SEARCH · Engineering Papers

Results for “active layer”

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 1,081 records · Page 60

All sources NASA NTRS DOE OSTI

NASA NTRS1981

A life history method for estimating convective rainfall

The remote sensing of rain amounts is of great interest for a great variety of operational applications, including hydrology, hydroelectricity and agriculture is discussed. The microwave radiometer represents the most obvious technique, however, poor spatial and temporal resolution, together with the problems associated with the estimation of effective rain layer height make visible and IR techniques more promising at the present time. Based on bivariate frequency distribution of brightness versus temperature, brightness enhancing or infrared technique alone may be inadequate to deduce details of convective activity. It is implied that better estimates of rainfall will come from visible and IR observations combined than from either used alone. The technique identifies clouds with high probability of rain as those which have large optical and presumably physical thickness as measured by the visible albedo in comparison with their height, determined by the intensity of the IR emission.

Martin, D. W.↗

NASA NTRS1992

Space Shuttle hypersonic flight research and the comparison to ground test results

Aerodynamic and aerothermodynamic comparisons between flight and ground test for the Space Shuttle at hypersonic speeds are discussed. All of the comparisons are taken from papers published by researchers active in the Space Shuttle program. The aerodynamic comparisons include stability and control derivatives, center-of-pressure location, and reaction control jet interaction. Comparisons are also discussed for various forms of heating including catalytic, boundary layer, top centerline, side fuselage, OMS pod, wing leading edge, and shock interaction. The jet interaction and center-of-pressure location flight values exceeded not only the predictions but the uncertainties of the predictions. Predictions were significantly exceeded for the heating caused by the vortex impingement on the OMS pods and for heating caused by the wing leading-edge shock interaction.

Iliff, Kenneth W.↗

NASA NTRS1993

Space Shuttle hypersonic aerodynamic and aerothermodynamic flight research and the comparison to ground test results

Aerodynamic and aerothermodynamic comparisons between flight and ground test for the Space Shuttle at hypersonic speeds are discussed. All of the comparisons are taken from papers published by researchers active in the Space Shuttle program. The aerodynamic comparisons include stability and control derivatives, center-of-pressure location, and reaction control jet interaction. Comparisons are also discussed for various forms of heating, including catalytic, boundary layer, top centerline, side fuselage, OMS pod, wing leading edge, and shock interaction. The jet interaction and center-of-pressure location flight values exceeded not only the predictions but also the uncertainties of the predictions. Predictions were significantly exceeded for the heating caused by the vortex impingement on the OMS pods and for heating caused by the wing leading-edge shock interaction.

Iliff, Kenneth W.↗

NASA NTRS1996

Helioseismic Constraints on the Gradient of Angular Velocity at the Base of the Solar Convection Zone

The layer of transition from the nearly rigid rotation of the radiative interior to the latitudinal differential rotation of the convection zone plays a significant role in the internal dynamics of the Sun. Using rotational splitting coefficients of the p-mode frequencies, obtained during 1986-1990 at the Big Bear Solar Observatory, we have found that the thickness of the transitional layer is 0.09 +/- 0.04 solar radii (63 +/- 28 Mm), and that most of the transition occurs beneath the adiabatically stratified part of the convection zone, as suggested by the dynamo theories of the 22 yr solar activity cycle.

Kosovichev, A. G.↗

NASA NTRS2009

Resilient Flexible Pressure-Activated Seal

A resilient, flexible, pressure-activated, high-temperature seal is adapted to be interposed between high and low pressure regions to provide sealing between opposing surfaces of adjacent relatively movable structures. The seal comprises at least one C-shaped sheet element. The C-shaped element design enables the seal to be pressure-activated to provide a radially outward biasing force, responsive to a seal-activating pressure differential acting across the seal thereby increasing resiliency. A centrally-located, resilient core structure provides load bearing and insulating properties. In an exemplary embodiment where at least two seal elements are used, each layer has a cutout slot pattern and the remaining strip material pattern. The slots provide flexibility to the seal, enabling the seal to be manually contoured to seal around corners and curves. The strip material of each layer covers the slots in each adjacent layer to minimize leakage through the slots. Attached barrier strips can block interface leakage between the seal and the opposing surfaces.

