synthesis and bounded adaptive gains: The continuous-time case

Model reference adaptive controllers designed via the Minimal Control Synthesis (MCS) approach are a viable solution to control plants affected by parameter uncertainty, unmodelled dynamics, and disturbances. Despite its effectiveness to impose the required reference dynamics, an apparent drift of the adaptive gains, which can eventually lead to closed-loop instability or alter tracking performance, may occasionally be induced by external disturbances. This problem has been recently addressed for this class of adaptive algorithms in the discrete-time case and for square-integrable perturbations by using a parameter projection strategy [1]. In this paper we tackle systematically this issue for MCS continuous-time adaptive systems with integral action by enhancing the adaptive mechanism not only with a parameter projection method, but also embedding a s-modification strategy. The former is used to preserve convergence to zero of the tracking error when the disturbance is bounded and L2, while the latter guarantees global uniform ultimate boundedness under continuous L8 disturbances. In both cases, the proposed control schemes ensure boundedness of all the closed-loop signals. The strategies are numerically validated by considering systems subject to different kinds of disturbances. In addition, an electrical power circuit is used to show the applicability of the algorithms to engineering problems requiring a precise tracking of a reference profile over a long time range despite disturbances, unmodelled dynamics, and parameter uncertainty.Postprint (author's final draft

The potential impact of Ocean Thermal Energy Conversion (OTEC) on fisheries

The commercial development of ocean thermal energy conversion (OTEC) operations will involve some environmental perturbations for which there is no precedent experience. The pumping of very large volumes of warm surface water and cold deep water and its subsequent discharge will result in the impingement, entrainment, and redistribution of biota. Additional stresses to biota will be caused by biocide usage and temperature depressions. However, the artificial upwelling of nutrients associated with the pumping of cold deep water, and the artificial reef created by an OTEC plant may have positive effects on the local environment. Although more detailed information is needed to assess the net effect of an OTEC operation on fisheries, certain assumptions and calculations are made supporting the conclusion that the potential risk to fisheries is not significant enough to deter the early development of IDEe. It will be necessary to monitor a commercial-scale plant in order to remove many of the remaining uncertainties. (PDF file contains 39 pages.

DEVELOPMENT OF INSTRUMENTATION AND CONTROL SYSTEMS FOR AN INTEGRAL LARGE SCALE PRESSURIZED WATER REACTOR

Small and large scale integral light water reactors are being developed to supply electrical power and to meet the needs of process heat, primarily for water desalination. This dissertation research focuses on the instrumentation and control of a large integral inherently safe light water reactor (designated as I2S-LWR) which is being designed as part of a grant by the U.S. Department of Energy Integrated Research Project (IRP). This 969 MWe integral pressurized water reactor (PWR) incorporates as many passive safety features as possible while maintaining competitive costs with current light water reactors. In support of this work, the University of Tennessee has been engaged in research to solve the instrumentation and control challenges posed by such a reactor design. This dissertation is a contribution to this effort. The objectives of this dissertation are to establish the feasibility and conceptual development of instrumentation strategies and control approaches for the I2S-LWR, with consideration to the state of the art of the field. The objectives of this work are accomplished by the completion of the following tasks: Assessment of instrumentation needs and technology gaps associated with the instrumentation of the I2S-LWR for process monitoring and control purposes. Development of dynamic models of a large integral PWR core, micro-channel heat exchangers (MCHX) that are contained within the reactor pressure vessel, and steam flashing drums located external to the containment building. Development and demonstration of control strategies for reactor power regulation, steam flashing drum pressure regulation, and flashing drum water level regulation for steady state and load-following conditions. Simulation, detection, and diagnosis of process anomalies in the I2S-LWR model. This dissertation is innovative and significant in that it reports the first instrumentation and control study of nuclear steam supply by integral pressurized water reactor coupled to an isenthalpic expansion vessel for steam generation. Further, this dissertation addresses the instrumentation and control challenges associated with integral reactors, as well as improvements to inherent safety possible in the instrumentation and control design of integral reactors. The results of analysis and simulation demonstrate the successful development of dynamic modeling, control strategies, and instrumentation for a large integral PWR

