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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 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Multiple Concurrent Visual-Motor Mappings: Implications for Models of Adaptation

Previous research on adaptation to visual-motor rearrangement suggests that the central nervous system represents accurately only 1 visual-motor mapping at a time. This idea was examined in 3 experiments where subjects tracked a moving target under repeated alternations between 2 initially interfering mappings (the 'normal' mapping characteristic of computer input devices and a 108' rotation of the normal mapping). Alternation between the 2 mappings led to significant reduction in error under the rotated mapping and significant reduction in the adaptation aftereffect ordinarily caused by switching between mappings. Color as a discriminative cue, interference versus decay in adaptation aftereffect, and intermanual transfer were also examined. The results reveal a capacity for multiple concurrent visual-motor mappings, possibly controlled by a parametric process near the motor output stage of processing.

Cunningham, H. A.↗
NASA NTRS1990

Dynamic Characteristics of Space Station Freedom Mars and Lunar Evolution Reference Configurations

One concept for a manned mission to Mars uses an evolutionary version of Space Station Freedom (SSF) as a transportation node. The station is modified by the addition of dual keels, an upper and lower boom, additional laboratory and habitation modules, increased power and an assembly platform. With these modifications the station is called the Mars Evolution Reference Configuration (MERC). The mass of the station is 65 percent greater than the mass of SSF and its moments of inertia through the mass center are greater by approximately a factor of four. Over a period of months, several flights from Earth to low-Earth-orbit carry the components of a manned Mars piloted vehicle (MPV) to the MERC where the vehicle is constructed on the assembly platform. After each flight the station is reboosted to an appropriate altitude, such that the orbit decay due to atmospheric drag forces lowers the spacecraft to the proper altitude at the appropriate time for rendezvous with the next assembly flight. When the assembly process is completed, the MPV, which has a mass of approximately 200,000 lbm, is situated on the evolutionary station. The mass increase of the MERC with MPV system over SSF is 112 percent and the moments of inertia about axes through the mass center increase by up to a factor of 12. When the MPV is assembled, inspected and verified, the mission is ready to proceed and the MPV is moved from the station to a staging area and mated with fueled trans-Mars injection stages for the flight to Mars. This presentation describes a finite element model of the MERC formulated to investigate the expected low frequency modes and its variation with the addition of a large payload. A basic reboost procedure using near-continuous firing of reaction control system jets is proposed with off-modulation of the jets used to control flight attitude. The reboost procedure is described with the closed-loop attitude control dictating jet on/off cycling based on feedback signals which contain both the rigid body rotation information and the elastic rotations local to the attitude sensor. The presentation contains a description of the dynamic response at critical points of the station during the reboost and concludes with results of a brief study of the dynamic characteristics of a Lunar transportation node configuration.

Ayers, J. Kirk↗
NASA NTRS2005

Emission Process I

Important processes in X-ray plasmas are: 1. Ionization: Electron/proton collisions. Electron/proton (photoionization). innershell ionization. 2. Recombination: Radiative. Dielectronic. Charge exchange. 3. Excitation/Decay: Electron/proton collisions. Photoexcitation. Radiative decay.

Smith, Randall K.↗
NASA NTRS1993

Study and modeling of finite rate chemistry effects in turbulent non-premixed flames

