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At least 1,405 records · Page 78
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Large scale advanced propeller blade pressure distributions - Prediction and data

Two Euler analysis techniques, finite difference and finite volume, are employed to predict the blade surface pressure distributions of a large scale advanced propeller. The predicted pressure distributions are compared with wind tunnel data. Both techniques produced blade pressure distributions which are in fairly good agreement with the data over the range of test Mach numbers of 0.2 to 0.78. However, the numerical simulations fail to predict correctly the measured pressure distributions for the low Mach number, high power case which seem to have a leading edge vortex. A discussion of the compressibility effects is also presented.

Nallasamy, M.↗
NASA NTRS1989

Stress distribution and topography of Tellus Regio, Venus

The Tellus Regio area of Venus represents a subset of a narrow latitude band where Pioneer Venus Orbiter (PVO) altimetry data, line-of-sight (LOS) gravity data, and Venera 15/16 radar images have all been obtained with good resolution. Tellus Regio also has a wide variety of surface morphologic features, elevations ranging up to 2.5 km, and a relatively low LOS gravity anomaly. This area was therefore chosen in order to examine the theoretical stress distributions resulting from various models of compensation of the observed topography. These surface stress distributions are then compared with the surface morphology revealed in the Venera 15/16 radar images. Conclusions drawn from these comparisons will enable constraints to be put on various tectonic parameters relevant to Tellus Regio. The stress distribution is calculated as a function of the topography, the equipotential anomaly, and the assumed model parameters. The topography data is obtained from the PVO altimetry. The equipotential anomaly is estimated from the PVO LOS gravity data. The PVO LOS gravity represents the spacecraft accelerations due to mass anomalies within the planet. These accelerations are measured at various altitudes and angles to the local vertical and therefore do not lend themselves to a straightforward conversion. A minimum variance estimator of the LOS gravity data is calculated, taking into account the various spacecraft altitudes and LOS angles and using the measured PVO topography as an a priori constraint. This results in an estimated equivalent surface mass distribution, from which the equipotential anomaly is determined.

Williams, David R.↗
NASA NTRS1989

Effects of microgravity on growth hormone concentration and distribution in plants

On earth, gravity affects the distribution of the plant growth hormone, indole-3-acetic acid (IAA), in a manner such that the plant grows into a normal vertical orientation (shoots up, roots down). How the plant controls the amount and distribution of IAA is only partially understood and is currently under investigation in this laboratory. The question to be answered in the flight experiment concerns the effect of gravity on the concentration, turn over, and distribution of the growth hormone. The answer to this question will aid in understanding the mechanism by which plants control the amount and distribution of growth hormone. Such knowledge of a plant's hormonal metabolism may aid in the growth of plants in space and will lead to agronomic advances.

Schulze, Aga↗
NASA NTRS1989

The role of order in distributed programs

The role of order in building distributed systems is discussed. It is the belief that a principle of event ordering underlies the wide range of operating systems mechanisms that were put forward for building robust distributed software. Stated concisely, this principle achieves correct distributed behavior by ordering classes of distributed events that conflict with one another. By focusing on order, simplified descriptions can be obtained and convincingly correct solutions to problems that might otherwise have looked extremely complex. Moreover, it is observed that there are a limited number of ways to obtain order, and that the choice made impacts greatly on performance.

Birman, Kenneth P.↗
NASA NTRS1989

Enhanced resolution particle size distributions by multiple angle photon correlation spectroscopy

Photon correlation spectroscopy (PCS) has become a method of choice for measuring submicrometer particles. It is capable of rapid, accurate measurements of mean particle size. Since the measurements are nonperturbing, it is ideal for monitoring systems undergoing dynamic changes. Despite its widespread acceptance, the information content of PCS measurements for particle size distributions is low and provides limited resolution. A method is presented whereby PCS measurements made at several scattering angles plus the angular distribution of light scattered from the particles are combined in a single simultaneous analysis to effect an enhanced resolution particle size distribution. The efficacy of the method is assessed by recovering size distributions from computer simulated data and by comparisons of conventional PCS measurements of polystyrene spheres with those made by the new method.

Bott, Steven E.↗
NASA NTRS1990

Comparison of drop size distributions from two droplet sizing systems

A comparison between the Phase Doppler Particle Analyzer and the combined measurements from Particle Measuring Systems' Forward Scattering Spectrometer Probe and the Optical Array Probe was conducted in an icing wind tunnel using NASA Icing Research Tunnel spray nozzles to produce the supercooled water droplet cloud. Clouds having a range of volume median diameters from 10 to greater than 50 microns were used for the instrument comparisons. A volume median diameter was calculated from combining the droplet distributions of the Optical Array Probe and the Forward Scattering Spectrometer Probe. A comparison of the combined volume median diameters and the Phase Doppler Particle Analyzer volume median diameters showed agreement from 10 microns up to 30 microns. Typical drop size distributions from the Phase Doppler Particle Analyzer, the Forward Scattering Spectrometer Probe, and Optical Array Probe are presented for several median volume diameters. A comparison of the distributions illustrates regions of the distributions where there is good agreement and other regions where there are discrepancies between the Phase Doppler Particle Analyzer and the Particle Measuring Systems' droplet size instruments.

