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All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Similarity rule for sidewall boundary-layer effects in airfoil testing

The simplified form of the similarity rule for sidewall boundary layer effects presented envisions the generation of changes in both airfoil thickness and freestream Mach number by the sidewall boundary layer. Within the small-disturbance approximation, this approach encompasses the methods of both Barnwell (1980) and Sewall (1982), and can accordingly be applied at speeds ranging from the lowest to transonic Mach numbers.

Murthy, A. V.↗
NASA NTRS1992

Calculation of unsteady transonic flows with mild separation by viscous-inviscid interaction

This paper presents a method for calculating viscous effects in two- and three-dimensional unsteady transonic flow fields. An integral boundary-layer method for turbulent viscous flow is coupled with the transonic small-disturbance potential equation in a quasi-steady manner. The viscous effects are modeled with Green's lag-entrainment equations for attached flow and an inverse boundary-layer method for flows that involve mild separation. The boundary-layer method is used stripwise to approximate three-dimensional effects. Applications are given for two-dimensional airfoils, aileron buzz, and a wing planform. Comparisons with inviscid calculations, other viscous calculation methods, and experimental data are presented. The results demonstrate that the present technique can economically and accurately calculate unsteady transonic flow fields that have viscous-inviscid interactions with mild flow separation.

Howlett, James T.↗
NASA NTRS1992

An implicit Navier-Stokes code for turbulent flow modeling

This paper presents a numerical approach to calculating turbulent flows employing advanced turbulence models. The main features include a line-by-line Gauss-Seidel algorithm using Roe's approximate Riemann solver, TVD numerical schemes, implicit boundary conditions and a decoupled turbulence-model solver. Based on the problems tested so far, the method has consistently demonstrated its ability in offering accuracy, boundedness and a fast rate of convergence to steady-state solution.

Huang, P. G.↗
NASA NTRS1992

The disconnection event of 16.0 March 1986 in comet Halley

From kinematic extrapolation of tail/nucleus distance measurements on photographic images in the International Halley Watch (IHW) archive, we calculated the disconnection time of the 16-19 March 1986 event to be 16.0 (plus or minus 0.1) March. The solar wind conditions around Comet Halley at the time of the DE, inferred by corotation of IMP-8 satellite data to the comet, were such that (1) Comet Halley had just crossed the interplanetary magnetic field (IMF) sector boundary; (2) the solar wind density was approximately 8 cm(exp -3); (3) the solar wind speed was approximately 600 km/sec; (4) the IMF magnitude was approximately 8 nT. Given these conditions, we conclude that the most likely cause of the 16.0 March DE was front-side magnetic reconnection, as described in the model of Niedner and Brandt (1978).

Randall, Cora E.↗
NASA NTRS1993

Multiscale Morphological Filtering for Analysis of Noisy and Complex Images

Images acquired with passive sensing techniques suffer from illumination variations and poor local contrasts that create major difficulties in interpretation and identification tasks. On the other hand, images acquired with active sensing techniques based on monochromatic illumination are degraded with speckle noise. Mathematical morphology offers elegant techniques to handle a wide range of image degradation problems. Unlike linear filters, morphological filters do not blur the edges and hence maintain higher image resolution. Their rich mathematical framework facilitates the design and analysis of these filters as well as their hardware implementation. Morphological filters are easier to implement and are more cost effective and efficient than several conventional linear filters. Morphological filters to remove speckle noise while maintaining high resolution and preserving thin image regions that are particularly vulnerable to speckle noise were developed and applied to SAR imagery. These filters used combination of linear (one-dimensional) structuring elements in different (typically four) orientations. Although this approach preserves more details than the simple morphological filters using two-dimensional structuring elements, the limited orientations of one-dimensional elements approximate the fine details of the region boundaries. A more robust filter designed recently overcomes the limitation of the fixed orientations. This filter uses a combination of concave and convex structuring elements. Morphological operators are also useful in extracting features from visible and infrared imagery. A multiresolution image pyramid obtained with successive filtering and a subsampling process aids in the removal of the illumination variations and enhances local contrasts. A morphology-based interpolation scheme was also introduced to reduce intensity discontinuities created in any morphological filtering task. The generality of morphological filtering techniques in extracting information from a wide variety of images obtained with active and passive sensing techniques is discussed. Such techniques are particularly useful in obtaining more information from fusion of complex images by different sensors such as SAR, visible, and infrared.

