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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 649 records · Page 36
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Integration of tools for the Design and Assessment of High-Performance, Highly Reliable Computing Systems (DAHPHRS), phase 1

Systems for Space Defense Initiative (SDI) space applications typically require both high performance and very high reliability. These requirements present the systems engineer evaluating such systems with the extremely difficult problem of conducting performance and reliability trade-offs over large design spaces. A controlled development process supported by appropriate automated tools must be used to assure that the system will meet design objectives. This report describes an investigation of methods, tools, and techniques necessary to support performance and reliability modeling for SDI systems development. Models of the JPL Hypercubes, the Encore Multimax, and the C.S. Draper Lab Fault-Tolerant Parallel Processor (FTPP) parallel-computing architectures using candidate SDI weapons-to-target assignment algorithms as workloads were built and analyzed as a means of identifying the necessary system models, how the models interact, and what experiments and analyses should be performed. As a result of this effort, weaknesses in the existing methods and tools were revealed and capabilities that will be required for both individual tools and an integrated toolset were identified.

Scheper, C.↗
NASA NTRS1991

Nonlinear response of infinitely long circular cylindrical shells to subharmonic radial loads

The nonlinear response of infinitely long circular cylindrical shells (thin circular rings) in the presence of a two-to-one internal (autoparametric) resonance to a subharmonic excitation of order one-half of the higher mode is analyzed with the multiple-scale method. Four autonomous first-order ordinary differential equations are derived for the modulation of the amplitudes and phases of the interacting models. These modulation equations are used to determine the fixed points and their stability. The fixed points correspond to periodic oscillations of the shell, whereas the limit-cycle solutions of the modulation equations correspond to amplitude and phase-modulated oscillations of the shell. The force response curves exhibit saturation, jumps, and Hopf bifurcation. As excitation frequency changes, all limit cycles deform and lose stability through either pitchfork or cyclic-fold (saddle-node) bifurcations. Some of these saddle-node bifurcations cause a transition to chaos. The pitchfork bifurcations break the symmetry of the limit cycles.

Nayfeh, Ali H.↗
NASA NTRS1992

Combined bending and thermal fatigue of high-temperature metal-matrix composites - Computational simulation

The nonlinear behavior of a high-temperature metal-matrix composite (HT-MMC) was simulated by using the metal matrix composite analyzer (METCAN) computer code. The simulation started with the fabrication process, proceeded to thermomechanical cyclic loading, and ended with the application of a monotonic load. Classical laminate theory and composite micromechanics and macromechanics are used in METCAN, along with a multifactor interaction model for the constituents behavior. The simulation of the stress-strain behavior from the macromechanical and the micromechanical points of view, as well as the initiation and final failure of the constituents and the plies in the composite, were examined in detail. It was shown that, when the fibers and the matrix were perfectly bonded, the fracture started in the matrix and then propagated with increasing load to the fibers. After the fibers fractured, the composite lost its capacity to carry additional load and fractured.

Gotsis, Pascal K.↗
NASA NTRS1992

Applied-field magnetoplasmadynamic engine developments

There are potential space exploration missions which may significantly benefit from the use of electric propulsion at power levels of hundreds of kilowatts. The applied magnetic field MPD thruster is potentially capable of efficient, high specific impulse operation in this power range. This paper describes current experimental and analytical efforts to further the development of such a thruster and presents the latest results. In particular, efforts to measure, simultaneously, the thrust developed by the archead and by the electromagnet, and to evaluate the effect of a diffuser on vacuum tank back pressure, are presented and discussed. It was found that with ammonia vapor as propellant, the vacuum tank pressure was reduced from 8 to 4.9 Pa at a power level of 80 kW. This pressure decrease is expected to become greater as the power and applied field are increased. Also, the development of a cathode/plasma interaction model for determining the heat loads to the cathode as functions of the various free stream plasma parameters is presented. This model is combined with a cathode thermal model in order to provide a complete and integrated picture of MPD thruster cathode operation. Several computational examples are used to illustrate the combined model.

Goodfellow, K. D.↗
NASA NTRS1992

Experimental and numerical investigations of low-density nozzle and plume flows of nitrogen

New experimental data are used to show that the direct simulation Monte Carlo (DSMC) method provides an accurate description of a low-density flow in the nozzle and the near-field expansion of a small rocket for two slightly different experimental configurations. These results verify the DSMC method in an expansion flow for the first time. From a number of different gas/surface interaction models, it is found that fully diffuse reflection gives the best agreement with experiment.

Boyd, Iain D.↗
NASA NTRS1992

Slew disturbance compensation for multiple payloads of a flexible spacecrafts

This paper extends an earlier developed mirror motion compensation (MMC) scheme (Chu, 1989, 1990) which calculates, on-board and in real time, the spacecraft motion induced by a slewing payload, to cases where one of the four conditions of the MMC scheme is not met. The analysis, the design methodology, and a case study related to the application of MMC to compensation for flexibility effects are presented. A sensitivity study is carried out to determine the compensation efficiency when uncertainties exist in parameters of the dynamic interaction model.

