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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Surface reconstruction from scattered data through pruning of unstructured grids

This paper describes an algorithm for reconstructing a surface from a randomly digitized object. Scan data (treated as a cloud of points) is first tesselated out to its convex hull using Delaunay triangulation. The line-of-sight between each surface point and the scanning device is traversed, and any tetrahedra which are pierced by it are removed. The remaining tetrahedra form an approximate solid model of the scanned object. Due to the inherently limited resolution of any scan, this algorithm requires two additional procedures to produce a smooth, polyhedral surface: one process removes long, narrow tetrahedra which span indentations in the surface between digitized points; the other smooths sharp edges. The results for a moderately resolved sample body and a highly resolved aircraft are displayed.

Maksymiuk, C. M.↗
NASA NTRS1992

A gridless Euler/Navier-Stokes solution algorithm for complex two-dimensional applications

The development of a gridless computational fluid dynamics (CFD) method for the solution of the two-dimensional Euler and Navier-Stokes equations is described. The method uses only clouds of points and does not require that the points be connected to form a grid as is necessary in conventional CFD algorithms. The gridless CFD approach appears to resolve the problems and inefficiencies encountered with structured or unstructured grid methods. As a result, the method offers the greatest potential for accurately and efficiently solving viscous flows about complex aircraft configurations. The method is described in detail, and calculations are presented for standard Euler and Navier-Stokes cases to assess the accuracy and efficiency of the capability.

Batina, John T.↗
NASA NTRS1992

Vertical structure and size distributions of Martian aerosols from solar occultation measurements

Phobos 2 spectrometer measurements of solar occultations close to the evening terminator have furnished data on the vertical structure of the Martian aerosols near the northern spring equinox. Since the thermal structure derived from saturated IR profiles of water vapor does not allow the reaching of the CO2 frost point at cloud altitudes, said clouds' particles may be formed by H2O ice. Dust was also monitored at two wavelengths; it is assumed that the dust particles are levitated by eddy mixing. A parallel is drawn between these thin clouds and the polar mesospheric clouds observed on earth.

Chassefiere, E.↗
NASA NTRS1993

A gridless Euler/Navier-Stokes solution algorithm for complex-aircraft applications

The development of a gridless computational fluid dynamics (CFD) method for the solution of the two- and three-dimensional Euler and Navier-Stokes equations is described. The method uses only clouds of points and does not require that the points be connected to form a grid as is necessary in conventional CFD algorithms. The gridless CFD approach appears to resolve the inefficiencies encountered with structured or unstructured grid methods, and consequently offers great potential for accurately and efficiently solving viscous flows about complex aircraft configurations. The method is described in detail and calculations are presented for standard Euler and Navier-Stokes cases to assess the accuracy and efficiency of the capability.

Batina, John T.↗
NASA NTRS1993

A gridless Euler/Navier-Stokes solution algorithm for complex-aircraft applications

The development of a gridless computational fluid dynamics (CFD) method for the solution of the two- and three-dimensional Euler and Navier-Stokes equations is described. The method uses only clouds of points and does not require that the points be connected to form a grid as a necessary in conventional CFD algorithms. The gridless CFD approach appears to resolve the inefficiencies encountered with structured or unstructured grid methods, and consequently offers great potential for accurately and efficiently solving viscous flows about complex aircraft configurations. The method is described in detail and calculations are presented for standard Euler and Navier-Stokes cases to assess the accuracy and efficiency of the capability.

Batina, John T.↗
NASA NTRS2004

Lidar Data Products and Applications Enabled by Conical Scanning

Several new data products and applications for elastic backscatter lidar are achieved using simple conical scanning. Atmospheric boundary layer spatial and temporal structure is revealed with resolution not possible with static pointing lidars. Cloud fractional coverage as a function of altitude is possible with high temporal resolution. Wind profiles are retrieved from the cloud and aerosol structure motions revealed by scanning. New holographic technology will soon allow quasi-conical scanning and push-broom lidar imaging without mechanical scanning, high resolution, on the order of seconds.

