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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 Corporation Melbourne Florida

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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Development and validation of a massively parallel flow solver for turbomachinery flows

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JOURNAL OF PROPULSION AND POWER 2001年第3期17卷 659-668页

作者： Yao, JX Jameson, A Alonso, JJ Liu, F Stanford Univ Dept Aeronaut & Astronaut Stanford CA 94305 USA Univ Calif Irvine Dept Mech & Aerosp Engn Irvine CA 92697 USA

The development and validation of the unsteady, three-dimensional, multiblock, parallel turbomachinery how solver TFLO is presented, The unsteady Reynolds-averaged Navier-Stokes equations are solved using a cell-centered discretization on arbitrary multiblock meshes. The solution procedure is based on efficient explicit Runge-Kutta methods with several convergence acceleration techniques such as multigrid, implicit residual smoothing, and local time stepping. The solver is parallelized using domain decomposition, a single program multiple data strategy, and the message passing interface standard, Details of the communication scheme and load balancing algorithms are discussed. A general and efficient procedure for parallel interblade row interfacing is developed. The dual-time stepping technique is used to advance unsteady computations in time, The focus is on improving the parallel efficiency and scalability of the flow solver, as well as on its initial validation of steady-state calculations in multiblade row environment. The result of this careful implementation is a solver with demonstrated scalability up to 1024 processors. For validation and verification purposes, results from TFLO are compared with both existing experimental data and computational results from other computational fluid dynamics codes used in aircraft engine industry.

关键词： Turbomachinery Parallel Computing Techniques Reynolds Averaged Navier Stokes Runge Kutta Integration Parallel Flow Rotor Stator Interactions Parallel Computers solution algorithm Low Pressure Turbine Numerical Stability

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UNSTEADY EULER AIRFOIL solutionS USING UNSTRUCTURED DYNAMIC MESHES

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AIAA JOURNAL 1990年第8期28卷 1381-1388页

作者： BATINA, JT NASA Langley Research Center Hampton Virginia 23665

Two algorithms for the solution of the time-dependent Euler equations are presented for unsteady aerodynamic analysis of oscillating airfoils. Both algorithms were developed for use on an unstructured grid made up of triangles. The first flow solver involves a Runge-Kutta time-stepping scheme with a finite-volume spatial discretization that reduces to central differencing on a rectangular mesh. The second flow solver involves a modified Euler time-integration scheme with an upwind-biased spatial discretization based on the flux-vector splitting of Van Leer. A significant aspect of the research is the implementation of a dynamic mesh algorithm that is employed for problems where the airfoil moves. Steady and unsteady results are presented for the NACA 0012 airfoil to demonstrate application of the Euler solvers and dynamic mesh algorithm. The unsteady flow results were obtained for the airfoil pitching harmonically about the quarter chord. The two sets of calculated instantaneous pressure distributions and lift and moment coefficients during a cycle of motion compare well with each other and with the experimental data. The paper presents descriptions of the Euler solvers and dynamic mesh algorithm along with results which assess the capability. © 1990 American Institute of Aeronautics and Astronautics, Inc., All rights reserved.

关键词： Pitching Airfoil Unstructured Grid Flow Conditions Euler Equations Unsteady Aerodynamic Analysis Lift Coefficient CFL Condition solution algorithm Freestream Mach Number Aircraft Configurations

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STRAKE-GENERATED VORTEX INTERACTIONS FOR A FIGHTER-LIKE CONFIGURATION

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JOURNAL OF AIRCRAFT 1989年第4期26卷 289-294页

作者： REZNICK, SG FLORES, J U.S. Space Command Headquarters Peterson Air Force Base Colorado NASA Ames Research Center Moffett Field California

A combination of the Euler and thin-layer Navier-Stokes equations were solved for the flowfield around a wingstrake- fuselage configuration similar to the General Dynamics F-16A aircraft. Steady-state solutions were obtained at angles-of-attack ranging from 6 to 10 deg at M_∞ = 0.3, 0.6, and 0.9, and Reynolds numbers matching those of wind-tunnel and water-tunnel experiments. The flowfield was divided into multiple blocks using a zoning program and the transonic Navier-Stokes wing-fuselage (TNSWF) solution program, based on an implicit solution algorithm, which updates each subregion of the flowfield sequentially. The total grid contained approximately 300, 000 grid points, and clustering was affected normal to all aircraft surfaces. The computed solutions agreed well quantitatively with wind-tunnel pressure distribution data, and they agreed well qualitatively with flow visualization from wind- and water-tunnel tests. © 1989 American Institute of Aeronautics and Astronautics, Inc.

