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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 739 records · Page 41
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Teleconferencing: Cost optimization of satellite and ground systems for continuing progressional education and medical services

A set of analytical capabilities that are needed to assess the role satellite communications technology will play in public and other services was developed. It is user oriented in that it starts from descriptions of user demand and develops the ability to estimate the cost of satisfying that demand with the lowest cost communications system. To ensure that the analysis could cope with the complexities of the real users, two services were chosen as examples, continuing professional education and medical services. Telecommunications costs are effected greatly by demographic factors, involving distribution of users in urban areas and distances between towns in rural regions. For this reason the analytical tools were exercised on sample locations. San Jose, California and Denver, Colorado were used to represent an urban area and the Rocky Mountain states were used to represent a rural region. In assessing the range of satellite system costs, two example coverage areas were considered, one appropriate to cover the contiguous forty-eight states, a second appropriate to cover about one-third that area.

Dunn, D.↗
NASA NTRS1974

Voltage-spike analysis for a free-running parallel inverter

Unwanted and sometimes damaging high-amplitude voltage spikes occur during each half cycle in many transistor saturable-core inverters at the moment when the core saturates and the transistors switch. The analysis shows that spikes are an intrinsic characteristic of certain types of inverters even with negligible leakage inductance and purely resistive load. The small but unavoidable after-saturation inductance of the saturable-core transformer plays an essential role in creating these undesired thigh-voltage spikes. State-plane analysis provides insight into the complex interaction between core and transistors, and shows the circuit parameters upon which the magnitude of these spikes depends.

Lee, F. C. Y.↗
NASA NTRS1982

A study of the nature of solid particle impact and shape on the erosion morphology of ductile metals

Impulsive versus steady jet impingement of spherical glass bead particles on metal surfaces was studied using a gas gun facility and a commercial sand blasting apparatus. Crushed glass particles were also used in the sand blasting apparatus as well as glass beads. Comparisons of the different types of erosion patterns were made. Scanning electron microscopy, surface profilometry and energy dispersive X-ray spectroscopy analysis were used to characterize erosion patterns. The nature of the wear can be divided into cutting and deformation, each with its own characteristic features. Surface chemistry analysis indicates the possibility of complex chemical and/or mechanical interactions between erodants and target materials.

Rao, P. V.↗
NASA NTRS1984

A new dimension in space experimentation

Based on the Space Shuttle's ability to place the Long Duration Exposure Facility (LDEF) in space and later retrieve it, a new opportunity for scientific exploration in space is studied. The LDEF which is scheduled to be placed in orbit in 1984 and returned to earth after one year in space is described. It is a large unmanned facility 9 m in length and 4 m in diameter and flying at an 482 km orbit. It is pointed out that the LDEF allows investigators to have their experiments returned to them for in-depth analysis, eliminates the need for complex systems to transmit data to earth, does not require propulsion equipment, and increases the kinds of experiments that can be performed. A description is given for each of the five categories of the experiments provided by the LDEF: (1) evaluation of the impact of space environments on materials used for thermal coatings on polymer-matrix composites, on optics, and on quartz-crystal oscillators; (2) experiments with unique heat pipe systems having the goal to achieve temperature control of + or - 6 F; (3) evaluation of solar array materials; (4) growth of single crystals of lead sulfite, calcium carbonate, and synthetic metals; and (5) scientific experiments to determine the chemistry of micrometeoroids and to identify isotopes in interstellar gas and ultra-heavy cosmic ray nuclei. Finally, the project SEEDS (Space Exposed Experiment Developed for Students) which experiments with tomato seeds behavior in zero gravity is discussed.

