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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 739 records · Page 41
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Flow visualization and motion analysis for a series of four sequential brush seals

Applying the Full Flow Field Tracking (FFFT) method, the flow patterns and the accompanying fluid velocities inside a series of brushes were nonintrusively determined and graphically reconstructed. The visualized flow field revealed regions that are characteristically river-jetting, vortical, and crossflow, and exist upstream, downstream, or within the seal. These flows are especially engendered by variations in fiber void that are spatial and temporal and affect changes in seal leakage and stability. The deformation of the upper half of each of the four sequential brushes as a function of upstream pressure and mass flow was determined. The axial pressure variation across the set of four brushes and the mass flow as a function of the pressure drops are also presented.

Braun, M. J.↗
NASA NTRS1990

Self-similar perturbations of a Friedmann universe

The present analysis of spherically symmetric self-similar solutions to the Einstein equations gives attention to those solutions that are asymptotically k = 0 Friedmann at large z values, and possess finite but perturbed density at the origin. Such solutions represent nonlinear density fluctuations which grow at the same rate as the universe's particle horizon. The overdense solutions span only a narrow range of parameters, and resemble static isothermal gas spheres just within the sonic point; the underdense solutions may have arbitrarily low density at the origin while exhibiting a unique relationship between amplitude and scale. Their relevance to large-scale void formation is considered.

Carr, Bernard J.↗
NASA NTRS1990

Thermographic inspection of solid-fuel rocket booster field joint components

Thermographic nondestructive evaluation techniques were investigated for possible application on Space Shuttle solid rocket booster field joint hardware. This investigation included evaluation of the clevis and tang mating surfaces for scratches and measurement of grease film thickness. The field joint insulation system was inspected for voids and disbonds.

Thompson, Karen G.↗
NASA NTRS1991

Eliminating Unbonded Edges In Explosive Bonding

Explosive-bonding technique elminates sharp unbonded notch normally occurring between flyer plate and baseplate. Makes it possible to simply break away unbonded outer extremity of flyer plate; no longer necessary to grind away unbonded edge to prevent collection of corrosive contaminants in edge voids. Method not limited to flat surfaces.

Bement, Laurence J.↗
NASA NTRS1989

Hybrid propulsion technology program: Phase 1, volume 1

A number of booster propulsion system concepts are being considered for the next generation of manned and unmanned space launch vehicles. The one propulsion system concept that has potential for reducing costs with increased safety, reliability, and performance is hybrid propulsion (HP). A HP system may be thought of as a liquid propulsion system with solid fuel or a solid propulsion system with a liquid oxidizer. The liquid propulsion features that are most attractive are the higher specific impulse, clean exhaust, separated propellants, and oxidizer loading just prior to launch. The most attractive solid propulsion features includes low life cycle costs, no rotating machinery, compact size, and a robust case. In addition, a HP system has a robust LO2 tank; provides thrust control for ignition, to alleviate flight loads, and for thrust termination; and uses an inert grain that is not sensitive to anomalies such as cracks, voids, and separations. The object is to develop the technology to enable the application of HP to manned and unmanned space launch vehicles. This program will identify the necessary technology, acquire that technology, and demonstrate that technology. This volume is the executive summary.

Schuler, A. L.↗
NASA NTRS1991

Solar dynamic heat receiver technology

A full-size, solar dynamic heat receiver was designed to meet the requirements specified for electrical power modules on the U.S. Space Station, Freedom. The heat receiver supplies thermal energy to power a heat engine in a closed Brayton cycle using a mixture of helium-xenon gas as the working fluid. The electrical power output of the engine, 25 kW, requires a 100 kW thermal input throughout a 90 minute orbit, including when the spacecraft is eclipsed for up to 36 minutes from the sun. The heat receiver employs an integral thermal energy storage system utilizing the latent heat available through the phase change of a high-temperature salt mixture. A near eutectic mixture of lithium fluoride and calcium difluoride is used as the phase change material. The salt is contained within a felt metal matrix which enhances heat transfer and controls the salt void distribution during solidification. Fabrication of the receiver is complete and it was delivered to NASA for verification testing in a simulated low-Earth-orbit environment. This document reviews the receiver design and describes its fabrication history. The major elements required to operate the receiver during testing are also described.

Sedgwick, Leigh M.↗
NASA NTRS1990

Ladder polymers for use as high temperature stable resins or coatings

An object of the invention is to synthesize a new class of ladder and partial ladder polymers. In accordance with the invention, the new class of ladder and partial ladder polymers are synthesized by polymerizing a bis-dienophile with a bis-diene. Another object of the invention is to provide a fabricated, electrically conducting, void free composite comprising the new class of the ladder and partial ladder polymers described above. The novelty of the invention relates to a new class of ladder and partial ladder polymers and a process for synthesizing these polymers. These polymers are soluble in common organic solvents and are characterized with a unique dehydration property at temperatures of 300 to 400 C to provide thermo-oxidatively stable pentiptycene units along the polymeric backbone. These polymers are further characterized with high softening points and good thermo-oxidative stability properties. Thus these polymers have potential as processable, matrix resins for high temperature composite applications.

