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REDUCED-ORDER COMPENSATION - LINEAR-QUADRATIC REDUCTION VERSUS OPTIMAL PROJECTION

JOURNAL OF GUIDANCE CONTROL AND DYNAMICS 1988年第4期11卷 328-335页

作者： GREELEY, SW HYLAND, DC Harris Corp. Melbourne FL

Six methods for design of reduced-order compensation are compared using an example problem. The methods considered comprise five linear-quadratic reduction techniques, reviewed in a recent paper by Liu and Anderson, and the Optimal Projection theory as implemented via a simple homotopy solution algorithm. Design results obtained by the different methods for 42 different design cases are compared with respect to closed-loop stability and transient response characteristics. Of the linear-quadratic reduction procedures, two are found to offer distinctly superior performance. However, only the Optimal Projection method provided stable designs in all cases. Further details are given on the performance of the numerical algorithm for solving the optimal projection equations and the corresponding design results. © 1988 American Institute of Aeronautics and Astronautics, Inc., All rights reserved.

关键词： Closed Loop System Solution Algorithm Optimal Projection Equations numerical algorithms Riccati Equations Topological Degree Theory Iterative Solution Computing

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CALCULATION OF ANNULAR NOZZLE TRISONIC FLOWFIELDS BY THE METHOD OF CHARACTERISTICS

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JOURNAL OF PROPULSION AND POWER 1988年第3期4卷 228-235页

作者： WANG, BN HOFFMAN, JD PURDUE UNIV CTR THERMAL SCI & PROPW LAFAYETTEIN 47907

A numerical algorithm based on the unsteady two-dimensional method of characteristics is presented for calculating axisymmetric inviscid trisonic (i.e., subsonic-transonic-supersonic) flowfields in annular nozzles. The algorithm is an explicit second-order accurate predictor-corrector procedure. An inverse marching method based on a local network of wavelines and the pathline is employed wherein the solution grid in physical space is prespecified. An orthogonal uniform transformed space, obtained by an algebraic grid generation method, is used for flow property interpolation in the initial-data surface. Steady flow solutions are obtained as the asymptotic solution in time. Results for four annular nozzles are presented. Comparison of the predicted and measured wall pressure distributions and nozzle efficiencies shows good agreement. © 1987 American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

关键词： Expansion Deflection Nozzle Two Dimensional Flow numerical algorithms numerical Integration Continuity Equation Mach Number Courant Friedrichs Lewy Flow Separation Computer Programs Isentropic Expansion

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CALCULATION OF 3-DIMENSIONAL INVISCID FLOWFIELDS IN PROPULSIVE NOZZLES WITH CENTERBODIES

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JOURNAL OF PROPULSION AND POWER 1988年第2期4卷 172-179页

作者： MARCUM, DL HOFFMAN, JD PURDUE UNIV CTR THERMAL SCI & PROPW LAFAYETTEIN 47907

A numerical procedure for calculating three-dimensional inviscid subsonic/transonic/supersonic (i.e., trisonic) flowfields in propulsive nozzles with centerbodies is presented. The procedure can be used to investigate advanced propulsive nozzle concepts for improved engine-airframe integration. The interior point unit process is based on the MacCormack explicit predictor-corrector method, and the boundary point unit processes are based on a variation of the method of characteristics due to Kentzer. The overall numerical algorithm is an explicit second-order accurate time-marching procedure. Steady flow solutions are obtained as the asymptotic solution in time. Results are presented for several two-dimensional and three-dimensional inviscid nozzle flowfields. Solutions obtained by the present method agree well with solutions obtained by method of characteristics algorithms and experimental data. © 1987 American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

关键词： Axisymmetric Nozzles Supersonic Flow Airframes Cylindrical Coordinate System numerical algorithms Predictor Corrector Method Static Pressure Mach Number Specific Heat Stagnation Pressure

