An algorithm that estimates the region of attraction of the origin using a convex polytope is developed for piecewise-linear dynamical systems. This is equivalent to the problem of computing a Lyapunov function. The R...
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An algorithm that estimates the region of attraction of the origin using a convex polytope is developed for piecewise-linear dynamical systems. This is equivalent to the problem of computing a Lyapunov function. The R(2) case is studied here for simplicity. Copyright (C) 1996 Elsevier Science Ltd.
A two-point second-order uniform box-scheme has been developed for numerical analysis of the gas flow in the boundary layer under the conditions of intensive blowing on the body surface. An effective regularization al...
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A two-point second-order uniform box-scheme has been developed for numerical analysis of the gas flow in the boundary layer under the conditions of intensive blowing on the body surface. An effective regularization algorithm has been created, The numerical analysis indicates the second order of the uniform convergence of this box-scheme, Flowfield parameters in the boundary layer near the stagnation point of a blunt body were calculated for different magnitudes of blowing and temperature factor. numerical results have been compared with earlier obtained data by the three-point exponential box-scheme.
For a class of nonlinear engine dynamic models of arbitrary order that can also be Mach, altitude, and angle-of-attack dependent, it is shown that the optimal throttle setting for aircraft terrain-following flight is ...
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For a class of nonlinear engine dynamic models of arbitrary order that can also be Mach, altitude, and angle-of-attack dependent, it is shown that the optimal throttle setting for aircraft terrain-following flight is generally of the bang-bang type whenever the optimal angle of attack is interior. The only case where a singular throttle control may appear is when the time-of-flight is not included in the performance index and the terrain is not followed exactly. A comparison with the results of Lu and Pierson (1995) suggests that ignoring engine dynamics in aircraft trajectory optimization does not lead to incorrect conclusions. (AIAA)
This paper deals with the development and characterization of Dynamic Programming Predictive Controllers (DPPC), advanced predictive controllers that make use of dynamic programming to solve highly nonlinear / nonquad...
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This paper deals with the development and characterization of Dynamic Programming Predictive Controllers (DPPC), advanced predictive controllers that make use of dynamic programming to solve highly nonlinear / nonquadratic constrained control problems. Some computational techniques to reduce the computational load are proposed, and an application example, pH control, is analyzed using this new methodology.
A control strategy for the reduction of a narrow-band disturbance is presented. The controller is based on a modified version of the Internal Model Principle within an LQ state feedback. The performance of the control...
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A control strategy for the reduction of a narrow-band disturbance is presented. The controller is based on a modified version of the Internal Model Principle within an LQ state feedback. The performance of the controller is further increased by means of a suitable optimization procedure.
Mixed structured singular value analysis tests that allow the structure of the multipliers to a priori be specified have been developed. These tests can be characterized in terms of the existence of positive definite ...
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Mixed structured singular value analysis tests that allow the structure of the multipliers to a priori be specified have been developed. These tests can be characterized in terms of the existence of positive definite solutions to certain Riccati equations. Probability-one homotopy algorithms are developed to find a solution. These results easily extend to provide computationally tractable algorithms for fixed-architecture, robust control design.
In this paper, a robust switching surface design procedure is developed for use in variable structure output feedback control. The presence of stable invariant zeros and matched uncertainty in the system is incorporat...
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In this paper, a robust switching surface design procedure is developed for use in variable structure output feedback control. The presence of stable invariant zeros and matched uncertainty in the system is incorporated into the design procedure. It. gives the theoretical background of methods appropriate for the design of the hyperplane such that closed-loop robustness properties are maximised, The controller is synthesised to tokrate certain amounts of nonlinearity and model uncertainty. The controller is straightforward and is based on Lyapunov theory. The measurements of robustness are described. The example of a multi variable helicopter problem is presented to show the effectiveness of the method.
High emission levels and the unfavourable topography are the main reasons for the alarming photochemical air pollution levels in Athens. An analysis of available air quality data proves that air pollution levels in At...
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High emission levels and the unfavourable topography are the main reasons for the alarming photochemical air pollution levels in Athens. An analysis of available air quality data proves that air pollution levels in Athens are largely affected by local wind circulation systems. The most frequent of these systems is dominated by the phenomenon of the sea breeze. Severe air pollution episodes occur, however, primarily under synoptic situations leading to stagnant conditions in the atmosphere over Athens. Photosmog formation in the Athens Basin is studied with the photochemical dispersion model MARS. The implicit solution algorithm incorporated in MARS is characterized by a variable time increment and a variable order. This solver allows avoiding unnecessary operator splitting by a coupled treatment of vertical diffusion and chemical kinetics. In this paper, MARS is used to analyse the situation on 25 May 1990, a day for which very high air pollution levels were reported in Athens. The simulation results elucidate the characteristics of a photosmog episode under stagnant conditions in Athens. In general, the model results reproduce satisfactorily the observed air pollution patterns.
A method is presented for testing whether or not two n-simplices in R(n) intersect, and if so, deciding whether or not the intersection has a nonempty interior. The algorithm is an application of a method by Stewart f...
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A method is presented for testing whether or not two n-simplices in R(n) intersect, and if so, deciding whether or not the intersection has a nonempty interior. The algorithm is an application of a method by Stewart for solving linear inequalities [1].
We investigate the generalized mid-point algorithms for the integration of elastoplastic constitutive equations for the pressure-dependent Gurson-Tvergaard yield model. By exact linearization of the algorithms and dec...
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We investigate the generalized mid-point algorithms for the integration of elastoplastic constitutive equations for the pressure-dependent Gurson-Tvergaard yield model. By exact linearization of the algorithms and decomposition of the stresses into hydrostatic and deviatoric parts, a formula for explicitly calculating the consistent tangent moduli with the generalized mid-point algorithms is derived for the Gurson-Tvergaard model. The generalized mid-point algorithms, together with the consistent tangent moduli, have been implemented into ABAQUS via the user material subroutine. An analytical solution of the Gurson-Tvergaard model for the plane strain tension case is given and the performances of the generalized mid-point algorithms have been assessed for plane strain tension and hydrostatic tension problems and compared with the exact solutions. We find that, in the two problems considered, the generalized mid-point algorithms give reasonably good accuracy even for the case using very large time increment steps, with the true mid-point algorithm (alpha = 0.5) the most accurate one. Considering the extra non-symmetrical property of the consistent tangent moduli of the algorithms with alpha < 1, the Euler backward algorithm (alpha = 1) is, perhaps, the best choice.
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