SEARCH · Engineering Papers

Results for “density modification”

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.

SourceResearch connectionFrom yearThrough year

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

At least 73 records · Page 4

All sources NASA NTRS DOE OSTI

NASA NTRS1980

FFT methods in signal processing of the coal interface detector radar

The FM radar for the coal interface detector, operating in the frequency band 2 to 4 GHz, is intended for the display of thicknesses between 2 cm and 20 cm. Because of such a short range, the thickness information is contained in the very few lowest spectral components of the output signal. To overcome this inconvenience, the Fourier series of the output signal was augmented to approximate a Fourier integral. This modification in the signal processing resulted in a higher spectral density, which in turn enabled an easier identification of the interface position in the laboratory. The orientation and spacing of the receiving and transmitting antennas is found to have an important influence on the system performance.

Kajfez, D.↗

NASA NTRS1991

Bending waves and orbital inclinations

Disk tides may play an important role in the formation of a planetary system. Modification of protoplanet semi-major axes and eccentricities through density waves was suggested and calculations of linear and non-linear protoplanet-nebula interactions were carried out by a number of researchers. The possible significance of radial drift to the accretion process was discussed, while the evolution of orbital eccentricities was studied for a perturber orbiting external to a ring and for a perturber embedded in the ring. The possible importance of bending waves to the early evolution of protoplanet inclinations is described.

Ward, William R.↗

NASA NTRS2007

Impact of Ring Current Ions on Electromagnetic Ion Cyclotron Wave Dispersion Relation

Effect of the ring current ions in the real part of electromagnetic ion Cyclotron wave dispersion relation is studied on global scale. Recent Cluster observations by Engebretson et al. showed that although the temperature anisotropy of is energetic (> 10 keV) ring current protons was high during the entire 22 November 2003 perigee pass, electromagnetic ion cyclotron waves were observed only in conjunction with intensification of the ion fluxes below 1 keV by over an order of magnitude. To study the effect of the ring current ions on the wave dispersive properties and the corresponding global wave redistribution, we use a self-consistent model of interacting ring current and electromagnetic ion cyclotron waves, and simulate the May 1998 storm. The main findings of our simulation can be summarized as follows: First, the plasma density enhancement in the night MLT sector during the main and recovery storm phases is mostly caused by injection of suprathermal plasma sheet H + (approximately < 1 keV), which dominate the thermal plasma density. Second, during the recovery storm phases, the ring current modification of the wave dispersion relation leads to a qualitative change of the wave patterns in the postmidnight-dawn sector for L > 4.75. This "new" wave activity is well organized by outward edges of dense suprathermal ring current spots, and the waves are not observed if the ring current ions are not included in the real part of dispersion relation. Third, the most intense wave-induced ring current precipitation is located in the night MLT sector and caused by modification of the wave dispersion relation. The strongest precipitating fluxes of about 8 X 10(exp 6)/ (cm(exp 2) - s X st) are found near L=5.75, MLT=2 during the early recovery phase on 4 May. Finally, the nightside precipitation is more intense than the dayside fluxes, even if there are less intense waves, because the convection field moves ring current ions into the loss cone on the nightside, but drives them out of the loss cone on the dayside. So convection and wave scattering reinforce each other in the nightside, but interfere in the dayside sector.

Khazanov, G. V.↗

NASA NTRS2000

Gas storage using fullerene based adsorbents

This invention is directed to the synthesis of high bulk density high gas absorption capacity adsorbents for gas storage applications. Specifically, this invention is concerned with novel gas absorbents with high gravimetric and volumetric gas adsorption capacities which are made from fullerene-based materials. By pressing fullerene powder into pellet form using a conventional press, then polymerizing it by subjecting the fullerene to high temperature and high inert gas pressure, the resulting fullerene-based materials have high bulk densities and high gas adsorption capacities. By pre-chemical modification or post-polymerization activation processes, the gas adsorption capacities of the fullerene-based adsorbents can be further enhanced. These materials are suitable for low pressure gas storage applications, such as oxygen storage for home oxygen therapy uses or on-board vehicle natural gas storage. They are also suitable for storing gases and vapors such as hydrogen, nitrogen, carbon dioxide, and water vapor.

