bluuebunny/crossref_metadata_2025 huggingface dataset:
REVISITING THE ZIEGLER‐NICHOLS TUNING RULES FOR PI CONTROL — PART II THE FREQUENCY RESPONSE METHOD
Authors: Hägglund T. , J.Åström K.
Published: September 2010

This paper presents an analysis of the Ziegler‐Nichols frequency response method for tuning PI controllers, showing that this method has severe limitations. The limitations can be overcome by a simple modification for processes where the time delay is not too short. By a major modification it is possible to obtain new tuning rules that also cover processes that are lag dominated.
DIGITAL PID CONTROLLER DESIGN FOR DELAYED MULTIVARIABLE SYSTEMS
Authors: Zhang Yongpeng , Shieh Leang‐San , Akujuobi Cajetan M. , Ali Warsame
Published: September 2010

A new methodology is proposed to design digital PID controllers for multivariable systems with time delays. Except for a few parameters that are preliminarily selected, most of the PID parameters are systematically tuned using the developed plant state‐feedback and controller state‐feedforward LQR approach, such that satisfactory performance with guaranteed closed‐loop stability is achieved. In order to deal with the modeling error owing to the delay time rational approximation, an IMC structure is utilized, such that robust stability is achieved, without need for an observer, and with improved online tuning convenience. Using the prediction‐based digital redesign method, the digital implementation is obtained based on the above‐proposed analog controller, such that the resulting mixed‐signal system performance will closely match that of the analog controlled system. An illustrative example is given for comparison with alternative techniques.
STABILITY OF LINEAR TIME‐INVARIANT OPEN‐LOOP UNSTABLE SYSTEMS WITH INPUT SATURATION
Authors: Wang Wen‐Liang A. , Mukai Hiro
Published: September 2010

This paper analyzes the stability of a linear time‐invariant open‐loop unstable system subject to input saturation. First, we extend the idea of approximating the locally asymptotically stable region (controllable set) of the system for the case where the control is small enough to be unsaturated (inside the linear region), to the case when the control is allowed to saturate. It is shown that, when the Lyapunov descent criterion and the Kuhn‐Tucker Theorem is applied, a superior locally asymptotically stable region is found. A technique for approximating the locally asymptotically stable region is presented.
DISCRETIZING CONTINUOUS‐TIME CONTROLLERS WITH FUZZY LOGIC SYSTEMS AND ITS STABILITY ANALYSIS
Authors: Chuang Chen‐Chia , Jeng Jin‐Tsong , Lee Yung‐Cheng
Published: September 2010

In this paper, a new method, applying the fuzzy logic system, is proposed to discretize the continuous‐time controller in computer‐controlled systems. All the continuous‐time controllers can be reconstructed by the proposed method under the Sampling Theorem. That is, the fuzzy logic systems are used to add nonlinearity and to approximate smooth functions. Hence, the proposed controller is a new smooth controller that can replace the original controller, independent of the sampling time under the Sampling Theorem. Consequently, the proposed controller not only can discretize the continuous‐time controllers, but also can tolerate a wider range of sampling time uncertainty. Besides, the input‐output stability is proposed for discretizing the continuous‐time controller of the fuzzy logic systems. Finally, computer simulation shows that the proposed method can easily reconstructthe continuous‐time controller and has very good robustness for different sampling times.
INCORPORATING PRACTICAL AND SYNTHESIS CONTENTS IN UNDERGRADUATE CONTROL EDUCATION
Authors: Hang C.C.
Published: September 2010

This paper revisits the effort over the last decade in making undergraduate control education more useful and attractive to both the control engineers and the engineers at large. With the help of further coverage in new textbooks, more practical and synthesis contents in the control courses have been incorporated. Gaps still exist, particularly in the areas of PID control and auto‐tuning, fuzzy control, overall control strategy, control structure and systems thinking, and these will be elaborated. A major challenge is in the coverage of more practical and synthesis contents in the introductory common control course for all engineers. How this may be resolved is discussed. Finally, the need for new teaching approaches such as the use of interesting case studies and the use of problem‐based learning will be outlined.
OPTIMAL TRACKING CONTROL FOR DISCRETE TIME‐DELAY SYSTEMS WITH PERSISTENT DISTURBANCES
Authors: Tang Gong‐You , Sun Hui‐Ying , Liu Yi‐Min
Published: September 2010

Optimal tracking control (OTC) for discrete time‐delay systems affected by persistent disturbances with quadratic performance indexes is considered. Optimal tracking controller is designed based on a sensitivity approximation approach. By introducing a sensitivity parameter, we transform the original OTC problem into a series of difference equations without time‐advance on time‐delay terms. The obtained OTC law consists of analytic feedback and feedforward terms, and a compensation term, which is the sum of the infinite series of adjoint vectors. The compensation term can be obtained with an iterated formula for the adjoint vectors. A simulation example shows that the approximation approach is effective in tracking the reference input and robust with respect to exogenous persistent disturbances.
ROBUST FAULT DETECTION AND ISOLATION FOR UNCERTAIN LINEAR RETARDED SYSTEMS
Authors: Jiang Canghua , Zhou Donghua , Gao Furong
Published: September 2010

