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At least 217 records · Page 12

All sources NASA NTRS DOE OSTI

DOE OSTI2013

COLLIDING DECIMETER DUST

Collisional evolution is a key process in planetesimal formation and decimeter bodies play a key role in the different models. However, the outcome of collisions between two dusty decimeter bodies has never been studied experimentally. Therefore, we carried out microgravity collision experiments in the Bremen drop tower. The agglomerates consist of quartz with irregularly shaped micrometer-sized grains and the mean volume filling factor is 0.437 {+-} 0.004. The aggregates are cylindrical with 12 cm in height and 12 cm in diameter, and typical masses are 1.5 kg. These are the largest and most massive dust aggregates studied in collisions to date. We observed rebound and fragmentation but no sticking in the velocity range between 0.8 and 25.7 cm s{sup -1}. The critical fragmentation velocity for split up of an aggregate is 16.2 {+-} 0.4 cm s{sup -1}. At lower velocities the aggregates bounce off each other. In this velocity range, the coefficient of restitution decreases with increasing collision velocity from 0.8 to 0.3. While the aggregates are very weak, the critical specific kinetic energy for fragmentation Q{sub {mu}=1} is a factor of six larger than expected. Collisions of large bodies in protoplanetary disks are supposed to be much faster and the generation of smaller fragments is likely. In planetary rings, collision velocities are of the order of a few cm s{sup -1} and are thereby in the same range investigated in these experiments. The coefficient of restitution of dust agglomerates and regolith-covered ice particles, which are common in planetary rings, are similar.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRSDate not supplied

Progress on the Development of a Step Height Sensor for the BOLT Flight Vehicle

This presentation will summarize progress on the development of a step height sensor for the BOLT flight vehicle. Two methods have been proposed to measure the step size in this effort.The first method involves the application of miniaturized camera embedded in the flight vehicle that views the step through a rearward-facing port (shown in Fig. 1a inset). The second method involves the application of a linear fiber optic array bundle to measure the intensity of light reflected back from the aft body step (concept shown in Fig. 1b). Preliminary testing with the miniaturized camera has been performed in the lab and shows that displacements of ≤10 μm can be measured using this method. Final testing with both methods will be performed on the test stand shown in Fig. 1a. This test stand will include a fine adjustment vertical translation stage that will be used to adjust the step height in steps of 1-2 μm. A high-magnification imaging system will also be used to verify the step height. The miniaturized camera and linear fiber optic array bundle will be mounted in one of several port holes with varying degrees of inclination relative to the top surface in the opposing aft-section slab. BOLT flight vehicle details and information on the steps can be found in Ref. [1].

BOLT↗

NASA NTRS2020

Evolution of an Atmospheric Kármán Vortex Street From High‐Resolution Satellite Winds: Guadalupe Island Case Study

Vortex streets formed in the stratocumulus‐capped wake of mountainous islands are the atmospheric analogues of the classic Kármán vortex street observed in laboratory ﬂows past bluff bodies. The quantitative analysis of these mesoscale unsteady atmospheric ﬂows has been hampered by the lack of satellite wind retrievals of sufﬁciently high spatial and temporal resolution. Taking advantage of the cutting‐edge Advanced Baseline Imager, we derived kilometer‐scale cloud‐motion winds at 5‐min frequency for a vortex street in the lee of Guadalupe Island imaged by Geostationary Operational Environmental Satellite‐16. Combined with Moderate Resolution Imaging Spectroradiometer data, the geostationary imagery also provided accurate stereo cloud‐top heights. The time series of geostationary winds, supplemented with snapshots of ocean surface winds from the Advanced Scatterometer, allowed us to capture the wake oscillations and measure vortex shedding dynamics. The retrievals revealed a markedly asymmetric vortex decay, with cyclonic eddies having larger peak vorticities than anticyclonic eddies at the same downstream location. Drawing on the vast knowledge accumulated about laboratory bluff body ﬂows, we argue that the asymmetric island wake arises from the combined effects of Earth's rotation and Guadalupe's nonaxisymmetric shape resembling an inclined ﬂat plate at low angle of attack. However, numerical simulations will need to establish whether or not the selective destabilization of the shallow atmospheric anticyclonic eddies is caused by the same mechanisms that destabilize the deep columnar anticyclones of laboratory ﬂows, such as three‐dimensional vertical perturbations due to centrifugal or elliptical instabilities.