Oldenburg, John R.↗
NASA NTRS1989

Monte Carlo models and analysis of galactic disk gamma-ray burst distributions

Gamma-ray bursts are transient astronomical phenomena which have no quiescent counterparts in any region of the electromagnetic spectrum. Although temporal and spectral properties indicate that these events are likely energetic, their unknown spatial distribution complicates astrophysical interpretation. Monte Carlo samples of gamma-ray burst sources are created which belong to Galactic disk populations. Spatial analysis techniques are used to compare these samples to the observed distribution. From this, both quantitative and qualitative conclusions are drawn concerning allowed luminosity and spatial distributions of the actual sample. Although the Burst and Transient Source Experiment (BATSE) experiment on Gamma Ray Observatory (GRO) will significantly improve knowledge of the gamma-ray burst source spatial characteristics within only a few months of launch, the analysis techniques described herein will not be superceded. Rather, they may be used with BATSE results to obtain detailed information about both the luminosity and spatial distributions of the sources.

Hakkila, Jon↗
NASA NTRS1987

Exploiting virtual synchrony in distributed systems

Applications of a virtually synchronous environment are described for distributed programming, which underlies a collection of distributed programming tools in the ISIS2 system. A virtually synchronous environment allows processes to be structured into process groups, and makes events like broadcasts to the group as an entity, group membership changes, and even migration of an activity from one place to another appear to occur instantaneously, in other words, synchronously. A major advantage to this approach is that many aspects of a distributed application can be treated independently without compromising correctness. Moreover, user code that is designed as if the system were synchronous can often be executed concurrently. It is argued that this approach to building distributed and fault tolerant software is more straightforward, more flexible, and more likely to yield correct solutions than alternative approaches.

Birman, Kenneth P.↗
NASA NTRS1989

Large-scale advanced propeller blade pressure distributions: Prediction and data

Two Euler analyses techniques, finite difference and finite volume, were employed to predict the blade surface pressure distributions of a large scale advanced propeller. The predicted pressure distributions were compared with wind tunnel data. Both techniques produced blade pressure distributions that are in fairly good agreement with the data over the range of test Mach numbers of 0.2 to 0.78. However, the numerical simulations fail to predict correctly the measured pressure distributions for the low Mach number, high power case. The data indicate the presence of a leading edge vortex for this case. A discussion of the compressibility effects is also presented.

Nallasamy, M.↗
NASA NTRS1990

An approach to a real-time distribution system

The requirements of a real-time data distribution system are to provide fast, reliable delivery of data from source to destination with little or no impact to the data source. In this particular case, the data sources are inside an operational environment, the Mission Control Center (MCC), and any workstation receiving data directly from the operational computer must conform to the software standards of the MCC. In order to supply data to development workstations outside of the MCC, it is necessary to use gateway computers that prevent unauthorized data transfer back to the operational computers. Many software programs produced on the development workstations are targeted for real-time operation. Therefore, these programs must migrate from the development workstation to the operational workstation. It is yet another requirement for the Data Distribution System to ensure smooth transition of the data interfaces for the application developers. A standard data interface model has already been set up for the operational environment, so the interface between the distribution system and the application software was developed to match that model as closely as possible. The system as a whole therefore allows the rapid development of real-time applications without impacting the data sources. In summary, this approach to a real-time data distribution system provides development users outside of the MCC with an interface to MCC real-time data sources. In addition, the data interface was developed with a flexible and portable software design. This design allows for the smooth transition of new real-time applications to the MCC operational environment.

Kittle, Frank P., Jr.↗
NASA NTRS1990

Tools for distributed application management

Distributed application management consists of monitoring and controlling an application as it executes in a distributed environment. It encompasses such activities as configuration, initialization, performance monitoring, resource scheduling, and failure response. The Meta system (a collection of tools for constructing distributed application management software) is described. Meta provides the mechanism, while the programmer specifies the policy for application management. The policy is manifested as a control program which is a soft real-time reactive program. The underlying application is instrumented with a variety of built-in and user-defined sensors and actuators. These define the interface between the control program and the application. The control program also has access to a database describing the structure of the application and the characteristics of its environment. Some of the more difficult problems for application management occur when preexisting, nondistributed programs are integrated into a distributed application for which they may not have been intended. Meta allows management functions to be retrofitted to such programs with a minimum of effort.

Marzullo, Keith↗
NASA NTRS1990

Tools for distributed application management

Distributed application management consists of monitoring and controlling an application as it executes in a distributed environment. It encompasses such activities as configuration, initialization, performance monitoring, resource scheduling, and failure response. The Meta system is described: a collection of tools for constructing distributed application management software. Meta provides the mechanism, while the programmer specifies the policy for application management. The policy is manifested as a control program which is a soft real time reactive program. The underlying application is instrumented with a variety of built-in and user defined sensors and actuators. These define the interface between the control program and the application. The control program also has access to a database describing the structure of the application and the characteristics of its environment. Some of the more difficult problems for application management occur when pre-existing, nondistributed programs are integrated into a distributed application for which they may not have been intended. Meta allows management functions to be retrofitted to such programs with a minimum of effort.