Mclaren, Mark D.↗
NASA NTRS1992

Investigation of hypersonic shock-induced combustion in a hydrogen-air system

A numerical study is conducted to simulate the ballistic range experiments at Mach 5.11 and 6.46. The flow field is found to be unsteady with periodic instabilities originating in the stagnation zone. The unsteadiness of the flow field decreased with increase in the Mach number, thus indicating that it is possible to stabilize such flow fields with a high degree of overdrive. The frequency of periodic instability is determined using Fourier power spectrum and is found to be in good agreement with the experimental data. The physics of the instability is explained by the wave interaction models available in the literature.

Ahuja, J. K.↗
NASA NTRS1992

Electrical and Chemical Interactions at Mars Workshop. Part 2: Appendix

The objectives of the workshop were the following: (1) to identify issues related to electrical and chemical interactions between systems and their local environments at Mars; and (2) to recommend means of addressing those issues, including the dispatch of robotic spacecraft to Mars to acquire necessary information. Presentations about Mars' surface and orbital environments, Space Exploration Initiative (SEI) systems, environmental interactions, modeling and analysis, and plans for exploration are presented in viewgraph form.

Source record↗
NASA NTRS1992

A determination of twisting of the Earth's magnetotail at distances 115-220 RE - ISEE 3

Observations from magnetic field and plasma experiments on ISEE 3 are used to identify and to analyze 16 crossings of the distant magnetotail neutral sheet. Four methods of analyses have been employed to measure the extent of the magnetotail twisting, which is found to be much greater than what was previously observed or, the theoretically inferred twist. A twist of more than 90 deg has frequently been observed on both open and closed magnetic field lines. In addition, the location of the magnetic neutral line of the magnetotail has been found to move over the distance interval of 115 to 220 Earth radii. Some features of these results suggest that a modification of the present solar wind-geomagnetic field interaction model may be needed.

Macwan, Snehavadan E.↗
NASA NTRS1993

DSMC and continuum analyses of low-density nozzle flow

Two different approaches, the direct-simulation Monte Carlo (DSMC) method based on molecular gas dynamics and a finite-volume approximation of the Navier-Stokes equations, which are based on continuum gas dynamics, are employed in the analysis of a low-density gas flow in a small converging-diverging nozzle. The fluid experiences various kinds of flow regimes including continuum, slip, transition, and free-molecular. Results from the two numerical methods are compared with Rothe's experimental dam, in which density and rotational temperature variations along the centerline and at various locations inside a low density nozzle were measured by the electron-beam fluorescence technique. The continuum approach showed good agreement with the experimental data as far as density is concerned. The results from the DSMC method showed good agreement with the experimental data both in the density and the rotational temperature. It is also shown that the simulation parameters, such as the gas/surface interaction model, the energy exchange model between rotational and translational modes, and the viscosity temperature exponent, have substantial effects on the results of the DSMC method.

Chung, Chan-Hong↗
NASA NTRS1993

Comment on 'Comparison of observed and calculated implanted ion distributions outside Comet Halley's bow shock' by T. I. Gombosi, M. Neugebauer, A. D. Johnstone, A. J. Coates, and D. E. Huddleston

It is argued that the formulation used by Gombosi (1991) does not distinguish between two fundamental types of resonant interactions (those between cometary pickup ions and LF electromagnetic waves). Two problems arise from using their overly simplified expressions. The wave polarization of the solar wind Alfven wave is not purely right-handed, and values from alpha sub com and alpha sub sw are not well known, nor are the 'polarizations' of the 'backward'-going waves in either case. Gombosi et al. discuss the antisunward vs the sunward propagating solar wind Alfven wave, and assume a reasonable value of 0.2 for alpha sub sw. However, alpha sub com is totally unknown. It is concluded that a more correct analysis of wave polarization can lead to significant changes in the formulation and results from Gombosi et al. In his reply Gombosi argues that his simplified wave-particle interaction model is consistent with Giotto observations and plasma kinetic simulations and it leads to a reasonable approximation of the implanted ion transport coefficients. The more complicated approach suggested by Tsurutani & Thorne (1993) requires the introduction of several ad hoc parameters and it does not lead to any change of the energy diffusion coefficient.

Tsurutani, Bruce T.↗
NASA NTRS1993

Thermal evolution of neutron stars with internal frictional heating

It has been suggested that the frictional interaction of neutron superfluids with normal matter in the inner crust of neutron stars dissipates rotational energy of superfluids and generates heat. Incorporating a general formula of internal heating into the detailed numerical codes of thermal evolution, we examine the effects of the internal heating on thermal evolution of neutron stars. We find that when a very stiff equation of state is used, it takes as long as about 2 x 10 exp 4 yr for the interior of a neutron star to reach the isothermal state, even if a strong heat source is placed in a thin layer of the inner crust. This time scale reduces to a few hundred years or less when medium to soft equations of state are used. A neutron star cools by neutrino emissions during the earlier stages referred to as the neutrino cooling era, while during the later photon cooling era it cools primarily by emission of photons from its surface. We show that heating rates expected in the current superfluid-crust interaction model can greatly increase the surface temperature in the photon cooling era, significantly changing the thermal evolution of relatively old neutron stars if a stiff equation of state is adopted.

