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RICCATI EQUATION APPROACHES FOR SMALL GAIN, POSITIVITY, AND POPOV ROBUSTNESS ANALYSIS

JOURNAL OF GUIDANCE CONTROL AND DYNAMICS 1994年第2期17卷 322-329页

作者： COLLINS, EG HADDAD, WM DAVIS, LD FLORIDA INST TECHNOL DEPT MECH & AEROSP ENGN MELBOURNE FL 32901 USA

In recent years, small gain (or H(infinity)) analysis has been used to analyze feedback systems for robust stability and performance. However, since small gain analysis allows uncertainty with arbitrary phase in the frequency domain and arbitrary time variations in the time domain, it can be overly conservative for constant real parametric uncertainty. More recent results have led to the development of robustness analysis tools, such as extensions of Popov analysis, that are less conservative. These tests are based on parameter-dependent Lyapunov functions, in contrast to the small gain test, which is based on a fixed quadratic Lyapunov function. This paper uses a benchmark problem to compare Popov analysis with small gain analysis and positivity analysis (a special case of Popov analysis that corresponds to a fixed quadratic Lyapunov function). The state-space versions of these tests, based on Riccati equations, are implemented using continuation algorithms. The results show that the Popov test is significantly less conservative than the other two tests and for this example is completely nonconservative in terms of its prediction of robust stability.

关键词： Riccati Equations Frequency Domain State Space Representation Mass Spring System Single Input Single Output numerical algorithms Small Gain Theorem Feedback Loop White Noise

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numerical INVESTIGATIONS ON 2-DIMENSIONAL CANARD-WING AERODYNAMIC INTERFERENCE

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JOURNAL OF AIRCRAFT 1994年第3期31卷 672-679页

作者： LIN, SY CHIN, YS WANG, YY Institute of Aeronautics and Astronautics Tainan Taiwan Republic of China

A finite element method for solving of the Euler and Navier-Stokes equations is used to study the unsteady aerodynamics of a two-dimensional canard-wing aerodynamic interference. The method used a discontinuous finite element method for spatial discretization and an explicit Runge-Kutta time integration for temporal discretization. The problems of a flow over an airfoil with/without viscosity, a flow over a pitching airfoil, and an airfoil-vortex interaction are tested to show the accuracy of the proposed numerical method. Finally, the results of two-dimensional canard-wing aerodynamic interference in steady and unsteady transonic flows are shown to demonstrate the robustness of the numerical algorithm, and qualitative and quantitative aerodynamic influence of one airfoil on the other.

关键词： Aerodynamic Interference Canard Pitching Airfoil Vortices Finite Element Method Unsteady Transonic Flow Navier Stokes Equations numerical algorithms Viscosity Unsteady Aerodynamics

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FUZZY CONTROLLER AND NEURON MODELS OF HARTEN 2ND-ORDER TOTAL VARIATION DIMINISHING SCHEME

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AIAA JOURNAL 1994年第10期32卷 2122-2124页

作者： SMITHWICK, Q EBERHARDT, S UNIV WASHINGTON DEPT AERONAUT & ASTRONAUTSEATTLEWA 98195

The application of fuzzy controllers and neural networks in industrial and consumer products is steadily gaining grounds. These practical utilities included reading handwritten addresses, analyzing satellite data, and stabilizing hand-held video camera representations. The extension of fuzzy controllers and neural networks applications to computational fluid dynamics was suggested. In this article, Harten's second-order total variation diminishing scheme was discussed as a fuzzy controller and as a single-input single-output neuron.

关键词： Total Variation Diminishing Primitive Variable Multiple Input Multiple Output Neural Networks Fuzzy Logic Astronautics Aeronautics Shock Tube Computational Fluid Dynamics Code numerical algorithms

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ASSESSMENT OF 2ND-ORDER CLOSURE MODELS IN TURBULENT SHEAR FLOWS

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AIAA JOURNAL 1994年第10期32卷 2113-2115页

作者： SPEZIALE, CG GATSKI, TB NASA LANGLEY RES CTRTHEORET FLOW PHYS BRANCHHAMPTONVA 23665

The demand for sophisticated turbulence models to efficiently compute the complex aerodynamic flows of technological focus has promoted a revived interest in second-order closure models. It was implied in research conducted by Shih-Lumley that second-order closure models in turbulent shear flows performed better that two other previously recommended second-order closure models in homogeneous shear flow as well as in even more complex boundary-free turbulent shear flows. However, the current studies of second-order closure models in benchmark turbulent shear flows produced dissimilar results.

