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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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At least 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
NASA NTRS1929

Travel of the center of pressure of airfoils transversely to the air stream

The experiments here described were performed for the purpose of obtaining the essential facts concerning the distribution of the air force along the span. We did not follow, however, the time-consuming method of point-to-point measurements of the pressure distribution on the wing surfaces, but determined directly the moment of mean force about an axis passing through the middle of the span parallel to the direction of flight.

AIRFOILS - ASPECT RATIO↗
NASA NTRS1984

Extensions of the Ritz-Galerkin method for the forced, damped vibrations of structural elements

The Ritz-Galerkin methods were used to obtain approximate solutions for free undamped, vibration problems. It is demonstrated that these same methods may be used straightforwardly to analyze forced vibrations with damping without requiring the free vibration eigenfunctions. It was shown that the Galerkin method is an effective technique for these types of problems. The Ritz method has the advantage that it does not need to satisfy the force-type boundary conditions, which is particularly important for plates and shells. Proper functionals representing the forcing and damping terms were developed. Two types of damping--viscous and material (hysteretic) are discussed. Distributed and concentrated exciting forces are treated. Numerical results are obtained for cantilevered beams and rectangular plates. The rates of convergence of the solutions are shown. Approximate solutions from the present methods are compared with the exact solutions for the cantilever beam.

Leissa, A. W.↗
NASA NTRS1990

Radiative forcing of climate by changes in the vertical distribution of ozone

Results from a one-dimensional radiative-convective equilibrium model (similar to that of Lacis et al., 1981) of surface-temperature changes induced by changes in the vertical distribution of O3 in the atmosphere are parameterized and applied to measurement data for the northern midlatitudes during the 1970s. The construction of the model is outlined, and the results are presented in tables and graphs and discussed in detail. It is found that decreases in O3 in the lower stratosphere in the 1970s caused atmospheric cooling greater than that due to CO2 (thus possibly obscuring the CO2 greenhouse effect) and surface cooling which outweighed the warming effect of increased O3 in the troposphere. The net surface cooling is shown to be equal to about half of the estimated CO2 warming effect for the period.

Lacis, Andrew A.↗
NASA NTRS1922

Influence of elliptical distribution of lift on strength of airplane wings

Hitherto it has been generally assumed, in calculating the fall of an airplane, that the forces withstood by the latter were distributed uniformly throughout the whole length of the wing. In reality this is not the case and German engineers in particular are now assuming an elliptical distribution of the forces. The latter hypothesis has made it possible to carry out a certain number of calculations which have been verified by experiment.

LIFT DISTRIBUITON, ELLIPTICAL - WINGS↗
DOE OSTI2021

Hyporheic Exchange in Sand Dunes Under a Freely Deforming River Water Surface

Bedform-driven hyporheic exchange is conditioned by the head gradients at the sediment-water interface. Local exchange phenomena between the surface and the subsurface are often driven by the dynamic forces related to the velocity distributions around sediment waves. In open channels, the static forces are represented by the water depth, yet most computational fluid dynamics models use a rigid-lid approximation. Here, we investigated whether and when the deformation of the river’s free-surface influences bedform-driven hyporheic exchange. This was done through simulations of coupled open channel and hyporheic flows with the air-water interface modeled either as a free-surface or a rigid-lid across increasing subcritical Froude numbers from ~0.05 to ~0.95. The normalized hyporheic flux was higher when considering free-surface deformation across most of the range of Froude numbers considered. When the Froude number was larger than 0.6 and smaller than 0.85, both hydrostatic and nonhydrostatic-driven fluxes increased significantly compared to the rigid-lid approach and the total flux was about five times that predicted with the rigid-lid. These results indicate that bedform-driven hyporheic fluxes are underestimated in most studies that use a rigid-lid assumption in subcritical flows.

