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NASA NTRS1992

Some aspects of unsteady separation

Unsteady separation can be forced in a variety of ways and in this presentation two fundamental means will be considered: (1) the introduction of convected vorticular disturbances into the flow; and (2) the influence of a specific type of three-dimensional geometry. In both situations a response of the viscous flow near the wall is provoked wherein the fluid near the surface abruptly focuses into a narrow region that erupts from the surface into the mainstream. In two-dimensional flows, the eruption takes the form of a narrow, explosively-growing spike, while in three-dimensional situations, examples are presented which indicate that the eruption is along a narrow zone in the shape of a crescent-shaped plume. The nature of the three-dimensional flow near a circular cylinder, which is mounted normal to a flat plate, is also examined in this study. Here the three-dimensional geometry induces complex three-dimensional separations periodically. The dynamics of the generation process is studied experimentally in a water channel using hydrogen bubble wires and a laser sheet, and the main features of the laminar regime through to transition are documented.

Smith, C. R.↗

NASA NTRS1994

Unstructured-grid large-eddy simulation of flow over an airfoil

Historically, large-eddy simulations (LES) have been restricted to simple geometries where spectral or finite difference methods have dominated due to their efficient use of structured grids. Structured grids, however, not only difficulty representing complex domains and adapting to complicated flow features, but also are rather inefficient for simulating flows at high Reynolds numbers. The lack of efficiency stems from the need to resolve the viscous sublayer, which requires very fine resolution in all three directions near the wall. Structured grids make use of a stretching to reduce the normal grid spacing but must carry the fine resolution in the streamwise and spanwise directions throughout the domain. The unnecessarily fine grid for much of the domain leads to disturbingly high grid estimates. Chapman (1979), and later Moin & Jimenez (1993), pointed out that, in order to advance the technology to airfoils at flight Reynolds numbers, structured grids must be abandoned in lieu of what are known as nested or unstructured grids. The finite element method can efficiently solve the Navier-Stokes equations on unstructured grids. Although the CPU cost per time step per element is somewhat higher than structured grid methods, this effect is more than offset by the reduction in the number of elements. The use of unstructured grids, coupled with the advances in dynamic subgrid-scale modeling such as those made by Germano et al. (1991) and Ghosal et al. (1994), make LES of an airfoil tractable. We have chosen the NACA 4412 airfoil at maximum lift as the first simulation since this flow has not been successfully simulated with the Reynolds-averaged Navier-Stokes equations.

Jansen, Kenneth↗

NASA NTRS1995

A study of flux transfer events at different planets

Flux transfer events (FTEs) are disturbances in and near the magnetopause current layer that cause a characteristic signature in the component of the magnetic field parallel to the average boundary normal. These disturbances have been observed at Mercury, Earth and Jupiter but not at Saturn, Uranus or Neptune. At Earth, FTEs last about 1 minute and repeat about every 8 but at Mercury, a much smaller magnetosphere, the events last seconds and are tens of seconds apart. These features have been interpreted in terms of magnetospheric flux ropes connected to the interplanetary magnetic field, arising as the result of reconnection. An analogous phenomenon occurs at Venus where magnetic flux ropes arise at the ionosphere, a boundary between a very strongly magnetized one. However, here the flux ropes do not appear to be due to reconnection.

