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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 595 records · Page 33
All sourcesNASA NTRSDOE OSTI
NASA NTRS1996

The 29 July 1994 Merritt Island, Fl Microburst: A Case Study Intercomparing Kennedy Space Center Three-Dimensional Lightning Data (LDAR) and WSR-88D Radar Data

Many researchers have shown that the development and evolution of electrical discharges within convective clouds is fundamentally related to the growth and dynamics of precipitation particles aloft. In the presence of strong updrafts above the freezing level collisions among mixed-phase particles (i.e., hail. ice, supercooled water) promote the necessary charge separation needed to initiate intra-cloud lightning. A precipitation core that descends below the freezing level is often accompanied by a change in the electrical structure of the cloud. Consequently, more Cloud-to-Ground (CG) than Intra-Cloud (IC) lightning flashes appear. Descending precipitation cores can also play a significant role in the evolution of mesoscale features at the surface (e.g., microbursts, downbursts) because of latent heat and mass loading effects of water and ice. For this reason, some believe that lightning and microbursts are fundamentally linked by the presence of ice particles in thunderstorms. Several radar and lightning studies of microburst thunderstorms from COHMEX in 1986 showed that the peak IC lightning systematically occurred ten minutes before the onset of a microburst. In contrast, most CG lightning occurred at the time of the microburst. Many of the preceding studies have been done using high-resolution research radars and experimental lightning detection systems in focused field projects. In addition, these studies could only determine the vertical origin or occurrence of IC lightning, and not a true three-dimensional representation. Currently, the WSR-88D radar system and a real-time, state-of-the-art lightning system (LDAR) at the Kennedy Space Center (KSC) in Florida provide an opportunity to extend these kinds of studies in a more meaningful operational setting.

Hoffert, Steven G.↗
NASA NTRS1996

Exact-Output Tracking Theory for Systems with Parameter Jumps

In this paper we consider the exact output tracking problem for systems with parameter jumps. Necessary and sufficient conditions are derived for the elimination of switching-introduced output transient. Previous works have studied this problem by developing a regulator that maintains exact tracking through parameter jumps (switches). Such techniques are, however, only applicable to minimum-phase systems. In contrast, our approach is applicable to nonminimum-phase systems and obtains bounded but possibly non-causal solutions. If the reference trajectories are generated by an exo-system, then we develop an exact-tracking controller in a feedback form. As in standard regulator theory, we obtain a linear map from the states of the exo-system to the desired system state which is defined via a matrix differential equation. The constant solution of this differential equation provides asymptotic tracking, and coincides with the feedback law used in standard regulator theory. The obtained results are applied to a simple flexible manipulator with jumps in the pay-load mass.

Devasia, Santosh↗
NASA NTRS1997

Spin-Tunnel Investigation of a 1/28-Scale Model of the NASA F-18 High Alpha Research Vehicle (HARV) with and without Vertical Tails

An investigation was conducted in the NASA Langley 20-Foot Vertical Spin Tunnel to determine the developed spin and spin-recovery characteristics of a 1/28-scale, free-spinning model of the NASA F-18 HARV (High Alpha Research Vehicle) airplane that can configured with and without the vertical tails installed. The purpose of the test was to determine what effects, if any, the absence of vertical tails (and rudders) had on the spin and spin-recovery capabilities of the HARV. The model was ballasted to dynamically represent the full-scale airplane at an altitude of 25,000 feet. Erect and inverted spin tests with symmetric mass loadings were conducted with the free-spinning model. The model results indicate that the basic airplane with vertical tails installed (with unaugmented control system) will exhibit fast, flat erect and inverted spins from which acceptable recoveries can be made. Removing the vertical tails had little effect on the erect spin mode, but did degrade recoveries from erect spins. In contrast, inverted spins without the vertical tails were significantly more severe than those with the tails installed.

