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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 1,117 records · Page 62
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Simultaneous in situ measurements and diurnal variations of NO, NO2, O3, jNO2, CH4, H2O, and CO2 in the 40- to 26-km region using an open path tunable diode laser spectrometer

Simultaneous in situ measurements of temperature, pressure, and the NO, NO2, O3, jNO2, CH4, H2O, and CO2 concentrations were conducted in the 40- to 26-km region of the stratosphere using the JPL Balloon-borne Laser In Situ Sensor, a tunable diode laser absorption spectrometer. The NO, NO2, CH4, H2O, and CO2 concentration measurements generally show good agreement with previous observations, with a tendency for somewhat lower NO2 amounts. Measured O3 concentrations at 38 km agree well with comparable measurements from in situ UV photometers, but at 28 km they are lower by about 10 percent and agree more closely with the solar backscattered UV data. A decline was found in NO2 during the night over a 5-km altitude range, which implies either lower NO2 postsunset profiles, or an NO2 decay rate that is significantly higher than current model predictions that use N2O5 chemistry.

Webster, Christopher R.↗
NASA NTRS1988

Inhomogeneous conditions at open boundaries for wave propagation problems

Absorbing boundary conditions contain differential operators even for first-order systems. There is a fundamental difficulty with this, since the conditions are applied on the ingoing variables, and the approximations necessarily become weakly unstable. This difficulty is more pronounced for inhomogeneous boundary conditions which occur if there is a source outside the computational domain D, or if the initial data are nonzero outside D. In this paper this is further investigated and it is shown that reasonable estimates can still be obtained if the solution is smooth. However, it is demonstrated that the approximations are less robust. A cure for this is proposed and an implementation of high-order conditions for first-order systems is described.

Gustafsson, Bertil↗
NASA NTRS1987

Chromospheric activity in open clusters

Spectra of Ca II H and K are being taken for stars of similar mass in the Hyades, the Pleiades, and NGC 752. These spectra will be used to create indices of chromospheric activity on these stars. The dispersion in these indices will then be compared to model dispersions which take into account stellar inclination, position of active regions, and filling factor. Only a few observations have been made to date. These show that a high signal to noise is achievable over reasonable exposure times. Modeling has only just begun.

Pilger, E. J.↗
NASA NTRS1989

Completing the forward kinematic calibration of open loop manipulators when single point position sensors are used

Single-point sensors can measure the position of one point fixed to a manipulator's end effector. When single-point sensors have been used for calibration, it has not been possible to calibrate the orientation of the tool. Furthermore, it can be difficult to calibrate the sensor system. Results in the literature seldom provide a complete kinematic calibration of the manipulator. Presented here is a technique that enables single-point sensors to gather sufficient information to complete kinematic calibration. In addition, the method can reduce the burden of calibrating the sensor system.

Everett, Louis J.↗
NASA NTRS1988

Navier-Stokes calculations of transonic flows past open and transitional cavities

Computational simulations of deep and transitional cavities at transonic regimes were performed. The three-dimensional unsteady separation on the cavity floor was analyzed, and computational flow visualization inside the cavity was done. A parametric study was performed to investigate the effects of varying Mach number and the ratio delta/D, where delta is the instantaneous boundary layer thickness at the upstream lip and D is the depth. Both time-averaged and instantaneous solutions were obtained. Comparison of the solutions with experimental data were generally favorable; some discrepancies are explained.

Srinivasan, S.↗
NASA NTRS1989

Micromechanics of compression failures in open hole composite laminates

The local softening in the damage zone that precedes compression failures in laminates with holes was modeled using a Dugdale-type approach, and the calculated load to damage-size relationships were compared to the actual data obtained in two composite systems, AS4/PEEK and T2C145/F155, loaded to compression. The comparison indicates that the Dugdale model, which works well for metals, did not accurately predict the load-damage zone size relationship in these specimens. Possible reasons for the poor agreement are considered to be the fact that the constitutive relationship used in the Dugdale model is not an accurate description of material response in the crush zone, and the fact that the crush zone size is measured on the surface of the specimen, while this size is not an accurate indication of the actual crush zone size through the laminate.

Guynn, E. Gail↗
NASA NTRS1990

Results of aircraft open-loop tests of an experimental magnetic leader cable system for guidance during roll-out and turnoff

An experimental magnetic leader cable (MLC) system designed to measure aircraft lateral displacement from centerline and heading relative to centerline during rollout, turnoff, and taxi was tested at NASA's Wallops Flight Facility using NASA's Transport System Research Vehicle (TSRV), a modified B-737. The MLC system consisted of ground equipment that produced a magnetic field about a wire along runway centerline and airborne equipment that detected the strength and direction of this field and computed displacement and heading. Results of these tests indicate that estimates of aircraft displacement from centerline produced by the magnetic leader cable system using either of the two algorithms appear to be adequate for use by an automatic control system during rollout, turnoff, and taxi. Estimates of heading, however, are not sufficiently accurate for use, probably because of distortion of the magnetic field by the metal aircraft.