Meador, Mary Ann↗
NASA NTRS1990

On the large-scale structures formed by wakes of open cosmic strings

Large-scale structures of the universe have been variously described as sheetlike, filamentary, cellular, bubbles or spongelike. Recently cosmic strings became one of viable candidates for a galaxy formation scenario, and some of the large-scale structures seem to be simply explained by the open cosmic strings. According to this scenario, sheets are wakes which are traces of moving open cosmic strings where dark matter and baryonic matter have accumulated. Filaments are intersections of such wakes and high density regions are places where three wakes intersect almost orthogonally. The wakes formed at t sub eq become the largest surface density among all wakes, where t sub eq is the epoch when matter density equals to radiation density. If we assume that there is one open cosmic string per each horizon, then it can be explained that the typical distances among wakes, filaments and clusters are also approx. 10(exp 2) Mpc. This model does not exclude a much more large scale structure. Open cosmic string may move even now and accumulate cold dark matter after its traces. However, the surface density is much smaller than the ones formed at t sub eq. From this model, it is expected that the typical high density region will have extended features such as six filaments and three sheets and be surrounded by eight empty regions (voids). Here, the authors are mainly concerned with such structures and have made numerical simulations for the formation of such large scale structures.

Hara, Tetsuya↗
NASA NTRS1990

The metrology of spherical shells using synchrotron x ray microtomography

With recent advances in solid state imaging technology and the increasing availability of synchrotron x-ray radiation sources, synchrotron x-ray microtomography is emerging as a nondestructive technique for the evaluation of the structure and composition of small specimens with spatial resolution in the micron range. Synchrotron radiation offers the following advantages over conventional x-ray sources: high brightness, continuous emission which is tunable over a large energy range, faster data collection rates, and a highly collimated beam of large cross section permitting the illumination of large specimens. Synchrotron x-ray microtomography enables the structure of individual spheres to be evaluated in order to reveal the concentricity and sphericity of the internal void and the uniformity of the shell wall in the case of high quality spherical shells for Sandia National Laboratories' Inertial Confinement Fusion project.

Hmelo, Anthony B.↗
NASA NTRS1989

The effect of hydrogen on the deformation behavior of a single crystal nickel-base superalloy

The effect of hydrogen on the tensile deformation behavior of PWA 1480 is presented. Tensile tests were interrupted at different plastic strain levels to observe the development of the dislocation structure. Transmission electron microscopy (TEM) foils were cut perpendicular to the tensile axis to allow the deformation of both phases to be simultaneously observed as well as parallel to zone axes (III) to show the superdislocations on their slip planes. Similar to other nickel-base superalloys, hydrogen was detrimental to the room temperature tensile properties of PWA 1480. There was little effect on strength, however the material was severely embrittled. Even without hydrogen, the elongation-to-failure was only approximately 3 percent. The tensile fracture surface was made up primarily of ductile voids with regions of cleavage fracture. These cleavage facets are the eutectic (gamma') in the microstructure. It was shown by quantitative fractography that hydrogen embrittles the eutectic (gamma') and causes the crack path to seek out and fracture through the eutectic (gamma'). There was two to three times the amount of cleavage on the fracture surface of the hydrogen-charged samples than on the surface of the uncharged samples. The effect of hydrogen can also be seen in the dislocation structure. There is a marked tendency for dislocation trapping in the gamma matrix with and without hydrogen at all plastic strain levels. Without hydrogen there is a high dislocation density in the gamma matrix leading to strain exhaustion in this region and failure through the matrix. The dislocation structure at failure with hydrogen is slightly different. The TEM foils cut parallel to zone axes (III) showed dislocations wrapping around gamma precipitates. Zone axes (001) foils show that there is a lower dislocation density in the gamma matrix which can be linked to the effects of hydrogen on the fracture behavior. The primary activity in the gamma precipitates is in the form of superlattice intrinsic stacking faults (SISFs). These faults have also been reported in other ordered alloys and superalloys.

Walston, W. S.↗
NASA NTRS1991

Wet spinning of solid polyamic acid fibers

The invention is a process for the production of solid aromatic polyamic acid and polyimide fibers from a wet gel or coagulation bath wet gel using N,N-dimethylacetamide (DMAc) solutions of the polyamic acid derived from aromatic dianhydrides such as 3,3',4,4' benzophenonetetra carboxylic dianhydride (BTDA) and aromatic diamines such as 4,4'-oxydianiline (4,4'-ODA). By utilizing the relationship among coagulation medium and concentration, resin inherent viscosity, resin percent solids, filament diameter, and fiber void content, it is possible to make improved polyamic acid fibers. Solid polyimide fibers, obtained by the thermal cyclization of the polyamic acid precursor, have increased tensile properties compared to fibers containing macropores from the same resin system.

