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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 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Thematic Mapper and field investigations at the intersection of the Death Valley and Garlock fault zones, California

Analysis of processed images and detailed field investigations have provided significant information concerning the late-Pliocene and Quaternary evolution of the intersection of the Garlock and Death Valley fault zones. The imagery was used to determine patterns of sedimentation and age relationships on alluvial fans and to determine the geometry, styles of deformation, and relative ages of movements on major and minor faults in the study area. The field investigation often confirmed the inferences drawn from the images and provided additional tectonic and geomorphologic data about the Quaternary deformation of the region. All the data gathered in the course of this project support the contention that the Garlock fault zone terminates in the Avawatz Mountains and that the Death Valley fault zone continues south of the intersection for at least 50 km, forming the eastern boundary of the Mojave province.

Brady, Roland H., III↗
NASA NTRS1990

The effects of g-jitter and surface tension induced convection on float zones

The effects of g-jitter on nonencapsulated and encapsulated liquid bridges were investigated numerically, using fluid characteristics and parameters from three fluid systems: a silicone oil bridge, a methanol bridge, and a silicon melt. Results showed that complex flow patterns can arise in g-jitter environment which significantly modify the heat-transfer characteristics of the system. It was found that the nonencapsulated liquid bridges and float zone melts were dominated by surface-tension driven convection, with very little impact on the flows by residual and g-jitter accelerations. Zone encapsulation resulted in a sizeable drop in the maximum fluid velocities. The g-jitter computations on the encapsulated float zones resulted in significant augmentation of the maximum velocities and heat transfer, with the silicon melt being the least sensitive to g-jitter acceleration.

Ramachandran, N.↗
NASA NTRS1989

Thermocapillary convection in zone-melting crystal growth - An open-boat physical simulation

Thermocapillary convection in a molten zone of NaNO3 contained in a boat with a free horizontal surface, that is heated from above by a centered wire heater, was studied to simulate flow in zone-melting crystal growth. Using a laser-light-cut technique and fine SiO powder as a tracer, convection in the melt zone was visualized in two different cases. In the first case, the entire melt surface was free, while in the second the melt surface was free only in the immediate vicinity of one vertical wall and was covered elsewhere, this wall being to simulate the melt/crystal interface during crystal growth. It was observed that thermocapillary convection near this wall prevailed in the first case, but was reduced significantly in the second. Since thermocapillary rather than natural convection dominated in the melt, the effect of the partial covering of the melt surface on thermocapillary convection in the melt observed in this study is expected to be similar under microgravity.

Kim, Y. J.↗
NASA NTRS1989

Primary zone dynamics in a gas turbine combustor

Fluid mechanical investigations simulating the flow in the primary zone of a gas turbine combustor are presented using three generic test rigs: (1) rotating pipe yielding a swirling jet of air; (2) primary zone model with a single swirler and various primary jet configurations, operated with air; and (3) two rectangular models of a (stretched-out) annular combustor with five swirlers in the backwall and with various primary jet configurations, one operated with air and the other with water. Concentration measurements are obtained using laser sheet imaging techniques and velocity measurements using a laser Doppler velocimeter. The results show recirculation zones, intense mixing, instabilities of the interacting jets and the presence of large random vortical motions. The flowfields are shown to exhibit bimodal behavior, have asymmetries despite symmetrical geometry and inlet conditions and display strong jet/swirler and swirler/swirler interactions.

Sullivan, J. P.↗
NASA NTRS1988

Knowledge-based flow field zoning

Automation flow field zoning in two dimensions is an important step towards easing the three-dimensional grid generation bottleneck in computational fluid dynamics. A knowledge based approach works well, but certain aspects of flow field zoning make the use of such an approach challenging. A knowledge based flow field zoner, called EZGrid, was implemented and tested on representative two-dimensional aerodynamic configurations. Results are shown which illustrate the way in which EZGrid incorporates the effects of physics, shape description, position, and user bias in a flow field zoning.