Technical Change and Industrial Dynamics as Evolutionary Processes

This work prepared for B. Hall and N. Rosenberg (eds.) Handbook of Innovation, Elsevier (2010), lays out the basic premises of this research and review and integrate much of what has been learned on the processes of technological evolution, their main features and their effects on the evolution of industries. First, we map and integrate the various pieces of evidence concerning the nature and structure of technological knowledge the sources of novel opportunities, the dynamics through which they are tapped and the revealed outcomes in terms of advances in production techniques and product characteristics. Explicit recognition of the evolutionary manners through which technological change proceed has also profound implications for the way economists theorize about and analyze a number of topics central to the discipline. One is the theory of the firm in industries where technological and organizational innovation is important. Indeed a large literature has grown up on this topic, addressing the nature of the technological and organizational capabilities which business firms embody and the ways they evolve over time. Another domain concerns the nature of competition in such industries, wherein innovation and diffusion affect growth and survival probabilities of heterogeneous firms, and, relatedly, the determinants of industrial structure. The processes of knowledge accumulation and diffusion involve winners and losers, changing distributions of competitive abilities across different firms, and, with that, changing industrial structures. Both the sector-specific characteristics of technologies and their degrees of maturity over their life cycles influence the patterns of industrial organization ? including of course size distributions, degrees of concentration, relative importance of incumbents and entrants, etc. This is the second set of topics which we address. Finally, in the conclusions, we briefly flag some fundamental aspects of economic growth and development as an innovation driven evolutionary process.Innovation, Technological paradigms, Technological regimes and trajectories, Evolution, Learning, Capability-based theories of the firm, Selection, Industrial dynamics, Emergent properties, Endogenous growth

The underground electrocarbonization and gasification of mineral fuels

The development of underground gasification methods for recovering mineral fuels is comparatively recent and several methods have been evolved for treating the various source materials. The problem of recovering solid and liquid fuels by underground gasification in gaseous form was primarily approached by means of opening underground entries which created the required fire-drift for starting the gasification in place. Increasing knowledge of the whole problem of gasification in situ led to the evolution of new improvements in the underground gasification technique and, in the course of progressive research the preparations required for starting the gasification were accomplished from the surface. This procedure simplified the gasification and reduced the cost of the underground fuel. The trend of this development has been called “shaftless underground gasification”. The aim of this research was the investigation of the possibility to use electric current for underground gasification and carbonization purpose. The current passed through the fuel bed, which acts as conductor, initiates the decomposition of original organic substance of the fuel. This phenomenon has been utilized for recovering various fuels like coal, oil shale and oil sand. The process is called “Electrocarbonization” and is a shaftless gasification method. The field experimentation was perforated at the Tiger” Mine (Sinclair Coal Company), Hume, Missouri. On the bases of research data made available by 4 years of experimentation (from September, 1947 to May, 1951) embodied in this dissertation, it is believed that a large scale underground electrocarbonization and gasification pilot plant can be designed and operated successfully. The research has proved that gas suitable for domestic and industrial use can be produced physically and economically by the underground Electrocarbonization process. Further development of the process is largely the responsibility of industry --Abstract, pages iii-iv

Discrete-time integral MRAC with minimal controller synthesis and parameter projection

Model reference adaptive controllers with Minimal Control Synthesis are effective control algorithms to guarantee asymptotic convergence of the tracking error to zero not only for disturbance-free uncertain linear systems, but also for highly nonlinear plants with unknown parameters, unmodeled dynamics and subject to perturbations. However, an apparent drift in adaptive gains may occasionally arise, which can eventually lead to closed-loop instability. In this paper, we address this key issue for discrete-time systems under L-2 disturbances using a parameter projection algorithm. A consistent proof of stability of all the closed-loop signals is provided, while tracking error is shown to asymptotically converge to zero. We also show the applicability of the adaptive algorithm for digitally controlled continuous-time plants. The proposed algorithm is numerically validated taking into account a discrete-time LTI system subject to parameter uncertainty, parameter variations and L-2 disturbances. Finally, as a possible engineering application of this novel adaptive strategy, the control of a highly nonlinear electromechanical actuator is considered. (C) 2015 The Franldin Institute. Published by Elsevier Ltd. All rights reserved.Postprint (author's final draft

