Adaptable large-scale-integrated military and space systems.
Adaptable large scale integrated military and space systems, discussing microelectronic circuit, logistics and dynamic redundancy
REDUNDANT SYSTEM↗
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A large-scale pattern in the solar magnetic field.
Large scale pattern in solar magnetic field correlated with interplanetary magnetic field
Howard, R.↗
Large-scale properties of the interplanetary magnetic field
Large scale spiral variations of interplanetary magnetic field related to structures in solar wind, including polar field and out of ecliptic models
Schatten, K. H.↗
On the decentralized control of large-scale systems
The decentralized control of stochastic large scale systems was considered. Particular emphasis was given to control strategies which utilize decentralized information and can be computed in a decentralized manner. The deterministic constrained optimization problem is generalized to the stochastic case when each decision variable depends on different information and the constraint is only required to be satisfied on the average. For problems with a particular structure, a hierarchical decomposition is obtained. For the stochastic control of dynamic systems with different information sets, a new kind of optimality is proposed which exploits the coupled nature of the dynamic system. The subsystems are assumed to be uncoupled and then certain constraints are required to be satisfied, either in a off-line or on-line fashion. For off-line coordination, a hierarchical approach of solving the problem is obtained. The lower level problems are all uncoupled. For on-line coordination, distinction is made between open loop feedback optimal coordination and closed loop optimal coordination.
Chong, C.↗
Simulation of large-scale dynamic systems
The classes of large-scale dynamic systems are discussed in terms of modeling with emphasis on air transportation system modeling.
Roberts, L.↗
Seasonal dependence of large-scale Birkeland currents
Seasonal variations of large-scale Birkeland currents are examined in a study of the source mechanisms and the closure of the three-dimensional current systems in the ionosphere. Vector magnetic field data acquired by the TRIAD satellite in the Northern Hemisphere were analyzed for the statistics of single sheet and double sheet Birkeland currents during 555 passes during the summer and 408 passes during the winter. The single sheet currents are observed more frequently in the dayside of the auroral zone, and more often in summer than in winter. The intensities of both the single and double dayside currents are found to be greater in the summer than in the winter by a factor of two, while the intensities of the double sheet Birkeland currents on the nightside do not show a significant difference from summer to winter. Both the single and double sheet currents are found at higher latitudes in the summer than in the winter on the dayside. Results suggest that the Birkeland current intensities are controlled by the ionospheric conductivity in the polar region, and that the currents close via the polar cap when the conductivity there is sufficiently high. It is also concluded that an important source of these currents must be a voltage generator in the magnetosphere.
Fujii, R.↗
Large scale topography of Io
To investigate the large scale topography of the Jovian satellite Io, both limb observations and stereographic techniques applied to landmarks are used. The raw data for this study consists of Voyager 1 images of Io, 800x800 arrays of picture elements each of which can take on 256 possible brightness values. In analyzing this data it was necessary to identify and locate landmarks and limb points on the raw images, remove the image distortions caused by the camera electronics and translate the corrected locations into positions relative to a reference geoid. Minimizing the uncertainty in the corrected locations is crucial to the success of this project. In the highest resolution frames, an error of a tenth of a pixel in image space location can lead to a 300 m error in true location. In the lowest resolution frames, the same error can lead to an uncertainty of several km.
Gaskell, R. W.↗
Preliminary simulations of the large-scale environment during the FIRE cirrus IFO
Large scale forcing (scales greater than 500 km) is the dominant factor in the generation, maintenance, and dissipation of cirrus cloud systems. However, the analyses of data acquired during the first Cirrus IFO have highlighted the importance of mesoscale processes (scales of 20 to 500 km) to the development of cirrus cloud systems. Unfortunately, Starr and Wylie found that the temporal and spatial resolution of the standard and supplemental rawinsonde data were insufficient to allow an explanation of all of the mesoscale cloud features that were present on the 27 to 28 Oct. 1986. It is described how dynamic initialization, or 4-D data assimilation (FDDA) can provide a method to address this problem. The first steps towards application of FDDA to FIRE are also described.