The development of numerical models that reflect some of the most important features of turbulent reacting flows requires information about the behavior of key quantities in well defined combustion regimes. In turbulent flames, the coupling between turbulent and chemical processes is so strong that it is extremely difficult to isolate the role played by one individual physical phenomenon. Direct numerical simulation (hereafter DNS) allows us to study in detail the turbulence-chemistry interaction in some restricted but completely defined situations. Globally, non-premixed flames are controlled by two limiting regimes: the fast chemistry case, where the turbulent flame can be pictured as a random distribution of local chemical equilibrium problems; and the slow chemistry case, where the chemistry integrates in time the turbulent fluctuations. The Damkoehler number, ratio of a mechanical time scale to chemical time scale, is used to distinguish between these regimes. Today most of the industrial computer codes are able to perform predictions in the hypothesis of local equilibrium chemistry using a presumed shape for the probability density function (pdt) of the conserved scalar. However, the finite rate chemistry situation is of great interest because industrial burners usually generate regimes in which, at some points, the flame is undergoing local extinction or at least non-equilibrium situations. Moreover, this variety of situations strongly influences the production of pollutants. To quantify finite rate chemistry effect, the interaction between a non-premixed flame and a free decaying turbulence is studied using DNS. The attention is focused on the dynamic of extinction, and an attempt is made to quantify the effect of the reaction on the small scale mixing process. The unequal diffusivity effect is also addressed. Finally, a simple turbulent combustion model based on the DNS observations and tractable in real flow configurations is proposed.

Vervisch, Luc↗
NASA NTRS1984

Applications of spectral methods to turbulent magnetofluids in space and fusion research

Recent and potential applications of spectral method computation to incompressible, dissipative magnetohydrodynamics are surveyed. Linear stability problems for one dimensional, quasi-equilibria are approachable through a close analogue of the Orr-Sommerfeld equation. It is likely that for Reynolds-like numbers above certain as-yet-undetermined thresholds, all magnetofluids are turbulent. Four recent effects in MHD turbulence are remarked upon, as they have displayed themselves in spectral method computations: (1) inverse cascades; (2) small-scale intermittent dissipative structures; (3) selective decays of ideal global invariants relative to each other; and (4) anisotropy induced by a mean dc magnetic field. Two more conjectured applications are suggested. All the turbulent processes discussed are sometimes involved in current carrying confined fusion magnetoplasmas and in space plasmas.

Montgomery, D.↗
NASA NTRS1986

Experiments in software reliability - Life-critical applications

The paper discusses four reliability data gathering experiments which were conducted using a small sample of programs for two problems having ultrareliability requirements, n-version programming for fault detection, and repetitive run modeling for failure and fault rate estimation. The experimental results agree with those of Nagel and Skrivan in that the program error rates suggest an approximate log-linear pattern and the individual faults occurred with significantly different error rates. Additional analysis of the experimental data raises new questions concerning the phenomenon of interacting faults. This phenomenon may provide one explanation for software reliability decay. The fourth experiment underscored the difficulty in distinguishing between observations of deficiencies in the design of the algorithm and observations of software faults for real-time process control software. These experiments are a part of a program of serial experiments being pursued by the System Validation Methods of NASA-Langley Research Center to find a means of credibly performing reliability evaluations of flight control software.

Dunham, J. R.↗
NASA NTRS2001

Use of Individual Flight Corridors to Avoid Vortex Wakes

Vortex wakes of aircraft pose a hazard to following aircraft until the energetic parts of their flow fields have decayed to a harmless level. It is suggested here that in-trail spacings between aircraft can be significantly and safely reduced by designing an individual, vortex-free flight corridor for each aircraft. Because each aircraft will then have its own flight corridor, which is free of vortex wakes while in use by the assigned aircraft, the time intervals between aircraft operations can be safely reduced to the order of seconds. The productivity of airports can then be substantially increased. How large the offset distances between operational corridors need to be to have them vortex free, and how airports need to be changed to accommodate an individual flight-corridor process for landing and takeoff operations, are explored. Estimates are then made of the productivity of an individual flight-corridor system as a function of the in-trail time interval between operations for various values of wake decay time, runway width, and the velocity of a sidewind. The results confirm the need for short time intervals between aircraft operations if smaller offset distances and increased productivity are to be achieved.

