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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 991 records · Page 55
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Automatic blocking of nested loops

Blocked algorithms have much better properties of data locality and therefore can be much more efficient than ordinary algorithms when a memory hierarchy is involved. On the other hand, they are very difficult to write and to tune for particular machines. The reorganization is considered of nested loops through the use of known program transformations in order to create blocked algorithms automatically. The program transformations used are strip mining, loop interchange, and a variant of loop skewing in which invertible linear transformations (with integer coordinates) of the loop indices are allowed. Some problems are solved concerning the optimal application of these transformations. It is shown, in a very general setting, how to choose a nearly optimal set of transformed indices. It is then shown, in one particular but rather frequently occurring situation, how to choose an optimal set of block sizes.

Schreiber, Robert↗
NASA NTRS1991

High resolution measurements of density structures in the Jovian plasma sheet

A recent effort to digitize the plasma density by using the low frequency cutoff of trapped continuum radiation in the vicinity of the Jovian plasma sheet has revealed the existence of sharply defined density structures in the plasma sheet. These structures typically have a plasma density which is relatively constant but of order 50 percent greater or less than in the surrounding plasma. At the boundaries of these structures, the transitions from low to high density occur on time scales of about ten seconds, which correspond to spatial dimensions on the order of a few ion Larmor radii. The structures themselves last for intervals from less than a minute to more than five minutes, corresponding to size scales from a fraction of a Jovian radius to more than a Jovian radius, depending of the velocity of the structure relative to the spacecraft. In view of the importance of near corotation plasma flows, these structures are likely to be limited in both the longitudinal and radial dimensions and, therefore, could represent flux tubes with greatly varying plasma content. These observations are presented as among the first to directly address the theoretically proposed interchange instability.

Ansher, J. A.↗
NASA NTRS1990

High performance VLSI telemetry data systems

NASA-Goddard has over the last five years developed generic ground telemetry data system elements addressing the budget limitations-driven demand for greater modularity, flexibility, and interchangeability. These design solutions, which may be characterized as a 'functional components approach', encompasses both hardware and software components; the former involve telemetry application-specific ICs for data rate requirements of up to 300 Mbps, while the latter extend to embedded local software intelligence. Attention is given to the consequences of the functional components approach for VLSI components.

Chesney, J.↗
NASA NTRS1990

Data dictionaries in information systems - Standards, usage , and application

An overview of data dictionary systems and the role of standardization in the interchange of data dictionaries is presented. The development of the data dictionary for the Planetary Data System is cited as an example. The data element dictionary (DED), which is the repository of the definitions of the vocabulary utilized in an information system, is an important part of this service. A DED provides the definitions of the fields of the data set as well as the data elements of the catalog system. Finally, international efforts such as the Consultative Committee on Space Data Systems and other committees set up to provide standard recommendations on the usage and structure of data dictionaries in the international space science community are discussed.

Johnson, Margaret↗
NASA NTRS1991

Aerothermal study in an axial compression corner with shock impingement at Mach 6

An experimental study of an axial-compression interior-corner region with shock impingement was conducted in the NASA Langley 20-inch Mach 6 Tunnel to obtain aerodynamic heating rate distributions. The model, a generic hypersonic engine inlet, had a sharp leading edge forebody, cowl, and interchangeable struts with sharp and blunt leading edges. Experiments were conducted at free-stream unit Reynolds numbers of 1.68 x 10 to the 6th and 3.35 x 10 to the 6th per foot for the blunt and sharp-strut configurations, respectively. For the sharp-strut configuration, with and without trips, the peak heating occurred on the cowl, near the compression corner, downstream of the forebody oblique shock impingement region. The peak heating levels, for both the tripped and untripped boundary-layer flows were about 45 and 50 times the reference laminar heating levels, respectively. The peak heating for the blunt leading edge strut model, which was 30 times the reference value, occurred on the cowl, away from the corner, where the bow shock from the strut leading edge intersected the cowl surface.

Venkateswaran, S.↗
NASA NTRS1991

Effect of a simulated ice accretion on the aerodynamics of a swept wing

The effect of a simulated glaze ice accretion on the aerodynamic performance of a three-dimensional swept wing is studied experimentally. A semispan wing of effective aspect ratio four was mounted from the sidewall of the UIUC subsonic wind tunnel. The model uses a NACA 0012 airfoil section on a rectangular planform with interchangeable tip and root sections to allow for 0- and 30-degree sweep. A sidewall suction system is used to minmize the tunnel boundary-layer interaction with the model. Surface pressure data from five spanwise stations are compared to earlier data from a similar tunnel. A three-component sidewall balance has been designed, built and used to measure lift, drag and pitching moment on the clean and iced model. The data compare well to the integrated pressure data and to theory on the clean model. In addition, helium-bubble flow visualization has been performed on the iced model and reveals extensive spanwise flow in the separation bubble aft of the upper surface horn. This compares well to the computational results of other researchers. Sidewall suction was found to have no effect on the aerodynamics of the swept wing.