Kher, A.↗
NASA NTRS1991

Flow of superfluid helium in tubes with heated walls

The equations for superfluid helium flowing through a straight tube with heated walls are integrated. The model equations are based on those of Landau as modified for superfluid turbulence by Gorter and Mellink (1949). The model is implemented by the program SUPERFLOW which runs on a personal computer. The effect of the heating level on the mass flux, the energy flux, and the pressure and temperature profiles is investigated. The four types of profiles which occur without sidewall heating are also found with heated walls. The progression through these four types is shown to depend primarily on the dimensionless parameter, defined previously to characterize the unheated profiles, and a dimensionless ratio of heat fluxes. The pressure and temperature maxima which rise well above the boundary values increase significantly with sidewall heating. Approximate design equations for estimating the mass flux and the profiles are presented. The physical basis of the results is discussed. These results are useful in the design of optimal cooling loops and other superfluid flow systems.

Snyder, H. A.↗
NASA NTRS1993

U-Pb provenance ages of shocked zircons from the K-T boundary, Raton Basin, Colorado

U-Pb isotopic systematics from analyses of single zircons identify at least two provenance ages, approximately 575 Ma and approximately 330 Ma, for zircons from the impact layer of the K-T boundary, Raton Basin, Colorado. These data are a preliminary confirmation of results reported from the same layer. The zircon provenance ages provide a unique signature for identification of the source crater since igneous rocks of these ages (or sedimentary rocks derived from them) must characterize part of the impact stratigraphy.

Premo, W. R.↗
NASA NTRS1994

Multigrid one shot methods for optimal control problems: Infinite dimensional control

The multigrid one shot method for optimal control problems, governed by elliptic systems, is introduced for the infinite dimensional control space. ln this case, the control variable is a function whose discrete representation involves_an increasing number of variables with grid refinement. The minimization algorithm uses Lagrange multipliers to calculate sensitivity gradients. A preconditioned gradient descent algorithm is accelerated by a set of coarse grids. It optimizes for different scales in the representation of the control variable on different discretization levels. An analysis which reduces the problem to the boundary is introduced. It is used to approximate the two level asymptotic convergence rate, to determine the amplitude of the minimization steps, and the choice of a high pass filter to be used when necessary. The effectiveness of the method is demonstrated on a series of test problems. The new method enables the solutions of optimal control problems at the same cost of solving the corresponding analysis problems just a few times.

Arian, Eyal↗
NASA NTRS1992

Analysis of stresses in finite anisotropic panels with centrally located cutouts

A method for analyzing biaxial- and shear-loaded anisotropic rectangular panels with centrally located circular and elliptical cutouts is presented in the present paper. The method is based on Lekhnitskii's complex variable equations of plane elastostatics combined with a boundary collocation method and a Laurent series approximation. Results are presented for anisotropic panels with elliptical cutouts and subjected to combined shear and compression loading. The effects on the stress field of panel aspect ratio, anisotropy, cutout size, and cutout orientation are addressed. Angle-ply laminates, unidirectional off-axis laminates, and ((+ or - 45/0/90)(sub 3))s, ((+ or - 45/0(sub 2))(sub 3))s, and ((+ or - 45/90(sub 2))(sub 3))s laminates are examined.

Britt, Vicki O.↗
NASA NTRS1995

Plane-wave analysis of solar acoustic-gravity waves: A (slightly) new approach

The plane-wave decomposition of the acoustic-gravity wave effects observed in the photosphere provides a computationally efficient technique that probes the structure of the upper convective zone and boundary. In this region, the flat sun approximation is considered as being reasonably accurate. A technique to be used for the systematic plane-wave analysis of Michelson Doppler imager data, as part of the solar oscillations investigation, is described. Estimates of sensitivity are presented, and the effects of using different planar mappings are discussed. The technique is compared with previous approaches to the three dimensional plane-wave problem.

Bogart, Richard S.↗
NASA NTRS1997

Reentry-F Flowfield Solutions at 80,000 ft.