Andrews, Alison E.↗
NASA NTRS1990

Thermocapillary flow and melt/solid interfaces in floating-zone crystal growth under microgravity

Computer simulation of steady-state axisymmetrical heat transfer and fluid flow was conducted to study thermocapillary flow and melt/solid interfaces in floating-zone crystal growth under microgravity. The effects of key variables on the extent of thermocapillary flow in the melt zone, the shapes of melt/solid interfaces and the length of the melt zone were discussed. These variables are: (1) the temperature coefficient of surface tension (or the Marangoni number), (2) the pulling speed (or the Peclet number), (3) the feed rod radius, (4) the ambient temperature distribution, (5) the heat transfer coefficient (or the Biot number), and (6) the thermal diffusivity of the material (or the Prandtl number).

Lan, C. W.↗
NASA NTRS1989

Multipolarization P-, L-, and C-band radar for coastal zone mapping - The Louisiana example

Multipolarization P-, L-, and C-band airborne SAR data sets were acquired over a coastal zone and a forested wetland of southern Louisiana. The data sets were used with field-collected surface-parameter data in order to determine the value of SAR systems in assessing and mapping coastal-zone surface features. The coastal-zone surface features in this study are sediments, sediment distribution, and the formation of new isles and banks. Results of the data analysis indicate that the P-band radar with 68-cm wavelength is capable of detecting the submerged sediment if the area is very shallow (i.e., a water depth of less than one meter). The penetration capability of P-band radar is also demonstrated in the forested wetland area. The composition and condition of the ground surface can be detected, as well as the standing water beneath dense tree leaves.

Wu, Shih-Tseng↗
NASA NTRS1990

Direct numerical simulation of the transitional zone

Properties of the transitional zone in channel and boundary-layer flow are determined from the results of direct numerical simulations of forced transition. Three channel flow cases produce similar behavior, particularly in the 'transition function' relevant for some algebraic eddy viscosity models of the transitional zone. Moreover, the transitional zone from the computed forced boundary-layer transition is qualitatively similar to experimental data for natural transition and to the computed channel flow transition.

Zang, Thomas A.↗
NASA NTRS1991

A review of the regional geophysics of the Arizona Transition Zone

A review of existing geophysical information and new data presented in this special section indicate that major changes in crustal properties between the Basin and Range and Colorado Plateau occur in, or directly adjacent to, the region defined as the Arizona Transition Zone. Although this region was designated on a physiographic basis, studies indicate that it is also the geophysical transition between adjoining provinces. The Transition Zone displays anomalous crustal and upper mantle seismic properties, shallow Curie isotherms, high heat flow, and steep down-to-the-plateau Bouguer gravity gradients. Seismic and gravity studies suggest that the change in crustal thickness, from thin crust in the Basin and Range to thick crust in the Colorado Plateau, may occur as a series of steps rather than a planar surface. Anomalous P wave velocities, high heat flow, shallow Curie isotherms, and results of gravity modeling suggest that the upper mantle is heterogeneous in this region. A relatively shallow asthenosphere beneath the Basin and Range and Transition Zone contrasted with a thick lithosphere beneath the Colorado Plateau would be one explanation that would satisfy these geophysical observations.

Hendricks, J. D.↗
NASA NTRS1991

Ultrastructural and cytochemical evidence for single impulse initiation zones in vestibular macular nerve fibers of rat

Cupric ion-ferricyanide labeling methods and related ferrocyanide-stained tissues were used to locate the characterize, at the ultrastructural level, presumptive impulse initiation zones in the three types of vestibular macular nerve fibers. Large-diameter, M-type vestibular nerve fibers terminate in a calyx at the heminode, and labeling is coextensive with the base of the calyx. Intermediate, M/U-type nerve fibers have short, unmyelinated preterminal segments that sometimes bifurcate intamacularly, and small-diameter, U-type nerve fibers have long, unmyelinated preterminal axons and up to three branches. Preterminals of these nerve fibers display ultrastructural heterogeneity that is correlated with labeling patterns for sodium channels and/or associated polyanionic sites. They have a nodelike ultrastructure and label heavily from near the heminode to the base of the macula. Their intramacular branches, less organized ultrastructurally, label only slightly. Results indicate that vestibular nerve fibers have one impulse initiation zone, located near the heminode, that varies in length according to nerve fiber type. Structural heterogeneity may favor impulse conduction in the central direction, and length of the impulse initiation zone could influence nerve discharge patterns.

