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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 631 records · Page 35
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

A mathematical model of a single main rotor helicopter for piloted simulation

A mathematical model, suitable for piloted simulation of the flying qualities of helicopters, is a nonlinear, total force and moment model of a single main rotor helicopter. The model has ten degrees of freedom: six rigid body, three rotor flapping, and the rotor rotational degrees of freedom. The rotor model assumes rigid blades with rotor forces and moments radially integrated and summed about the azimuth. The fuselage aerodynamic model uses a detailed representation over a nominal angle of attack and sideslip range of + or - 15 deg., as well as a simplified curve fit at large angles of attack or sideslip. Stabilizing surface aerodynamics are modeled with a lift curve slope between stall limits and a general curve fit for large angles of attack. A generalized stability and control augmentation system is described. Additional computer subroutines provide options for a simplified engine/governor model, atmospheric turbulence, and a linearized six degree of freedom dynamic model for stability and control analysis.

Talbot, P. D.↗
NASA NTRS1990

Supernova remnants and diffuse ionized gas in M31

Researchers have compiled an initial list of radio/optical supernova remnants (SNRs) in M31, by searching for radio identifications of emission-line sources with a high (SII)/H alpha ratio (greater than 0.60). The (SII) filter included both sulfur lines and the H alpha filter did not include (NII). This search revealed 11 SNRs, of which only two were known. In addition, researchers detected radio emission from 3 SNRs that were identified in previous optical surveys (D'Odorico et al., 1980), but that were outside the charge coupled device (CCD) fields. The 14 objects only include the most obvious candidates, but a full search is in progress and the researchers expect to find several more SNRs. Also not all optical SNRs show detectable radio emission and a pure optical list of SNR candidates based only on the ratio of (SII)/H alpha emission contains many more objects. Two conclusions are apparent. First, the radio properties of the SNRs in M31 are quite similar to those of Galactic SNRs as is illustrated. The brightnesses are not systematically lower as has been suggested in the past (Dickel and D'Odorico, 1984). Second, the slope of the relation is close to -2; this slope is expected from the intrinsic dependence between surface brightness and diameter. The radio luminosity of the SNRs does not seem to depend strongly on diameter, or age, contrary to model predictions. Selection effects, however, play an important role in these plots. The CCD images show widespread diffuse ionized gas with a ratio of (SII)/H alpha that is higher than that of discrete HII regions. Discrete HII regions typically show ratios between 0.2 to 0.3, while the diffuse gas in the arms consistently shows ratios of 0.5. Researchers can trace this gas across the spiral arms to emission measures below 5 pc cm (-6). Its properties seem to be similar to that of the diffuse gas in the solar neighborhood.

Walterbos, Rene↗
NASA NTRS1958

The measured and estimated rotary stability derivatives of the X-15 airplane

Measurements of the rotary derivatives of the X-15 aircraft were made in several of the wind tunnels of the National Advisory Committee for Aeronautics. The speed range was from landing speed up to Mach number, 3.5. The measurements were made on the steady-state, forced-oscillation equipment. The apparatus measures the rotary derivatives during small-amplitude, single-degree-of-freedom oscillations. In this paper the results of the wind-tunnel tests are compared with the values of the rotary derivatives estimated by the available procedures. Whenever possible, the results of wind-tunnel measurements of the static forces and moments on the X-15 have been utilized in the estimation procedures to obtain lift-curve slopes and centers of pressure of the tail surfaces. In this way, at least a partial account is taken of the effects of the fuselage and wing downwash and pressure field on the tail surfaces.

Tinling, Bruce↗
NASA NTRS1994

Gripping System For Mechanical Testing Of Composites

Specimens held without slippage, even at high temperatures. Improved gripping system designed to securely hold ends of specimen of composite material during creep or tensile test. Each grip includes pair of wedges having sharply corrugated gripping surfaces. Wedges held between two plates containing cavities sloped to accommodate wedges. Two such grips (one for each end) holds specimen in furnace connected to tensile test machine for creep measurements.

Mackay, Rebecca A.↗
NASA NTRS1993

Observations of topographic planetary waves in the Bering Slope Current using the Geosat altimeter

Topographic planetary waves associated with the downstream leg of the Bering Slope Current are observed in measurements of sea surface height anomalies acquired by the Geosat altimeter during 1987 and 1988 The waves are most prominent from May to August 1987, during which time the estimated wave period and wavelength are about 72 days and 103 km, respectively. The direction of propagation is roughly north-northeast.

