Nominal Cases Research Articles

Modified impulsive synchronization of hyperchaotic systems

In an original impulsive synchronization only instantaneous errors are used to determine the impulsive inputs. To improve the synchronization performance, addition of an integral term of the errors is proposed here. In comparison with the original form, the proposed modification increases the impulse distances which leads to reduction in the control cost as the most important characteristic of the impulsive synchronization technique. It can also decrease the error magnitude in the presence of noise. Sufficient conditions are presented through four theorems for different situations (nominal, uncertain, noisy, and noisy uncertain cases) under which stability of the error dynamics is guaranteed. Results from computer based simulations are provided to illustrate feasibility and effectiveness of the modified impulsive synchronization method applied on Rossler hyperchaotic systems.

How big can case systems get? Evidence from Scottish Gaelic

It is well known that case systems can be augmented by the accretion of adpositions to their objects. This paper documents and explores an extensive instance of such augmentation, far exceeding any studied to date, based on an analysis of a class of words in modern Scottish Gaelic (SG) the members of which have attributes of both prepositions and pronouns. Pedagogical materials tend to call these forms prepositional pronouns, yet present the forms in paradigms organized by prepositional element, as if they represented person-number inflections on prepositional bases. This approach does not translate well into a synchronic description, however, because deriving these forms from underlying sequences requires numerous ad hoc morphophonemic stipulations. Regardless of diachronic source(s), these forms are synchronically pronominal in distribution. Shifting to a whole-heartedly pronominal analysis entails a targeted expansion of pronominal paradigms, beyond the traditional 3 nominal cases to 14. Although a number of languages present a richer array of distinct pronominal case forms than those found among nouns (e.g. English, Spanish), SG is unique in the extent to which pronoun case forms exceed those of nouns. Moreover, English and Spanish pronouns show the remnants of a case system, whereas SG has created these distinctions.

Enhanced disturbance rejection for open-loop unstable process with time delay

The present study suggests a disturbance estimator design method for application to a recently published, two-degree-of-freedom, control scheme for open-loop, unstable processes with time delay. A simple PID controller cascaded with a lead–lag filter replaces the high-order disturbance estimator for enhanced performance. A new analytical method on the basis of the IMC design principle, featuring only one user-defined tuning parameter, is developed for the design of the disturbance estimator. Several illustrative examples taken from previous works are included to demonstrate the superiority of the proposed disturbance estimator. The results confirm the superior performance of the proposed disturbance estimator in both nominal and robust cases. The proposed method also offers several important advantages for industrial process engineers: it covers several classes of unstable process with time delay in a unified manner, and is simple and easy to design and tune.

Experimentally Verified Optimal Serpentine Gait and Hyperredundancy of a Rigid-Link Snake Robot

In this study, we examine, for a six-link snake robot, how an optimal gait might change as a function of the snake- surface interaction model and how the overall locomotion performance changes under nonoptimal conditions such as joint failure. Simulations are evaluated for three different types of friction models, and it is shown that the gait parameters for serpentine motion are very dependant on the frictional model if minimum power expenditure is desired for a given velocity. Experimental investigations then motivate a surface interaction model not commonly used in snake locomotion studies. Using this new model, simulation results are compared to experiments for nominal and nonnominal locomotion cases including actuator faults. It is shown that this model quite accurately predicts locomotion velocities and link profiles, but that the accuracy of these predictions degrades severely at speeds where actuator dynamics become significant.

Robust fault estimation of uncertain systems using an LMI‐based approach

AbstractGeneral recent techniques in fault detection and isolation (FDI) are based on H∞ optimization methods to address the issue of robustness in the presence of disturbances, uncertainties and modeling errors. Recently developed linear matrix inequality (LMI) optimization methods are currently used to design controllers and filters, which present several advantages over the Riccati equation‐based design methods. This article presents an LMI formulation to design full‐order and reduced‐order robust H∞ FDI filters to estimate the faulty input signals in the presence of uncertainty and model errors. Several cases are examined for nominal and uncertain plants, which consider a weight function for the disturbance and a reference model for the faults. The FDI LMI synthesis conditions are obtained based on the bounded real lemma for the nominal case and on a sufficient extension for the uncertain case. The conditions for the existence of a feasible solution form a convex problem for the full‐order filter, which may be solved via recently developed LMI optimization techniques. For the reduced‐order FDI filter, the inequalities include a non‐convex constraint, and an alternating projections method is presented to address this case. The examples presented in this paper compare the simulated results of a structural model for the nominal and uncertain cases and show that a degree of conservatism exists in the robust fault estimation; however, more reliable solutions are achieved than the nominal design. Copyright © 2008 John Wiley & Sons, Ltd.

