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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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS2011

Numerical Simulations of Single and Multiple Scattering by Fractal Ice Clusters

We consider the scattering model in the form of a vertically and horizontally homogeneous particulate slab of an arbitrary optical thickness composed of widely separated fractal aggregates built of small spherical ice monomers. The aggregates are generated by applying three different approaches, including simulated cluster-cluster aggregation (CCA) and diffusion-limited aggregation (DLA) procedures. Having in mind radar remote-sensing applications, we report and analyze the results of computations of the backscattering circular polarization ratio obtained using efficient superposition T-matrix and vector radiative-transfer codes. The computations have been performed at a wavelength of 12.6 cm for fractal aggregates with the following characteristics: monomer refractive index m=1.78+i0.003, monomer radius r=1 cm, monomer packing density p=0.2, overall aggregate radii R in the range 4<=R<=10 cm and fractal dimensions D(sub f) 2.5 and 3. We show that for aggregates generated with simulated CCA and DLA procedures, the respective values of the backscattering circular polarization ratio differ weakly for D(sub f) 2.5, but the differences can increase somewhat for D(sub f)3, especially in case of an optically semi-infinite medium. For aggregates with a spheroidal overall shape, the dependence of the circular polarization ratio on the cluster morphology can be quite significant and increases with increasing the aspect ratio of the circumscribing spheroid.

Dlugach, Janna M.↗
NASA NTRS1980

Polar symmetry in three-dimensional analysis of laminates with angle plies

An improved procedure for the three dimensional finite element analysis of an angle ply laminate with a circular hole is discussed. The procecure exploits polar symmetry and is the basis for a new finite element computer code. For the broad class of laminates that contain angle plies, this code requires only one half as much computing capacity as conventional codes.

Raju, I. S.↗
NASA NTRS1987

Duct flows with swirl

The physics of the flow interaction between swirl and secondary flow was studied in duct bends relevant to the design of advanced aircraft nozzle systems. Both laminar and turbulent subsonic flows were investigated in generic duct bends for different amounts of swirl. The flow calculations are based on an economical three-dimensional spatial marching method employed in an existing computer code (PEPSIG). The computational method and code were extended to allow azimuthal periodicity and solutions in which the polar coordinate singularity occurs in the interior of the flow field. These extensions are needed to address swirling flow and twisted centerlines arising in out-of-plane bends. It was found that appropriate amounts of swirl can reduce total pressure loss relative to nonswirling cases. This conclusion was found to be insensitive to computational mesh.

Tsai, Tommy M.↗
NASA NTRS1991

First ultraviolet spectropolarimetry of hot supergiants

UV spectropolarimetric observations of the early-type supergiant stars P Cygni and Kappa Cassiopeiae obtained with the Wisconsin UV Photo-Polarimeter Experiment (WUPPE) are presented. Contrary to model predictions, the intrinsic polarization of P Cyg remains constant in the Balmer continuum except for a broad dip between 2600 and 3000 A. This decrease in polarization is discussed in terms of possible Fe line blanketing effects. The intrinsic position angle is essentially constant in the UV except for a rotation across the feature between 2600 and 3000 A. The intrinsic polarization of Kappa Cas is small; most of the observed polarization is interstellar in nature. The Serkowski curve extrapolated into the UV is found to fall consistently below the observed polarization. A slight rotation in position angle from optical to UV wavelengths is noted. Very good agreement is found between the mean continuum polarization obtained by WUPPE and the broadband UV polarization measurement obtained by Gehrels (1968).

Taylor, M.↗
NASA NTRS1996

Ocean observations with EOS/MODIS: Algorithm development and post launch studies

Several significant accomplishments were made during the present reporting period. We have completed our basic study of using the 1.38 micron MODIS band for removal of the effects of thin cirrus clouds and stratospheric aerosol. The results suggest that it should be possible to correct imagery for thin cirrus clouds with optical thicknesses as large as 0.5 to 1.0. We have also acquired reflectance data for oceanic whitecaps during a cruise on the RV Malcolm Baldrige in the Gulf of Mexico. The reflectance spectrum of whitecaps was found to be similar to that for breaking waves in the surf zone measured by Frouin, Schwindling and Deschamps. We installed a CIMEL sun photometer at Fort Jefferson on the Dry Tortugas off Key West in the Gulf of Mexico. The instrument has yielded a continuous stream of data since February. It shows that the aerosol optical thickness at 669 nm is often less than 0.1 in winter. This suggests that the Southern Gulf of Mexico will be an excellent winter site for vicarious calibration. In addition, we completed a study of the effect of vicarious calibration, i.e., the accuracy with which the radiance at the top of the atmosphere (TOA) can be predicted from measurement of the sky radiance at the bottom of the atmosphere (BOA). The results suggest that the neglect of polarization in the aerosol optical property inversion algorithm and in the prediction code for the TOA radiances is the largest error associated with the radiative transfer process. Overall, the study showed that the accuracy of the TOA radiance prediction is now limited by the racliometric calibration error in the sky radiometer. Finally, considerable coccolith light scattering data were obtained in the Gulf of Maine with a flow-through instrument, along with data relating to calcite concentration and the rate of calcite production.