关键词： Aircraft Configurations Vortices Reynolds Averaged Navier Stokes Angle of Attack Reynolds Numbers Wind Tunnels Navier Stokes Equations solution algorithm Irrotational Flow Wing Root

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VORTICAL FLOW solutionS USING A TIME-LAGGED, THIN-LAYER, NAVIER-STOKES algorithm

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AIAA JOURNAL 1991年第6期29卷 876-877页

作者： MOUNTS, JS BELK, DM MILTON, JE USAF ARMAMENT LABAERODYNAM BRANCHEGLIN AFBFL 32542 UNIV FLORIDA CTR GRAD ENGNEGLIN AFBFL

A PROVEN inviscid algorithm (Program EAGLE - Flow Solver) 1-3 has been modified to use the flux-difference split scheme of Roe 4 to solve the time-lagged, thin-layer approximation to the Navier-Stokes equations. 5,6 Calculations are presented evaluating the ability of the time-lagged, thin-layer Navier-Stokes algorithm to obtain transonic solutions for lifting bodies at incidence angles sufficient for the flow to be dominated by large-scale free vortices in the leeside flowfield.

关键词： Navier Stokes algorithm Vortex Sheet Navier Stokes Calculations Lifting Body Turbulence Models Turbulent Flow Aerodynamics solution algorithm Euler Equations Computing

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Unstructured grid arbitrarily shaped element method for fluid flow simulation

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AIAA JOURNAL 2000年第12期38卷 2246-2252页

作者： Lai, YG Univ Iowa Iowa Inst Hydraul Res Iowa City IA 52242 USA

A three-dimensional unstructured grid arbitrarily shaped element method is developed for solving the Navier-Stokes equations. The proposed method is generally applicable to arbitrarily shaped elements and, thus, offers the potential to unify many of the different grid topologies into a single formulation Examples of grid topologies include a structured hexahedral mesh;unstructured tetrahedral mesh;hybrid mesh using a combination of hexahedra, tetrahedra, prisms, and pyramids;Cartesian mesh with elements (cubes) cut by now boundaries;and mixed arbitrary multiblock meshes. The concept of such an arbitrary element method is developed and implemented into a pressure-based finite volume solver. It utilizes a collocated and cell-centered storage scheme. Expressions for second-order discretizatious of the convection and diffusion terms are derived and presented for an arbitrarily shaped element. The developed code, as a first step, is applied to two selected three dimensional viscous flows using a structured hexahedral mesh and an unstructured tetrahedral mesh. It is demonstrated that the concept of the arbitrarily shaped element method can be viable and efficient.

关键词： Unstructured Grid Fluid Flow Navier Stokes Equations Peclet Number Tetrahedral Element solution algorithm Radial Velocity Convection Diffusion Equation Conservation Equations Predictor Corrector Method

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VORTICAL AND TURBULENT STRUCTURE OF A LOBED MIXER FREE SHEAR-LAYER

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AIAA JOURNAL 1994年第9期32卷 1852-1859页

作者： MCCORMICK, DC BENNETT, JC UNIV CONNECTICUT DEPT MECH ENGN STORRS CT 06268 USA

An experimental investigation of the vortical and turbulent structure in a free shear layer downstream of a lobed mixer has been conducted. Pulsed-laser sheet flow visualization with smoke and three-dimensional velocity measurements with hot-film anemometry were obtained for a lobed-mixer configuration and a baseline, planar configuration. Laminar and turbulent initial boundary-layer conditions were documented for both cases. The main result of this investigation is that a new vortex structure was confirmed to exist for the lobed mixer in addition to the well-known streamwise vortex array, consistent with the work of Manning. The normal vortex (due to the Kelvin-Helmholtz instability) sheds periodically from the convoluted trailing edge of the lobed mixer and plays a major part in the enhanced mixing process in combination with the streamwise vorticity. The streamwise vorticity deforms the normal vortex into a pinched-off structure that is unstable and creates intense small-scale turbulence and mixing.

