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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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Polymer resisting degradation by monatomic oxygen undergoing commercial development under trade name "Aorimide" ("atomic-oxygen-resistant imidazole"). Intended for use in thermal blankets for spacecraft in low orbit, useful on Earth in outdoor applications in which sunlight and ozone degrades other plastics. Also used, for example, to make threads and to make films coated with metals for reflectivity.
Redesigned clevis joint incorporates dual mating eccentric cylindrical bushings to accommodate dimensional tolerances. Eliminates need for combination of oppositely threaded collar and bushing and makes overall joint hardware fit within available space.
A 3-D MHD simulation of a global, tilted-dipole solar wind flow pattern is analyzed to determine flow properties along individual magnetic field lines. In the model, flow conditions near the Sun are chosen to provide a reasonable match to the interplanetary configuration prevailing during the recent south polar passage by Ulysses, i.e., a streamer belt inclined approximately 30 deg to the solar equator and speeds ranging from 325-800 km/s. Field lines all across the stream pattern are traced from 1 to 10 AU by following the motion of marker particles embedded in the flow. It is found that those field lines threading the core of the interaction region are subject to significant latitudinal and relative longitudinal displacement over this range of heliocentric distance. Thus, observations taken at a fixed latitude in the inner solar system sample, over the course of a solar rotation, field lines which connect to a range of latitudes in the outer heliosphere. Maps of the field line displacements are presented to help visualize these connections. In addition, it is found that depending upon the location relative to the CIR structure, the radial evolution of fluid elements frozen to different field lines can deviate considerably from that of the canonical solar wind. That is, for selected subsets of field lines, large speed changes (not just at shocks) can be experienced; the density variation can be far from 1/r(exp 2), and the magnetic field intensity need not decay monotonically with distance.
Between May 1993 and January 1995, the Ulysses spacecraft has probed the southern polar heliosphere at latitudes greater than 30 deg S, reaching a maximum latitude of 80.2 deg S in September 1994. Using hourly averages of the data obtained by the magnetometer experiment on Ulysses we have studied the underlying direction of the magnetic field threading this region of the heliosphere, away from the influence of the magnetic sector structure which complicates similar analyses in the ecliptic plane. We have constructed histograms of the measured magnetic field direction using the simple Parker spiral model field direction as a reference. We find that throughout this region the meridional angle between the field vector and the Parker model direction has a distribution which is symmetric and has a most probable value consistent with the model. At latitudes below about 60 deg S the azimuthal angle distribution also has a most probable value consistent with the model but this distribution is highly asymmetric with a greater number of observations of field lines less tightly wound than the expected spiral direction. At latitudes greater than 60 deg S the most probable value of the azimuthal angle is found to have become nearly 30 more tightly wound than the expected direction, but due to the asymmetric distribution still with a greater number of observations less tightly wound than expected. We consider possible causes of both the asymmetry in the distributions and the shift in the most probable value at the highest latitudes, one of which may be the presence of large amplitude, long period Alfven waves in the magnetic field originating from the Sun's southern polar coronal hole.
We present a multithreaded model for the dynamic load-balancing of numerical, adaptive computations required for the solution of Partial Differential Equations (PDE's) on multiprocessors. Multithreading is used as a means of exploring concurrency in the processor level in order to tolerate synchronization costs inherent to traditional (non-threaded) parallel adaptive PDE solvers. Our preliminary analysis for parallel, adaptive PDE solvers indicates that multithreading can be used an a mechanism to mask overheads required for the dynamic balancing of processor workloads with computations required for the actual numerical solution of the PDE's. Also, multithreading can simplify the implementation of dynamic load-balancing algorithms, a task that is very difficult for traditional data parallel adaptive PDE computations. Unfortunately, multithreading does not always simplify program complexity, often makes code re-usability not an easy task, and increases software complexity.
