Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “STRONG INTERACTIONS”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,531 records · Page 85
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Hot hydrogen testing of metallic turbo pump materials

The objectives of this investigation are to expose heat resistant alloys to hydrogen at elevated temperatures and to use various microstructural and analytical techniques to determine the chemical and rate process involved in degradation of these materials due to hydrogen environment. Inconel 718 and NASA-23 (wrought and cast) are candidate materials. The degradation of these materials in the presence of 1 to 5 atmospheric pressure of hydrogen from 450 C to 1100 C was examined. The hydrogen facility at Auburn University was used for this purpose. Control experiments were also conducted wherein the samples were exposed to vacuum so that a direct comparison of the results would separate the thermal contribution from the hydrogen effects. The samples were analyzed prior to and after exposure. A residual gas collection system was used to determine the gaseous species produced by any chemical reaction that may have occurred during the exposure. Analysis of this gas sample shows only the presence of H2 as expected. Analyses of the samples were conducted using optical microscopy, x-ray diffraction, scanning electron microscopy, and weight change. There appears to be no change in weight of the samples as a result of hydrogen exposure. In addition no visible change on the surface structure was detected. This indicates that the materials of interest do not have strong interaction with hot hydrogen. This is consistent with the microstructure results.

Zee, Ralph↗
NASA NTRS1994

Cross section parameterizations for cosmic-ray nuclei. 2: Double nucleon removal

Parameterizations of double nucleon removal from the electromagnetic and strong interactions of cosmic rays with nuclei are presented. These parameterizations are an extension of previous single nucleon removal parameterizations and combined they represent the dominant part of the electromagnetic dissociation encountered by a cosmic ray on its traversal through matter. Such parameterizations should be very useful in studying cosmic-ray transport through the interstellar medium, the Earth's atmosphere, spacecraft walls, and extraterrestrial matter.

Norbury, John W.↗
NASA NTRS1994

Counts of galaxies in a merger model

A model for the photometric evolution of galaxies has been developed and has been applied to the problem of galaxy counts. The integrated colors of galaxies are calculated using the most recently computed evolutionary tracks from Maeder and collaborators complemented with evolutionary tracks derived by other authors. The asymptotic giant branch lifetime is left as a free parameter. A series of cosmological models using different values of the cosmological constant, lambda(sub 0), and the density parameter, omega(sub 0), have been computed. The universality hypothesis of the luminosity function of galaxies has been abandoned. The influence of galaxy merging on the counts has been considered in a simple manner by assuming that the number of strongly interacting galaxies in a comoving volume increases with redshift as a power law given by (1 + z)(exp 3.8). Taking a Schechter parametrization for the luminosity function of the different types of galaxies, we are able to reproduce the observations reasonably well. We have also considered models with a Gaussian distribution for the luminosity function of the brighter galaxies that provide a poorer fit to the observations. It is shown that galaxy count data are not yet able to make unambiguous cosmological statements since evolutionary assumptions are critical. In particular, an omega(sub 0) = 1, lambda(sub 0) = 0 cosmology is shown to be consistent with the data.

Colin, P.↗
NASA NTRS1994

Global, quasi-steady dynamics of the distant solar wind 2: Deformation of the heliospheric current sheet