Okkonen, Stephen R.↗
NASA NTRS2002

Constrained Aerothermodynamic Design of Hypersonic Vehicles

An investigation was conducted into possible methods of incorporating a hypersonic design capability with aerothermodynamic constraints into the CDISC aerodynamic design tool. The work was divided into two distinct phases: develop relations between surface curvature and hypersonic pressure coefficient which are compatible with CDISC's direct-iterative design method; and explore and implement possible methods of constraining the heat transfer rate over all or portions of the design surface. The main problem in implementing this method has been the weak relationship between surface shape and pressure coefficient at the stagnation point and the need to design around the surface blunt leading edge where there is a slope singularity. The final results show that some success has been achieved, but further improvements are needed.

Gally, Tom↗
NASA NTRS2008

MISSE Results Used for RF Plasma Ground Testing-To-Space-Exposure Correlation for Coated Kapton

The ability to predict the durability of materials in the low Earth orbit (LEO) environment by exposing them in ground-based facilities is important because one can achieve test results sooner, expose more types of materials, and do it much more cost effectively than to test them in flight. However, flight experiments to determine the durability of groups or classes of materials that behave similarly are needed in order to provide correlations of how much time in ground-based facilities represents certain durations in LEO for the material type of interest. An experiment was designed and flown on the Materials International Space Station Experiment (MISSE) 2 (3.95 yr in LEO) and MISSE 4 (1.04 yr in LEO) in order to develop this type of correlation between ground-based RF plasma exposure and LEO exposure for coated Kapton. The experiment consisted of a sample of Kapton H (DuPont) polyimide coated with 1300 of silicon dioxide by Sheldahl, Inc. The samples were exposed to atomic oxygen in a radio frequency (RF) generated atomic oxygen plasma. Mass change was measured for the samples and then the same samples were exposed in flight on MISSE and the mass change was again recorded post-flight. After documentation, the samples were exposed again in the ground-based RF plasma in order to determine if the erosion would be the same as it had been in the same facility pre-flight which would indicate whether or not the sample had been damaged during flight and if the defects on the surface were those that were there preflight. The slopes of the mass change versus fluence plots were then used to develop a correlation factor that can be used to help predict the durability of coated Kapton in ground-based isotropic atomic oxygen plasma systems. This paper describes the experiment and presents the correlation factor results.

Miller, Sharon K. R.↗
NASA NTRS1986

A comparison of the regional slope characteristics of Venus and earth - Implications for geologic processes on Venus

The range of 3 degree by 3 degree regional slopes of the Earth and Venus is similar (approximately 0.0-2.4 degrees), although the surface distribution of these values differs significantly. On earth, cratonic and abyssal plains form extensive regions of 0.0 degree slope. Within these regions a variety of features (mid-ocean ridges, volcanic island chains, subduction zones, and floded mountains) have regional slope characteristics influenced by seafloor spreading and plate recycling, as well as an active weathering regime. The plains provinces of Venus are much more rugged than earth's plains and are marked by numerous closely spaced circular and linear features (0.1-0.2 degree regional slope) concentrated into broad linear zones of global extent. Although Venus highlands are bounded by narrow zones of relatively steep slope, the margins of Aphrodite Terra and Beta Regio are not as steep as earth's continental margins and appear to be best developed parallel to the trends of major chasmata within these regions. Ishtar Terra's margins are significantly steeper and more continuous than other highland margins and are comparable to passive margins on earth. The Venus highlands do not contain appreciable smooth, flat interior regions, implying that highland topography is not significantly modified by erosion or deposition.

Sharpton, V. L.↗
DOE OSTI2016

Room-temperature Fe{sup 2+}:ZnS single crystal laser pumped by an electric-discharge HF laser

A room-temperature laser based on a Fe{sup 2+}:ZnS single crystal has been studied. The crystal was pumped by a nonchain electric-discharge HF laser with a light pulse FWHM of ∼140 ns. The pump spot diameter on the crystal surface (d) varied from 3.9 to 11.6 mm. The slope efficiency at these values of d was 37% – 39 %, respectively. The maximum laser energy was 380 mJ (at d=11.6 mm) with the total efficiency with respect to the absorbed pump energy of ∼19%. A further increase in the laser energy was not achieved because the crystal was destroyed at an incident pump energy and power of 3.4 J and ∼24 MW, respectively. The damaged region has a form of a long narrow channel shifted from the entrance surface inside the active element. (lasers)

42 ENGINEERING↗
NASA NTRS1985

Transformation of Polar Ice Sublimate Residue into Martian Circumpolar Sand

The experimental demonstration that a credible Martian sand may be formed from dust-bearing ice provides a new set of possible explanations for some of the observed Martian aeolian landforms. It is hypothesized that a light-weight fluffy rind is formed on the polar caps. This could provide material easily entrainable by Martian winds, which generally blow equatorward from the poles. These winds would peel the fluffy rind from the surface of the sublimating summer polar caps and from the equatorward slopes of the polar troughs. These pieces of material would then be rolled into lumps (of high sailarea/mass ratio) by the wind. They would become pigmented as they saltate across the surface, perhaps gathering carbonaceous meteoritic dust or other impurities on their surfaces, or through chemical reactions with the ice-free environment away from their point of origin. Once they became trapped in topographic wind shadows, they would form dune structures because they are hydraulically equivalent to sand particles.