58 GEOSCIENCES↗
NASA NTRS1987

Integrating nonlinear aerodynamic and structural analysis for a complete fighter configuration

The coupling of a nonlinear aerodynamics program with a structural analysis program to include the effects of static aeroelasticity in early preliminary design studies is described. A nonlinear, full potential aerodynamics method with capability to model geometric details of a complete aircraft in supersonic flow is used. The deflections of the lifting surfaces are calculated using an equivalent plate structural representation which can readily accommodate the changes in stiffness and geometric properties required during the preliminary design process. An iterative solution procedure is used to obtain consistent aerodynamic loads and structural deflections at the specified flight conditions. The volume of data transmitted between programs is minimized. The procedure is applied to a complete aircraft and the numerical results illustrate the aeroelastic effects on pressure distribution as well as total forces and moments. During this design study, the thickness distribution of the wing cover skins was initially sized based on rigid loads and subsequently resized under aeroelastic loads. Comparisons are made between these nonlinear aeroelastic results and results obtained from linear aerodynamic methods applied to a rigid shape during conceptual design studies.

Tatum, Kenneth E.↗
DOE OSTI2016

The GEWEX LandFlux project: Evaluation of model evaporation using tower-based and globally gridded forcing data

Determining the spatial distribution and temporal development of evaporation at regional and global scales is required to improve our understanding of the coupled water and energy cycles and to better monitor any changes in observed trends and variability of linked hydrological processes. With recent international efforts guiding the development of long-term and globally distributed flux estimates, continued product assessments are required to inform upon the selection of suitable model structures and also to establish the appropriateness of these multi-model simulations for global application. In support of the objectives of the Global Energy and Water Cycle Exchanges (GEWEX) LandFlux project, four commonly used evaporation models are evaluated against data from tower-based eddy-covariance observations, distributed across a range of biomes and climate zones. The selected schemes include the Surface Energy Balance System (SEBS) approach, the Priestley–Taylor Jet Propulsion Laboratory (PT-JPL) model, the Penman–Monteith-based Mu model (PM-Mu) and the Global Land Evaporation Amsterdam Model (GLEAM). Here we seek to examine the fidelity of global evaporation simulations by examining the multi-model response to varying sources of forcing data. To do this, we perform parallel and collocated model simulations using tower-based data together with a global-scale grid-based forcing product. Through quantifying the multi-model response to high-quality tower data, a better understanding of the subsequent model response to the coarse-scale globally gridded data that underlies the LandFlux product can be obtained, while also providing a relative evaluation and assessment of model performance. Using surface flux observations from 45 globally distributed eddy-covariance stations as independent metrics of performance, the tower-based analysis indicated that PT-JPL provided the highest overall statistical performance (0.72; 61 W m –2 ; 0.65), followed closely by GLEAM (0.68; 64 W m –2 ; 0.62), with values in parentheses representing the R 2 , RMSD and Nash–Sutcliffe efficiency (NSE), respectively. PM-Mu (0.51; 78 W m –2 ; 0.45) tended to underestimate fluxes, while SEBS (0.72; 101 W m –2 ; 0.24) overestimated values relative to observations. A focused analysis across specific biome types and climate zones showed considerable variability in the performance of all models, with no single model consistently able to outperform any other. Results also indicated that the global gridded data tended to reduce the performance for all of the studied models when compared to the tower data, likely a response to scale mismatch and issues related to forcing quality. Rather than relying on any single model simulation, the spatial and temporal variability at both the tower- and grid-scale highlighted the potential benefits of developing an ensemble or blended evaporation product for global-scale LandFlux applications. Hence, challenges related to the robust assessment of the LandFlux product are also discussed.

58 GEOSCIENCES↗
NASA NTRS1979

Wind tunnel force and pressure tests of a 21% thick general aviation airfoil with 20% aileron, 25% slotted flap and 10% slot-lip spoiler

Force and surface pressure distributions were measured for the 21% LS(1)-0421 modified airfoil fitted with 20% aileron, 25% slotted flap and 10% slot lip spoiler. All tests were conducted at a Reynolds number of 2.2 x 10 to the 6th power and a Mach number of 0.13. The lift, drag, pitching moments, control surface normal force and hinge moments, and surface pressure distributions are included in the results. Incremental performance of flap and aileron are discussed and compared to the GA(W)-2 airfoil. Spoiler control which shows a slight reversal tendency at high alpha, is examined.

