SEARCH · Engineering Papers

Results for “Distributed”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,207 records · Page 67

All sources NASA NTRS DOE OSTI

NASA NTRS2002

Intelligent Systems for Power Management and Distribution

The motivation behind an advanced technology program to develop intelligent power management and distribution (PMAD) systems is described. The program concentrates on developing digital control and distributed processing algorithms for PMAD components and systems to improve their size, weight, efficiency, and reliability. Specific areas of research in developing intelligent DC-DC converters and distributed switchgear are described. Results from recent development efforts are presented along with expected future benefits to the overall PMAD system performance.

Button, Robert M.↗

NASA NTRS2002

Variable Order and Distributed Order Fractional Operators

Many physical processes appear to exhibit fractional order behavior that may vary with time or space. The continuum of order in the fractional calculus allows the order of the fractional operator to be considered as a variable. This paper develops the concept of variable and distributed order fractional operators. Definitions based on the Riemann-Liouville definitions are introduced and behavior of the operators is studied. Several time domain definitions that assign different arguments to the order q in the Riemann-Liouville definition are introduced. For each of these definitions various characteristics are determined. These include: time invariance of the operator, operator initialization, physical realization, linearity, operational transforms. and memory characteristics of the defining kernels. A measure (m2) for memory retentiveness of the order history is introduced. A generalized linear argument for the order q allows the concept of "tailored" variable order fractional operators whose a, memory may be chosen for a particular application. Memory retentiveness (m2) and order dynamic behavior are investigated and applications are shown. The concept of distributed order operators where the order of the time based operator depends on an additional independent (spatial) variable is also forwarded. Several definitions and their Laplace transforms are developed, analysis methods with these operators are demonstrated, and examples shown. Finally operators of multivariable and distributed order are defined in their various applications are outlined.

Lorenzo, Carl F.↗

NASA NTRS1997

Statistical Models of Areal Distribution of Fragmented Land Cover Types

Imagery of coarse resolution, such weather satellite imagery with 1 square kilometer pixels, is increasingly used to monitor dynamic and fragmented types of land surface types, such as scars from recent fires and ponds in wetlands. Accurate estimates of these land cover types at regional to global scales are required to assess the roles of fires and wetlands in global warming, yet difficult to compute when much of the area is accounted for by fragments about the same size as the pixels. In previous research, we found that size distribution of the fragments in several example scenes fit simple two-parameter models and related effects of coarse resolution to errors in area estimates based on pixel counts. We summarize our model based approach to improved area estimations and report on progress to develop accurate areas estimates based on modeling the size distribution of the fragments, including analysis of size distributions on an expanded set of maps developed from digital imagery.

Hlavka, C.↗

NASA NTRS1998

Ion Energy Distributions and their Relative Abundance in Inductively Coupled Plasmas

Study of kinetics of ions and neutrals produced in high density inductively coupled plasma (ICP) discharges is of great importance for achieving a high degree of plasma assisted deposition and etching. In this paper, we present the ion energy distributions (IEDs) of various ions arriving at the grounded lower electrode. The ions were energy as well as mass analyzed by a combination of electrostatic analyzer-quadrupole mass spectrometer for pure Ar and CF4/Ar mixtures. The measurements have been made at gas pressures ranging from 30 to 100 mTorr. In addition, the IEDs were measured when the wafer-supporting electrode was also rf-powered and the effect of the self-bias was observed in the energy distributions of ions. The shapes of the IEDs are discussed an related to the sheath properties and measured electrical waveforms, as a function of pressure and applied power. Relative ion intensities were obtained by integration of each ion kinetic energy distribution function over its energy range.

Kim, J. S.↗

NASA NTRS1995

Security for Multimedia Space Data Distribution over the Internet

Distribution of interactive multimedia to remote investigators will be required for high quality science on the International Space Station (ISS). The Internet with the World Wide Web (WWW) and the JAVA environment are a good match for distribution of data, video and voice to remote science centers. Utilizing the "open" Internet in a secure manner is the major hurdle in making use of this cost effective, off-the-shelf, universal resource. This paper examines the major security threats to an Internet distribution system for payload data and the mitigation of these threats. A proposed security environment for the Space Station Biological Research Facility (SSBRP) is presented with a short description of the tools that have been implemented or planned. Formulating and implementing a security policy, firewalls, host hardware and software security are also discussed in this paper. Security is a vast topic and this paper can only give an overview of important issues. This paper postulates that a structured approach is required and stresses that security must be built into a network from the start. Ignoring security issues or putting them off until late in the development cycle can be disastrous.