Westphal, Douglas L.↗
Design and Use of a Large-Scale Liquid Helium Conversion System
A large-scale liquid helium (LHe) to high-pressure (HP) gas conversion system has been implemented at the John F. Kennedy Space Center (KSC). Helium is used by the Space Shuttle, Titan, Atlas, and Delta programs for prelaunch processing, during launch count-down, and for postlaunch securing. The first phase of modifications to the Compressor Converter Facility (CCF), operational in April 1998, allowed the facility to accept bulk liquid helium from tanker containers and to off-load the helium at super-critical pressures. The second phase of modifications, planned to be operational by January 2001, will implement a 227-cubic-meter (m(sup 3)) on-site liquid helium storage system. This paper describes the design and operation of the current system and discusses the design and implementation for the second phase system.
Knudsen, P. N.↗
Status of the Combined-Cycle Engine Large-Scale Inlet Mode Transition Experiment
The Large-Scale Inlet Mode Transition (LIMX) experiment is currently being conducted in the 10x10 foot supersonic wind tunnel at the NASA Glenn Research Center. The experiment has involved the efforts of a team for over four years to get to the first phase of testing, which is examining the aerodynamic characteristics of the inlet. The LIMX inlet involves dual flowpaths: one to provide flow to a turbine engine and one to provide flow to a dual-mode ramjet/scramjet. A rotating splitter cowl can close off the turbine flowpath, which would occur as the propulsion system transitions from turbine power to ramjet/scramjet power at Mach 4. The first phase of the experiment will simulate the turbine and ramjet/scramjet flows using cold pipes with flow rates controlled by mass-flow plugs. Much of the testing will characterize the performance of the turbine flowpath (total pressure recovery and distortion at the engine face location) as factors such as bleed rates and configuration and vortex generators are varied during the inlet mode transition. The performance of the inlet will also be examined at off-design Mach numbers (2.5-3.0) and at angle-of-attack.
Slater, John W.↗
Icing Simulation Research Supporting the Ice-Accretion Testing of Large-Scale Swept-Wing Models
The work summarized in this report is a continuation of NASA's Large-Scale, Swept-Wing Test Articles Fabrication; Research and Test Support for NASA IRT contract (NNC10BA05 -NNC14TA36T) performed by Boeing under the NASA Research and Technology for Aerospace Propulsion Systems (RTAPS) contract. In the study conducted under RTAPS, a series of icing tests in the Icing Research Tunnel (IRT) have been conducted to characterize ice formations on large-scale swept wings representative of modern commercial transport airplanes. The outcome of that campaign was a large database of ice-accretion geometries that can be used for subsequent aerodynamic evaluation in other experimental facilities and for validation of ice-accretion prediction codes.
Aerodynamics↗
Large-scale structure in a texture-seeded cold dark matter cosmogony
This paper studies the formation of large-scale structure by global texture in a flat universe dominated by cold dark matter. A code for evolution of the texture fields was combined with an N-body code for evolving the dark matter. The results indicate some promising aspects: with only one free parameter, the observed galaxy-galaxy correlation function is reproduced, clusters of galaxies are found to be significantly clustered on a scale of 20-50/h Mpc, and coherent structures of over 50/h Mpc in the galaxy distribution were found. The large-scale streaming motions observed are in good agreement with the observations: the average magnitude of the velocity field smoothed over 30/h Mpc is 430 km/sec. Global texture produces a cosmic Mach number that is compatible with observation. Also, significant evolution of clusters at low redshift was seen. Possible problems for the theory include too high velocity dispersions in clusters, and voids which are not as empty as those observed.
Park, Changbom↗
Fractals and cosmological large-scale structure
Observations of galaxy-galaxy and cluster-cluster correlations as well as other large-scale structure can be fit with a 'limited' fractal with dimension D of about 1.2. This is not a 'pure' fractal out to the horizon: the distribution shifts from power law to random behavior at some large scale. If the observed patterns and structures are formed through an aggregation growth process, the fractal dimension D can serve as an interesting constraint on the properties of the stochastic motion responsible for limiting the fractal structure. In particular, it is found that the observed fractal should have grown from two-dimensional sheetlike objects such as pancakes, domain walls, or string wakes. This result is generic and does not depend on the details of the growth process.
Luo, Xiaochun↗
Large-scale turbulent structures in jets and in flows over cavities and their relationship to entrainment and mixing
Large scale structures in jets and in flows over cavities were investigated experimentally to determine their role in entrainment, mixing, and noise production. The presence of these structures resulted in growth of the shear layer and entrainment. Merging of adjacent large scale structures caused the near field pressure signal in excited flows. It is believed that both the entrained fluid as well as its eventual mixing with the jet flow can be controlled by introducing pulsation in the jet flow at a frequency for which the flow is most unstable.