Marzullo, Keith↗
NASA NTRS1987

Simulation of real-gas effects on pressure distributions for a proposed Aeroassist Flight Experiment vehicle and comparison to prediction

Pressure distributions measured on a 60-deg elliptic cone, raked off at a 73-deg angle and having an ellipsoid nose (ellipticity equal to 2.0), are presented for a range of angle of attack from -10 to 15 deg. The high normal shock density ratio aspect of a real gas was simulated by testing in Mach-6 air (normal shock density ratio equal to 5.25) and Mach 6 CF4 (normal shock density ratio equal to 12.0). The effects of Reynolds number, angle of attack, and normal shock density ratio on these measurements are examined, and comparisons are made to an inviscid flowfield computer code known as HALIS. A significant effect of density ratio on pressure distributions on the cone section of the configuration was observed; the magnitude of this effect decreased with increased angle of attack. The effect of Reynolds number on pressures was negligible for forebody pressure distributions, but a measurable effect was noted on base pressures. In general, the HALIS code accurately predicted the measured pressure distributions in air and CF4.

Micol, John R.↗
NASA NTRS1989

On the problem of modeling for parameter identification in distributed structures

Structures are often characterized by parameters, such as mass and stiffness, that are spatially distributed. Parameter identification of distributed structures is subject to many of the difficulties involved in the modeling problem, and the choice of the model can greatly affect the results of the parameter identification process. Analogously to control spillover in the control of distributed-parameter systems, identification spillover is shown to exist as well and its effect is to degrade the parameter estimates. Moreover, as in modeling by the Rayleigh-Ritz method, it is shown that, for a Rayleigh-Ritz type identification algorithm, an inclusion principle exists in the identification of distributed-parameter systems as well, so that the identified natural frequencies approach the actual natural frequencies monotonically from above.

Norris, Mark A.↗
NASA NTRS1989

Identification of local modes using modal mass distributions

An approach for local modal identification using a modal mass spatial distribution matrix is proposed. This modal mass matrix is obtained by overlay multiplying the modal matrix to the product of the mass and the modal matrices of the structure. Each column in the spatial modal mass matrix can be interpreted as a measure of the kinetic energy distribution over the physical degrees of freedom for the corresponding mode. Local modes are identified due to the highly concentrated kinetic energy distribution in the localized regions. This spatial modal mass approach is more sensitive than the modal amplitude ratio method, since kinetic energy is in the quadratic form of modal amplitudes. Numerical examples involving identification of local modes using the proposed modal mass spatial distribution matrix approach are presented and discussed.

Chou, Chaur-Ming↗
NASA NTRS1989

Infrared radiometric technique for rapid quantitative evaluation of heat flux distribution over large areas

This paper describes a novel approach for rapid, quantitative measurement of spatially distributed heat flux incident on a plane. The technique utilizes the spatial temperature distribution on an opaque thin film at the location of interest, as measured by an imaging infrared radiometer. Knowledge of film radiative properties, plus quantitative estimates of convection cooling permit the steady state energy balance at any location on the film sheet to be solved for the incident heat flux. Absolute accuracies on the order of 10-15 percent have been obtained in tests performed in air. The method is particularly useful for evaluation of spatial heat flux uniformity from distributed heat sources over large areas. It has recently been used in several applications at the Jet Propulsion Laboratory, including flux uniformity measurements from large distributed quartz lamp arrays used during thermal vacuum testing of several spacecraft components, and flux mapping of a low power NdYg laser beam.

Glazer, Stuart↗
NASA NTRS1990

Recoverable distributed shared virtual memory

The problem of rollback recovery in distributed shared virtual environments, in which the shared memory is implemented in software in a loosely coupled distributed multicomputer system, is examined. A user-transparent checkpointing recovery scheme and a new twin-page disk storage management technique are presented for implementing recoverable distributed shared virtual memory. The checkpointing scheme can be integrated with the memory coherence protocol for managing the shared virtual memory. The twin-page disk design allows checkpointing to proceed in an incremental fashion without an explicit undo at the time of recovery. The recoverable distributed shared virtual memory allows the system to restart computation from a checkpoint without a global restart.

Wu, Kun-Lung↗
NASA NTRS1990

Kinetic instability associated with spherical shell distribution of cometary pickup ions

The stability of ion shell distribution is an interesting and important issue in view of the fact that it is stable under perturbations propagating parallel to the ambient magnetic field, despite large amount of free energy it contains. It was found, however, that if the shell distribution of ions has a sufficient amount of drift speed with respect to the solar wind hydromagnetic waves, it can become unstable. The obliquely propagating hydromagnetic instability associated with the ion shell distribution was recently discovered. This letter presents the unified stability analysis of the ion shell distribution, under what condition the drift-induced instability of the type first discussed by Gary and Sinha (1989), and the oblique hydromagnetic instability discussed by Wu and Yoon (1990) are excited, and how the two types of instabilities are related.

Yoon, Peter H.↗