Steinetz, Bruce M.↗

NASA NTRS2004

NASA Tech Briefs, July 2004

Topics: Optoelectronic Sensor System for Guidance in Docking; Hybrid Piezoelectric/Fiber-Optic Sensor Sheets; Multisensor Arrays for Greater Reliability and Accuracy; Integrated-Optic Oxygen Sensors; Ka-Band Autonomous Formation Flying Sensor; CMOS VLSI Active-Pixel Sensor for Tracking; Lightweight, Self-Deploying Foam Antenna Structures; Electrically Small Microstrip Quarter-Wave Monopole Antennas; A 2-to-28-MHz Phase-Locked Loop; Portable Electromyograph; Open-Source Software for Modeling of Nanoelectronic Devices; Software for Generating Strip Maps from SAR Data; Calibration Software for use with Jurassicprok; Software for Probabilistic Risk Reduction; Software Processes SAR Motion-Measurement Data; Improved Method of Purifying Carbon Nanotubes; Patterned Growth of Carbon Nanotubes or Nanofibers; Lightweight, Rack-Mountable Composite Cold Plate/Shelves; SiC-Based Miniature High-Temperature Cantilever Anemometer; Inlet Housing for a Partial-Admission Turbine; Lightweight Thermoformed Structural Components and Optics; Growing High-Quality InAs Quantum Dots for Infrared Lasers; Selected Papers on Protoplanetary Disks; Module for Oxygenating Water without Generating Bubbles; Coastal Research Imaging Spectrometer; Rapid Switching and Modulation by use of Coupled VCSELs; Laser-Induced-Fluorescence Photogrammetry and Videogrammetry; Laboratory Apparatus Generates Dual-Species Cold Atomic Beam; Laser Ablation of Materials for Propulsion of Spacecraft; Small Active Radiation Monitor; Hybrid Image-Plane/Stereo Manipulation; Partitioning a Gridded Rectangle into Smaller Rectangles; Digital Radar-Signal Processors Implemented in FPGAs; Part 1 of a Computational Study of a Drop-Laden Mixing Layer; and Some Improvements in Signal-Conditioning Circuits.

Source record↗

NASA NTRS2012

Mechanical Stress and Antioxidant Protection in the Retina of Hindlimb Suspended Rats

It has been postulated that hindlimb suspension (HS) causes a cephalad fluid shift in quadrupeds similar to that occurring to humans in microgravity. Therefore, HS may provide a suitable animal model in which to recapitulate the ocular changes observed in the human Visual Impairment and Intracranial Pressure (VIIP) syndrome. This work reports preliminary results from a tissue sharing project using 34 week-old Brown Norway rats. Two different experiments compared normal posture controls and HS rats for 2 weeks and rats exposed to HS for 2 weeks but allowed to recover in normal posture for 2 additional weeks. The effects of two nutritional countermeasures, green tea extract (GT) and plant polyphenol resveratrol (Rv), were also evaluated. Green tea contains the antioxidant epigallocatechin gallate (EGCG). qPCR gene expression analysis of selected targets was performed on RNA from isolated retinas, and histologic analysis was done on one fixed eye per rat. The transcription factor early growth response protein 1 (Egr1) was upregulated almost 2-fold in HS retinas relative to controls (P = 0.059), and its expression returned to control levels after 2 weeks of recovery in normal posture (P = 0.023). HS-induced upregulation of Egr1 was attenuated (but not significantly) in retinas from rats fed an antioxidant rich (GT extract) diet. In rats fed the GT-enriched diet, antioxidant enzymes were induced, evidenced by the upregulation of the gene heme oxygenase 1 (Hmox1) (P = 0.042) and the gene superoxide dismutase 2 (Sod2) (P = 0.0001). Egr1 is a stretch-activated transcription factor, and the Egr1 mechanosensitive response to HS may have been caused by a change in the translaminal pressure and/or mechanical deformation of the eye globe. The observed histologic measurements of the various retinal layers in the HS rats were lower in value than those of the control animal (n = 1), however insufficient data were available for statistical analysis. Aquaporin 4, a water-selective channel involved in interstitial fluid homeostasis, showed an upregulated trend in HS retinas; however, these results are preliminary. Total retinal thickness increased significantly (P = 0.049) in HS rats fed a resveratrol enriched diet compared to HS rats on a normal diet. This change appeared to be reversed during the 2 weeks of recovery post HS, but no differences in retina thickness were observed between HS animals and HS recovered animals when both groups consumed a normal diet. The reversibility of the increase in retinal thickness induced by resveratrol during HS may therefore reflect an interaction between the stress provoked by HS and the cytoprotective mechanisms elicited by resveratrol