Fremaux, C. Michael↗
NASA NTRS1998

Evaluation of Relative Sensitivity of SAW and Flexural Plate Wave Devices for Atmospheric Sensing

The objective of this project is to evaluate the suitability of the ultrasonic flexural plate wave (FPW) device as the detector in a gas chromatograph (GC). Of particular interest is the detection of nitrous oxide (N2O). From experimental results we conclude analyte detection is achieved through two mechanisms: changes in gas density, and mass loading of the device membrane due to the sorption of gas molecules. Reducing the dead volume of the FPW chamber increased the FPW response. A comparison of the FPW response to that of the surface acoustic wave (SAW) detector provided with the GC (made by MSI, Microsensor Technologies, Inc.), shows that for unseparated N2O in N2, the FPW exhibits a sensitivity that is at least 550 times greater than that of the SAW device. A Porapak Q column was found to separate N2O from its carrier gas, N2 or He. With the Porapak Q column, a coated FPW detected 1 ppm N2O in N2 or He, with a response magnitude of 7 Hz. A coated SAW exhibited a response of 25 Hz to pure N2O. The minimal detectable N2O concentrations of the sensors were not evaluated.

White, Richard M.↗
NASA NTRS1997

Exact-Output Tracking Theory for Systems with Parameter Jumps

We consider the exact output tracking problem for systems with parameter jumps. Necessary and sufficient conditions are derived for the elimination of switching-introduced output transient. Previous works have studied this problem by developing a regulator that maintains exact tracking through parameter jumps (switches). Such techniques are, however, only applicable to minimum-phase systems. In contrast, our approach is applicable to non-minimum-phase systems and it obtains bounded but possibly non-causal solutions. If the reference trajectories are generated by an exosystem, then we develop an exact-tracking controller in a feed-back form. As in standard regulator theory, we obtain a linear map from the states of the exosystem to the desired system state which is defined via a matrix differential equation. The constant solution of this differential equation provides asymptotic tracking, and coincides with the feedback law used in standard regulator theory. The obtained results are applied to a simple flexible manipulator with jumps in the pay-load mass.

Devasia, Santosh↗
NASA NTRS1999

Principles in Remote Sensing of Aerosol from MODIS Over Land and Ocean

The well-calibrated spectral radiances measured by MODIS will be processed to retrieve daily aerosol properties that include optical thickness and mass loading over land and optical thickness, the mean particle size of the dominant mode and the ratio between aerosol modes over ocean. In addition, after launch, aerosol single scattering albedo will be calculated as an experimental product. The retrieval process over land is based on a dark target method that identifies appropriate targets in the mid-IR channels and uses an empirical relationship found between the mid-ER and the visible channels to estimate surface reflectance in the visible from the mid-HZ reflectance measured by satellite. The method employs new aerosol models for industrial, smoke and dust aerosol. The process for retrieving aerosol over the ocean makes use of the wide spectral band from 0.55-2.13 microns and a look-up table constructed from combinations of five accumulation modes and five coarse modes. Both the over land and over ocean algorithms have been validated with satellite and airborne radiance measurements. We estimate that MODIS will be able to measure aerosol optical thickness (t) to within 0.05 +/- 0.2t over land and to within 0.05 +/- 0.05t over ocean. Much of the earth's surface is located far from aerosol sources and experience very low aerosol optical thickness. Will the accuracy expected from MODIS retrievals be sufficient to measure the global aerosol direct and indirect forcing? We are attempting to answer this question using global model results and cloud climatology.

