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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 667 records · Page 37
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Improved silicon nitride for advanced heat engines

The AiResearch Casting Company baseline silicon nitride (92 percent GTE SN-502 Si sub 3 N sub 4 plus 6 percent Y sub 2 O sub 3 plus 2 percent Al sub 2 O sub 3) was characterized with methods that included chemical analysis, oxygen content determination, electrophoresis, particle size distribution analysis, surface area determination, and analysis of the degree of agglomeration and maximum particle size of elutriated powder. Test bars were injection molded and processed through sintering at 0.68 MPa (100 psi) of nitrogen. The as-sintered test bars were evaluated by X-ray phase analysis, room and elevated temperature modulus of rupture strength, Weibull modulus, stress rupture, strength after oxidation, fracture origins, microstructure, and density from quantities of samples sufficiently large to generate statistically valid results. A series of small test matrices were conducted to study the effects and interactions of processing parameters which included raw materials, binder systems, binder removal cycles, injection molding temperatures, particle size distribution, sintering additives, and sintering cycle parameters.

Yeh, H. C.↗
NASA NTRS1987

Multiple-mode large deflection random response of beams with nonlinear damping subjected to acoustic excitation

Multiple-mode nonlinear analysis is carried out for beams subjected to acoustic excitation. Effects of both nonlinear damping and large-deflection are included in the analysis in an attempt to explain the experimental phenomena of aircraft panels excited at high sound pressure levels; that is the broadening of the strain response peaks and the increase of modal frequency. An amplitude dependent nonlinear damping model is used in the anlaysis to study the effects and interactions of multiple modes, nonlinear stiffness and nonlinear damping on the random response of beams. Mean square maximum deflection, mean square maximum strain, and spectral density function of maximum strain for simple supported and clamped beams are obtained. It is shown analytically that nonlinear damping contributes significantly to the broadening of the response peak and to the mean square deflection and strain.

Prasad, C. B.↗
NASA NTRS1988

Experimental study of unsteadiness of the flow around an ogive-cylinder at incidence

Flow visualization, surface mounted pressure transducers and hot-wires anemometers have been used to measure the leeside vortex flowfield on an ogive-cylinder at high angles of attack. The results show that there is a high degree of flowfield unsteadiness which arises due to several phenomena. The phenomena include large scale von Karman-type shedding, high frequency pressure and velocity fluctuations indicative of the presence of free shear-layer vortices, and a vortex interaction. The effects of position along the body, angle of attack and wind tunnel speed on the surface pressure and velocity in the wake have been investigated.

Degani, D.↗
NASA NTRS1989

Bearing-Bypass Loading On Bolted Composite Joints

Unexpected interaction between effects of bypass and bearing loads reported. Combined experimental and analytical study described in NASA technical memorandum conducted to investigate effects of simultaneous bearing and bypass loading on graphite/epoxy laminate. Results important in emerging technology of composites for use in wide range of applications. Includes applications in aircraft, boats, and automobiles, in which bolted connections to composites increasingly important.

Crews, John H.↗
NASA NTRS1989

Simulation evaluation of TIMER, a time-based, terminal air traffic, flow-management concept

A description of a time-based, extended terminal area ATC concept called Traffic Intelligence for the Management of Efficient Runway scheduling (TIMER) and the results of a fast-time evaluation are presented. The TIMER concept is intended to bridge the gap between today's ATC system and a future automated time-based ATC system. The TIMER concept integrates en route metering, fuel-efficient cruise and profile descents, terminal time-based sequencing and spacing together with computer-generated controller aids, to improve delivery precision for fuller use of runway capacity. Simulation results identify and show the effects and interactions of such key variables as horizon of control location, delivery time error at both the metering fix and runway threshold, aircraft separation requirements, delay discounting, wind, aircraft heading and speed errors, and knowledge of final approach speed.

Credeur, Leonard↗
NASA NTRS1989

Updated users' guide for TAWFIVE with multigrid

A program for the Transonic Analysis of a Wing and Fuselage with Interacted Viscous Effects (TAWFIVE) was improved by the incorporation of multigrid and a method to specify lift coefficient rather than angle-of-attack. A finite volume full potential multigrid method is used to model the outer inviscid flow field. First order viscous effects are modeled by a 3-D integral boundary layer method. Both turbulent and laminar boundary layers are treated. Wake thickness effects are modeled using a 2-D strip method. A brief discussion of the engineering aspects of the program is given. The input, output, and use of the program are covered in detail. Sample results are given showing the effects of boundary layer corrections and the capability of the lift specification method.

