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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 1,027 records · Page 57
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

Analysis of short pulse laser altimetry data obtained over horizontal path

Recent pulsed measurements of atmospheric delay obtained by ranging to the more realistic targets including a simulated ocean target and an extended plate target are discussed. These measurements are used to estimate the expected timing accuracy of a correlation receiver system. The experimental work was conducted using a pulsed two color laser altimeter.

Im, K. E.↗
NASA NTRS1984

Horizontal energy propagation in a baroclinic atmosphere with meridional and zonal structure

A baroclinic model was developed. The model is linear, steady state, baroclinic (2 level) and based on the primitive equations. The unique features of the model are: (1) The basic state u and T fields are functions of wavelength, theta, and rho, (2) A mean meridional circulation v, w, which may be a function of wavelength, theta, and rho, and p may be included, (3) Dissipation may be a function of theta, wavelength, rho, p (e.g., differ over land and sea). Because the basic state is a function of longitude, the equations are not separable in wavelength and the usual semi-spectral solution procedure is not applicable. The model solutions can be found in a straight forward (brute force) way by discretizing the model equations directly on a wavelength, theta, rho, p grid. There are six dependent (perturbation) variables: u, v, and geopotential at levels 1 and 2. The thermal forcing is prescribed at the intermediate vertical level. The linearized equations may be written.

Youngblut, C.↗
NASA NTRS1983

Techniques for measurement of vertical and horizontal velocities: Monostatic versus bistatic measurements

Three techniques of direct measurement are presented from which velocities may be obtained: (1) Doppler frequency shift, (2) spaced antenna drift, (3) spatially modulated transverse beam measurements. Emphasis is placed on the Doppler frequency measurement approach. It will compare bistatic with monostatic configurations as regards received power (or sensitivity), spatial resolution, Doppler shift and avoidance of ground clutter.

Waterman, A. T.↗
NASA NTRS1985

Sound propagation studies for a large horizontal axis wind turbine

Systematic noise measurements in three directions with respect to the wind vector, over a range of distances to 1050 m, over a range of frequencies from 8 Hz to 2000 Hz, and for a stable wind turbine noise source (WTS-4) in windy conditions (V = 9.4 to 13.0 m/s) are presented. At frequencies above 63 Hz in the downwind and crosswind directions the sound pressure levels decay with distance according to predictions based on atmospheric absorption and spherical spreading, assuming no excess attenuation due to ground effects. In the upwind direction there is excess attenuation due to an acoustic shadow zone. The assumption of a distributed noise source leads to better noise estimates in the upwind direction. For very low frequencies 8 to 16 Hz no excess attenuation was observed in the upwind direction at distances up to 1050 m and a sound pressure level decay rate of approximately 3 dB per doubling of distance was observed in the downwind direction.

Shepherd, K. P.↗
NASA NTRS1985

Results of a search for monopoles and tachyons in horizontal cosmic ray flux

A search for monopoles and tachyons at ground level was carried out using an arrangement consisting of an ionization calorimeter and two hodoscope detectors. No clear evidence for these particles was obtained. The flux of monopoles with velocities beta approximately 0.01 is found to be less than 5.1 x 10 to the minus 13th power square centimeters s(-1) sr(-1) (95% cl.). The upper limit on the tachyon flux density is set as a 6 x 10 the minus 9th power particle/square centimeter event.

Ashitkov, V. D.↗
NASA NTRS1986

Sensing Horizontal Heading in Aircraft Maneuvers

Modified gyroscopic system indicates geographic heading even in nearly vertical flight. Gyroscopes and gimbals of system assume this configuration when aircraft has pitched into vertical dive. Outer roll gimbal fixed with respect to aircraft frame in this orientation. Now, azimuth signal in modified system indicates what aircraft heading would be if it were to resume level flight from climb or dive.

Cowdin, K. T.↗
NASA NTRS1987

Performance and aerodynamic braking of a horizontal-axis wind turbine from small-scale wind tunnel tests

Wind tunnel tests of three 20" diameter, zero twist, zero pitch wind turbine rotor models were conducted in a 7' x 10' wind tunnel to determine the performance of such rotors with NACA 23024 and NACA 64 sub 3-621 airfoil sections. Aerodynamic braking characteristics of a 38% span, 30% chord, vented aileron configuration were measured on the NACA 23024 rotor. Surface flow patterns were observed using fluorescent mini-tufts attached to the suction side of the rotor blades. Experimental results with and without ailerons are compared to predictions using airfoil section data and a momentum performance code. Results of the performance studies show that the 64 sub 3-621 rotor produces higher peak power than the 23024 rotor for a given rotor speed. Analytical studies, however, indicate that the 23024 should produce higher power. Transition strip experiments show that the 23024 rotor is much more sensitive to roughness than the 64 sub 3-621 rotor. These trends agree with analytical predictions. Results of the aileron test show that this aileron, when deflected, produces a braking torque at all tip speed ratios. In free wheeling coastdowns the rotor blade stopped, then rotated backward at a tip speed ratio of -0.6.