The Parable of the Boiled System Safety Professional: Drift to Failure

Recall from the Parable of the Boiled Frog, that tossing a frog into boiling water causes the frog to jump out and hop away while placing a frog in suitable temperature water and slowly bringing the water to a boil results in the frog boiling due to not being aware of the slowly increasing danger, theoretically, of course. System safety professionals must guard against allowing dangers to creep unnoticed into their projects and be ever alert to notice signs of impending problems. People have used various phrases related to the idea, most notably, latent conditions, James Reason in Managing the Risks of Organizational Accidents (1, pp 10-11), Drift to Failure, Sydney Dekker (2, pp 82-86) in Resilience Engineering: Chronicling the Emergence of Confused Consensus in Resilience Engineering: Concepts and Precepts, Hollnagel, Woods and Leveson, and normalization of deviance, Diane Vaughan in The Challenger Launch Decision: Risky Technology, Culture, and Deviance at NASA (3). Reason also said, If eternal vigilance is the price of liberty, then chronic unease is the price of safety (1, p 37). Our challenge as system safety professionals is to be aware of the emergence of signals that warn us of slowly eroding safety margins. This paper will discuss how system safety professionals might better perform in that regard

Temperature Control of a Gas Flow

This MQP addresses the lack of laboratory process control at WPI by expanding the Gas Flow Apparatus experiment in the Unit Operations course. A LabVIEW PID controller and a vortex tube were installed in the experiment. The PID controller successfully controls the heater on the gas flow. The vortex tube separates compressed air into hot and cold streams. An energy balance was derived for the vortex tube. Classroom procedures were developed to use these devices for the Unit Operations course

In quest of code

Architects who apply their generative modelling and scripting skills for creating virtual and prototypical spaces through the usage of algorithms and bespoke coding are increasingly confronted with an application in the real material world. The article suggests computational design strategies and two different architectural and urban prototypes for an era in which intelligent material, robotic assistants, smart geometries, changing human habitat converge with demographic, cultural and natural earth data to govern a global rethinking of socio-architectural ecologies. Since the beginning of humankind our ecosystem planet earth has served as feeding ground and shelter. Civilisation and industrialisation have triggered a verification of territory, ownership, economic wealth and power. Henceforth ethical rules, societal regulation and intuitive values were partly overridden and replaced. Long-distant transport vehicles such as cargo ships and trains allowed for accelerating the mixing up of goods and technologies. Architects solved industrial and infrastructural problems with new ideas and emerging building types; shaping urban and peripheral environments. A great idea manifested through extensive exchange of cultures and knowledge - however, strangely enough climaxed in an ultimate exploitation of our natural resources. A situation we can hardly understand or handle. As a result we are facing a situation of re-scripting our human, urban and architectural ecological system. Thus the article touches upon this very shift starting in the 18th century traversing through the implementation of the Internet, to regulate our physical world and data-autobahns filled with informing bits and bytes. The question is, which questions to ask for the best solution we can offer.Architekten, die ihre generativen Modellierungs- und Skripting-Fähigkeiten zur Erstellung virtueller und prototypischer Räume durch den Einsatz von Algorithmen und maßgeschneiderter Codierung anwenden, werden zunehmend mit einer Anwendung in der realen materiellen Welt konfrontiert. Die Autorin präsentiert computergestützte Entwurfsstrategien an zwei architektonische und urbane Prototypen für eine Ära vor, in der intelligentes Material, Roboterassistenten und sich ändernder menschlicher Lebensraum mit demographischen, kulturellen und natürlichen Geodaten konvergieren, um ein globales Umdenken sozialarchitektonischer Ökologien zu steuern. Seit dem Beginn der Menschheit dient unser Ökosystem Planet Erde als Nahrungsgrund und Zufluchtsort. Zivilisation und Industrialisierung haben Decetten von Territorium, Eigentum, wirtschaftlichem Reichtum und Macht ausgelöst. Fortan wurden ethische Regeln, gesellschaftliche Regulierung und intuitive Werte teilweise außer Kraft gesetzt und ersetzt. Fernverkehrsfahrzeuge wie Frachtschiffe und Züge ermöglichten eine beschleunigte Vermischung von Gütern und Technologien. Architekten lösen industrielle und infrastrukturelle Probleme mit neuen Ideen und neuen Gebäudetypen; Gestaltung städtischer und peripherer Umgebungen. Eine großartige Idee, die sich in einem ausgedehnten Austausch von Kulturen und Wissen manifestierte, endete seltsamerweise in einer ultimativen Ausbeutung unserer natürlichen Ressourcen. Eine Situation, die wir kaum verstehen oder handhaben können. Als Ergebnis stehen wir vor der Frage, wie wir unser menschliches, urbanes und architektonisches Ökosystem umgestalten. Der Artikel greift diese Verschiebung auf