Stone, Thom↗

NASA NTRS2002

Intelligent Systems for Power Management and Distribution

Button, Robert M.↗

NASA NTRS1999

In Situ Aerosol-Size Distributions and Clear-Column Radiative Closure During ACE-2

As part of the second Aerosol Characterization Experiment (ACE-2) during June and July of 1997, aerosol-size distributions were measured on board the CIRPAS Pelican aircraft through the use of a Differential Mobility Analyzer (DMA) and 2 Optical Particle Counters (OPCs). During the campaign, the boundary-layer aerosol typically possessed characteristics representative of a background marine aerosol or a continentally influenced aerosol, while the free-tropospheric aerosol was characterized by the presence or absence of a Saharan dust layer. A range of radiative closure comparisons were made using the data obtained during vertical profiles flown on 4 missions. Of particular interest here are the comparisons made between the optical properties as determined through the use of measured aerosol-size distributions and those measured directly by an airborne 14-wavelength sunphotometer and 3 nephelometers. Variations in the relative humidity associated with each of the direct measurements required consideration of the hygroscopic properties of the aerosol for size-distribution-based calculations. Simultaneous comparison with such a wide range of directly-measured optical parameters not only offers evidence of the validity of the physicochemical description of the aerosol when closure is achieved, but also provides insight into potential sources of error when some or all of the comparisons result in disagreement. Agreement between the derived and directly-measured optical properties varied for different measurements and for different cases. Averaged over the 4 case studies, the derived extinction coefficient at 525 nm exceeded that measured by the sunphotometer by 2.5% in the clean boundary layer, but underestimated measurements by 13% during pollution events. For measurements within the free troposphere, the mean derived extinction coefficient was 3.3% and 17% less than that measured by the sunphotometer during dusty and non-dusty conditions, respectively. Likewise, averaged discrepancies between the derived and measured scattering coefficient were -9.6%, +4.7%, +17%, and -41% for measurements within the clean boundary layer, polluted boundary layer, free troposphere with a dust layer, and free troposphere without a dust layer, respectively. Each of these quantities, as well as the majority of the more than 100 individual comparisons from which they were averaged, were within estimated uncertainties.

Collins, R.↗

NASA NTRS2002

The Distribution of Ozone in the Early Stages of Polar Vortex Development

Previous analysis has shown that the distribution of O3 at high northern latitudes in the lower-to-middle stratosphere at the beginning of the winter season, 1999-2000 has a characteristic distribution, which is consistent between in situ and satellite measurements [Kawa et al., The Interaction Between Dynamics and Chemistry of Ozone in the Set-up Phase of the Northern Hemisphere Polar Vortex, submitted manuscript, 2001 ]. Initial O3 profiles in the vortex are similar to each other and are quite different from outside the vortex at the same latitude and also from a zonal mean climatology. In the vortex, O3 is nearly constant from 500 to above 800 K with a value at 3 ppmv +/- approx.10%. Values outside the vortex are up to a factor of 2 higher and increase significantly with potential temperature. The seasonal time series of POAM data shows that relatively low O3 mixing ratios, which characterize the vortex in late fall, are already present at high latitudes at the end of summer in September before the vortex circulation sets up. This suggests a possible feedback role between O3 chemistry and the formation of the vortex, which is dominated by the seasonal radiation balance. Here we show that these characteristic O3 distributions are consistent from year to year and between the hemispheres. We will attempt to determine whether variations in fall vortex O3 are related in any way to O3 abundances and vortex structure later during winter and into spring.

Kawa, S. R.↗

NASA NTRS2002

Collaborative Simulation Grid: Multiscale Quantum-Mechanical/Classical Atomistic Simulations on Distributed PC Clusters in the US and Japan

A multidisciplinary, collaborative simulation has been performed on a Grid of geographically distributed PC clusters. The multiscale simulation approach seamlessly combines i) atomistic simulation backed on the molecular dynamics (MD) method and ii) quantum mechanical (QM) calculation based on the density functional theory (DFT), so that accurate but less scalable computations are performed only where they are needed. The multiscale MD/QM simulation code has been Grid-enabled using i) a modular, additive hybridization scheme, ii) multiple QM clustering, and iii) computation/communication overlapping. The Gridified MD/QM simulation code has been used to study environmental effects of water molecules on fracture in silicon. A preliminary run of the code has achieved a parallel efficiency of 94% on 25 PCs distributed over 3 PC clusters in the US and Japan, and a larger test involving 154 processors on 5 distributed PC clusters is in progress.

