Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Process Scaling”

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 1,279 records · Page 71
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Surface energy fluxes at Central Florida during the convection and precipitation electrification experiment

One of the objectives of CaPE is to better understand the convective process in central and south Florida during the warm season. The energy and moisture exchanges between the surface and the atmosphere are closely related to this process. Some recent studies have shown that the surface energy balance plays an important role in the climatic fields (Shukla and Mintz, 1982; Sud and Smith, 1985; Sato et. al, 1989). Surface energy fluxes and related surface processes such as evapotranspiration and sensible heat transfer directly effect the temperature, humidity, cloud formation and precipitation. For example, mesoscale circulation around a discontinuity in vegetation type were shown to be stronger with wet soil than with dry soil using an evapotranspiration model (Pinty et. al, 1989). In order to better describe the processes in the atmosphere at various scales and improve our ability of modeling and predicting weather related events, it is crucial to understand the mechanism of surface energy transfer in relation to atmospheric events. Surface energy flux measurements are required to fully understand the interactions between the atmosphere and the surface.

Nie, D.↗
NASA NTRS1993

Evolution of molecular clouds

The evolution of interstellar molecular hydrogen was studied, with a special interest for the formation and evolution of molecular clouds and star formation within them, by a two-dimensional hydrodynamical simulation performed on a rectangular grid of physical sizes on the order of 100 pc. It is filled with an initial density of approx. 1 cm(exp -3), except for one cell (approx. 1 pc(exp 2)) at the center of the grid where an accretion core of 1-10(exp 3) solar masses is placed. The grid is co-moving with the gridcenter that is on a circular orbit around the Galactic center and that also is the guiding center of epicyclic approximation of orbits of the matter surrounding it. The initial radial velocity is zero; to account for differential rotation the initial tangential velocity (i.e. the movement around the galactic center) is proportional to the radial distance to the grid center. The rate is comparable to the rotation rate at the Local Standard of Rest. The influence of galactic rotation is noticed by spiral or elliptical forms, but on much longer time scales than self gravitation and cooling processes. Density and temperature are kept constant at the boundaries and no inflow is allowed along the tangential boundaries.

Sevenster, M.↗
NASA NTRS1992

Erosional and depositional history of central Chryse Planitia

This map uses high resolution image data to assess the detailed depositional and erosional history of part of Chryse Planitia. This area is significant to the study of the global geology of Mars because it represents one of only two areas on the martian surface where planetary geologic mapping is assisted with 'ground truth.' In this case the ground truth was provided by Viking Lander 1. Additional questions addressed in this study are concerned with the following: the geologic context of the regional plains surface and the local surface of the Viking Lander 1 site; and the relative influence of volcanic, sedimentary, impact, aeolian, and tectonic processes at the regional and local scales.

Crumpler, L. S.↗
NASA NTRS1992

CELIAS: Charge, Element and Isotope Analysis System for the SOHO mission

The status and further development as well as first calibration of the CELIAS experiment on SOHO is presented. CELIAS is designed to measure the mass, ionic charge, and energy of low and high speed solar wind of suprathermal ions and of low energy flare particles. Through analysis of the elemental and isotopic abundances (the ionic charge state and velocity distributions of ions originating on the solar atmosphere), the investigation focuses on studying the plasma processes in various temporal and spatial scales in the solar chromosphere, transition zone, and corona. Additionally, the CELIAS experiment includes the Solar EUV Monitor (SEM). This unit, which consists of an EUV transmission grating spectrometer and three isolated silicon photodiodes as detectors, is described. The three mass and charge discriminating sensors based on the time of flight technique are also described.

Hovestadt, D.↗
NASA NTRS1992

Buffering of stratospheric circulation by changing amounts of tropical ozone - A Pinatubo case study

Stratospheric aerosol from Mount Pinatubo heated the tropical lower stratosphere by about 0.3 K/day mainly due to absorption of terrestrial infrared radiation. This heating was dissipated by: (1) an observed increase in stratospheric temperatures, which enhanced the radiation cooling; (2) additional mean upward motion, observed for the aerosol cloud, which led to adiabatic cooling; and (3) reductions in ozone concentrations resulting from enhanced upward motions. Each of these processes operated on a different time scale: maximum temperatures were observed after about 90 days; maximum ozone losses of about -1.5 ppm occurred after 140 days when the enhanced vertical velocities effectively lifted the ozone profile by about 2 km. We believe this shows that ozone plays an important role in buffering vertical motion in the tropical lower stratosphere, and hence the residual Brewer Dobson circulation of the whole stratosphere.