Cao, H. V.↗
NASA NTRS1987

Elemental abundance analyses with coadded DAO spectrograms. I - The field horizontal-branch stars HD-64488, 109995 and 161817

It is possible to improve the quality of elemental-abundance analyses by using higher-S/N data than has been the practice at high resolution. The procedures developed at the Dominion Astrophysical Observatory to coadd high-dispersion coude spectrograms are used with a minimum of 10 6.5-A/mm IIa-O spectrograms of each of three field hoorizontal-branch (FHB) A stars to increase the S/N of the photographic data over a considerable wavelength region. Fine analyses of the sharp-lined prototype FHB stars HD 109995 and 161817 show an internal consistency which justifies this effort. Their photospheric elemental abundances are similar to those of Population II globular cluster giants. As their photometric and spectrophotometric properties are similar to blue HB stars in such clusters, they are confirmed to be the brighter analogs of such stars. HD 64488, which is photometrically and spectrophotometrically similar to the FHB stars, is found to be metal-poor (Fe/H = -1) with much broader lines (v sin i = 147 km/s). The implications of the abundance anomalies of all three stars are discussed.

Adelman, Saul J.↗
NASA NTRS1987

The effect of increased horizontal resolution on GLA Fourth Order model forecasts

A benchmark series of ten-day weather forecasts has been run with the GLA Fourth Order GCM with both a 4 deg latitude by 5 deg longitude resolution and a 2 deg latitude by 2.5 deg longitude resolution. Ensemble statistics of forecast skill and maps of systematic error fields have been generated for both resolutions. The enhanced resolution added 24 hours of useful predictive skill to the sea level pressure forecasts and 6 hours to the 500 mb height forecasts, but 5 to 6 days into the forecasts the advantage of the finer resolution was lost. The systematic error fields showed that by 8 days the 'climate drift' of the 2 x 2.5 deg forecasts had become pronounced and had caused the loss of predictive skill relative to the 4 x 5 deg forecasts. Additional results indicate that a gravity wave drag parameterization scheme might alleviate the climate drift problem.

Helfand, H. M.↗
NASA NTRS1988

Onset of finger convection in a horizontal porous layer underlying a fluid layer

The problem of the onset of finger convection in a porous layer underlying a fluid layer is considered using linear stability analysis. The linear stability equations for the porous layer are formulated for temperature and salinity gradients existing in both layers. The eigenvalue problem is solved by a shooting method. The solution method and associated computer program are validated by comparison with the results of Sun (1973) for the thermal convection case. Results are also presented for the onset of salt-finger convection.

Chen, F.↗
NASA NTRS1988

Numerical modeling of chemical vapor deposition (CVD) in a horizontal reactor

In the present numerical prediction of the deposition rate of silicon from silane in a CVD process, the conservation equations for mass, momentum, energy, and chemical species are solved on a staggered grid using the SIMPLE algorithm, while the rate of chemical reactions in the gas phase and on the susceptor surface is obtained from an Arrhenius rate equation. Predicted deposition rates as a function of position along the susceptor with and without the gas phase chemical reaction are compared with the available experimental and numerical data; agreement is excellent except at the leading edge of the susceptor, where the deposition rate is overpredicted.

Sheikholeslami, M. Z.↗
NASA NTRS1988

Eulerian measurements of horizontal accelerations in shoaling gravity waves

Laboratory and field measurements of suspended sediment in the nearshore suggest that fluid accelerations are an important factor in sediment transport by oscillatory waves. Here, Eulerian accelerations of the cross-shore velocity are calculated from measurements of velocity obtained by an array of bottom-mounted electromagnetic flow meters spanning a natural surf zone. Large shoreward accelerations of brief duration are associated with the steep front faces of both near-breaking and breaking waves. Weaker offshore accelerations of longer duration occur during passage of the more gently sloped rear faces. The acceleration field is thus strongly skewed in the shoreward direction. Power spectra and bispectra indicate, as expected, that statistics of the acceleration field are significantly influenced by high-frequency motions but are rather insensitive to surf beat.

Elgar, Steve↗
NASA NTRS1987

Linear quadratic regulators with eigenvalue placement in a horizontal strip

A method for optimally shifting the imaginary parts of the open-loop poles of a multivariable control system to the desirable closed-loop locations is presented. The optimal solution with respect to a quadratic performance index is obtained by solving a linear matrix Liapunov equation.

Shieh, Leang S.↗