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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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Criteria for Side-Force Control in Air-to-Ground Target Acquisition and Tracking

A moving-base simulator experiment conducted at Ames Research Center demonstrated that a wings-level-turn control mode improved flying qualities for air-to-ground weapons delivery compared with those of a conventional aircraft. Evaluations of criteria for dynamic response for this system have shown that pilot ratings correlate well with equivalent time constant of the initial response and with system bandwidth. Ranges of this time constant, as well as digital-system transport delays and lateral-acceleration control authorities that encompassed level 1 through level 3 handling qualities, were determined.

Sammonds, Robert I.↗
NASA NTRS1982

The effect of delta 3 on a yawing HAWT blade and on yaw dynamics

A single degree of freedom aeroelastic computer model, WMSTAB3, was employed to perform a parametric analysis of HAWT blade behavior during yaw maneuvers. Over 1,000 different combinations of delta sub 3 and normal frequency were analyzed. The effect of delta sub 3 and flapping stiffness on flapping frequency, phase, and magnitude are discussed. The moments transmitted to the fixed system during yaw maneuvers were calculated and reduced to time constants of response to step changes in wind direction. The significance of the time constants for the configurations considered relative to yaw response rate and lag angle is discussed, along with their possible significance for large HAWT.

Perkins, F. W.↗
NASA NTRS1982

The effects of multiplicative motor noise on the optimal human operator model

The effects of a multiplicative motor noise model on the optimal-control human operator model were analyzed. A study of the interaction between multiplicative motor noise variance, plant dynamics, and predicted operator response behavior shows that, in general, an increase in motor noise variance produces a decrease in operator gain and a decrease in high-frequency remnant. An increase in multiplicative motor noise variance is also reflected by an increase in the effective motor time constant; in the absence of a cost penalty on commanded control, the motor time constant equals the motor noise variance.

Caglayan, A. K.↗
NASA NTRS2003

Depth-Penetrating Temperature Measurements of Thermal Barrier Coatings Incorporating Thermographic Phosphors

Thermographic phosphors have been previously demonstrated to provide effective non-contact, emissivity-independent surface temperature measurements. Because of the translucent nature of thermal barrier coatings (TBCs), thermographic phosphor-based temperature measurements can be extended beyond the surface to provide depth-selective temperature measurements by incorporating the thermographic phosphor layer at the depth where the temperature measurement is desired. In this paper, thermographic phosphor (Y2O3:Eu) fluorescence decay time measurements are demonstrated to provide through-the-coating thickness temperature readings up to 1100 C with the phosphor layer residing beneath a 100 micron thick TBC (plasma-sprayed 8wt% yttria-stabilized zirconia). With an appropriately chosen excitation wavelength and detection configuration, it is shown that sufficient phosphor emission is generated to provide effective temperature measurements, despite the attenuation of both the excitation and emission intensities by the overlying TBC. This depth-penetrating temperature measurement capability should prove particularly useful for TBC diagnostics where a large thermal gradient is typically present across the TBC thickness. The fluorescence decay from the Y2O3:Eu layer exhibited both an initial short-term exponential rise and a longer-term exponential decay. The rise time constant was demonstrated to provide better temperature indication below 500 C while the decay time constant was a better indicator at higher temperatures.

Eldridge, Jeffrey I.↗
NASA NTRS1984

Shuffle-exchanges on augmented meshes

A mesh connected array of size N = two to the Kth power, K an integer, can be augmented by adding at most one edge per node such that it can perform a shuffle-exchange of size N/2 in constant time. A shuffle-exchange of size N is performed on this augmented array in constant time. This is done by combining the available perfect shuffle of size N/2 with the existing nearest neighbor connections of the mesh. By carefully scheduling the different permutations that are composed in order to achieve the shuffle, the time required is reduced to 5 steps, which is optimal for this network.

