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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

An inference engine for embedded diagnostic systems

The implementation of an inference engine for embedded diagnostic systems is described. The system consists of two distinct parts. The first is an off-line compiler which accepts a propositional logical statement of the relationship between facts and conclusions and produces data structures required by the on-line inference engine. The second part consists of the inference engine and interface routines which accept assertions of fact and return the conclusions which necessarily follow. Given a set of assertions, it will generate exactly the conclusions which logically follow. At the same time, it will detect any inconsistencies which may propagate from an inconsistent set of assertions or a poorly formulated set of rules. The memory requirements are fixed and the worst case execution times are bounded at compile time. The data structures and inference algorithms are very simple and well understood. The data structures and algorithms are described in detail. The system has been implemented on Lisp, Pascal, and Modula-2.

Fox, Barry R.↗
NASA NTRS1987

ESSAA: Embedded system safety analysis assistant

The Embedded System Safety Analysis Assistant (ESSAA) is a knowledge-based tool that can assist in identifying disaster scenarios. Imbedded software issues hazardous control commands to the surrounding hardware. ESSAA is intended to work from outputs to inputs, as a complement to simulation and verification methods. Rather than treating the software in isolation, it examines the context in which the software is to be deployed. Given a specified disasterous outcome, ESSAA works from a qualitative, abstract model of the complete system to infer sets of environmental conditions and/or failures that could cause a disasterous outcome. The scenarios can then be examined in depth for plausibility using existing techniques.

Wallace, Peter↗
NASA NTRS1988

Slender wing theory including regions of embedded total pressure loss

An aerodynamic theory of the flow about slender delta wings is described. The theory includes a treatment of the self-consistent development of the vortex wake patterns above the wing necessary to maintain smooth flow at the wing edges. The paper focuses especially on the formation within the wake of vortex 'cores' as embedded regions of total pressure loss, fed and maintained by umbilical vortex sheets emanating from the wing edges. Criteria are developed for determining the growing size and location of these cores, as well as the distribution and strength of the vorticity within them. In this paper, however, the possibility of vortex breakup is omitted. The aerodynamic consequences of the presence and evolution of the cores and the associated wake structure are illustrated and discussed. It is noted that wake history effects can have substantial influence on the distribution of normal force on the wing as well as on its magnitude.

Mccune, James E.↗
NASA NTRS1987

A simple device for the preparation of embedded materials science specimens for ultramicrotomy

A simple hand-held grinding fixture is discussed which can produce microtome mounts of hard materials, oriented interfaces, and powders embedded in a 5/16-in plastic rod. The device has been used for the ultramicrotomy of meteorite samples, 10-50 micron interplanetary dust particles, and thin films on plastic. Results are presented for a layer lattice silicate from the Murchison carbonaceous chondrite, illustrating the resolution and structural detail that can be obtained with the method.

Blake, D. F.↗
NASA NTRS1988

A streamwise vortex embedded in a plane mixing layer

Experimental results are presented on the interaction of a single streamwise vortex with a plane turbulent mixing layer. In the present setup, the vortex is generated by a half-delta wing mounted in the settling chamber of a blower-driven wind tunnel. Initially, the vortex is shown to ride just below the mixing layer, locally distorting the mean velocity and turbulence Reynolds stress distributions in the lower part of the mixing layer. Once the vortex becomes embedded within the mixing layer, the distortions are found to spread through the whole width of the layer, and the induced extra strain rates in the mixing layer result in the generation of additional, relatively large, Reynolds normal and shear stresses, mainly in the regions above the vortex.

Bell, James H.↗
NASA NTRS1988

Grid embedding technique using Cartesian grids for Euler solutions

Grid-embedding techniques are presently applied to the solutions of the Euler equations on Cartesian grids for the NACA 0012 airfoil and the multielement SKF1.1 airfoil at transonic speeds. Based on comparisons with solutions on fine grids, it is shown that the present scheme, when used in conjunction with the Runge-Kutta time-stepping scheme as well as Cartesian grids, yields reduced memory requirements and a substantial reduction in computational time, without loss of accuracy.

Micheltree, R. A.↗
NASA NTRS1986

Some design constraints required for the use of generic software in embedded systems: Packages which manage abstract dynamic structures without the need for garbage collection

The embedded systems running real-time applications, for which Ada was designed, require their own mechanisms for the management of dynamically allocated storage. There is a need for packages which manage their own internalo structures to control their deallocation as well, due to the performance implications of garbage collection by the KAPSE. This places a requirement upon the design of generic packages which manage generically structured private types built-up from application-defined input types. These kinds of generic packages should figure greatly in the development of lower-level software such as operating systems, schedulers, controllers, and device driver; and will manage structures such as queues, stacks, link-lists, files, and binary multary (hierarchical) trees. Controlled to prevent inadvertent de-designation of dynamic elements, which is implicit in the assignment operation A study was made of the use of limited private type, in solving the problems of controlling the accumulation of anonymous, detached objects in running systems. The use of deallocator prodecures for run-down of application-defined input types during deallocation operations during satellites.