Ross, Muriel D.↗
NASA NTRS1991

The depth of the solar convection zone

The transition of the temperature gradient between being subadiabatic and adiabatic at the base of the solar convection zone gives rise to a clear signature in the sound speed. Helioseismic measurements of the sound speed therefore permit a determination of the location of the base of the convection zone. Two techniques were tested by applying them to artifical data, obtained by adding simulated noise to frequencies computed from two different solar models. The determinations appear to be relatively insensitive to uncertainties of the physics of the solar interior. From an analysis of observed frequencies of solar oscillation it is concluded that the depth of the solar convection zone is (0.287 + or - 0.003) solar radii.

Christensen-Dalsgaard, J.↗
NASA NTRS1991

The width of fault zones in a brittle-viscous lithosphere: Strike-slip faults

A fault zone in an ideal brittle material overlying a very weak substrate could, in principle, consist of a single slip surface. Real fault zones have a finite width consisting of a number of nearly parallel slip surfaces on which deformation is distributed. The hypothesis that the finite width of fault zones reflects stresses due to quasistatic flow in the ductile substrate of a brittle surface layer is explored. Because of the simplicity of theory and observations, strike-slip faults are examined first, but the analysis can be extended to normal and thrust faulting.

Parmentier, E. M.↗
NASA NTRS1992

The first identification of a mainbelt asteroid source for a meteorite Class E-type Apollo asteroid (3103) 1982BB: A link between the Hungaria asteroid zone and the Aubrite meteorites

One of the major goals of asteroid investigators has been to determine the source bodies of the meteorites, and, thus, to provide the needed spatial context. However, despite careful investigation of many of these asteroids, no specific mainbelt asteroidal parent bodies for particular meteorites have yet been identified. Results are reported that represent the first direct link of a set of meteorites (the aubrites or enstatite achondrites) back to a particular source region in the asteroid belt (the Hungaria zone of the innermost belt located at a heliocentric distance of about 1.9 AU (1.9 times the Earth's distance from the Sun)). Since most asteroids in the belt are still located near their original heliocentric formation distances, this link allows the composition and temperature of the solar nebula to be determined at a specific distance from the Sun during the time of planetesimal formation. Orbital considerations suggest that 3103 could be derived from the Hungaria zone. However, the spectral gype of 3103 makes such a source probable. The Hungaria zone is the only region of the asteroid belt where E-type asteroids are common. E-type objects constitute about 55 percent of the classified Hungaria population. Although a more detailed investigation of the dynamical evolution of this object is needed, it appears highly probable that 3103 1982BB was derived from the Hungaria region of the innermost asteroid belt, that it is a fragment of the collisional breakup of an E-object near 1.9 AU, and escaped the mainbelt via the nu sup 16 resonance.

Gaffey, M. J.↗
NASA NTRS1991

Orbit crowding of molecular gas at a bar-spiral arm transition zone in M83

The southwestern bar-spiral arm transition zone in M83 is been studied in CO, H-alpha, H I, red light, and the radio continuum. A massive molecular gas complex in the heart of the transition zone is composed or two principal components which have the morphology and kinematics expected from orbit crowding, where gas on highly elliptical orbits form the bar region converges with gas on more circular orbits from the spiral arm region. Three mechanisms for the origin of the orbit crowding are investigated, and it is proposed that the crowding is due primarily to density wave streaming motions caused by the bar and spiral arms. The inner CO component is partially coincident with a region of highly polarized radio continuum emission which precedes the H-alpha spiral arm by 15-25 arcsec, indicating that it lies on or just downstream from a shock front. This suggests that the bar gas approaching the transition zone is shocked and explains the ridge of dense gas seen upstream from the spiral arm.