Dorogy, William E., Jr.↗
NASA NTRS1991

A linear control design structure to maintain loop properties during limit operation in a multi-nozzle turbofan engine

The implementation of multi-variable control systems on turbofan engines requires the use of limit protection to maintain safe engine operation. Since a turbofan engine typically encounters limits during transient operation, the use of a limit protection scheme that modifies the feedback loop may void the desired 'guarantees' associated with linear multi-variable control design methods, necessitating considerable simulation to validate the control with limited protection. An alternative control design structure is proposed that maintains the desired linear feedback properties when certain safety limits are encountered by moving the limit protection scheme outside the feedback loop. This proposed structure is compared to a structure with a limit protection scheme that modifies the feedback loop properties. The two design structures are compared using both linear and nonlinear simulations. The evaluation emphasizes responses where the fan surge margin limit is encountered.

Mattern, Duane↗
NASA NTRS1990

The universe in a box - Thermal effects in the standard cold dark matter scenario

An attempt is made to compute the evolution of a representative piece of the universe at a minimal resolution of a flux-based mesh code coupled with a standard particle-mesh dark matter code. It is found that, on scales greater than 1/h Mpc, dark matter is more clumped than gas. Bremsstrahlung and Compton cooling are unimportant on scales of 1 Mpc or greater. Shocks gradually heat the gas, leaving most of it in voids at T = 10 exp 3.5 K or less, but with a small fraction reaching T = 10 million K or more. Ultraviolet and soft X-ray emission from the heated gas is significant, providing an important part of the background radiation field and significant ionizing of the intergalactic medium. The mean induced Delta T/T for microwave background radiation in the Rayleigh-Jeans part of the spectrum is 1.1 x 10 to the -6th with fluctuation of 5.6 x 10 to the -7th on arcmin scales and a mean y parameter of 5.5 x 10 to the -7th, which is potentially detectable by the COBE satellite.

Cen, R. Y.↗
NASA NTRS1990

A deep Abell cluster redshift survey

Redshifts have been measured for a complete sample of 145 Abell clusters of galaxies of median redshift 0.16 covering a 561 sq deg region at high Galactic latitude. Clustering on scales greater than about 70/h Mpc cannot be detected. A large void of diameter about 20,000 km/s seen in maps of the cluster distribution is consistent with smaller scale behavior of the correlation function of the survey. Large-scale peculiar motions are about 1000 km/s or less, a limit inconsistent with the claimed detection by Bahcall et al. (1986) of peculiar motions of about 2000 km/s.

Huchra, John P.↗
NASA NTRS1990

Filament winding cylinders. I - Process model

A model was developed which describes the filament winding process of composite cylinders. The model relates the significant process variables such as winding speed, fiber tension, and applied temperature to the thermal, chemical and mechanical behavior of the composite cylinder and the mandrel. Based on the model, a user friendly code was written which can be used to calculate (1) the temperature in the cylinder and the mandrel, (2) the degree of cure and viscosity in the cylinder, (3) the fiber tensions and fiber positions, (4) the stresses and strains in the cylinder and in the mandrel, and (5) the void diameters in the cylinder.

Lee, Soo-Yong↗
NASA NTRS1990

Filament winding cylinders. III - Selection of the process variables

By using the Lee-Springer filament winding model temperatures, degrees of cure, viscosities, stresses, strains, fiber tensions, fiber motions, and void diameters were calculated in graphite-epoxy composite cylinders during the winding and subsequent curing. The results demonstrate the type of information which can be generated by the model. It is shown, in reference to these results, how the model, and the corresponding WINDTHICK code, can be used to select the appropriate process variables.

Lee, Soo-Yong↗
NASA NTRS1990

Coherent backscatter and the radar characteristics of outer planet satellites

It is presently suggested that the diffuse component-dominated high radar reflectivities and large polarization of Europa, Ganymede, and Callisto could be due to the illumination by a collimated source of a weakly absorbing particulate medium in which wavelength-scaled scatterers are separated by distances somewhat larger than the wavelength. A plausible medium could be a regolith composed of voids and/or silicate rocks imbedded in an icy matrix; multiply-scattered parts of the wavefront traversing the same path in opposite directions combine coherently in the backscatter direction to generate increased intensity, and the enhancement is different for the two components of polarized reflected radiation.

Hapke, Bruce↗
NASA NTRS1991

Flow visualization and quantitative velocity and pressure measurements in simulated single and double brush seals

A method to visualize and characterize the complex flow fields in simulated single and double brush seals is presented. The brush seal configuration was tested in a gravity fed water tunnel and a pump driven pressurized oil tunnel. Visualization of the flow field revealed regions that are characteristically river jetting, vortical, crossflow and exist upstream, downstream or within the seal. Such flows are especially engendered by variations in fiber void that are spatial and temporal and affect changes in seal leakage and stability. While the effects of interface motion and cylindrical configuration have not been considered herein, it is believed that the observed flow fields and pressure drop patterns characterize flow phenomenology in brush seals. The axial pressure profiles upstream, across and downstream of the brush have been measured under a variety of inlet pressure conditions and the ensuing pressure maps are presented and discussed. Through the application of the Full Flow Field Tracking method developed by the authors, the flow patterns and the accompanying fluid velocities inside the brush were non-intrusively determined and graphically reconstructed.

Braun, M. J.↗