Remer, L. A.↗
NASA NTRS1999

Remote Sensing of Aerosol and their Radiative Forcing of Climate

Remote sensing of aerosol and aerosol radiative forcing of climate is going through a major transformation. The launch in next few years of new satellites designed specifically for remote sensing of aerosol is expected to further revolutionized aerosol measurements: until five years ago satellites were not designed for remote sensing of aerosol. Aerosol optical thickness was derived as a by product, only over the oceans using one AVHRR channel with errors of approx. 50%. However it already revealed a very important first global picture of the distribution and sources of aerosol. In the last 5 years we saw the introduction of polarization and multi-view observations (POLDER and ATSR) for satellite remote sensing of aerosol over land and ocean. Better products are derived from AVHRR using its two channels. The new TOMS aerosol index shows the location and transport of aerosol over land and ocean. Now we anticipate the launch of EOS-Terra with MODIS, MISR and CERES on board for multi-view, multi-spectral remote sensing of aerosol and its radiative forcing. This will allow application of new techniques, e.g. using a wide spectral range (0.55-2.2 microns) to derive precise optical thickness, particle size and mass loading. Aerosol is transparent in the 2.2 microns channel, therefore this channel can be used to detect surface features that in turn are used to derive the aerosol optical thickness in the visible part of the spectrum. New techniques are developed to derive the aerosol single scattering albedo, a measure of absorption of sunlight, and techniques to derive directly the aerosol forcing at the top of the atmosphere. In the last 5 years a global network of sun/sky radiometers was formed, designed to communicate in real time the spectral optical thickness from 50-80 locations every day, every 15 minutes. The sky angular and spectral information is also measured and used to retrieve the aerosol size distribution, refractive index, single scattering albedo and the spectral flux reaching the surface. Effort to introduce remote sensing from lidars will literally additional dimension to aerosol remote sensing. The vertical dimension is a critical link between the global satellite observations and modeling of aerosol transport. Lidars are also critical to study aerosol impact on cloud microphysics and reflectance. Both lidar ground networks and satellite systems are in development. This new capability is expected to put remote sensing in the forefront of aerosol and climate studies. Together with field experiments, chemical analysis and chemical transport models we anticipate, in the next decade, to be able to resolve some of the outstanding questions regarding the role of aerosol in climate, in atmospheric chemistry and its influence on human health and life on this planet.

Kaufman, Yoram J.↗
NASA NTRS1999

Highlights of Part I: Propagation Through Mars Environment: Propagation through Mars Environment - Part 1

We recommend using the dayside Martian ionosphere as a reflector for global communication, because it has a stable density peak and usable critical frequency. This is very crucial for the future Mars ground to ground communication. The dayside ionosphere has been well modeled as a Chapman layer. We suggest performing the Martian nightside ionosphere modeling study. Because the nightside ionosphere has very little measurements available, we propose to drop a digital ionosound instrument into the Mars surface for data collection. Even though the Martian tropospheric radio refractivity had a small value, it still can cause ray bending and multipath effects. We recommend performing an accurate calculation on excess phase and group delays (range and time delays). Other effects, such as range rate errors, appearance angle deviation, defocusing loss on Mars, etc. should be estimated. Ice depolarization effects due to Martian clouds on radio waves are unknown yet, but they are expected to be small, because of lower optical depth and the thinner layer of cloud. Total Martian atmospheric gaseous attenuation is expected to be less than 1 dB on microwaves and, because the Martian atmosphere had very low concentration in uncondensed H2O and O2. An accurate calculation for zenith opacity requires the information about scale heights of H2O and O2 distribution. An accurate water vapor altitude profile at Mars is not available et. Under the normal condition, CO2 and N2 gases ddo not have electric or magnetic dipoles and do not absorb electromagnetic energy from the waves. However, they may generate the dipoles through a collision and interact with waves under a high density condition and absorb electromagnetic waves in the infrared and visible band. Dust storm is the most dominant factor on the radio wave attenuation. Large Martian dust storms can cause at least 3 dB or higher loss to Ka band wave. For a normal dust storm, the attenuation is about 1 dB. The attenuation much depends on dust mass loading, dust size distribution, etc. Most large dust storms occur in the southern hemisphere during later spring and early summer when the southern hemisphere becomes suddenly hot.

