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Results for “H-V”

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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9 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Optimal landing of a helicopter in autorotation

The landing of a helicopter in autorotation is formulated as a nonlinear optimal control problem. A unique feature in the present formulation is the addition of path inequality constraints on both the control and the state vectors. The control variable inequality constraint is a reflection of the limitation on the rotor thrust coefficient. The state-variable inequality constraint is an upper bound on the vertical sink-rate of the helicopter during descent. Optimal trajectories are calculated for entry conditions well within the height-velocity (H-V) restriction curve, with the helicopter initially in hover or in forward flight. The optimal solutions exhibited control techniques similar to those used by helicopter pilots in actual autorotational landings. The study indicates that, subject to pilot acceptability, a substantial reduction could be made in the H-V restriction zone using optimal control techniques.

Lee, A. Y.↗
NASA NTRS1991

Polarization radar measurements in rain at 5 and 9 GHz

Potential techniques for measuring rainfall rate R and rainwater content W at 9 and 5 GHz are explored. An investigation is made of a previous technique to use the polarization propagation differential phase shift with increasing distance from the radar Phi(H-V) to estimate and remove the effects of specific and polarization differential attenuation from Z(H) and Z(DR), respectively. It is shown that in rain this technique is sensitive to variations in the drop-size distribution. It is confirmed that Phi(H-V) can be used to extend the distance over which useful measurements of Z(H) and Z(DR) can be obtained. While residual errors introduced by attenuation and the 'noise' from the correction scheme itself eclipse the potential of many possible techniques for quantitative rainfall measurements at these frequencies, the attenuation recovery scheme is argued to be adequate for obtaining useful polarization microphysical measurements, particularly above the melting level, even after encounters with rain.

Jameson, A. R.↗
NASA NTRS1992

The effect of temperature on attenuation-correction schemes in rain using polarization propagation differential phase shift

The study elucidates and quantifies differences in the response of the rate of change of polarization propagation differential phase shift Phi, the rate of attenuation for a horizontally/vertically polarized wave A(H,V), and the rate of polarization differential attenuation A(H-V) to temperature. It is shown that if the effects of temperature when estimating A(H) and A(H-V) from Phi are neglected, the average fractional standard error increases only slightly at 9 GHz but significantly at 5 and 3 GHz. Errors at 5 and 3 GHz are about two to three times those at 9 GHz. The performance of Phi-based schemes of attenuation correction at these lower frequencies is much more significantly degraded by temperature uncertainty than at 9 GHz. It is concluded that it is best to use Phi to correct for attenuation at the least-attenuating frequencies.

Jameson, A. R.↗
NASA NTRS1975

Thermal boundaries analysis program document

The digital program TBAP has been developed to provide thermal boundaries in the DD/M-relative velocity (D-V), dynamic pressure-relative velocity (q-V), and altitude-relative velocity (h-V) planes. These thermal boundaries are used to design and/or analyze shuttle orbiter entry trajectories. The TBAP has been used extensively in supporting the Flight Performance Branch of NASA in evaluating candidate trajectories for the thermal protection system design trajectory.

Evans, M. E.↗
DOE OSTI2020

Materials Data on VH2 by Materials Project

VH2 is Fluorite structured and crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. V2+ is bonded in a body-centered cubic geometry to eight equivalent H1- atoms. All V–H bond lengths are 1.83 Å. H1- is bonded to four equivalent V2+ atoms to form a mixture of corner and edge-sharing HV4 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on VH by Materials Project

HV1 is Halite, Rock Salt structured and crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. V is bonded to six equivalent H atoms to form a mixture of edge and corner-sharing VH6 octahedra. The corner-sharing octahedral tilt angles are 0°. All V–H bond lengths are 1.97 Å. H is bonded to six equivalent V atoms to form a mixture of edge and corner-sharing HV6 octahedra. The corner-sharing octahedral tilt angles are 0°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on V2H by Materials Project

V2H is Calaverite-like structured and crystallizes in the monoclinic C2/m space group. The structure is two-dimensional and consists of one V2H sheet oriented in the (0, 0, 1) direction. V is bonded in a 3-coordinate geometry to three equivalent H atoms. There is one shorter (1.79 Å) and two longer (2.08 Å) V–H bond length. H is bonded to six equivalent V atoms to form edge-sharing HV6 octahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on V2H by Materials Project

V2H is Calaverite-like structured and crystallizes in the tetragonal I4_1/amd space group. The structure is three-dimensional. V is bonded in a 3-coordinate geometry to three equivalent H atoms. There is one shorter (1.80 Å) and two longer (2.08 Å) V–H bond length. H is bonded to six equivalent V atoms to form edge-sharing HV6 octahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on VH by Materials Project

HV1 is Molybdenum Carbide MAX Phase-like structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. V is bonded to six equivalent H atoms to form a mixture of face, edge, and corner-sharing VH6 octahedra. The corner-sharing octahedral tilt angles are 46°. All V–H bond lengths are 2.00 Å. H is bonded to six equivalent V atoms to form a mixture of distorted edge and corner-sharing HV6 pentagonal pyramids.

36 MATERIALS SCIENCE↗