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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 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS2007

Effects of Artificial Gravity and Bed Rest on Spatial Orientation and Balance Control

While the vestibular system should be well-adapted to bed rest (a condition it experiences approximately 8/24 hrs each day), questions remain regarding the degree to which repeated exposures to the unusual gravito-inertial force environment of a short-radius centrifuge might affect central processing of vestibular information used in spatial orientation and balance control. Should these functions be impaired by intermittent AG, its feasibility as a counter-measure would be diminished. We, therefore, examined the effects of AG on spatial orientation and balance control in 15 male volunteers before and after 21 days of 6 HDT bed rest (BR). Eight of the subjects were treated with daily 1hr AG exposures (2.5g at the feet; 1.0g at the heart) aboard a short radius (3m) centrifuge, while the other seven served as controls (C). Spatial orientation was assessed by measures of ocular counter-rolling (OCR; rotation of the eye about the line of sight, an otolith-mediated reflex) and subjective visual vertical (SVV; perception of the spatial upright). Both OCR and SVV measurements were made with the subject upright, lying on their left sides, and lying on their right sides. OCR was measured from binocular eye orientation recordings made while the subjects fixated for 10s on a point target directly in front of the face at a distance of 1 m. SVV was assessed by asking subjects (in the dark) to adjust to upright (using a handheld controller) the orientation of a luminous bar randomly perturbed (15) to either side of the vertical meridian. Balance control performance was assessed using a computerized dynamic posturography (CDP) protocol similar to that currently required for all returning crew members. During each session, the subjects completed a combination of trials of sensory organization test (SOT) 2 (eyes closed, fixed platform) and SOT 5 (eyes closed, sway-referenced platform) with and without static and dynamic pitch plane head movements (plus or minus 20 deg., dynamic paced by an audible tone at 0.33Hz). OCR and CDP performance were unaffected by BR and BR+AG; post-BR measures were unchanged from baseline for both AG and C groups. Similarly, BR did not affect SVV in the C group. However, BR+AG disrupted one measure of spatial orientation: SVV error was significantly increased on R+0 and R+1 following BR in the AG group. These results suggest a transient untoward effect on central vestibular processing may accompany repeated exposure to intermittent AG, a potential side-effect that should be studied more closely in future studies.

Paloski, William H.↗
NASA NTRS1998

New Estimates of Hydrological and Oceanic Excitations of Variations of Earth's Rotation, Geocenter and Gravitational Field

Hydrological mass transport in the geophysical fluids of the atmosphere-hydrosphere-solid Earth surface system can excite Earth's rotational variations in both length-of-day and polar motion. These effects can be computed in terms of the hydrological angular momentum by proper integration of global meteorological data. We do so using the 40-year NCEP data and the 18-year NASA GEOS-1 data, where the precipitation and evapotranspiration budgets are computed via the water mass balance of the atmosphere based on Oki et al.'s (1995) algorithm. This hydrological mass redistribution will also cause geocenter motion and changes in Earth's gravitational field, which are similarly computed using the same data sets. Corresponding geodynamic effects due to the oceanic mass transports (i.e. oceanic angular momentum and ocean-induced geocenter/gravity changes) have also been computed in a similar manner. We here compare two independent sets of the result from: (1) non-steric ocean surface topography observations based on Topex/Poseidon, and (2) the model output of the mass field by the Parallel Ocean Climate Model. Finally, the hydrological and the oceanic time series are combined in an effort to better explain the observed non-atmospheric effects. The latter are obtained by subtracting the atmospheric angular momentum from Earth rotation observations, and the atmosphere- induced geocenter/gravity effects from corresponding geodetic observations, both using the above-mentioned atmospheric data sets.