Ho, Christian↗
NASA NTRS1999

A Priori Subgrid Analysis of Temporal Mixing Layers with Evaporating Droplets

Subgrid analysis of a transitional temporal mixing layer with evaporating droplets has been performed using three sets of results from a Direct Numerical Simulation (DNS) database, with Reynolds numbers (based on initial vorticity thickness) as large as 600 and with droplet mass loadings as large as 0.5. In the DNS, the gas phase is computed using a Eulerian formulation, with Lagrangian droplet tracking. The Large Eddy Simulation (LES) equations corresponding to the DNS are first derived, and key assumptions in deriving them are first confirmed by computing the terms using the DNS database. Since LES of this flow requires the computation of unfiltered gas-phase variables at droplet locations from filtered gas-phase variables at the grid points, it is proposed to model these by assuming the gas-phase variables to be the sum of the filtered variables and a correction based on the filtered standard deviation; this correction is then computed from the Subgrid Scale (SGS) standard deviation. This model predicts the unfiltered variables at droplet locations considerably better than simply interpolating the filtered variables. Three methods are investigated for modeling the SGS standard deviation: the Smagorinsky approach, the Gradient model and the Scale-Similarity formulation. When the proportionality constant inherent in the SGS models is properly calculated, the Gradient and Scale-Similarity methods give results in excellent agreement with the DNS.

Okongo, Nora↗
NASA NTRS1999

Radio Wave Propagation for Communication on and around Mars: Highlights: Propagation Through Mars Environment - Part 1

We recommend to use the dayside Martian ionosphere as a reflector for global communication, because the dayside ionosphere has stable density peak and usable critic frequency. This is very crucial for the future Mars ground to around communication. The dayside ionosphere has been well modeled as a Chapman layer. We suggest to perform the Martian nightside ionospheric modeling study. Because the nightside ionosphere has very little measurements available, we propose to drop a digital ionosond instrument into the Mars surface for data collection. Even though the Martian tropospheric radio refractivity has small value, it still can cause the ray bending and multipath effects. We recommend to perform an accurate calculation on excess phase and group delays (range and time delays). Other effects, such as range rate errors, appearance angle deviation, defocusing loss on Mars, etc. are also needed to be estimated. Ice depolarization effects due to Martian clouds on radio waves is unknown yet, which is expected to be small, because lower optical depth and thinner layer of cloud: Total Martian atmospheric gaseous attenuation is expected to be less than 1 dB on microwaves band, because the Martian atmosphere has very low concentration in uncondensed H2O and O2. An accurate calculation for zenith opacity requires the information about scale heights of H2O and O2 distribution. An accurate water vapor altitude profile at Mars is not available yet. Under the normal condition, CO2 and N2 gases do not have electric or magnetic dipoles and do not absorb electromagnetic energy from the waves. However, they may generate the dipoles through a collision and interact with waves under a high density condition and absorb electromagnetic waves in the infrared and visible band. Dust storm is most dominant factor to the radio wave attenuation. Large Martian dust storm can cause at least 3 dB or higher loss to Ka band wave. For a normal dust storm, the attenuation is about 1 dB. The attenuation much depends on dust mass loading, dust size distribution, etc. Most large dust storm occur in the southern hemisphere during later spring and early summer when the southern hemisphere become suddenly hot.

Ho, Christian↗
NASA NTRS2000

A Priori Subgrid Scale Modeling for a Droplet Laden Temporal Mixing Layer

Subgrid analysis of a transitional temporal mixing layer with evaporating droplets has been performed using a direct numerical simulation (DNS) database. The DNS is for a Reynolds number (based on initial vorticity thickness) of 600, with droplet mass loading of 0.2. The gas phase is computed using a Eulerian formulation, with Lagrangian droplet tracking. Since Large Eddy Simulation (LES) of this flow requires the computation of unfiltered gas-phase variables at droplet locations from filtered gas-phase variables at the grid points, it is proposed to model these by assuming the gas-phase variables to be given by the filtered variables plus a correction based on the filtered standard deviation, which can be computed from the sub-grid scale (SGS) standard deviation. This model predicts unfiltered variables at droplet locations better than simply interpolating the filtered variables. Three methods are investigated for modeling the SGS standard deviation: Smagorinsky, gradient and scale-similarity. When properly calibrated, the gradient and scale-similarity methods give results in excellent agreement with the DNS.