Glass, Aziza↗

NASA NTRS2016

Thermophysics Issues Relevant to High-Speed Earth Entry of Large Asteroids

Physics of atmospheric entry of meteoroids was an active area of research at NASA ARC up to the early 1970s (e.g., the oft-cited work of Baldwin and Sheaffer). However, research in the area seems to have ended with the Apollo program, and any ties with an active international meteor physics community seem to have significantly diminished thereafter. In the decades following the 1970s, the focus of entry physics at NASA ARC has been on improvement of the math models of shock-layer physics (especially in chemical kinetics and radiation) and thermal response of ablative materials used for capsule heatshields. With the overarching objectives of understanding energy deposition into the atmosphere and fragmentation, could these modern analysis tools and processes be applied to the problem of atmospheric entry of meteoroids as well? In the presentation we will explore: (i) the physics of atmospheric entries of meteoroids using our current state-of-the-art tools and processes, (ii) how multiple bodies interact, and (iii) the influence of wall blowing on flow dynamics.

Atmospheric Entry↗

NASA NTRS2015

Meteor Entry and Breakup Based on Evolution of NASAs Entry Capsule Design Tools

Physics of atmospheric entry of meteoroids was an active area of research at NASA ARC up to the early 1970s (e.g., the oft-cited work of Baldwin and Sheaffer). However, research in the area seems to have ended with the Apollo program, and any ties with an active international meteor physics community seem to have significantly diminished thereafter. In the decades following the 1970s, the focus of entry physics at NASA ARC has been on improvement of the math models of shock-layer physics (especially in chemical kinetics and radiation) and thermal response of ablative materials used for capsule heatshields. With the overarching objectives of understanding energy deposition into the atmosphere and fragmentation, could these modern analysis tools and processes be applied to the problem of atmospheric entry of meteoroids as well? In the presentation we will explore: (i) the physics of atmospheric entries of meteoroids using our current state-of-the-art tools and processes, (ii) the influence of shape (and shape change) on flow characteristics, and (iii) how multiple bodies interact.

Prabku, Dinesh K.↗

NASA NTRS2020

Determining the Shallow Surface Velocity at the Apollo 17 Landing Site

Many studies have been performed to determine the shallow surface velocity model at the Apollo 17 landing site. The Lunar Seismic Profiling Experiment (LSPE) had both an active component with eight explosive packages (EPs) and a passive experiment collecting data at various time intervals. Using the eight EPs, the initial shallow surface velocity model was determined to be 250 m/s in the first layer of depth 248 m, 1200 m/s with a depth of 927 m in the second layer, and 4000 m/s down to a depth of 2 km in the third layer. Have performed variations on this study to produce new velocity models shown. Recent studies have also been reanalyzing the passive LSPE data and have found three different thermal moonquake event types occurring at different times within the lunar day. The current goal of the project is to collocate the thermal moonquakes to physical surface features to determine the breakdown of lunar rocks. However, to locate shallow surface events, an accurate velocity model is needed. Presented a thermal moonquake location algorithm using first order approximation, including surface events only. To improve these approximations, a shallow surface velocity is needed.

Phillips, D.↗

NASA NTRSDate not supplied

Influence of sediment resuspension on deep-ocean Pa-231 and Th-230 cycling: A PROGRESS REPORT