The Performance Analysis of a Multi-Duct Proton Exchange Membrane Fuel Cell Cathode

A 3-D numerical study was carried out first to analyze flow, heat and mass transfer as well as current distribution in a single half-cell cathode duct of a Proton Exchange Membrane (PEM) fuel cell. From practical point of view, it is necessary to put the appropriate number of cells in a stack. Hence, the above study on a single half-cell is extended to a multiple ducts. Due to multi-duct configuration the assumption of uniform flow distribution would no longer hold true. Therefore, the duct flow maldistribution is considered in the simulation of the multiple ducts. The flow arrangement of the PEM fuel cell resembles that of the plate heat exchangers. Hence, the various types of flow distributions pertinent to the plate heat exchangers are applied to the PEM fuel cell ducts and their effects on heat and mass transfer as well as current distribution are studied in detail. The water formed at the active surface due to the electrochemical reaction diffuses through the porous layer and eventually enters the gas flow duct. A high gas velocity removes the product water at a faster rate from the duct. In nominal-linear and hyperbolic flow distribution cases, the mass fraction of water in the duct is more than that in severe-linear and hyperbolic flow distribution cases. This means that the membrane retains higher water content in nominal distribution cases. This in turn results in higher membrane conductivity and lower ohmic loss. This is the reason for better performance for nominal maldistribution cases over the severe maldistribution cases.

Efficient terrain correction in airborne and seaborne gravity gradiometry surveys

SUMMARY Proper terrain correction in airborne and seaborne gravity gradiometry surveys requires detailed digital elevation models (DEMs). However, due to standard low-pass filter techniques applied during acquisition, the required resolution of the DEMs is altered in commercial surveys. We quantify the ideal resolution for an example dataset with a new and practical method for performing terrain corrections based on Parker's 1972 Fourier domain calculation. In the same vein, we quantify the required spatial extents of DEMs for nominal cases. With these parameters quantified, we can optimize the terrain correction to improve efficiency in both gravity gradiometry forward modeling as well as terrain corrections. In an ideal case, we find that the required spatial extent of the DEM is roughly nine times the greatest relief in the terrain outside the survey area. For the specific case, we find that 20 meter resolution is suitable.

Predictor-Corrector Reentry Guidance Algorithm with Path Constraints for Atmospheric Entry Vehicles

The problem of reentry guidance for an atmospheric entry vehicle is taken up for the study with focus on the evolution of a guidance strategy, which satisfies both terminal and path constraints. For this purpose, the numerical predictor–corrector approach is adopted, and an algorithm, based on real-time trajectory planning, is presented. The proposed guidance algorithm generates a feasible trajectory at each guidance cycle during the reentry flight, which is a function of the reference trajectory generated at the previous cycle and the measured parameter dispersions. The predictor steering program includes the bank reversal philosophy, and the corrector algorithm is formulated based on two control parameters and two terminal constraints. The path constraints on heat rate, aerodynamic load, and dynamic pressure are implemented as part of the predictor–corrector algorithm, by designing a control law for following the allowable drag and drag rate profiles. This control law is implemented through steering corrections in each predictor step, which ensures that each predicted trajectory satisfies the path constraints. The performance results for nominal and dispersed cases show that the algorithm steers a typical entry vehicle along a feasible 3-D trajectory, which satisfies both terminal and path constraints.

Anti-windup design for the controllers of integrating processes with long delay.

For several superior controllers of theffrst-order integrating processes with long delay, the windup problems are analyzed in detail when the control signal saturates. The results show that these controllers have similar characteristics about the process input limitation. And then, a simple and effective anti-windup scheme, without an additional parameter, is designed for these controllers. Simulations run with three main controllers, and the results illustrate that the proposed method may achieve good performance under the nominal and model uncertainty cases.

Reliable$rm H_infty $Fuzzy Control for Continuous-Time Nonlinear Systems With Actuator Failures

This paper is concerned with the design of reliable Hinfin fuzzy controllers for continuous-time nonlinear systems with actuator failures. The Takagi and Sugeno fuzzy model is employed to represent a nonlinear system. The objective is to find a stabilizing state-feedback fuzzy controller such that the nominal Hinfin performance is optimized while satisfying a prescribed Hinfin performance constraint in the actuator failure cases. Based on the linear matrix inequality (LMI) techniques, two efficient methods for the design of a suboptimal reliable Hinfin fuzzy controller are proposed. Different Lyapunov functions are used during the design for the nominal and actuator failure cases, which lead to a less conservative controller design. In the first method, a single Lyapunov function is used for the actuator failure cases. The second method adopts a parameter-dependent Lyapunov function for the actuator failure cases, which further reduces the conservatism of the design. Finally, numerical simulations on the chaotic Rossler system are given to illustrate the effectiveness of the proposed design methods