Umeda, Hideyuki↗
NASA NTRS1993

Transportable Applications Environment (TAE) Tenth Users' Conference

Conference proceedings are represented in graphic visual-aid form. Presentation and panel discussion topics include user experiences with C++ and Ada; the design and interaction of the user interface; the history and goals of TAE; commercialization and testing of TAE Plus; Computer-Human Interaction Models (CHIMES); data driven objects; item-to-item connections and object dependencies; and integration with other software. There follows a list of conference attendees.

Rouff, Chris↗
NASA NTRS1993

Automating a human factors evaluation of graphical user interfaces for NASA applications: An update on CHIMES

Capturing human factors knowledge about the design of graphical user interfaces (GUI's) and applying this knowledge on-line are the primary objectives of the Computer-Human Interaction Models (CHIMES) project. The current CHIMES prototype is designed to check a GUI's compliance with industry-standard guidelines, general human factors guidelines, and human factors recommendations on color usage. Following the evaluation, CHIMES presents human factors feedback and advice to the GUI designer. The paper describes the approach to modeling human factors guidelines, the system architecture, a new method developed to convert quantitative RGB primaries into qualitative color representations, and the potential for integrating CHIMES with user interface management systems (UIMS). Both the conceptual approach and its implementation are discussed. This paper updates the presentation on CHIMES at the first International Symposium on Ground Data Systems for Spacecraft Control.

Jiang, Jian-Ping↗
NASA NTRS1994

Ocean-ice interaction in the marginal ice zone

Ocean ice interaction processes in the Marginal Ice Zone (MIZ) by wind, waves, and mesoscale features, such as upwelling and eddies, are studied using ERS-1 Synthetic Aperture Radar (SAR) images and ocean ice interaction model. A sequence of SAR images of the Chukchi Sea MIZ with three days interval are studied for ice edge advance/retreat. Simultaneous current measurements from the northeast Chukchi Sea as well as the Barrow wind record are used to interpret the MIZ dynamics.

Liu, Antony K.↗
NASA NTRS1992

Lumley's PODT definition of large eddies and a trio of numerical procedures

Lumley's 1967 Moscow paper provided, for the first time, a completely rational definition of the physically-useful term 'large eddy', popular for a half-century. The numerical procedures based upon his results are: (1) PODT (Proper Orthogonal Decomposition Theorem), which extracts the Large Eddy structure of stochastic processes from physical or computer simulation two-point covariances, and 2) LEIM (Large-Eddy Interaction Model), a predictive scheme for the dynamical large eddies based upon higher order turbulence modeling. Earlier Lumley's work (1964) forms the basis for the final member of the triad of numerical procedures: this predicts the global neutral modes of turbulence which have surprising agreement with both structural eigenmodes and those obtained from the dynamical equations. The ultimate goal of improved engineering design tools for turbulence may be near at hand, partly due to the power and storage of 'supermicrocomputer' workstations finally becoming adequate for the demanding numerics of these procedures.

Payne, Fred R.↗
NASA NTRS1994

Numerical simulation of shock-induced combustion past blunt bodies using shock-fitting technique

Two-dimensional axisymmetric, reacting viscous flow over blunt projectiles is computed to study shock-induced combustion at Mach 5.11 and Mach 6.46 in hydrogen-air mixture. A finite-difference, shock-fitting method is used to solve the complete set of Navier-Stokes and species conservation equations. In this approach, the bow shock represents a boundary of the computational domain and is treated as a discontinuity across which Rankine-Hugoniot conditions are applied. All interior details of the flow such as compression waves, reaction front, and the wall boundary layer are captured automatically in the solution. Since shock-fitting approach reduces the amount of artificial dissipation, all the intricate details of the flow are captured much more clearly than has been possible with the shock-capturing approach. This has allowed an improved understanding of the physics of shock-induced combustion over blunt projectiles and the numerical results can now be explained more readily with one-dimensional wave-interaction model than before.

Ahuja, J. K.↗
NASA NTRS1994

Parametric study of shock-induced combustion in a hydrogen air system

A numerical parametric study is conducted to simulate shock-induced combustion under various free-stream conditions and varying blunt body diameter. A steady combustion front is established if the free-stream Mach number is above the Chapman-Jouguet speed of the mixture, whereas an unsteady reaction front is established if the free-stream Mach number is below or at the Chapman-Jouguet speed of the mixture. The above two cases have been simulated for Mach 5.11 and Mach 6.46 with a projectile diameter of 15 mm. Mach 5.11, which is an underdriven case, shows an unsteady reaction front, whereas Mach 6.46, which is an overdriven case, shows a steady reaction front. Next for Mach 5. 11 reducing the diameter to 2.5 mm causes the instabilities to disappear, whereas, for Mach 6.46 increasing the diameter of the projectile to 225 mm causes the instabilities to reappear, indicating that Chapman-Jouguet speed is not the only deciding factor for these instabilities to trigger. The other key parameters are the projectile diameter, induction time, activation energy and the heat release. The appearance and disappearance of the instabilities have been explained by the one-dimensional wave interaction model.

Ahuja, J. K.↗