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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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Design of a nonlinear adaptive filter for suppression of shuttle pilot-induced oscillation tendencies

Analysis of a longitudinal pilot-induced oscillation (PIO) experienced just prior to touchdown on the final flight of the space shuttle's approach landing tests indicated that the source of the problem was a combination of poor basic handling qualities aggravated by time delays through the digital flight control computer and rate limiting of the elevator actuators due to high pilot gain. A nonlinear PIO suppression (PIOS) filter was designed and developed to alleviate the vehicle's PIO tendencies by reducing the gain in the command path. From analytical and simulator studies it was shown that the PIOS filter, in an adaptive fashion, can attenuate the command path gain without adding phase lag to the system. With the pitch attitude loop of a simulated shuttle model closed, the PIOS filter increased the gain margin by a factor of about two.

Smith, J. W.↗
NASA NTRS1981

Semi-actuator disk theory for compressor choke flutter

A mathematical anaysis predict the unsteady aerodynamic utilizing semi actuator theory environment for a cascade of airfoils harmonically oscillating in choked flow was developed. A normal shock is located in the blade passage, its position depending on the time dependent geometry, and pressure perturbations of the system. In addition to shock dynamics, the model includes the effect of compressibility, interblade phase lag, and an unsteady flow field upstream and downstream of the cascade. Calculated unsteady aerodynamics were compared with isolated airfoil wind tunnel data, and choke flutter onset boundaries were compared with data from testing of an F100 high pressure compressor stage.

Micklow, J.↗
NASA NTRS1981

A remark on the theory of measuring thermal diffusivity by the modified Angstrom's method

A theory of the measurement of the thermal diffusivity of a sample by the modified Angstrom method is developed for the case in which radiative heat loss from the end surface of the sample is not negligible, and applied to measurements performed on lunar samples. Formulas allowing sample thermal diffusivity to be determined from the amplitude decay and phase lag of a temperature wave traveling through the sample are derived for a flat disk sample for which only heat loss from the end surface is important, and a sample of finite diameter and length for which heat loss through the end and side surfaces must be considered. It is noted that in the case of a flat disk, measurements at a single angular frequency of the temperature wave are sufficient, while the sample of finite diameter and length requires measurements at two discrete angular frequencies. Comparison of the values of the thermal diffusivities of two lunar samples of dimensions approximately 1 x 1 x 2 cm derived by the present methods and by the Angstrom theory for a finite bar reveals them to differ by not more than 5%, and indicates that more refined data are required as the measurement theory becomes more complicated.

Horai, K.-I.↗
NASA NTRS1981

Estimation of trends

The application of statistical methods to recorded ozone measurements. The effects of a long term depletion of ozone at magnitudes predicted by the NAS is harmful to most forms of life. Empirical prewhitening filters the derivation of which is independent of the underlying physical mechanisms were analyzed. Statistical analysis performs a checks and balances effort. Time series filters variations into systematic and random parts, errors are uncorrelated, and significant phase lag dependencies are identified. The use of time series modeling to enhance the capability of detecting trends is discussed.

Source record↗
NASA NTRS1981

A comparison of head and manual control for a position-control pursuit tracking task

Head control was compared with manual control in a pursuit tracking task involving proportional controlled-element dynamics. An integrated control/display system was used to explore tracking effectiveness in horizontal and vertical axes tracked singly and concurrently. Compared with manual tracking, head tracking resulted in a 50 percent greater rms error score, lower pilot gain, greater high-frequency phase lag and greater low-frequency remnant. These differences were statistically significant, but differences between horizontal- and vertical-axis tracking and between 1- and 2-axis tracking were generally small and not highly significant. Manual tracking results were matched with the optimal control model using pilot-related parameters typical of those found in previous manual control studies. Head tracking performance was predicted with good accuracy using the manual tracking model plus a model for head/neck response dynamics obtained from the literature.