A robust fault detection and isolation scheme is proposed for uncertain continuous linear systems with discrete state delays for both additive and multiplicative faults. Model uncertainties, disturbances and noises are represented as unstructured unknown inputs. The proposed scheme consists of a Luenberger observer for fault detection and a group of adaptive observers, one for each class of faults, for fault isolation. The threshold determination and fault isolation are based on a multi‐observer strategy. Robustness to model uncertainties and disturbances can be guaranteed for the scheme by selecting proper thresholds. All the signals, i.e., the fault estimate and the state and output estimation errors of each isolation observer can be shown to be uniformly bounded, and the estimate of the fault by the matched observer is shown to be satisfactory in the sense of extended H2 norm. Furthermore, the sensitivity to fault and the fault isolability condition are analyzed also in the paper. Simulations of a heating process for detecting and isolating an actuator gain fault and an additive fault show the proposed scheme is effective.
A NEW INTEGRAL INEQUALITY APPROACH TO DELAY‐DEPENDENT ROBUST H∞ CONTROL
Authors: Zhang Xian‐Ming , Wu Min , Han Qing‐Long , She Jin‐Hua
Published: September 2010

A design method for the robust H∞ control of an uncertain linear system with a time‐varying state delay is proposed. First, an integral inequality that we recently obtained is employed to establish a new delay‐dependent bounded real lemma for a system with a time‐varying delay. The lemma uses neither a model transformation nor a bounding technique for cross terms. Then, the lemma is used in combination with a matrix decomposition method to derive delay‐dependent conditions for the existence of robust H∞ control based on linear matrix inequalities. Finally, some numerical examples are given to demonstrate the validity of the method.
A COMPARATIVE STUDY ON COMPUTATIONAL SCHEMES FOR NONLINEAR MODEL PREDICTIVE CONTROL
Authors: Minh Vu Trieu , Afzulpurkar Nitin
Published: September 2010

This paper briefly reviews development of nonlinear model predictive control (NMPC) schemes for finite horizon prediction and basic computational algorithms that can solve the stable real‐time implementation of NMPC in space state form with state and input constraints. In order to ensure stability within a finite prediction horizon, most NMPC schemes use a terminal region constraint at the end of the prediction horizon — a particular NMPC scheme using a terminal region constraint, namely quasi‐infinite horizon, that guarantees asymptotic closed‐loop stability with input constraints is presented. However, when nonlinear processes have both input and state constraints, difficulty arises from failure to satisfy the state constraints due to constraints on input. Therefore, a new NMPC scheme without a terminal region constraint is developed using soften state constraints. A brief comparative simulation study of two NMPC schemes: quasi‐infinite horizon and soften state constraints is done via simple nonlinear examples to demonstrate the ability of the soften state constraints scheme. Finally, some features of future research from this study are discussed.
EVOLUTIONARY SEARCH FOR LIMIT CYCLE AND CONTROLLER DESIGN IN MULTIVARIABLE NONLINEAR SYSTEMS
Authors: Eftekhari M. , Katebi S. D.
Published: September 2010

A feature of many practical control systems is a Multi‐Input Multi‐Output (MIMO) interactive structure with one or more gross nonlinearities. A primary controller design task in such circumstances is to predict and ensure the avoidance of limit cycling conditions followed by achieving other design objectives. This paper outlines how such a system may be investigated using the Sinusoidal Input Describing Function (SIDF) philosophy quantifying magnitude, frequency and phase of any possible limit cycle operation. While Sinusoidal Input Describing function is a suitable linearization technique in the frequency domain for assessment of stability and limit cycle operation, it can not be employed in time domain. In order to be able to incorporate the time domain requirements in an overall controller design technique, the appropriate linearization technique suggested here is the Exponential Input Describing Function (EIDF).

First, an evolutionary search based on a multi‐objective formulation is employed for the direct solution of the harmonic balance system matrix equation. The search is based on Multi‐Objective Genetic Algorithms (MOGA) and is capable of predicting specified modes of theoretically possible limit cycle operation.

Second, the design requirements in time as well as frequency domain are formulated by a set of constraint inequalities. A numerical synthesis procedure also based on Multi‐Objective Genetic Algorithm is employed to adjust the initial compensator parameters to meet the imposed constraints. Robust stability and robust performance are investigated with respect to linearization uncertainty within the context of multiobjective formulation. In order to make the Genetic Algorithm (GA) search more amenable to design trade‐off between different and often contradictory specifications, a weighted sum of the functions is introduced. This criterion is subsequently optimized subject to the nonlinear system dynamics and a set of design requirements. Examples of use are given to illustrate the effectiveness of the proposed approach.
INTELLIGENT MODELING AND CONTROL OF WASHING MACHINE USING LOCALLY LINEAR NEURO‐FUZZY (LLNF) MODELING AND MODIFIED BRAIN EMOTIONAL LEARNING BASED INTELLIGENT CONTROLLER (BELBIC)
Authors: Lucas Caro , Milasi Rasoul M. , Araabi Babak N.
Published: September 2010

