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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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The application is described of computational fluid dynamics (CFD) to a hypersonic propulsion system. An overview of the problems associated with a propulsion system of this type is presented, highlighting the special role that CFD plays in the design of said systems.
Animal movements are linked to infectious disease dynamics in wildlife through multiple mechanisms across various spatial and temporal scales. For example, infections can impede the movement of infected individuals, but infected hosts can also disperse infectious agents as they move. Individuals inevitably vary in their responses to infections and their roles in determining infection dynamics, which means that considering variation among individuals – whether across species, across time, or within populations – is important for understanding movement-disease relationships and their implications for epidemiology. Here, I draw on studies from multiple systems to examine how variation in movement behavior links to infectious disease epidemiology. For example, a comparative study of habitat selection across multiple waterfowl species highlights that diel behavioral patterns, rather than individual or seasonal variation, is the most important driver of the risk of overlap between waterfowl and poultry farms, and therefore for the risk of avian influenza spillover. Together, these studies show that individual traits interact with the environment to influence the roles of individuals for infectious disease ecology.
Advanced computational methods for composite structures can enable smarter testing and potentially certification by analysis. These methods, known as progressive damage and failure analysis (PDFA) methods, can predict lamina level mechanics including failure and subsequent propagation. When introduced into a commercial off the shelf finite element solver such as ABAQUS, LS-DYNA, or ANSYS, it enables end users to effectively exercise PDFA methods; however, it requires an understanding of the assumed mechanics and underlying coded response. In this paper, verification benchmarks developed under the NASA Advanced Composite Consortium for a class of PDFA methods known as continuum damage mechanics approaches are applied to the native LS-DYNA material model MAT261. As a result of the verification, an instability was discovered and subsequently corrected with an engineering solution. The results of the preliminary MAT261 simulations for high energy dynamic impact and the engineering solution are compared and a discussion about the significance is presented.
The aerodynamic contours for two new nozzles have been designed for the NASA Langley Research Center 8-Foot High Temperature Tunnel. The new Mach-4 and Mach-6 contours have 54.5-inch exit-diameters allowing for testing at high dynamic pressures. The Mach-4 nozzle will extend the test capability of the facility and allow turbine-based combined-cycle propulsion systems to be tested at conditions appropriate for the transition from the turbine to the scramjet flowpath. The Mach-6 nozzle will serve a dual purpose; to provide a Mach-6 test capability at high dynamic pressure and to be used in conjunction with an existing mixer section for testing at lower enthalpy conditions. This second use will extend the life of the existing Mach-7 nozzle which has been used for this purpose. The two new nozzles, in conjunction with existing nozzles, will allow for testing at Mach numbers of 3, 4, 5 and 6 at high dynamic pressures, and Mach 4, 5 and 7 at lower dynamic pressures but larger scales.
This presentation gives an overview of the NASA Advanced Composites Project and a summary of the progress and plans of the High Energy Impact Dynamics Team.
Progress is reported on the high-resolution three-dimensional numerical simulation of flows characteristic of the Antarctic wintertime stratosphere. The numerical model is a modified version of the Reading University sigma-coordinate used previously for tropospheric studies. Physical parameterizations are kept to a minimum in order to concentrate as much computing power as possible on simulating details of the dynamical processes. The major question addressed is whether the features observed in recent high-resolution two-dimensional simulations - namely: (1) the formation of a sharp edge to the vortex (seen in the potential vorticity field), (2) the survival of the polar vortex in a material entity, and (3) the formation of small-scale eddies rough the break-up of tongues of high potential vorticity drawn out from the polar vortex - are realized in three-dimensional simulations.
Simple parameterization of gimbaled platform pointing produces a complete set of 13 calibration parameters-9 misalignment angles, 2 scale factors and 2 biases. By modifying the parameter representation, redundancy can be eliminated and a minimum set of 9 independent parameters defined. These consist of 5 misalignment angles, 2 scale factors, and 2 biases. Of these, only 4 misalignment angles and 2 biases are significant for the Solar Dynamics Observatory (SDO) High Gain Antennas (HGAs). An algorithm to determine these parameters after launch has been developed and tested with simulated SDO data. The algorithm consists of a direct minimization of the root-sum-square of the differences between expected power and measured power. The results show that sufficient parameter accuracy can be attained even when time-dependent thermal distortions are present, if measurements from a pattern of intentional offset pointing positions is included.
