Robust digital control of a high-performance engine

The design of a robust digital multivariable feedback control system for the F-100 turbofan jet engine is considered. The control system design problem is posed, and conditions for satisfying performance specifications and stability robustness are stated. The discrete LQG/LTR methodology is used to design a compensator that meets the stated specifications. New results for multi-input LQR loop shaping are derived. To get a reasonably low-order compensator, frequency-weighted reduced-order models are exploited, with the reduction error treated as an uncertainty.     

Rotary flexible joint control by fractional order controllers

In this paper, a fractional order control law is proposed and implemented for the evaluation of trajectory tracking performance of a rotary flexible-joint system. A state feedback based fractional integral control scheme is used in this proposed method. In this scheme, state feedback is responsible for stabilizing the system. The compensator, in series with the fractional integrator leads to obtain a similar closed-loop transient response like Bode’s ideal transfer function. The effectiveness of the proposed controller in tracking and being robust against parameter uncertainties is demonstrated through simulation. In addition, to show the usefulness of the proposed control scheme, the fractional controller is compared to an integer state feedback control by simulation and through experimentation on the Quanser’s rotary flexible-joint system.     

The Online Public Sphere in the Arab World: The War in Iraq on the Al Arabiya Website

Many aspects make online media attractive to news readers, including low cost, ease and speed of access, and the opportunity for readers to ask questions, provide feedback, participate in discussions, and interact with other readers in ways not previously possible. Given that traditional media in the Arab world generally are subject to strict government control, the participatory features that accompany the new online media should make these sources even more attractive to users. However, comments posted by readers of online media in the Arab world are still subject to some monitoring and content regulation. This study explores the potential of online media in the Arab world to foster civic engagement. The online source selected for study is www.alarabiya.net , the official website for the popular TV station Al Arabiya in Dubai. Ethnographic observation and analysis of the content of articles published during the Iraq War on Al Arabiya’s site and the responses they received show that Arabs not only challenged the views of the Al Arabiya site about the war, but they also offered their own versions of the truth.     

An approximation technique to tune PID controllers

Advanced controller synthesis techniques often result in high order controllers whose order exceeds the order of the plant and it is impractical to implement. The main use of the advanced synthesis techniques is to find the possible optimal performance of the system and thus to check how a practical simpler controller comes close to achieving that optimum. PID controllers are the most found in industry and here we describe a novel technique, based on approximation, to tune the parameters of PID controllers.     

Subsystem interconnection and near optimum control of discretebalanced systems

The relationship between subsystem interconnection of discrete balanced systems and the Hankel singular values is explored. Upper bounds on the spectral norm of the submatrices of the discrete balanced representation are derived by approximating the matrix Riccati equation by its power series expansion with respect to two scalar parameters related to the Hankel singular values. For diagonalizable symmetric discrete-time systems, the relation between the eigenvalues of the subsystems and the eigenvalues of the overall system is explored. It is shown that an upper bound on the distance between corresponding eigenvalues in these two sets is related to the ratio of the Hankel singular values     

Service Quality Gaps Analysis at SCECO-East, Saudi Arabia

This research examines the Saudi Consolidated Electric Company in the Eastern Province, a typical service provider in Saudi Arabia in which service quality is of primary importance. Four gaps have an impact on the consumer's evaluation of service quality: consumer expectation-management perception, service quality specification, service performance, and external communication. The study revealed that Gap 3 (service performance) is more critical than the others in affecting perceived service quality, making service delivery the main area of improvement. Frontline staff also agree that Gap 4 contributed to the problem (i.e., when delivery does not match the company's promises) but to a lesser degree than Gap 3.     