Okongo, Nora↗
NASA NTRS2000

Preliminary Results from an Assimilation of TOMS Aerosol Observations Into the GOCART Model

At NASA Goddard we are developing a global aerosol data assimilation system that combines advances in remote sensing and modeling of atmospheric aerosols. The goal is to provide high resolution, 3-D aerosol distributions to the research community. Our first step is to develop a simple assimilation system for Saharan mineral aerosol. The Goddard Chemistry and Aerosol Radiation model (GOCART) provides accurate 3-D mineral aerosol size distributions that compare well with TOMS satellite observations. Surface, mobilization, wet and dry deposition, convective and long-range transport are all driven by assimilated fields from the Goddard Earth Observing System Data Assimilation System, GEOS-DAS. Our version of GOCART transports sizes from.08-10 microns and only simulates Saharan dust. TOMS radiance observations in the ultra violet provide information on the mineral and carbonaceous aerosol fields. We use two main observables in this study: the TOMS aerosol index (AI) which is directly related to the ratio of the 340 and 380 radiances and the 380 radiance. These are sensitive to the aerosol optical thickness, the single scattering albedo and the height of the aerosol layer. The Goddard Aerosol Assimilation System (GAAS) uses the Data Assimilation Office's Physical-space Statistical Analysis System (PSAS) to combine TOMS observations and GOCART model first guess fields. At this initial phase we only assimilate observations into the the GOCART model over regions of Africa and the Atlantic where mineral aerosols dominant and carbonaceous aerosols are minimal, Our preliminary results during summer show that the assimilation with TOMS data modifies both the aerosol mass loading and the single scattering albedo. Assimilated aerosol fields will be compared with assimilated aerosol fields from GOCART and AERONET observations over Cape Verde.

daSilva, Arlindo↗
NASA NTRS2001

Assessment of the Contribution of the Atmosphere to Uncertainties in Normalized Water-Leaving Radiance: A Combined Modeling and Data Analysis Approach

Our research for the Sensor Intercomparison and Merger for Biological and Interdisciplinary Oceanic Studies (SIMBIOS) program has been focused on modeling and simulation studies as well as the development of atmospheric correction algorithms. Based on our original proposal and discussions at the SIMBIOS team meetings and workshops, the objectives of our research can be summarized as follows: (1) Use our radiative transfer model for the coupled atmosphere-ocean system to simulate the radiation field at arbitrary levels and in any desired direction in the atmosphere and ocean so as to provide a firm connection between the signal received by the satellite sensor and by a sensor looking down into the water column just above the surface and just below it; (2) Use the simulations to quantify the influence of atmospheric aerosols on the water-leaving radiance, and to quantify the error in the water-leaving radiance as a function of uncertainties in the aerosol optical properties, mass loading and vertical extent; (3) Use the model simulations in conjunction with validation measurements taken by other SIMBIOS investigators (for satellite overpasses) to assess our understanding of the radiative transfer process in the coupled atmosphere-ocean column, and to examine the extent to which the model provides a realistic prediction of simultaneously measured in situ water-leaving radiance and the radiance received by the satellite sensor; (4) Modify and improve an existing atmospheric correction algorithm, based on the work above, as needed by constructing new look-up tables that include scattering by ocean particles; and (5) Carry out approaches to developing an atmospheric correction algorithm for ocean color imagery with strongly absorbing aerosols.

Stamnes, Knut↗
NASA NTRS2001

Membrane Vibration Studies Using a Scanning Laser Vibrometer

This paper summarizes on-going experimental work at NASA Langley Research Center to measure the dynamics of a 1.016 m (40 in.) square polyimide film Kapton membrane. A fixed fully automated impact hammer and Polytec PSV-300-H scanning laser vibrometer were used for non-contact modal testing of the membrane with zero-mass-loading. The paper discusses the results obtained by testing the membrane at various tension levels and at various excitation locations. Results obtained by direct shaker excitation to the membrane are also discussed.