The evolution of the transient extensional stresses in dilute and semi-dilute viscoelastic polymer solutions are measured with a filament stretching rheometer of a design similar to that first introduced by Sridhar, et al. The solutions are polystyrene-based (PS) Boger fluids that are stretched at constant strain rates ranging from 0.6 less than or equal to epsilon(0) less than or equal to 4s(exp -1) and to Hencky strains of epsilon greater than 4. The test fluids all strain harden and Trouton ratios exceeding 1000 are obtained at high strains. The experimental data strain hardens at lower strain levels than predicted by bead-spring FENE models. In addition to measuring the transient tensile stress growth, we also monitor the decay of the tensile viscoelastic stress difference in the fluid column following cessation of uniaxial elongation as a function of the total imposed Hencky strain and the strain rate. The extensional stresses initially decay very rapidly upon cessation of uniaxial elongation followed by a slower viscoelastic relaxation, and deviate significantly from FENE relaxation predictions. The relaxation at long times t is greater than or equal to 5 s, is compromised by gravitational draining leading to non-uniform filament profiles. For the most elastic fluids, partial decohension of the fluid filament from the endplates of the rheometer is observed in tests conducted at high strain rates. This elastic instability is initiated near the rigid endplate fixtures of the device and it results in the progressive breakup of the fluid column into individual threads or 'fibrils' with a regular azimuthal spacing. These fibrils elongate and bifurcate as the fluid sample is elongated further. Flow visualization experiments using a modified stretching device show that the instability develops as a consequence of an axisymmetry-breaking meniscus instability in the nonhomogeneous region of highly deformed fluid near the rigid endplate.
Our success over the past ten years evaluating and developing advanced computing technologies has been due to a simple research and development (R/D) model. Our model has three phases: (a) evaluating the state-of-the-art, (b) identifying problems and creating innovations, and (c) developing solutions, improving the state- of-the-art. This cycle has four basic requirements: a large production testbed with real users, a diverse collection of state-of-the-art hardware, facilities for evalua- tion of emerging technologies and development of innovations, and control over system management on these testbeds. Future research will be irrelevant and future products will not work if any of these requirements is eliminated. In order to retain our effectiveness, the numerical aerospace simulator (NAS) must replace out-of-date production testbeds in as timely a fashion as possible, and cannot afford to ignore innovative designs such as new distributed shared memory machines, clustered commodity-based computers, and multi-threaded architectures.
Part one of this report is intended to bring back into focus some of the facts, circumstances, and background of space exploration. A recapitulation of the flight of Apollo 11, the first lunar landing missions, provides an opportunity to introduce some of the hardware and nomenclature of the Apollo-Saturn program. An historical overview of rocketry, including the main threads of Saturn's origins, provides a background for the scope and boldness of Apollo 11 and the Saturn adventure. The management structure developed by NASA to implement the Apollo-Saturn missions is described in some detail.
Methods and apparatus are provided for a torque driver including a laterally displaceable gear support member to carry an output spur gear. A biasing assembly biases the output spur gear into engagement with a pinion to which is applied an input torque greater than a desired output torque limit for a threaded fastener such as a nut or screw. A coiled output linkage connects the output spur gear with a fastener adaptor which may be a socket for a nut. A gear tooth profile provides a separation force that overcomes the bias to limit torque at the desired torque limit. Multiple fasteners may be rotated simultaneously to a desired torque limit if additional output spur gears are provided. A gauged selector mechanism is provided to laterally displace multiple driven members for fasteners arranged in differing configurations. The torque limit is selectably adjustable and may be different for fasteners within the same fastener configuration.