Russell, C. T.↗

NASA NTRS2017

Enabling NLDAS-2 Anomaly Analysis Using Giovanni

A newly implemented feature in Giovanni (GES DISC Interactive Online Visualization and Analysis Interface) allows users to explore and visualize anomaly data from the NLDAS-2 Primary Forcing and Noah model data sets. For a given measurement and location, an anomaly describes how conditions for a particular time period compare to normal conditions, based on long-term averages. Analyzing anomalies is important for monitoring droughts, determining weather trends, and studying land surface processes relevant for meteorology, hydrology, and climate. Using Giovanni to analyze anomalies for NLDAS-2 data allows for these studies to be efficiently conducted for the central North American region. Phase 2 of NLDAS (NLDAS-2) currently runs at an 1/8th degree resolution, in near-real time, with data sets extending back to January 1979. NLDAS-2 provides data for soil moisture, precipitation, temperature, and other hydrology measurements. Hourly, monthly, and 30-year (1980-2009) monthly climatology data are available for several land surface models and forcing data sets. The Giovanni anomaly tool calculates monthly anomalies, for a given user-defined variable, as the difference between the NLDAS-2 monthly climatology data and the monthly data. The resulting anomaly describes how a chosen month compares to the 30-year monthly average. The presentation will demonstrate the capabilities and usefulness of Giovanni's anomaly tool, detail the recently added NLDAS-2 variables for which anomalies are available, and show how users can access the data.

drough↗

NASA NTRS2021

Quantifying and Characterizing Striping of Microwave Humidity Sounder with Observation and Simulation

Striping has been observed in the MetOp-A Microwave Humidity Sounder (MHS) data since its degradation in November 2018. However, accurate striping quantification and characterization remain challenging due to the large scene dynamics observed at W/G bands of MHS. Here we have developed a set of novel algorithms for striping quantification, decomposition, characterization, and simulation. Our algorithm extracts striping from the warm-load and cold-space scenes that are relatively stable. We break down the striping into two parts of thermal and 1/f noise and quantify their absolute magnitude and relative ratio. We found a significant increase in striping at 157 GHz that has more than quadrupled by October 2019 relative to its normal level. Regardless of the degradation, the ratio of thermal and 1/f noise remains the same. Our simulation reproduces all the characteristics of striping against observation. It is shown that 1/f noise generates sharp, non-periodic stripes, while thermal noise also generates stripes but with smoother band features. The latter is due to the periodic calibration that has a chopping effect. The striping percentage, defined as the ratio of 1/f to total noise, shows no dependence on the scene temperature. Striping is pronounced not only in 157 GHz but also in 89 and190 GHz with the striping percentage over 50%, while lower in183 GHz of 20%. The results provide insights for quantifying and understanding striping. Our algorithm can be applied to other radiometers and to simulate striping for evaluating its impact in data assimilation and science products.

John Xun Yang↗

NASA NTRS2026

X-Ray Polarization of Z-Type Neutron Star Low-Mass X-Ray Binaries II. Spectropolarimetric Analysis

IXPE has provided for the first time detailed energy- and time-resolved X-ray polarimetry of Z-type neutron star low-mass X-ray binaries (NS-LMXBs) as they move along their color-color diagrams (CCDs). These sources can reach the highest polarization observed for NS-LXMBs in the 2–8 keV range when they move along the horizontal branch. In a previous paper, we characterized the spectral state of a sample of Z-sources using the CCD and estimated the polarization with model-independent analysis. Here, we present detailed spectropolarimetric analysis for each source on each branch using data from IXPE, NICER, and NuSTAR. The continuum X-ray emission of all the sources is well described with a combination of thermal accretion disk emission plus a harder Comptonized component. In addition, reflection features, in particular the relativistically broadened Fe Kα line, are observed for our sources, except GX 5–1. For most of the sources and branches, the main contribution to the X-ray emission and polarization is due to Comptonization: moving from the horizontal branch (HB) to the normal branch (NB), the polarization degree (PD) in the 2–8 keV band varies from about 6% to 3–4%, while the PD is loosely constrained in the flaring branch (FB), due to the shorter exposures. These PD values are significantly higher than theoretical expectations for typical spreading or boundary layer configurations. The polarization of the disk is generally lower (below 3%) but still higher than predictions for an electron scattering-dominated, plane-parallel atmosphere above the disk observed at the corresponding inclination. Moreover, the polarization angle (PA) of the disk seems to be significantly misaligned and not perpendicular to that of Comptonization. We find no correlation between the polarization signal and the inclination, nor with the contribution of reflected photons throughout the Z-track.

accretion↗

NASA NTRS1987

Generation of spiral bevel gears with conjugate tooth surfaces and tooth contact analysis

A new method for generation of spiral bevel gears is proposed. The main features of this method are as follows: (1) the gear tooth surfaces are conjugated and can transform rotation with zero transmission errors; (2) the tooth bearing contact is localized; (3) the center of the instantaneous contact ellipse moves in a plane that has a fixed orientation; (4) the contact normal performs in the process of meshing a parallel motion; (5) the motion of the contact ellipse provides improved conditions of lubrication; and (6) the gears can be manufactured by use of Gleason's equipment.