Gaspar, James L.↗
NASA NTRS1995

Limits on Deceleration and Asymmetry of Solar Wind Speed

It has been suggested by Richardson et al. [1995] that the solar wind shows signs of deceleration due to mass-loading by interstellar pickup ions. They based their conclusion on observations from the Voyager 2 and IMP 8 spacecraft. Observations from the Pioneer Venus Orbiter (PVO), Voyager 2, and Pioneer 10 spacecraft are compared to look for this deceleration. While these comparisons suggests the possibility of deceleration at Voyager 2, the magnitude of this deceleration appears to be significantly less than the deceleration reported by Richardson et al. [1995]. Some of this difference could be explained by a north-south asymmetry in solar wind speed. The implications of these results are discussed, along with possibilities for further investigations.

Gazis, P. R.↗
NASA NTRS1996

Interaction of Particles and Turbulence in the Solar Nebula

The most widely accepted theories for the formation of the Solar system claim that small solid particles continue to settle into a thin layer at the midplane of the Solar nebula until it becomes gravitationally unstable and collapses directly into km-sized planetesimals. This scenario has been challenged on at least two grounds: (1) due to turbulence, the particles may not settle into a thin layer, and (2) a thin layer may not be unstable. The Solar nebula contains at least three sources of turbulence: radial shear, vertical shear, and thermal convection. The first of these is small and probably negligible, while the last is poorly understood. However, the second contribution is likely to be substantial. The particle-rich layer rotates at nearly the Keplerian speed, but the surrounding gaseous nebula rotates slower because it is partly supported by pressure. The resulting shear generates a turbulent boundary layer which stirs the particles away from the midplane, and forestalls gravitational instability. Our previous work used a 'zero-equation' (Prandtl) model to predict the intensity of shear-generated turbulence, and enabled us to demonstrate numerically that settling of particles to the midplane is self-limiting. However, we neglected the possibility that mass loading by particles might damp the turbulence. To explore this, we have developed a more sophisticated 'one-equation' model which incorporates local generation, transport, and dissipation of turbulence, as well as explicit damping of turbulence by particles. We also include a background level of global turbulence to represent other sources. Our results indicate that damping flattens the distribution of particles somewhat, but that background turbulence thickens the particle layer.

Dacles-Mariani, Jennifer S.↗
NASA NTRS2001

Io's Magnetospheric Interaction: An MHD Model with Day-Night Asymmetry

In this paper we present the results of all improved three-dimensional MHD model for Io's interaction with Jupiter's magnetosphere. We have included the day-night asymmetry into the spatial distribution of our mass-loading, which allowed us to reproduce several smaller features or the Galileo December 1995 data set. The calculation is performed using our newly modified description of the pick-up processes that accounts for the effects of the corotational electric field existing in the Jovian magnetosphere. This change in the formulation of the source terms for the MHD equations resulted in significant improvements in the comparison with the Galileo measurements. We briefly discuss the limitations of our model and possible future improvements.

Kabin, K.↗
NASA NTRS2000

Two-Species, 3D, MHD Simulation of Europa's Interaction with Jupiter's Magnetosphere

The interaction of Europa with the Jovian a magnetosphere has been studied by using a two species in ideal magnetohydrodynamic (MHD) numerical model. This model considers the upstream plasma in the Jovian magnetosphere and the molecular oxygen ions in the ionosphere of Europa, separately. We present results a from simulation studies, which take into account impact ionization, recombination, and the effect of a possible induced dipole magnetic field of Europa. The total mass loading of the magnetospheric flow and the ionization frequency used in the model are consistent with the estimates of Europa's ionosphere and atmosphere. The multi-species MHD equations are solved by using a finite volume, high-order, Godunov-type method on an adoptively refined unstructured grid, which allows a detailed modeling of the region near Europa's surface, while still resolving both the upstream region and the satellite's wake. We have paid special attention to the wake of Europa, in order to be able to make comparisons with the Galileo's E4 flyby observations, as well as other model calculations. The calculated escape flux of a O2+ down the tail was found to be about 5.6 x 10(exp 25) s(sup -1).

Liu, Yifan↗