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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 253 records · Page 14
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NASA NTRS1981

Computation of inverse magnetic cascades

Inverse cascades of magnetic quantities for turbulent incompressible magnetohydrodynamics are reviewed, for two and three dimensions. The theory is extended to the Strauss equations, a description intermediate between two and three dimensions appropriate to Tokamak magnetofluids. Consideration of the absolute equilibrium Gibbs ensemble for the system leads to a prediction of an inverse cascade of magnetic helicity, which may manifest itself as a major disruption. An agenda for computational investigation of this conjecture is proposed.

Montgomery, D.↗
NASA NTRS1982

Major disruptions, inverse cascades, and the Strauss equations

Current-carrying plasmas in a strong d.c. magnetic field are subject to violent disruptions above certain thresholds. At present difficult to verify, explanations are typically sought in terms of 'tearing modes'. An alternative explanation is in terms of inverse magnetic helicity cascades, generated from a variety of possible sources of small-scale MHD turbulence. Strongly anisotropic MHD plasmas may be described by the Strauss equations. Indications of turbulent inverse cascade behavior for the Strauss equations are sought, in parallel with earlier examples from MHD and fluid mechanics.

Montgomery, D.↗
NASA NTRS1983

A time-dependent approach for calculating steady inverse boundary-layer flows with separation

An unsteady inverse boundary-layer method is developed which can be used to calculate steady flows with separation. Two versions of Keller's box method with the Mechul function formulation developed by Cebeci (1976) are employed, depending on the complexity of the flow. The regular box is employed in regions of positive streamwise velocity component u, whereas the zigzag box is employed in regions where u becomes negative (t greater than 0). The regular box with the FLARE approximation is employed when t = 0 and u becomes negative in some region across the layer. Results of calculations show that the use of a time-dependent inverse boundary-layer method in which time is used as an iteration parameter provides a good approach in improving the accuracy of the solutions obtained from the FLARE approximation.

Cebeci, T.↗
NASA NTRS1983

Measurements of mantle wave velocities and inversion for lateral heterogeneity and anisotropy. I - Analysis of great circle phase velocities

The global lateral heterogeneity of the upper mantle is investigated using the classical Fourier-transform method of Sato(1958) and IDA/GDSN data from 25 1980 earthquakes. The great-circle phase velocities of 200 Love and 250 Rayleigh 100-330-sec-period fundamental-mode wave paths are determined and interpreted in terms of regional phase-velocity variation, using additional data on surface tectonics to extrapolate odd-harmonic information from the even-harmonic data. The results are presented in extensive tables, maps, and graphs. Regionalized inversion using the seven-region model of Okal (1977) is found to give maximum variance reductions of 65 percent for Love waves and 85 percent for Rayleigh waves, compared to 60 and 90 percent for l(max) = 2 inversion. Significant interregion differences are found in the regionalized Love-wave phase velocities.

Nakanishi, I.↗
NASA NTRS1984

Calibration or inverse regression: Which is appropriate for crop surveys using LANDSAT data?

Calibration and inverse regression estimators of crop proportions are investigated where the auxiliary variable is obtained from binary classification of multivariate LANDSAT data. The appropriate model relating classifier proportions and ground observed proportions for a given crop type is the calibration model. Under this model the inverse regression estimator is superior to the calibration estimator in estimating the crop acreage or proportion for a region of interest.

Chhikara, R. S.↗
NASA NTRS1985

Convex-profile Inversion of Asteroid Lightcurves

A lightcurve inversion method that yields a two-dimensional convex profile is introduced. The number of parameters that characterize the profile is limited only by the number of Fourier harmonics used to represent the parent lightcurve. The implementation of the method is outlined by a recursive quadratic programming algorithm, and its application to photoelectric lightcurves and radar measurements is discussed. Special properties of the lightcurves of geometrically scattering ellipsoids are pointed out, and those properties are used to test the inversion method and obtained a criterion for judging whether any lightcurve could actually be due to such an object. Convex profiles for several asteroids are shown, and the method's validity is discussed from a physical as well as purely statistical point of view.