Loutfy, Raouf O.↗

NASA NTRS2013

Radiative Transfer Theory Verified by Controlled Laboratory Experiments

We report the results of high-accuracy controlled laboratory measurements of the Stokes reflection matrix for suspensions of submicrometer-sized latex particles in water and compare them with the results of a numerically exact computer solution of the vector radiative transfer equation (VRTE). The quantitative performance of the VRTE is monitored by increasing the volume packing density of the latex particles from 2 to 10. Our results indicate that the VRTE can be applied safely to random particulate media with packing densities up to 2. VRTE results for packing densities of the order of 5 should be taken with caution, whereas the polarized bidirectional reflectivity of suspensions with larger packing densities cannot be accurately predicted. We demonstrate that a simple modification of the phase matrix entering the VRTE based on the so-called static structure factor can be a promising remedy that deserves further examination.

Radiative transfer↗

NASA NTRS1994

Dynamics and Thermodynamics of Dense and Dilute Clusters of Drops

Collective drop behavior is encountered in sprays produced for a variety of applications. The existence of clusters of drops indicates that the interaction among the drops is important in determining the dynamics of the drops because the drop proximity changes the flow around the individual drops in a way that affects the drag on each drop. Additionally, if there is a phase change between the liquid drops and the gaseous surroundings (either evaporation or condensation), this will also influence the flow around the individual drops; and phase change is also affected by the drop proximity. What will be discussed are studies of collections of drops where the dynamics and thermodynamics of the drops are coupled. This means the modification of the drag force due to the drop number density, the evaporation rate and the slip velocity are all taken into account. In turn, the enhancement in the evaporation rate due to the slip velocity , and the hindering of evaporation due to the drop proximity are also part of the models.

thermodynamics↗

NASA NTRS1976

Air transportation energy efficiency - Alternatives and implications

Results from recent studies of air transportation energy efficiency alternatives are discussed, along with some of the implications of these alternatives. The fuel-saving alternatives considered include aircraft operation, aircraft modification, derivative aircraft, and new aircraft. In the near-term, energy efficiency improvements should be possible through small improvements in fuel-saving flight procedures, higher density seating, and higher load factors. Additional small near-term improvements could be obtained through aircraft modifications, such as the relatively inexpensive drag reduction modifications. Derivatives of existing aircraft could meet the requirements for new aircraft and provide energy improvements until advanced technology is available to justify the cost of a completely new design. In order to obtain significant improvements in energy efficiency, new aircraft must truly exploit advanced technology in such areas as aerodynamics, composite structures, active controls, and advanced propulsion.

Williams, L. J.↗

NASA NTRS2024

Airfoil Table Modification for Improved Calculation of Ingenuity Rotor Performance

To better characterize the behavior of the Ingenuity helicopter, multiple test campaigns were conducted. These tests included the Engineering Design Model 1 (EDM1) tests and the Transonic Rotor Test (TRT), both of which assessed Ingenuity rotor performance at various conditions. Using a comprehensive rotorcraft analysis tool, CAMRAD II, test setups of the two different Ingenuity test campaigns were simulated. The EDM1 test used coaxial test stand which focused on varying collective at various feasible Martian atmospheric densities and the TRT test used a single rotor test stand which focused on varying RPM to assess performance at different blade tip Mach numbers. Initial CAMRAD II analyses yielded performance results which differed significantly from experimental results. To reconcile the experimental results and the CAMRAD II analyses, modifications were made to the input airfoil decks for CAMRAD II. After several iterations of modifications, a specific method of modification was found that more accurately predicted experimental behavior at all tested densities for the coaxial rotor. This same modification was less successful for the single rotor test results. There are a number of differences between coaxial and single rotor aerodynamics and between the two test stands (hub and control system); also, there is a small influence of RPM (mainly tip Mach number) on dimensionless performance. These differences may be causing the coaxial rotor modifications not being successful for the single rotor.

Airfoil↗

NASA NTRS1984

Edge Stabilized Ribbon (ESR); Stress, Dislocation Density and Electronic Performance

The edge stabilized ribbon (ESR) silicon ribbon was grown in widths of 1, 2.2 and 4.0 inches at speeds ranging from .6 to 7 in/min, which result in ribbon thicknesses of 5 to 400 microns. One of the primary problems remaining in ESR growth is that of thermally induced mechanical stresses. This problem is manifested as ribbon with a high degree of residual stress or as ribbon with buckled ribbon. Thermal stresses result in a high dislocation density in the grown material, resulting in compromised electronic performance. Improvements in ribbon flatness were accomplished by modification of the ribbon cooling profile. Ribbon flatness and other experimental observations of ESR ribbon are discussed. Laser scanner measurements show a good correlation between diffusion length and dislocation density which indicates that the high dislocation densities are the primary cause of the poor current performance of ESR materials. Dislocation densities were reduced and improved electronic performance resulted. Laser scanner data on new and old material are presented.

