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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 937 records · Page 52
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Derated ion thruster development status

A 30 cm diameter xenon ion thruster is under development at NASA to provide an ion propulsion option for auxiliary and primary propulsion on missions of national interest. Specific efforts include thruster design optimizations, component life testing and validation, vibration testing, and performance characterizations. Under this program, the ion thruster will be brought to engineering model development status. This paper discusses the activities and preliminary test results to develop a 30 cm engineering model thruster.

Patterson, Michael J.↗
NASA NTRS1993

Derated ion thruster development status

A 30 cm diameter xenon ion thruster is under development at NASA to provide an ion propulsion option for auxiliary and primary propulsion on missions of national interest. Specific efforts include thruster design optimizations, component life testing and validation, vibration testing, and performance characterizations. Under this program, the ion thruster will be brought to engineering model development status. The activities and preliminary test results to develop a 30 cm engineering model thruster are discussed.

Patterson, Michael J.↗
NASA NTRS2003

Subgrid Scale Modeling in Solar Convection Simulations using the ASH Code

The turbulent solar convection zone has remained one of the most challenging and important subjects in physics. Understanding the complex dynamics in the solar con- vection zone is crucial for gaining insight into the solar dynamo problem. Many solar observatories have generated revealing data with great details of large scale motions in the solar convection zone. For example, a strong di erential rotation is observed: the angular rotation is observed to be faster at the equator than near the poles not only near the solar surface, but also deep in the convection zone. On the other hand, due to the wide range of dynamical scales of turbulence in the solar convection zone, both theory and simulation have limited success. Thus, cutting edge solar models and numerical simulations of the solar convection zone have focused more narrowly on a few key features of the solar convection zone, such as the time-averaged di erential rotation. For example, Brun & Toomre (2002) report computational finding of differential rotation in an anelastic model for solar convection. A critical shortcoming in this model is that the viscous dissipation is based on application of mixing length theory to stellar dynamics with some ad hoc parameter tuning. The goal of our work is to implement the subgrid scale model developed at CTR into the solar simulation code and examine how the differential rotation will be a affected as a result. Specifically, we implement a Smagorinsky-Lilly subgrid scale model into the ASH (anelastic spherical harmonic) code developed over the years by various authors. This paper is organized as follows. In x2 we briefly formulate the anelastic system that describes the solar convection. In x3 we formulate the Smagorinsky-Lilly subgrid scale model for unstably stratifed convection. We then present some preliminary results in x4, where we also provide some conclusions and future directions.

Young, Y.-N.↗
NASA NTRS1979

A survey of Applied Psychological Services' models of the human operator

A historical perspective is presented in terms of the major features and status of two families of computer simulation models in which the human operator plays the primary role. Both task oriented and message oriented models are included. Two other recent efforts are summarized which deal with visual information processing. They involve not whole model development but a family of subroutines customized to add the human aspects to existing models. A global diagram of the generalized model development/validation process is presented and related to 15 criteria for model evaluation.

Siegel, A. I.↗
NASA NTRS1985

A New CO2 Transmittance Parameterization and Its Impact on the GLA GCM

The Wu-Kaplan radiation parameterization (Krishnamurthy, 1982) used in the GLA Global Circulation Model (GCM) was improved by replacing its fixed tables of CO2 transmittance in the 15 micron band with models developed by regression on line-by-line transmittances. The transmittances between layers are modeled as products of effective sublayer transmittances. The GLA GCM was integrated for 20 days starting at OZ, January 21, 1979, using the transmittance model. In the control run the fixed table of 15 micron CO2 transmittances is used. The effect of the change of initial cooling rate is illustrated by a map of the difference of 50 mb temperature after 6 hours. The cooling is reduced over high topography, where the fixed table underestimates the transmittance, and is reduced slightly throughout the tropics and the north polar area where the stratosphere is relatively cold. Over elevated topography the surface cooling increases, also as expected. The stratospheric temperature increases over a degree in the arctic and smaller amounts over Antarctica and elsewhere. Tropospheric equilibrium temperature response is obscured by time dependent differences in synoptic disturbances.