Seasonal vegetation phenology can significantly alter surface albedo which in turn affects the global energy balance and the albedo warmingcooling feedbacks that impact climate change. To monitor and quantify the surface dynamics of heterogeneous landscapes, high temporal and spatial resolution synthetic time series of albedo and the enhanced vegetation index (EVI) were generated from the 500-meter Moderate Resolution Imaging Spectroradiometer (MODIS) operational Collection V006 daily BRDF (Bidirectional Reflectance Distribution Function) / NBAR (Nadir BRDF-Adjusted Reflectance) / albedo products and 30-meter Landsat 5 albedo and near-nadir reflectance data through the use of the Spatial and Temporal Adaptive Reflectance Fusion Model (STARFM). The traditional Landsat Albedo (Shuai et al., 2011) makes use of the MODIS BRDFAlbedo products (MCD43) by assigning appropriate BRDFs from coincident MODIS products to each Landsat image to generate a 30-meter Landsat albedo product for that acquisition date. The available cloud free Landsat 5 albedos (due to clouds, generated every 16 days at best) were used in conjunction with the daily MODIS albedos to determine the appropriate 30-meter albedos for the intervening daily time steps in this study. These enhanced daily 30-meter spatial resolution synthetic time series were then used to track albedo and vegetation phenology dynamics over three Ameriflux tower sites (Harvard Forest in 2007, Santa Rita in 2011 and Walker Branch in 2005). These Ameriflux sites were chosen as they are all quite nearby new towers coming on line for the National Ecological Observatory Network (NEON), and thus represent locations which will be served by spatially paired albedo measures in the near future. The availability of data from the NEON towers will greatly expand the sources of tower albedometer data available for evaluation of satellite products. At these three Ameriflux tower sites the synthetic time series of broadband shortwave albedos were evaluated using the tower albedo measurements with a Root Mean Square Error (RMSE) less than 0.013 and a bias within the range of 0.006. These synthetic time series provide much greater spatial detail than the 500 meter gridded MODIS data, especially over more heterogeneous surfaces, which improves the efforts to characterize and monitor the spatial variation across species and communities. The mean of the difference between maximum and minimum synthetic time series of albedo within the MODIS pixels over a subset of satellite data of Harvard Forest (16 kilometers by 14 kilometers) was as high as 0.2 during the snow-covered period and reduced to around 0.1 during the snow-free period. Similarly, we have used STARFM to also couple MODIS Nadir BRDF-Adjusted Reflectances (NBAR) values with Landsat 5 reflectances to generate daily synthetic times series of NBAR and thus Enhanced Vegetation Index (NBAR-EVI) at a 30-meter resolution. While normally STARFM is used with directional reflectances, the use of the view angle corrected daily MODIS NBAR values will provide more consistent time series. These synthetic times series of EVI are shown to capture seasonal vegetation dynamics with finer spatial and temporal details, especially over heterogeneous land surfaces.
Capabilities of existing structural and gas dynamics test facilities for space shuttle structural development
Results are presented which define unsteady flow conditions associated with high dynamic response experienced on a high aspect ratio elastic supercritical wing at transonic test conditions while being tested in the NASA Langley Transonic Dynamics Tunnel. The supercritical wing, designed for a cruise Mach number of 0.80, experienced the high dynamic response in the Mach number range from 0.90 to 0.94 with the maximum response occurring at a Mach number of approximately 0.92. At the maximum wing response condition the forcing function appears to be the oscillatory chordwise movement of strong shocks located on both the wing upper and lower surfaces in conjunction with the flow separating and reattaching in the trailing edge region.
Results are presented which define unsteady flow conditions associated with high dynamic response experienced on a high aspect ratio elastic supercritical wing at transonic test conditions while being tested in the NASA Langley Transonic Dynamics Tunnel. The supercritical wing, designed for a cruise Mach number of 0.80, experienced the high dynamic response in the Mach number range from 0.90 to 0.94 with the maximum response occurring at a Mach number of approximately 0.92. At the maximum wing response condition the forcing function appears to be the oscillatory chordwise movement of strong shocks located on both the wing upper and lower surfaces in conjuction with the flow separating and reattaching in the trailing edge region.
Dynamic equations which include the effects of unsteady aerodynamic forces and a flexible body structure were developed for a free flying high performance fighter aircraft. The linear and angular deformations are assumed to be small in the body reference frame, allowing the equations to be linearized in the deformation variables. Equations for total body dynamics and flexible body dynamics are formulated using the hybrid coordinate method and integrated in a state space format. A detailed finite element model of a generic high performance fighter aircraft is used to generate the mass and stiffness matrices. Unsteady aerodynamics are represented by a rational function approximation of the doublet lattice matrices. The equations simplify for the case of constant angular rate of the body reference frame, allowing the effect of roll rate to be studied by computing the eigenvalues of the system. It is found that the rigid body modes of the aircraft are greatly affected by introducing a constant roll rate, while the effect on the flexible modes is minimal for this configuration.