Sachs, E. M.↗

NASA NTRS1993

Parameterized study of the ionospheric modification associated with sun-aligned polar cap arcs

The local ionospheric modification that is due to a generalized steady state solar aligned (SA) arc structure is addressed. For a representative set of SA arc parameters which includes both convection and precipitation, emphasis is placed on the modification by SA polar cap arcs upon the F region electron density and the height integrated conductivity. At low fluxes and low characteristic energies, SA polar cap arcs have the most pronounced relative effect at F region altitudes in darkness for winter solar minimum conditions. The absolute enhancement in summer solar minimum and winter solar maximum is equivalent to that of winter solar minimum, but the higher ambient densities make the relative enhancement less. The TEC enhancement associated with an SA arc may be used to indicate the degree of plasma cross flow across the arc.

Crain, D. J.↗

NASA NTRS1923

Adaptation of aeronautical engines to high altitude flying

Issues and techniques relative to the adaptation of aircraft engines to high altitude flight are discussed. Covered here are the limits of engine output, modifications and characteristics of high altitude engines, the influence of air density on the proportions of fuel mixtures, methods of varying the proportions of fuel mixtures, the automatic prevention of fuel waste, and the design and application of air pressure regulators to high altitude flying. Summary: 1. Limits of engine output. 2. High altitude engines. 3. Influence of air density on proportions of mixture. 4. Methods of varying proportions of mixture. 5. Automatic prevention of fuel waste. 6. Design and application of air pressure regulators to high altitude flying.

Kutzbach, K↗

NASA NTRS2009

Hardware Evaluation of the Horizontal Exercise Fixture with Weight Stack

HEF with weight stack seems to be a very sturdy and reliable exercise device that should function well in a bed rest training setting. A few improvements should be made to both the hardware and software to improve usage efficiency, but largely, this evaluation has demonstrated HEF's robustness. The hardware offers loading to muscles, bones, and joints, potentially sufficient to mitigate the loss of muscle mass and bone mineral density during long-duration bed rest campaigns. With some minor modifications, the HEF with weight stack equipment provides the best currently available means of performing squat, heel raise, prone row, bench press, and hip flexion/extension exercise in a supine orientation.

Newby, Nate↗

NASA NTRS2012

A High-resolution Model of Field-aligned Currents Through Empirical Orthogonal Functions Analysis (MFACE)

Ten years of CHAMP magnetic field measurements are integrated into MFACE, a model of field-aligned currents (FACs) using empirical orthogonal functions (EOFs). EOF1 gives the basic Region-1/Region-2 pattern varying mainly with the interplanetary magnetic field Bz component. EOF2 captures separately the cusp current signature and By-related variability. Compared to existing models, MFACE yields significantly better spatial resolution, reproduces typically observed FAC thickness and intensity, improves on the magnetic local time (MLT) distribution, and gives the seasonal dependence of FAC latitudes and the NBZ current signature. MFACE further reveals systematic dependences on By, including 1) Region-1/Region-2 topology modifications around noon; 2) imbalance between upward and downward maximum current density; 3) MLT location of the Harang discontinuity. Furthermore, our procedure allows quantifying response times of FACs to solar wind driving at the bow shock nose: we obtain 20 minutes and 35-40 minutes lags for the FAC density and latitude, respectively.