Gordan, Howard R.↗
NASA NTRS1999

Review of Recent Results in Global MHD Modeling: ISTP Project Scientist for Theory and Ground-Based Observations

Global MHD (magnetohydrodynamic) simulations have shown a remarkable ability to describe the global dynamics of geospace. The limitations of the physical approximations underlying MHD would seem to limit the effectiveness of these codes, since kinetic and hybrid effects should manifest themselves by cross-scale coupling from microscales to mesoscales to global scales. However three effects appear to allow the codes to operate much more successfully than one would at first believe. They are:(l) the globally self-consistent nature of the codes with very well defined exterior boundary conditions (the solar wind) which allows the proper intercommunication between magnetospheric regions on MHD scales, (2) the control by global dynamics of the boundary layer locations where micro and meso scale processes operate, and (3) the critical role of numerical diffusion and with a sufficiently high resolution grid, the use of an empirical resistivity term, which if set at a level where the major magnetosphere boundaries properly calibrate against their observed locations, appear to well represent the effects of kinetic and hybrid processes on the global dynamics. The effectiveness of the global MHD codes, which have been developed under the ISTP mission, in describing Wind, Polar and Geotail observations, as well as ground-based observations are described. Particular emphasis is placed upon the Polar imaging data which when combined with ground-based data and global MHD-based synthetic aurora and convection patterns provide a powerful tool in understanding the final link in the solar-terrestrial chain: coupling into the atmosphere and ionosphere.

Curtis, Steven↗
NASA NTRS2001

Numerical Model of the Plasma Sheath Generated by the Plasma Source Instrument Aboard the Polar Satellite

The plasma sheath generated by the operation of the Plasma Source Instrument (PSI) aboard the Polar satellite is studied by using a three-dimensional particle-in-cell (PIC) code. When the satellite passes through the region of low-density plasma, the satellite charges to positive potentials as high as 40-50 V, owing to the photoelectron emission. In such a case, ambient core ions cannot accurately be measured or detected. The goal of the onboard PSI is to reduce the floating potential of the satellite to a sufficiently low value so that the ions in the polar wind become detectable. When the PSI is operated, ion-rich xenon plasma is ejected from the satellite, such that the floating potential of the satellite is reduced and is maintained at approximately 2 V. Accordingly, in our three-dimensional PIC simulation we considered that the potential of the satellite is 2 V as a fixed bias. Considering the relatively high density of the xenon plasma in the sheath (10-10(exp 3)/cc), the ambient plasma of low density (<1/cc) is neglected. In the simulations the electric fields and plasma dynamics are calculated self-consistently. We found that an 'apple'-shape positive potential sheath forms surrounding the satellite. In the region near the PSI emission a high positive potential hill develops. Near the Thermal Ion Dynamics Experiment detector away from the PSI, the potentials are sufficiently low for the ambient polar wind ions to reach it. In the simulations it takes only about a couple of tens of electron gyroperiods for the sheath to reach a quasi steady state. This time is approximately the time taken by the heavy Xe(+) ions to expand up to about one average Larmor radius of electrons from the satellite surface. After this time the expansion of the sheath in directions transverse to the ambient magnetic field slows down because the electrons are magnetized. Using the quasi steady sheath, we performed trajectory calculations to characterize the detector response to a highly supersonic polar wind flow. The detected ions' velocity distribution shows significant deviations from a shifted Maxwellian in the ambient polar wind population. The deviations are caused by the effects of electric fields on the ions' motion as they traverse the sheath.