Horváth, Á.↗

NASA NTRS1982

Study of VTOL in ground-effect flow field including temperature effect

Detailed pressure, temperature, and velocity data were obtained for twin-fan configurations in-ground-effect and flow models to aid in predicting pressures and upwash forces on aircraft surfaces were developed. For the basic experiments, 49.5 mm-diameter jets were used, oriented normal to a simulated round plane, with pressurized, heated air providing a jet. The experimental data consisted of: (1) the effect of jet height and temperature on the ground, model, and upwash pressures, and temperatures, (2) the effect of simulated aircraft surfaces on the isolated flow field, (3) the jet-induced forces on a three-dimensional body with various strakes, (4) the effects of non-uniform coannular jets. For the uniform circular jets, temperature was varied from room temperature (24 C) to 232 C. Jet total pressure was varied between 9,300 Pascals and 31,500 Pascals. For the coannular jets, intended to represent turbofan engines, fan temperature was maintained at room temperature while core temperature was varied from room temperature to 437 C. Results are presented.

Hill, W. G.↗

DOE OSTI2014

SU-E-T-260: Pediatric Total Body Irradiation Calculations and In-Vivo Dosimetry Using Diodes and OSLD's

Purpose: To verify that a photon total body irradiation (TBI) calculation method scales properly from adult to pediatric dimensions and to determine TBI in-vivo dosimetry correction factors for diodes and optically stimulated luminescent dosimeters (OSLD's). Methods: TBI technique used is 400 SAD 18 MV opposed laterals with beam spoiler. Water bags are used to supplement narrower lateral dimensions for patient treatments. To verify that dose calculations scale properly with decreasing dimensions, CAX doses were measured and compared to calculations for different rectangular phantom geometries: (L=length(cm), H=height(cm), d=depth(cm)): L(30)xH(30) (d=3-25), L(30)xH(12)(d=2–20), L(13)xH(13) (d=5–13), L(30)x(H=10–40) d=15, L(30–150) x H(10) (d=15). In infant geometry, measured off axis “leg” dose (L(30)xH(2.5–10.6), d=7)) was compared to CAX (“body” L(30)xH(10)(d=7) adjacent to “leg”). Entrance and exit doses were measured with surface diodes, diodes with buildup, OSLD's, as well as ion chambers for comparison. Correction factors ((ion chamber CAX dose)/(in vivo dose)) were calculated for surface diodes, diodes with buildup, OSLD's, and ion chamber. Results: All rectangular phantom measurements agree with calculated within 2.5%. For L(30)xH(30), L(30)xH(12), L(13)xH(13), L(30)x(H=10–40) and L(30–80)xH(10) agreement was within 1%. For the infant geometry, the ratio of leg dose to CAX varies from 0.956 (h=2.5) to 0.995 (h=10.6). The range of in-vivo dosimetry entrance+exit to CAX dose correction factors varied by dosimeter (diode: 0.883–1.015, surface diode: 1.008–1.214, ion chamber: 0.924–1.084, OSLD: 0.920–1.106). Conclusion: TBI calculations scaled properly to pediatric dimensions. In-vivo dosimetry with various detectors demonstrated similar trends with different magnitudes. OSLD measurements agreed well with ion chamber measurements.

60 APPLIED LIFE SCIENCES↗

NASA NTRS1976

Ballistic range experiments on superbooms generated by refraction

The enhanced sonic boom or supersonic boom generated as a result of atmospheric refraction in threshold Mach number flights was recreated in a ballistic range by firing projectiles at low supersonic speeds into a stratified medium obtained by slowly injecting carbon dioxide into air. The range was equipped with a fast-response dynamic pressure transducer and schlieren photographic equipment, and the sound speed variation with height was controlled by regulating the flow rate of the CO2. The schlieren observations of the resulting flow field indicate that the generated shocks are reflected near the sonic cutoff altitude where local sound speed equals body speed, provided such an altitude exists. Maximum shock strength occurs very nearly at the point where the incident and reflected shocks join, indicating that the presence of the reflected shock may have an appreciable effect on the magnitude of the focus factor. The largest focus factor detected was 1.7 and leads to an estimate that the constant in the Guiraud-Thery scaling law should have a value of 1.30.