Dynamics of Retrograde Electrons Returning From the Output Cavity in Klystrons

Loss of efficiency and tube oscillations have been attributed to electrons returning from the output cavity in klystrons due to excessive output cavity voltages. It is generally believed that the retrograde electrons lead to a relatively large harmonic current component in the input cavity, which overwhelms the input drive. Here, for the first time, detailed simulations describing the dynamics of retrograde particles for a nominal klystron design and cases with the shunt impedance of the output cavity increased, which show persistent harmonic bunching induced by the penultimate cavity, are presented. The maximum retrograde harmonic current is comparable to the current induced in the input cavity without the retrograde particles and can significantly influence the overall klystron behavior

Practical plastic layout optimization of trusses incorporating stability considerations

Frequently the topologies generated using conventional discrete structural layout optimization methods may be shown to be in unstable equilibrium with the specified applied loading. Previously proposed methods to overcome this problem have tended to suffer from either a lack of rigour in identifying unstable solutions, a failure to properly consider all means of ensuring the stability of a framework, or are likely to be very computationally expensive. This paper discusses the drawbacks of current methods and introduces a conceptually simple approach that incorporates nominal lateral force load cases in a plastic linear programming problem formulation. Examples of stable solutions identified by this approach are discussed along with future developments to increase the practicality and efficiency of the method.

Formula omitted] anti-windup for linear dead-time systems

In this paper, we address and solve the problem of anti-windup augmentation for linear systems with input and output delay. In particular, we give a formal definition of an optimal L 2 gain based anti-windup design problem in the global, local, robust and nominal cases. For each of these cases we show that a specific anti-windup compensation structure (which is a generalization of the approach in the Proceedings of the Fourth ECC, Brussels, Belgium, July 1997) is capable of solving the anti-windup problem whenever this solvable. The effectiveness of the proposed scheme is shown on a simple example taken from the literature, in which the plant is a marginally stable linear system.

Temperature Dependent Fracture Toughness of a Single Crystal Nickel Superalloy

Abstract An important application of nickel base superalloys is in the industrial gas turbine (IGT) industry, where the high temperature capabilities of these alloys are exploited. Extensive testing has focused on the tensile and fatigue properties of single crystal versions of these alloys. The single crystals are utilized in the hottest parts of the turbine, where a detailed knowledge of material behavior is critical to design and life assessment. However, studies on the effects of temperature on fracture toughness have largely been absent in both past and present literature. Therefore, the goal of this research is to characterize the fracture toughness properties of a second-generation single crystal nickel superalloy at elevated temperatures. The experimental methods follow ASTM guidelines, as does the analysis for the elastic (K) and plastic (J integral) deformation. The toughness values were invalid for plain strain fracture toughness, but this should be expected from a structural material. In spite of this fact, both the K- and J-based analyses reveal consistent trends. Increased plasticity at elevated temperatures results in an overall increase in toughness as temperature increases. Unusual cases with inclined pre-cracks and microstructural defects did not technically yield valid results, although they were consistent with the nominal cases. Overall, the results indicate that the toughness of single crystal nickel alloys is actually quite high. Thus, the lack of work in this subject is understandable. However, it would seem that any design and lifting work would benefit from an understanding of such a fundamental property.

Controllability assessment of plate-like structures with uncertainties under piezoelectric actuation

A controllability assessment of plate-like structures with uncertainties under piezoelectric actuation is performed in this paper. Different from the previous studies, a novel index is proposed to quantify the degree of controllability using the sensor/actuator transfer function. Influences of unmodelled high-frequency dynamics and structural parameter variations on controllability are discussed, and the relationship between the indices for the nominal and uncertain cases is derived. In order to validate the controllability assessment numerically, the modelling of a plate with piezoelectric actuation is developed with the consideration of the full coupling between the PZT actuators and the host plate, and verified by experiments. It is demonstrated that a proper design of the polyvinylidene flouride sensor would help eliminate effects of higher order modes on the basis of strain mode shapes. Since the latter is very sensitive to the mass and stiffness added by PZT actuators, the dynamics of PZT actuators must be taken into account during the design, as opposed to the case where a point transducer is used.