Wentz, W. H., Jr.↗
NASA NTRS1981

Wind tunnel force and pressure tests

Force and surface pressure distributions were measured for a 13% medium speed (NASA MS(1)-0313) airfoil fitted with 20% aileron, 25% slotted flap and 10% slot lip spoiler. All tests were conducted in the Walter Beech Memorial Wind Tunnel at a Reynolds number of 2.2 million and a Mach number of 0.13. Results include lift, drag, pitching moments, control surface normal force and hinge moments, and surface pressure distributions. The basic airfoil exhibits low speed characteristics similar to the GA(W)-2 airfoil. Incremental aileron and spoiler performance are quite comparable to that obtained on the GA(W)-2 airfoil. Slotted flap performance on this section is reduced compared to the GA(W)-2, resulting in a highest c sub l max of 3.00 compared to 3.35 for the GA(W)-2.

Wentz, W. H., Jr.↗
DOE OSTI2015

Kinetic effects on double hysteresis in spin crossover molecular magnets analyzed with first order reversal curve diagram technique

In this paper, we analyze two types of hysteresis in spin crossover molecular magnets compounds in the framework of the First Order Reversal Curve (FORC) method. The switching between the two stable states in these compounds is accompanied by hysteresis phenomena if the intermolecular interactions are higher than a threshold. We have measured the static thermal hysteresis (TH) and the kinetic light induced thermal hysteresis (LITH) major loops and FORCs for the polycrystalline Fe(II) spin crossover compound [Fe{sub 1−x}Zn{sub x}(bbtr){sub 3}](ClO{sub 4}){sub 2} (bbtr = 1,4-di(1,2,3-triazol-1-yl)butane), either in a pure state (x = 0) or doped with Zn ions (x = 0.33) considering different sweeping rates. Here, we use this method not only to infer the domains distribution but also to disentangle between kinetic and static components of the LITH and to estimate the changes in the intermolecular interactions introduced by dopants. We also determined the qualitative relationship between FORC distributions measured for TH and LITH.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1993

Seasonal variation of surface and atmospheric cloud radiative forcing over the globe derived from satellite data

Global distributions of surface and atmospheric cloud radiative forcing parameters have been derived using parameterized radiation models with satellite meteorological data from the International Satellite Cloud Climatology Project, and directly measured top-of-atmosphere radiative fluxes from the Earth Radiation Budget Experiment. Specifically, shortwave, longwave, and total cloud forcing at the surface, and column-averaged values of longwave cloud forcing of the atmosphere were derived for the midseasonal months of April, July, and October 1985 and January 1986, covering a complete annual cycle. Seasonal variability is illustrated by comparing the results for July 1985 and January 1986, which represent the seasonal extremes. Surface shortwave cloud forcing is always negative, representing a cooling of the surface, with strongest cooling (-120 to -180 W/sq m) occurring over midlatitude storm tracks of the summer hemisphere. Surface longwave cloud forcing is always positive, representing a warming of the surface, with strongest warming (60 to 75 W/sq m) occurring over storm tracks of the winter hemisphere. Zonal averages show the entire summer hemisphere dominated by shortwave cooling, the middle and high latitudes of the winter hemisphere dominated by longwave warming, and a broad zone of transition in between. The globally averaged total cloud forcing amounts to a cooling throughout the year, ranging from a low of about -12 W/sq m for July 1985 to a high of about -25 W/sq m for January 1986. The longwave cloud forcing of the atmosphere shows a strong warming over deep convective regions in the tropics and a moderate cooling outside the tropics, amounting to a weak cooling (-2 to -5 W/sq m) in the global average. Comparisons of the results with general circulation model simulations show broad qualitative agreement regarding the locations of prominent warming and cooling regions. Quantitative comparisons, on the other hand, show significant differences between the magnitudes of warming and cooling in these regions. Most of the larger differences can be attributed to known deficiences of the general circulation model simulations. Comparisons with satellite-derived results of other investigators show much better agreement.

Gupta, Shashi K.↗
DOE OSTI2019

Dynamic phases, stratification, laning, and pattern formation for driven bidisperse disk systems in the presence of quenched disorder