Kinne, S.↗
NASA NTRS1993

Effects of Gravity on the Transition to Turbulence of Gas Jet Diffusion Flames

An ongoing study of the transition to turbulence of gas jet diffusion flames conducted in a reduced microgravity environment at the NASA Lewis 2.2 second drop tower is described. The experiments were based on propane injected into quiescent air. Several differences with the corresponding normal gravity process were observed. In particular, large scale structures appeared intermittently in microgravity which are manifested at the flame base and convected down stream. As the Reynolds number increased, a continuous train of structures was observed along the flame front. These observations are explained by instability of the shear layer associated with injection of flow into quiescent surroundings.

Bahadori, M. Y.↗
NASA NTRS1993

Experimental instrumentation system for the Phased Array Mirror Extendible Large Aperture (PAMELA) test program

Adaptive optics are used in telescopes for both viewing objects with minimum distortion and for transmitting laser beams with minimum beam divergence and dance. In order to test concepts on a smaller scale, NASA MSFC is in the process of setting up an adaptive optics test facility with precision (fraction of wavelengths) measurement equipment. The initial system under test is the adaptive optical telescope called PAMELA (Phased Array Mirror Extendible Large Aperture). Goals of this test are: assessment of test hardware specifications for PAMELA application and the determination of the sensitivities of instruments for measuring PAMELA (and other adaptive optical telescopes) imperfections; evaluation of the PAMELA system integration effort and test progress and recommended actions to enhance these activities; and development of concepts and prototypes of experimental apparatuses for PAMELA.

Boykin, William H., Jr.↗
NASA NTRS1992

The Lightcraft project: Flight technology for a hypersonic mass transit system

Rensselaer Polytechnic Institute has been developing transatmospheric 'Lightcraft' technology aimed at creating an efficient, economically affordable, hypersonic mass transportation system. The system utilizes laser-energized airbreathing engines to accelerate minimum-volume passenger capsules. The system gains a high level of reliability by using remote 'centralized' space power sources, e.g., satellite solar power stations. The most critical portion of the Lightcraft's acceleration trajectory involves flight propulsion at hypersonic velocities within the Earth's atmosphere, using a 'Magneto-Hydro-Dynamic (MHD) Fanjet' mode. Of all the propulsion modes proposed for the Lightcraft's combined-cycle engine, the MHD-Fanjet mode has received the least critical inquiry, largely because of its complexity. During the 1991-1992 academic year, Rensselaer's ADP teams produced a detailed conceptual design for the MHD-Fanjet engine, including the specific details of its integration with the other three propulsive modes. To facilitate this process, students built a full-scale mockup of a 1/12th section of this annular engine, complete with a working model of the shroud translation system. The class also made preliminary design calculations for the double-dipole, 'cuspfield' superconducting magnets that provide the external magnetic field needed by the MHD air accelerator, as well as for an onboard microwave power system to enhance the electrical conductivity of the air plasma working fluid. In addition, a large hypersonic model of the MHD accelerator was designed for future tests in RPI's Hypersonic Shock Tunnel in order to validate present analytical performance models. Another group continued design work on a full-sized prototype of a one-person 'Mercury Lightcraft' (a transatmospheric flight simulator), with major emphasis on the detailed design of the major structure, robotic landing gear, and exterior aeroshell.

Myrabo, Leik↗
NASA NTRS1995

TOGA COARE Satellite data summaries available on the World Wide Web

Satellite data summary images and analysis plots from the Tropical Ocean Global Atmosphere Coupled Ocean-Atmosphere Response Experiment (TOGA COARE), which were initially prepared in the field at the Honiara Operations Center, are now available on the Internet via World Wide Web browsers such as Mosaic. These satellite data summaries consist of products derived from the Japanese Geosynchronous Meteorological Satellite IR data: a time-size series of the distribution of contiguous cold cloudiness areas, weekly percent high cloudiness (PHC) maps, and a five-month time-longitudinal diagram illustrating the zonal motion of large areas of cold cloudiness. The weekly PHC maps are overlaid with weekly mean 850-hPa wind calculated from the European Centre for Medium-Range Weather Forecasts (ECMWF) global analysis field and can be viewed as an animation loop. These satellite summaries provide an overview of spatial and temporal variabilities of the cloud population and a large-scale context for studies concerning specific processes of various components of TOGA COARE.