Ostro, S. J.↗
NASA NTRS1985

An Indirect Role for Ethylene in Shoot-inversion Release of Apical Dominance in Pharbitis Nil

Evidence is presented which indicated that ethylene does not play a direct role in promoting or inhibiting bud outgrowth as a gravity response. It is concluded that the treatment of inactive or induced lateral buds with ethylene inhibitors or ethrel has no significant effect on bud outgrowth and that no changes occur in ethylene emanation in the Highest Lateral Bud (HLB) or HLB node following shoot inversion. Possible mechanisms by which ethylene released by shoot inversion may indirectly promote outgrowth of the HLB is presented.

Cline, M. G.↗
NASA NTRS1985

Least squares inversion of Stokes profiles in the presence of velocity gradients

The Auer, Heasley and House Stokes inversion procedure in use at High Altitude Observatory is based on the analytic solution of the equation of transfer for polarized light where the representation of the thermodynamic and magnetic structure of the atmosphere is assumed to have a high degree of invariance, namely, a Milne-Eddington (ME) structure with a constant magnetic field. In the presence of invariance breaking gradients the resultant Stokes profiles are represented only approximately, if at all, by analytic forms. The accuracy of the inversion parameters and their significance as measures of actual structure are explored for the ME and the Landman-Finn sunspot models under the effects of velocity gradients. The resulting field parameters are good to a few percent and prove to be insensitive to the errors committed by the use of a ME-representation, but the resulting ME parameters yield a less precise measure of thermal structure.

Skumanich, A.↗
NASA NTRS1984

Tomographic inversion of satellite photometry

An inversion algorithm capable of reconstructing the volume emission rate of thermospheric airglow features from satellite photometry has been developed. The accuracy and resolution of this technique are investigated using simulated data, and the inversions of several sets of observations taken by the Visible Airglow Experiment are presented.

Solomon, S. C.↗
NASA NTRS1985

Inversion problems in SAR imaging

Attention is given to two classes of SAR imaging inversion problems: fine resolution imagery of stationary scenes, and the imaging of a moving surface. Absolute scattering coefficient values are obtained from the output image by means of reference reflectors. The inversion of SAR data obtained from a moving surface requires consideration of motion effects in addition to those for the fixed scatterer; systematic displacements on a scale greater than the resolution result in azimuth shifts in the mapping of the scene onto the SAR image.

Larson, R. W.↗
NASA NTRS1986

Inverse design of axisymmetric flow passages using compressible viscous flow theory

A study reported by Yang and Hudson (1971) was extended by Nelson (1971), who presented a method of inverse design for axisymmetric diffusers. The diffusers obtained with the aid of this method were found to function well under certain conditions, while, for other cases, a modification of the analytical design procedure was required. An outline is provided of the method of inverse solution in simple axisymmetric internal flow passages. Attention is given to governing equations, the method of solution, and examples which illustrate the feasibility of the design procedure. The discussed method, which is based on viscous compressible flow theory, has some limitations. However, it is expected to yield good designs in many practical cases in which the existing design must be modified.

Ntone, F.↗
NASA NTRS1986

Inversion of limb radiance measurements - An operational algorithm

The limb radiance inversion radiometer (LRIR) and limb infrared monitor of the stratosphere (LIMS) experiments aboard the Nimbus 6 and 7 spacecraft have made observations of infrared emission by CO2, O3, H2O, HNO3, and NO2 at the earth's limb. This paper describes a method by which such measurements can be inverted to give vertical distributions of temperature and mixing ratios as functions of pressure. The simple and efficient approach was successfully applied to the LRIR data and subsequently in the initial assessment of the LIMS data. Inversion of synthetic data indicates the size of the errors to be expected as a result of the assumptions and instrumental errors. Retrievals of measured LIMS radiances are shown as examples and compared to in situ observations. The differences are comparable to those obtained with the more complex retrieval scheme used to process the LIMS archival products. Some problems are noted.

Bailey, P. L.↗
NASA NTRS1986

An inverse method for subcritical flows

An exact method is presented for two-dimensional subsonic flow within the limitations of the tangent gas approximation. While Woods (1961) studied these equations and proposed iterative methods for the solution of both the iterative and inverse problems, the inverse method here presented is noniterative and exact. It is shown that the direct Euler solution over the designed airfoil is very close to the input speed distribution, and that the constraints necessitated by upstream condition and closure requirements are easily incorporated.