Schwemmer, Geary K.↗
NASA NTRS2005

Probing the Reverse Shock in an Oxygen-Rich Supernovae Remnant

The purpose of this investigation is to examine the O VI emission from the X-ray bright ring of the supernova remnant 1 E0102.2-729 in the small Magellanic cloud. Three pointings were positioned tangent to the ring, north (N), northeast (NE), and southeast (SE), to examine a range of X-ray emitting regions overlapping a range of optical [O III] nebulosity and to examine the velocity structure. One background pointing was also obtained, but it was contaminated by a star. The background levels in the pointings on the remnant were low enough that the background pointing was not required for the remaining analysis. The SE pointing was reobserved in August, 2004, in order to bring the total exposure up to the originally requested 15 ks. The archive notified us of the data's availability in mid September. Significant broad O VI 1032 and O VI 1038 emission was found, brightest in the NE and SE pointings. In the NE and SE pointings, the FWHM of the broad O VI component is approx.800-1000 km/s, while in the N pointing, the line is approx.1500 km/s wide. The O VI is redshifted in the N (approx.380 km/s) and NE (approx.60 km/s) but is blueshifted in the SE (approx. -160 km/s). These FUSE O VI velocity dispersions can be compared to the X-ray gas velocities inferred from Doppler distortions in the Chandra X-ray data as reported by Flanagan et al. 2004 (ApJ 605, 230). The bulk velocities in the X-ray bright ring of order +/- 1000 km/s, comparable to the velocity dispersion seen in the FUSE data. However, the X-ray data indicates a redshift of approx.1000 km/s in the SE, while the FUSE data show a blueshift of approx.160 km/s, underscoring the complex velocity structure in this remnant. The O VI fluxes estimated from the fits to the FUSE data were combined with X-ray (XMM- Newton) O VI1 and O VIII fluxes and compared with predictions from a plasma nonequilibrium ionization model in a "line-based" analysis. We found that the plasma departs significantly from collisional ionization equilibrium, particularly in the SE, and that the plasma excitation conditions vary among the pointings: the O plasma sees different conditions than the Ne and Mg plasmas.

Gaetz, Terrance↗
NASA NTRS2012

Development of a Robust and Efficient Parallel Solver for Unsteady Turbomachinery Flows

The traditional design and analysis practice for advanced propulsion systems relies heavily on expensive full-scale prototype development and testing. Over the past decade, use of high-fidelity analysis and design tools such as CFD early in the product development cycle has been identified as one way to alleviate testing costs and to develop these devices better, faster and cheaper. In the design of advanced propulsion systems, CFD plays a major role in defining the required performance over the entire flight regime, as well as in testing the sensitivity of the design to the different modes of operation. Increased emphasis is being placed on developing and applying CFD models to simulate the flow field environments and performance of advanced propulsion systems. This necessitates the development of next generation computational tools which can be used effectively and reliably in a design environment. The turbomachinery simulation capability presented here is being developed in a computational tool called Loci-STREAM [1]. It integrates proven numerical methods for generalized grids and state-of-the-art physical models in a novel rule-based programming framework called Loci [2] which allows: (a) seamless integration of multidisciplinary physics in a unified manner, and (b) automatic handling of massively parallel computing. The objective is to be able to routinely simulate problems involving complex geometries requiring large unstructured grids and complex multidisciplinary physics. An immediate application of interest is simulation of unsteady flows in rocket turbopumps, particularly in cryogenic liquid rocket engines. The key components of the overall methodology presented in this paper are the following: (a) high fidelity unsteady simulation capability based on Detached Eddy Simulation (DES) in conjunction with second-order temporal discretization, (b) compliance with Geometric Conservation Law (GCL) in order to maintain conservative property on moving meshes for second-order time-stepping scheme, (c) a novel cloud-of-points interpolation method (based on a fast parallel kd-tree search algorithm) for interfaces between turbomachinery components in relative motion which is demonstrated to be highly scalable, and (d) demonstrated accuracy and parallel scalability on large grids (approx 250 million cells) in full turbomachinery geometries.