Chao, Benjamin F.↗
NASA NTRS1991

The temperature of the circumstellar envelope of Alpha Orionis

The processes that heat and cool the circumstellar envelope of Alpha Ori are analyzed and the temperature calculated as a function of distance from the star. Cooling by fine structure lines is included for the first time in a general way in the theory of the thermal balance of a circumstellar envelope. Adiabatic cooling, dust-drag heating, and various line coolants contribute in the outer envelope, whereas the fine structure lines of O I and Si II and adiabatic cooling are dominant in the inner envelope. The rotational levels of CO cool the gas only at very small and at very large distances; elsewhere they provide a small amount of heating. The temperature declines very rapidly at first and then varies roughly as r exp -1/2 in the outer envelope. At very large distances, the temperature distribution flattens out due to photoelectron heating and reaches a minimum of about 4 K at about 250 arcsec.

Rodgers, Bernadette↗
NASA NTRS2001

Spinning Rocket Simulator Turntable Design

Contained herein is the research and data acquired from the Turntable Design portion of the Spinning Rocket Simulator (SRS) project. The SRS Project studies and eliminates the effect of coning on thrust-propelled spacecraft. This design and construction of the turntable adds a structural support for the SRS model and two degrees of freedom. The two degrees of freedom, radial and circumferential, will help develop a simulated thrust force perpendicular to the plane of the spacecraft model while undergoing an unstable coning motion. The Turntable consists of a ten-foot linear track mounted to a sprocket and press-fit to a thrust bearing. A two-inch high column grounded by a Triangular Baseplate supports this bearing and houses the slip rings and pressurized, air-line swivel. The thrust bearing allows the entire system to rotate under the moment applied through the chain-driven sprocket producing a circumferential degree of freedom. The radial degree of freedom is given to the model through the helically threaded linear track. This track allows the Model Support and Counter Balance to simultaneously reposition according to the coning motion of the Model. Two design factors that hinder the linear track are bending and twist due to torsion. A Standard Aluminum "C" channel significantly reduces these two deflections. Safety considerations dictate the design of all the components involved in this project.

Miles, Robert W.↗
NASA NTRS1990

Balanced-Bridge Feedback Control Of Motor

Sensitivity to variations in electrical and mechanical characteristics reduced. Proposed control system for motor-driven rotary actuator includes three nested feedback loops which, when properly designed, decoupled from each other. Intended to increase accuracy of control by mitigating such degrading effects as vibrations and variations in electrical and mechanical characteristics of structure rotated. Lends itself to optimization of performance via independent optimization of each of three loops. Includes outer, actuator, and driver feedback loops, configured so that actuator is subsystem, and driver is subsystem of actuator.

Lurie, Boris J.↗
NASA NTRS1988

Super magnets for large tunnels

The development and use of a large Magnetic Suspension and Balance System (MSBS) in wind tunnels is examined, discussing NASA-sponsored research to develop a large MSBS, and the 2 MSBS already in use. The MSBS holds the model in an arbitrary position in the wind tunnel test section and measures the forces and moments acting on the model. Technologies for building a large MSBS have been developed, and research is being done to reduce building costs. Magnetic suspension is advantageous because it completely eliminates interference from mechanical support systems such as stings or struts and it allows for easy rotation and translation of the model. Advances allowing operation at higher temperatures, probably using liquid nitrogen instead of liquid helium may reduce the cost of MSBS operation. A large MSBS would require power controllers with capacity up to 10 MW, efficiency approaching 98 percent and the ability to reverse the sign of both voltage and current. Technologies include the electro-magnetic position sensor, model positioning sensing, digital controller, and a precalibrated resistance strain-gage balance.

Boyden, Richmond P.↗
NASA NTRS1992

Inertial Oscillation of a Vertical Rotating Draft with Application to a Supercell Storm: Video Supplement to NASA-TP-3230

In this video (8 min., color, sound, VHS), animation depicts the inertial oscillation of a new mathematical model ('vertical rotating draft') for spinning up a single supercell storm. The oscillation consists of a long quiescent phase when the draft is large in diameter and rotates anticyclonically and a short intense phase when the draft is small and cyclonic. During the intense phase, the rotating draft resembles a supercell. The physical basis for the oscillation is depicted by tracking air parcels in the draft as they move along inertial circles (projected on a horizontal plane), where the horizontal pressure gradient is zero and the Coriolis force balances the centrifugal force. A side view of the oscillation shows that contraction and expansion are linked, respectively, to buoyantly driven compressible downdraft and updraft. An aerial view tracks the draft as it moves above the surface of the Earth and turns to the right during the intense phase. Radar echoes from a supercell storm are superimposed for comparison. The data appear to support only the intense phase. A critical experiment would measure the predominantly downward flow that theoretically occurs before the right turn in a supercell track and causes contraction and spin-up.