关键词： Kinematic Viscosity Wall Bounded Turbulent Flows Turbulent Boundary Layer Direct numerical Simulation Turbulent Diffusion Kinetic Energy Static Pressure numerical algorithms Turbulence Models Adiabatic Flow

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UNSTEADY SUPERSONIC CAVITY FLOW SIMULATIONS USING COUPLED KAPPA-EPSILON AND NAVIER-STOKES EQUATIONS

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AIAA JOURNAL 1994年第10期32卷 2015-2021页

作者： SHIH, SH HAMED, A YEUAN, JJ University of Cincinnati Cincinnati Ohio 45221

A numerical procedure is developed for the simultaneous implicit numerical solution of the coupled k-epsilon and Navier-Stokes equations for compressible viscous flows. The numerical algorithm is based on the approximate factorization scheme of Beam and Warming for the strongly coupled set of equations. The scheme incorporates a new second-order Jameson type damping model that enhances the stability and relieves the stiffness associated with the solution to the k-epsilon equations. The model, which is based on the changes in both pressure and turbulent kinetic energy, eliminates the need to use subiteration techniques. Unsteady calculations were performed for supersonic flow over an open cavity at a freestream Mach number of 1.5 and Reynolds number of 1.09 x 10(6). The computed results are compared with experiments and predictions from computations using uncoupled k-epsilon and Navier-Stokes equations.

关键词： Navier Stokes Equations Freestream Mach Number In Compressible Viscous Flows Static Pressure Kinetic Energy Coordinate Transformations Pressure Coefficient numerical algorithms Total Energy Shear Layers

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Logic derivation of parallel linear equation system solvers within elimination strategy

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Parallel algorithms and Applications 1994年第1-2期4卷 21-40页

In this paper we describe a systematic technique for designing parallel algorithms to solve linear systems. Our approach is based on the logic derivation of a target algorithm from specification of basic relations in the linear equations domain and their properties. Both input specification and the resulting algorithm are expressed in the declarative computer-independent form. The methodology is illustrated by deriving the parallel Gaussian triangular solver. © 1994, Taylor & Francis Group, LLC. All rights reserved.

关键词： Algorithm synthesis Formal specification Gaussian elimination Logic derivation numerical algorithms Parallel computations

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numerical INVESTIGATION OF SUBSONIC AND SUPERSONIC ASYMMETRIC VORTICAL FLOW

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AIAA JOURNAL 1993年第8期31卷 1377-1383页

作者： VANDEN, KJ BELK, DM Wright Laboratory Armament Directorate Eglin Air Force Base Florida 32542

The high angle of attack flow about a slender body in supersonic and subsonic flow was computed for an angle of attack of 38.5 deg to study the phenomena associated with vortex asymmetry. A laminar thin-layer Navier-Stokes algorithm was used to determine whether vortex asymmetry in numerical computations is the result of a numerically induced perturbation or a property of the governing equations. The fully upwind code used in this study was symmetric in the crossflow plane to 12 orders of magnitude, the level of roundoff error on the Cray Y-MP. It was found that, with a completely symmetric grid and algorithm with respect to the crossflow plane, a bump was needed to perturb the flow to asymmetry. When the bump was taken away, the flow returned to a symmetric state. This corroborates the previous assertion of other investigators that vortex asymmetry at high angles of attack on slender bodies is due lo a convective instability.