Intelligent control of home appliances has, in recent years, attracted much theoretical attention, as well as becoming a major factor for industrial and economic success and rapid market penetration. Washing Machines represent an important market. Intelligent control techniques are capable of providing useful means for both easier use and energy and water conservation. In this paper, the authors use two techniques that have successfully been used in other intelligent modeling and control applications. Firstly, the authors use a neuro‐fuzzy locally linear model tree system for data driven modeling of the machine. Secondly, the authors use a neural computing technique, based on a mathematical model of amygdala and the limbic system, for emotional control of the washing machine. The obtained results indicate the applicability of the proposed techniques in this important business sector.
A DIRECT APPROACH TO THE DESIGN OF ROBUST TRACKING CONTROLLERS FOR UNCERTAIN DELAY SYSTEMS
Authors: Ni Mao‐Lin , Li Guo
Published: September 2010

The robust tracking and model following problem of linear uncertain time‐delay systems is investigated in this paper. By using the solution of the algebraic Riccati equation, this paper presents a direct approach to the design of robust tracking controllers. The system is controlled to track dynamic inputs generated from a reference model. In the case of matched uncertainties, the proposed controller ensures uniform ultimate boundedness of tracking errors and, furthermore, the bounds can be made arbitrarily small. In the case of mismatched uncertainties, a sufficient condition is presented such that the controller guarantees uniform ultimate boundedness of tracking errors. Compared with existing results, the main feature of the approach proposed in this paper is that it does not require any precompensator even for the non‐Hurwitz nominal system and, obviously, it is a direct method. It also employs linear controllers rather than nonlinear ones. Therefore, the designing method is simple for use and the resulting controller is easy to implement. Numerical examples show that this scheme can accommodate larger uncertainties and is likely to produce less conservative results.
STABILITY ANALYSIS OF UNCERTAIN DISCRETE‐TIME SYSTEMS WITH TIME‐VARYING STATE DELAY: A PARAMETER‐DEPENDENT LYAPUNOV FUNCTION APPROACH
Authors: Gao Huijun , Lam James , Chen Tongwen , Wang Changhong
Published: September 2010

This paper presents several new robust stability conditions for linear discrete‐time systems with polytopic parameter uncertainties and time‐varying delay in the state. These stability criteria, derived by defining parameter‐dependent Lyapunov functions, are not only dependent on the maximum and minimum delay bounds, but also dependent on uncertain parameters in the sense that different Lyapunov functions are used for the entire uncertainty domain. It is established, theoretically, that these robust stability criteria for the nominal and constant‐delay case encompass some existing result as their special case. The delay‐dependent and parameter‐dependent nature of these results guarantees the proposed robust stability criteria to be potentially less conservative.
PERSISTENT EXCITATION IN A SHUNT DC MOTOR UNDER ADAPTIVE CONTROL
Authors: Huang Jeng‐Tze
Published: September 2010

The adaptive input‐output linearizing control has been successful in achieving the asymptotic output tracking stability of a shunt DC motor, however, persistent excitation (PE) of the regressor has not been investigated. PE is known to be the necessary and sufficient condition for the exponential stability of a general adaptive system. Its fulfillment can be checked a priori when all the states entering the regressor track a prescribed trajectory asymptotically. However, it is rather difficult for this application because the regressor depends partly on the estimated parameters and the unobservable state which do not converge to any known signal at all. Nevertheless, it is found that such a task can actually be accomplished under some mild assumptions on the system and the reference trajectories. Simulation results confirming the assertion are given in the final sectien.
SIMPLE INSTABILITY CRITERION FOR A CLASS OF SINGULAR SYSTEMS WITH MULTIPLE TIME DELAYS
Authors: Sun Yeong‐Jeu
Published: September 2010

In this paper, the instability for a class of singular systems with discrete and distributed time delays is investigated. Simple instability criterion, which is a delay‐dependent criterion, is derived to guarantee the instability of such systems. Finally, a numerical example is given to illustrate the use of the main result.
ON ROBUST STABILITY OF LINEAR NEUTRAL SYSTEMS WITH MIXED DELAYS AND NORM‐BOUNDED UNCERTAINTY
Authors: Yang Bin , Jiang Yanhong , Wang Jincheng , Zhong Chongquan , Wang Wei
Published: September 2010

This paper investigates the robust stability of linear neutral systems with mixed delays and norm‐bounded uncertainty. Using new Lyapunov‐Krasovskii functionals, less conservative delay‐dependent robust stability conditions for such systems in terms of linear matrix inequalities (LMIs) are derived. Numerical examples show that the results obtained in this paper significantly improve the estimate of the stability limit over some existing results in other literature.
DECENTRALIZED STABILIZATION OF H FUZZY CONTROL FOR NONLINEAR MULTIPLE TIME‐DELAY INTERCONNECTED SYSTEMS
Authors: Hsiao Feng‐Hsiag , Xu Sheng‐Dong , Lin Chia‐Yen , Chou Yu‐Jun , Chen Yu‐Ching
Published: September 2010

A robustness design of fuzzy control is proposed in this paper to overcome the effect of modeling errors between nonlinear multiple time‐delay systems and fuzzy models. In terms of Lyapunov's direct method, a stability criterion is derived to guarantee the UUB (uniformly ultimately bounded) stability of nonlinear multiple time‐delay interconnected systems with disturbances. Based on this criterion and the decentralized control scheme, a set of fuzzy controllers is then synthesized via the technique of parallel distributed compensation (PDC) to stabilize the nonlinear multiple time‐delay interconnected systems and the Hcontrol performance is achieved in the mean time.
DEADLOCK AVOIDANCE FOR FLEXIBLE MANUFACTURING SYSTEMS WITH CHOICES BASED ON DIGRAPH CIRCUIT ANALYSIS
Authors: Zhang Wenle , Judd Robert P.
Published: September 2010