Sandy, M. L.↗
NASA NTRS1984

A study of the effect of solid particle impact and particle shape on the erosion morphology of ductile metals

Impulsive versus steady jet impingement of spherical glass bead particles on metal surfaces was studied using a gas gun facility and a commercial sand blasting apparatus. Crushed glass particles were also used in the sand blasting apparatus as well as glass beads. Comparisons of the different types of erosion patterns were made. Scanning electron microscopy, surface profilometry and energy dispersive X-ray spectroscopy analysis were used to characterize erosion patterns. The nature of the wear can be divided into cutting and deformation, each with its own characteristic features. Surface chemistry analysis indicates the possiblity of complex chemical and/or mechanical interactions between erodants and target materials.

Rao, P. V.↗
NASA NTRS1985

The loss of material from the cathode of metal arcs

A study was made of the effect of arc length, cathode thickness, current strength, gas pressure and the chemical nature of the cathode material and filling gases upon the material loss from Cu, Fe, and Ag cathodes in arcs. The results show that the analysis of the phenomenon is complex and the energy balance is difficult to formulate.

Seeliger, R.↗
NASA NTRS1984

Current research on shear buckling and thermal loads with PASCO - Panel analysis and sizing code

The stiffened composite structural panel analysis and sizing code designated 'PASCO' encompasses both the generality required for the exploitation of composite materials' design flexibility and an accurate buckling analysis for the detection of complex buckling modes. PASCO can accordingly design for buckling, frequency, material strength, and panel stiffness requirements. Attention is given to an additional thermal loading design capability. Design studies illustrate the importance of the multiple load condition capability when thermal loads are present.

Stroud, W. J.↗
NASA NTRS1985

Post flight analysis of NASA standard star trackers recovered from the solar maximum mission

The flight hardware returned after the Solar Maximum Mission Repair Mission was analyzed to determine the effects of 4 years in space. The NASA Standard Star Tracker would be a good candidate for such analysis because it is moderately complex and had a very elaborate calibration during the acceptance procedure. However, the recovery process extensively damaged the cathode of the image dissector detector making proper operation of the tracker and a comparison with preflight characteristics impossible. Otherwise, the tracker functioned nominally during testing.

Newman, P.↗
NASA NTRS1987

The structure and evolution of seasonal wind anomalies over the near-equatorial eastern Indian and western Pacific Oceans

The longitude-height-time structure and evolution of near-equatorial wind variability over the eastern Indian and western Pacific Oceans are studied using data obtained from a network of eight radiosonde stations extending from southern India to the central Pacific Ocean. The seasonal zonal wind anomalies observed at the cross section beween Trivandrum and Majuro stations are analyzed using an empirical orthogonal function. The Walker Circulation fluctuations are described in terms of standing oscillations in the longitude-height plane, and it is determined that Southern Oscillation propagation anomaly best represents the wind fluctuations. A complex empirical orthogonal function (CEOF) analysis and an El Nino compositing methodology are applied to the seasonal zonal wind anomalies. It is determined that the composite El Nino anomalies correspond to the spatial structure and temporal evolution of anomalies implied by the CEOF analysis.

Gutzler, David S.↗
NASA NTRS1989

Advances in fluid dynamics

Various papers on advances in fluid dynamics are presented. Individual topics addressed include: nonunique solutions of the Euler equations; numerical solution of the biharmonic equation using a spectral multigrid method; finite-volume shape and placement for efficiency, accuracy, and physics; NND schemes and their application to numerical simulation of complex plume flow problems; symbolic analysis and computational algorithm construction; and velocity and mass flux distribution measurements of spherical glass beads in air flow in a 90-deg vertical-to-horizontal bend. Also discussed are: hyperbolic solution adaptive mesh generation; progress and future directions in CFD; numerical simulation of shock focusing; microbubble formation and splitting in a turbulent boundary layer for turbulence reduction; numerical study of spherical Taylor-Couette flow, trajectories of vortex lines beneath a free surface or above a plane; and a mathematical model for response of the coronary circulation to high sustained gravitational force fields.

