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NASA NTRS1986

Procedural knowledge

Much of commonsense knowledge about the real world is in the form of procedures or sequences of actions for achieving particular goals. In this paper, a formalism is presented for representing such knowledge using the notion of process. A declarative semantics for the representation is given, which allows a user to state facts about the effects of doing things in the problem domain of interest. An operational semantics is also provided, which shows how this knowledge can be used to achieve particular goals or to form intentions regarding their achievement. Given both semantics, the formalism additionally serves as an executable specification language suitable for constructing complex systems. A system based on this formalism is described, and examples involving control of an autonomous robot and fault diagnosis for NASA's Space Shuttle are provided.

Georgeff, Michael P.↗
NASA NTRS1987

A three-dimensional dual potential procedure for inlets and indraft wind tunnels

A dual potential decomposition of the velocity field into a scalar and a vector potential function is extended to three dimensions and used in the finite-difference simulation of steady three-dimensional inviscid rotational flow through ducts and inlets. The procedure has been used to simulate the flow through the 80- by 120-Foot Wind Tunnel at NASA Ames Research Center. Vanes and screens located at the entrance of the inlet are modeled using actuator disk theory. The numerical predictions are in good agreement with experimental data.

Rao, K. V.↗
NASA NTRS1987

A generalized procedure for constructing an upwind-based TVD scheme

A generalized formulation for constructing second- and higher-order accurate TVD (total variation diminishing) schemes is presented. A given scheme is made TVD by limiting antidiffusive flux differences with some nonlinear functions, so-called limiters. The general idea of the formulation and its mathematical proof of Harten's TVD conditions is shown by applying the Lax-Wendroff method to a scalar nonlinear equation and constant-coefficient system of conservation laws. For the system of equations, several definitions are derived for the argument used in the limiter function and present their performance to numerical experiments. Then the formulation is formally extended to the nonlinear system of equations. It is demonstrated that use of the present procedure allows easy conversion of existing central or upwind, and second- or higher-order differencing schemes so as to preserve monotonicity and to yield physically admissible solutions. The formulation is simple mathematically as well as numerically; neither matrix-vector multiplication nor Riemann solver is required. Roughly twice as much computational effort is needed as compared to conventional scheme. Although the notion of TVD is based on the initial value problem, application to the steady Euler equations of the formulation is also made. Numerical examples including various ranges of problems show both time- and spatial-accuracy in comparison with exact solutions.

Liou, Meng-Sing↗
NASA NTRS1986

A coupled marching procedure for the partially parabolized Navier-Stokes equations

A coupled finite-difference formulation is described for solving a reduced form of the compressible Navier-Stokes equations by a multiple space marching procedure. The properties of the equations are discussed and the solution algorithm presented. The scheme is used to compute incompressible flows by taking the incompressible limit (M about 0.1) of the compressible formulation. A separate Poisson equation is not required for the pressure. Results are compared with experimental data and other numerical predictions for low Reynolds number channel inlet flow, flow over a rearward-facing step in a channel, and flow near the trailing edge of a flat plate.

Liu, Xuezong↗
NASA NTRS1987

A simultaneous viscous-inviscid interaction calculation procedure for transonic turbulent flows

A new simultaneous viscous-inviscid interaction scheme has been developed for the analysis of steady turbulent transonic separated flows. The viscous and inviscid solutions are coupled through the displacement concept using a transpiration velocity. The local solutions of the full potential and boundary-layer equations are treated simultaneously using the finite-difference method. The displacement thickness is treated as an unknown and is obtained as a part of the solution through a global iteration procedure of the space marching scheme. The Cebeci-Smith and Johnson-King models are used to simulate the turbulence. The computational examples showed that the simultaneous method is more efficient and robust than the semi-inverse method for transonic flows with a strong interaction.

Lee, D.↗
NASA NTRS1987

Interdisciplinary analysis procedures in the modeling and control of large space-based structures

The paper describes a computer software system called the Integrated Multidisciplinary Analysis Tool, IMAT, that has been developed at NASA Langley Research Center. IMAT provides researchers and analysts with an efficient capability to analyze satellite control systems influenced by structural dynamics. Using a menu-driven interactive executive program, IMAT links a relational database to commercial structural and controls analysis codes. The paper describes the procedures followed to analyze a complex satellite structure and control system. The codes used to accomplish the analysis are described, and an example is provided of an application of IMAT to the analysis of a reference space station subject to a rectangular pulse loading at its docking port.

Cooper, Paul A.↗
NASA NTRS1987

A procedural method for the efficient implementation of full-custom VLSI designs

An imbedded language system for the layout of very large scale integration (VLSI) circuits is examined. It is shown that through the judicious use of this system, a large variety of circuits can be designed with circuit density and performance comparable to traditional full-custom design methods, but with design costs more comparable to semi-custom design methods. The high performance of this methodology is attributable to the flexibility of procedural descriptions of VLSI layouts and to a number of automatic and semi-automatic tools within the system.