Saunders, R. S.↗
NASA NTRS1992

Characterization of Martian near-subsurface materials by determination of cohesion and angle of internal friction

Back-analysis (reconstruction) of the stability of thirty avalanche chutes was performed in the very limited areas where high resolution imaging overlapped with available 1:500 K topographic map coverage. A new technique was developed to incorporate the third dimension (width) of an avalanche chute in stability back-analysis in order to yield unambiguous values of cohesion and angle of internal friction. The procedure is based upon extending the ordinary method of slices to three dimensions, in order to construct avalanche chute cross-sections whose widths and depths vary as a function of gradient, gravity, density of material, and phi and c. Applying the technique to the well documented slide at Lodalen, Norway as a test produces excellent correspondence with reality. Generally, the technique reveals that the width:depth ratio of any avalanche chute decreases with increasing contrast between the average slope angle and the angle of internal friction. Applying this technique to the martian avalanche chute yields results consistent with indications from earlier work, but with greater certainty. Values of cohesion and angle of internal friction identify the materials at the time of failure as moderately cohesive debris. If Sharp's identification of these features as avalanche chutes is correct, then the results here imply that weathering processes have had a significant effect to depths of tens of meters (where failure has occured) below the martian surface. It is also implied that on relatively steep slopes within Valles Marineris, sizable, unaltered, unmantled bedrock exposures for high resolution spectral and spatial scanning by Mars Observer may be scarce.

Sullivan, R. J.↗
NASA NTRS1979

Laminar and turbulent flows over spherically blunted cone and hyperboloid with massive surface blowing

Numerical solutions are presented for the flow over a spherically blunted cone and hyperboloid with massive surface blowing. Time-dependent viscous shock-layer equations are used to describe the flow field. The boundary conditions on the body surface include a prescribed blowing-rate distribution. The governing equations are solved by a time-asymptotic finite-difference method. Results presented here are only for a perfect gas-type flow at zero angle of attack. Both laminar and turbulent flow solutions are obtained. It is found that the effect of the surface blowing on the laminar flow field is to smooth out the curvature discontinuity at the sphere-cone juncture point, which results in a positive pressure gradient over the body. The shock slope increases on the downstream portion of the body as the surface blowing rate is increased. The turbulent flow with surface blowing is found to redevelop a boundary-layer-like region near the surface. The effects of this boundary-layer region on the flow field and heating rates are discussed.

Kumar, A.↗
NASA NTRS1979

Laminar and turbulent flows over a spherically blunted cone with massive surface blowing

Numerical solutions are presented for the flow over a spherically blunted cone with massive surface blowing. Time-dependent viscous shock layer equations are used to describe the flowfield. The boundary conditions on the body surface include a prescribed blowing rate distribution. The governing equations are solved by a time-asymptotic finite-difference method. Results presented here are only for a perfect gas-type flow at zero angle of attack. Both laminar and turbulent flow solutions are obtained. It is found that the surface blowing smooths out the effect of the curvature discontinuity at the sphere-cone juncture point on the laminar flowfield and results in a negative pressure gradient over the body. The shock slope increases on the downstream portion of the body as the surface blowing rate is increased. The turbulent flow with surface blowing is found to redevelop a boundary-layer-like region near the surface. The effects of this boundary-layer-like region on the flowfield and heating rates are discussed.

Kumar, A.↗
DOE OSTI2024

Sensitivities of the West Greenland Current to Greenland Ice Sheet Meltwater in a Mesoscale Ocean/Sea Ice Model