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NAVIER-STOKES CALCULATIONS OF HOVERING ROTOR FLOWFIELDS

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JOURNAL OF AIRCRAFT 1988年第10期25卷 865-874页

作者： SRINIVASAN, GR MCCROSKEY, WJ JAI Associates Inc. Mountain View California NASA Ames Research Center Moffett Field California

Unsteady, thin-layer Navier-Stokes equations written in rotor coordinates are solved using a partially fluxsplit, implicit numerical algorithm to calculate the flowfields of a hovering rotor blade at subsonic and transonic conditions. numerical results are in good agreement with experimental data for both nonlifting and lifting rectangular blades. For the lifting case, the rotor wake effects are modeled by applying a correction to the geometric angle of attack of the blades. Alternate methods of calculating the hovering rotor flowfields in blade-fixed mode that have the same circulation distribution as a hovering blade are explored. All of the results presented in this paper were computed on a Cray-2 supercomputer. © American Institute of Aeronautics and Astronautics, Inc., 1988. All rights reserved.

关键词： Navier Stokes Calculations Lift Coefficient Rotor Blades Supercomputers numerical algorithms Rotor Wake Complex Vortex Wake Freestream Mach Number Supercritical Flow Pressure Coefficient

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CONTROLLED EXPERIMENTS OF THE DIFFRACTION OF SOUND BY A CURVED SURFACE

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JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA 1988年第6期83卷 2047-2058页

作者： BERRY, A DAIGLE, GA NATL RES COUNCIL CANADA DIV PHYSOTTAWA K1A 0R6ONTARIOCANADA

Controlled measurements of the sound field from a point source above a curved surface are described. The measurements were made in the frequency range between 0.3 and 10 kHz, in the case of a rigid boundary and a surface of finite impedance. Receiver positions include all of the area within, and above, the shadow zone and for various source heights. Particular attention is given to the region across the shadow boundary. The measurements are compared to diffraction theory expressed in terms of a residue series, or creeping wave solution. The calculation is extended by removing restrictive approximations and by carrying the computation to higher‐order terms. A numerical algorithm allows the extension to the general case of a finite impedance. Above the shadow boundary, the sound field is calculated using geometrical theory that accounts for reflections from a curved surface. Deep within the shadow, theory and measurements agree to, typically, 0.5 dB. The same agreement is obtained between measurements and the geometrical theory well above the shadow boundary. In the vicinity of the shadow boundary, both theories agree to within 0.5 dB but differ from the measured results by 2 to 5 dB. Finally, the theory is compared to measurements obtained outdoors above a grass covered curved ground with no refraction and above flat ground with refraction.

关键词： Acoustic waves Acoustical measurements Creep measurement Diffraction theory numerical algorithms

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SIMULATION OF SURFACE EVOLUTION DURING ION-BOMBARDMENT

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JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A 1988年第4期6卷 2434-2442页

作者： KATARDJIEV, IV UNIV SALFORD DEPT ELECTR & ELECT ENGN SALFORD M5 4WT LANCS ENGLAND

Some theoretical aspects of surface topography evolution during ion beamerosion are discussed. In particular, the theory of characteristics is considered in some detail and its limitations pointed out. Further theoretical development based on the Huygens principle of wave propagation is discussed also with respect to numerical evaluation of surface evolution. A new numerical algorithm based on the contemporary theoretical concepts of surface and edge propagation is proposed and compared with existing numerical models and theoretical expectations.