Sanai, M.↗

NASA NTRS2011

Standardization of a Volumetric Displacement Measurement for Two-Body Abrasion Scratch Test Data Analysis

A limitation has been identified in the existing test standards used for making controlled, two-body abrasion scratch measurements based solely on the width of the resultant score on the surface of the material. A new, more robust method is proposed for analyzing a surface scratch that takes into account the full three-dimensional profile of the displaced material. To accomplish this, a set of four volume- displacement metrics was systematically defined by normalizing the overall surface profile to denote statistically the area of relevance, termed the Zone of Interaction. From this baseline, depth of the trough and height of the plowed material are factored into the overall deformation assessment. Proof-of-concept data were collected and analyzed to demonstrate the performance of this proposed methodology. This technique takes advantage of advanced imaging capabilities that allow resolution of the scratched surface to be quantified in greater detail than was previously achievable. When reviewing existing data analysis techniques for conducting two-body abrasive scratch tests, it was found that the ASTM International Standard G 171 specified a generic metric based only on visually determined scratch width as a way to compare abraded materials. A limitation to this method was identified in that the scratch width is based on optical surface measurements, manually defined by approximating the boundaries, but does not consider the three-dimensional volume of material that was displaced. With large, potentially irregular deformations occurring on softer materials, it becomes unclear where to systematically determine the scratch width. Specifically, surface scratches on different samples may look the same from a top view, resulting in an identical scratch width measurement, but may vary in actual penetration depth and/or plowing deformation. Therefore, two different scratch profiles would be measured as having identical abrasion properties, although they differ significantly.

Street, K. W. Jr.↗

NASA NTRS2011

The Dawn Topography Investigation

The objective of the Dawn topography investigation is to derive the detailed shapes of 4 Vesta and 1 Ceres in order to create orthorectified image mosaics for geologic interpretation, as well as to study the asteroids' landforms, interior structure, and the processes that have modified their surfaces over geologic time. In this paper we describe our approaches for producing shape models, plans for acquiring the needed image data for Vesta, and the results of a numerical simulation of the Vesta mapping campaign that quantify the expected accuracy of our results. Multi-angle images obtained by Dawn's framing camera will be used to create topographic models with 100 m/pixel horizontal resolution and 10 m height accuracy at Vesta, and 200 m/pixel horizontal resolution and 20 m height accuracy at Ceres. Two different techniques, stereophotogrammetry and stereophotoclinometry, are employed to model the shape; these models will be merged with the asteroidal gravity fields obtained by Dawn to produce geodetically controlled topographic models for each body. The resulting digital topography models, together with the gravity data, will reveal the tectonic, volcanic and impact history of Vesta, and enable co-registration of data sets to determine Vesta's geologic history. At Ceres, the topography will likely reveal much about processes of surface modification as well as the internal structure and evolution of this dwarf planet.

dawn↗

DOE OSTI2022

Laser-driven ionization mechanisms of aluminum for single particle aerosol mass spectrometry

Single particle aerosol mass spectrometry (SPAMS), an analytical technique for measuring the size and composition of individual micron-scale particles, is capable of analyzing atmospheric pollutants and bioaerosols much more efficiently and with more detail than conventional methods which require the collection of particles onto filters for analysis in the laboratory. Despite SPAMS’ demonstrated capabilities, the primary mechanisms of ionization are not fully understood, which creates challenges in optimizing and interpreting SPAMS signals. In this paper, we present a well-stirred reactor model for the reactions involved with the laser-induced vaporization and ionization of an individual particle. The SPAMS conditions modeled in this paper include a 248 nm laser which is pulsed for 8 ns to vaporize and ionize each particle in vacuum. The ionization of 1 μm, spherical Al particles was studied by approximating them with a 0-dimensional plasma chemistry model. The primary mechanism of absorption of the 248 nm photons was pressure-broadened direct photoexcitation to Al(y 2 D). Atoms in this highly excited state then undergo superelastic collisions with electrons, heating the electrons and populating the lower energy excited states. We found that the primary ionization mechanism is electron impact ionization of various excited state Al atoms, especially Al(y 2 D). Because the gas expands rapidly into vacuum, its temperature decreases rapidly. The rate of three-body recombination (e - + e - + Al + → Al + e - ) increases at low temperature, and most of the electrons and ions produced recombine within several μs of the laser pulse. The importance of the direct photoexcitation indicates that the relative peak heights of different elements in SPAMS mass spectra may be sensitive to the available photoexcitation transitions. We also discuss the effects of laser intensity, particle diameter, and expansion dynamics.