Wobus, R.↗
NASA NTRS1986

Computing Benefits and Costs for Propulsion Systems

Flexible computer model developed for evaluating benefits and costs of placing large space systems into operational orbits. Model contains performance envelopes of three primary propulsion systems for orbit transfer based on three low-thrust engines. Allows for any mission model to be input into program. Model also allows user to easily vary program to examine effects of various ratings and weighting of benefit parameters for baseline engines. Program written in FORTRAN IV for use on IBM 370 computer.

Hamlyn, K.↗
NASA NTRS1991

A half century historical review of the k-omega model

A brief historical review is presented tracing evolution of the k-omega two-equation turbulence model. The review compares the various k-omega models developed since 1942, and contrasts them to the well-known k-epsilon model. Straight-forward results based on perturbation analysis illustrate advantages offered by k-omega models for flows with adverse pressure gradient and for integration through the sublayer. As part of the historical perspective, the paper shows that Kolmogorov did remarkably well in formulating his model without the aid of a computer.

Wilcox, David C.↗
NASA NTRS1994

Piloted simulation study of an ILS approach of a twin-pusher business/commuter turboprop aircraft configuration

A six-degree-of-freedom nonlinear simulation of a twin-pusher, turboprop business/commuter aircraft configuration representative of the Cessna ATPTB (Advanced turboprop test bed) was developed for use in piloted studies with the Langley General Aviation Simulator. The math models developed are provided, simulation predictions are compared with with Cessna flight-test data for validation purposes, and results of a handling quality study during simulated ILS (instrument landing system) approaches and missed approaches are presented. Simulated flight trajectories, task performance measures, and pilot evaluations are presented for the ILS approach and missed-approach tasks conducted with the vehicle in the presence of moderate turbulence, varying horizontal winds and engine-out conditions. Six test subjects consisting of two research pilots, a Cessna test pilot, and three general aviation pilots participated in the study. This effort was undertaken in cooperation with the Cessna Aircraft Company.

Riley, Donald R.↗
NASA NTRS1995

The FU Orionis outburst as a thermal accretion event: Observational constraints for protostellar disk models

The results of the time-dependent disk models developed in Bell & Lin are compared with observed properties of FU Orionis variables. Specific models are fit to the light curves of Fu Ori, V1515 Cyg, and V1057 Cyg. The slow risetime of V1515 Cyg can be matched by a self-regulated outburst model. The rapid risetimes of FU Ori and V1057 Cyg can be fitted with the application of modest perturbations to the disk surface density. Model disks display spectral features characteristic of observed objects. The color evolution of V1057 Cyg is naturally explained if mass flux drops in the inner disk (r less than 1/4 AU) while remaining steady in the outer disk. The decrease in optical line width (rotational velocity) observed during the decay of V1057 Cyg may be accounted for by an outward-propagating ionization front. We predict that before final decay to the quiescent phase, short-wavelength line widths (lambda less than 1.5 microns) will again increase. It is suggested that FU Orionis outbursts primarily occur to systems during the embedded phase with ages less than several times 10(exp 5) yr.

Bell, K. R.↗
NASA NTRS1995

Two Unipolar Terminal-Attractor-Based Associative Memories

Two unipolar mathematical models of electronic neural network functioning as terminal-attractor-based associative memory (TABAM) developed. Models comprise sets of equations describing interactions between time-varying inputs and outputs of neural-network memory, regarded as dynamical system. Simplifies design and operation of optoelectronic processor to implement TABAM performing associative recall of images. TABAM concept described in "Optoelectronic Terminal-Attractor-Based Associative Memory" (NPO-18790). Experimental optoelectronic apparatus that performed associative recall of binary images described in "Optoelectronic Inner-Product Neural Associative Memory" (NPO-18491).