Chen, S. S.↗
NASA NTRS1995

Thermal instability in the inner coma of a comet

The spacecraft and ground based observations of comet Halley inner coma showed a localized ion density depletion region whose origin is not well understood. Although it has been linked to a thermal instability associated with negative ions, the photodetachment lifetime of negative ions (approximately 1 sec) is too short compared to the electron attachment time scale (approximately 100 sec) for this process to have a significant effect. A mechanism for the ion density depletion based on the thermal instability of the cometary plasma due to the excitation of rotational and vibrational levels of water molecules is proposed. The electron energy losses due to these processes peak near 4000 K (0.36 eV) and at temperatures higher than this value a localized cooling leads to further cooling (thermal instability) due to the increased radiation loss. The resulting increase in recombination leads to an ion density depletion and the estimates for this depletion at comet Halley agree with the observations.

Milikh, G. M.↗
NASA NTRS2002

Modeling the Stability of Volatile Deposits in Lunar Cold Traps

There are several mechanisms acting at the cold traps that can alter the inventory of volatiles there. Primarily, the lunar surface is bombarded by meteoroids which impact, melt, process, and redistribute the regolith. Further, solar wind and magnetospheric ion fluxes are allowed limited access onto the regions in permanent shadow. Also, although cold traps are in the permanent shadow of the Sun, there is a small flux of radiation incident on the regions from interstellar sources. We investigate the effects of these space weathering processes on a deposit of volatiles in a lunar cold trap through simulations. We simulate the development of a column of material near the surface of the Moon resulting from space weathering. This simulation treats a column of material at a lunar cold trap and focuses on the hydrogen content of the column. We model space weathering processes on several time and spatial scales to simulate the constant rain of micrometeoroids as well as sporadic larger impactors occurring near the cold traps to determine the retention efficiency of the cold traps. We perform the Monte Carlo simulation over many columns of material to determine the expectation value for hydrogen content of the top few meters of soil for comparison with Lunar Prospector neutron data.

Crider, D. H.↗
NASA NTRS2002

Transient Mixing Driven by Buoyancy Flows

Mixing driven by buoyancy-induced flows is of particular interest to microgravity processes, as the body force that governs the intensity of flow fields can be directly controlled. We consider a model experimental system to explore the dynamics of mixing which employs two miscible liquids inside a cavity separated initially by a divider. The two liquids are oriented vertically inside a rectangular cavity with constant width and height, and varying depths to span the range of a Hele-Shaw cell to a 3-[) configuration. The two miscible liquids can be sufficiently diluted and died, for example water and deuterium oxide, such that a distinct interface exists across the divider. The transient mixing characteristic of the two fluids is addressed by following the Lagrangian history of the interface for various aspect ratios in the z-plane (depth variation) as well as a range of pulling velocities of the divider. The mixing characteristics of the two fluids are quantified from measurement of the length stretch of the interface and its flow field using respectively image processing techniques and Particle Imaging Velocimetry. Scaling analysis shows that the length stretch depends on four governing parameters, namely the Grashof number (Gr), Schmidt number (Sc), aspect ratio (Ar), and Reynolds number (Re). Variation of the Schmidt number is taken into account through thermophysical property variation. Thus our problem reduces to a codimension three bifurcation in parametric space for Gr, Ar, and Re. Our experimental results show that for Gr on the order of 106 and a nominal cavity aspect ratio Ar = 0.2, the net effect of removal of the divider and the overwhelming buoyancy force causes an overturning motion which stretches and folds the interface to produce ml internal breakwave. The structure of the breakwave is similar to the ubiquitous Rayleigh-Taylor instability morphology. The breakwave is dissipated either through internal or wall collision depending on the impulsive velocity of the divider as prescribed by the Reynolds number. The decay of the collision event occurs through sloshing oscillations over a short time scale. The two fluids then become stably stratified with a diffusive band at the interface indicating local mass transport. The local bifurcation of the internal breakwave is investigated as a function of aspect ratio. Results show that for narrow cavities on the order of 2mm (Ar = 0.04) folding does not occur, the interface only stretches. As the cavity size increases folding occurs through a supercritical bifurcation. Insight into the mechanism of folding is obtained from measurement of the flow field which shows that in the neighborhood of the folding event, there exists hyperbolic points caused by multiple vortex interactions. The global length stretch of the interface as a function of time is nearly Gaussian; calculations of finite-time Liapunov exponents as well as construction of horseshoe maps indicate the likelihood of a chaotic transient.

