http://www.nt.ntnu.no/users/skoge/prost/proceedings/ifac2008/data/papers/3557

State-Dependent Riccati Equation (SDRE) Control: A Survey

Successful building design is becoming an increasingly complex task, due to a growing demand to satisfy more ambitious environmental, societal and economical performance requirements. The application of climate adaptive building shells (CABS) has recently been put forward as a promising alternative within this strive for higher levels of sustainability in the built environment. Compared to conventional facades, CABS offer potential opportunities for energy savings as well improvement of indoor environmental quality. By combining the complementary beneficial aspects of both active and passive building technologies into the building envelope, CABS can draw upon the concepts of adaptability, multi-ability and evolvability. The aim of this paper is to present a comprehensive review of research, design and development efforts in the field of CABS. Based on a structured literature review, a classification of 44 CABS is made to place the variety of concepts in context with each other, and concurrent developments. In doing so, the overall motivations, enabling technologies, and characteristic features that have contributed to the development of CABS are highlighted. Despite the positive perspectives, it was found that the concept of CABS cannot yet be considered mature. Future research needs and further challenges to be resolved are therefore identified as well.

/pdf/climate-adaptive-building-shells-state-of-the-art-and-future-jmf64i6vb8.pdf

Climate adaptive building shells: state-of-the-art and future challenges

Multirobot systems (MRS) are, nowadays, an important research area within robotics and artificial intelligence and a growing number of systems have recently been presented in the literature. Since application domains and tasks that are faced by MRS are of increasing complexity, the ability of the robots to cooperate can be regarded as a fundamental feature. In this paper, we present a survey of the recent work in the area by specifically examining the forms of cooperation and coordination realized in the MRS. In particular, we propose a new taxonomy for classification of the approaches to coordination in MRS and we describe some systems, which we consider representative in our taxonomy. We finally discuss the outcomes of our analysis and try to highlight future trends of the research on MRS.

/pdf/multirobot-systems-a-classification-focused-on-coordination-263wxuffb6.pdf

Multirobot systems: a classification focused on coordination

El artículo tiene como objetivo evaluar el nivel de desarrollo de la capacidad de absorción realizada (RACAP) en las Pyme colombianas. Se parte de una muestra de 363 Pyme colombianas (Dane,2012), se usa una revisión de literatura con apoyo del análisis de contenido y un modelo de regresión lineal, que permiten mostrar la existencia de una correlación lineal positiva entre la adquisición y asimilación del conocimiento externo en las organizaciones objeto de estudio,. Palabras clave: Capacidades de absorción, capacidades de absorción potencial, medición de las capacidades de absorción ABSTRACT:

Measurement of potential absorption capacity in Colombia's innovative companies [Medición de la capacidad de absorción potencial en las empresas innovadoras de Colombia]

A EROSPACE engineering applications greatly stimulated the development of optimal control theory during the 1950s and 1960s, where the objective was to drive the system states in such a way that some defined cost was minimized. This turned out to have very useful applications in the design of regulators (where some steady state is to be maintained) and in tracking control strategies (where some predetermined state trajectory is to be followed). Among such applications was the problem of optimal flight trajectories for aircraft and space vehicles. Linear optimal control theory in particular has been very well documented and widely applied, where the plant that is controlled is assumed linear and the feedback controller is constrained to be linear with respect to its input. However, the availability of powerful low-cost microprocessors has spurred great advantages in the theory and applications of nonlinear control. The competitive era of rapid technological change, particularly in aerospace exploration, now demands stringent accuracy and cost requirements in nonlinear control systems. This has motivated the rapid development of nonlinear control theory for application to challenging, complex, dynamical real-world problems, particularly those that bear major practical significance in aerospace, marine, and defense industries. Infinite-time horizon nonlinear optimal control (ITHNOC) presents a viable option for synthesizing stabilizing controllers for nonlinear systems by making a state-input tradeoff, where the objective is to minimize the cost given by a performance index. The original theory of nonlinear optimal control dates from the 1960s. Various theoretical and practical aspects of the problem have been addressed in the literature over the decades since. In particular, the continuous-time nonlinear deterministic optimal control problem associated with autonomous (time-invariant) nonlinear regulator systems that are affine (linear) in the controls has been studied by many authors. The long-established theory of optimal control offers quite mature and well-documented techniques for solving this control-affine nonlinear optimization problem, based on dynamic programming or calculus of variations, but their application is generally a very tedious task. Bellman’s dynamic programming approach reduces to solving a nonlinear first-order partial differential equation (PDE), expressed by the Hamilton–Jacobi–Bellman (HJB) equation. The solution to the HJB equation gives the optimal performance/cost value (or storage) function and determines an optimal control in feedback form under some smoothness assumptions. Alternatively, in the classical calculus of variations, optimal control problems can be characterized locally in terms of the Hamiltonian dynamics arising from Pontryagin’s minimum principle. These are the characteristic equations of the HJB PDE, which result in a nonlinear, constrained two-point boundary value problem (TPBVP) that, in general, can only be solved by successive approximation of the optimal control input using iterative numerical techniques for each set of initial conditions. Numerically, even though the nonlinear TPBVP is somewhat easier to solve than the HJBPDE, control signals can only be determined offline and are thus best suited for feedforward control of plants for which the state trajectories are known a priori. Therefore, contrary to the dynamic programming approach, the resultant control law is not generally in feedback form. Open-loop control, however, is sensitive to random disturbances and requires that the initial state be on the optimal trajectory. In contrast, nonlinear optimal feedback has inherent robustness properties (inherent in the sense that it is obtained by ignoring uncertainty and disturbances). The potential difficulty with the HJB approach is that no efficient algorithm is available to solve the PDE when it is nonlinear and the problem dimension is high, making it impossible to derive exact expressions for optimal controls for most nontrivial problems of interest. The optimal can only be computed in special cases, such as linear dynamics and quadratic cost, or very low-dimensional systems. In particular, if the plant is linear time invariant (LTI) and the (infinite-time) performance index is quadratic, then the corresponding HJB equation for this infamous linear-quadratic regulator (LQR) problem reduces to an algebraic Riccati equation (ARE). Contrary to the well-developed and widely applied theory and computational tools for theRiccati equation (for example, see [1]), theHJB equation is difficult, if not impossible, to solve for most practical applications. The exact solution for the optimal control policies is very complex

