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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 829 records · Page 46
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

An unconditionally stable Runge-Kutta method for unsteady flows

A quasi-three dimensional analysis was developed for unsteady rotor-stator interaction in turbomachinery. The analysis solves the unsteady Euler or thin-layer Navier-Stokes equations in a body fitted coordinate system. It accounts for the effects of rotation, radius change, and stream surface thickness. The Baldwin-Lomax eddy viscosity model is used for turbulent flows. The equations are integrated in time using a four stage Runge-Kutta scheme with a constant time step. Implicit residual smoothing was employed to accelerate the solution of the time accurate computations. The scheme is described and accuracy analyses are given. Results are shown for a supersonic through-flow fan designed for NASA Lewis. The rotor:stator blade ratio was taken as 1:1. Results are also shown for the first stage of the Space Shuttle Main Engine high pressure fuel turbopump. Here the blade ratio is 2:3. Implicit residual smoothing was used to increase the time step limit of the unsmoothed scheme by a factor of six with negligible differences in the unsteady results. It is felt that the implicitly smoothed Runge-Kutta scheme is easily competitive with implicit schemes for unsteady flows while retaining the simplicity of an explicit scheme.

Jorgenson, Philip C. E.↗
NASA NTRS1983

What changes and what endures - The capabilities and limitations of training and selection

The contributions of psychology to aviation in the areas of selection, training, and evaluation, and the implementation of new technologies are discussed. The concept of personality traits versus modification of human behavior through principles of learning are analyzed. Particular consideration is given to achievement motivation (defined in terms of mastery, work, and competitiveness) and the differences between traits and attitudes. It is argued that personality traits are important dimensions of the self and are useful measures of individual differences. The selection of individuals with desired personality characteristics and the training of personnel to improve crew coordination, flight-deck management, and interpersonal efficacy are examined.

Helmreich, Robert L.↗
NASA NTRS1986

Overview of advanced components for fiber optic systems

The basic operating principles and potential performance of several state-of-the-art fiber-optic devices are illustrated with diagrams and briefly characterized. Technologies examined include high-birefringence polarization-maintaining fibers and directional couplers, single-mode fiber polarizers and cut-off polarizers, optical-fiber modulators with radially poled piezoactive polymer (PVF2) jackets, and piezoelectric-squeezer polarization modulators. The need for improved manufacturing techniques to make such fiber-optic devices cost-competitive with their thin-film integrated-optics analogs is indicated.

Depaula, Ramon P.↗
NASA NTRS1987

A new interpretation of plasma-line overshoot phenomena

The temporal evolution of Langmuir waves excited by high-power, high-frequency (HF) radio waves in the ionosphere is studied theoretically. This study is motivated by past observations made with the 450 MHz radar at Arecibo Observatory in Puerto Rico. Two kinds of nonlinear damping to the parametric decay instability are considered in the derivation of the rate equation for the spectral intensity of enhanced Langmuir waves. They are Langmuir wave cascading caused by nonlinear Landau damping and cross-field electron diffusion. The first damping process leads to the saturation of individual unstable Langmuir wave. The second process, which results from the incoherent scattering of electron orbits by the total excited Langmuir waves, yields anomalous damping that applies to each Langmuir wave. Consequently, Langmuir waves with smaller growth rates will be suppressed by those with larger growth rates. Such a mode competition process may cause the overshoot of the HF-enhanced plasma line observed with the Arecibo 430 MHz radar. Favorable agreement is obtained between theory and the Arecibo observations.

Kuo, S. P.↗
NASA NTRS1987

Curvilinear crack layer propagation

An account is given of an experiment designed to allow observation of the effect of damage orientation on the direction of crack growth in the case of crack layer propagation, using polystyrene as the model material. The direction of crack advance under a given loading condition is noted to be determined by a competition between the tendency of the crack to maintain its current direction and the tendency to follow the orientation of the crazes at its tip. The orientation of the crazes is, on the other hand, determined by the stress field due to the interaction of the crack, the crazes, and the hole. The changes in craze rotation relative to the crack define the active zone rotation.

Chudnovsky, Alexander↗
NASA NTRS1987

Disuse atrophy, plasma corticosterone, and muscle glucocorticoid receptor levels

The effect of whole-body suspension on the time course and the extent of plasma corticosterone changes and the tissue sensitivity to glucocorticoids were investigated in rats subjected to seven days of whole-body suspension. Plasma corticosterone increased significantly on the first and the third days of suspension, but returned to control levels by day seven. Muscle glucocorticoid receptors exhibited a characteristic hormonal specificity (evaluated in competitive-displacement experiments). In controls, receptor site concentration in the slow-twitch soleus was comparable to that in the fast-twitch gastrocnemius and plantaris, but was significantly less than in the extensor; seven days of suspension resulted in significant differential effects on muscle receptor levels. The largest increase in receptor concentration was observed in the soleus in which it remained elevated after the receptor levels in other muscles returned to normal.