Belk, P.↗
NASA NTRS1988

Simplified procedures for designing composite bolted joints

Simplified procedures are described to design and analyze single and multi-bolt composite joints. Numerical examples illustrate the use of these methods. Factors affecting composite bolted joints are summarized. References are cited where more detailed discussion is presented on specific aspects of composite bolted joints. Design variables associated with these joints are summarized in the appendix.

Chamis, Christos C.↗
NASA NTRS1988

Are windshear training aid recommendations appropriate for other than large jet transports? Pilot procedures: Shear models

Information is given in vugraph form on pilot procedures in windshear, typical winds in a downburst, a downburst encounter at takeoff by a large jet transport and a light turboprop twin, and a comparison of pitch algorithms in an approach encounter with downburst shear. It is observed that the light turboprop appears no less tolerant of a downburst encounter than the large jet.

Bray, R. S.↗
NASA NTRS1986

Interface procedures for overlapping grids

The solution of partial differential equations by means of either implicit or conservative explicit finite-difference methods, on the one hand, or multicomponent overlapping grid schemes on the other, is presently subjected to interpolation at grid boundaries in an attempt to eliminate the time lag. The accuracy of the transient solution of a hyperbolic or parabolic partial differential equation is dependent on the procedures used to transfer information between grids in a composite grid system. The present techniques reduce numerical solution errors.

Mastin, C. Wayne↗
NASA NTRS1988

Response function of a tunable diode laser spectrometer from an iterative deconvolution procedure

A deconvolution procedure commonly used for resolution enhancement of spectra has been applied to the determination of the response function of a tunable diode laser spectrometer. The method is sufficiently fast and simple for routine application when correcting for nonnegligible instrumental broadening. Absolute linestrengths of CH4 in the 1327/cm region and line positions of HNO3 in the 1335/cm region, measured with the aid of the deconvolution technique, are reported here.

May, Randy D.↗
NASA NTRS1988

A panel method procedure for interference assessment in slotted-wall wind tunnels

This paper describes a method for three-dimensional wind tunnel interference assessment developed specifically for slotted-wall tunnels. The method is an adaptation to the assessment problem of a previously published high-order panel method procedure for simulating the flow in slotted-wall tunnel test sections. The method uses a mixed outer boundary condition, primarily a Neumann condition, with measured pressure constraints used to control only those boundary phenomena which can not be specified accurately a priori. Assessment results are illustrated from a calibration test with variations in wall geometry, and from tests of a generic subsonic transport aircraft configuration.

Kemp, William B., Jr.↗
NASA NTRS1988

Unsteady viscous-inviscid interaction procedures for transonic airfoils using Cartesian grids

A viscous-inviscid interaction procedure for transonic airfoils using an Euler/integral boundary layer formulation and Cartesian grids is presented. The approach is based on a time dependent formulation for both the integral boundary layer equations and the Euler equations. Effects of upstream history on the shear stress are modeled by a time dependent rate equation derived from the turbulent kinetic energy equation. Results are presented for two of the test cases reported by Cook et al. (1979) for the RAE 2822 supercritical airfoil and one of the cases reported by Harris (1981) for the NACA 0012 symmetric airfoil. In general, the results are in good agreement with experiment.

Fenno, Charles C., Jr.↗
NASA NTRS1988

Reanalysis procedure for large structural systems

Global-basis-vector approximate reanalysis techniques for use in automated structural optimization schemes are developed and demonstrated. The vibrational response of a modified structure (MS) is estimated by lumping the design variables into a single tracing parameter, applying an operator splitting procedure to express the FEM equations of the MS in terms of the original-structure equations plus correction terms, and reducing the MS equations via a classical Bubnov-Galerkin scheme. The sensitivity of the vibrational response to structural modifications is evaluated, and the relationship between this method and the preconditioned conjugate-gradient method (Noor and Peters, 1988) is explored. Numerical results for linear static and free vibration problems involving beamlike lattices, double-layered hexahedral grids, and structural gridworks are presented in tables and graphs and briefly characterized.

Noor, Ahmed K.↗
NASA NTRS1988

PIPS: A Procedure for Interactive Pyramid Segmentation

The Procedure for Interactive Pyramid Segementation was designed to identify regions of spatially connected and spectrally homogeneous pixels in multispectral image data, and to allow these regions to be interactively manipulated without the use of processing parameters. The objective is to provide the user with the capability to easily extract and identify regions corresponding to target objects of interest. The approach is to segment a multispectral image into a set of regions and to allow the analyst to interactively refine the segmentation by direct manipulation. The user can elect to: interactively display maps of the spatial distribution of regions for any designated image subset; display the statistics of a given region; and label, merge, or split regions.

Wharton, S. W.↗
NASA NTRS1987

Development of generalized block correction procedures for the solution of discretized Navier-Stokes equations

Effort is directed towards developing a solution method which combines advantages of both the iterative and the direct methods. It involves iterative solution on the fine grid, convergence of which is enhanced by a direct solution for correction quantities on a coarse grid. The proposed block correction procedure was applied to compute recirculating flow in a driven cavity.

Kelkar, Kanchan M.↗