Johnson, Charles S.↗
NASA NTRS1989

Energy in elastic fiber embedded in elastic matrix containing incident SH wave

A single elastic fiber embedded in an infinite elastic matrix is considered. An incident plane SH wave is assumed in the infinite matrix, and an expression is derived for the total energy in the fiber due to the incident SH wave. A nondimensional form of the fiber energy is plotted as a function of the nondimensional wavenumber of the SH wave. It is shown that the fiber energy attains maximum values at specific values of the wavenumber of the incident wave. The results obtained here are interpreted in the context of phenomena observed in acousto-ultrasonic experiments on fiber reinforced composite materials.

Williams, James H., Jr.↗
NASA NTRS1989

Reliability and performance evaluation of systems containing embedded rule-based expert systems

A method for evaluating the reliability of real-time systems containing embedded rule-based expert systems is proposed and investigated. It is a three stage technique that addresses the impact of knowledge-base uncertainties on the performance of expert systems. In the first stage, a Markov reliability model of the system is developed which identifies the key performance parameters of the expert system. In the second stage, the evaluation method is used to determine the values of the expert system's key performance parameters. The performance parameters can be evaluated directly by using a probabilistic model of uncertainties in the knowledge-base or by using sensitivity analyses. In the third and final state, the performance parameters of the expert system are combined with performance parameters for other system components and subsystems to evaluate the reliability and performance of the complete system. The evaluation method is demonstrated in the context of a simple expert system used to supervise the performances of an FDI algorithm associated with an aircraft longitudinal flight-control system.

Beaton, Robert M.↗
NASA NTRS1989

An embedded mesh procedure for leading-edge vortex flows

A cell-vertex scheme is outlined for solving the flow about a delta wing with M (sub infinity) is greater than 1. Embedded regions of mesh refinement allow solutions to be obtained which have much higher resolution than those achieved to date. Effects of mesh refinement and artificial viscosity on the solutions are studied, to determine at what point leading-edge vortex solutions are grid-converged. A macroscale and a microscale for the size of the vortex are defined, and it is shown that the macroscale (which includes the wing surface properties) is converged on a moderately refined grid, while the microscale is very sensitive to grid spacing. The level of numerical diffusion in the core of the vortex is found to be substantial. Comparisons with the experiment are made for two cases which have transonic cross-flow velocities.

Powell, Kenneth G.↗
NASA NTRS1989

The free-wake prediction of rotor hover performance using a vortex embedding method

A method is developed to predict the rotor hover performance. This method solves the compressible mass conservation equation much like current full potential codes and can therefore predict the transonic flows on a rotor. However, the newly developed approach also allows for the free convection of shed vorticity and permits the computation of the entire hover wake system. The method uses a vortex embedding scheme in potential flow and has been implemented in a computer code, HELIX -I. To predict power we implement a simple boundary layer and two different induced-drag integration schemes. The induced-drag is obtained from surface pressure integration and an energy flux integral. Comparisons between computations and experiment show good agreement for the prediction of power polars, surface pressure distribution, and tip vortex geometry.

Ramachandran, K.↗
NASA NTRS1989

Observational constraints on an embedded cloud model for the soft X-ray diffuse background

The reason for the observed anticorrelation between soft X-ray diffuse background (SXRB) and neutral hydrogen column densities are considered. Using the B and C band data from an all-sky survey of the SXRB, as well as data in the Be band, it is shown that the Jakobsen and Kahn (1986) embedded cloud model, in which several statistical properties of the SXRB in the B and C bands were used to constrain their model parameters, cannot fit the observed band ratios, except in the limit in which virtually all of the emission originates in the near side of the absorbing gas. It was also shown that model parameters corresponding to appreciably mixed emission and absorption, as proposed by Bunner et al. (1969) and Davidsen et al. (1972), do not fit the data. Model parameters corresponding to the absorption models of Bowyer et al. (1968), Bunner et al. (1969), Davidsen et al. (1972), and Yentis et al. (1972), cannot fit the data unless the absorbing material is more strongly clumped than is permitted by 21-cm observations.