A three-dimensional (3-D) magnetohydrodynamic (MHD) numerical model is used to trace global deformations of the heliospheric current sheet (HCS) caused by large-scale dynamical interactions associated with corotating solar wind flows. Configurations incorporating the tilted-dipole geometry are investigated out past 30 AU for a variety of dipole tilt angles, alpha. Inclusion of the full, 3-D interplanetary dynamics allows north-south displacements and the east-west warping of the HCS by advective corotational effects to be accurately assessed for the first time. It is found that large-scale spatial correlations between velocity and density imposed at the coronal source (i.e., the geometric arrangement whereby regions of high-speed low-density material lying adjacent to areas of slow, dense flow interact obliquely under the influence of solar rotation) result in a distinctive pattern of deformation of the HCS. For an alpha = 30 deg tilted-dipole example, it is shown that typical zonal variations in radial velocity lead to significant folding of the HCS within about 5 AU of the Sun. By 10 AU, additional sharp bends appear near the latitudinal extremes of the HCS surface, where it is overtaken by shock fronts driven by 3-D corotating interaction regions (CIRs). Moreover, the model suggests that inside about 20 AU, major plasma structures are systematically organized, about the HCS, such that the greatest concentrations of material and magnetic field (the centroids of the 3-D CIR structures) are coincident with the folded crests of the HCS (near heliographic latitudes lambda = +/- alpha). Thus, in these circumstances many of the more interesting dynamical features inconveniently lie well away from the heliographic equator. At larger heliocentric distances, where neighboring CIRs begin to interact strongly, the warping of the HCS abates dramatically and the association between folds in the HCS and major field and density concentrations is weakened and ultimately breaks down. On the basis of the model calculations, quasi-steady deformations and related phenomena should figure prominently in the interplanetary medium, except during those periods when the magnetic dipole and solar spin axes are nearly aligned (alpha is approximately less than 10 deg). Even then, they may be of significance if there are any substantial local warps or kinks in the streamer belt.

Pizzo, V. J.↗
NASA NTRS1994

Near-infrared imaging of FSC 10214+4724 with the W. M. Keck Telescope

Near-infrared observations of the z = 2.286 IRAS source FSC 10214+4724, made with the near-infrared camera on the W. M. Keck Telescope, are reported. Deep broad-band images at 2.15 and 1.27 micrometers, and narrow-band images at 2.165 and 2.125 micrometers with 0.6 sec to 0.9 sec seeing show that FSC 10214+4724 consists of at least three distinct components in a compact group of galaxies. The source of the infrared luminosity appears to be in a strongly interacting galaxy that has a luminosity of approximately 100 times that of a present-day L* galaxy. The interaction suggests and 'age' of this galaxy of approximately equal to 10(exp 9) yr. The H-alpha emission is resolved as a source of diameter approximately equal to 5 kpc, suggesting that a starburst contributes to the observed H-alpha emission. There is an excess of objects in the FSC 10214+4724 field that could represent galaxies in an associated cluster.

Matthews, K.↗
NASA NTRS1995

Nonlinear Landau damping and Alfven wave dissipation

Nonlinear Landau damping has been often suggested to be the cause of the dissipation of Alfven waves in the solar wind as well as the mechanism for ion heating and selective preacceleration in solar flares. We discuss the viability of these processes in light of our theoretical and numerical results. We present one-dimensional hybrid plasma simulations of the nonlinear Landau damping of parallel Alfven waves. In this scenario, two Alfven waves nonresonantly combine to create second-order magnetic field pressure gradients, which then drive density fluctuations, which in turn drive a second-order longitudinal electric field. Under certain conditions, this electric field strongly interacts with the ambient ions via the Landau resonance which leads to a rapid dissipation of the Alfven wave energy. While there is a net flux of energy from the waves to the ions, one of the Alfven waves will grow if both have the same polarization. We compare damping and growth rates from plasma simulations with those predicted by Lee and Volk (1973), and also discuss the evolution of the ambient ion distribution. We then consider this nonlinear interaction in the presence of a spectrum of Alfven waves, and discuss the spectrum's influence on the growth or damping of a single wave. We also discuss the implications for wave dissipation and ion heating in the solar wind.

Vinas, Adolfo F.↗
NASA NTRS1995

Some Progress in Large-Eddy Simulation using the 3-D Vortex Particle Method

This two-month visit at CTR was devoted to investigating possibilities in LES modeling in the context of the 3-D vortex particle method (=vortex element method, VEM) for unbounded flows. A dedicated code was developed for that purpose. Although O(N(sup 2)) and thus slow, it offers the advantage that it can easily be modified to try out many ideas on problems involving up to N approx. 10(exp 4) particles. Energy spectrums (which require O(N(sup 2)) operations per wavenumber) are also computed. Progress was realized in the following areas: particle redistribution schemes, relaxation schemes to maintain the solenoidal condition on the particle vorticity field, simple LES models and their VEM extension, possible new avenues in LES. Model problems that involve strong interaction between vortex tubes were computed, together with diagnostics: total vorticity, linear and angular impulse, energy and energy spectrum, enstrophy. More work is needed, however, especially regarding relaxation schemes and further validation and development of LES models for VEM. Finally, what works well will eventually have to be incorporated into the fast parallel tree code.