West, Jeff↗
NASA NTRS2013

Summary of Data from the Fifth AIAA CFD Drag Prediction Workshop

Results from the Fifth AIAA CFD Drag Prediction Workshop (DPW-V) are presented. As with past workshops, numerical calculations are performed using industry-relevant geometry, methodology, and test cases. This workshop focused on force/moment predictions for the NASA Common Research Model wing-body configuration, including a grid refinement study and an optional buffet study. The grid refinement study used a common grid sequence derived from a multiblock topology structured grid. Six levels of refinement were created resulting in grids ranging from 0.64x10(exp 6) to 138x10(exp 6) hexahedra - a much larger range than is typically seen. The grids were then transformed into structured overset and hexahedral, prismatic, tetrahedral, and hybrid unstructured formats all using the same basic cloud of points. This unique collection of grids was designed to isolate the effects of grid type and solution algorithm by using identical point distributions. This study showed reduced scatter and standard deviation from previous workshops. The second test case studied buffet onset at M=0.85 using the Medium grid (5.1x106 nodes) from the above described sequence. The prescribed alpha sweep used finely spaced intervals through the zone where wing separation was expected to begin. Some solutions exhibited a large side of body separation bubble that was not observed in the wind tunnel results. An optional third case used three sets of geometry, grids, and conditions from the Turbulence Model Resource website prepared by the Turbulence Model Benchmarking Working Group. These simple cases were intended to help identify potential differences in turbulence model implementation. Although a few outliers and issues affecting consistency were identified, the majority of participants produced consistent results.

Levy, David W.↗
NASA NTRS1983

Interpretation of spectral optical thickness observations of the El Chichon eruption cloud

It is pointed out that the recent El Chichon eruption has provided a unique opportunity to observe a short-term climate change event. In October 1982 and in May 1983 observation experiments were undertaken to determine the spectral optical thickness of the El Chichon eruption cloud during airborne latitudinal surveys. One of two basic objectives to the observation experiment was the conduction of direct measurements of the optical thickness for radiation and climate studies. In connection with the second objective, inferences of the physical characteristic of the volcanic cloud were to be obtained on the basis of an application of remote sensing techniques. The present paper is concerned with the second objective, taking into account questions regarding the feasibility to conduct a meaningful analysis of the variation of the aerosol size distribution with latitude on the basis of the accuracy of the measured data.

Spinhirne, J. D.↗
NASA NTRS1984

The formation of solar type stars - IRAS observations of the dark cloud Barnard 5

Observations of the dark cloud Barnard 5 show two compact sources of radiation within the dense core. IRS 1 is associated with 30-800 K dust, has a total luminosity of about 10 solar luminosities, and is presumably a newly formed star of roughly solar mass. IRS 2 has a much cooler color temperature, approximately 25 K, and emits only 1.3 solar luminosities. Its status is unclear, but IRS 2 may be at a very early stage of gravitational collapse or a density enhancement within the cloud heated by the interstellar radiation field. Also within the confines of the cloud are two point sources, which, if associated with the cloud, each emit about 0.5 solar luminosities in the IRAS bands. These may be T Tauri stars, separated from the cloud but still enshrouded in dust shells.

Beichman, C. A.↗
NASA NTRS1998

Evaluation of Clouds and the Earth's Radiant Energy System (CERES) Scanner Pointing Accuracy using a Coastline Detection System

Clouds and the Earth's Radiant Energy System (CERES) is a National Aeronautics and Space Administration (NASA) investigation to examine the role of clouds in the radiative energy flow through the Earth-atmosphere system. The first CERES scanning radiometer was launched on November 27, 1997 into a 35 inclination, 350 km altitude orbit, on the Tropical Rainfall Measuring Mission (TRMM) spacecraft. The CERES instrument consists of a three channel scanning broadband radiometer. The spectral bands measure shortwave (0.3 - 5 microns), window (8 - 12 microns), and total (0.3 - 100 microns) radiation reflected or emitted from the Earth-atmosphere system. Each Earth viewing measurement is geolocated to the Earth fixed coordinate system using satellite ephemeris, Earth rotation and geoid, and instrument pointing data. The interactive CERES coastline detection system is used to assess the accuracy of the CERES geolocation process. By analyzing radiative flux gradients at the boundaries of ocean and land masses, the accuracy of the scanner measurement locations may be derived for the CERES/TRMM instrument/satellite system. The resulting CERES measurement location errors are within 10% of the nadir footprint size. Precise pointing knowledge of the Visible and Infrared Scanner (VIRS) is required for convolution of cloud properties onto the CERES footprint; initial VIRS coastline results are included.

Currey, Chris↗
NASA NTRS1990

Automated cloud base height determination from high resolution Landsat data - A Hough transform approach

A direct method for determining the cloud base height derived from the displacement of the shadow from the cloud, and the solar azimuth and zenith angle is presented. Cumulus cloud scenes over land from Landsat MSS imagery are considered. The clouds are first matched with the corresponding shadows; the pixel distance of a reference point in the cloud is computed from the corresponding reference point in the shadow; and then the solar zenith angle is used to compute the cloud base height. Observations indicate that the cloud base height appears to be size-dependent with larger clouds generally associated with higher cloud bases and that clouds within the same size range and within the same scene region are approximately of the same height.