Survey of State-Dependent Riccati Equation in Nonlinear Optimal Feedback Control Synthesis

The main objective of this research is to develop and evaluate the performance of strategies for cooperative control of autonomous air vehicles that seek to gather information about a dynamic target environment, evade threats, and coordinate strikes against targets. The air vehicles are equipped with sensors to view a limited region of the environment they are visiting, and are able to communicate with one another to enable cooperation. They are assumed to have some “physical” limitations including possibly maneuverability limitations, fuel/time constraints and sensor range and accuracy. The developed cooperative search framework is based on two inter-dependent tasks: (i) on-line learning of the environment and storing of the information in the form of a “target search map”; and (ii) utilization of the target search map and other information to compute on-line a guidance trajectory for the vehicle to follow. We study the stability of vehicular swarms to try to understand what types of communications are needed to achieve cooperative search and engagement, and characteristics that affect swarm aggregation and disintegration. Finally, we explore the utility of using-biomimicry of social foraging strategies to develop coordination strategies.

Cooperative Control for Autonomous Air Vehicles

: For nearly thirty years, both government and industry have actively explored research on interoperability measurement with the goal of creating a straightforward way of measuring, reporting, then improving the interoperability of complex networks of people, equipment, processes and organizations. Researchers have created frameworks and models, proposed measures, described levels, and listed a variety of qualitative factors in support of an interoperability measure. Within extant interoperability research, the authors' research has uncovered nearly three dozen definitions of interoperability, over five dozen distinct types of interoperability, numerous interoperability attributes, and fourteen foundational interoperability measurement models and methodologies. At least eleven research groups have been the centers-of-gravity for interoperability measurement research. This survey paper summarizes and focuses the current body of knowledge on interoperability measurement and identifies areas where further research is needed.

/pdf/survey-on-interoperability-measurement-1vz9yqvwlg.pdf

Survey on Interoperability Measurement

This paper explores the benefits of flying in a tight formation, mimicking the natural behavior of migratory birds such as geese. Based on computational work, some reduction in drag for the wingman is predicted based on the amount of wingtip overlap with the leader. The flight test looked specifically at four different lateral positions with varying degrees of wingtip overlap, all flown at 300 KIAS and 10,000 feet pressure altitude. The flight test had two primary objectives: 1.) The first objective was to evaluate the fuel savings in four different formation positions, and determine which was optimal. 2.) The second objective was to determine if the savings would increase further for trailing positions in a larger formation. The aircraft were manually flown, and positioning in the formation was achieved using visual clues. The results of the two-ship flight tests showed with 80% confidence that the wingman saved fuel in the predicted optimal position, 86% wingspan lateral spacing. This position yielded fuel savings of 8.8% ± 5.0%. The other lateral positions did not show a statistically significant fuel savings. The results were inconclusive as to the best position for the wingman to fly since none of them are statistically distinct. The three-ship formation results did not yield the expected results. Not only was there no significant difference between the two wingmen, but neither wingman showed any statistically significant fuel savings. The authors feel that the three-ship formation data is inconclusive due to the difficulty of trying to fly a stable position as the third aircraft in a formation, without precise relative location information and station-keeping ability.

Flight Test Results of Close Formation Flight for Fuel Savings

: As the U.S. military seeks to advance its ability to perform network-centric operations clearly an important factor is improving interoperability of systems of all types. Since only a rare system operates alone, improving the interoperability of networks of systems becomes our research goal. Many nonhomogeneous networks of technological human, and organizational systems are employed in all types of military operations. Within DoD, these systems and their operational uses are often described by Department of Defense Architecture Framework (DoDAF) architectures and include system, technical and operational views. With architecture as a foundation, a methodology for measuring interoperability called an Interoperability Score, is introduced. The methodology first defines a baseline measurement of interoperability for a non-homogeneous network of systems as they are used within an operational scenario or thread. The methodology then defines the theoretical optimum interoperability score and proposes some heuristics which can be used to improve overall network interoperability.

/pdf/the-interoperability-score-9ijgx4q3ht.pdf

The Interoperability Score

Despite its ubiquity in the systems engineering literature, flexibility remains an ambiguous concept. There exist a multitude of definitions, which vary not only by domain, but within domains as well. Furthermore, these definitions often conflict with one another, making it difficult to discern the intended meaning in a given study or to form generalizations across studies. Complicating matters, there is a plethora of related terminology that is often used carelessly and/or inter-changeably with flexibility. In this paper, we employ a novel ontological framework for clarifying salient aspects of extant flexibility-related terminology. While it was not possible to distill consensus definitions from the literature, we did identify certain dominant characteristics that enabled us to formulate a set of democratic definitions for flexibility, adaptability, and robustness, as well as recommended definitions for agility and versatility. We believe that the proposed definitions of these key system design principles may provide a baseline for improving analysis and communication among systems engineering practitioners and academics. © 2012 Wiley Periodicals, Inc. Syst Eng 16:

David R. Jacques

Papers

Cooperative Control for Autonomous Air Vehicles

Survey on Interoperability Measurement

Flight Test Results of Close Formation Flight for Fuel Savings

The Interoperability Score

An ontological framework for clarifying flexibility-related terminology via literature survey