Litvin, Faydor L.↗

NASA NTRS1993

Training high performance skills using above real-time training

The Above Real-Time Training (ARTT) concept is a unique approach to training high performance skills. ARTT refers to a training paradigm that places the operator in a simulated environment that functions at faster than normal time. Such a training paradigm represents a departure from the intuitive, but not often supported, feeling that the best practice is determined by the training environment with the highest fidelity. This approach is hypothesized to provide greater 'transfer value' per simulation trial, by incorporating training techniques and instructional features into the simulator. These techniques allow individuals to acquire these critical skills faster and with greater retention. ARTT also allows an individual trained in 'fast time' to operate at what appears to be a more confident state, when the same task is performed in a real-time environment. Two related experiments are discussed. The findings appear to be consistent with previous findings that show positive effects of task variation during training. Moreover, ARTT has merit in improving or maintaining transfer with sharp reductions in training time. There are indications that the effectiveness of ARTT varies as a function of task content and possibly task difficulty. Other implications for ARTT are discussed along with future research directions.

Guckenberger, Dutch↗

NASA NTRS1993

Spatially extensive uniform stress fields on Venus inferred from radial dike swarm geometries: The Aphrodite Terra example

The high resolution and near global coverage of Magellan radar images is facilitating attempts to systematically investigate the stresses that have deformed the venusian crust. Here we continue earlier efforts to utilize approximately 170 large, radially lineated structures interpreted as dike swarms to assess the orientation of the regional maximum horizontal compressive stress (MHCS) which existed in their vicinities during emplacement. Examination of swarms near the equator reveals a link to broad scale regional structures, such as Aphrodite Terra, across distances in excess of 1000 km, suggesting the existence of first order stress fields which affect areas of more than 10(exp 6) sq km in a uniform fashion. Focusing further upon the Aphrodite Terra region, the MHCS field in the surrounding lowlands inferred from radial swarms is oriented approximately normal to the slope of the highland topography. This stress configuration appears, at a simple level, to be incompatible with that expected during either upwelling or downwelling construction of the highlands. In addition, the relatively undeformed geometry of the radial structures within the highlands implies that these dike swarm features formed more recently than their highly deformed surroundings. We conclude that the differential stresses which existed during emplacement of the dike swarms within and adjacent to the Aphrodite Terra highlands are related to the gravitational relaxation of pre-existing topography.

Grosfils, Eric B.↗

NASA NTRS1994

The development and validation of a simple snow model for the GISS GCM

Five years of meteorological and hydrological data from a typical New England watershed where winter snow cover is significant were used to drive and validate two off-line land surface schemes suitable for use in the Goddard Institute for Space Studies (GISS) general circulation model (GCM): a baseline scheme that does not model the physics of a snowpack and therefore, neglects the insulating properties of snow cover; and a modified scheme in which a three-layer snowpack is modeled. Comparing baseline model results with validation data reveals several model deficiencies. Surface radiation temperatures could not adequately be modeled and the ground froze to unreasonable depths. Furthermore, because of ground cooling resulting from large surface heat fluxes to the atmosphere from the uninsulated surface, deeper model layers did not unfreeze until midsummer. As such, the normal hydrologic processes of runoff, ground water infiltration, and movement, etc., are compromised for a good part of the year. With the inclusion of a simple three-layer snow model into the baseline model, not only are the ground and surface radiation temperatures adequately modeled but all the features of snowpack ripening that characterize pack growth/ablation are simulated.