Due to existence of concurrent part flows and resource sharing in modern automated flexible manufacturing systems (FMS), deadlock is a common problem and its occurrence causes loss of productivity. When a manufacturing system is modeled by a digraph, existence of circuits in such a graph is a necessary condition for deadlock. Our previous work further showed that the knot and order of a circuit is closely related to impending deadlocks — a type of deadlock that is more difficult to detect. In this paper, we extend our previous work on deadlock avoidance for flexible manufacturing systems to allow choices in process flows (a.k.a., flexible part routing). Due to introduction of choices, part flow dynamics become more sophisticated and our previous results are no longer valid. A systematic circuit analysis is performed in this paper. New concepts such as broken circuit, basic circuit, choice circuit and supremal circuit are introduced to reduce significantly the number of circuits thus improving efficiency of our approach. The extended method is highly permissive with the adjusted effective free space calculation to capture more necessary parts flow dynamics, especially when multiple knots exist in the digraph model. The online policy runs in polynomial time once the set of basic circuits of the digraph is computed offline. Simulation results on selected examples are given.
DESIGN, DEVELOPMENT AND PERFORMANCE STUDIES OF EMBEDDED ELECTRONIC CONTROLLED ONE AXIS SOLAR TRACKING SYSTEM
Authors: Arasu A. Valan , Sornakumar T.
Published: September 2010

An electronic embedded system controlled one axis automatic solar tracking system is designed and developed for parabolic trough collector employed for hot water generation. The electronic circuit diagram with detailed description and performance of the tracking system are presented. The position of Sun is successfully detected using light dependent resistors, with an accuracy of 0.1°. The accuracy is much greater than the required 0.5°, which is determined from the collector acceptance angle test. The tracking mechanism maximum error is found to be 0.18°. The tracking mechanism has proved to be sufficiently accurate for the present solar energy application i.e. hot water generation. Extensive testing of the parabolic trough solar collector hot water generation system proved that the tracking mechanism is very effective.
IS A MIXED DESIGN OF OBSERVER‐CONTROLLERS FOR TIME‐DELAY SYSTEMS INTERESTING?
Authors: Sename O.
Published: September 2010

This paper deals with H∞ observer‐based feedback control for linear time‐delay systems, in the framework of delay independent stability. We will propose a new LMI solution to observer‐controller design that ensures a disturbance attenuation level for the controlled output as well as for the state estimation error, which is an open problem. This will be compared with a well‐known solution and with a usual strategy in control which consists in designing the observer and the controller separately. Our aim is to try to bring a positive answer to the following question: is there an interest to solve the problem in a single (unique) formulation or should we design separately the observer and the controller? An application to a wind tunnel model is provided to emphasize the interest of the given results, particularly in comparison with existing results on H∞ observer‐based control.
DISTURBANCE DECOUPLING FOR NONLINEAR TIME‐DELAY SYSTEMS
Authors: Mérquez‐Martínez L.A. , Moog C.H.
Published: September 2010

The disturbance decoupling problem is studied for a general class of nonlinear systems with multiple delays. Necessary and sufficient conditions are given for the solvability of the problem, in geometric terms involving so‐called controlled invariant modules. An example is included which shows that there is no unique “standard” solution to disturbance decoupling in opposition to the well known situation of systems without delays.
COMPLEXITY RELAXATION OF THE TENSOR PRODUCT MODEL TRANSFORMATION FOR HIGHER DIMENSIONAL PROBLEMS
Authors: Baranyi Péter , Petres Zoltén , Korondi Péter , Yam Yeung , Hashimoto Hideki
Published: September 2010

The Tensor Product (TP) model transformation method was proposed recently as an automated gateway between a class of non‐linear models and linear matrix inequality based control design. The core of the TP model transformation is the higher order singular value decomposition of a large sized tensor, which requires high computational power that is usually outside of a regular computer capacity in cases of higher dimensionality. This disadvantage restricts the utilization of the TP model transformation to models having smaller dimensionality. The aim of this paper is to propose a computationally relaxed version of the TP model transformation. The paper also presents a 6 dimensional example to show the effectiveness of the modified transformation.
H∞ CONTROL FOR DELAYED DISCRETE FUZZY SYSTEMS
Authors: Liu Huaping , Sun Fuchun , Sun Zengqi
Published: September 2010

In this paper, the H∞ controller design for discrete‐time fuzzy systems with time‐delay is investigated. An improved Lyapunov‐ Krasovskii function which is explicitly dependent on the membership functions is proposed to obtain less conservative results. The controller design problem can be cast into a set of linear matrix inequalities. Finally, a simulation example is given to show the effectiveness of the proposed design approaches.
APPROXIMATION PROPERTIES OF TP MODEL FORMS AND ITS CONSEQUENCES TO TPDC DESIGN FRAMEWORK
Authors: Tikk Domonkos , Baranyi Péter , Patton Ron J.
Published: September 2010