Bokhari, S. H.↗
NASA NTRS1990

NASA supporting studies for microgravity research on eye movements

The purpose of the work on this project was to provide support for ground-based studies on the effects of gravity on eye movements. The effects of microgravity on the optokinetic eye movements of humans are investigated. OKN was induced by having subjects watch 3.3 deg stripes moving at 35 deg/s for 45 s in a binocular, head-fixed apparatus. The field (hor., 88 deg; vert., 72 deg), was rotated about axes that were upright or tilted 45 deg or 90 deg. The head was upright or tilted 45 deg on the body. Head-horizontal (yaw axis) and head-vertical (pitch axis) components of OKN were recorded with electro-oculography (EOG). Slow phase velocity vectors were determined relative to gravity. With the head upright, the axis of eye rotation during yaw axis OKN was coincident with the stimulus axis and the spatial vertical. With the head tilted 45 deg on the body, a persistent vertical component of eye velocity developed during yaw axis stimulation, and there was an average shift of the axis of eye rotation toward the spatial vertical of approximately 18 deg in six subjects. During oblique optokinetic stimulation with the head upright, the axis of eye rotation shifted 12 deg toward the spatial vertical. When the head was tilted, the axis of eye rotation rotated to the other side of the spatial vertical by 5.4 deg during the same oblique stimulation. This counter-rotation of the axis of eye rotation is similar to the 'Muller (E) effect', in which the perception of the upright counter-rotates to the opposite side of the spatial vertical when subjects are tilted in darkness. The data were simulated by a model of OKN. Despite the short OKAN time constants, strong horizontal to vertical cross-coupling was produced if the horizontal and vertical time constants were in proper ratio, and there was no suppression of nystagmus orthogonal to the stimulus direction. This shows that the spatial orientation of OKN can be due to a restructuring of the system matrix of velocity storage as a function of gravity. It is concluded that although human OKAN is weak, velocity storage orients the slow phase velocity of OKN towards the spatial vertical.

Cohen, Bernard↗
NASA NTRS1974

Analysis of the feedback system in a nonintrusive dynamic flowmeter for measuring Pogo oscillations

Equations were developed which describe the closed loop feedback system operation of a proposed ultrasonic, dynamic, nonintrusive flowmeter whose design is based on a constant phase, voltage controlled frequency feedback concept. These equations are based on linear feedback system theory. The time constant of a low pass filter is taken into account. The equations show that the larger the open loop gain, the smaller the error due to fluctuations in the speed of sound and the smaller the effective time constant.

Chapin, W. G.↗
NASA NTRS1972

Direction-specific adaptation effects acquired in a slow rotation room.

Thirty-eight subjects were required to execute 120 head movements in a slow rotation room at each 1-rpm increase in velocity of the room between 0 and 6 rpm and, after a single-step gradual return to zero velocity, execute 120 head movements either immediately after return or after delay periods varying from 1 to 24 hours unless, at any time, more than mild symptoms of motion sickness were elicited. A second stress profile differed by the sequential addition of an incremental adaptation schedule (identical to the first) in which the direction of rotation was reversed. The experimental findings demonstrated the acquisition of direction-specific adaptation effects that underwent spontaneous decay with a short time constant (hours). With their disappearance a nondirection-specific adaptation was revealed with a long-time constant (days). Speculations are presented which could account for the simultaneous acquisition of short-term and long-term adaptation effects.

Graybiel, A.↗
NASA NTRS1994

Orientation of human optokinetic nystagmus to gravity: a model-based approach

Optokinetic nystagmus (OKN) was induced by having subjects watch a moving display in a binocular, head-fixed apparatus. The display was composed of 3.3 degrees stripes moving at 35 degrees/s for 45 s. It subtended 88 degrees horizontally by 72 degrees vertically of the central visual field and could be oriented to rotate about axes that were upright or tilted 45 degrees or 90 degrees. The head was held upright or was tilted 45 degrees left or right on the body during stimulation. Head-horizontal (yaw axis) and head-vertical (pitch axis) components of OKN were recorded with electro-oculography (EOG). Slow phase velocity vectors were determined and compared with the axis of stimulation and the spatial vertical (gravity axis). With the head upright, the axis of eye rotation during yaw axis OKN was coincident with the stimulus axis and the spatial vertical. With the head tilted, a significant vertical component of eye velocity appeared during yaw axis stimulation. As a result the axis of eye rotation shifted from the stimulus axis toward the spatial vertical. Vertical components developed within 1-2 s of stimulus onset and persisted until the end of stimulation. In the six subjects there was a mean shift of the axis of eye rotation during yaw axis stimulation of approximately 18 degrees with the head tilted 45 degrees on the body. Oblique optokinetic stimulation with the head upright was associated with a mean shift of the axis of eye rotation toward the spatial vertical of 9.2 degrees. When the head was tilted and the same oblique stimulation was given, the axis of eye rotation rotated to the other side of the spatial vertical by 5.4 degrees. This counterrotation of the axis of eye rotation is similar to the "Muller (E) effect," in which the perception of the upright is counterrotated to the opposite side of the spatial vertical when subjects are tilted in darkness. The data were simulated by a model of OKN with a "direct" and "indirect" pathway. It was assumed that the direct visual pathway is oriented in a body, not a spatial frame of reference. Despite the short optokinetic after-nystagmus time constants, strong horizontal to vertical cross-coupling could be produced if the horizontal and vertical time constants were in proper ratio and there were no suppression of nystagmus in directions orthogonal to the stimulus direction. The model demonstrates that the spatial orientation of OKN can be achieved by restructuring the system matrix of velocity storage. We conclude that an important function of velocity storage is to orient slow-phase velocity toward the spatial vertical during movement in a terrestrial environment.