Sarohia, V.↗
The large-scale morphology of IRAS galaxies
At present, visual inspection is the only method for comparing the large-scale morphologies in the distribution of galaxies to those in model universes generated by N-body simulations. To remedy the situation, we have developed a set of three structure functions (S1, S2, S3) that quantify the degree of large-scale prolateness, oblateness, and sphericity/uniformity of a 3-D particle distribution and have applied them to a volume-limited (less than = 4000 km/s) sample of 699 IRAS galaxies with f sub 60 greater than 1.2 Jy. To determine the structure functions, we randomly select 500 galaxies as origins of spherical windows of radius R sub w, locate the centroid of the galaxies in the window (assuming all galaxies have equal mass) and then, compute the principal moments of inertia (I sub 1, I sub 2, I sub 3) about the centroid. Each S sub i is a function of (I sub 2)/(I sub 1) and (I sub 3)/I sub 1). S1, S2, and S3 tend to unity for highly prolate, oblate, and uniform distributions, respectively and tend to zero otherwise. The resulting 500 values of S sub i at each scale R sub w are used to construct a histogram.
Babul, Arif↗
Experimental feasibility study of the application of magnetic suspension techniques to large-scale aerodynamic test facilities
Based on the premises that (1) magnetic suspension techniques can play a useful role in large-scale aerodynamic testing and (2) superconductor technology offers the only practical hope for building large-scale magnetic suspensions, an all-superconductor three-component magnetic suspension and balance facility was built as a prototype and was tested successfully. Quantitative extrapolations of design and performance characteristics of this prototype system to larger systems compatible with existing and planned high Reynolds number facilities have been made and show that this experimental technique should be particularly attractive when used in conjunction with large cryogenic wind tunnels.
Zapata, R. N.↗
The global climate of December 1992-February 1993. Part 2: Large-scale variability across the tropical western Pacific during TOGA COARE
Recently, scientists from more than a dozen countries carried out the field phase of a project called the Coupled-Atmosphere Response Experiment (COARE), devoted to describing the ocean-atmosphere system of the western Pacific near-equatorial warm pool. The project was conceived, organized, and funded under the auspices of the International Tropical Ocean Global Atmosphere (TOGA) Program. Although COARE consisted of several field phases, including a year-long atmospheric enhanced monitoring period (1 July 1992 -- 30 June 1993), the heart of COARE was its four-month Intensive Observation Period (IOP) extending from 1 Nov. 1992 through 28 Feb. 1993. An overview of large-scale variability during COARE is presented. The weather and climate observed in the IOP is placed into context with regard to large-scale, low-frequency fluctuations of the ocean-atmosphere system. Aspects of tropical variability beginning in Aug. 1992 and extending through Mar. 1993, with some sounding data for Apr. 1993 are considered. Variability over the large-scale sounding array (LSA) and the intensive flux array (IFA) is emphasized.
Gutzler, D. S.↗
Material extrusion with integrated compression molding of NdFeB/SmFeN nylon bonded magnets using small- and large-scale pellet-based 3D-printers
High-density bonded rare-earth magnets are manufactured using pellet-fed additive manufacturing (AM)/material extrusion and an integrated additive manufacturing-compression molding (AM-CM) process. Neodymium iron boron – samarium iron nitride in polyamide 12 (NdFeB-SmFeN/PA12) of 93 % weight fraction (65 % volume fraction) are used for the study. The mechanical properties (tensile strength and modulus), magnetic properties (maximum energy density, coercivity, remanence) are reported. Manufacturing parameters such as layer height, barrel temperatures, screw speed and gantry feed rate are optimized to obtain the highest possible density of the magnets using a small-scale desktop material extrusion printer. Large scale integrated additive manufacturing-compression molding (AM-CM) is then utilized to increase the density of the magnets by reducing porosity defects common in the material extrusion process. The density of as-printed magnets was 5.2 g/cm 3 with a BH max value of 124.14 kJ/m 3 , tensile strength of 20 MPa and a modulus of 2 GPa. AM-CM increased the density of the compound by 5.5 % (5.49 g/cm 3 ). The reduction in porosity was confirmed using X-ray tomography (XCT). Improvement in mechanical strength of the material was also observed, with an increase in tensile strength of 25 % (25.09 MPa) and increase in tensile modulus of 275 % (5.49 GPa). Scanning electron microscopy showed increased particle-matrix adhesion with the integrated AM-CM process.
36 MATERIALS SCIENCE↗