The naturally-occurring particle-reactive radionuclides protactinium-231 (231Pa) and thorium-230 (230Th) are used as tracers of a variety of oceanic processes, both at present and in the past. Most notably, the sediment 231Pa/230Th ratio has been used to infer changes in the Atlantic Meridional Overturning Circulation over the last (de)glaciation. However, recent measurements along the U.S. GEOTRACES North Atlantic transect (GA03) revealed two features which are at odds with current understanding about 231Pa and 230Th behaviour in the ocean: (i) a sharp decrease in dissolved 231Pa and 230Th activities with depth below 2000-4000 m and (ii) very large particulate 231Pa and 230Th activities near the bottom, at a number of stations between the New England continental shelf and Bermuda. Concomitant measurements of particulate matter concentration and potential temperature showed that both features are associated with the benthic nepheloid layer (BNL) and the bottom mixed layer (BML) that are present at these stations. Here we develop and apply a simplified model of the exchange of particles, 231Pa, and 230Th between the BNL and the upper sediment, to explore the extent to which the radionuclide anomalies observed near the bottom at a number of GA03 stations can be explained by local sediment resuspension. We find that the model can broadly reproduce the observed anomalies at two stations where samples for radionuclide analyses were collected near the seafloor. Sensitivity tests with the model show that the 231Pa/230Th ratio of particles in the BML and the sediment varies by a factor of 3 as the sediment resuspension rate fluctuates within a range consistent with observational estimates. The modelled variability is comparable to the spatial variability of 231Pa/230Th of suspended particles in the modern North Atlantic and to the variability of Atlantic sediment 231Pa/230Th records across the last (de)glacial period. Two factors are found to contribute to the modelled sensitivity of the sediment 231Pa/230Th to sediment resuspension rate: the vertical turbulent mixing in the BML and the differential scavenging intensity of Pa and Th due to variation in particle concentration. Overall, our study indicates that the exchange of material between the BNL and the upper sediment can affect the particulate 231Pa/230Th ratio in the bottom water and the sediment, which may complicate the use of sediment 231Pa/230Th as a palaeoceanographic tracer.

particle-reactive radionuclides↗

NASA NTRSDate not supplied

Identifying and Mapping Agricultural Areas Using Synthetic Aperture Radar Time Series

This study uses Synthetic Aperture Radar (SAR) data to identify active agricultural extent in Mato Grosso, Brazil. Coefficient of variation (CoVar) calculations were applied to year-long time series stacks to identify areas of crop growth. A CoVar threshold value was determined using crop reference layers, then applied to create a crop/non-crop binary map. In the Mato Grosso region, CoVar-based processing resulted in high performance crop classification and allowed for the monitoring of dynamic cropland expansion between 2016 and 2021.

Jordan Bell↗

NASA NTRS2000

Sweep and Compressibility Effects on Active Separation Control at High Reynolds Numbers

This paper explores the effects of compressibility, sweep and excitation location on active separation control at high Reynolds numbers. The model, which was tested in a cryogenic pressurized wind tunnel, simulates the upper surface of a 20% thick Glauert Goldschmied type airfoil at zero angle of attack. The flow is fully turbulent since the tunnel sidewall boundary layer flows over the model. Without control, the flow separates at the highly convex area and a large turbulent separation bubble is formed. Periodic excitation is applied to gradually eliminate the separation bubble. Two alternative blowing slot locations as well as the effect of compressibility, sweep and steady suction or blowing were studied. During the test the Reynolds numbers ranged from 2 to 40 million and Mach numbers ranged from 0.2 to 0.7. Sweep angles were 0 and 30 deg. It was found that excitation must be introduced slightly upstream of the separation region regardless of the sweep angle at low Mach number. Introduction of excitation upstream of the shock wave is more effective than at its foot. Compressibility reduces the ability of steady mass transfer and periodic excitation to control the separation bubble but excitation has an effect on the integral parameters, which is similar to that observed in low Mach numbers. The conventional swept flow scaling is valid for fully and even partially attached flow, but different scaling is required for the separated 3D flow. The effectiveness of the active control is not reduced by sweep. Detailed flow field dynamics are described in the accompanying paper.

Seifert, Avi↗

NASA NTRS1986

Turbulence in a convective marine atmospheric boundary layer

The structure and kinetic energy budget of turbulence in the convective marine atmospheric boundary layer as observed by aircraft during a cold air outbreak have been studied using mixed layer scaling. The results are significantly different from those of previous studies under conditions closer to free convection. The normalized turbulent kinetic energy and turbulent transport are about twice those found during the Air Mass Transformation Experiment (AMTEX). This implies that for a given surface heating the present case is dynamically more active. The difference is mainly due to the greater importance of wind shear in the present case. This case is closer to the roll vortex regime, whereas AMTEX observed mesoscale cellular convection which is closer to free convection. Shear generation is found to provide a significant energy source, in addition to buoyancy production, to maintain a larger normalized turbulent kinetic energy and to balance a larger normalized dissipation. The interaction between turbulent pressure and divergence (i.e., pressure scrambling) is also found to transfer energy from the vertical to the horizontal components, and is expected to be stronger in roll vortices than in m esoscale cells. The sensible heat flux is found to fit well with a linear vertical profile in a clear or subcloud planetary boundary layer (PBL), in good agreement with the results of Lenschow et al., (1980). The heat flux ratio between the PBL top and the surface, derived from the linear fitted curve, is approximately -0.14, in good agreement with that derived from the lidar data for the same case. Near the PBL top, the heat flux profiles are consistent with those of Deardoff (1979) and Deardorff et al. (1980).