Thermische Kopplung chemischer Rührkesselreaktoren mit weiteren Anlagekomponenten (Teil 2)

Zusammenfassung Energiekosten k?nnen zus?tzlich verringert werden, wenn Energiestr?me, die durch chemische Reaktionen umgesetzt werden, bereits beim Erstellen der Schaltung der W?rmeübertrager berücksichtigt werden. Das Reaktionsgemisch kann durch einen aufzuheizenden Stoffstrom gekühlt oder durch einen abzukühlenden Stoffstrom aufgeheizt werden. In diesem Fall spricht man von einer thermischen Kopplung des chemischen Reaktors mit der betreffenden Anlagenkomponente. In der vorliegenden Arbeit wird die thermische Kopplung von Rührkesselreaktoren mit einer beliebigen Anlagenkomponente untersucht. Zun?chst wird der Bereich der Proze?parameter bestimmt, in welchem die Reaktionsführung technisch verwirklicht werden kann. Dieser wird als zul?ssiger Betriebsbereich bezeichnet. Anschlie?end wird ermittelt, für welche Reaktionsbedingungen die Energiekosten durch die thermische Kopplung verringert werden k?nnen. Dies schr?nkt den zul?ssigen Betriebsbereich zus?tzlich ein. Die kostengünstigste Schaltung der Apparate wird durch die Minimierung der j?hrlichen Gesamtkosten ermittelt. An einem vereinfachten Beispiel wird das vorgestellte Verfahren erl?utert. Teil 1 erschien als VDI-Forschungsheft 655/1989 (mit Kapitel 1 bis 3), 25 S., 30 Bilder und 83 Literaturhinweise überarbeitete Fassung der von der Fakult?t für Maschinenwesen der Universit?t Hannover genehmigten Dissertation des erstgenannten Verfassers.     

Model reduction via balanced realizations: an extension andfrequency weighting techniques

Two model-reduction methods for discrete systems related to balanced realizations are described. The first is a technique which utilizes the least controllable and observable subsystem in deriving a balanced discrete reduced-order model. For this technique as L ^∞ norm bound on the reduction error is given. The second method is a frequency-weighting technique for discrete- and continuous-time systems where the input-normal or output-normal realizations are modified to include a simple frequency weighting. For this technique, L^∞ norm bounds on the weighted reduction errors are obtained     

State feedback with fractional integral control design based on the Bode’s ideal transfer function

State feedback technique through a gain matrix has been a well-known method for pole assignment of a linear system. The technique could encounter a difficulty in eliminating the steady-state errors in some states. Introducing an integral element can effectively eliminate these errors. State feedback with fractional integral control is proposed, in this work, for pole placement of a linear time invariant system. The proposed method yields simple gain formulae. The paper presents the derivation of the design formulae. The method is applied to stabilise an inherently unstable inverted pendulum-cart system. Simulation and experimental results show the effectiveness of the proposed method for set-point tracking, disturbance rejection and stabilising the inverted pendulum. Comparison with the results obtained from applying Achermann’s formula is also presented.     

On modeling and performance analysis of non-cooperative multi-antenna multi-user MIMO systems

This work presents modeling and performance analysis of beamforming in non-cooperative multi-user multiple-input multiple-output (MU-MIMO) cellular systems using stochastic geometry based abstraction models. Particularly, a downlink MU-MIMO system is investigated in which an array of antenna elements at the base stations (BS) serves several user devices. We derive the closed-form expression of the complimentary cumulative distribution function (CCDF) of signal-to-interference-plus-noise ratio (SINR) representing the coverage probability for orthogonal pilot sequences and thereby characterize a number of related special cases. Moreover, closed-form expressions are also obtained for the CCDF of signal-to-interference ratio (SIR) for non-orthogonal pilot sequences and we also derive useful special cases of it and identify the support region of our analysis. Lastly, we define the numerical expression of ergodic capacity and utilize a partial fraction expansion to solve a simple form. Our contribution in this work is twofold, we not only provide a pedagogical tutorial-like exposition of stochastic geometry technique to model terrestrial networks, but also augment the existing literature in the field with aspects of frequency reuse factor, an indicator function for pilot usage, and the effect of pilot contamination. Simulation results are presented to support the theoretical part.