Winckelmans, G. S.↗
NASA NTRS1996

The NASA Electric Propulsion Program

Nearly all space missions require on-board propulsion systems and these systems typically have a major impact on spacecraft mass and cost. Electric propulsion systems offer major performance advantages over conventional chemical systems for many mission functions and the NASA Office of Space Access and Technology (OSAT) supports an extensive effort to develop the technology for high-performance, on-board electric propulsion system options to enhance and enable near- and far-term US space missions. This program includes research and development efforts on electrothermal, electrostatic, and electromagnetic propulsion system technologies to cover a wide range of potential applications. To maximize expectations of technology transfer, the program emphasizes strong interaction with the user community through a variety of cooperative and contracted approaches. This paper provides an overview of the OSAT electric propulsion program with an emphasis on recent progress and future directions.

Callahan, Lisa Wood↗
NASA NTRS1994

Static aeroelastic analysis of wings using Euler/Navier-Stokes equations coupled with improved wing-box finite element structures

Strong interactions between flow about an aircraft wing and the wing structure can result in aeroelastic phenomena which significantly impact aircraft performance. Time-accurate methods for solving the unsteady Navier-Stokes equations have matured to the point where reliable results can be obtained with reasonable computational costs for complex non-linear flows with shock waves, vortices and separations. The ability to combine such a flow solver with a general finite element structural model is key to an aeroelastic analysis in these flows. Earlier work involved time-accurate integration of modal structural models based on plate elements. A finite element model was developed to handle three-dimensional wing boxes, and incorporated into the flow solver without the need for modal analysis. Static condensation is performed on the structural model to reduce the structural degrees of freedom for the aeroelastic analysis. Direct incorporation of the finite element wing-box structural model with the flow solver requires finding adequate methods for transferring aerodynamic pressures to the structural grid and returning deflections to the aerodynamic grid. Several schemes were explored for handling the grid-to-grid transfer of information. The complex, built-up nature of the wing-box complicated this transfer. Aeroelastic calculations for a sample wing in transonic flow comparing various simple transfer schemes are presented and discussed.

Guruswamy, Guru P.↗
NASA NTRS1997

Study of Buoyancy Effects in Diffusion Flames Using Rainbow Schlieren Deflectometry

Diffusion flames are extensively encountered in many domestic and industrial processes. Even after many decades of research, a complete understanding of the diffusion flame structure is not available. The structure and properties of the flames are governed by the mixing (laminar or turbulent), chemical kinetics, radiation and soot processes. Another important phenomenon that affects flame structure in normal gravity is buoyancy. The presence of buoyancy has long hindered the rational understanding of many combustion processes. In gas jet diffusion flames, buoyancy affects the structure of the shear layer, the development of fluid instabilities, and formation of the coherent structures in the near nozzle region of the gas jets. The buoyancy driven instabilities generate vorticial structures outside the flame resulting in flame flicker. The vortices also strongly interact with the small-scale structures in the jet shear layer. This affects the transitional and turbulence characteristics of the flame. For a fundamental understanding of diffusion flames it is essential to isolate the effects of buoyancy. This is the primary goal of the experiments conducted in microgravity. Previous investigations, have shown dramatic differences between the jet flames in microgravity and normal gravity. It has been observed that flames in microgravity are taller and more sooty than in normal gravity. The fuels used in these experiments were primarily hydrocarbons. In the absence of buoyancy the soot resides near the flame region, which adversely affects the entrainment of reactants. It is very important to eliminate the interference of soot on flame characteristics in microgravity. The present work, therefore, focuses on the changes in the flame structure due to buoyancy without the added complexities of heterogeneous reactions. Clean burning hydrogen is used as the fuel to avoid soot formation and minimize radiative losses. Because of the low luminosity of hydrogen flames, we use rainbow schlieren deflectometry for visualization. The visualized images are digitized for quantification.The work reported here is divided into three sections; rainbow schlieren deflectometry (RSD), microgravity experiments and sub-atmospheric pressure experiments. The first section demonstrates the application of RSD for quantitative measurements in non-reacting and reacting flow systems. A computational effort to complement the experimental work is also included. In the second section, the experiments conducted at the 2.2s NASA Lewis Drop tower facility are described. The experiments were conducted to study the behavior of laminar, transitional and turbulent hydrogen flames in microgravity. The ability of RSD technique to provide quantitative data is highlighted. The final section deals with the sub-atmospheric pressure tests, which demonstrate that buoyancy in hydrogen diffusion flames can be scaled with pressure at normal gravity.

