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VALIDATION OF FINITE-DIMENSIONAL APPROXIMATE solutionS FOR DYNAMICS OF DISTRIBUTED-PARAMETER SYSTEMS

JOURNAL OF GUIDANCE CONTROL AND DYNAMICS 1995年第1期18卷 87-95页

作者： JUNKINS, JL LEE, SC Texas A&M University College Station Texas 77843

An inverse dynamics method is introduced for constructing exact special-case solutions for hybrid coordinate ordinary/partial systems of differential equations (hybrid ODE/PDE systems). The solution is constructed such that it lies near a given approximate numerical solution, and therefore the special-case solutions can be generated in a versatile and physically meaningful fashion and can serve as a benchmark problem to validate approximate solution methods. The exact solution is constructed such that it is a differentiable, continuous-function neighbor of the given approximate numerical solution. This continuous solution is then substituted into the governing system of ODEs/PDEs and a full complement of distributed and boundary forces is determined algebraically to exactly satisfy the differential equations, This process has been automated by computer symbol manipulation. Since the exact special-case algebraic solutions can be evaluated anywhere in space and time, this approach is ideally suited to providing a true exact motion and the corresponding forces for studying the convergence errors in a family of approximate solutions. This methodology makes it possible for one to rigorously determine exact solution errors for a significant class of ODE/PDE systems for which the initial-value problem is not, in general, exactly solvable. We explore the utility of this method in validating numerical solution methods.

关键词： Distributed Parameter System Finite Element Approximation Second Order Differential Equations Flexible Structures Numerical Simulation solution algorithm Runge Kutta Methods Shear Deformation Feedback Control Riccati Equations

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MULTIZONAL NAVIER-STOKES solutionS FOR THE MULTIBODY SPACE-SHUTTLE CONFIGURATION

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JOURNAL OF SPACECRAFT AND ROCKETS 1992年第1期29卷 129-137页

作者： CHEN, CL RAMAKRISHNAN, S SZEMA, KY DRESSER, HS RAJAGOPAL, K ROCKWELL INT CORP DIV SPACEDOWNEYCA 90241

Numerical simulation of flow past the multibody Shuttle configuration in ascent mode has been carried out using the USA (unified solution algorithms) code, which is a finite volume, unified time/space marching, zonal, Reynolds-averaged Navier-Stokes solver featuring an implicit, upwind-biased scheme and total variation diminishing discretization for high accuracy. Body conforming elliptic multizonal grids were used in the computation. The agreement between computed and experimental results is reasonable. The interference effects of various components on the surface pressure distribution are discussed. The results show the importance of ensuring simulation of proper blockages due to various components of the mated Space Shuttle vehicle to obtain a reliable prediction of aerodynamic forces. Agreement between computed and experimental results could be improved by refining the definition of various geometric features and by including all geometric complexities.

关键词： Space Shuttle Total Variation Diminishing Reynolds Averaged Navier Stokes Freestream Conditions solution algorithm Solid Rocket Boosters Roe Approximate Riemann Solver Flight Testing Wind Tunnel Walls Turbulent Boundary Layer

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An empirical study of predicting software faults with case-based reasoning

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SOFTWARE QUALITY JOURNAL 2006年第2期14卷 85-111页

作者： Khoshgoftaar, Taghi M. Seliya, Naeem Sundaresh, Nandini Florida Atlantic Univ Dept Comp Sci & Engn Empir Software Engn Lab Boca Raton FL 33431 USA

The resources allocated for software quality assurance and improvement have not increased with the ever-increasing need for better software quality. A targeted software quality inspection can detect faulty modules and reduce the number of faults occurring during operations. We present a software fault prediction modeling approach with case-based reasoning (CBR), a part of the computational intelligence field focusing on automated reasoning processes. A CBR system functions as a software fault prediction model by quantifying, for a module under development, the expected number of faults based on similar modules that were previously developed. Such a system is composed of a similarity function, the number of nearest neighbor cases used for fault prediction, and a solution algorithm. The selection of a particular similarity function and solution algorithm may affect the performance accuracy of a CBR-based software fault prediction system. This paper presents an empirical study investigating the effects of using three different similarity functions and two different solution algorithms on the prediction accuracy of our CBR system. The influence of varying the number of nearest neighbor cases on the performance accuracy is also explored. Moreover, the benefits of using metric-selection procedures for our CBR system is also evaluated. Case studies of a large legacy telecommunications system are used for our analysis. It is observed that the CBR system using the Mahalanobis distance similarity function and the inverse distance weighted solution algorithm yielded the best fault prediction. In addition, the CBR models have better performance than models based on multiple linear regression.