Tensor Product Distributed Compensation (TPDC) is a recently established controller design framework, that links TP model transformation and Parallel Distributed Compensation (PDC) framework. TP model transformation converts different models to a common representational form: the TP model form. The primary aim of this paper is to investigate the approximation capabilities of TP model forms, because the universal applicability of TPDC framework strongly relies on it. We point out that the set of functions that can be approximated arbitrarily well by TP forms with bounded number of components lies no‐where dense in the set of continuous functions. Consequently, in a class of control problems this property necessitates the usage of tradeoff techniques between the accuracy and the complexity of the TP form, which is easily feasible within the TPDC framework unlike in analytic models.
ADAPTIVE FUZZY‐BASED MIXED H2/H∞ TRACKING CONTROL DESIGN IN UNCERTAIN ROBOTIC SYSTEMS
Authors: Tseng Chung‐Shi , Jan Rong‐Maw
Published: September 2010

In this study, an adaptive fuzzy‐based mixed H2/H∞ tracking control design is developed in robotic systems under unknown or uncertain plant parameters and external disturbances. The mixed H2/H∞ control design has the advantage of both H2 optimal control performance and H∞ robust control performance and the fuzzy adaptive control scheme is used to compensate for the plant uncertainties. By virtue of the skew‐symmetric property in the robotic systems and adequate choice of state variable transformation, sufficient conditions are developed for the adaptive fuzzy‐based mixed H2/H∞ tracking control problems in terms of a pair of coupled algebraic equations instead of a pair of coupled differential equations. The proposed methods are simple and the coupled algebraic equations can be solved analytically. Simulation results indicate that the desired performance of the proposed adaptive fuzzy‐based mixed H2/H∞ tracking control schemes for the uncertain robotic systems can be achieved.
ANALYSIS AND DESIGN OF FEEDBACK CONTROL SYSTEMS WITH TRACKING ERRORS SQUARE
Authors: Tsay Tain‐Sou
Published: September 2010

In this study, a command tracking error square control scheme is first proposed for analysis and design of feedback control systems. One of the tracking errors is low‐pass filtered and used in the feedback loop for gain adaptation; the other is used in the forward loop for command tracking control. The overall systems are nonlinear feedback systems, and can be reconfigured to an automatic gain control (AGC) loop with command tracking error input. The stability and robustness of the controlled systems are verified by time response, frequency response, and large parameter variation testing with a simple illustrating example and are finally applied to a complicated electro‐hydraulic velocity servo system with large load disturbance.
A ROBUST SENSOR FAULT TOLERANT CONTROL SCHEME IMPLEMENTED ON A CRANE
Authors: Tan Chee Pin , Edwards Christopher
Published: September 2010

This paper presents a sensor fault tolerant control scheme applied to a crane system. Sensor faults affect the system's performance in the closed‐loop when the faulty sensor readings are used to generate the control input. In this paper, the measured outputs are separated into potentially faulty and nonfaulty components, and the latter are injected into a linear observer to reconstruct the faults. The reconstruction is subtracted from the faulty sensors to form a compensated ‘virtual sensor’ and this signal is then used to generate the control input. A design method for the observer is also presented in which the reconstruction signal is made as insensitive as possible to any uncertainties or nonlinearities present in the system. Good results have been obtained; with reduced performance degradation during faulty conditions.
DISCRETE‐TIME OBSERVER‐BASED OUTPUT TRACKING CONTROLLER DESIGN FOR NONMINIMUM PHASE SYSTEMS WITH PERTURBATIONS
Authors: Chang Jeang‐Lin
Published: September 2010

In this paper, an observer‐based output tracking controller for an SISO nonminimum phase discrete‐time system is proposed. When the disturbances between two consecutive sampling instances do not vary significantly, the observer algorithm can simultaneously estimate the system states and the unknown perturbation, and can render the estimation errors of system states and perturbation constrained in a small bounded region. The control law, including a feedforward term and a feedback input, can make the tracking error constrained in a small bounded region with guaranteed system stability. A numerical example is presented to demonstrate the applicability of the proposed control scheme.
PARAMETRIC SOLUTIONS TO THE GENERALIZED SYLVESTER MATRIX EQUATION AX ‐ XF = BY AND THE REGULATOR EQUATION AX ‐ XF = BY + R
Authors: Zhou Bin , Duan Guang‐Ren
Published: September 2010

In this paper, explicit parametric solutions to the generalized Sylvester matrix equation AX ‐ XF = BY and the regulator matrix equation AX ‐ XF = BY + R are proposed without any transformation and factorization. The proposed solutions are presented in terms of the Krylov matrix of matrix pair (A, B), a symmetric operator and the generalized observability matrix of matrix pair (Z, F) where Z is an arbitrary matrix and is used to denote the degree of freedom in the solution. Due to its elegant form and convenient computation, these proposed solutions will play an important role in solving and analyzing these types of equations in control systems theory.
Blood–brain‐barrier disruption in chronic canine hypothyroidism
Authors: Pancotto Theresa , Rossmeisl John H. , Panciera David L. , Zimmerman Kurt L.
Published: September 2010

Background:Central nervous system (CNS) manifestations of hypothyroidism have been associated with cerebrovascular complications. Reports of cerebrospinal fluid (CSF) abnormalities are rare in hypothyroid dogs.