Kikuchi, Hideaki↗

NASA NTRS1947

Cooling of Gas Turbines: Computed Temperature Distribution Through Cross Section of Water-Cooled Turbine Blade - 6

A theoretical analysis of the cross-sectional temperature distribution of a water-cooled turbine blade was made using the relaxation method to solve the differential equation derived from the analysis. The analysis was applied to specific turbine blade and the studies icluded investigations of the accuracy of simple methods to determine the temperature distribution along the mean line of the rear part of the blade, of the possible effect of varying the perimetric distribution of the hot gas-to -metal heat transfer coefficient, and of the effect of changing the thermal conductivity of the blade metal for a constant cross sectional area blade with two quarter inch diameter coolant passages.

Livingood, John N. B.↗

NASA NTRS2003

Effect of Individual Component Life Distribution on Engine Life Prediction

The effect of individual engine component life distributions on engine life prediction was determined. A Weibull-based life and reliability analysis of the NASA Energy Efficient Engine was conducted. The engine s life at a 95 and 99.9 percent probability of survival was determined based upon the engine manufacturer s original life calculations and assumed values of each of the component s cumulative life distributions as represented by a Weibull slope. The lives of the high-pressure turbine (HPT) disks and blades were also evaluated individually and as a system in a similar manner. Knowing the statistical cumulative distribution of each engine component with reasonable engineering certainty is a condition precedent to predicting the life and reliability of an entire engine. The life of a system at a given reliability will be less than the lowest-lived component in the system at the same reliability (probability of survival). Where Weibull slopes of all the engine components are equal, the Weibull slope had a minimal effect on engine L(sub 0.1) life prediction. However, at a probability of survival of 95 percent (L(sub 5) life), life decreased with increasing Weibull slope.

Zaretsky, Erwin V.↗

NASA NTRS2003

The Size Distribution of Jupiter-Family Cometary Nuclei

Introduction: We are continuing our program to determine the size distribution of cometary nuclei. We have compiled a catalog of 105 measurements of 57 cometary nuclei, drawn from the general literature, from our own program of CCD photometry of distant cometary nuclei (Lowry and Weissman), and from unpublished observations by colleagues. We model the cumulative size distribution of the nuclei as a power law. Previous determinations of the size distribution slope do not agree. Fernandez et al. found a slope of alpha = 2.65+/-0.25 whereas Lowry et al. and Weissman and Lowry each found a slope of alpha = 1.60+/-0.10.

Weissman, Paul R.↗

NASA NTRS2003

UAV Flight Control Using Distributed Actuation and Sensing

An array of effectors and sensors has been designed, tested and implemented on a Blended Wing Body Uninhabited Aerial Vehicle (UAV). This UAV is modified to serve as a flying, controls research, testbed. This effectorhensor array provides for the dynamic vehicle testing of controller designs and the study of decentralized control techniques. Each wing of the UAV is equipped with 12 distributed effectors that comprise a segmented array of independently actuated, contoured control surfaces. A single pressure sensor is installed near the base of each effector to provide a measure of deflections of the effectors. The UAV wings were tested in the North Carolina State University Subsonic Wind Tunnel and the pressure distribution that result from the deflections of the effectors are characterized. The results of the experiments are used to develop a simple, but accurate, prediction method, such that for any arrangement of the effector array the corresponding pressure distribution can be determined. Numerical analysis using the panel code CMARC verifies this prediction method.