CHAMP↗

NASA NTRS2011

Wind and Temperature Spectrometry of the Upper Atmosphere in Low-Earth Orbit

Wind and Temperature Spectrometry (WATS) is a new approach to measure the full wind vector, temperature, and relative densities of major neutral species in the Earth's thermosphere. The method uses an energy-angle spectrometer moving through the tenuous upper atmosphere to measure directly the angular and energy distributions of the air stream that enters the spectrometer. The angular distribution gives the direction of the total velocity of the air entering the spectrometer, and the energy distribution gives the magnitude of the total velocity. The wind velocity vector is uniquely determined since the measured total velocity depends on the wind vector and the orbiting velocity vector. The orbiting spectrometer moves supersonically, Mach 8 or greater, through the air and must point within a few degrees of its orbital velocity vector (the ram direction). Pointing knowledge is critical; for example, pointing errors 0.1 lead to errors of about 10 m/s in the wind. The WATS method may also be applied without modification to measure the ion-drift vector, ion temperature, and relative ion densities of major ionic species in the ionosphere. In such an application it may be called IDTS: Ion-Drift Temperature Spectrometry. A spectrometer-based coordinate system with one axis instantaneously pointing along the ram direction makes it possible to transform the Maxwellian velocity distribution of the air molecules to a Maxwellian energy-angle distribution for the molecular flux entering the spectrometer. This implementation of WATS is called the gas kinetic method (GKM) because it is applied to the case of the Maxwellian distribution. The WATS method follows from the recognition that in a supersonic platform moving at 8,000 m/s, the measurement of small wind velocities in the air on the order of a few 100 m/s and less requires precise knowledge of the angle of incidence of the neutral atoms and molecules. The same is true for the case of ion-drift measurements. WATS also provides a general approach that can obtain non-equilibrium distributions as may exist in the upper regions of the thermosphere, above 500 km and into the exosphere. Finally, WATS serves as a mass spectrometer, with very low mass resolution of roughly 1 part in 3, but easily separating atomic oxygen from molecular nitrogen.

Herrero, Federico↗

NASA NTRS1982

Planetary radio astronomy observations during the Voyager 1 Titan flyby

During the Voyager 1 Titan flyby, unusual radio emissions were observed by the planetary radio astronomy experiment in the 20- to 97-kHz frequency range. It is shown that Titan itself is not the source of the observed radio emission. The emission features are attributed to modification of the normal Saturn kilometric radiation by propagation effects in enhanced density structures within the Titan wake. Furthermore, spiky emissions observed in the magnetic wake of Titan are interpreted in terms of local electrostatic instabilities at the electron plasma frequency. From these measurements a range of electron densities in the wake region is derived, and the consistency of the results is discussed.

Daigne, G.↗

NASA NTRS1988

The NASA Marshall engineering thermosphere model

Described is the NASA Marshall Engineering Thermosphere (MET) Model, which is a modified version of the MFSC/J70 Orbital Atmospheric Density Model as currently used in the J70MM program at MSFC. The modifications to the MFSC/J70 model required for the MET model are described, graphical and numerical examples of the models are included, as is a listing of the MET model computer program. Major differences between the numerical output from the MET model and the MFSC/J70 model are discussed.

Hickey, Michael Philip↗

NASA NTRS1982

HF produced ionospheric electron density irregularities diagnosed by UHF radio star scintillations

Three observations of radio star intensity fluctuations at UHF are reported for HF ionospheric modification experiments carried out at the Arecibo Observatory. Two observations at 430 MHz and one at 1400 MHz suggest that the the thin phase screen theory is a good approximation to the observed power spectra. It is noted, however, that the theory has to be extended to include antenna filtering. This type of filtering is important for UHF radio star scintillations since the antenna usually has a narrow beamwidth. HF power densities of less than 37 microwatts/sq m incident on the ionosphere give rise to electron density irregularities larger than 13% of the ambient density (at 260 km) having scale sizes of approximately 510 m perpendicular to the geomagnetic field. The irregularities are found to form within 20-25 s after the HF power is turned on. The drift velocities of the irregularities can be estimated from the observed power spectra.

Frey, A.↗

NASA NTRS1989

Surface energy and radiation balance systems - General description and improvements

Surface evaluation of sensible and latent heat flux densities and the components of the radiation balance were desired for various vegetative surfaces during the ASCOT84 experiment to compare with modeled results and to relate these values to drainage winds. Five battery operated data systems equipped with sensors to determine the above values were operated for 105 station days during the ASCOT84 experiment. The Bowen ratio energy balance technique was used to partition the available energy into the sensible and latent heat flux densities. A description of the sensors and battery operated equipment used to collect and process the data is presented. In addition, improvements and modifications made since the 1984 experiment are given. Details of calculations of soil heat flow at the surface and an alternate method to calculate sensible and latent heat flux densities are provided.

Fritschen, Leo J.↗