W.M.B. Duval↗
NASA NTRS2003

Beta Pic-like Circumstellar Gas Disk Around 2 And

This grant was awarded to support the data analysis and publication of results from our project entitled P Pic-like Circumstellar Gas Disk Around 2 And . We proposed to obtain FUSE observations of 2 And and study the characteristics and origin of its circumstellar gas. We observed 2 Andromedae with FUSE on 3-4 July 2001 in 11 exposures with a total exposure time of 21,289 seconds through the LWRS aperture. Our data were calibrated with Version 1.8.7 of the CALFUSE pipeline processing software. We corrected the wavelength scale for the heliocentric velocity error in this version of the CALFUSE software. The relative accuracy of the calibrated wavelength scale is +/- 9 km/s . We produced a co-added spectrum in the LiF 1B and LiF 2A channels (covering the 1100 to 1180 A region) by cross-correlating the 11 individual exposures and doing an exposure-time weighted average flux. The final co-added spectra have a signal-to-noise ratio in the stellar continuum near 1150 A of about 20. To obtain an absolute wavelength calibration, we cross-correlated our observed spectra with a model spectrum to obtain the best fit for the photospheric C I lines. Because the photospheric lines are very broad, this yields an absolute accuracy for the wavelength scale of approx.+/- 15 km/s. We then rebinned 5 original pixels to yield the optimal sampling of .033 A for each new pixel, because the calibrated spectra oversample the spectral resolution for FUSE+LWRS (R = 20,000 +/- 2,000).

Cheng, Patricia↗
NASA NTRS2003

Regional-Scale Modeling at NASA Goddard Space Flight Center

Over the past decade, the Goddard Mesoscale Modeling and Dynamics Group has used a popular regional scale model, MM5, to study precipitation processes. Our group is making contributions to the MM5 by incorporating the following physical and numerical packages: improved Goddard cloud processes, a land processes model (Parameterization for Land-Atmosphere-Cloud Exchange - PLACE), efficient but sophisticated radiative processes, conservation of hydrometeor mass (water budget), four-dimensional data assimilation for rainfall, and better computational methods for trace gas transport. At NASA Goddard, the MM5 has been used to study: (1) the impact of initial conditions, assimilation of satellite-derived rainfall, and cumulus parameterizations on rapidly intensifying oceanic cyclones, hurricanes and typhoons, (2) the dynamic and thermodynamic processes associated with the development of narrow cold frontal rainbands, (3) regional climate and water cycles, (4) the impact of vertical transport by clouds and lightning on trace gas distributiodproduction associated with South and North American mesoscale convective systems, (5) the development of a westerly wind burst (WWB) that occurred during the TOGA COARE and the diurnal variation of precipitation in the tropics, (6) a Florida sea breeze convective event and a Mid-US flood event using a sophisticated land surface model, (7) the influence of soil heterogeneity on land surface energy balance in the southwest GCIP region, (8) explicit simulations (with 1.33 to 4 km horizontal resolution) of hurricanes Bob (1991) and Bonnie (1998), (9) a heavy precipitation event over Taiwan, and (10) to make real time forecasts for a major NASA field program. In this paper, the modifications and simulated cases will be described and discussed.

Tao, W.-K.↗
NASA NTRS2003

Scaling and Single Event Effects (SEE) Sensitivity

This paper begins by discussing the potential for scaling down transistors and other components to fit more of them on chips in order to increasing computer processing speed. It also addresses technical challenges to further scaling. Components have been scaled down enough to allow single particles to have an effect, known as a Single Event Effect (SEE). This paper explores the relationship between scaling and the following SEEs: Single Event Upsets (SEU) on DRAMs and SRAMs, Latch-up, Snap-back, Single Event Burnout (SEB), Single Event Gate Rupture (SEGR), and Ion-induced soft breakdown (SBD).