Using numerical simulations, we examine the dynamics of driven two-dimensional bidisperse disks flowing over quenched disorder. The system exhibits a series of distinct dynamical phases as a function of applied driving force and packing fraction, including a phase-separated state as well as a smectic state with liquid-like or polycrystalline features. At low driving forces, we find a clogged phase with an isotropic density distribution, while at intermediate driving forces the disks separate into bands of high and low densities with either liquid-like or polycrystalline structure in the high-density bands. In addition to the density phase separation, we find that in some cases there is a fractionation of the disk species, particularly when the disk size ratio is large. The species phase-separated regimes form a variety of patterns such as large disks separated by chains of smaller disks. Here, our results show that the formation of laning states can be enhanced by tuning the ratio of disk radius of the two species, due to the clumping of small disks in the interstitial regions between the large disks. This system could be experimentally realized using sterically interacting colloidal particles suspended in a viscous fluid driven over random pinning arrays or granular matter suspended in fluid moving over a random landscape.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Ab Initio Computation of Charge Densities for Sn and Xe Isotopes

We present the first ab initio calculations for open-shell nuclei past the tin isotopic line, focusing on Xe isotopes as well as doubly magic Sn isotopes. We show that, even for moderately hard interactions, it is possible to obtain meaningful predictions and that the NNLO sat chiral interaction predicts radii and charge density distributions close to the experiment. We then make a new prediction for 100 Sn. This paves the way for ab initio studies of exotic charge density distributions at the limit of the present ab initio mass domain, where experimental data is becoming available. The present study closes the gap between the largest isotopes reachable by ab initio methods and the smallest exotic nuclei accessible to electron scattering experiments.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
NASA NTRS1986

Boundary force method for analyzing two-dimensional cracked bodies

The Boundary Force Method (BFM) was formulated for the two-dimensional stress analysis of complex crack configurations. In this method, only the boundaries of the region of interest are modeled. The boundaries are divided into a finite number of straight-line segments, and at the center of each segment, concentrated forces and a moment are applied. This set of unknown forces and moments is calculated to satisfy the prescribed boundary conditions of the problem. The elasticity solution for the stress distribution due to concentrated forces and a moment applied at an arbitrary point in a cracked infinite plate are used as the fundamental solution. Thus, the crack need not be modeled as part of the boundary. The formulation of the BFM is described and the accuracy of the method is established by analyzing several crack configurations for which accepted stress-intensity factor solutions are known. The crack configurations investigated include mode I and mixed mode (mode I and II) problems. The results obtained are, in general, within + or - 0.5 percent of accurate numerical solutions. The versatility of the method is demonstrated through the analysis of complex crack configurations for which limited or no solutions are known.

Tan, P. W.↗
NASA NTRS1988

Boundary force method for analyzing two-dimensional cracked plates

The Boundary Force Method (BFM) was formulated for the two-dimensional stress analysis of complex crack configurations. In this method, only the boundaries of the region of interest are modeled. The boundaries are divided into a finite number of straight-line segments, and at the center of each segment, concentrated forces and a moment are applied. This set of unknown forces and moments is calculated to satisfy the prescribed boundary conditions of the problem. The elasticity solution for the stress distribution due to concentrated forces and a moment applied at an arbitrary point in a cracked infinite plate are used as the fundamental solution. Thus, the crack need not be modeled as part of the boundary. The formulation of the BFM is described and the accuracy of the method is established by analyzing several crack configurations for which accepted stress-intensity factor solutions are known. The crack configurations investigated include mode I and mixed mode (mode I and II) problems. The results obtained are, in general, within + or - 0.5 percent of accurate numerical solutions. The versatility of the method is demonstrated through the analysis of complex crack configurations for which limited or no solutions are known.

Tan, Paul W.↗
DOE OSTI2019

Defect chemistry of Eu dopants in NaI scintillators studied by atomically resolved force microscopy

Activator impurities and their distribution in the host lattice play a key role in scintillation phenomena. In this work a combination of cross-sectional noncontact atomic force microscopy, x-ray photoelectron spectroscopy, and density-functional theory were used to study the distribution of Eu 2+ dopants in a NaI scintillator activated by 3% EuI 2 . A variety of Eu-based structures were determined in crystals subjected to different postgrowth treatments. Transparent crystals with good scintillation properties contained mainly small precipitates with a cubic crystal structure and a size below 4 nm. Upon annealing, Eu segregated toward the surface, resulting in the formation of an ordered hexagonal overlayer with a EuI 2 composition and a pronounced, unidirectional moiré pattern. Crystals with poor optical transparency showed a significant degree of mosaicity and the presence of precipitates. All observed crystals contained a very low concentration of Eu dopants present as isolated point defects; most of the europium was incorporated in larger structures.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