关键词： Vortices Angle of Attack Supersonic Flow Computational Fluid Dynamics No Slip Condition Ogive Cylinder Air to Air Missiles Atmospheric Flight Mechanics Finite Volume Formulation numerical algorithms

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LINEARIZED EULER PREDICTIONS OF UNSTEADY AERODYNAMIC LOADS IN CASCADES (VOL 31, PG 540, 1993)

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AIAA JOURNAL 1993年第5期31卷 970-970页

作者： HALL, KC CLARK, WS Duke University Durham North Carolina 27706

A linearized Euler solver for calculating unsteady flows in turbomachinery blade rows due to both incident gusts and vibratory blade motion is presented. Using the linearized Euler technique, one decomposes the flow into a mean (or steady) flow plus an unsteady, harmonically varying, small-disturbance flow. Linear variable coefficient equations describe the small-disturbance behavior of the flow and are solved using a pseudotime time-marching Lax-Wendroff scheme. For the blade-motion problem, a harmonically deforming computational grid that conforms to the motion of vibrating blades eliminates large error producing mean flow gradient terms that would otherwise appear in the unsteady flow tangency boundary condition. Also presented is a new, numerically exact, nonreflecting far-field boundary condition based on an eigenanalysis of the discretized equations. Computed flow solutions demonstrate the computational accuracy and efficiency of the present method. The solution of the linearized Euler equations requires one to two orders of magnitude less computer time than solution of the nonlinear Euler equations using traditional time-accurate time-marching techniques. Furthermore, it is shown that the deformable grid technique significantly improves the accuracy of the solution. © 1993 American Institute of Aeronautics and Astronautics, Inc., All rights reserved.

关键词： Aerodynamic Damping Small Perturbation Flow Euler Equations Turbomachinery Compressor Cascade Perturbation Analysis Conservation of Mass numerical Integration numerical algorithms Specific Heat

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EULER CALCULATIONS OF UNSTEADY INTERACTION OF ADVANCING ROTOR WITH A LINE VORTEX

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AIAA JOURNAL 1993年第9期31卷 1659-1666页

作者： SRINIVASAN, GR MCCROSKEY, WJ NASA AMES RES CTRMOFFETT FIELDCA 94035

The unsteady, three-dimensional flowfield of a helicopter rotor blade in forward night encountering a concentrated line vortex is calculated using an implicit, finite difference numerical procedure for the solution of Euler equations. A prescribed vortex method is adopted to preserve the structure of the interacting vortex. The test cases considered for computation correspond to the two-bladed model rotor experimental conditions of Caradonna et al. and consist of parallel and oblique interactions. Comparison of numerical results with the test data show good agreement for the surface pressures for both parallel and oblique interactions at subsonic and transonic flow conditions. The results indicate that the subsonic parallel blade-vortex interaction is nearly two-dimensional-like and the unsteady time-lag effects appear to be negligible. However, both the three-dimensional and unsteady time-lag effects are found to be important under supercritical now conditions and these effects are accentuated in the presence of transonic shocks. In contrast, the oblique blade-vortex interaction is unsteady and three dimensional at both the subsonic and transonic now conditions.

关键词： Vortex Structure Blade Vortex Interaction Supercritical Flow Helicopter Rotor Primitive Variable Freestream Mach Number Rotor Blades Total Energy NACA 64A006 numerical algorithms

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DESIGNING REDUCED-ORDER LINEAR-MULTIVARIABLE CONTROLLERS USING EXPERIMENTALLY DERIVED PLANT-DATA

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JOURNAL OF GUIDANCE CONTROL AND DYNAMICS 1993年第1期16卷 53-58页

作者： FRAZIER, WG IRWIN, RD Ohio University Athens Ohio 45701

An iterative numerical algorithm for simultaneously improving multiple performance and stability robustness criteria for multivariable feedback systems is developed. The unsatisfied design criteria are improved by updating the free parameters of an initial, stabilizing controller's state-space matrices. Analytical expressions for the gradients of the design criteria are employed to determine a parameter correction that improves all of the feasible, unsatisfied design criteria al each iteration. A controller design is performed using the algorithm with experimentally derived data from a large space structure test facility. Experimental results of the controller's performance at the facility are presented.

关键词： Large Space Structures numerical algorithms Open Loop Controller Linear Quadratic Gaussian Mathematical Models Control System Design Algorithm Performance Frequency Domain NASA Marshall Space Flight Center Search Algorithm

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