Lynch-Stieglitz, Marc↗

NASA NTRS2002

Increased sympathetic activation in idiopathic orthostatic intolerance: role of systemic adrenoreceptor sensitivity

Idiopathic orthostatic intolerance (OI) is characterized by adrenergic symptoms with standing. Changes in central sympathetic tone or in adrenoreceptor sensitivity could contribute to this syndrome. In OI patients and control subjects, we determined heart rate (HR) and systolic blood pressure (SBP) changes after incremental bolus doses of isoproterenol and phenylephrine before and during ganglionic blockade with trimethaphan. SBP decreased by 17+/-1.6 mm Hg in patients and 3.9+/-3.8 mm Hg in control subjects (P<0.01) with trimethaphan. Patients with a larger decrease (28+/-3.8 mm Hg, n=7) in SBP with trimethaphan had greater supine SBP and supine and upright plasma norepinephrine levels than did patients with a lesser decrease (3.0+/-3.0 mm Hg, n=7) in SBP. Supine and orthostatic HRs were similar for the groups. The majority of patients had a normal HR response to isoproterenol before and during ganglionic blockade. Phenylephrine increased SBP similarly in patients and control subjects before and during blockade. Sympathetic support is increased in a subgroup of OI patients. Hyperadrenergic and nonhyperadrenergic subgroups have similar degrees of orthostatic tachycardia. Our findings suggest that the hyperadrenergic features of OI cannot be completely explained by systemic hypersensitivity of postsynaptic alpha(1)- and beta-adrenoreceptors but rather originates in enhanced sympathetic activation.

Non-NASA Center↗

NASA NTRSDate not supplied

Parallelized Quadrupole Simulations of Thermographic Responses of Composites

Thermography has been shown to be a viable technique for inspection of composites. Model inversion of the thermography data requires a fast method for performing the forward problem. Viable numerical methods for the thermal response forward problem are finite element, finite difference and the quadrupole method. Normally both the finite element and finite difference methods solve for the thermal response in the time domain which limits one’s ability to increase the speed of the simulation by parallelization. In contrast, the quadrupole method solves for the Laplace transform of the thermal response. One of the features of the Laplace transform methodology is the solution at any discrete time is independent of the solution at all other times. Therefore, it is easy to separate into a set of independent calculations with each of the times of interest being performed in parallel. Additionally, the numeric inversion of the Laplace transform typically involves numerically solving for the Laplace transform at multiple Laplace frequencies. Each of those solutions are also independent of solutions at other frequencies and can be calculated in parallel. By parallelization of this method, it is possible to perform the simulations of three-dimensional configurations in seconds. When the input stimulus for thermal response is a delta function heat flux (a reasonable approximation for flash heating), the thermal response is smooth. For this case, it is possible to accurately estimate the thermal response at any time within a given time interval from a set of simulations separated by exponentially increasing time steps. From these simulations, it is possible to accurately interpolate to find the response at intermediate times by a spline interpolation of the logarithm of time versus logarithm of temperature. The thermal response with exponential time stepping is shown to produce values for the thermal response which are within 1% of values within the time interval. The simulations are compared to finite element simulations of the same inspection configurations. The simulations are also compared to the thermographic measurements on composites where shape and depth of the delaminations are obtained from other inspection methods.

Thermography↗

NASA NTRSDate not supplied

Parallelized Quadrupole Simulations of Thermographic Responses of Composites

Thermography↗

NASA NTRS1977

Effect of microstructure on Na/+/ diffusion in beta alumina

The effect of microstructural features, such as grain size and orientation, on sodium ion diffusion in polycrystalline beta alumina is investigated; the ionic solid is suitable for use in high-energy and power density batteries. Two types of hot-pressed polycrystalline samples are studied, one with grains highly oriented in the direction normal to the pressing direction, the other with significantly less preferred orientation normal to the pressing direction. Results of the experimental assessments indicate that grain size and diffusion path tortuosity have little effect on diffusion kinetics, while grain boundary type and grain aspect ratio are important factors in determining the diffusion rate.