47 OTHER INSTRUMENTATION↗

NASA NTRS1982

The geology of Io

A preliminary geologic map of 34.8 percent of the surface of Io has been compiled using best-resolution Voyager 1 images. Nine volcanic units are identified, including materials of mountains, plains, flows, cones, and crater vents, in addition to six types of structural features. Photogeologic evidence indicates a dominantly silicate composition for the mountain material. Sulfur flows of diverse viscosity and sulfur-silicate mixtures may compose the extensive plans. Pit-crater and shield-crater vent-wall scarps reach heights of over two km, and layered-plains boundary scarps have estimated heights of 150 to 1700 m, indicating a material with considerable strength. A cumulative size-frequency distribution plot for 170 volcanic craters with diameters over 14 km is similar to the curves for impact craters on other bodies in the solar system, attesting to a similar nonrandom distribution of crater diameters and a surplus of small craters. A total of 151 lineaments and grabens forming two nearly orthogonal sets is recognized.

Schaber, G. G.↗

NASA NTRS1988

Computational and theoretical analysis of free surface flow in a thin liquid film under zero and normal gravity

The results of a numerical computation and theoretical analysis are presented for the flow of a thin liquid film in the presence and absence of a gravitational body force. Five different flow systems were used. Also presented are the governing equations and boundary conditions for the situation of a thin liquid emanating from a pressure vessel; traveling along a horizontal plate with a constant initial height and uniform initial velocity; and traveling radially along a horizontal disk with a constant initial height and uniform initial velocity.

Faghri, Amir↗

DOE OSTI2025

Collaborative Proposal: Improving understanding of the internal structure and dynamics of deep convection using ARM observations and large eddy simulations

Recent observational and large eddy simulation (LES) modeling studies have nearly unanimously supported the view of deep cumulus convection being composed of a series of quasi-spherical bubbles of buoyant air, known as moist thermals. Despite the prevalence of moist thermals in deep convection, a comprehensive theory for the dynamics of these structures is lacking. Most current conceptual models for cumulus convection are based on canonical scaling theories for dry thermals or plumes; however, there is considerable evidence that the behavior of moist thermals differs markedly from these theories. Furthermore, the theoretical basis for most cumulus parameterizations originates from the plume conceptual model, and therefore these parameterizations are inconsistent with the real structure of moist convection. Motivated by the aforementioned knowledge gaps, this “end-to-end” research effort use theory, observations, numerical simulations, and direct improvements to the Zhang-McFarlane (ZM) convection scheme in the global climate Community Atmosphere Model (CAM) to address the following research questions: What key environmental parameters determine whether or not shallow convection will transition into deep convection, in the context of thermal-like updrafts? What factors regulate the size of thermals within cumulus updrafts? How does vertical wind shear influence thermal behavior, and as a consequence, vertical velocity and mass flux profiles and the shallow-to-deep convective transition? What are the critical processes that determine updraft vertical velocities and their connection to the vertical mass flux profile for thermal-like updrafts? Idealized LES modeling will be used in conjunction with theoretical models for the core properties of thermal-like updrafts to better understand key processes that regulate thermal ascent rates and entrainment properties. Thermal-tracking procedures will be used to characterize the behavior of thermals within the LES, and recently developed direct measures of entrainment and detrainment will be used to quantify entrainment/detrainment rates. Building from these results, we will analyze the structure of moist thermals from hemispheric range-height indicator scans taken during the Atmospheric Radiation Measurement Cloud, Aerosol, and Complex Terrain Interactions (CACTI) field campaign, and from “real case” LES of CACTI events. This combined modeling and observational analysis will provide essential validation for the existing body of research on moist thermal dynamics, which is based primarily on modeling studies. With the insight gained from the aforementioned activities, we will modify the Zhang-McFarlane convection scheme to improve its representation of updraft vertical velocity and entrainment rate profiles. These process-level changes will be tested in the Community Atmosphere Model to assess the impact on global climate simulations.