关键词： software quality case-based reasoning software fault prediction similarity functions solution algorithm software metrics

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CALCULATION OF UNSTEADY FAN ROTOR RESPONSE CAUSED BY DOWNSTREAM FLOW DISTORTIONS

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JOURNAL OF PROPULSION AND POWER 1985年第6期1卷 464-469页

作者： OBRIEN, WF NG, WF RICHARDSON, SM Virginia Polytechnic Institute and State University Blacksburg

A method for the calculation of the circumferentially-varying flow field in an axial-flow fan with downstream stator guide vanes and casing support struts is described. A time-marching solution for the rotor is coupled to a potential flow solution for downstream flow in the vane and strut regions. The influence of strut design parameters is studied employing the method. It is found that strut thickness, circumferential spacing, and sepation distance from the rotor are primary variables determining unsteady rotor response. The stator row is shown to reduce the effective rotor-strut spacing, contributing to increased rotor-strut flow interaction. Good agreement is obtained between predicted and measured on-rotor pressure fluctuations from a test rig. © 1985 American Institute of Aeronautics and Astronautics, Inc., All rights reserved.

关键词： Incompressible Flow Pressure Coefficient Angle of Attack Rotor Blades Euler Equations Fluid Mechanics Mach Number solution algorithm Turbofan Engines Perfect Gas

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

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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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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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Spinning projectile's attitude measurement with LW infrared radiation under sea-sky background

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INFRARED PHYSICS & TECHNOLOGY 2018年 90卷 214-220页

作者： Xu, Miaomiao Bu, Xiongzhu Yu, Jing He, Zilu Nanjing Univ Sci & Technol Sch Mech Engn 200 Xiaolingwei Nanjing 210094 Jiangsu Peoples R China

With the further development of infrared radiation research in sea-sky background and the requirement of spinning projectile's attitude measurement, the sea-sky infrared radiation field is used to carry out spinning projectile's attitude angle instead of inertial sensors. Firstly, the generation mechanism of sea-sky infrared radiation is analysed. The mathematical model of sea-sky infrared radiation is deduced in LW (long wave) infrared 8 similar to 14 mu m band by calculating the sea surface and sky infrared radiation. Secondly, according to the movement characteristics of spinning projectile, the attitude measurement model of infrared sensors on projectile's three axis is established. And the feasibility of the model is analysed by simulation. Finally, the projectile's attitude calculation algorithm is designed to improve the attitude angle estimation accuracy. The results of semi-physical experiments show that the segmented interactive algorithm estimation error of pitch and roll angle is within +/- 1.5 degrees. The attitude measurement method is effective and feasible, and provides accurate measurement basis for the guidance of spinning projectile. (C) 2018 Elsevier B.V. All rights reserved.

关键词： Sea-sky infrared radiation Spinning projectile Attitude measurement solution algorithm

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ADAPTIVE TRIANGULAR MESH GENERATION

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AIAA JOURNAL 1987年第10期25卷 1356-1364页

作者： ERLEBACHER, G EISEMAN, PR COLUMBIA UNIV DEPT APPL PHYS & NUCL ENGNNEW YORKNY 10027

A general adaptive algorithm is developed on triangular meshes. The adaptivity is provided by a combination of node addition, dynamic node connectivity and a simple node movement strategy. While the local restructuring process and the node addition mechanism take place in the physical plane, the nodes are displaced on a monitor surface, constructed from the salient features of the physical problem. An approximation to mean curvature detects changes in the direction of the monitor surface, and provides the pulling force on the nodes. solutions to the axisymmetric Grad-Shafranov equation demonstrate the capturing, by triangles, of the plasmavacuum interface in a free boundary equilibrium configuration. © 1987 American Institute of Aeronautics and Astronautics, Inc., All rights reserved.

关键词： Mesh Generation solution algorithm Numerical algorithms Grad Shafranov Equation Parallel Processing (Computers) Hardware Development Compressible Flow Reacting Flow Taylor Series Magnetic Flux

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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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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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