Bragg, M. B.↗
NASA NTRS1991

Effects of initial spanwise perturbations and three-dimensionality in a plane mixing layer

An experimental study concerning the influence of small changaes in initial conditions on the near- and far-field evolution of the th ree-dimensional structure in a plane mixing layer has been conducted. A two-stream mixing layer with a velocity ratio of 0.6 was generated with the initial boundary layers laminar and nominally two-dimensional. The initial conditions were changed slightly by interchanging the high- and low-speed sides of the wind tunnel, while maintaining the same velocity ratio. The results indicate that, even with this minor change in initial conditions, the near-field regions of the two cases differ significantly, with the peak Reynolds stress levels varying by up to 100 percent. In addition, the distribution of the individual streamwise vortical structures differs in intensity and position for the two cases, although the overall qualitative description is comparable.

Plesniak, M. W.↗
NASA NTRS1990

Modular Containerless Processing Facility

The Modular Containerless Processing Facility (MCPF) of the Space Station Freedom, being developed by the Jet Propulsion Laboratory, is described. The MCPF will be capable of positioning, manipulating, and performing processing operations on samples completely free of container walls. It will be comprised of a host facility and a series of interchangeable plug-in modules. Initial iterations of MCPF modules will be flown on the U.S. Microgravity Laboratory (USML) series of Shuttle flights. The Drop Physics Module schedualed to fly on USML-1 in March 1992 is also considered.

Morrison, Andrew D.↗
NASA NTRS1991

Simulation of cryogenic liquid flows with vapor bubbles

Liquid flows in rocket engine components (such as bearings, seals, and pumps) often involve the formation of vapor bubbles due to local superheating of the fluid (either boiling or cavitation). Under the present effort, an analysis has been developed for liquid flows with vapor bubbles, based on a combined Eulerian-Lagrangian technique, in which the continuous (liquid) phase is treated by solving a system of Eulerian conservation equations, while the discrete (vapor bubble) phase is dealt with by integrating Lagrangian equations of motion in computational coordinates. Vapor bubbles of changing size can be accommodated easily by this analysis, and models for the simulation of bubble formation, growth, and motion have been included. The effect of bubble motion and other bubble processes on the continuous (liquid) phase has been accounted for by appropriate bubble mass, momentum, and energy interchange source terms in the Eulerian conservation equations. To demonstrate the viability of the resulting procedure, the cavitating flow of liquid oxygen through a simplified model of a labyrinth seal has been successfully calculated.

De Jong, Frederik J.↗
NASA NTRS1991

Simulation of high-speed (orbital) releases of electron attachment materials in the ionosphere

The dynamics of ionospheric plasma irregularities produced by the release of electron attachment materials at orbital velocities across the geomagnetic field is studied. A two-dimensional electrostatic fluid model which includes electron attachment and mutual neutralization chemistry, self-consistent electric fields, and three-species transport is developed. Numerical simulations are performed to study the behavior at early and at late times after the release. At early times, of the order of or less than the attachment material neutral collision time, the negative ion cloud produced by the release may structure owing to the shear in the E x B velocity within the cloud. At high altitudes the cloud may bifurcate and form vortices on the back. At lower altitudes where ion-neutral collisional effects dominate, this structuring is suppressed. At late times, after a plasma depletion has formed due to neutralization chemistry, the cloud structures by the E x B interchange instability. Depending on the release altitude, the depletion structures by the collisional or inertial limit of this instability.

Scales, W. A.↗
NASA NTRS1991

Drift wave instability in the Io plasma torus

A linear normal mode analysis of the drift wave instability in the Io plasma torus was carried out on the basis of the Richmond (1973) and Huang et al. (1990) analyses of drift waves in the vicinity of the earth's plasmapause. Results indicate that the outer torus boundary is linearly unstable to the growth of electrostatic drift waves. It is shown that the linear growth rate is proportional to the ion drift frequency and to the ratio of the flux tube charge content to the Jovian ionospheric Pedersen conductance. It is also shown that various theoretical models of global radial transport in Jupiter's atmosphere (including corotating convection, interchange diffusion, and transient flux tube convection) can be understood as plausible nonlinear evolutions of electrostatic drift waves.