Oldham, Timothy R.↗
NASA NTRS2005

Martian Atmospheric Circulation and Climate

This project was submitted with four work tasks. The reviews recommended focusing on the following three, with an appropriately reduced budget: 1. In the first, we proposed to use Thermal Emission Spectrometer (TES) data to examine the general circulation of the atmosphere and to better constrain and validate a Mars General Circulation Model (GCM). 2. In the second, we proposed to examine processes responsible for the injection of dust into the atmosphere. We will conduct a global, seasonal survey of dust lifting events, and specifically of dust devil activity, using MGS MOC, MGS TES, and Odyssey THEMIS data. The results of this survey will be compared with model predictions of dust devil and other dust lifting processes. It is expected that some of the observational results will motivate specific simulations with the GCM and mesoscale models. 3. In the third task, we proposed to extract seasonal and spatial near-surface wind information from aeolian streaks. Detailed analysis will focus on streaks in the polar regions and in regions of large topography (such as Tharsis). The streak information will be used along with the mesoscale model to examine the processes that control local and regional scale flow patterns.

Richardson, Mark I.↗
NASA NTRS2006

Maximizing the Scientific Return of the Sentinels Mission Using Global MHD Models

The Sentinels mission promises to provide a unique view of the acceleration and transport processes of energetic particles as well as the initiation and evolution of coronal mass ejections (CMEs). A crucial component in understanding the physics associated with these processes lies in the large-scale structure of the corona and heliosphere, particularly during the eruption and propagation of fast CMEs. In this talk we review the current status of our MHD modeling efforts, focusing on Sentinels-specific science, and project forward to envisage what capabilities we may have developed by the time that the Sentinels launch (2012). In conjunction with Solar Orbiter, the farside and near-Earth Sentinels spacecraft will provide simultaneous photospheric magnetograph measurements at multiple longitudes, which will lead to major improvements in our ability to prescribe accurate, time-dependent global boundary conditions. Data returned from the inner heliospheric Sentinels will be used to validate these results. The model results can be used in a variety of ways to interpret the observations. For example, products from the model, such as the properties of CME-driven shocks and CME-associated reconnection sites can be used to interpret complex energetic particle profiles. Also, by tracing along magnetic field lines, the inferred sites of the energetic particles can be connected directly with the in situ measurements at each spacecraft. Perhaps more so than any previous mission, sophisticated models will be required to unravel the broad and disparate measurements returned by the suite of Sentinels spacecraft.

Riley, P.↗
NASA NTRS2008

Magnetotail Current Sheet Thinning and Magnetic Reconnection Dynamics in Global Modeling of Substorms

Magnetotail current sheet thinning and magnetic reconnection are key elements of magnetospheric substorms. We utilized the global MHD model BATS-R-US with Adaptive Mesh Refinement developed at the University of Michigan to investigate the formation and dynamic evolution of the magnetotail thin current sheet. The BATSRUS adaptive grid structure allows resolving magnetotail regions with increased current density up to ion kinetic scales. We investigated dynamics of magnetotail current sheet thinning in response to southwards IMF turning. Gradual slow current sheet thinning during the early growth phase become exponentially fast during the last few minutes prior to nightside reconnection onset. The later stage of current sheet thinning is accompanied by earthward flows and rapid suppression of normal magnetic field component $B-z$. Current sheet thinning set the stage for near-earth magnetic reconnection. In collisionless magnetospheric plasma, the primary mechanism controlling the dissipation in the vicinity of the reconnection site is non-gyrotropic effects with spatial scales comparable with the particle Larmor radius. One of the major challenges in global MHD modeling of the magnetotail magnetic reconnection is to reproduce fast reconnection rates typically observed in smallscale kinetic simulations. Bursts of fast reconnection cause fast magnetic field reconfiguration typical for magnetospheric substorms. To incorporate nongyritropic effects in diffusion regions we developed an algorithm to search for magnetotail reconnection sites, specifically where the magnetic field components perpendicular to the local current direction approaches zero and form an X-type configuration. Spatial scales of the diffusion region and magnitude of the reconnection electric field are calculated self-consistently using MHD plasma and field parameters in the vicinity of the reconnection site. The location of the reconnection sites and spatial scales of the diffusion region are updated during the simulations. Such an approach allows quantifying the interaction between large-scale global magnetospheric dynamics and microphysical processes in diffusion regions localized near reconnection sites. To clarify the role of smallscale non-MHD effects in diffusion region on the global magnetospheric dynamic and to test different models of dissipation we perform simulations with steady southward IMF driving of the magnetosphere.

Kuznetsova, M. M.↗