Objective:The aim of this study was to determine if chronic hypothyroidism causes blood–brain‐barrier (BBB) abnormalities that are detectable using indirect CSF biomarkers.

Methods:The study included 18 normal, euthyroid, female mixed‐breed dogs. Hypothyroidism was induced by131iodine administration in 9 dogs; 9 served as untreated controls. Evaluations included physical and neurologic examination, complete CSF analysis, serum and CSF protein electrophoresis, measurement of plasma vascular endothelial growth factor (VEGF) and serum S‐100B concentrations, and calculation of CSF albumin quota (AQ) and were conducted at baseline and 6, 12, and 18 months after induction of hypothyroidism. Data were analyzed using repeated measures ANOVA.

Results:At baseline, differences between groups were not detected for any variable. Throughout the study, controls dogs remained free of neurologic disease and had test variables that remained within reference intervals. Two hypothyroid dogs developed CNS signs during the study, and evidence of cerebrovascular disease was found at necropsy. At 12 and 18 months, the CSF total protein, VEGF, S‐100B, and fractional albumin concentrations, and AQ were significantly higher (P<.04) in hypothyroid dogs than controls. Among test variables assayed in serum or plasma, the only significant difference was a higher S‐100B concentration in hypothyroid dogs (P=.003) at 18 months.

Conclusions:BBB integrity is disrupted in chronic hypothyroidism. Significant increases in CSF concentrations of VEGF and S100‐B in hypothyroid dogs indicate dysfunction in both endothelial and glial elements of the BBB.
Classification, location and legitimacy of web-based suppliers of Viagra to the UK
Authors: Gallagher Cathal T , Chapman Laura E
Published: September 2010

Objectives

To categorise online suppliers of Viagra based on their legal status, and to quantify the suppliers within each category.

Methods

Google was used to search for websites offering to sell or supply either proprietary Viagra tablets or generic versions containing sildenafil citrate. Relevant websites were classified as falling into one of three categories, which were further subclassified. Simple descriptive statistics were calculated.

Key findings

The number of relevant sites found within the first 100 Google hits, following the removal of mirror and affiliate sites, was 44. Only 6.8% of sites identified were legitimate online pharmacies. Some 34.1% of sites offered to sell Viagra to patients in the UK without any form of medical consultation. Whether or not the online consultation offered by 59.1% of sites had to be completed in order to make a purchase could not be confirmed. The location of only three pharmacies could be ascertained; the remainder made various claims as to their location, which could not be verified.

Conclusions

We have been unable to verify that the questionnaires used for online consultations are scrutinised by any healthcare practitioners to determine the appropriateness of the treatment sought. This represents a serious safety concern for UK residents who procure drugs for erectile dysfunction on the internet.
Ca2+ imaging of activity in ICC‐MY during local mucosal reflexes and the colonic migrating motor complex in the murine large intestine
Authors: Bayguinov Peter O. , Hennig Grant W. , Smith Terence K.
Published: September 2010

Colonic migrating motor complexes (CMMCs) are neurally mediated, cyclical contractile and electrical events, which typically propagate along the colon every 2–3 min in the mouse. We examined the interactions between myenteric neurons, interstitial cells of Cajal in the myenteric region (ICC‐MY) and smooth muscle cells during CMMCs using Ca2+ imaging. CMMCs occurred spontaneously or were evoked by stimulating the mucosa locally, or by brushing it at either end of the colon. Between CMMCs, most ICC‐MY were often quiescent; their lack of activity was correlated with ongoing Ca2+ transients in varicosities on the axons of presumably inhibitory motor neurons that were on or surrounded ICC‐MY. Ca2+ transients in other varicosities initiated intracellular Ca2+ waves in adjacent ICC‐MY, which were blocked by atropine, suggesting they were on the axons of excitatory motor neurons. Following TTX (1 μm), or blockade of inhibitory neurotransmission with Nω‐nitro‐l‐arginine (l‐NA, a NO synthesis inhibitor, 10 μm) and MRS 2500 (a P2Y1 antagonist, 1 μm), ongoing spark/puff like activity and rhythmic intracellular Ca2+ waves (38.1 ± 2.9 cycles min−1) were observed, yet this activity was uncoupled, even between ICC‐MY in close apposition. During spontaneous or evoked CMMCs there was an increase in the frequency (62.9 ± 1.4 cycles min−1) and amplitude of Ca2+ transients in ICC‐MY and muscle, which often had synchronized activity. At the same time, activity in varicosites along excitatory and inhibitory motor nerve fibres increased and decreased respectively, leading to an overall excitation of ICC‐MY. Atropine (1 μm) reduced the evoked responses in ICC‐MY, and subsequent addition of an NK1 antagonist (RP 67580, 500 nm) completely blocked the responses to stimulation, as did applying these drugs in reverse order. An NKII antagonist (MEN 10,376, 500 nm) had no effect on the evoked responses in ICC‐MY. Following TTX application, carbachol (1 μm), substance P (1 μm) and an NKI agonist (GR73632, 100 nm) produced the fast oscillations superimposed on a slow increase in Ca2+ in ICC‐MY, whereas SNP (an NO donor, 10 μm) abolished all activity in ICC‐MY. In conclusion, ICC‐MY, which are under tonic inhibition, are pacemakers whose activity can be synchronized by excitatory nerves to couple the longitudinal and circular muscles during the CMMC. ICC‐MY receive excitatory input from motor neurons that release acetylcholine and tachykinins acting on muscarinic and NK1 receptors, respectively.
Development of a Two-Dimensional Streamline Curvature Code
Authors: Templalexis Ioannis , Pilidis Pericles , Pachidis Vassilios , Kotsiopoulos Petros
Published: September 2010