Liu, Hua-Kuang↗
NASA NTRS1996

The High Latitude Ionosphere-Magnetosphere Transition Region: Simulation and Data Comparison

This technical paper presents a brief decription of the major activities for this grant during the last three years. Technologyical areas discussed include: model development, ExB convection heating study, study of energetic electron precipitation, polar cap data-model comparison, study of wave heating of O(+), study of photoelectron effects, and study of molecular ion outflow.

Wilson, Gordon R.↗
NASA NTRS1999

Structure Damage Simulations Accounting for Inertial Effects and Impact and Optimization of Grid-Stiffened Non-Circular Shells

The goal of this research project is to develop modelling and analysis strategy for the penetration of aluminium plates impacted by titanium impactors. Finite element analysis is used to study the penetration of aluminium plates impacted by titanium impactors in order to study the effect of such uncontained engine debris impacts on aircraft-like skin panels. LS-DYNA3D) is used in the simulations to model the impactor, test fixture frame and target barrier plate. The effects of mesh refinement, contact modeling, and impactor initial velocity and orientation were studied. The research project also includes development of a design tool for optimum design of grid-stiffened non-circular shells or panels subjected to buckling.

Mei, Chuh↗
NASA NTRS2004

Computational Modeling of NEXT 2000-Hour Wear Test Results

Ion optics computational models are invaluable tools for the design of ion optics systems. In this study, a new computational model developed by an outside vendor for NASA Glenn Research Center (GRC) is presented. This model is a gun code which has been modified to model the plasma sheaths both upstream and downstream of the ion optics. The model handles multiple species (e.g. singly and doubly-charged ions) and includes a charge-exchange model for erosion estimates. The model uses commercially available solid design and meshing software, allowing high flexibility in ion optics geometric configurations. This computational model is compared to experimental results from the NASA Evolutionary Xenon Thruster (NEXT) 2000-hour wear test, including over-focusing along the edge apertures, pit-and-groove erosion due to charge exchange, and beamlet distortion at the edge of the hole pattern.

Malone, Shane P.↗
NASA NTRS2004

Discharge Chamber Performance of the NEXIS Ion Thruster

The Nuclear-Electric Xenon Ion System (NEXIS) thruster was designed to produce greater than or equal to 70% efficiency at ISPs in excess of 6500 sec and total power levels in excess of 15 kW. In order to achieve this performance, the thruster requires a large area plasma generator capable of high propellant utilimtion efficiency and low discharge loss while producing a very flat, uniform beam profile. Fortunately, larger thrusters can be made more uniform and efficient due to the higher volume to surface ratio, provided that the magnetic cusp confinement is designed properly and the thruster length to diameter ratio is adequate. This paper describes the discharge chamber performance of the NEXIS Laboratory Model (LM) thruster. The LM discharge chamber is 65 cm in diameter at the grid plane and uses 6 ring-cusps to provide magnetic confinement of the plasma. The thruster was tested with flat carbon-carbon composite grids with the hole pattern masked to 57 cm in diameter and a conventional Type-B "1/2" diameter hollow cathode. During the preliminary "discharge only" tests, the LM thruster demonstrated profile factors of 0.84 and a discharge loss of about 160 eV/ion at 25 V discharge voltage and over 90% propellant utilization efficiency in simulated beam extraction experiments at 3.9 A of beam current. Analysis of the data from these tests used the discharge-only model developed by Brophy. Subsequent beam extraction experiments validated the key variables used in the model to predict the performance from the discharge-only data, and demonstrated 3.9 A of beam current at over 90% propellant utilization efficiency with a flatness parameter of better than 0.8 and a discharge loss of about 185 eV/ion. The slightly higher discharge loss measured during beam extractions was found to be due to a lower screen transparency in the as-manufactured LM grid set. Plasma measurements with a scanning probe internal to the thruster near the screen grid showed plasma densities over l x 10(exp 11) per cubic centimeter and electron temperatures of 3.5 to 5.5 eV depending on the operation parameters. The performance of the NEXIS discharge chamber contributed to the over 78% thruster efficiency measured during beam extraction at 7500 sec ISP and 25 kW of power, and over 81% thruster efficiency measured at 8500 sec ISP.