Supercell thunderstorm↗
NASA NTRS1985

Generation, modulation and reception of orthogonally polarized signals

The radiating electromagnetic field of a dipole antenna is considered. By allowing the dipole to rotate about its midpoint, one can construct an entire set of signal polarizations wherein distinct members of the set are mutually orthogonal. It is shown how these signals can be modulated and demodulated to convey information. These ideas are then generalized, and both balanced, as well as unbalanced quadrapole modulations are defined. Methods of receiver synchronization to such signals are described, as well as their potential application to multiple access and anti-jam communications.

Lesh, J. R.↗
NASA NTRS1983

Comparison of CARS combustion temperatures with standard techniques

This paper describes a comparative study of temperatures measured with Coherent Anti-Stokes Raman Spectroscopy (CARS) and those using standard measurement techniques. CARS temperatures from nitrogen vibrational-rotational spectra have been obtained in a premixed hydrogen-air laboratory flame supported on a flat flame burner over a temperature range from about 1000 K to 2100 K. The techniques used for comparison were sodium line reversal, thin wire thermocouples and heat balance calculations. These studies show a good agreement over the entire temperature range studied.

Antcliff, R. R.↗
NASA NTRS1998

Mechanistic Models of Friction Stir Welding

Friction stir welding is a welding process developed at The Welding Institute (TWI) in England. The method uses very large strain plastic deformation of the material to join two pieces of metal together. The material is deformed using a tool which is forced between the two pieces which rotates causing a bond. Beyond this, very little is actually known although many people working in the field are willing to speculate on the detailed mechanisms involved. Some measurements made using sacrificial thermocouples at the weld joint indicate that the maximum temperature during the weld process is on the order of 370C - well below the melting temperature of the material. However, at this temperature, the material properties are highly temperature dependent, and the yield stress is approximately an order of magnitude less at this temperature than it is at room temperature. As expected, there are many interpretations of the physical mechanisms occurring during the weld process. Although there is very little published concerned with FSW, some of the anecdotal theories will be described. One describes the primary mechanism as frictional heating at the front of the tool caused by slip between the tool and the material. At elevated temperatures, the weld material becomes soft and deforms around the tool but not essentially altered by the tool rotation, similar to an extrusion. As the material meets again at the rear of the tool, the temperatures and pressures are sufficient to cause the material to bond. All other structures seen are secondary and unimportant. Another theory examined last summer at NASA's Marshall Space Flight Center (MSFC) was that there was no slip between the tool and the material resulting in a rotating mass of plastic weld material traveling at a variety of angular velocities - the greatest at the tool surface diminishing to zero at the outer edge of the plastic mass surrounding the tool. This conceptual model was followed by simplified calculations which showed that the balance of moments through the weld plug was not possible under steady state conditions and realistic temperature profiles. This led to some consideration of a quasi-steady oscillating process. Later when force measurements became available some models were modified and new ones were proposed.

Stewart, Michael B.↗
NASA NTRS2000

Singular Isothermal Disks and the Formation of Multiple Stars

A crucial missing ingredient in previous theoretical studies of fragmentation is the inclusion of dynamically important levels of magnetic fields. As a minimal model for a candidate presursor to the formation of binary and multiple stars, we therefore consider the equilibrium configuration of isopedically magnetized, scale-free, singular isothermal disks, without the assumption of axial symmetry. We find that lopsided (M = 1) configurations exist at any dimensionless rotation rate, including zero. Multiple-lobed (M = 2, 3, 4, ...) configurations bifurcate from an underlying axisymmetric sequence at progressively higher dimensionless rates of rotation, but such nonaxisymmetric sequences always terminate in shockwaves before they have a chance to fission into separate bodies. We advance the hypothesis that binary and multiple star-formation from smooth (i.e., not highly turbulent) starting states that are supercritical but in unstable mechanical balance requires the rapid (i.e., dynamical) loss of magnetic flux at some stage of the ensuing gravitational collapse.