Abstract Meltwater from the Greenland Ice Sheet can alter the continental shelf/slope circulation and cross-shelf freshwater fluxes and limit deep convection in adjacent basins through surface freshening. We explore the impacts on the West Greenland Current and eastern Labrador Sea with different vertical distributions of the meltwater forcing. In this study, we present the results from global coupled ocean/sea ice simulations, forced with atmospheric reanalysis, that are mesoscale eddy-active (∼2–3-km horizontal spacing) and eddy-permitting (∼6–7-km horizontal spacing) in the study region. We compare the West Greenland Current in mesoscale eddy-active and eddy-permitting without meltwater to highlight the role of small-scale features. The mesoscale eddy-active configuration is then used to assess the change in the eastern Labrador Sea when meltwater is added to the surface or vertically distributed to account for mixing within fjords. In both simulations with meltwater, the West Greenland and West Greenland Coastal Currents are faster than in the simulation with no meltwater; their mean surface speeds are the highest in the vertical distribution case. In the latter case, there is enhanced baroclinic conversion at the shelf break compared to the simulation with no meltwater. When meltwater is vertically distributed, there is an increase in baroclinic conversion at the shelf break associated with increased eddy kinetic energy. In addition, in the eastern Labrador Sea, the salinity is lower and the meltwater volume is greater when meltwater is vertically distributed. Therefore, the West Greenland Current is sensitive to how meltwater is added to the ocean with implications for the freshening of the Labrador Sea. Significance Statement Our goal is to understand how the flux of freshwater across the West Greenland continental slope into the Labrador Sea is modified by meltwater from the Greenland Ice Sheet. We compare the simulations of the ocean that capture key dynamics along the West Greenland continental slope that have no meltwater, meltwater added to the ocean surface, and meltwater distributed vertically to represent the mixing within fjords. When meltwater is added, the currents along the continental slope are faster, with the greatest increase when meltwater is vertically distributed. In that case, there is enhanced freshening of the Labrador Sea because modified density gradients generate more eddies. Proper representation of the vertical structure of meltwater is important for projecting the impact of freshwater on the subpolar North Atlantic.

58 GEOSCIENCES↗
NASA NTRS1987

An interactive approach to surface-fitting complex geometries for flowfield applications

Numerical flowfield methods require a geometry subprogram which can calculate body coordinates, slopes, and radii of curvature for typical aircraft and spacecraft configurations. The objective of this paper is to develop a new surface-fitting technique which addresses two major problems with existing geometry packages: computer storage requirements and the time required of the user for the initial set-up of the geometry model. In the present method, coordinates of cross sections are fit in a least-squares sense using segments of general conic sections. After fitting each cross section, the next step is to blend the cross-sectional curve-fits in the longitudinal direction using general conics to fit specific meridional half-planes. For the initial setup of the geometry model, an interactive, completely menu-driven computer code has been developed to allow the user to make modifications to the initial fit for a given cross section or meridional cut. Graphic displays are provided to assist the user in the visualization of the effect of each modification. The completed model may be viewed from any angle using the code's three-dimensional graphics package. Geometry results for the modeling of the Space Shuttle and a proposed Aeroassist Flight Experiment (AFE) geometry are presented, in addition to calculated heat-transfer rates based on these models.

Dejarnette, Fred R.↗
NASA NTRS1986

The nearby Abell clusters. I - Abell 168

As part of a large program to study the spatial and luminosity distributions of galaxies in the nearby Abell clusters, the results of a photometric study of Abell 168 are presented and compared to the previous results of Dressler (1978). The previous result is confirmed that the faint end of the luminosity function for the galaxies in the central 0.2 sq deg of this cluster is quite flat (alpha = -1.0 in the Schechter formalism). The slope of the faint end appears to be fairly normal if galaxies from a larger region (1 sq deg) are included, but this may be due to a larger than expected contribution of background galaxies. Consequently, the faint end of the luminosity function of galaxies in a 0.2 sq deg region (and possibly also in a 1 sq deg region) centered on A168 is flatter than the 'universal' luminosity function (a Schechter function with alpha = -1.25). Nevertheless, the luminosity functions for both these regions are well fit by Schechter functions. A study of the spatial distribution of galaxies indicates that the radial dependence of the projected surface density is consistent with a power law of slope - 1.01 + or - 0.09.

Oegerle, W. R.↗
DOE OSTI2019

Chlorine evolution reaction electrocatalysis on RuO 2 (110) and IrO 2 (110) grown using molecular-beam epitaxy

Herein, we report the electrocatalysis of the chlorine evolution reaction (CER) on well-defined RuO 2 (110) and IrO 2 (110) surfaces. RuO 2 and IrO 2 are known for their capabilities to catalyze the CER. Until now, the CER measurements have only been reported on well-defined RuO 2 surfaces and only at high Cl - concentrations. We present the CER measurement and the role of Cl - at lower concentration on single-orientation RuO 2 (110) and IrO 2 (110) films. We find that RuO 2 (110) is two orders of magnitude more active than IrO 2 (110). Moreover, we observe the correlation between the CER activity and the O ad formation potential on RuO 2 and IrO 2 , supporting the prior suggestion that the O ad is the active site for the CER. We further use the reaction order analysis to support the Volmer-Heyrovsky mechanism of the CER, which was previously suggested from the Tafel slope analysis. Our finding highlights the importance of the surface O ad species on oxides for the CER electrocatalysis and suggests the electrochemical formation of Cl ad on O ad (for example, Cl - + O ad ↔ OCl ad + e - ) as the crucial step in the CER electrocatalysis.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