Daripa, P. K.↗
NASA NTRS1986

Determining the general circulation of the ocean - A nonlinear inverse problem

The usual inversion procedures for determining the oceanic circulation take the density field as given. This does not explicitly account for the mismatch between the data (which are typically a single realization of the density field) and the circulation being estimated (which may be a time mean or some other smoothed quantity), but explicit consideration of the uncertainty of the density data renders the problem nonlinear, and new estimation methods have to be used. As an example, a nonlinear inversion is successfully applied here to the simple analytical model of Stommel and Veronis (1981). It is also shown that their linear procedure, if properly used, yields a much better result than they obtained.

Mercier, H.↗
NASA NTRS1986

ERBE data inversion

The Earth Radiation Budget Experiment (ERBE) involves the use of a system of three spacecraft with instrument packages for measuring the earth's radiation balance to an accuracy which has been unattainable in previous experiments. The experiment is to determine the monthly averaged radiant exitances at te 'top of the atmosphere' (TOA) over the earth with a resolution of 250 km. The realization of this goal requires the conduction of high accuracy measurements, and the computation of the instantaneous radiant exitances from these measurements. The operation involved in this computation is called an 'inversion'. A third requirement is related to the computation of the daily and monthly averaged regional values from the instantaneous values. A brief description is provided of the algorithms for the inversion of the measurements to TOA radiant exitances, taking into account also the techniques which are used to validate the methods and results.

Smith, G. L.↗
NASA NTRS1986

Inversion of 2 wavelength Lidar data for cloud properties

The inversion of the lidar equation to derive quantitative properties of the atmosphere has continued to present considerable difficulty. The results of a study in which Klett's procedure was utilized for the analysis of cloud backscatter measurements made simulataneously at two ruby lidar wavelengths (694nm,347nmm) are presented. With one lidar system a cloud is probed at the two wavelength and the backscatter measured simulataneously by separate receivers. As a result two sigma profiles which should differ only because the wavlength dependence of the scattering. Experimental data presented to demonstrate the effects and the implications of the applications of the inversion method will be discussed.

Pal, S. R.↗
NASA NTRS1987

Lewis inverse design code (LINDES): Users manual

The method of complex characteristics and hodograph transformation for the design of shockless airfoils was introduced by Bauer, Garabedian, and Korn and has been extended by the author to design subcritical and supercritical cascades with high solidities and large inlet angles. This new capability was achieved by introducing a new conformal mapping of the hodograph domain onto an ellipse and expanding the solution in terms of Chebyshev polynomials. A new computer code, the NASA Lewis inverse design code, was developed based on this idea. This new design code is an efficient method for the design of airfoils in cascade. In particular, the design of subcritical cascades of airfoils is a very fast, robust, and versatile process. The inverse design code can be made to interact with a turbulent boundary layer calculation to obtain airfoils with no separated flows at the design condition. This report is intended to serve as a users manual for this design code. Material previously reported by the author is included here for completeness and quick access to the user. The manual contains a description of the method followed by a discussion of the design procedure and examples. The input parameters necessary to run the code are then described and their default values given. Output listings corresponding to six different blade shapes designed with the code are given, as well as the necessary input data to reproduce the computer runs. The examples have been chosen to show that a wide range of applications can be covered with the code, ranging from supercritical propeller sections to wind tunnel turning vanes that can operate with a large inlet flow angle range.

Sanz, Jose M.↗
NASA NTRS1987

Inverse problems in the modeling of vibrations of flexible beams

The formulation and solution of inverse problems for the estimation of parameters which describe damping and other dynamic properties in distributed models for the vibration of flexible structures is considered. Motivated by a slewing beam experiment, the identification of a nonlinear velocity dependent term which models air drag damping in the Euler-Bernoulli equation is investigated. Galerkin techniques are used to generate finite dimensional approximations. Convergence estimates and numerical results are given. The modeling of, and related inverse problems for the dynamics of a high pressure hose line feeding a gas thruster actuator at the tip of a cantilevered beam are then considered. Approximation and convergence are discussed and numerical results involving experimental data are presented.

Banks, H. T.↗