Levison, W. H.↗
NASA NTRS1982

Determination of intercontinental baselines and Earth orientation using VLBI

A series of experiments was conducted during the last decade to explore the capability of very long baseline interferometry (VLBI) to measure the crustal and rotational motions of the Earth with accuracies at the centimeter level. The observing stations are those of NASA's Deep Space Network in California, Spain and Australia. A multiparameter fit to the observed values of delay and delay rate yields radio source positions, polar motion, universal time, the precession constant, baseline vectors, and solid Earth tides. Source positions are obtained with formal errors of the order of 0''.01. UT1-UTC and polar motion are determined at 49 epochs, with formal error estimates for the more recent data of 0.5 msec for UT1-UTC and 2 to 6 mas for polar motion. Intercontinental baseline lengths are determined with formal errors of 5 to 10 cm. The Love numbers and Earth tide phase lag agree with the commonly accepted values.

Sovers, O. J.↗
NASA NTRS1983

Io's sodium cloud - Explanation of the east-west asymmetries. II

A three- dimensional model for Io's sodium cloud incorporating the full effects of solar radiation acceleration associated with solar resonance scattering of atoms in the D-1 and D-2 lines is developed and applied to interpret two different but related east-west asymmetries exhibited in the cloud, using data obtained from ground-based telescopes. The physical changes produced in the cloud by the solar radiation acceleration as a function of satellite phase angle are documented, and how these changes explain the asymmetries is clarified. The model results suggest an east-west phase lag asymmetry of 10-15 degrees; results for the observed east-west intensity asymmetry of Bergstrahl (1977) are also presented. The east-west shape and intensity asymmetries are found to follow directly from the lack of circular symmetry about Jupiter of the forces acting on the cloud atoms.

Smyth, W. H.↗
NASA NTRS1984

The Z3 model of Saturns magnetic field and the Pioneer 11 vector helium magnetometer observations

Magnetic field observations obtained by the Pioneer 11 vector helium magnetometer are compared with the Z(sub 3) model magnetic field. These Pioneer 11 observations, obtained at close-in radial distances, constitute an important and independent test of the Z(sub 3) zonal harmonic model, which was derived from Voyager 1 and Voyager 2 fluxgate magnetometer observations. Differences between the Pioneer 11 magnetometer and the Z(sub 3) model field are found to be small (approximately 1%) and quantitatively consistent with the expected instrumental accuracy. A detailed examination of these differences in spacecraft payload coordinates shows that they are uniquely associated with the instrument frame of reference and operation. A much improved fit to the Pioneer 11 observations is obtained by rotation of the instrument coordinate system about the spacecraft spin axis by 1.4 degree. With this adjustment, possibly associated with an instrumental phase lag or roll attitude error, the Pioneer 11 vector helium magnetometer observations are fully consistent with the Voyager Z(sub 3) model.

Connerney, J. E. P.↗
NASA NTRS1984

The Z3 model of Saturn's magnetic field and the Pioneer 11 vector helium magnetometer observations

Magnetic field observations obtained by the Pioneer 11 vector helium magnetometer are compared with the Z(sub 3) model magnetic field. These Pioneer 11 observations, obtained at close-in radial distances, constitute an important and independent test of the Z(sub 3) zonal harmonic model, which was derived from Voyager 1 and Voyager 2 fluxgate magnetometer observations. Differences between the Pioneer 11 magnetometer and the Z(sub 3) model field are found to be small (approximately 1 percent) and quantitatively consistent with the expected instrumental accuracy. A detailed examination of these differences in spacecraft payload coordinates shows that they are uniquely associated with the instrument frame of reference and operation. A much improved fit to the Pioneer 11 observations is obtained by rotation of the instrument coordinate system about the spacecraft spin axis by 1.4 degree. With this adjustment, possibly associated with an instrumental phase lag or roll attitude error, the Pioneer 11 vector helium magnetometer observations are fully consistent with the Voyager Z(sub 3) model.