Kenney, Jeffrey D. P.↗
NASA NTRS1991

Dynamical behavior of strong magnetic fields in the solar convection zone

Magnetic buoyancy is thought to play an important role in the dynamical behavior of the sun's magnetic field in the convection zone. Magnetic buoyancy is commonly thought to cause inescapable rapid loss of toroidal flux from much of the convection zone, thereby suppressing effective operation of a solar dynamo. This paper reexamines the detailed character of magnetic buoyancy, especially as it is influenced by the magnetic field's effect on heat transport and temperature gradients in the convection zone. It is suggested that suppression of convective heat transport across strong magnetic flux tubes can alter the temperature within the tubes and can subdue, or even reverse, the effect of magnetic buoyancy.

Vainshtein, S.↗
NASA NTRS1992

Effects on post-glacial rebound from the hard rheology in the transition zone

The effect of an increase of viscosity in the earth-mantle's transition zone between 420 and 670 km on the geophysical signatures induced by postglacial rebound was analyzed using a self-gravitating model consisting of an elastic lithosphere, a three-layer viscoelastic mantle, and an inviscid core. Results show that the horizontal displacements and velocities as well as the stress pattern are extremely sensitive to the viscosity increase and to the chemical stratification of the transition zone. The findings indicate that geodetic data on intraplate deformation can be used to put constraints on the viscosity increase in the transition zone and on the amount of chemical stratification in the mantle.

Spada, Giorgio↗
NASA NTRS1992

Lyman alpha line shapes from electron impact H2 dissociative processes in the Jovian auroral zone

Over the past two years several Lyman alpha line profile spectra of Jupiter were obtained using the International Ultraviolet Explorer (IUE) telescope. Several different regions of the planet were observed including the auroral zone, the low and mid latitudes, and the equatorial region which includes the Lyman alpha bulge region. These results have presented a very interesting picture of atomic hydrogen on Jupiter with explanations that range from ion outflow in the auroral zone to large thermospheric winds at low and mid latitudes. New data are needed to address the outstanding questions. Almost certainly, high resolution spectra from the Hubble Space Telescope will play a role in new observations. Better data also require better models, and better models require new laboratory data as inputs. The purpose of this program is two-fold: (1) to introduce a method by which new laboratory electron impact measurements of H2 dissociation can be used to calculate both the slow and fast H(S-2) and H(P-2) fragments in an H2 atmosphere; and (2) to determine the predicted Lyman alpha line shape that would result from electron impact production of these dissociative fragments in the Jovian auroral zone.

Waite, J. H., Jr.↗
NASA NTRS1993

Stability and instability of thermocapillary convection in models of the float-zone crystal-growth process

This project was concerned with the determination of conditions of guaranteed stability and instability for thermocapillary convection in a model of the float-zone crystal-growth process. This model, referred to as the half-zone, was studied extensively, both experimentally and theoretically. Our own earlier research determined, using energy-stability theory, sufficient conditions for stability to axisymmetric disturbances. Nearly all results computed were for the case of a liquid with Prandtl Number Pr = 1. Attempts to compute cases for higher Prandtl numbers to allow comparison with the experimental results of other researchers were unsuccessful, but indicated that the condition guaranteeing stability against axisymmetric disturbances would be a value of the Marangoni number (Ma), significantly higher than that at which oscillatory convection was observed experimentally. Thus, additional results were needed to round out the stability picture for this model problem. The research performed under this grant consisted of the following: (1) computation of energy-stability limits for non-axisymmetric disturbances; (2) computation of linear-stability limits for axisymmetric and non-axisymmetric disturbances; (3) numerical simulation of the basic state for half- and full-zones with a deformable free surface; and (4) incorporation of radiation heat transfer into a model energy-stability problem. Each of these is summarized briefly below.

Neitzel, G. P.↗