Agrawal, Ajay K.↗
NASA NTRS1995

Navier-Stokes Computations on Full Wing-Body Configuration with Oscillating Control Surfaces

Unsteady Navier-Stokes simulations have been performed for vortical flows over an "arrow-wing" configuration of a supersonic transport in the transonic regime. Computed steady pressures and integrated force coefficients with and without control surface deflection at a moderate angle of attack are compared with experiment. For unsteady cases, oscillating trailing-edge control surfaces are modeled by using moving grids. Response characteristics between symmetric and antisymmetric oscillatory motions of the control surfaces on the left and right wings are studied. The antisymmetric case produces higher lift than the steady case with no deflection and the unsteady symmetric case produces higher lift than the antisymmetric case. The detailed analysis of the wake structure revealed a strong interaction between the primary vortex and the wake vortex sheet from the flap region when the flap is deflected up.

Obayashi, Shigeru↗
NASA NTRS1998

Experiments to Determine Whether Recursive Partitioning (CART) or an Artificial Neural Network Overcomes Theoretical Limitations of Cox Proportional Hazards Regression

New computationally intensive tools for medical survival analyses include recursive partitioning (also called CART) and artificial neural networks. A challenge that remains is to better understand the behavior of these techniques in effort to know when they will be effective tools. Theoretically they may overcome limitations of the traditional multivariable survival technique, the Cox proportional hazards regression model. Experiments were designed to test whether the new tools would, in practice, overcome these limitations. Two datasets in which theory suggests CART and the neural network should outperform the Cox model were selected. The first was a published leukemia dataset manipulated to have a strong interaction that CART should detect. The second was a published cirrhosis dataset with pronounced nonlinear effects that a neural network should fit. Repeated sampling of 50 training and testing subsets was applied to each technique. The concordance index C was calculated as a measure of predictive accuracy by each technique on the testing dataset. In the interaction dataset, CART outperformed Cox (P less than 0.05) with a C improvement of 0.1 (95% Cl, 0.08 to 0.12). In the nonlinear dataset, the neural network outperformed the Cox model (P less than 0.05), but by a very slight amount (0.015). As predicted by theory, CART and the neural network were able to overcome limitations of the Cox model. Experiments like these are important to increase our understanding of when one of these new techniques will outperform the standard Cox model. Further research is necessary to predict which technique will do best a priori and to assess the magnitude of superiority.