Singh, N.↗
NASA NTRS2015

IPRT Polarized Radiative Transfer Model Intercomparison Project-Phase A

The polarization state of electromagnetic radiation scattered by atmospheric particles such as aerosols, cloud droplets, or ice crystals contains much more information about the optical and microphysical properties than the total intensity alone. For this reason an increasing number of polarimetric observations are performed from space, from the ground and from aircraft. Polarized radiative transfer models are required to interpret and analyse these measurements and to develop retrieval algorithms exploiting polarimetric observations. In the last years a large number of new codes have been developed, mostly for specific applications. Benchmark results are available for specific cases, but not for more sophisticated scenarios including polarized surface reflection and multi-layer atmospheres. The International Polarized Radiative Transfer (IPRT) working group of the International Radiation Commission (IRC) has initiated a model intercomparison project in order to fill this gap. This paper presents the results of the first phase A of the IPRT project which includes ten test cases, from simple setups with only one layer and Rayleigh scattering to rather sophisticated setups with a cloud embedded in a standard atmosphere above an ocean surface. All scenarios in the first phase A of the intercomparison project are for a one-dimensional plane-parallel model geometry. The commonly established benchmark results are available at the IPRT website

radiative transfer↗
NASA NTRS2006

Efficiency of a Grazing-incidence Off-plane Grating in the Soft-x-ray Region

Efficiency measurements of a grazing-incidence diffraction grating in the off-plane mount were performed using polarized synchrotron radiation. The grating had 5000 grooves/mm, an effective blaze angle of 14 deg., and was gold coated. The efficiencies in the two polarization orientations (TM and TE) were measured in the 1.5-5.O nm wavelength range and were compared with the efficiencies calculated using the PCGrate-SX code. The TM and TE efficiencies differ, offering the possibility of performing unique science studies of astrophysical, solar, and laboratory sources by exploiting the polarization sensitivity of the off-plane grating.

Seely, J. F.↗
DOE OSTI2024

Polarization–frequency hyperentangled photons: generation, characterization, and manipulation

Frequency-bin encoding is massively parallelizable and robust for optical fiber transmission. When coupled with an additional degree of freedom (DoF), the expansion of the Hilbert space allows for deterministic controlled operations between two DoFs within a single photon. Such capabilities, when combined with photonic hyperentanglement, are of great value for quantum communication protocols, including dense coding and single-copy entanglement distillation. In this talk, we present an all-fiber-coupled, ultrabroadband polarization–frequency hyperentangled source and conduct comprehensive quantum state tomography across multiple dense wavelength division multiplexing channels spanning the optical C+L-band (1530–1625 nm). In addition, we design and implement a high-fidelity controlled-NOT (cnot) operation between polarization and frequency DoFs by exploiting electro-optic phase modulation within a fiber Sagnac loop. Collectively, our hyperentangled source and two-qubit gate should unlock new opportunities for harnessing polarization–frequency resources in established telecommunication fiber networks for future quantum applications.

Lu, Hsuan-Hao↗
NASA NTRS1995

Semikinetic modeling and observations of high-latitude plasma outflow

In one fo the most exciting areas of progress, we have now developed a dynamic semikinetic model for examining the synergistic effects of waves and magnetospheric hot plasma populations on the outflowing ionospheric plasma. We have done this by imposing hot biMaxwellian ion and electron distributions at the top of our auroral simulation flux tube (4 R(sub e)), as well as a spectrum of waves with altitude which perpendicularly heats the ionospheric ions. We have also addressed the quasi-statistical properties of out flowing O(+) through bulk parameter analysis of DE-1/RIMS observations when DE-1 was in the midaltitude polar cap magnetosphere. A very exciting paper which was both submitted and appeared during this period in JGR concerned the centrifugal acceleration effect on the polar wind. During this year, we also developed the extension of our GSK code to include the lower ionosphere and associated processes. Finally, perhaps our most exciting project currently is a study of F-region upflows using a modification of the FLIP ionospheric fluid dynamics model of Richards and Torr to allow for the effects of soft electron precipitation ionization and convection-driven ion heating, and performed comparisons with satellite and radar data. A list of reference papers that have been published is listed.

Horwitz, James L.↗
NASA NTRSDate not supplied

Inertia of Ionospheric Conductance During Electron Precipitation Events in Pulsating Aurora and Polar Arcs

Using coupled SuperThermal Electron Transport (STET) and Super-thermal Proton Electron Atomic Hydrogen – tRansport in the Ionosphere and Thermosphere (SPEAH-RIT) codes, we demonstrate that temporal variability of ionospheric conductance is defined by several time scales: magnetospheric source time variations, starting time of electron precipitation, and termination of the corresponding source of magnetospheric origin. In this case, the time scales are defined by dissipation of energetic electrons and effective recombination processes. The results presented in this paper were applied in the regions of pulsating aurora and polar arcs, demonstrating the fact that ionospheric conductance requires some time to form and decay. These time delays constitute an effective “inertia” in the conductance calculation which is not accounted for in many global models which assume an instantaneous connection between precipitation and conductance. Ionospheric conductance inertia influences the temporal variation in ionospheric and magnetospheric electric fields, and as a result, impacts magnetospheric dynamics and ultimately reconfigures the electron precipitation.