关键词： Number theory Erosion Ion beams numerical algorithms numerical modeling

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MOMENT PROBLEM FORMULATION OF THE SIMPLIFIED IDEAL MAGNETOHYDRODYNAMICS BALLOONING EQUATION

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JOURNAL OF MATHEMATICAL PHYSICS 1988年第3期29卷 717-720页

作者： HANDY, CR BESSIS, D WILLIAMS, RM Department of Physics Atlanta University Atlanta Georgia 30314

A fundamentally new method for determining the eigenvalues of linear differential operators is presented. The method involves the application of moment analysis and affords a fast and precise numerical algorithm for eigenvalue computation, particularly in the intermediate and strong coupling regimes. The most remarkable feature of this approach is that it provides exponentially converging lower and upper bounds to the eigenvalues. The effectiveness of this method is demonstrated by applying it to an important magnetohydrodynamics problem recently studied by Paris, Auby, and Dagazian [J. Math. Phys. 2 7, 2188 (1986)]. Through the very precise lower and upper bounds obtained, this approach gives full support to their analysis.

关键词： Eigenvalues Magnetohydrodynamics Differential equations Magnetohydrodynamic equations numerical algorithms

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SEVERAL numerical SCHEMES FOR THE COMPUTATION OF UNSTEADY-FLOW IN PULSED LASERS

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AIAA JOURNAL 1987年第6期25卷 845-854页

作者： SRIVASTAVA, BN WALDMAN, G CRUICKSHANK, J MORAN, J AVCO SYST DIV WILMINGTON MA 01887 USA

This paper describes numerical formulation issues aimed at developing an accurate computational approach for two-dimensional acoustic studies in a typical pulsed laser system. This goal is achieved through a series of numerical algorithm studies, optimizations thereof, and improved boundary formulation techniques related to the complex laser system environment. Several model test problems are computed and successfully compared with available data/analyses to demonstrate the accuracy of the computational approach. © 1987 American Institute of Aeronautics and Astronautics, Inc., All rights reserved.

关键词： Lasers Unsteady Flows numerical algorithms Mass Flow Flux Corrected Transport Conservation Equations Damping Coefficient Beam and Warming Scheme Discharge Coefficient Total Energy

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numerical BOUNDARY-CONDITION PROCEDURES FOR EULER SOLVERS

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AIAA JOURNAL 1987年第8期25卷 1054-1062页

作者： MARCUM, DL HOFFMAN, JD PURDUE UNIV CTR THERMAL SCI & PROPW LAFAYETTEIN 47907

A numerical boundary condition procedure for Euler solvers is presented. The procedure is based on a variation of the method of characteristics due to Kentzer. A second-order-accurate numerical algorithm using this procedure and the MacCormack explicit finite-difference method is presented. Results are presented for several two-dimensional and three-dimensional inviscid nozzle flowfields. Solutions obtained by the present method agree well with solutions obtained by method of characteristics algorithms and experimental data. © 1987 American Institute of Aeronautics and Astronautics, Inc., All rights reserved.

关键词： Finite Difference Method numerical algorithms Static Pressure Mach Number Courant Friedrichs Lewy Stagnation Temperature Continuity Equation Two Dimensional Flow Conical Nozzles Subsonic Inlets

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numerical-SIMULATION OF TRANSIENT INVISCID SHOCK-TUBE FLOWS

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AIAA JOURNAL 1987年第2期25卷 245-251页

作者： YANG, JY LOMBARD, CK BERSHADER, D PEDA CORP PALO ALTO CA USA STANFORD UNIV DEPT AERONAUT & ASTRONAUT STANFORD CA 94305 USA

Time-dependent upwind high resolution schemes for solving the Euler equations were developed and applied to simulate one- and two-dimensional transient inviscid gas flows in a shock tube. Using obstacles of different geometries, a series of calculations were carried out to investigate the transient complex shock wave diffraction phenomena. Shock wave and object interaction with shock Mach numbers ranging from 2-20 were simulated. Comparison with analytical and available experimental results indicate good agreement. Display of detailed flow structures including multiple Mach shocks, sliplines, and vortex are also given. © 1987 American Institute of Aeronautics and Astronautics, Inc., All rights reserved.

关键词： Rotor Aerodynamics numerical Simulation Shock Wave Propagation Primitive Variable Vortices numerical algorithms Transonic Flow Solid Propellant Rocket Gas Dynamics Specific Heat

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