Ballhaus, W. F., Jr.↗
NASA NTRS1989

Prediction of turbine rotor-stator interaction using Navier-Stokes methods

Flows in turbomachinery are generally complex and do not easily lend themselves to numerical computation. The flows are three-dimensional and inherently unsteady. Complicated blade geometries and flow phenomena such as separation and periodic transition from laminar to turbulent flow add to the numerical complexity. Nevertheless, the accurate numerical analysis of such flows is a problem of considerable interest and practical importance to the turbomachinery community. Much of the early work in turbomachinery flow prediction focussed on airfoil cascades. While such analyses of flows in isolated airfoil rows have helped improve understanding of the flow phenomena and have gained widespread acceptance in the industrial community as a design tool, they do not yield any information regarding the unsteady effects arising out of rotor-stator aerodynamic interaction. These interaction effects become increasingly important as the distance between successive stator and rotor rows is decreased. Thus, the need exists for analytical tools that treat the rotor and stator airfoils as a system and provide information regarding the magnitude and the impact of the unsteady effects. The focus a three-dimensional, time-accurate, thin-layer Navier-Stokes code that was recently developed to study rotor-stator interaction problems. A system of patched and overlaid grids that move relative to each other is used to discretize the flow field and the governing equations are integrated using a third-order upwind scheme set in an iterative, implicit framework. The code was used to simulate subsonic flow through an axial turbine configuration for which considerable experimental data exists. Grid refinement studies were also conducted as part of the code validation process. The current status of the research, along with planned future directions, are also discussed.

Madavan, Nateri K.↗
NASA NTRS1991

Multivariable control of the Space Shuttle remote manipulator system using H2 and H(infinity) optimization

Three linear controllers are desiged to regulate the end effector of the Space Shuttle Remote Manipulator System (SRMS) operating in Position Hold Mode. In this mode of operation, jet firings of the Orbiter can be treated as disturbances while the controller tries to keep the end effector stationary in an orbiter-fixed reference frame. The three design techniques used include: the Linear Quadratic Regulator (LQR), H2 optimization, and H-infinity optimization. The nonlinear SRMS is linearized by modelling the effects of the significant nonlinearities as uncertain parameters. Each regulator design is evaluated for robust stability in light of the parametric uncertanties using both the small gain theorem with an H-infinity norm and the less conservative micro-analysis test. All three regulator designs offer significant improvement over the current system on the nominal plant. Unfortunately, even after dropping performance requirements and designing exclusively for robust stability, robust stability cannot be achieved. The SRMS suffers from lightly damped poles with real parametric uncertainties. Such a system renders the micro-analysis test, which allows for complex peturbations, too conservative.

Prakash, OM, II↗
NASA NTRS1991

First results from the Goddard High-Resolution Spectrograph - Spectroscopic determination of stellar parameters of Melnick 42, an O3f star in the Large Magellanic Cloud

GHRS and optical (ESO 3.6 m) observations of the O3f star Melnick 42 in the 30 Doradus complex are reported. A first analysis reveals that with a luminosity of 2.3 million L(solar) and a present mass of 100 M(solar), Melnick 42 is one of the most luminous and massive stars known. An estimate of abundances indicates that iron and oxygen are very likely reduced by a factor of four relative to the sun, whereas carbon is more strongly depleted and nitrogen is approximately solar. The terminal velocity of the stellar wind is 3000 km/s. The mass-loss rate is 4 x 10 to the -6th M(solar)/yr, with a large uncertainty. The excellent quality GHRS spectrum taken in a crowded region of the LMC demonstrates the superiority of the HST for quantitative ultraviolet spectroscopy of hot stars in other galaxies.

Heap, S. R.↗
NASA NTRS1991

Multivariable control of the Space Shuttle Remote Manipulator System

Linear controllers are designed to regulate the end effector of the Space Shuttle Remote Manipulator System (SRMS) operating in position hold mode. Design techniques used include H2 and H-infinity optimization. The nonlinear SRMS is linearized by modeling the effects of the significant nonlinearities as uncertain parameters. Each regulator design is evaluated for robust stability using both the small gain theorem with an H-infinity norm and the less conservative mu-analysis test. Regulator designs offer significant improvement over the current system for the nominal plant. Unfortunately, the SRMS model suffers from lightly damped poles with real parametric uncertainty. Under such conditions, the mu-analysis test, which allows for complex perturbations, cannot guarantee robust stability.