Connerney, J. E. P.↗
NASA NTRS1984

Recurrent mass ejections observed in H-alpha and CIV

Time sequences of recurrent mass ejections have been observed during a coordinated SMY program (Sept. 1, 1980 - Sept. 23, 1980 - Oct. 2, 1980). Comparison of the temporal evolution of H-alpha and CIV brightnesses shows a weak phase lag between H-alpha and CIV maxima, in the case of homologous flares, with CIV brightness maxima preceding H-alpha maxima. The analysis of the variation of the ejection velocities is expected to lead to the determination of an energy balance. Such recurrent ejections could be due to periodic energy storage and periodic reorganization of magnetic field as envisaged to occur for flares, but at lower energy levels.

Schmieder, B.↗
NASA NTRS1983

Simple models of climate and radiation

The validity of several energy balance climate models and the infrared terrestrial radiation rule are reassessed in the context of determining the effect of the adjustable parameters present in phenomenological and semiempirical model on the validity of their predictions. The study includes comparisons between modeled and observed amplitudes of the annual and semiannual surface temperature cycles, phase lag of the annual surface temperature cycle, and amplitude response to a high-frequency solar constant oscillation of 0.8 percent.

North, G. R.↗
NASA NTRS1985

Activity-driven structure variations as a cause of period changes in RS Canis Venaticorum-like systems

Magnetic activity cycles of a convective star in a close binary system may lead to orbit period changes through tidal spin-orbit coupling. An increase in the mean magnetic field throughout the convection zone provides an additional pressure support and increases the star's moment of inertia. In order for the system to conserve angular momentum instantaneously, the convective star must reduce its rotation rate. When this happens, the system is no longer synchronous; in particular, the equilibrium tide now suffers a phase lag. A tidal torque must act, transferring angular momentum from the star's rotation to the orbit, lengthening the period. When the field decays, these events reverse and the period shortens. Observed period changes in RS CVn-like systems are of the order delta p/p = 10 to the -6th, implying variations in the mean field strength at the base of the convection zone of approximately 1000 G over time scales of 10-30 yr. It is predicted that the strength of magnetic activity indicators will track orbital period changes in a given system: the period will be largest during the active portion of the magnetic cycle and smallest during the quiescent part.

Van Buren, D.↗
NASA NTRS1986

Cyclogenesis

In order to extend the conventional baroclinic instability concept, one has to picture the growth process as resulting from the superposition of two neutrally stable baroclinic waves, an upper and a lower one, each wave propagating along a near-discontinuity in the potential vorticity (PV) field. The PV discontinuity for the lower wave is given by the non-uniformity of the thermal field at the ground, while the discontinuity for the upper wave is given by the contrast, in the 400 to 200 mb range, between the high-PV polar stratosphere and the low-PV subtropical troposphere. The horizontal PV radients mentioned are approximately opposed to each other, causing the wo waves to travel in the opposite direction. As Hoskins et al. (1985) show convincingly, a phase lock between the upper and lower wave may occur, coupled with a tendency toward mutual amplification. The conceptual model just outlined is particularly attractive to synoptic meteorologists because it does not require the two waves to be of initially small amplitude and thus does not fly in the face of observational evidence. This model, by allowing a finite perturbation velocity and a considerable range of relative phase speeds at the time when the upper and lower wave reach the proper phase lag for amplification, may lead to growth rates larger than those predicted by linear theory. aba R.J.F.

Bleck, R.↗
NASA NTRS1985

Infrared studies of the bipolar nebula OHO739

Infrared studies have been made of the M9 giant OHO739, which is embedded in a bipolar nebula, in order to study the structure and density distribution of the circumstellar disk, and preliminary results are reported. The degree of polarization across the 3.1 micron ice band in an 8 arcsec beam centered at the 2.2 micron peak is found to increase with extinction in the ice band, as expected for a bipolar scattering nebula. A distance of 2 kpc is inferred from the tilt angle of the bipolar axis and phase lag measurements of the OH maser. Maps made in the K band and in narrow bands at 2.85, 3.1, and 3.5 microns by raster-scanning OHO739 are presented. In all maps, the object is clearly elongated along the bipolar axis. Patterns of increases and decreases in extinction in the object are inferred to indicate that ice particles are widespread through the nebula and not just concentrated in the disk.