Sarian, S.↗

NASA NTRS1984

Growth and maintenance of large-scale magnetic fields in the dayside Venus ionosphere

Observations from the Pioneer Venus orbiter magnetometer reveal the presence of large-scale magnetic fields in the dayside ionosphere during or after periods of high solar wind dynamic pressure. Various hypotheses have been proposed concerning the spatial and temporal evolution of these field structures. The hypothesis that the field is produced by a diffusion/convection process rather than by currents driven by electric fields resulting from the solar wind interaction is examined. Dynamic pressure variations occur on various time scales at Venus, producing transient and quasi-steady magnetization features. A one-dimensional diffusion/convection calculation is performed, using typical ionopause field and pressure values for a variety of altitudes. The Venus ionopause is considered to be the altitude at which ionospheric thermal pressure is equal to the magnetosheath magnetic pressure, which in turn is well correlated with the normal component of solar wind dynamic pressure. A subsolar model of downward plasma velocity in the 140-290 km range is used. The calculated growth of the ionospheric magnetic field, and the resulting quasi-steady altitude profiles, compare favorably with the observed profiles. The majority of the observed magnetic structures are best explained as the quasi-steady effects of the prevailing solar wind dynamic pressure, which determines the altitude and magnetic field strength of the ionopause boundary.

Phillips, J. L.↗

NASA NTRS1995

An edge-based solution-adaptive method applied to the AIRPLANE code

Computational methods to solve large-scale realistic problems in fluid flow can be made more efficient and cost effective by using them in conjunction with dynamic mesh adaption procedures that perform simultaneous coarsening and refinement to capture flow features of interest. This work couples the tetrahedral mesh adaption scheme, 3D_TAG, with the AIRPLANE code to solve complete aircraft configuration problems in transonic and supersonic flow regimes. Results indicate that the near-field sonic boom pressure signature of a cone-cylinder is improved, the oblique and normal shocks are better resolved on a transonic wing, and the bow shock ahead of an unstarted inlet is better defined.

Biswas, Rupak↗

NASA NTRS2001

Validating the use of Satellite SAR for Measuring Small-Scale Surface Wind Variations

We present aircraft measurements of near-surface atmospheric boundary layer roll signatures and radar-derived sea surface roughness. The open-ocean data were collected at an altitude of 20 m using NOAA's Long-EZ aircraft. In addition, the flight was coincident with a RADARSAT SAR overpass where presumed boundary layer roll impacts are prevalent in the SAR backscatter image. The Long-EZ air and sea data are completely coincident in space and time and this unique feature allows us to validate the supposed link between SAR backscatter signatures and organized large eddy surface impacts. We find remarkable correlation between measured modulations in the along-wind component of wind speed and radar backscatter for the atmospheric eddy scale of 1 to 1.5 km. Close agreement between normalized modulation amplitudes suggests the radar-inferred surface slope variance is changing linearly with wind speed. Implications for SAR usage in coastal regions and for boundary layer study will be discussed.

Vandemark, Douglas↗

NASA NTRS2003

The Global S$_1$ Ocean Tide

The small S$_1$ ocean tide is caused primarily by diurnal atmospheric pressure loading. Its excitation is therefore unlike any other diurnal tide. The global character of $S-1$ is here determined by numerical modeling and by analysis of Topex/Poseidon satellite altimeter data. The two approaches yield reasonably consistent results, and large ( $ greater than $l\cm) amplitudes in several regions are further confirmed by comparison with coastal tide gauges. Notwithstanding their excitation differences, S$-1$ and other diurnal tides are found to share several common features, such as relatively large amplitudes in the Arabian Sea, the Sea of Okhotsk, and the Gulf of Alaska. The most noticeable difference is the lack of an S$-1$ Antarctic Kelvin wave. These similarities and differences can be explained in terms of the coherences between near-diurnal oceanic normal modes and the underlying tidal forcings. While gravitational diurnal tidal forces excite primarily a 28-hour Antarctic-Pacific mode, the S$_1$ air tide excites several other near-diurnal modes, none of which has large amplitudes near Antarctica.

Ray, Richard D.↗