Three equilibrium-air numerical solutions are presented for the Reentry-F flight-test vehicle at Mach 20, 80,000 Ft. conditions, including turbulent flow predictions. The three solutions are from a thin-layer Navier-Stokes code, coupled thin-layer and parabolized Navier-Stokes codes, and an approximate viscous shock-layer code. Boundary-layer and shock-layer profiles are presented and compared between the three solutions, revealing close agreement between the three solution methods. Notable exceptions to the close agreement, with 7-10 percent discrepancies, occur in the density profiles at the boundary-layer edge, in the boundary-layer velocity profiles, and in the shock-layer profiles in regions influenced by the nose bluntness.

Wood, William A.↗
NASA NTRS1998

Analysis of Daily, Seasonal, and Interannual Changes in Hofsjokull Ice Cap, Iceland, using Satellite Data

Analysis of a time series of European Remote Sensing Satellite (ERS)-1 and -2, RADARSAT ScanSAR synthetic aperture radar (SAR) and Landsat images from 1973 to 1998, shows daily to interannual changes in Hofsjokull, a 923 sq km ice cap in central Iceland. A digital elevation model of Hofsjokull was constructed using interferometry, and then SAR backscatter coefficient (d) was plotted with elevation, and air temperature along a transect across the ice cap. Most of the a' changes measured along the transect are caused by a change in the state (frozen or thawed) of the surficial snow or ice when air temperature rises above or below about -5 to O C. Seasonal (sigma)deg patterns are identified in a 4-year time series of 57 ERS-1 and -2 images. In addition, June 1997 ScanSAR images display rapid changes in brightness that are tied closely to daily meteorological events. SAR and Landsat data were also used to measure changes in the areal extent of Hofsjokull, from 1973 to 1997, and to locate (sigma)deg and reflectance boundaries that relate to the glacier facies. Late-summer 1997 (sigma)deg and reflectance boundaries agree and are coincident with the approximate location of the fim line, and the January 1998 position of the equilibrium line as determined from ERS-2 data.

Hall, D. K.↗
NASA NTRS2000

Accuracy Improvement in Magnetic Field Modeling for an Axisymmetric Electromagnet

This paper examines the accuracy and calculation speed for the magnetic field computation in an axisymmetric electromagnet. Different numerical techniques, based on an adaptive nonuniform grid, high order finite difference approximations, and semi-analitical calculation of boundary conditions are considered. These techniques are being applied to the modeling of the Variable Specific Impulse Magnetoplasma Rocket. For high-accuracy calculations, a fourth-order scheme offers dramatic advantages over a second order scheme. For complex physical configurations of interest in plasma propulsion, a second-order scheme with nonuniform mesh gives the best results. Also, the relative advantages of various methods are described when the speed of computation is an important consideration.

Ilin, Andrew V.↗
NASA NTRS1961

The General Equations of Equilibrium of Rotationally Symmetric Membranes and some Static Solutions for Uniform Centrifugal Loading

The general equations of equilibrium of a rotationally symmetrical body undergoing large arbitrary deflections but small strains are derived by means of the principle of virtual work. All deflections are referred to a reference surface which, in general, may be taken to coincide with any intermediate state of the membrane. Static solutions of the general equations for steadily rotating membranes are considered for the cases in which the final or the initial configuration of the membrane is specified. For problems in which the final configuration is specified, conditions are given under which such a configuration is obtainable from a stress-free initial state. Such conditions being satisfied, it is shown that the stresses and radial displacements are determinate while axial displacements may be obtained by quadrature. For problems in which the initial configuration is given, the determination of the stresses and deflections is reduced to the solution of a second-order nonlinear differential equation for a stress function. An approximate method of solution based on boundary-layer considerations is presented for the case of a spinning sphere of constant thickness. Specific examples are given for both classes of problems.

Simmonds, James G.↗
NASA NTRS2019

On the Calculation of Exact Cumulative Distribution Statistics for Burgers Equation

A mathematical procedure is presented for the calculation of exact cumulative distribution statistics for a viscosity-free variant of Burgers nonlinear partial differential equation (PDE) in one space dimension and time subject to sinusoidal initial data with uncertain (random variable) amplitude or phase shift. Analytical solutions of nonlinear PDEs with uncertain initial and/or boundary data are invaluable benchmarks in assessing approximate uncertainty quantification techniques. The Burgers equation solution with uncertain initial data results in nonsmooth solution behavior in both physical and random variable dimensions which provides a severe test for approximate uncertainty quantification techniques. Mathematical proofs are provided to verify that exact cumulative distribution statistics can be systematically and robustly obtained for all forward time.