Burrows, D. N.↗
NASA NTRS1990

Adaptive grid embedding for the two-dimensional flux-split Euler equations

A numerical algorithm is presented for solving the 2-D flux-split Euler equations using a multigrid method with adaptive grid embedding. The method uses an unstructured data set along with a system of pointers for communication on the irregularly shaped grid topologies. An explicit two-stage time advancement scheme is implemented. A multigrid algorithm is used to provide grid level communication and to accelerate the convergence of the solution to steady state. Results are presented for a subcritical airfoil and a transonic airfoil with 3 levels of adaptation. Comparisons are made with a structured upwind Euler code which uses the same flux integration techniques of the present algorithm. Good agreement is obtained with converged surface pressure coefficients. The lift coefficients of the adaptive code are within 2 1/2 percent of the structured code for the sub-critical case and within 4 1/2 percent of the structured code for the transonic case using approximately one-third the number of grid points.

Warren, Gary Patrick↗
NASA NTRS1988

Instability-related delamination growth of embedded and edge delaminations

Compressive loads can cause local buckling in composite laminates that have a near surface delamination. This buckling causes load redistribution and secondary loads, which in turn cause interlaminar stresses and delamination growth. The goal of this research was to enhance the understanding of this instability-related delamination growth in laminates containing either an embedded or an edge delamination.

Whitcomb, John D.↗
NASA NTRS1989

Embedded adaptation for time dependent real fluid/gas flows

An embedded adaptation algorithm is used to illustrate applications and requirements for Navier-Stokes and nonequilibrium unsteady two-dimensional flow fields. Both grid refinement and equation modification are included for unstructured distributions of quadrilateral cells. Multiple refinement parameters for distinct physical phenomena serve to monitor the evolving nonuniform field and to recognize flow features in isolated and overlapping subdomains. Examples from subsonic, hypersonic, internal, and external fields show substantial advantages for the adaptive approach.

Baron, Judson R.↗
NASA NTRS1988

Experiences with Ada in an embedded system

Recent experiences with using Ada in a real time environment are described. The application was the control system for an experimental robotic arm. The objectives of the effort were to experiment with developing embedded applications in Ada, evaluating the suitability of the language for the application, and determining the performance of the system. Additional objectives were to develop a control system based on the NASA/NBS Standard Reference Model for Telerobot Control System Architecture (NASREM) in Ada, and to experiment with the control laws and how to incorporate them into the NASREM architecture.

Labaugh, Robert J.↗
NASA NTRS1990

Hot interstellar gas and ionization of embedded clouds

Researchers present detailed photoionization calculations for the instellar cloud in which the Sun is embedded. They consider the EUV radiation field with contribution from discrete stellar sources and from a thermal bremsstrahlung-radiative recombination spectrum emitted from the surrounding 10 to the 6th power k coronal substrate. They establish lower limits to the fractional ionization of hydrogen and helium of 0.17 and 0.29 respectively. The high He ionization fraction results primarily from very strong line emission below 500 A originating in the surrounding coronal substrate while the H ionization is dominated by the EUV radiation from the discrete stellar sources. The dual effects of thermal conduction and the EUV spectrum of the 10 to the 6th k plasma on ionization in the cloud skin are explored. The EUV radiation field and Auger ionization have insignificant effects on the resulting ionic column densities of Si IV, C IV, N V and O VI through the cloud skin. Calculations show that the abundances of these species are dominated by collisional ionization in the thermal conduction front. Because of a low charge exchange rate with hydrogen, the ionic column density ratios of N (CIII)/N (CII) and N (NII)/N (NI) are dominated by the EUV radiation field in the local interstellar medium. These ratios should be important diagnostics for the EUV radiation field and serve as surrogate indicators of the interstellar He and H ionization fraction respectively. Spacecraft such as Lyman which is designed to obtain high resolution spectral data down to the Lyman limit at 912 A could sample interstellar lines of these ions.

Cheng, K.-P.↗
NASA NTRS1989

The embedded objects in epsilon Cha I cloud

A study was made of the embedded objects in the epsilon Cha I cloud. General shapes of the spectra were constructed for the members in the cloud. The near infrared data were compiled from the literature and combined with the IRAS Point Source Catalog information. Pointed observations by the IRAS were used in the regions of high source density where the Point Source Catalog is confused. Member objects near the late B star HD 97300 were measured recently in the 3 to 10 micron bands using the ESO 2.2 m telescope in order to study the effects of disks seen in other young stellar objects. A picture is presented of the complete initial luminosity function in the epsilon Cha I cloud. The observations were compared with the theoretical views on low mass star formation.

Prusti, Timo↗