Steffen, J. M.↗
NASA NTRS1987

Partial redistribution in high-density, highly ionized plasmas

The conditions for which partial redistribution functions must be used for radiation transport in high-Z, high-density, laser-produced plasmas are examined. A previously developed two-photon formalism based on the model microfield method is used to calculate redistribution functions including electron and ion Stark broadening with ion dynamic effects. The competition between the relaxation rates and spontaneous emission is shown to determine the conditions for partial redistribution. The discussion makes use of microfield fluctuation rates and broadening coefficients which can be determined from simulation calculations. The redistribution function for the Ly-alpha transition of Ar XVIII is presented for typical plasma conditions.

Talin, B.↗
NASA NTRS1987

Crystallization behavior of a melt-spun Fe-Ni based steel

Whether Fe-Ni-based alloys solidify with a bcc or fcc structure has been observed by many investigators to be a stronger function of kinetics and undercooling than strictly free-energy minimization. Such behavior has been observed in an Fe(52.8)Ni(28.7)Al(3.4)Ti(6.1)B(9.0) alloy. The alloy was cast as ribbons about 45 microns thick using a dual free-jet variation of chillbock melt spinning against a Cu wheel. Optical, X-ray, and electron analyses of the as-cast and annealed ribbons were performed. A microstructure of at least four layers containing combinations of ecc, bcc, and amorphous phases in differing proportions was observed in the as-cast ribbon. The midthickness layer had the most unusual features, containing fcc grains about 75 nm in size encompassing spherulitic regions as large as 15 microns comprised of fcc grains about 25 nm in size. The crystallization sequence responsible for the as-cast microstructure is discussed in terms of the competition between the formation of bcc and fcc phases as influenced by undercooling, recalescence, and variations in cooling rate experienced by the as-cast ribbon.

Michal, G. M.↗
NASA NTRS1987

Analysis, prediction, and prevention of edge delamination in rotor system structures

Analytical methods such as simple sublaminate analysis, as well as quasi three-dimensional finite element analysis, provide insight into delamination characteristics and reliable trend data with which to make rapid evaluations of competitive concepts in the design environment. It is concluded that free edge delamination can be managed by analysis and prevented by design. However, in order to ensure durable composite structures, more work is needed to characterize delamination that occurs from other sources, such as matrix cracking and ply drops.

Chan, Wen S.↗
NASA NTRS1987

Solid hydrocarbon aerosols produced in simulated Uranian and Neptunian stratospheres

Solid hydrocarbon films were deposited in an RF plasma discharge of various CH4/H2/He mixtures under conditions simulating the formation of solid aerosols by magnetospheric charged particles in the stratospheres of Uranus and Neptune. The percentage of CH4 ranged from 0.0002 to 100 percent; the pressure in the discharge chamber was either 130 or 660 microbar; and the films produced were yellow to deep red-brown in color and 2-25 microns thick. The real and imaginary parts of the refractive index at wavelengths from 350 nm to 2.5 microns were determined for all the films, and the results are compared with observational data and the predictions of theoretical models in extensive tables and graphs. Good agreement is demonstrated, suggesting that aerosol production by this mechanism may be competitive with UV or charged-particle irradiation of hydrocarbon condensates.

Khare, B. N.↗
NASA NTRS1988

Communications satellites in non-geostationary orbits

The design of a satellite communications system in an orbit lower than GEO is described. Two sun-synchronous orbits which lie in the equatorial plane have been selected: (1) the apogee at constant time-of-day equatorial orbit, a highly eccentric orbit with five revolutions per day, which allows 77-135 percent more satellite mass to be placed in orbit than for GEO; and (2) the sun-synchronous 12-hour equatorial orbit, a circular orbit with two revolutions per day, which allows 23-29 percent more mass. The results of a life cycle economic analysis illustrate that nongeostationary satellite systems could be competitive with geostationary satellite systems.

Price, Kent M.↗
NASA NTRS1987

Issues in space photovoltaic research and technology

Key issues and opportunities in space photovoltaic research and technology are addressed relative to future NASA mission requirements and drivers. Examples are given of future space missions and/or operational capabilities that are on NASA's planning horizon, presenting major technology challenges to the use of photovoltaic power generation in space. A brief description of the capabilities ascribed to the competing technologies of nuclear and solar thermal power systems are discussed. The performance goals that space photovoltaic power systems must meet to remain competitive are described.