Two-dimensional (2D) compressor flow simulation software has always been a very valuable tool in compressor preliminary design studies, as well as in compressor performance assessment operating under uniform and non-uniform inlet conditions. This type of software can also be used as a supplementary teaching tool. In this context, a new streamline curvature (SLC) software has been developed capable of analyzing the flow inside a compressor in two dimensions. The software was developed to provide great flexibility, in the sense that it can be used as: (a) a performance prediction tool for compressors of a known design, (b) a development tool to assess the changes in performance of a known compressor after implementing small geometrical changes, (c) a design tool to verify and refine the outcome of a preliminary compressor design analysis, and (d) a teaching tool to provide the student with an insight of the 2D flow field inside a compressor and how this could be effectively predicted using the SLC method combined with various algorithms and cascade models. Apart from describing in detail the design, structure, and execution of the SLC software, this paper also stresses the importance of developing robust, well thought-out software and highlights the main areas a potential programmer should focus on in order to achieve this. This text also highlights the programming features incorporated into the development of the software in order to make it amenable for teaching purposes. The paper reviews in detail the set of cascade models incorporated for subsonic and supersonic flow, for design and off-design operating conditions. Moreover, the methods used for the prediction of surge and choke are discussed in detail. The code has been validated against experimental results, which are presented in this paper together with the strong and weak points of this first version of the software and the potential for future development. Finally, an indicative case study is presented in which the shift of streamlines and radial velocity profiles is demonstrated under the influence of two sets of compressor inlet boundary conditions.
Experimental Measurements of Gas Turbine Flow Capacity Using a Novel Transient Technique
Authors: Povey T. , Sharpe M. , Rawlinson A.
Published: September 2010

Nozzle guide vane (NGV) flow capacity is perhaps the most important parameter for engine optimization. Inaccurate evaluation of capacity would lead to incorrect performance evaluation, and unmatched stages. A new semi-transient technique has been developed and demonstrated that will allow turbine designers to measure experimentally the effective throat area of an annular cascade of nozzle guide vanes at engine-representative Mach number, Reynolds number, and mainstream-to-cooling-flow pressure ratio. The technique allows NGV capacity to be measured to bias and precision uncertainties to 95% confidence of ±0.546% and ±0.028%, which compares well to large scale industrial facilities. Order-of-magnitude cost savings are offered over typical continuously running industrial facilities by running in blowdown mode from a receiver tank, thus removing the need for large scale compressor plant. To demonstrate the technique, a high mass flow rate blowdown tunnel was developed and commissioned at the University of Oxford, and the capacity of a high-pressure NGV from a large civil aircraft engine was experimentally determined. Experimental results are presented, which allow the precision error to be accurately calculated. A detailed uncertainty analysis is given from which the bias error is computed. It is shown that the low precision error the new technique offers means that it is ideally suited to investigations in which secondary influences on capacity are the subject of the investigation. The technique is of industrial significance because methods to compute engine capacity analytically or computationally do not yet provide sufficient accuracy for engine optimization, and the new technique offers equivalent accuracy at a much reduced cost over conventional experimental techniques. By performing an uncertainty analysis using experimental data it is shown that the increase in uncertainty due to the semi-transient (as opposed to steady state) nature of the technique is approximately 0.004% (to 95% confidence), and is entirely negligible. The experimentally measured trend of capacity against pressure ratio is compared with simple 1D, 2D, and 3D inviscid models, and an analytical correction for total pressure loss is performed. It is shown that while a simple 3D model is better than a 1D model (up to 1.5% improvement) for crude estimates of engine capacity, experimental trends are poorly predicted by such simple techniques. An analytical correction for total pressure loss increases the difference between 3D prediction and experiment. The experimental data demonstrate the complex nature of the process by which nozzle capacity is determined and the need for accurate, low-cost experimental techniques for capacity measurement. Correction to engine conditions is discussed.
Investigation of Periodically Unsteady Flow in a Radial Pump by CFD Simulations and LDV Measurements
Authors: Feng Jianjun , Benra Friedrich-Karl , Dohmen Hans Josef
Published: September 2010