Rossow, Vernon J.↗
NASA NTRS1979

Empirical data on the origin of 'new' comets

The mass distribution of a group of 62 comets from the sample of Marsden et al (1978) was determined by assuming that the size of a comet is in proportion to the surface area of its vaporizing nucleus. A bimodal distribution was found, with a gap between magnitudes 8.1 and 9. The 50 brighter comets (magnitudes 1 to 8) have been tentatively identified as true 'new' comets; their size distribution cannot be fit to a constant slope on a log-log graph. These comets were apparently formed by a mechanism which differs from the fragmentation process. The 12 fainter may be fragments of comets which split or dimmed during their first passages. Results indicate that new comets could be identified with pristine planetesimals; they decay rapidly, probably by splitting when they enter the inner solar system.

Delsemme, A. H.↗
NASA NTRS1992

Numerical Study of Mixing of Two Fluids Under Low Gravity

The mixing characteristics of two fluids inside a cavity due to buoyancy driven flow fields for low gravity conditions is investigated via numerical experiments. The buoyancy driven flow, depending on the parametric region, stretches and deforms the material interface into a wave morphological pattern. The morphological pattern affects the resulting stratification thickness of the mixed region. Three basic mixing regimes occur: convective, diffusive, and chaotic. In the convective regime, an overturning motion occurs which gives rise to a stable wave formation. This wave oscillates and its decay leads to a stable stratification. Whereas, in the diffusive regime, the length of the interface remains constant while mixing occurs. This limiting behavior is very important to materials processing in space, and it admits a closed form solution corresponding to vanishing convective terms which agrees with computational results. Finally, in the chaotic regime, the material interface continuously stretches and folds on itself similar to a horseshoe map. The length of stretch of the interface increases exponentially. Internal wavebreaking occurs for this case. This wavebreaking generates local turbulence, and provides an effective mechanism for mixing.

Duval, Walter M. B.↗
NASA NTRS2013

An Evolving Compact Jet in the Black Hole X-Ray Binary Maxi J1836-194

We report striking changes in the broadband spectrum of the compact jet of the black hole transient MAXI J1836−194 over state transitions during its discovery outburst in 2011. A fading of the optical-infrared (IR) flux occurred as the source entered the hard-intermediate state, followed by a brightening as it returned to the hard state. The optical-IR spectrum was consistent with a power law from optically thin synchrotron emission, except when the X-ray spectrum was softest. By fitting the radio to optical spectra with a broken power law, we constrain the frequency and flux of the optically thick/thin break in the jet synchrotron spectrum. The break gradually shifted to higher frequencies as the source hardened at X-ray energies, from approx 10(exp 11) to approx 4 × 10(exp 13) Hz. The radiative jet luminosity integrated over the spectrum appeared to be greatest when the source entered the hard state during the outburst decay (although this is dependent on the high-energy cooling break, which is not seen directly), even though the radio flux was fading at the time. The physical process responsible for suppressing and reactivating the jet (neither of which are instantaneous but occur on timescales of weeks) is uncertain, but could arise from the varying inner accretion disk radius regulating the fraction of accreting matter that is channeled into the jet. This provides an unprecedented insight into the connection between inflow and outflow, and has implications for the conditions required for jets to be produced, and hence their launching process.

binary↗
NASA NTRS2024

Inertia of Ionospheric Conductance During Electron Precipitation Events

Using the SuperThermal Electron Transport (STET) model coupled with the Super‐thermal Proton Electron Atomic Hydrogen—tRansport in the Ionosphere and Thermosphere (SPEAH‐RIT) codes, we demonstrate that temporal variability of ionospheric conductance is defined by several time scales: the temporal variations of the magnetospheric source, the start time of electron precipitation, and the termination of the corresponding source. In these cases, the time scales are defined by dissipation of energetic electrons and effective recombination processes. The results presented in this paper were applied in the regions of pulsating aurora and polararcs, demonstrating the fact that ionospheric conductance requires some time to form and decay. These time delays constitute an effective “inertia” in the conductance calculation which is- not accounted for in many global models which assume an instantaneous connection between precipitation and conductance. Ionospheric conductance inertia influences the temporal variation in ionospheric and magnetospheric electric fields, and as a result, impacts magnetosphere‐ionosphere (MI) dynamics on a global scale.