Non-NASA Center↗
NASA NTRS1992

Nystagmus induced by electrical stimulation of the vestibular and prepositus hypoglossi nuclei in the monkey: evidence for site of induction of velocity storage

Electrical stimulation of the vestibular nuclei (VN) and prepositus hypoglossi nuclei (PPH) of alert cynomolgus monkeys evoked nystagmus and eye deviation while they were in darkness. At some sites in VN, nystagmus and after-nystagmus were induced with characteristics suggesting that velocity storage had been excited. We analyzed these responses and compared them to the slow component of optokinetic nystagmus (OKN) and to optokinetic after-nystagmus (OKAN). We then recorded unit activity in VN and determined which types of nystagmus would be evoked from the sites of recording. Nystagmus and eye deviations were also elicited by electrical stimulation of PPH, and we characterized the responses where unit activity was recorded in PPH. Horizontal slow phase velocity of the VN "storage" responses was contralateral to the side of stimulation. The rising time constants and peak steady-state velocities were similar to those of OKN, and the falling time constants of the after-nystagmus and of OKAN were approximately equal. Both the induced after-nystagmus and OKAN were habituated by stimulation of the VN. When horizontal after-nystagmus was evoked with animals on their sides, it developed yaw and pitch components that tended to shift the vector of the slow phase velocity toward the spatial vertical. Similar "cross-coupling" occurs for horizontal OKAN or for vestibular post-rotatory nystagmus elicited in tilted positions. Thus, the storage component of nystagmus induced by VN stimulation had the same characteristics as the slow component of OKN and the VOR. Positive stimulus sites for inducing nystagmus with typical storage components were located in rostral portions of VN. They lay in caudal ventral superior vestibular nucleus (SVN), dorsal portions of central medial vestibular nucleus (MVN) caudal to the abducens nuclei and in adjacent lateral vestibular nucleus (LVN). More complex stimulus responses, but with contralateral after-nystagmus, were induced from surrounding regions of ventral MVN and LVN, rostral descending vestibular nucleus and the marginal zone between MVN and PPH. Vestibular-only (VO), vestibular plus saccade (VPS) and tonic vestibular pause (TVP) units were identified by extracellular recording. Stimulation near type I lateral and vertical canal-related VO units elicited typical "storage" responses with after-nystagmus in 23 of 29 tracks (79%). Stimulus responses were more complex from the region of neurons with oculomotor-related signals, i.e., TVP or VPS cells, although after-nystagmus was also elicited from these sites. Effects of vestibular nerve and nucleus stimulation were compared.(ABSTRACT TRUNCATED AT 400 WORDS).

NASA Discipline Neuroscience↗
NASA NTRS1988

Ionosphere-thermosphere momentum coupling at solar maximum and solar minimum from DE-2 and AE-C data

DE-2 and AE-C measurements of plasma and neutral densities were used to derive time constants for momentum transfer (MT) to neutrals from ions in the high-latitude thermosphere. The MT time constants for solar cycle maximum (DE-2) and for solar cycle minimum (AE-C) were averaged and binned according to geomagnetic latitude and LT to provide a quantitative measure for the tightness of ion-neutral momentum coupling (MC) in the 250-350-km altitude range. Comparisons with results obtained using the Chiu and MSIS-83 empirical models have provided an indication of the accuracy with which thermospheric general circulation models quantitatively reproduce the MC between ions and neutrals in the high-latitude F-region.

Ponthieu, J. J.↗
NASA NTRS1972

Observation of solar particle fluxes over extended solar longitudes.

Detailed particle observations from various Pioneer spacecraft located at different heliolongitudes during the complex solar flare events of Mar. 30 to Apr. 10, 1969, have been utilized to investigate the energy dependence of azimuthal gradients of cosmic ray particles and its effect on the decay of the flare intensity. For an observer located to the east of the centroid of the population, the azimuthal corotation term and the convection term will be additive, resulting in a short decay time constant. An observer located to the west of the centroid of the population will experience a much longer decay time constant, the corotation term partially or completely compensating the loss of particles due to convection. At very low energies, the azimuthal corotation term may even be more than the convection term, thus resulting in a rise in intensity instead of decay during the later part of the event.