Chou, S.-H.↗

NASA NTRS1972

Deformation of silicates in some Fra Mauro breccias.

The results of the studies conducted show that there is no unequivocal evidence for appreciable static deformation (other than annealing) in the Fra Mauro formation. These rocks probably have been derived from depths to about 10 km. It is suggested that there has been no substantial tectonic activity in the range from the surface to 10 km since these rocks and those of the other Apollo sites crystallized some 3 to 4 billion years ago. This negative conclusion implies that at least the outer layer of the moon has been static for this length of time.

Lallemant, H. G. A.↗

NASA NTRS1987

Numerical simulations of magnetospheric plasmas - Review and quadrennial report to the IUGG

This article provides a broad survey of U.S. progress during the quadrennium 1983-1986 in the category 'numerical simulations of magnetospheric plasmas'. There has been a substantial increase of activity in this area during this period. Simulations have been instrumental in providing valuable insights into large scale dynamic phenomena, nonlinear effects, and complex kinetic phenomena in a wide variety of subject areas, including shocks and double layers, ionosphere-magnetosphere coupling phenomena, and important microphysical processes such as broadband electrostatic noise. The methodology of computer simulation has also been advanced during this quadrennium. Vlasov algorithms have been improved; hybrid codes in 2 and 3D have been developed and applied to magnetospheric problems; and complex problems have been subjected with increasing frequency to a multipronged attack in which several types of simulation models, each designed to accurately model phenomena within a particular range of temporal or spatial scales, are employed synergistically.

Palmadesso, Peter J.↗

NASA NTRS1986

Transition and separation control on a low-Reynolds number airfoil

The major problem associated with the aerodynamic performance of airfoils at low Reynolds numbers is the presence of extensive laminar boundary-layer separation resulting in a large increase in presssure drag and a decrease in lift. The rapid deterioration in airfoil characteristics can be largely eliminated by artificially controlling the flow through the introduction of suitable disturbances in the boundary layer such that transition occurs ahead of the anticipated laminar separation. This paper presents the results of wind-tunnel tests conducted on a 10-cm model of LRN (1)-1007 airfoil with passive (roughness trips) and active (acoustic excitation) controls to trigger transition and suppress separation. Significant improvements in the aerodynamic characteristics of the airfoil were observed. Results of this study for a chord Reynolds number range of 40,000 to 250,000 are presented in this paper.

Mangalam, S. M.↗

NASA NTRS1988

Climate, atmosphere, and volatile inventory evolution: Polar processes, climate records, volatile inventories

Climate change on Mars was driven by long term changes in the solar luminosity, variations in the partitioning of volatiles between the atmosphere and near-surface reservoirs, and astronomical variations in axial and orbital properties. There are important parallels between these drives for Mars and comparable ones for Earth. In the early history of the solar system, the Sun's luminosity was 25 to 30 percent lower than its current value. It is suggested that an early benign climate on Earth was due to the presence of much more carbon dioxide in its atmosphere at these early times than currently resides there. Such a partitioning of carbon dioxide, at the expense of the carbonate rock reservoir, may have resulted from a more vigorous tectonic and volcanic style at early times. Such a line of reasoning may imply that much more carbon dioxide was present in the Martian atmosphere during the planet's early history than resides there today. It is now widely recognized that astronomical variations of the Earth's axial and orbital characteristics have played a dominant role in causing the succession of glacial and interglacial periods characterizing the last several million years. The magnitude of the axial and eccentricity variations are much larger for Mars than for Earth. Such changes on Mars could result in sizeable variations in atmospheric pressure, dust storm activity, and the stability of perennial carbon dioxide and water ice polar caps. These quasi-periodic climate changes occur on periods of 100,000 to 1,000,000 years and may be recorded in the sedimentary layers of the polar layered terrain.

Pollack, J. B.↗