Flood, Dennis J.↗
NASA NTRS1988

Angular navigation capabilities of short baseline phase delay interferometry

Short baseline phase delay interferometry can provide angular navigation capabilities which are competitive with current accuracies for group delay Very Long Baseline Interferometry (VLBI) on intercontinental baselines. In addition, a number of operational considerations make short baseline interferometry attractive, including enhanced mutual visibility, ability to observe at higher elevation angles, and the possibility of processing data in realtime. To make use of the higher precision phase delay datatype, however, the cycle ambiguity associated with the observed interferometric phase must be resolved. Results are presented for two experiments, on baselines of 5.9 and 253 km, for which RF phase connection appears to have been reliably achieved for several groups of angularly close radio sources. The dependence of the resulting phase delay residuals on elevation suggests that temporal fluctuations in the line-of-sight troposphere delay are a dominant error source. The observed RMS phase delay residuals of 10 psec or less suggest that baselines of order 100 km could provide high-efficiency angular navigation with accuracies well below 50 nrad. Plans for further work at the Goldstone Deep Space Communication Complex are reviewed.

Edwards, C. D.↗
NASA NTRS1988

Development of a commercial expendable launch vehicle industry

The privatization and commercialization of the expendable launch vehicle (ELV) industry is examined. The government policy to terminate ELV service with the development of the Shuttle is discussed. NASA support to commercial ELVs and privatization and commercialization ELV agreements executed by NASA are considered. The services offered by several companies producing and operating ELVs, and plans for NASA to procure launch services competitively from the private sector are presented.

Stone, Barbara A.↗
NASA NTRS1989

Algorithm For Optimal Control Of Large Structures

Cost of computation appears competitive with other methods. Problem to compute optimal control of forced response of structure with n degrees of freedom identified in terms of smaller number, r, of vibrational modes. Article begins with Hamilton-Jacobi formulation of mechanics and use of quadratic cost functional. Complexity reduced by alternative approach in which quadratic cost functional expressed in terms of control variables only. Leads to iterative solution of second-order time-integral matrix Volterra equation of second kind containing optimal control vector. Cost of algorithm, measured in terms of number of computations required, is of order of, or less than, cost of prior algoritms applied to similar problems.

Salama, Moktar A.↗
NASA NTRS1989

Diode-Laser Doppler Velocimeter

Diode-laser Doppler velocimeter measures nonintrusively flow of incompressible fluid in narrow tube. New velocimeter rugged, compact, and competitive in cost. Includes three-section optical head mounted on tube containing flow. In slightly different version, beam splitter and mirror used to split laser beam into two beams.

Getzer, Gregory J.↗
NASA NTRS1988

Rechargeable metal hydrides for spacecraft application

Storing hydrogen on board the Space Station presents both safety and logistics problems. Conventional storage using pressurized bottles requires large masses, pressures, and volumes to handle the hydrogen to be used in experiments in the U.S. Laboratory Module and residual hydrogen generated by the ECLSS. Rechargeable metal hydrides may be competitive with conventional storage techniques. The basic theory of hydride behavior is presented and the engineering properties of LaNi5 are discussed to gain a clear understanding of the potential of metal hydrides for handling spacecraft hydrogen resources. Applications to Space Station and the safety of metal hydrides are presented and compared to conventional hydride storage. This comparison indicates that metal hydrides may be safer and require lower pressures, less volume, and less mass to store an equivalent mass of hydrogen.

Perry, J. L.↗
NASA NTRS1988

An investigation of new methods for estimating parameter sensitivities

Parameter sensitivity is defined as the estimation of changes in the modeling functions and the design variables due to small changes in the fixed parameters of the formulation. There are currently several methods for estimating parameter sensitivities requiring either difficult to obtain second order information, or do not return reliable estimates for the derivatives. Additionally, all the methods assume that the set of active constraints does not change in a neighborhood of the estimation point. If the active set does in fact change, than any extrapolations based on these derivatives may be in error. The objective here is to investigate more efficient new methods for estimating parameter sensitivities when the active set changes. The new method is based on the recursive quadratic programming (RQP) method and in conjunction a differencing formula to produce estimates of the sensitivities. This is compared to existing methods and is shown to be very competitive in terms of the number of function evaluations required. In terms of accuracy, the method is shown to be equivalent to a modified version of the Kuhn-Tucker method, where the Hessian of the Lagrangian is estimated using the BFS method employed by the RPQ algorithm. Inital testing on a test set with known sensitivities demonstrates that the method can accurately calculate the parameter sensitivity. To handle changes in the active set, a deflection algorithm is proposed for those cases where the new set of active constraints remains linearly independent. For those cases where dependencies occur, a directional derivative is proposed. A few simple examples are included for the algorithm, but extensive testing has not yet been performed.

Beltracchi, Todd J.↗