Syntax and Morphology of Temporal-Aspectual Constructions in Korean

Abstract. Verbal nouns in Korean exhibit properties of both nouns and verbs in that they assign both verbal and nominal cases to the arguments. Such mixed categorial behavior of verbal nouns is manifest only in certain environments, namely in the complement position of ha (a so-called light verb in Korean) and in the complement position of aspectual morphemes such as cwung 'during', cen 'before', and hwu 'after. Due to their mixed properties, the categorial status of verbal nouns in these environments has long been an issue of debate. This paper mainly discusses temporal-aspectual constructions, and proposes that they can be distinguished into three types, Types A, B, and C. Each type of temporal-aspectual construction has a different morpho-syntactic structure. The paper further claims that verbal nouns are inherently unspecified for their grammatical category (following Alexiadou 1997, 1998, Halle and Marantz 1993, and van Hout and Roeper 1998 among others), and different morpho-syntactic structures trigger different categorial status of verbal nouns in these environments. The complex categorial behavior of verbal nouns in temporal-aspectual constructions, then, is not only explained under the analysis proposed in this paper but is also expected.

Dynamic optimization of double-sided cooking of meat patties

Optimal operating procedures for double-sided cooking of frozen hamburger patties were computed using dynamic optimization techniques. The mathematical statement was to find the optimal control (e.g., heating surface temperature) over cooking time to minimize (or maximize) the performance index J, for example minimize cooking loss, and to ensure the required lethality and safe cooking temperature. The control vector parameterization framework was applied, and stochastic algorithm was used to locate the global optimum with reasonable computation effort (Integrated Controlled Random Search for Dynamic Systems). The performance index improved when the heating temperature profile was considered as control variable and when two control elements of variable size were used (compared with the constant-temperature process or nominal case, Δ J<3%). When the lower bound was relaxed and two control elements were used, the performance index improved significantly (Δ J<7%). However, when the top and bottom plate temperatures were considered as two different controls, the plate temperature profiles obtained did not significantly improve the results compared with the nominal cases. When the temperature of the top and bottom plates and gap thickness were considered as control variables, and when two control elements of variable size for gap thickness were used, the performance index improved for long periods of cooking time (Δ J<2.5%).

Assessment of Reactivity Effects due to Localized Perturbations in BWR Lattices

Optimization criteria for the representability of numerical models for the estimation of relative reactivity changes, due to localized perturbations in boiling water reactor (BWR) lattices, have been theoretically developed and tested. The validity of the derived theoretical expressions has been assessed for the case of a reactivity perturbation corresponding to the removal of an individual fuel pin from a nominal BWR assembly, thus effectively substituting the pin by water. Such reactivity effects are of importance in the context of evaluating advanced fuel element designs, e.g., those employing part-length rods. Two different geometry models have been implemented for the LWR-PROTEUS critical research facility [full core (FC) and a smaller, reduced geometry (RG)], using the light water reactor assembly code BOXER, and calculations have been performed for the nominal cases (all pins present in the central test assembly) and the perturbed cases (individual pins removed). The FC results have been compared with the results of the RG model with two different boundary conditions (reflective and critical albedo). The comparisons have shown that the results of critical albedo calculations feature superior representability. Differences in relative reactivity effects, with respect to results of the FC calculation, are found to be within the range ±1 to ±4%.

Studies on the Use of Neural Networks in Nonlinear Control Strategies.

Reactor temperature control is very important as it affects chemical process operations and the product quality. Although PID controller, which is the linear controller and widely used in the chemical process industries, is able to control the temperature, the operating range is limited. Furthermore, its control performance when plant/model mismatches exist is not guaranteed. Recently, various advanced control techniques have been successfully applied to highly nonlinear systems. These include the Generic Model Control (GMC) and the Inverse-Model Control (IMC) techniques. However these methods still require reasonable and accurate process model and parameters, which are difficult to guarantee in many cases. For this reason we have used neural networks in conjunction with these methods to overcome this problem for the control of the reactor in this study. The neural network is used as a function estimator in the GMC method and as a model and controller in the IMC-PI method. Various simulations involving set point tracking and disturbance rejection under nominal and model-mismatch cases were performed using these hybrid methods. The results of these hybrid controllers were found to be better than the conventional PID and GMC methods in most cases. These results justify the use of the neural networks in such hybrid strategies as well as show their versatility in incorporating into the nonlinear control methods to cater for model mismatches and difficult to control process systems.

Time-dependent Closed Form Solutions for Fully Competitive Enzyme Reactions

An analytic formalism developed earlier to describe the time evolution of the basic enzyme reaction is extended to fully competitive systems. Time-dependent closed form solutions are derived for the three nominal cases of competition: even, slow and fast inhibitors, allowing for the first time the complete characterization of the reactions. In agreement with previous work, the time-independent Michaelis–Menten approach is shown to be inaccurate when a fast inhibitor is present. The validity of the quasi-steady-state approximation on which the present framework is based is also revised.