Burgers↗
NASA NTRS2020

The Role of Oceanic Processes in the Initiation of Boreal Winter Intraseasonal Oscillations Over the Indian Ocean

Observational analyses and ocean general circulation model experiments were performed to understand the influence of oceanic processes on warm sea surface temperature anomalies (SSTAs) prior to convection initiation of boreal winter intraseasonal oscillations (ISOs), including the Madden‐Julian Oscillation (MJO), in the tropical Indian Ocean. We found 39 strong ISOs that passed over the Indian Ocean Warm Pool (WP) region during the November–April season of the 2001–2012 period. Seventeen of them (44%) initiated over the Seychelles‐Chagos Thermocline Ridge (SCTR) before propagating eastward to the WP and Maritime Continent. Including only global‐scale MJOs, 71% (24%) of the remaining MJO events initiated from the SCTR (WP). Four (seven) SCTR (WP) ISO events were preceded by SSTAs that were strongly influenced by wind stress‐driven oceanic processes; all four (2/7) SCTR (WP) events were MJOs. Composite analyses of the four oceanic process influenced SCTR MJO events showed that wind stress‐driven oceanic processes contributed about 30% (between 0.1 and 0.2 °C) of the preconvection warming in the SCTR, which coincides with the Intertropical Convergence Zone with mean SST > 28 °C. Reduced upwelling and entrainment played a more important role than horizontal advection in elevating the +SSTAs. Case studies revealed that the two ocean process‐influenced primary MJO SCTR events were also associated with oceanic equatorial Rossby waves. Furthermore, results of a linear atmospheric mixed layer model indicated that boundary layer processes related to SSTAs contributed approximately half of the total convergence during MJO initiation, relative to the effect of the free troposphere, for the Rossby wave‐influenced events.

MJO Initiation↗
NASA NTRS1985

Symposium on Numerical and Physical Aspects of Aerodynamic Flows, 3rd, California State University, Long Beach, CA, January 21-24, 1985, Proceedings

Among the topics discussed are hydrodynamic stability and turbulent transition, separated flow simulations employing finite difference methods, a quasi-simultaneous finite difference approach for strongly interacting flow, the Newton solution of coupled Euler and boundary layer equations, multielement airfoil aerodynamics, vorticity dynamics, the significance of the thin layer Navier-Stokes approximation, a comparison of interactive and Navier-Stokes calculations of separating boundary layer flows, and a Navier-Stokes analysis for the mechanism of shock wave/boundary layer interactions. Also discussed are transonic interactions of unsteady vortical flows, boundary layers on oscillating airfoils, a laser-interferometer skin friction meter, flow over surface-mounted semibluff bodies, computations for spinning and spin-stabilized supersonic projectiles, transition calculations in three-dimensional flows, the effect of projectile boattailing in transonic flow, flow characteristics of a body of revolution at incidence, the influence of the boundary layer on the leading edge flow of a swept wing, and an interactive scheme for three-dimensional transonic flows.

Source record↗
NASA NTRS1983

The detection of X rays from Jupiter

X rays in the energy band 0.2-3.0 keV have been detected coming from both polar regions of Jupiter. The observations were made in 1979 and 1981 by using the imaging proportional counter and high resolution imaging detectors on the Einstein X-ray astronomy satellite. The measured flux density of approximately 0.0006/sq cm-sec at earth corresponds to an X ray luminosity of approximately 4 x 10 to the 9th W in the 0.2- to 3.0-keV energy band. The energy spectrum of the X rays is extremely soft and can be characterized by a power law with an exponent of approximately 2.3. Detector energy resolution is insufficient to distinguish a soft line spectrum from a continuum. However, the shape of the response and the observed X ray power indicate that the source of this auroral emission is not electron bremsstrahlung as on the earth, but is most probably line emission from O and S ions with energies between 0.03 and 4.0 MeV/nucleon precipitating from the outer boundary of the Io plasma torus at L approximately 8.

Metzger, A. E.↗