Khazanov, George V↗
NASA NTRS2015

Aerosol Correction for Improving OMPS/LP Ozone Retrieval

The Ozone Mapping and Profiler Suite Limb Profiler (OMPS-LP) on board the Suomi National Polar-orbiting Partnership (SNPP) satellite was launched on Oct. 28, 2011. Limb profilers measures the radiance scattered from the Earth's atmospheric in limb viewing mode from 290 to 1000 nm and infer ozone profiles from tropopause to 60 km. The recently released OMPS-LP Version 2 data product contains the first publicly released ozone profiles retrievals, and these are now available for the entire OMPS mission, which extends from April, 2012. The Version 2 data product retrievals incorporate several important improvements to the algorithm. One of the primary changes is to turn off the aerosol retrieval module. The aerosol profiles retrieved inside the ozone code was not helping the ozone retrieval and was adding noise and other artifacts. Aerosols including polar stratospheric cloud (PSC) and polar mesospheric clouds (PMC) have a detectable effect on OMPS-LP data. Our results show that ignoring the aerosol contribution would produce an ozone density bias of up to 10 percent in the region of maximum aerosol extinction. Therefore, aerosol correction is needed to improve the quality of the retrieved ozone concentration profile. We provide Aerosol Scattering Index (ASI) for detecting aerosols-PMC-PSC, defined as ln(Im-Ic) normalized at 45km, where Im is the measured radiance and Ic is the calculated radiance assuming no aerosols. Since ASI varies with wavelengths, latitude and altitude, we can start by assuming no aerosol profiles in calculating the ASIs and then use the aerosol profile to see if it significantly reduces the residuals. We also discuss the effect of aerosol size distribution on the ozone profile retrieval process. Finally, we present an aerosol-PMC-PSC correction scheme.

OMPS/LP↗
NASA NTRS1982

Additional extensions to the NASCAP computer code, volume 2

Particular attention is given to comparison of the actural response of the SCATHA (Spacecraft Charging AT High Altitudes) P78-2 satellite with theoretical (NASCAP) predictions. Extensive comparisons for a variety of environmental conditions confirm the validity of the NASCAP model. A summary of the capabilities and range of validity of NASCAP is presented, with extensive reference to previously published applications. It is shown that NASCAP is capable of providing quantitatively accurate results when the object and environment are adequately represented and fall within the range of conditions for which NASCAP was intended. Three dimensional electric field affects play an important role in determining the potential of dielectric surfaces and electrically isolated conducting surfaces, particularly in the presence of artificially imposed high voltages. A theory for such phenomena is presented and applied to the active control experiments carried out in SCATHA, as well as other space and laboratory experiments. Finally, some preliminary work toward modeling large spacecraft in polar Earth orbit is presented. An initial physical model is presented including charge emission. A simple code based upon the model is described along with code test results.

Stannard, P. R.↗
NASA NTRS2016

Constraining the Movement of the Spiral Features and the Locations of Planetary Bodies Within the AB Aur System

We present a new analysis of multi-epoch, H-band, scattered light images of the AB Aur system. We use a Monte Carlo radiative transfer code to simultaneously model the systems spectral energy distribution (SED) and H-band polarized intensity (PI) imagery. We find that a disk-dominated model, as opposed to one that is envelope dominated, can plausibly reproduce AB Aurs SED and near-IR imagery. This is consistent with previous modeling attempts presented in the literature and supports the idea that at least a subset of AB Aurs spirals originate within the disk. In light of this, we also analyzed the movement of spiral structures in multi-epoch H-band total light and PI imagery of the disk. We detect no significant rotation or change in spatial location of the spiral structures in these data, which span a 5.8-year baseline. If such structures are caused by disk planet interactions, the lack of observed rotation constrains the location of the orbit of planetary perturbers to be 47 au.