A Trans-Laminar-Reinforced (TLR) composite is defined as composite laminate with up to five percent volume of fibrous reinforcement oriented in a 'trans-laminar' fashion in the through-thickness direction. The TLR can be continuous threads as in 'stitched laminates', or it can be discontinuous rods or pins as in 'Z-Fiber(TM) materials. It has been repeatedly documented in the literature that adding TLR to an otherwise two dimensional laminate results in the following advantages: substantially improved compression-after-impact response; considerably increased fracture toughness in mode 1 (double cantilever beam) and mode 2 (end notch flexure); and severely restricted size and growth of impact damage and edge delamination. TLR has also been used to eliminate catastrophic stiffener disbonding in stiffened structures. TLR directly supports the 'Achilles heel' of laminated composites, that is delamination. As little as one percent volume of TLR significantly alters the mechanical response of laminates. The objective of this work was to characterize the effects of TLR on the in-plane and inter-laminar mechanical response of undamaged composite laminates. Detailed finite element models of 'unit cells', or representative volumes, were used to study the effects of adding TLR on the elastic constants; the in-plane strength; and the initiation of delamination. Parameters investigated included TLR material, TLR volume fraction, TLR diameter, TLR through-thickness angle, ply stacking sequence, and the microstructural features of pure resin regions and curved in-plane fibers. The work was limited to the linear response of undamaged material with at least one ply interface. An inter-laminar dominated problem of practical interest, a flanged skin in bending, was also modeled.
We present the first observational evidence for a collimated jet in a cataclysmic variable system; the recurrent nova T Pyxidis. Optical spectra show bipolar components of H(alpha) with velocities approx. 1400 km/s, very similar to those observed in the supersoft X-ray sources and in SS 433. We argue that a key ingredient of the formation of jets in the supersoft X-ray sources and T Pyx (in addition to an accretion disk threaded by a vertical magnetic field), is the presence of nuclear burning on the surface of the white dwarf.
A quick-connect bolt that can be inserted into a threaded receptacle without rotation and tightened with a minimum number of rotations is described.
We explore a model in which QSO broad absorption lines (BALS) are formed in a radiation pressure-driven wind emerging from a magnetized accretion disk. The magnetic field threading the disk material is dragged by the flow and is compressed by the radiation pressure until it is dynamically important and strong enough to contribute to the confinement of the BAL clouds. We construct a simple self-similar model for such radiatively driven magnetized disk winds, in order to explore their properties. It is found that solutions exist for which the entire magnetized flow is confined to a thin wedge over the surface of the disk. For reasonable values of the mass-loss rate, a typical magnetic field strength such that the magnetic pressure is comparable to the inferred gas pressure in BAL clouds, and a moderate amount of internal soft X-ray absorption, we find that the opening angle of the flow is approximately 0.1 rad, in good agreement with the observed covering factor of the broad absorption line region.
In a effort to address current needs for efficient, air propulsion systems, we have developed some new analytical predictive tools for understanding and alleviating aircraft engine instabilities which have led to accelerated high cycle fatigue and catastrophic failures of these machines during flight. A frequent cause of failure in Jets engines is excessive resonant vibrations and stall flutter instabilities. The likelihood of these phenomena is reduced when designers employ the analytical models we have developed. These prediction models will ultimately increase the nation's competitiveness in producing high performance Jets engines with enhanced operability, energy economy, and safety. The objectives of our current threads of research in the final year are directed along two lines. First, we want to improve the current state of blade stress and aeromechanical reduced-ordered modeling of high bypass engine fans, Specifically, a new reduced-order iterative redesign tool for passively controlling the mechanical authority of shroudless, wide chord, laminated composite transonic bypass engine fans has been developed. Second, we aim to advance current understanding of aeromechanical feedback control of dynamic flow instabilities in axial flow compressors. A systematic theoretical evaluation of several approaches to aeromechanical feedback control of rotating stall in axial compressors has been conducted. Attached are abstracts of two .papers under preparation for the 1998 ASME Turbo Expo in Stockholm, Sweden sponsored under Grant No. NAG3-1571. Our goals during the final year under Grant No. NAG3-1571 is to enhance NASA's capabilities of forced response of turbomachines (such as NASA FREPS). We with continue our development of the reduced-ordered, three-dimensional component synthesis models for aeromechanical evaluation of integrated bladeddisk assemblies (i.e., the disk, non-identical bladeing etc.). We will complete our development of component systems design optimization strategies for specified vibratory stresses and increased fatigue life prediction of assembly components, and for specified frequency margins on the Campbell diagrams of turbomachines. Finally, we will integrate the developed codes with NASA's turbomachinery aeromechanics prediction capability (such as NASA FREPS).