Barnwell, William G.↗

NASA NTRS2003

Observations of Dust Using the NASA Geoscience Laser Altimeter System (GLAS): New New Measurements of Aerosol Vertical Distribution From Space

On January 12, 2003 NASA launched the first satellite-based lidar, the Geoscience Laser -Altimeter System (GLAS), onboard the ICESat spacecraft. The GLAS atmospheric measurements introduce a fundamentally new and important tool for understanding the atmosphere and climate. In the past, aerosols have only been studied from space using images gathered by passive sensors. Analysis of this passive data has lead to an improved understanding of aerosol properties, spatial distribution, and their effect on the earth's climate. However, these images do not show the aerosol's vertical distribution. As a result, a key piece of information has been missing. The measurements now obtained by GLAS will provide information on the vertical distribution of aerosols and clouds, and improve our ability to study their transport processes and aerosol-cloud interactions. Here we show an overview of GLAS, provide an update of its current status, and present initial observations of dust profiles. In particular, a strategy of characterizing the height profile of dust plumes over source regions will be presented.

Welton, Ellsworth↗

NASA NTRS2003

Particle Size Distributions in Atmospheric Clouds

In this note, we derive a transport equation for a spatially integrated distribution function of particles size that is suitable for sparse particle systems, such as in atmospheric clouds. This is done by integrating a Boltzmann equation for a (local) distribution function over an arbitrary but finite volume. A methodology for evolving the moments of the integrated distribution is presented. These moments can be either tracked for a finite number of discrete populations ('clusters') or treated as continuum variables.

Paoli, Roberto↗

NASA NTRS2004

Measuring the Mass Distribution in Z is Approximately 0.2 Cluster Lenses with XMM, HST and CFHT

Being the most massive gravitationally bound objects in the Universe, clusters of galaxies are prime targets for studies of structure formation and evolution. Specifically the comoving space density of virialized clusters of a given mass (or X-ray temperature), but also the frequency and degree of substructure, as well as the shape of the cluster mass profile are quantities whose current values and evolution as a function of lookback time can provide important constraints on the cosmological and physical parameters of structure formation theories. The project funded by NASA grant NAG 5-10041 intended to take such studies to a new level by combining observations of a well-selected cluster sample by three state-of-the-art telescopes: HST, to accurately measure the mass distribution in the cluster core (approx. 0.5 h(sup -1)(sub 50) Mpc) via strong gravitational lensing; CFHT, to measure the large scale mass distribution out to approx. 3 Mpc via weak lensing; and XMM, to measure the gas density and temperature distribution accurately on intermediate scales < 1.5 Mpc. XMM plays a pivotal role in this context as the calibration of X-ray mass measurements through accurate, spatially resolved X-ray temperature measurements (particularly in the cosmologically most sensitive range of kT> 5 keV) is central to the questions outlined above. This set of observations promised to yield the best cluster mass measurements obtained so far for a representative sample, thus allowing us to: 1) Measure the high-mass end of the local cluster mass function; 2) Test predictions of a universal cluster mass profile; 3) calibrate the mass-temperature and temperature-luminosity relations for clusters and the scatter around these relations, which is vital for studies of cluster evolution using the X-ray temperature and X-ray luminosity functions.

Source record↗

NASA NTRS2004

Brine Pockets in the Icy Shell on Europa: Distribution, Chemistry, and Habitability

On Earth, sea ice is rich in brine, salt, and gas inclusions that form through capturing of seawater during ice formation. Cooling of the ice over time leads to sequential freezing of captured sea-water, precipitation of salts, exsolution of gases, and formation of brine channels and pockets. Distribution and composition of brines in sea ice depend on the rate of ice formation, vertical temperature gradient, and the age of the ice. With aging, the abundance of brine pockets decreases through downward migration. De- spite low temperatures and elevated salinities, brines in sea ice provide a habitat for photosynthetic and chemosynthetic organisms. On Europa, brine pockets and channels could exist in the icy shell that may be from a few km to a few tens of km thick and is probably underlain by a water ocean. If the icy shell is relatively thick, convection could develop, affecting the temperature pattern in the ice. To predict the distribution and chemistry of brine pockets in the icy shell we have combined numerical models of the temperature distribution within a convecting shell, a model for oceanic chemistry, and a model for freezing of Europan oceanic water. Possible effects of brine and gas inclusions on ice rheology and tectonics are discussed.

Zolotov, M. Yu↗

NASA NTRS2004

Global Distribution of Active Volcanism on Io as Known at the End of the Galileo Mission

Hot spots are manifestations of Io s mechanism of internal heating and heat transfer. Therefore, the global distribution of hot spots and their power output has important implications for how Io is losing heat. The end of the Galileo mission is an opportune time to revisit studies of the distribution of hot spots on Io, and to investigate the distribution of their power output.

Lopes, Rosaly M. C.↗