Melson, N. Duane↗
NASA NTRS1989

Improved silicon carbide for advanced heat engines. I - Process development for injection molding

Alternate processing methods have been investigated as a means of improving the mechanical properties of injection-molded SiC. Various mixing processes (dry, high-sheer, and fluid) were evaluated along with the morphology and particle size of the starting beta-SiC powder. Statistically-designed experiments were used to determine significant effects and interactions of variables in the mixing, injection molding, and binder removal process steps. Improvements in mechanical strength can be correlated with the reduction in flaw size observed in the injection molded green bodies obtained with improved processing methods.

Whalen, Thomas J.↗
NASA NTRS1989

A parametric study of three-dimensional separation at a wing/body junction for supersonic free-stream conditions

The problem of three-dimensional separation at a wing/body junction has been investigated numerically using a three-dimensional Navier-Stokes code which employs the MacCormack's time split finite volume technique. An algebraic grid generation technique is used for generating the grid at a wing/body junction. Specific computational results on velocity and pressure distribution in the separated flow region are compared with the experimental results. A parametric study of flow parameters such as Mach number and Reynolds number have been carried out to understand their effect in interaction flow field. The parametric study indicates a strong dependency of the number of vortices at the junction on Mach number and Reynolds number.

Lakshmanan, B.↗
NASA NTRS1989

A complete sample of double-lobed radio quasars for VLBI tests of source models - Definition and statistics

A complete, flux-density-limited sample of double-lobed radio quasars is defined, with nuclei bright enough to be mapped with the Mark III VLBI system. It is shown that the statistics of linear size, nuclear strength, and curvature are consistent with the assumption of random source orientations and simple relativistic beaming in the nuclei. However, these statistics are also consistent with the effects of interaction between the beams and the surrounding medium. The distribution of jet velocities in the nuclei, as measured with VLBI, will provide a powerful test of physical theories of extragalactic radio sources.

Hough, D. H.↗
NASA NTRS1990

Effect of crack-microcracks interaction on energy release rates

The energy release rates associated with the main crack advancing into its surrounding damage zone, and the damage zone translation relative to the main crack, as well as the energy of interaction between the crack and the damage zone are analyzed. The displacement and stress fields for this crack-damage interaction problem are reconstructed by employing a semi-empirical stress analysis which involves experimental evaluation of the average microcrack density in the damage zone.

Chudnovsky, A.↗
NASA NTRS1990

A description and evaluation of TIMER: A time-based terminal flow-control concept

A description of a time-based ATC concept called TIMER (Traffic Intelligence for the Management of Efficient Runway-scheduling) and the results of a fast time and real time computer evaluation are presented. The concept was designed to improve the efficiency of extended terminal area operations (en route approach, transition, and terminal flight to the runway). TIMER integrates en route metering, fuel efficient cruise and profile descents, terminal sequencing and spacing together with computer-generated controller aids, in order to fully use runway capacity and improve efficiency of delay absorption. The concept, by using simplified aircraft models, accommodates both 4-D and non 4-D equipped aircraft and is designed for integration into the manual, voice linked ATC system in an evolutionary manner and still be able to accommodate proposed system upgrade features such as data link and further ground automation. Fast time and real time computer simulation results identify and show the effects and interactions of such key variables as horizon of control, metering fix and final approach delivery time errors, aircraft separation requirements, delay discounting, wind, flight technical error, and knowledge of aircraft final approach speed. The current ATC system has a runway interarrival-error standard deviation of approx. 26 seconds. Simulation results indicate that, with computer aiding, the runway interarrival-error standard deviation for non 4-D equipped traffic can be reduced to the region of 8 to 12 seconds if expected final approach speed is known; however, the reduction is only in the region of 16 to 20 seconds if expected final approach speed is unknown. Another major finding is that en route metering fix delivery-error standard deviation should be kept to less than a number somewhere between 35 to 45 seconds to achieve full runway capacity. This requirement implies the need for either airborne automation or assistance to the controller since the current manual performance in today's en route metering environment is in the order of 1.5 minutes.

Credeur, Leonard↗
NASA NTRS1990

FIR statistics of paired galaxies

Much progress has been made in understanding the effects of interaction on galaxies (see reviews in this volume by Heckman and Kennicutt). Evidence for enhanced emission from galaxies in pairs first emerged in the radio (Sulentic 1976) and optical (Larson and Tinsley 1978) domains. Results in the far infrared (FIR) lagged behind until the advent of the Infrared Astronomy Satellite (IRAS). The last five years have seen numerous FIR studies of optical and IR selected samples of interacting galaxies (e.g., Cutri and McAlary 1985; Joseph and Wright 1985; Kennicutt et al. 1987; Haynes and Herter 1988). Despite all of this work, there are still contradictory ideas about the level and, even, the reality of an FIR enhancement in interacting galaxies. Much of the confusion originates in differences between the galaxy samples that were studied (i.e., optical morphology and redshift coverage). Here, the authors report on a study of the FIR detection properties for a large sample of interacting galaxies and a matching control sample. They focus on the distance independent detection fraction (DF) statistics of the sample. The results prove useful in interpreting the previously published work. A clarification of the phenomenology provides valuable clues about the physics of the FIR enhancement in galaxies.