Experimental measurements of the dispersion characteristics of a C-band helix structure were carried out and compared to the dispersion characteristics found from a helix model using the three-dimensional electromagnetic computer code MAFIA. A conceptually novel design comprising a helical thread of the same pitch and inner diameter in a cylindrical waveguide also were calculated using the MAFIA code. The helical-groove structure exhibits a smaller bandwidth but at a much higher frequency range than the traditional helical structure for similar physical dimensions. It is physically more robust in construction. The interaction impedance also compares favorably with those of the conventional structure.
The prominence that erupts in a prominence eruption is a magnetic structure in the chromosphere and corona. It is visible in chromospheric images by virtue of chromospheric-temperature plasma suspended in the magnetic field, and belongs to that large class of magnetic structures appropriately called filaments because of their characteristic sinewy sigmoidal form. Hence, the term "filament eruption" is used interchangeably with the term "prominence eruption". The magnetic field holding a filament is prone to undergo explosive changes in configuration. In these upheavals, because the filament material is compelled by its high conductivity to ride with the magnetic field that threads it, this material is a visible tracer of the field motion. The part of the magnetic explosion displayed by the entrained filament material is the phenomenon known as a filament eruption, the topic of this article. This article begins with a description of basic observed characteristics of filament eruptions, with attention to the magnetic fields, flares, and coronal mass ejections in which erupting filaments are embedded. The present understanding of these characteristics in terms of the form and action of the magnetic field is then laid out by means of a rudimentary three-dimensional model of the field. The article ends with basic questions that this picture leaves unresolved and with remarks on the observations needed to probe these questions.
A retractable indicator assembly may be mounted on a container which transmits air through the container and removes deleterious gases with an activated charcoal medium in the container. The assembly includes: an elongate indicator housing has a chamber therein; a male adaptor with an external threads is used for sealing engagement with the container; a plug located at the upper end of the housing; a housing that includes a transparent wall portion for viewing at least a portion of the chamber; a litmus indicator, moveable by a retractable rod from a retracted position within the container to an extended position within the chamber of the housing; and an outer housing that is secured to the upper end of the rod, and protects the indicator housing while the litmus indicator is in its normally retracted position. The assembly may be manually manipulated between its extended position wherein the litmus indicator may be viewed through the transparent wall of the indicator housing, and a retracted position wherein the outer housing encloses the indicator housing and engages the exterior of the container.
Landsat thematic mapper data are used to estimate instantaneous regional-scale surface water and energy fluxes in a semi-arid Great Basin desert of the western United States. Results suggest that it is possible to scale from point measurements of environmental state variables to regional estimates of water and energy exchange. This research characterizes the unifying thread in the classical climate-topography-soil-vegetation relation -the surface water and energy balance-through maps of the partitioning of energy throughout the landscape. The study was conducted in Goshute Valley of northeastern Nevada, which is characteristic of most faulted graben valleys of the Basin and Range Province of the western United States. The valley comprises a central playa and lake plain bordered by alluvial fans emanating from the surrounding mountains. The distribution of evapotranspiration (ET) is lowest in the middle reaches of the fans where the water table is deep and plants are small, resulting in low evaporation and transpiration. Highest ET occurs in the center of the valley, particularly in the playa, where limited to no vegetation occurs, but evaporation is relatively high because of a shallow water table and silty clay soil capable of large capillary movement. Intermediate values of ET are associated with large shrubs and is dominated by transpiration.