AB Aur system↗
NASA NTRS1991

Physics of heavy ions (1989-1990)

The results from studies on polar wind ion heating due to kinetic ion beam instabilities and the effects of such ion heating on the outflow of O(+) in the polar wind are presented and discussed. First, the linear instabilities associated with an O(+) and H(+) polar wind plasma in the presence of O(+) and H(+) beams for a range of O(+)/H(+) beam densities, T(sub e)/T(sub i), and ion beam speeds were examined. Then, nonlinear heating of the polar wind ions was studied, using numerical simulations. The O(+) and H(+) polar wind ions were modeled by isotropic Maxwellian distributions, and the electrons, O(+) beams, and H(+) beams were modeled by drifting Maxwellian distributions. The effects of the kinetic ion heating on the outflow of the polar wind ions were examined from the ionosphere, using a time-dependent hydrodynamic model. A numerical code to solve the O(+) and H(+) continuity and momentum equations in a flux tube from ionospheric to magnetospheric altitudes were developed. The effects of ion heating were included by allowing for the altitudinal variation of the ion temperatures in the momentum equation. The ion temperature profiles were specified based on the ion heating characteristics found from previous kinetic simulations. It was assumed that heating occurred above 1500 km and increased to a saturated value of temperature that was obtained directly from the kinetic simulation study. The characteristics of the dynamical polar wind without ion heating were studied, and a flux tube on closed field lines that suddenly became open at t = 0 was simulated. Then, the effects of ion heating were included. To gain some physical insight, two limiting cases were considered: preferential H(+) heating and preferential O(+) heating. How O(+) heating can lead to enhanced polar wind O(+) fluxes in the polar magnetosphere is shown.

Ashour-Abdalla, M.↗
NASA NTRS1999

Engineering Overview of a Multidisciplinary HSCT Design Framework Using Medium-Fidelity Analysis Codes

An objective of the HPCC Program at NASA Langley has been to promote the use of advanced computing techniques to more rapidly solve the problem of multidisciplinary optimization of a supersonic transport configuration. As a result, a software system has been designed and is being implemented to integrate a set of existing discipline analysis codes, some of them CPU-intensive, into a distributed computational framework for the design of a High Speed Civil Transport (HSCT) configuration. The proposed paper will describe the engineering aspects of integrating these analysis codes and additional interface codes into an automated design system. The objective of the design problem is to optimize the aircraft weight for given mission conditions, range, and payload requirements, subject to aerodynamic, structural, and performance constraints. The design variables include both thicknesses of structural elements and geometric parameters that define the external aircraft shape. An optimization model has been adopted that uses the multidisciplinary analysis results and the derivatives of the solution with respect to the design variables to formulate a linearized model that provides input to the CONMIN optimization code, which outputs new values for the design variables. The analysis process begins by deriving the updated geometries and grids from the baseline geometries and grids using the new values for the design variables. This free-form deformation approach provides internal FEM (finite element method) grids that are consistent with aerodynamic surface grids. The next step involves using the derived FEM and section properties in a weights process to calculate detailed weights and the center of gravity location for specified flight conditions. The weights process computes the as-built weight, weight distribution, and weight sensitivities for given aircraft configurations at various mass cases. Currently, two mass cases are considered: cruise and gross take-off weight (GTOW). Weights information is obtained from correlations of data from three sources: 1) as-built initial structural and non-structural weights from an existing database, 2) theoretical FEM structural weights and sensitivities from Genesis, and 3) empirical as-built weight increments, non-structural weights, and weight sensitivities from FLOPS. For the aeroelastic analysis, a variable-fidelity aerodynamic analysis has been adopted. This approach uses infrequent CPU-intensive non-linear CFD to calculate a non-linear correction relative to a linear aero calculation for the same aerodynamic surface at an angle of attack that results in the same configuration lift. For efficiency, this nonlinear correction is applied after each subsequent linear aero solution during the iterations between the aerodynamic and structural analyses. Convergence is achieved when the vehicle shape being used for the aerodynamic calculations is consistent with the structural deformations caused by the aerodynamic loads. To make the structural analyses more efficient, a linearized structural deformation model has been adopted, in which a single stiffness matrix can be used to solve for the deformations under all the load conditions. Using the converged aerodynamic loads, a final set of structural analyses are performed to determine the stress distributions and the buckling conditions for constraint calculation. Performance constraints are obtained by running FLOPS using drag polars that are computed using results from non-linear corrections to the linear aero code plus several codes to provide drag increments due to skin friction, wave drag, and other miscellaneous drag contributions. The status of the integration effort will be presented in the proposed paper, and results will be provided that illustrate the degree of accuracy in the linearizations that have been employed.

Weston, R. P.↗