George V Khazanov↗
NASA NTRS2003

Transient Evolution of a Planar Diffusion Flame Aft of a Translating Flat Plate

The high degree of spatial symmetry of a planar diffusion flame affords great simplifications for experimental and modeling studies of gaseous fuel combustion. Particularly, in a microgravity environment, where buoyancy effects are negligible, an effectively strain-rate-free, vigorous flame may be obtained. Such a flame can also provide long residence times and large length scales for practical probing of flame structures and soot processes. This 2-D numerical study explores the feasibility of establishing such a planar diffusion flame in an enclosed container utilizing a realistic test protocol for a microgravity experiment. Fuel and oxygen mixtures, initially segregated into two half-volumes of a squat rectangular container by a thin separator, are ignited as soon as a flammable mixture is formed in the wake of the separator withdrawn in the centerplane. A triple-flame ensues that propagates behind the trailing edge of the separator. The results of calculations show that the mechanically- and thermally-induced convection decays in about two seconds. The establishment of a planar diffusion flame after this period seems feasible in the central region of the container with sufficient quantities of reactants left over for subsequent studies. An analysis of the flame initiation and formation process suggests how the feasibility of creating such a flame can be further improved.

Gokoglu, Suleyman A.↗
NASA NTRS1989

Radial mixing of material in the asteroidal zone

The asteroid belt shows radial zoning of compositional structure. The most abundant types are successively S, C, and P types from the inner to the outer parts of the main belt, and D type in the Trojan clouds. This paper examines processes for producing this structure before, during, and after the accretion of asteroids. The initial structure is established by temperature and composition gradients in the turbulent solar nebula during the collapse of the presolar cloud. The radial scale of the zoning, comparable to the disk thickness, favors disk models with relatively low turbulent viscosity. Radial decay of solid bodies due to gas drag during settling to the central plane and planetesimal formation probably causes only a small degree of mixing, due to the systematic nature of drag-induced motions. The formation of Jupiter causes scattering of massive planetesimals from that planet's zone through the asteroid zone. The present random velocities of asteroids resulting from that stirring process are consistent with the radial scale of transitions between compositional types.

Ruzmaikina, T. V.↗
NASA NTRS1992

Dynamics of a phase conjugate resonator - Transient build-up and decay rates

The standard four wave mixing model in a sluggish photorefractive medium is employed to calculate the transient response of a phase conjugate resonator. General trends are revealed and discussed in view of the possible utilization of the system in image processing. Experimental results are given to confirm qualitatively the predicted behavior.

Liu, S. R.↗
NASA NTRS2002

Nonlinear Dynamic Models in Advanced Life Support

To facilitate analysis, ALS systems are often assumed to be linear and time invariant, but they usually have important nonlinear and dynamic aspects. Nonlinear dynamic behavior can be caused by time varying inputs, changes in system parameters, nonlinear system functions, closed loop feedback delays, and limits on buffer storage or processing rates. Dynamic models are usually cataloged according to the number of state variables. The simplest dynamic models are linear, using only integration, multiplication, addition, and subtraction of the state variables. A general linear model with only two state variables can produce all the possible dynamic behavior of linear systems with many state variables, including stability, oscillation, or exponential growth and decay. Linear systems can be described using mathematical analysis. Nonlinear dynamics can be fully explored only by computer simulations of models. Unexpected behavior is produced by simple models having only two or three state variables with simple mathematical relations between them. Closed loop feedback delays are a major source of system instability. Exceeding limits on buffer storage or processing rates forces systems to change operating mode. Different equilibrium points may be reached from different initial conditions. Instead of one stable equilibrium point, the system may have several equilibrium points, oscillate at different frequencies, or even behave chaotically, depending on the system inputs and initial conditions. The frequency spectrum of an output oscillation may contain harmonics and the sums and differences of input frequencies, but it may also contain a stable limit cycle oscillation not related to input frequencies. We must investigate the nonlinear dynamic aspects of advanced life support systems to understand and counter undesirable behavior.