Bundick, W. Thomas↗
NASA NTRS1989

Large-scale cosmic microwave background anisotropies in isocurvature baryon open universe models

The large-angular-scale cosmic microwave background anisotropy is calculated in a low-density baryon-dominated universe with isocurvature primordial inhomogeneities. In models in which the initial power spectra of perturbations are steeper than white noise, predictions for the quadrupole moment of the anisotropy are found to be in conflict with existing observational limits, if the universe remained fully ionized and Compton drag inhibited growth of inhomogeneities until z = about 100. In order to lower the amplitude of the anisotropy, it is necessary to substantially prolong the duration of the growth phase of density perturbations, while smearing out fine-scale anisotropies, thereby requiring reionization to occur at a redshift smaller than 100, but larger than the redshift of the last scattering surface (in a reionized model).

Gorski, Krzysztof M.↗
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 NTRS1990

Reflector spillover loss of an open-ended rectangular and circular waveguide feed

An important and frequently used parameter in the design of a feed for a reflector antenna is the spillover loss. A set of spillover curves is presented for several common feeds, namely circular waveguides with TE11 or TE21 excitations, rectangular guides for the monopulse application, etc. The difference between two common methods of normalizing the feed input power is also discussed.

Lee, Shung WU↗
NASA NTRS1991

Ultrasonic Device Would Open Pipe Bombs

Piezoelectric ultrasonic transducer, energized by frequency generator and power supply, vibrates shell of pipe bomb while hardly disturbing explosive inner material. Frequency-control circuitry senses resonance in shell and holds generator at that frequency to induce fatigue cracking in threads of end cap. In addition to disarming bombs, ultrasonically induced fatigue may have other applications. In manufacturing, replaces some machining and cutting operations. In repair of equipment, cleanly and quickly disassembles corroded parts. In demolition of buildings used to dismember steel framework safely and controllably.

El-Raheb, Michael S.↗
NASA NTRS1990

Ionization processes in collisions of open-shell atoms. III - The autoionizing states of nitrogen

Results of a study of the energy spectra of electrons produced in collisions of N atoms with inert gases at low keV energies are reported. Ionization here is partly due to production of the (1Dnl) autoionizing states of nitrogen and partly due to another mechanism, which is presumably quasi molecular Auger ionization. A discussion of the assignments of the autoionizing states is presented.

Boumsellek, S.↗
NASA NTRS1990

Map-based trigonometric parallaxes of open clusters - The Pleiades

The multichannel astrometric photometer and Thaw refractor of the University of Pittsburgh's Allegheny Observatory have been used to determine the trigonometric parallax of the Pleiades star cluster. The distance determined, 150 with a standard error of 18 parsecs, places the cluster slightly farther away than generally accepted. This suggests that the basis of many estimations of the cosmic distance scale is approximately 20 percent short. The accuracy of the determination is limited by the number and choice of reference stars. With careful attention to the selection of reference stars in several Pleiades regions, it should be possible to examine differences in the photometric and trigonometric modulus at a precision of 0.1 magnitudes.

Gatewood, George↗
NASA NTRS1991

Opening the cusp

This paper discusses the magnetic field topology (determined by the superposition of dipole, image, and uniform fields) for mapping the cusp to the ionosphere. The model results are compared to both new and published observations and are then used to map the footprint of a flux transfer event caused by a time variation in the merging rate. It is shown that the cusp geometry distorts the field lines mapped from the magnetopause to yield footprints with dawn and dusk protrusions into the region of closed magnetic flux.

Crooker, N. U.↗
NASA NTRS1991

Coupled rotor-flexible fuselage vibration reduction using open loop higher harmonic control

A fundamental study of vibration prediction and vibration reduction in helicopters using active controls was performed. The nonlinear equations of motion for a coupled rotor/flexible fuselage system have been derived using computer algebra on a special purpose symbolic computer facility. The trim state and vibratory response of the helicopter are obtained in a single pass by applying the harmonic balance technique and simultaneously satisfying the trim and the vibratory response of the helicopter for all rotor and fuselage degrees of freedom. The influence of the fuselage flexibility on the vibratory response is studied. It is shown that the conventional single frequency higher harmonic control is capable of reducing either the hub loads or only the fuselage vibrations but not both simultaneously. It is demonstrated that for simultaneous reduction of hub shears and fuselae vibrations a new scheme called multiple higher harmonic control is required.

Papavassiliou, I.↗