Huang, T. S.↗
NASA NTRS1991

Aerodynamic measurements on a finite wing with simulated ice

The effect of a simulated glaze ice accretion on the aerodynamic performance of a three-dimensional straight and swept wing is studied experimentally. A semispan wing of effective aspect ratio five was mounted from the sidewall of the UIUC subsonic wind tunnel. The model uses an NACA 0012 airfoil section on a rectangular planform with interchangeable tip and root sections to allow for 0- and 30-deg sweep. A sidewall suction system is used to minimize the tunnel boundary-layer interaction with the model. A three-component sidewall balance has been designed, built and used to measure lift, drag and pitching moment on the clean and iced model. Fluorescent oil flow visualization has been performed on the iced model and reveals extensive spanwise flow in the separation bubble aft of the upper surface horn. These results are compared to computational results for the surface pressures, span loads and surface oil flow.

Bragg, M. B.↗
NASA NTRS1990

Automation software for a materials testing laboratory

The software environment in use at the NASA-Lewis Research Center's High Temperature Fatigue and Structures Laboratory is reviewed. This software environment is aimed at supporting the tasks involved in performing materials behavior research. The features and capabilities of the approach to specifying a materials test include static and dynamic control mode switching, enabling multimode test control; dynamic alteration of the control waveform based upon events occurring in the response variables; precise control over the nature of both command waveform generation and data acquisition; and the nesting of waveform/data acquisition strategies so that material history dependencies may be explored. To eliminate repetitive tasks in the coventional research process, a communications network software system is established which provides file interchange and remote console capabilities.

Mcgaw, Michael A.↗
NASA NTRS1992

Latches For Equipment Drawers

Mechanism makes rack hardware interchangeable, regardless of drawer height. Provides quick connection and disconnection of equipment drawer. Pivoting lever is heart of mechanism. At insertion, lever rotated slightly counterclockwise so bottom hook slips over pin; then rotated clockwise to engage pin and lever lock. Rotation of lever to full counterclockwise position disengages panel from rack.

Martin, T. C.↗
NASA NTRS1992

Reformatting Data From X-Ray Photoelectron Spectroscopy

ASCITOVG program for IBM PC-series computers creates files in binary format from columns of numbers in American National Standard Code for Information Interchange (ASCII) format. Files suitable for DEC PDP-11/73 computer under Micro-RSX operating system running the VGS-5000 Enhanced Data Processing (EDP) software package which analyzes data with color graphics display, speeding up analysis compared with batch job processing. Written in FORTRAN.

Abel, P. B.↗
NASA NTRS1992

Study Of Robotic Replacement Of Equipment Modules

Report discusses issues pertaining to control of single-arm robotic manipulator to remove and install interchangeable equipment modules. Presents preliminary control strategy intended to guide development of control algorithms, along with analyses of problems arising in implementing strategy.

Backes, Paul G.↗
NASA NTRS1992

Program Assists Design Of Cabling

DFACS is interactive, multiuser, computer-aided-engineering software tool for system-level electrical-integration and cabling engineering. Purpose to provide engineering community with centralized data base for entering and gaining access to definitions of functions of systems, details of pin connections to circuits at subsystem and instrument ends and data on harnessing of cables. Primary objective provides instantaneous single point of interchange of information, avoiding error-prone, time-consuming, and costly multiple-path shuttling of data.

Billitti, Joseph W.↗
NASA NTRS1991

Information logistics: A production-line approach to information services

Logistics can be defined as the process of strategically managing the acquisition, movement, and storage of materials, parts, and finished inventory (and the related information flow) through the organization and its marketing channels in a cost effective manner. It is concerned with delivering the right product to the right customer in the right place at the right time. The logistics function is composed of inventory management, facilities management, communications unitization, transportation, materials management, and production scheduling. The relationship between logistics and information systems is clear. Systems such as Electronic Data Interchange (EDI), Point of Sale (POS) systems, and Just in Time (JIT) inventory management systems are important elements in the management of product development and delivery. With improved access to market demand figures, logisticians can decrease inventory sizes and better service customer demand. However, without accurate, timely information, little, if any, of this would be feasible in today's global markets. Information systems specialists can learn from logisticians. In a manner similar to logistics management, information logistics is concerned with the delivery of the right data, to the ring customer, at the right time. As such, information systems are integral components of the information logistics system charged with providing customers with accurate, timely, cost-effective, and useful information. Information logistics is a management style and is composed of elements similar to those associated with the traditional logistics activity: inventory management (data resource management), facilities management (distributed, centralized and decentralized information systems), communications (participative design and joint application development methodologies), unitization (input/output system design, i.e., packaging or formatting of the information), transportations (voice, data, image, and video communication systems), materials management (data acquisition, e.g., EDI, POS, external data bases, data entry) and production scheduling (job, staff, and project scheduling).

Adams, Dennis↗