Jones, Harry↗
NASA NTRS2003

Digital Particle Image Velocimetry (DPIV) Used for Space-Time Correlations in Nozzle Flow

An optical measurement technique known as Digital Particle Image Velocimetry (DPIV) was used previously to characterize the first- and second-order statistical properties of both cold and hot jet flows from externally mixed nozzles in NASA Glenn Research Center's Nozzle Acoustic Test Rig. In this technique, an electronic camera records particles entrained in a flow as a laser light sheet is pulsed at two instances in time. Correlation processing of the recorded particle image pairs yields the two-component velocity field across the imaged plane of the flow. The information acquired using DPIV is being used to improve our understanding of the decay of turbulence in jet flows-a critical element for understanding the acoustic properties of the flow. Recently, two independent DPIV systems were installed in Glenn's Small Hot Jet Acoustic Rig, enabling multiplane correlations in time and space. The data were collected over a range of different Mach numbers and temperature ratios. DPIV system 1 was fixed to a large traverse rig, and DPIV system 2 was mounted on a small traverse system mounted on the large traverse frame. The light sheets from the two DPIV systems were aligned to lie in the same axial plane, with DPIV system 2 being independently traversed downstream along the flow direction. For each measurement condition, the DPIV systems were started at a fully overlapping orientation. A polarization separation technique was used to avoid cross-talk between the two systems. Then, the DPIV systems fields were shifted axially apart, in successively increasing steps. The downstream DPIV system 2 was triggered at a short time delay after the upstream DPIV system 1, where the time delay was proportional to the convective flow velocity in the shear layer of the jet flow and the axial separation of the two DPIV systems. The acquired data were processed to obtain the instantaneous velocity vector maps over a range of time delays and spatial separations. The velocity fields from the different DPIV systems were then cross-correlated to determine the degree of correlation remaining in the flow as the downstream convection distance was increased. The new data provide Lagrangian measurements of the convective turbulent structures in the shear layer of an exhaust nozzle. These measurements, obtained in both cold and hot flows, will be used to validate and correct models for space-time velocity correlations-long a missing key to predicting jet noise.

Wernet, Mark P.↗
NASA NTRS1975

Determining the parameters of the prognostic operator for undamped fluctuations by the use of the D sub m(kappa; alpha 1,..., alpha sub m)

The prognostic operator is defined as the matrix or integral operation which, when applied to a set of known values of the vector for various earlier moments of time, predicts a value for the vector at a future moment by the amount ahead of time. If the vector represents a function that decays with time, then the predicted values of the function are given as series expansions in terms of the same functions but with unknown coefficients if some change in the process occurs at the moment of prediction. As examples of such changes are considered: (1) the circulation mechanisms of the atmosphere under the influence of solar activity; (2) brightness fields fluctuations; and (3) wave formations or currents in the ocean after a change in wind field.

Dmitriyev, A. A.↗
NASA NTRS1979

Models of an early lunar dynamo

The hypothesis that a dynamo once existed in the moon, and hence was the source of lunar paleomagnetism, is tested using a model for the global thermoremanent magnetization of spherical lithospheres. Various models of an ancient lunar dipole field are used which incorporate intensity variations and reversals, and which are consistent with lunar sample paleointensities. It is found that non-reversing lunar dynamos which have simple exponential decay histories beginning at 4.6 b.y. ago are inconsistent with this limit, unless the moon has been thoroughly demagnetized to a depth of tens of kilometers by impacts or other processes. An early lunar dynamo cannot be excluded by global scalar measurements unless the permanent lunar dipole moment is shown to be significantly less than 10 to the 13th power G/cu cm by future spacecraft measurements, which may be technologically impossible; vector measurements of lunar magnetic anomalies over the whole moon offer a possibility of determining the source of the field which magnetized the lunar crust.

Srnka, L. J.↗