Galli, Daniele↗
NASA NTRS1980

The effects of leading edge modifications on the post-stall characteristics of wings

An investigation of the effects of leading edge modifications on the post-stall characteristics of two rectangular planform wings in a series of low speed wind tunnel tests is presented. Abrupt discontinuities in the leading edge shape of the wings were produced by placing a nose glove over a portion of the span or by deflecting sections of a segmented leading edge flap. Six component balance data, oil flow visualization photographs, and pressure distribution measurements were obtained, and tests made to study the development of flow separation at stall on small scale planform wing models. Results of oil flow visualization tests at and beyond stall showed the formation of counter-rotating swirl patterns on the upper surface of the '2-D' and '3-D' wings, and results of a numerical lifting line technique applied to wings with leading edge modifications are included.

Winkelmann, A. E.↗
NASA NTRS1972

Rocket ascent G-limited moment-balanced optimization program (RAGMOP)

This document describes the RAGMOP (Rocket Ascent G-limited Momentbalanced Optimization Program) computer program for parametric ascent trajectory optimization. RAGMOP computes optimum polynomial-form attitude control histories, launch azimuth, engine burn-time, and gross liftoff weight for space shuttle type vehicles using a search-accelerated, gradient projection parameter optimization technique. The trajectory model available in RAGMOP includes a rotating oblate earth model, the option of input wind tables, discrete and/or continuous throttling for the purposes of limiting the thrust acceleration and/or the maximum dynamic pressure, limitation of the structural load indicators (the product of dynamic pressure with angle-of-attack and sideslip angle), and a wide selection of intermediate and terminal equality constraints.

Lyons, J. T.↗
NASA NTRS1995

Critical radiation fluxes and luminosities of black holes and relativistic stars

The critial luminosity at which the outward force of radiation balances the inward force of gravity plays an important role in many astrophysical systems. We present expressions for the radiation force on particles with arbitrary cross sections and analyze the radiation field produced by radiating matter, such as a disk, ring, boundary layer, or stellar surface, that rotates slowly around a slowly rotating gravitating mass. We then use these results to investigate the critical radiation flux and, where possible, the critical luminosity of such a system in genral relativity. We demonstrate that if the radiation source is axisymmetric and emission is back-front symmetric with repect to the local direction of motion of the radiating matter, as seen in the comoving frame, then the radial component of the radiation flux and the diagonal components of the radiation stress-energy tensor outside the source are the same, to first order in the rotation rates, as they would be if the radiation source and gravitating mass were not rotating. We argue that the critical radiation flux for matter at rest in the locally nonrotating frame is often satisfactory as an astrophysical benchmark flux and show that if this benchmark is adopted, many of the complications potentially introduced by rotation of the radiation source and the gravitating mass are avoided. We show that if the radiation field in the absence of rotation would be spherically symmetric and the opacity is independent of frequency and direction, one can define a critical luminosity for the system that is independent of frequency and direction, one can define a critical luminosity for the system that is independent of the spectrum and angular size of the radiation source and is unaffected by rotation of the source and mass and orbital motion of the matter, to first order. Finally, we analyze the conditions under which the maximum possible luminosity of a star or black hole powered by steady spherically symmetric radial accretion is the same in general relativity as in the Newtonian limit.

Lamb, Frederick K.↗
NASA NTRS1992

Electron impact cross-sections and cooling rates for methane

Energy transfer between electrons and methane gas by collisional processes plays an important role in the thermal balance of electrons in the atmospheres and ionospheres of planets and satellites in the outer solar system. The literature is reviewed for electron impact cross-sections for methane in this paper. Energy transfer rates are calculated for elastic and inelastic processes using a Maxwellian electron distribution. Vibrational, rotational, and electronic excitation and ionization are included. Results are presented for a wide range of electron temperatures and neutral temperatures.