关键词： Boundary Layer Thickness Horseshoe Vortex Kelvin Helmholtz Instability Trailing Edges Kinetic Energy High Speed Civil Transport Aspect Ratio solution algorithm Thrust Augmentation United Technologies Corporation

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Modification of a helicopter inverse simulation to include an enhanced rotor model

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JOURNAL OF AIRCRAFT 2000年第3期37卷 536-538页

作者： Doyle, SA Thomson, DG Univ Glasgow Dept Aerosp Engn Glasgow G12 8QQ Lanark Scotland

An engine governor model has been incorporated into the individual blade rotor model Hibrom for helicopter inverse simulation. The rotorspeed is now a degree of freedom within the modeled system. A series of modification has been made to the solution algorithm Genisa to accommodate the variation of rotorspeed. In particular, the control application interval is recalculated iteratively at each time step.

关键词： Helicopters Numerical Integration Aerodynamic Force Aerospace Engineering Nonlinear Systems Six Degree of Freedom Trailing Edge Flap solution algorithm Dynamic Response Frequency Domain

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STRUCTURAL MODEL CORRELATION USING LARGE ADMISSIBLE PERTURBATIONS IN COGNATE SPACE

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AIAA JOURNAL 1991年第12期29卷 2222-2232页

作者： BERNITSAS, MM TAWEKAL, RL University of Michigan Ann Arbor Michigan 48109

A nonlinear perturbation method is developed to solve the problem of correlating a finite element model (FEM) to a structure for which an incomplete set of natural frequencies and mode shapes and/or some static deflections have been measured. The solution algorithm can handle differences between FEM and structure, in design variables and response, as large as 100-300%, depending on the scale of the structure and correlation measures. This is achieved incrementally by making inadmissible predictions, identifying the modal cognate space relevant to the correlation measures, and making admissible corrections in the cognate space. The developed computer code postprocesses results of the FEM modal and/or static analyses of the initial model only. No additional finite element analysis is required. Lagrange multipliers reveal the dominant correlation requirements and the active admissible cognate subspace. Depending on the number of correlation variables and measures, an optimal, a unique, or an inadmissible minimal error solution may be produced. Beam and offshore tower examples are used to lest the algorithm and investigate conflicting requirements, definition of admissible cognate space, limits of allowable differences between FEM and structure, accuracy, and cost of the nonlinear perturbation method.

关键词： Structural Modeling Finite Element Analysis Lagrange Multipliers Perturbation Method solution algorithm Nastran Structural Element Mathematical Models Dynamic Response Computing

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Solving linear and quadratic quaternion equations

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JOURNAL OF GUIDANCE CONTROL AND DYNAMICS 2006年第6期29卷 1420-1423页

作者： Turner, James D. Dynacs Mil & Def Houston TX 77058 USA

Mathematical algorithms have been presented for solving linear and quadratic quaternion equations, which can be readily obtained when the problem coefficients are real or complex. The scalar and the vector parts of the solution are analytically uncoupled by the introduction of an exact change-of-variables substitution, resulting in a scalar polynomial equation in a single variable that must be solved. The advantage of this approach is that a 78th order polynomial is replaced with a second-through eighth-order polynomial, depending on the symmetries of the specific application. The four nonlinear equations defining the necessary conditions for the solutions are reduced to a single scalar equation by analytically eliminating the vector part of the solution from the scalar equation. After obtaining the scalar solutions, the vector part of the solution is thereby obtained by introducing the scalar solution into the transformation equation for the vector part of the solution.

关键词： Quaternions Numerical Stability solution algorithm Search algorithm Lyapunov Equation

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