54 ENVIRONMENTAL SCIENCES↗

NASA NTRS1991

Arecibo S-band radar program

The high powered 12.6 cm wavelength radar on the 1000 ft Arecibo reflector is used for a variety of studies of solar system bodies. These include: (1) the radar mapping of the surfaces of Mercury, Venus, the moon and Mars in both senses (usually the two circulars) of received polarization; (2) high time resolution ranging measurements to Mercury and Mars to obtain height profiles and scattering parameters in the equatorial region and to test relativistic and gravitational theories; (3) measurements of the orbital parameters, scattering properties, figure and spin vectors of asteroids and comets; and (4) observations of the satellites of Mars, Phobos and Deimos, and the Galilean satellites of Jupiter.

Campbell, Donald B.↗

NASA NTRS1993

Transition aerodynamics for 20-percent-scale VTOL unmanned aerial vehicle

An investigation was conducted in the Langley 14- by 22-Foot Subsonic Tunnel to establish a transition data base for an unmanned aerial vehicle utilizing a powered-lift ejector system and to evaluate alterations to the ejector system for improved vehicle performance. The model used in this investigation was a 20-percent-scale, blended-body, arrow-wing configuration with integrated twin rectangular ejectors. The test was conducted from hover through transition conditions with variations in angle of attack, angle of sideslip, free-stream dynamic pressure, nozzle pressure ratio, and model ground height. Force and moment data along with extensive surface pressure data were obtained. A laser velocimeter technique for measuring inlet flow velocities was demonstrated at a single flow condition, and also a low order panel method was successfully used to numerically simulate the ejector inlet flow.

Kjerstad, Kevin J.↗

NASA NTRS2004

An Algorithm for Converting Static Earth Sensor Measurements into Earth Observation Vectors

An algorithm has been developed that converts penetration angles reported by Static Earth Sensors (SESs) into Earth observation vectors. This algorithm allows compensation for variation in the horizon height including that caused by Earth oblateness. It also allows pitch and roll to be computed using any number (greater than 1) of simultaneous sensor penetration angles simplifying processing during periods of Sun and Moon interference. The algorithm computes body frame unit vectors through each SES cluster. It also computes GCI vectors from the spacecraft to the position on the Earth's limb where each cluster detects the Earth's limb. These body frame vectors are used as sensor observation vectors and the GCI vectors are used as reference vectors in an attitude solution. The attitude, with the unobservable yaw discarded, is iteratively refined to provide the Earth observation vector solution.

Harman, R.↗

NASA NTRSDate not supplied

Toward Adaptive Mixed-Element Unstructured Grids for Simulations of Viscous Flows

Accurate prediction of surface skin friction and heat transfer for viscous flow applications using computational fluid dynamics tools necessitates thin wall-normal elements in the boundary layer. A tetrahedral adaptation process is extended to incorporate the advancing front local reconnection procedure. Thin boundary-layer grids are adapted from the solution, which governs the boundary-layer grid parameters such as first cell height off the wall. The process enables grid-converged steady-state results from a CAD file. Results are presented across the speed range from low subsonic flow over an airfoil to high-speed flows over blunt bodies and a rocket.

CFD↗

NASA NTRSDate not supplied

Toward Adaptive Mixed-Element Unstructured Grids for Simulations of Viscous Flows

chemically reacting flow↗

DOE OSTI2019

A LiDAR–optical data fusion approach for identifying and measuring small stream impoundments and dams

This article outlines a semi-autonomous approach for using a fusion of light detection and ranging (LiDAR) and optical remote sensing data to identify and measure small impoundments (SIs) and their dams. Quantifying such water bodies as hydrologic network features is critical for ecosystem and species conservation, emergency management, and water resource planning; however, such features are incompletely mapped at national and state levels. By merging an airborne LiDAR-derived point cloud with a normalized water index using airborne optical imagery we demonstrate an improvement upon single-source methods for identifying these water bodies; classification accuracies increased over 10% by using this multi-source fusion method. Furthermore, the method presented here illustrates a cost-effective pathway to improve the National Inventory of Dams (NID) and includes a framework for estimating dam heights, with results showing strong correlations between derived dam heights and those recorded in the NID (r=.78). With the steady increase in available LiDAR coverage, the 87,000+ dams in the NID could be updated using this technique, a method which could also be expanded for global inventories of SIs and dams.

47 OTHER INSTRUMENTATION↗