Gan, L.↗
NASA NTRS1999

Middle Atmosphere Transport Properties of Assimilated Datasets

One of the most compelling reasons for performing data assimilation in the middle atmosphere is to obtain global, balanced datasets for studies of trace gas transport and chemistry. This is a major motivation behind the Goddard Earth observation System-Data Assimilation System (GEOS-DAS). Previous studies have shown that while this and other data assimilation systems can generally obtain good estimates of the extratropical rotational velocity field, the divergent part of the dynamical field is deficient; this impacts the "residual circulation" and leads to spurious trace gas transport on seasonal and interannual timescales. These problems are impacted by the quality and the method of use of the observational data and by deficiencies in the atmospheric general circulation model. Whichever the cause at any place and time, the "solution" is to introduce non-physical forcing terms into the system (the so-called incremental analysis updates); these can directly (thermal) or indirectly (mechanical) affect the residual circulation. This paper will illustrate how the divergent circulation is affected by deficiencies in both observations and models. Theoretical considerations will be illustrated with examples from the GEOS-DAS and from simplified numerical experiments. These are designed to isolate known problems, such as the inability of models to sustain a quasi-biennial oscillation and sparse observational constraints on tropical dynamics, or radiative inconsistencies in the presence of volcanic aerosols.

Pawson, Steven↗
NASA NTRS1999

Middle Atmospheric Transport Properties of Assimilated Datasets

One of the most compelling reasons for performing data assimilation in the middle atmosphere is to obtain global, balanced datasets for studies of trace gas transport and chemistry. This is a major motivation behind the Goddard Earth observation System-Data Assimilation System (GEOS-DAS). Previous studies have shown that while this and other data assimilation systems can generally obtain good estimates of the extratropical rotational velocity field, the divergent part of the dynamical field is deficient; this impacts the "residual circulation" and leads to spurious trace gas transport on seasonal and interannual timescales. These problems are impacted by the quality and the method of use of the observational data and by deficiencies in the atmospheric general circulation model. Whichever the cause at any place and time, the "solution" is to introduce non-physical forcing terms into the system (the so-called incremental analysis updates); these can directly (thermal) or indirectly (mechanical) affect the residual circulation. This paper will illustrate how the divergent circulation is affected by deficiencies in both observations and models. Theoretical considerations will be illustrated with examples from the GEOS-DAS and from simplified numerical experiments. These are designed to isolate known problems, such as the inability of models to sustain a quasi-biennial oscillation and sparse observational constraints on tropical dynamics, or radiative inconsistencies in the presence of volcanic aerosols.

Pawson, Steven↗
NASA NTRS1994

Maneuver Performance Enhancement for an Advanced Fighter/Attack Aircraft

A small scale wind tunnel test of a realistic fighter configuration has been completed in NASA Ames' 7'x10' wind tunnel. This test was part of the Fighter Lift and Control (FLAC) program, a joint NASA - USAF research program, involving small and large-scale wind-tunnel tests and computational analysis of unique lift augmentation and control devices. The goal of this program is to enhance the maneuver and control capability of next-generation Air Force multi-role fighter aircraft with low-observables geometries. The principal objective of this test was to determine the effectiveness of passive boundary layer control devices at increasing L/D at sustained maneuver lift coefficients. Vortex generators (VGs) were used to energize the boundary layer to prevent or delay separation. Corotating vanes, counter-rotating vanes, and Wheeler Wishbone VGs were used in the vicinity of the leading and trailing edge flap hinge lines. Principle test parameters were leading and trailing edge flap deflections, and location, size, spacing, and orientation for each VG type. Gurney flaps were also tested. Data gathered include balance force and moment data, surface pressures, and flow visualization for characterizing flow behavior and locating separation lines. Results were quite different for the two best flap configurations tested. All VG types tested showed improvement (up to 5%) in maneuver L/D with flaps at LE=20 degrees, TE=0 degrees. The same VGs degraded performance, in all but a few cases, with flaps at LE=15 degrees, TE=10 degrees.

Samuels, Jeff↗