Kattan, Michael W.↗
NASA NTRS1999

Deep Atmosphere Ammonia Mixing Ratio at Jupiter from the Galileo Probe Mass Spectrometer

New laboratory studies employing the Engineering Unit (EU) of the Galileo Probe Mass Spectrometer (GPMS) have resulted in a substantial reduction in the previously reported upper limit on the ammonia mixing ratio derived from the GPMS experiment at Jupiter. This measurement is complicated by background ammonia contributions in the GPMS during direct atmospheric sampling produced from the preceding gas enrichment experiments. These backgrounds can be quantified with the data from the EU studies when they are carried out in a manner that duplicates the descent profile of pressure and enrichment cell loading. This background is due to the tendency of ammonia to interact strongly with the walls of the mass spectrometer and on release to contribute to the gas being directly directed into the ion source from the atmosphere through a capillary pressure reduction leak. It is evident from the GPMS and other observations that the mixing ratio of ammonia at Jupiter reaches the deep atmosphere value at substantially higher pressures than previously assumed. This is a likely explanation for the previously perceived discrepancy between ammonia values derived from ground based microwave observations and those obtained from attenuation of the Galileo Probe radio signal.

Mahaffy, P. R.↗
NASA NTRS2000

Airbreathing Propulsion System Analysis Using Multithreaded Parallel Processing

In this paper, parallel processing is used to analyze the mixing, and combustion behavior of hypersonic flow. Preliminary work for a sonic transverse hydrogen jet injected from a slot into a Mach 4 airstream in a two-dimensional duct combustor has been completed [Moon and Chung, 1996]. Our aim is to extend this work to three-dimensional domain using multithreaded domain decomposition parallel processing based on the flowfield-dependent variation theory. Numerical simulations of chemically reacting flows are difficult because of the strong interactions between the turbulent hydrodynamic and chemical processes. The algorithm must provide an accurate representation of the flowfield, since unphysical flowfield calculations will lead to the faulty loss or creation of species mass fraction, or even premature ignition, which in turn alters the flowfield information. Another difficulty arises from the disparity in time scales between the flowfield and chemical reactions, which may require the use of finite rate chemistry. The situations are more complex when there is a disparity in length scales involved in turbulence. In order to cope with these complicated physical phenomena, it is our plan to utilize the flowfield-dependent variation theory mentioned above, facilitated by large eddy simulation. Undoubtedly, the proposed computation requires the most sophisticated computational strategies. The multithreaded domain decomposition parallel processing will be necessary in order to reduce both computational time and storage. Without special treatments involved in computer engineering, our attempt to analyze the airbreathing combustion appears to be difficult, if not impossible.

Schunk, Richard Gregory↗
NASA NTRS1999

New Approaches to Parameterizing Convection

Many general circulation models (GCMs) currently use separate schemes for planetary boundary layer (PBL) processes, shallow and deep cumulus (Cu) convection, and stratiform clouds. The conventional distinctions. among these processes are somewhat arbitrary. For example, in the stratocumulus-to-cumulus transition region, stratocumulus clouds break up into a combination of shallow cumulus and broken stratocumulus. Shallow cumulus clouds may be considered to reside completely within the PBL, or they may be regarded as starting in the PBL but terminating above it. Deeper cumulus clouds often originate within the PBL with also can originate aloft. To the extent that our models separately parameterize physical processes which interact strongly on small space and time scales, the currently fashionable practice of modularization may be doing more harm than good.