Bukata, R. P.↗
NASA NTRS1981

Titan's atmosphere - Temperature and dynamics

In the lower atmosphere of Titan IR brightness temperatures exhibit meridional contrast less than approximately 3 K. Seasonal variations are absent because of the large radiative time constant. In the upper stratosphere meridional contrasts are approximately 20 K, consistent with 100 m/s cyclostrophic zonal winds, and the radiative time constant is short, implying a large seasonal variation in the temperature and wind field. The absence of longitudinal thermal structure implies that zonally symmetric flows effect the meridional transport of heat. A simple model yields meridional velocities approximately 0.04 cm/s and vertical eddy viscosities approximately 1,000 sq cm/s in the lower troposphere, and meridional velocities approximately 5 cm/s in the upper stratosphere.

Flasar, F. M.↗
NASA NTRS1999

Real-time Adaptive Control Using Neural Generalized Predictive Control

The objective of this paper is to demonstrate the feasibility of a Nonlinear Generalized Predictive Control algorithm by showing real-time adaptive control on a plant with relatively fast time-constants. Generalized Predictive Control has classically been used in process control where linear control laws were formulated for plants with relatively slow time-constants. The plant of interest for this paper is a magnetic levitation device that is nonlinear and open-loop unstable. In this application, the reference model of the plant is a neural network that has an embedded nominal linear model in the network weights. The control based on the linear model provides initial stability at the beginning of network training. In using a neural network the control laws are nonlinear and online adaptation of the model is possible to capture unmodeled or time-varying dynamics. Newton-Raphson is the minimization algorithm. Newton-Raphson requires the calculation of the Hessian, but even with this computational expense the low iteration rate make this a viable algorithm for real-time control.

Haley, Pam↗
NASA NTRS1981

Frequency response of the vestibulo-ocular reflex /VOR/ in the monkey

The frequency response of the vestibulo-ocular reflex has been investigated in the alert monkey during sinusoidal rotation about a vertical axis in a frequency range of 0.001-0.5 Hz. Phase and gain of nystagmus slow phase velocity was determined. In the frequency range above 0.1 Hz, nystagmus slow phase velocity was in phase with (compensated for) head velocity. At lower frequencies, an increasing phase lead was present which could reach more than 90 deg. Gain fell off correspondingly at low frequencies. Calculated time constants were 10-40 s in different monkeys. Animals which had been exposed to numerous previous rotary stimuli in the laboratory showed much shorter time constants than did 'native' monkeys.

Buettner, U. W.↗
NASA NTRS2004

Spacecraft Orbits for Earth/Mars-Lander Radio Relay

A report discusses a network of spacecraft, in orbit around Mars, used to relay radio communications between Earth stations and mobile exploratory robots (rovers) as well as stationary scientific instruments that have been landed on the Mars surface. The relay spacecraft include two already in orbit plus several others planned to arrive at Mars in the years 2004 through 2008. A major portion of the report is devoted to the orbit of the G. Macroni Orbiter, which is in the midst of an iterative design process and is intended to be the first Mars orbiter designed primarily for radio relay. Candidate orbits are analyzed with a view toward choosing one that maximizes the amount of time available for communication with surface units, taking account of visibility as a function of position, the limit on communication distance at low power, and the fact that surface units can transmit more easily when they are in sunlight. Two promising new orbits for Mars relay satellites are identified: a 1/2-sol apoapsis-at-constant-time-of-day equatorial orbit and a 1/4-sol apoapsis-at-constant-time-of-day, critical-inclination orbit.

Noreen, Gary↗
NASA NTRS1989

Earth horizontal axis rotational responses in patients with unilateral peripheral vestibular deficits

The vestibulo-ocular reflex (VOR) of five patients with surgically confirmed unilateral peripheral vestibular lesions is evaluated. Testing used both earth vertical axis (EVA) and earth horizontal axis (EHA) yaw rotation. Results indicated that the patients had short VOR time constants, asymmetric responses to both EVA and EHA rotation, and normal EHA modulation components. These findings suggest that unilateral peripheral vestibular loss causes a shortened VOR time constant even with the addition of dynamic otolithic stimulation and causes an asymmetry in semicircular canal-ocular reflexes and one aspect of otolith-ocular reflexes.

Furman, Joseph M. R.↗
NASA NTRS1984

Injection-induced turbulence in stagnation-point boundary layers

A theory is developed for the stagnation point boundary layer with injection under the hypothesis that turbulence is produced at the wall by injection. From the existing experimental heat transfer rate data obtained in wind tunnels, the wall mixing length is deduced to be a product of a time constant and an injection velocity. The theory reproduces the observed increase in heat transfer rates at high injection rates. For graphite and carbon-carbon composite, the time constant is determined to be 0.0002 sec from the existing ablation data taken in an arc-jet tunnel and a balistic range.

Park, C.↗