Sengupta, S. K.↗
NASA NTRS2023

Smc-Last Point Source Catalog Spitzer'S Last Survey of the Small Magellanic Cloud

We present a processing for the point source catalog derived from Spitzer's final two surveys of the Small Magellanic Cloud (SMC). These 2017-2018 maps duplicate the footprint from the SAGE-SMC program from 2008 and were obtained at 3.6 and 4.5 μm with the Infrared Array Camera (IRAC). They provide a nearly 10-year baseline of all observations of the SMC made by Spitzer. We extracted point sources from both the basic calibrated data (BCD) as well as the final processed mosaics. We did not use any prior catalogs as inputs in order to search for moving objects (e.g., foreground brown dwarfs) and other transient phenomena. The extractions from two test fields are shown here: a field sparsely populated with stars and a second containing more complicated structures. Comparing our extractions between both of our epochs and with the SAGE epochs shows the completeness and range of our survey. The mosaics are currently available on the Infrared Science Archive (IRSA) and the Harvard Dataverse. The final point source catalog will be available at both archives, as well. This work is supported by NASA Award 80NSSC19K0585.

Thomas Kuchar↗
NASA NTRS1990

Magnetic field structure of interplanetary magnetic clouds at 1 AU

Interplanetary magnetic clouds emerge as a feature of the solar wind at 1 AU, exhibiting enhanced field strength and lower plasma temperature and density than the surrounding plasma. A least-squares program has been developed which fits magnetic field data within a cloud, while estimating such cloud properties as its size, maximum field strength, and axis inclination. The results obtained from a study of 12 clouds observed at 1 AU point to a probable cloud axis direction within 15 deg of the ecliptic plane and about 100 deg from the sun's direction, when projected into the ecliptic plane. A wide variety of orientations is observed; some extend to 80 deg from the ecliptic.

Lepping, R. P.↗
NASA NTRS1978

Formation of a rotational accretion column

We consider the problem of the flow produced by the accretion of gas from a rotating cloud onto a point gravitational source. It is shown that, for a cloud initially in uniform rotation, the effect of accretion is to produce a Taylor column in the cloud parallel to the rotation axis. Only gas within the column is accreted; the gas outside the column undergoes oscillatory flow, which is probably subject to shear instability. The column forms in approximately one-half rotation period from the time at which accretion begins. Its initial radius is determined by the accretion rate and the angular velocity of the cloud. Application of the results to the formation of Jupiter by accretion is discussed.

Cassen, P.↗
NASA NTRS2010

Automated Detection of Clouds in Satellite Imagery

Many different approaches have been used to automatically detect clouds in satellite imagery. Most approaches are deterministic and provide a binary cloud - no cloud product used in a variety of applications. Some of these applications require the identification of cloudy pixels for cloud parameter retrieval, while others require only an ability to mask out clouds for the retrieval of surface or atmospheric parameters in the absence of clouds. A few approaches estimate a probability of the presence of a cloud at each point in an image. These probabilities allow a user to select cloud information based on the tolerance of the application to uncertainty in the estimate. Many automated cloud detection techniques develop sophisticated tests using a combination of visible and infrared channels to determine the presence of clouds in both day and night imagery. Visible channels are quite effective in detecting clouds during the day, as long as test thresholds properly account for variations in surface features and atmospheric scattering. Cloud detection at night is more challenging, since only courser resolution infrared measurements are available. A few schemes use just two infrared channels for day and night cloud detection. The most influential factor in the success of a particular technique is the determination of the thresholds for each cloud test. The techniques which perform the best usually have thresholds that are varied based on the geographic region, time of year, time of day and solar angle.

Jedlovec, Gary↗
NASA NTRS1978

Sampling analysis for the Earth Radiation Budget Satellite System mission based on orbital coverage and cloud variability

It is pointed out that accurate computation of the earth's radiation budget from satellite measurements requires spatial and temporal sampling which accounts for variations in cloud and surface conditions. It is in this connection important that cloud radiative properties and areal cloud cover be accurately determined for the desired time period. The reported investigation represents an extension of a study by Harrison et al. (1976). The time and space coverage capabilities of various sampling schemes are analyzed for the proposed Earth Radiation Budget Satellite System. The effects of cloud cover variability on the measured monthly mean reflected shortwave (0.2-5.0 micrometers) irradiance are also analyzed for several spatial scales.

Harrison, E. F.↗