Taking advantage of the improved radiometric resolution of Landsat-8 OLI which, unlike previous Landsat sensors, does not saturate over snow, the progress of fire recovery progress at the landscape scale (less than 100 m) is examined. High quality Landsat-8 albedo retrievals can now capture the true reflective and layered character of snow cover over a full range of land surface conditions and vegetation densities. This new capability particularly improves the assessment of post-fire vegetation dynamics across low- to high-burn severity gradients in Arctic and boreal regions in the early spring, when the albedos during recovery show the greatest variation. We use 30 m resolution Landsat-8 surface reflectances with concurrent coarser resolution (500 m) MODIS high quality full inversion surface Bidirectional Reflectance Distribution Functions (BRDF) products to produce higher resolution values of surface albedo. The high resolution full expression shortwave blue sky albedo product performs well with an overall RMSE of 0.0267 between tower and satellite measures under both snow-free and snow-covered conditions. While the importance of post-fire albedo recovery can be discerned from the MODIS albedo product at regional and global scales, our study addresses the particular importance of early spring post-fire albedo recovery at the landscape scale by considering the significant spatial heterogeneity of burn severity, and the impact of snow on the early spring albedo of various vegetation recovery types. We found that variations in early spring albedo within a single MODIS gridded pixel can be larger than 0.6. Since the frequency and severity of wildfires in Arctic and boreal systems is expected to increase in the coming decades, the dynamics of albedo in response to these rapid surface changes will increasingly impact the energy balance and contribute to other climate processes and physical feedback mechanisms. Surface radiation products derived from Landsat-8 data will thus play an important role in characterizing the carbon cycle and ecosystem processes of high latitude systems.
The dynamics and three-dimensional (3-D) properties of the primate translational vestibuloocular reflex (trVOR) for high-frequency (4-12 Hz, +/-0.3-0.4 g) lateral motion were investigated during near-target viewing at center and eccentric targets. Horizontal response gains increased with frequency and depended on target eccentricity. The larger the horizontal and vertical target eccentricity, the steeper the dependence of horizontal response gain on frequency. In addition to horizontal eye movements, robust torsional response components also were present at all frequencies. During center-target fixation, torsional response phase was opposite (anticompensatory) to that expected for an "apparent" tilt response. Instead torsional response components depended systematically on vertical-target eccentricity, increasing in amplitude when looking down and reversing phase when looking up. As a result the trVOR eye velocity vector systematically tilted away from a purely horizontal direction, through an angle that increased with vertical eccentricity with a slope of approximately 0.7. This systematic dependence of torsional eye velocity tilt on vertical eye position suggests that the trVOR might follow the 3-D kinematic requirements that have been shown to govern visually guided eye movements and near-target fixation.
Results are presented which define unsteady flow conditions associated with the high-dynamic structural response of a high-aspect-ratio, elastic, supercritical wing at transonic speeds. The wing was tested in the Langley Transonic Dynamics Tunnel with a heavy gas test medium. The supercritical wing, designed for a cruise lift coefficient of 0.53 at a Mach number of 0.80, experienced the high-dynamic structural response from Mach 0.90 to 0.94 with the maximum response occurring at about Mach 0.92. At the maximum response conditions of the wing, the forcing function appears to be the oscillatory chordwise movement of strong shocks located on the upper and lower surfaces of the wing in conjunction with the flow separation on the lower surface of the wing in the trailing-edge cove region.
Un-cooled, MEMS-based silicon carbide (SiC) static pressure sensors were used for the first time to measure pressure perturbations at temperatures as high as 600 C during laboratory characterization, and subsequently evaluated in a combustor rig operated under various engine conditions to extract the frequencies that are associated with thermoacoustic instabilities. One SiC sensor was placed directly in the flow stream of the combustor rig while a benchmark commercial water-cooled piezoceramic dynamic pressure transducer was co-located axially but kept some distance away from the hot flow stream. In the combustor rig test, the SiC sensor detected thermoacoustic instabilities across a range of engine operating conditions, amplitude magnitude as low as 0.5 psi at 585 C, in good agreement with the benchmark piezoceramic sensor. The SiC sensor experienced low signal to noise ratio at higher temperature, primarily due to the fact that it was a static sensor with low sensitivity.
We observed ten well-known flare stars with the Arcibo radio telescope at 1.4 GHz and 5 GHz, using a special observing technique to discriminate between real flares and radio freqeuncy interference. With a high sensitivity of 5.5 K/Jy at 1.4 GHz when averaged over a 50 MHz band, we are able to recognize flux enhancements as weak as approximately 6 mJy above the sky background variations. In about 85 hours of observation, about a dozen bursts were detected, only from AD Leo. All had flux densities lower than 70 mJy, which probably explains their lack of fine structures (except for the strongest one), such as were reported in the literature for stronger flares. Half of the bursts that we recorded are 100% circularly polarized, and half are not circularly polarized. Our results are a first attempt of reliable statistics on dMe flare rates at 1.4 GHz. The high brightness temperatures we infer for the observed bursts are interpreted in terms of coherent emission processes, either the cyclotron maser instability or plasma radiation. Efficiencies are comparable to those of solar or planetary radio emissions in the case of the cyclotron maser, and higher than the solar efficiency in the case of plasma radiation, with the caveat that there are great uncertainties in the coronal model and the source size.
Data collected by the Georgia Tech Radio Meteor Wind Facility during the fall and winter of 1975 are analyzed indicating a relationship between lower thermospheric circulation at mid latitudes and polar stratospheric dynamics. Techniques of measurement of mixing processes in the upper atmosphere and the interpretation of those measurements are described along with a diffusion simulation program based on the Global Reference Atmosphere program.