Sulentic, Jack W.↗
NASA NTRS1991

Stochastic availability analysis of operational data systems in the Deep Space Network

Existing availability models of standby redundant systems consider only an operator's performance and its interaction with the hardware performance. In the case of operational data systems in the Deep Space Network (DSN), in addition to an operator system interface, a controller reconfigures the system and links a standby unit into the network data path upon failure of the operating unit. A stochastic (Markovian) process technique is used to model and analyze the availability performance and occurrence of degradation due to partial failures are quantitatively incorporated into the model. Exact expressions of the steady state availability and proportion degraded performance measures are derived for the systems under study. The interaction among the hardware, operator, and controller performance parameters and that interaction's effect on data availability are evaluated and illustrated for an operational data processing system.

Issa, T. N.↗
NASA NTRS1992

A comparative study of the effects of inhibitor stub length on solid rocket motor combustion chamber pressure oscillations: RSRM at T = 80 seconds, preliminary results

Results from a continuing, time-accurate computational study of the combustion gas flow inside the Space Shuttle Redesigned Solid Rocket Motor (RSRM) are presented. These computational fluid dynamic (CFD) analyses duplicate unsteady flow effects which interact in the RSRM to produce pressure oscillations, and resulting thrust oscillations, at nominally 15, 30, and 45 Hz. Results of the Navier-Stokes computations made at mean pressure and flow conditions corresponding to 80 seconds after motor ignition both with and without a protruding, rigid inhibitor at the forward joint cavity are presented here.

Chasman, D.↗
NASA NTRS1992

Characteristics of two adjacent rectangular jets

Rectangular supersonic (Design Mach number 1.8), single and twin free jets were tested in a Mach number range of 1.2 to 2.4. The objective was to study the interaction between the jets and the effect of the interaction on the spreading rate of the jets. Nozzle spacing in the range of one to four equivalent exit diameters, and jet Mach number were the parameters investigated. The experimental techniques used were Schlieren visualization and direct mixing (gas sampling) measurements from which jet spreading can be readily obtained. At the design Mach number of the nozzles and above the twin jets interact but the interaction does not affect the spreading rate of the jets. At lower Mach numbers, a moderate increase in the twin jets' spread compared to the single jet's spread was observed. The greater increase was observed for nozzle spacing of two equivalent exit diameters. Similar conclusions are drawn from both visualization and direct mixing results.

Zeierman, S.↗
NASA NTRS1991

Matrix cracking in composite laminates with resin-rich interlaminar layers

Fracture mechanics analysis and test data for a toughened composite material that has a resin-rich interlaminar layer (RIL) were used to investigate in situ strength. Exposure to a range of environmental conditions was considered. A parametric analysis study was performed to judge the effects of laminate and material variables. A finite thickness effect, indicating an interaction between ply group thickness and effective flaw size, was found dominant. The magnitude of the effect was directly related to RIL stiffness. In situ strength was found to decrease with decreasing RIL stiffness. This work indicates the need to use a fracture mechanics model of actual lamina microstructure and heterogeneous properties to predict in situ strength in materials with RIL.

Ilcewicz, Larry B.↗
NASA NTRS1992

The Gas-Grain Simulation Facility (GGSF) for Space Station Freedom - Design concept

The GGSF is specifically designed to accommodate micro-g experiments that investigate long-term effects and interactions between submicron to centimeter size particles. The paper introduces the science disciplines and the type of experiments that are currently envisioned for the GGSF. The broad range of science and technology requirements are discussed, and the Space Station Freedom (SSF) accommodations, and available utilities are reviewed. Based on the requirements and the available accommodations, a facility conceptual design is outlined. The required subsystems are listed, and the rationale and considerations that lead to the selected approach, delineated. The present GGSF concept is that of a modular facility system comprising a flight rack and an array of fully compatible and interchangeable subsystems that are designed to meet a diverse set of science requirements. The modularity allows for future upgrade of various subsystems as technology evolves and for introduction of new modules to accommodate new or different experiments. These features are essential for a facility that is expected to be in service on board the SSF for 10 years or more.

Gat, N.↗
NASA NTRS1992

On-orbit characterization of electric propulsion on LEO satellites

Utilizing commercial or military satellites as testbeds for subsystems is a potential platform for small devices. Electric propulsion is a viable and upcoming subsystem that is of high interest to planetary mission engineers as well as commercial satellite developers. It is proposed that by incorporating small lightweight electric propulsion devices onto small satellites as external or 'bolt-on' experiments, an increase in the number of flight opportunities can occur. Specific problems are spacecraft body interaction, contamination effects, thermal interface problems, power conditioning control electronics, and propulsion feed system interfaces.

Barnhart, D.↗