Tielens, A. G. G. M.↗
NASA NTRS1986

Ultraviolet and visual variability of Theta CrB during a normal B-phase following a shell phase (1980-1985)

Based on far-UV and visual observations made between 1980 and 1985, the phenomena characterizing the end of a shell phase of Theta-CrB, and the normal B-phase following it, are described as part of a long-term study of Be stars. The strength, shape, and velocity of the C IV, Si IV, and Al III resonance lines, and the Fe III lines of low excitation, show associated variability patterns over the whole range of ionization observable in the IUE and visual spectra. The observed variability pattern consists of a one-year narrow-line stage where the lines show narrow absorption cores close to rest wavelength, a two-year series of abrupt changes between a weak and a strong line, and a damping out of these variations leaving the observed spectrum in a lower ionization state. The existence of a phase-lag between similar phenomena occurring in the superionized and subionized/normally ionized regions, is noted.

Doazan, V.↗
NASA NTRS1986

Noise generated by convected gusts interacting with swept airfoil cascades

An analysis is developed for the noise generated by the interaction of a rotor viscous wake with a cascade of swept stator vanes. The stator vanes span a channel formed by infinite parallel walls and containing a subsonic mean flow. High frequency interactions, for which the noise generation is concentrated at the vane leading edge, are considered. The analysis utilizes a superposition of the solution to the isolated stator vane problem, presented in an earlier paper, to develop an approximate solution to the cascade problem. The rotor wake model includes the features of wake circumferential lean and a linear spanwise variation of the magnitude of the wake deficit velocity. Calculations are presented which show that, for rotor wakes with moderate circumferential lean, stator sweep produces substantial reductions in noise level. The vane sweep must be oriented to enhance the phase lags along the vane leading edge produced by wake lean. The noise levels are found to be fairly insensitive to spanwise variations in the wake deficit.

Envia, E.↗
NASA NTRS1986

The effect of a row of Helmholtz resonators on the turbulence in a boundary layer

Detailed acoustic measurements were made of the resonator's response as the free stream speed was varied from 30 mph to 155 mph. The average sound pressure level (SPL) and peak frequency response clearly show the existence of strong tuning between the boundary layer and the resonator for the Helmholtz (f sub 0) mode as well as for the first standing wave (f sub 1) mode. The narrow speed range for tuning and the gap between the strong tuning for the Helmholtz mode and the first standing wave mode is evident. The frequency at which the peak SPL response occurred at each speed is given. The peak response for the Helmholtz mode occurred at a free stream velocity of 26 m/s (at which RE sub theta = 6,560) with a resonant frequency of 570 Hz and a sound pressure level of 141 dB. The peak response for the first standing wave occurs at the maximum wind tunnel speed of 70 m/s (at which Re sub theta = 14,900) Hz with a resonant frequency of 1,890 Hz and a sound pressure level of 154 dB. At resonance the microphones do not maintain a constant SPL, but rather the latter fluctuates in a seemingly random fashion. The values presented here are time averaged rms values. Of interest was the occurrence of phase locking between adjacent resonators witha phase lag of 180 deg. This report covers the period from 5 May to 30 September on the subject project.

Panton, R. L.↗
NASA NTRS1987

Basic properties and variability

Giant and supergiant M, S, and C stars are discussed in this survey of research. Basic properties as determined by spectra, chemical composition, photometry, or variability type are discussed. Space motions and space distributions of cool giants are described. Distribution of these stars in our galaxy and those nearby is discussed. Mira variables in particular are surveyed with emphasis on the following topics: (1) phase lag phenomenon; (2) Mira light curves; (3) variations in color indices; (4) determination of multiple periods; (5) correlations between quantities such as period length, light-curve shape, infrared (IR) excess, and visible and IR color diagram; (6) semiregular (SR) variables and different time scales in SR light variations; (7) irregular variable Lb and Lc stars; (8) different time-scale light variations; (9) hydrogen-deficient carbon (HdC) stars, in particular RCB stars; and (10) irreversible changes and rapid evolution in red variable stars.

Querci, Francois R.↗