Adams, Neil J.↗
NASA NTRS1992

Finite-element-analysis model and preliminary ground testing of controls-structures interaction evolutionary model reflector

Results of two different nonlinear finite element analyses and preliminary test results for the final design of the Controls-Structures Interaction Evolutionary Model are presented. Load-deflection data bases are generalized from analysis and testing of the 16-foot diameter, dish shaped reflector. Natural frequencies and mode shapes are obtained from vibrational analysis. Experimental and analytical results show similar trends; however, future test hardware modifications and finite element model refinement would be necessary to obtain better correlation. The two nonlinear analysis procedures are both adequate techniques for the analysis of prestressed structures with complex geometries.

Reaves, Mercedes C.↗
NASA NTRS1993

Matrix isolation studies of the interactions of BF3 with water and substituted diethyl ethers. Chemical ionization mass spectrometric determination of the proton affinity of (CF3CH2)2O

BF3 was co-condensed with H2O, D2O, (C2H5)2O, (CF3CH2)2O, and (C2F5)2O in excess argon at 15 K. Infrared spectra of BF3/water isolated in solid argon provided a more complete analysis of the BF3--H2O complex than previously published. Infrared spectra of the matrices showed a definite Lewis acid-base interaction between BF3 and diethyl ether; a weak but definite interaction with bis (2,2,2-trifluorodiethyl) ether, and no observable interaction with perfluorodiethyl ether. Thus, the ether data indicate a clear trend between strength of interaction with BF3 and the degree of F substitution. To support and explain the emerging relationship between interaction strength and the basicity of the oxygen-containing molecule, the proton affinity of (CF3CH2)2O was measured using chemical ionization mass spectrometry. The implications of the results for lubricant/metal oxide surface interactions are discussed.

Ball, David W.↗
NASA NTRS1994

Accurate interlaminar stress recovery from finite element analysis

The accuracy and robustness of a two-dimensional smoothing methodology is examined for the problem of recovering accurate interlaminar shear stress distributions in laminated composite and sandwich plates. The smoothing methodology is based on a variational formulation which combines discrete least-squares and penalty-constraint functionals in a single variational form. The smoothing analysis utilizes optimal strains computed at discrete locations in a finite element analysis. These discrete strain data are smoothed with a smoothing element discretization, producing superior accuracy strains and their first gradients. The approach enables the resulting smooth strain field to be practically C1-continuous throughout the domain of smoothing, exhibiting superconvergent properties of the smoothed quantity. The continuous strain gradients are also obtained directly from the solution. The recovered strain gradients are subsequently employed in the integration o equilibrium equations to obtain accurate interlaminar shear stresses. The problem is a simply-supported rectangular plate under a doubly sinusoidal load. The problem has an exact analytic solution which serves as a measure of goodness of the recovered interlaminar shear stresses. The method has the versatility of being applicable to the analysis of rather general and complex structures built of distinct components and materials, such as found in aircraft design. For these types of structures, the smoothing is achieved with 'patches', each patch covering the domain in which the smoothed quantity is physically continuous.

Tessler, Alexander↗
NASA NTRS1994

ASCA observations of cooling flows in clusters of galaxies

ASCA spectra of the central regions of three cooling flows, in the Perseus, Centaurus, and A1795 clusters, together with the spectrum of the center of the Coma Cluster, are studied. Absorbed, cooler and/or cooling components are required for the cooling flow spectra but not for that of the Coma Cluster. Problems have been encountered with the basic plasma emission models in the energy range of the iron L complex, which preclude further detailed analysis at present. Our results show the potential of ASCA data for revealing the structure of cooling flows.

Fabian, A. C.↗