The periodically unsteady flow fields in a low specific speed radial diffuser pump have been investigated both numerically and experimentally for the design condition (Qdes) and also one part-load condition (0.5Qdes). Three-dimensional, unsteady Reynolds-averaged Navier–Stokes equations are solved on high-quality structured grids with the shear stress transport turbulence model by using the CFD (computational fluid dynamics) code CFX-10. Furthermore, two-dimensional laser Doppler velocimetry (LDV) measurements are successfully conducted in the interaction region between the impeller and the vaned diffuser, in order to capture the complex flow with abundant measurement data and to validate the CFD results. The analysis of the obtained results has been focused on the behavior of the periodic velocity field and the turbulence field, as well as the associated unsteady phenomena due to the unsteady interaction. In addition, the comparison between CFD and LDV results has also been addressed. The blade orientation effects caused by the impeller rotation are quantitatively examined and detailedly compared with the turbulence effect. This work offers a good data set to develop the comprehension of the impeller-diffuser interaction and how the flow varies with relative impeller position to the diffuser in radial diffuser pumps.
Numerical Assessment of the Noise Signature Sidewall Contamination of a Linear Cascade With Moving Bars
Authors: Burgos Manuel A. , Corral Roque
Published: September 2010

The effect of the finite extent of a linear cascade on the acoustic and vortical modes generated at the cascade exit by a set of moving bars located at the inlet is assessed by means of a numerical study. The sidewall interference is studied for an airfoil, which is representative of the midsection of a low pressure turbine airfoil. The deviations from the purely periodic steady state have been also investigated. It is concluded that both the unsteady pressure distributions on the airfoil and the mode-decomposition at the cascade exit show a reasonable matching with the purely periodic case, provided that the nominal interblade phase angle is taken into account to postprocess the numerical data. This conclusion is a key element to the investigation of the scattering and propagation of pure tones in turbomachinery in high speed linear cascades.
Redesign of a Low Speed Turbine Stage Using a New Viscous Inverse Design Method
Authors: Roidl Benedikt , Ghaly Wahid
Published: September 2010

The midspan section of a low speed subsonic turbine stage that is built and tested at DFVLR, Cologne, is redesigned using a new inverse blade design method, where the blade walls move with a virtual velocity distribution derived from the difference between the current and target pressure distributions on the blade surfaces. This new inverse method is fully consistent with the viscous flow assumption and is implemented into the time-accurate solution of the Reynolds-averaged Navier–Stokes equations. An algebraic Baldwin–Lomax turbulence model is used for turbulence closure. The mixing plane approach is used to couple the stator and rotor regions. The computational fluid dynamics (CFD) analysis formulation is first assessed against the turbine stage experimental data. The inverse formulation that is implemented in the same CFD code is assessed for its robustness and merits. The inverse design method is then used to study the effect of the rotor pressure loading on the blade shape and stage performance. It is also used to simultaneously redesign both stator and rotor blades for improved stage performance. The results show that by carefully tailoring the target pressure loading on both blade rows, improvement can be achieved in the stage performance.
Influence of Stator-Rotor Interaction on the Aerothermal Performance of Recess Blade Tips
Authors: Mischo Bob , Burdet André , Abhari Reza S.
Published: September 2010

This paper investigates the influence of stator-rotor interaction on the stage performance of three blade tip geometries. A reference flat tip is used to assess two different recess blade geometries. The study is made in the context of the realistic turbine stage configuration provided by the ETHZ 1.5-stage LISA turbine research facility. This numerical investigation describes the details of unsteady recess cavity flow structure and confirms the beneficial effects of the improved recess geometry over the flat tip and the nominal recess design both in terms of stage efficiency and tip heat load. The tip flow field obtained from the improved recess design combines the advantages of a nominal recess design (aerodynamic sealing) and the flat tip configuration. The turbine stage capacity is almost unchanged between the flat tip and the improved recess tip cases, which simplifies the design procedure when using the improved recess design. The overall heat load in the improved recess case is reduced by 26% compared with the flat tip and by 14% compared with the nominal recess. A key finding of this study is the difference in effects of the upstream stator wake on the recess cavity flow. Where cavity flow in the nominal design is only moderately influenced, the improved recess cavity flow shows enhanced flow unsteadiness. The tip Nusselt number from a purely steady-state prediction in the nominal recess case is nearly identical to the time-average prediction. The improved design shows a 6% difference between steady-state and time-average tip Nusselt number. This is due to the strong influence of the wake passing on the recess cavity flow. In fact, the wake enhances a small flow difference at the leading edge of the recess cavity between the nominal and improved recess cavities, which results in a completely different flow field further downstream in the recess cavity.
Computational Study of a Midpassage Gap and Upstream Slot on Vane Endwall Film-Cooling
Authors: Hada Satoshi , Thole Karen A.
Published: September 2010

Turbines are designed to operate with high inlet temperatures to improve engine performance. To reduce NOx resulting from combustion, designs for combustors attempt to achieve flat pattern factors that results in high levels of heat transfer to the endwall of the first stage vane. Film-cooling is still one of the most effective cooling methods for many component features including the endwall. This paper presents results from a computational study of a film-cooled endwall. The endwall design considers both an upstream slot, representing the combustor—turbine junction, and a midpassage slot, representing the mating between the adjacent vanes. The focus of this study is on comparing adiabatic effectiveness levels on the endwall with varying leakage flowrates and gap widths. Results indicate reasonable agreement between computational predictions and experimental measurements of adiabatic effectiveness levels along the endwall. The results of this study show that the midpassage slot has a large influence on the coolant coverage. It was also shown that by raising the combustor relative to the downstream vane endwall, better coolant coverage from the combustor-turbine slot could be achieved.