plasma generation↗
NASA NTRS2011

More-Accurate Model of Flows in Rocket Injectors

An improved computational model for simulating flows in liquid-propellant injectors in rocket engines has been developed. Models like this one are needed for predicting fluxes of heat in, and performances of, the engines. An important part of predicting performance is predicting fluctuations of temperature, fluctuations of concentrations of chemical species, and effects of turbulence on diffusion of heat and chemical species. Customarily, diffusion effects are represented by parameters known in the art as the Prandtl and Schmidt numbers. Prior formulations include ad hoc assumptions of constant values of these parameters, but these assumptions and, hence, the formulations, are inaccurate for complex flows. In the improved model, these parameters are neither constant nor specified in advance: instead, they are variables obtained as part of the solution. Consequently, this model represents the effects of turbulence on diffusion of heat and chemical species more accurately than prior formulations do, and may enable more-accurate prediction of mixing and flows of heat in rocket-engine combustion chambers. The model has been implemented within CRUNCH CFD, a proprietary computational fluid dynamics (CFD) computer program, and has been tested within that program. The model could also be implemented within other CFD programs.

Hosangadi, Ashvin↗
NASA NTRS2016

End-of-Discharge and End-of-Life Prediction in Lithium-Ion Batteries with Electrochemistry-Based Aging Models

As batteries become increasingly prevalent in complex systems such as aircraft and electric cars, monitoring and predicting battery state of charge and state of health becomes critical. In order to accurately predict the remaining battery power to support system operations for informed operational decision-making, age-dependent changes in dynamics must be accounted for. Using an electrochemistry-based model, we investigate how key parameters of the battery change as aging occurs, and develop models to describe aging through these key parameters. Using these models, we demonstrate how we can (i) accurately predict end-of-discharge for aged batteries, and (ii) predict the end-of-life of a battery as a function of anticipated usage. The approach is validated through an experimental set of randomized discharge profiles.

batteries↗
NASA NTRS2016

Chemistry Simulations Using MERRA-2 Reanalysis with the GMI CTM and Replay in Support of the Atmospheric Composition Community

Simulations using reanalyzed meteorological conditions have been long used to understand causes of atmospheric composition change over the recent past. Using the new Modern-Era Retrospective analysis for Research and Applications, version 2 (MERRA-2) meteorology, chemistry simulations are being conducted to create products covering 1980-2016 for the atmospheric composition community. These simulations use the Global Modeling Initiative (GMI) chemical mechanism in two different models: the GMI Chemical Transport Model (CTM) and the GEOS-5 model developed Replay mode. Replay mode means an integration of the GEOS-5 general circulation model that is incrementally adjusted each time step toward the MERRA-2 analysis. The GMI CTM is a 1 x 1.25 simulation and the MERRA-2 GMI Replay simulation uses the native MERRA-2 approximately horizontal resolution on the cubed sphere. The Replay simulations is driven by the online use of key MERRA-2 meteorological variables (i.e. U, V, T, and surface pressure) with all other variables calculated in response to those variables. A specialized set of transport diagnostics is included in both runs to better understand trace gas transport and changes over the recent past.

Chemistry-Climate Model↗
NASA NTRS2016

NASA AVOSS Fast-Time Models for Aircraft Wake Prediction: User's Guide (APA3.8 and TDP2.1)

NASA's current distribution of fast-time wake vortex decay and transport models includes APA (Version 3.8) and TDP (Version 2.1). This User's Guide provides detailed information on the model inputs, file formats, and model outputs. A brief description of the Memphis 1995, Dallas/Fort Worth 1997, and the Denver 2003 wake vortex datasets is given along with the evaluation of models. A detailed bibliography is provided which includes publications on model development, wake field experiment descriptions, and applications of the fast-time wake vortex models.

Ahmad, Nash'at N.↗