Randall, David A.↗
NASA NTRS2002

Hawaii Ocean Mixing Experiment: Program Summary

It is becoming apparent that insufficient mixing occurs in the pelagic ocean to maintain the large scale thermohaline circulation. Observed mixing rates fall a factor of ten short of classical indices such as Munk's "Abyssal Recipe." The growing suspicion is that most of the mixing in the sea occurs near topography. Exciting recent observations by Polzin et al., among others, fuel this speculation. If topographic mixing is indeed important, it must be acknowledged that its geographic distribution, both laterally and vertically, is presently unknown. The vertical distribution of mixing plays a critical role in the Stommel Arons model of the ocean interior circulation. In recent numerical studies, Samelson demonstrates the extreme sensitivity of flow in the abyssal ocean to the spatial distribution of mixing. We propose to study the topographic mixing problem through an integrated program of modeling and observation. We focus on tidally forced mixing as the global energetics of this process have received (and are receiving) considerable study. Also, the well defined frequency of the forcing and the unique geometry of tidal scattering serve to focus the experiment design. The Hawaiian Ridge is selected as a study site. Strong interaction between the barotropic tide and the Ridge is known to take place. The goals of the Hawaiian Ocean Mixing Experiment (HOME) are to quantify the rate of tidal energy loss to mixing at the Ridge and to identify the mechanisms by which energy is lost and mixing generated. We are challenged to develop a sufficiently comprehensive picture that results can be generalized from Hawaii to the global ocean. To achieve these goals, investigators from five institutions have designed HOME, a program of historic data analysis, modeling and field observation. The Analysis and Modeling efforts support the design of the field experiments. As the program progresses, a global model of the barotropic (depth independent) tide, and two models of the baroclinic (depth varying) tide, all validated with near-Ridge data, will be applied, to reveal the mechanisms of tidal energy conversion along the Ridge, and allow spatial and temporal integration of the rate of conversion. Field experiments include a survey to identify "hot spots" of enhanced mixing and barotropic to baroclinic conversion, a Nearfield study identifying the dominant mechanisms responsible for topographic mixing, and a Farfield program which quantifies the barotropic energy flux convergence at the Ridge and the flux divergence associated with low mode baroclinic waves radiation. The difference is a measure of the tidal power available for mixing at the Ridge. Field work is planned from years 2000 through 2002, with analysis and modeling efforts extending through early 2006. If successful, HOME will yield an understanding of the dominant topographic mixing processes applicable throughout the global ocean. It will advance understanding of two central problems in ocean science, the maintenance of the abyssal stratification, and the dissipation of the tides. HOME data will be used to improve the parameterization of dissipation in models which presently assimilate TOPEX-POSEIDON observations. The improved understanding of the dynamics and spatial distribution of mixing processes will benefit future long-term programs such as CLIVAR.

Ray, Richard D.↗
NASA NTRS2002

Exclusive Reactions Involving Pions and Nucleons

The HZETRN code requires inclusive cross sections as input. One of the methods used to calculate these cross sections requires knowledge of all exclusive processes contributing to the inclusive reaction. Conservation laws are used to determine all possible exclusive reactions involving strong interactions between pions and nucleons. Inclusive particle masses are subsequently determined and are needed in cross-section calculations for inclusive pion production.

Norbury, John W.↗
NASA NTRS2003

Calculation of Supersonic Combustion Using Implicit Schemes

One of the technology goals of NASA for advanced space transportation is to develop highly efficient propulsion systems to reduce the cost of payload for space missions. Developments of rockets for the second generation Reusable Launch Vehicle (RLV) in the past several years have been focused on low-cost versions of conventional engines. However, recent changes in the Integrated Space Transportation Program to build a crew transportation vehicle to extend the life of the Space Shuttle fleet might suggest that air-breathing rockets could reemerge as a possible propulsion system for the third generation RLV to replace the Space Shuttle after 2015. The weight of the oxygen tank exceeds thirty percent of the total weight of the Space Shuttle at launch while the payload is only one percent of the total weight. The air-breathing rocket propulsion systems, which consume oxygen in the air, offer clear advantages by making vehicles lighter and more efficient. Experience in the National Aerospace Plane Program in the late 1980s indicates that scramjet engines can achieve high specific impulse for low hypersonic vehicle speeds. Whether taking a form of Rocket Based Combined Cycle (RBCC) or Turbine Based Combined Cycle (TBCC), the scramjet is an essential mode of operation for air-breathing rockets. It is well known that fuel-air mixing and rapid combustion are of crucial importance for the success of scramjet engines since the spreading rate of the supersonic mixing layer decreases as the Mach number increases. A factored form of the Gauss-Seidel relaxation method has been widely used in hypersonic flow research since its first application to non-equilibrium flows. However, difficulties in stability and convergence have been encountered when there is strong interaction between fluid motion and chemical reaction, such as multiple fuel injection problems. The present paper reports the results from investigation of the effect of modifications to the original algorithm on the performance for multiple injectors.

Yoon, Seokkwan↗