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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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Wave theory of turbulence in compressible media

An acoustical theory of turbulence was developed to aid in the study of the generation of sound in turbulent flows. The statistical framework adopted is a quantum-like wave dynamical formulation in terms of complex distribution functions. This formulation results in nonlinear diffusion-type transport equations for the probability densities of the five modes of wave propagation: two vorticity modes, one entropy mode, and two acoustic modes. This system of nonlinear equations is closed and complete. The technique of analysis was chosen such that direct applications to practical problems can be obtained with relative ease.

Kentzer, C. P.↗
NASA NTRS1977

Aircraft equipment

The complex of functionally interconnected instruments and devices for controlling flight, engine operations, electrical systems, communications, and vital systems for passengers and crew is described. The aggregates of the aircraft automatic equipment are also discussed.

Source record↗
NASA NTRS1979

Orbital heat rate package

Package consisting of three separate programs used to accurately predict temperature distribution of spacecraft in planetary orbit is invaluable tool for design and analysis of other structures that must function in complex thermal environment.

Lovin, J. K.↗
NASA NTRS1978

An exact derivation of contact resistance to planar devices

A mixed boundary-value problem is formulated for an imperfect rectangular contact to a semiconducting sheet (layer). An exact model for derivation of contact resistance is developed and its solution by conformal mapping and eigenfunction expansion is presented. The expression for contact resistance is similar to that for a perfect (lossless) contact but includes an additional term containing the lowest-order coefficient in the infinite series expansion of the complex potential function. The calculated contact resistances are compared with those obtained from three approximate models: lossless contact, transmission line, and extended transmission line models. The extended transmission line model appears to be a very satisfactory approximation provided the ratio of contact length to sheet thickness is no less than 0.5.

Schuldt, S. B.↗
NASA NTRS1978

An analysis of delamination in angle-ply fiber reinforced composites

An analytical investigation of the mechanics and failure modes of delamination initiated from a service-induced surface flaw in angle-ply fiber reinforced composites is presented. The analysis employs a hybrid-stress finite element method including a crack-tip singular element with its field variables expressed by Muskhelishvili's complex stress functions. Solutions are obtained for delaminated composites with various laminate parameters. The results elucidate unique and important characteristics of delamination crack-tip response and interlaminar stress transfer mechanisms. Of particular interest are the mixed-mode stress intensity factors associated with the delamination crack. The influence of ply orientation on KI and KII and their effects on subsequent crack extension are discussed.

Wang, S. S.↗
NASA NTRS1979

An impulse test technique with application to acoustic measurements

A method has been presented for measuring the acoustic properties of an absorbent material and a duct/nozzle system (with or without airflow) using a high voltage spark discharge as an impulse source of sound. The cross-spectra of the incident, reflected and transmitted acoustic pressure transients are analyzed by way of a FFT digital processor in the form of complex transfer functions. These transfer functions have a direct relationship to the termination impedance and radiation directivity. The impulse method has been justified by comparisons, with data obtained from existing methods (both experimental and theoretical), that show excellent agreement. Reflection coefficients and radiation impedances of various duct-nozzle systems and their associated far-field directivities are also presented as some of the applications of the impulse technique.

Salikuddin, M.↗
NASA NTRS1979

Programs for high-speed Fourier, Mellin and Fourier-Bessel transforms

Several FORTRAN program modules for performing one-dimensional and two-dimensional discrete Fourier transforms, Mellin, and Fourier-Bessel transforms are described along with programs that realize the algebra of high speed Fourier transforms on a computer. The programs can perform numerical harmonic analysis of functions, synthesize complex optical filters on a computer, and model holographic image processing methods.

Ikhabisimov, D. K.↗
NASA NTRS1980

The sensitivity of a very long baseline interferometer

The theoretical sensitivity of various methods of acquiring and processing interferometer data are compared. It is shown that for a fixed digital recording capacity one bit quantization of single sideband data filtered with a rectangular bandpass and sampled at the Nyquist rate yields the optimum signal to noise ratio. The losses which result from imperfect bandpass, poor image rejection, approximate methods of fringe rotation, fractional bit correction, and loss of quadrature are discussed. Also discussed is the use of the complex delay function as a maximum likelihood fringe estimator.

Rogers, A. E. E.↗
NASA NTRS1979

Boundary layer thermal stresses in angle-ply composite laminates

Boundary-layer thermal stress singularities and distributions of angle-ply composite laminates under uniform thermal loading are investigated through a system of sixth-order governing partial differential equations developed with the aid of the anisotropic elasticity field equations and Lekhnitskii's complex stress functions. Results are presented for cases of various angle-ply graphite/epoxy laminates, and it is shown that the boundary-layer thickness depends on the degree of anisotropy of each individual lamina, thermomechanical properties of each ply, and the relative thickness of adjacent layers.

Wang, S. S.↗
NASA NTRS1980

An analysis of delamination in angle-ply fiber-reinforced composites

A study of the mechanics and failure modes of delamination initiated from a surface flaw in angle-ply fiber-reinforced composites is presented. The analysis employs a hybrid-stress finite-element method including a crack-tip singular element with its field variables expressed by Muskhelishvili's complex stress functions. Solutions are obtained for the delaminated composites with various laminate parameters. The results elucidate unique and important characteristics of delamination crack-tip response and interlaminar stress transfer mechanisms. Of particular interest are the mixed-mode stress-intensity factors associated with the delamination crack. The influence of ply orientation on KI and KII and their effects on subsequent crack extension are discussed.

Wang, S. S.↗
NASA NTRS1982

Inter-image matching

Interimage matching is the process of determining the geometric transformation required to conform spatially one image to another. In principle, the parameters of that transformation are varied until some measure of some difference between the two images is minimized or some measure of sameness (e.g., cross-correlation) is maximized. The number of such parameters to vary is faily large (six for merely an affine transformation), and it is customary to attempt an a priori transformation reducing the complexity of the residual transformation or subdivide the image into small enough match zones (control points or patches) that a simple transformation (e.g., pure translation) is applicable, yet large enough to facilitate matching. In the latter case, a complex mapping function is fit to the results (e.g., translation offsets) in all the patches. The methods reviewed have all chosen one or both of the above options, ranging from a priori along-line correction for line-dependent effects (the high-frequency correction) to a full sensor-to-geobase transformation with subsequent subdivision into a grid of match points.

Wolfe, R. H., Jr.↗
NASA NTRS1982

On the modelling and simulation of the dynamics and control of large flexible orbiting systems

This paper attempts to review the steps involved in the development of mathematical models that can be used to simulate the in-orbit dynamics of large flexible systems. The use of graph theoretic techniques can often be used to reduce the computational effort involved for calculating the eigenvalues of large ordered systems. Computer generated graphical techniques may provide additional insight into the understanding of elastic modal shape functions of complex systems. Finally the numerical techniques commonly used to develop shape and attitude control laws will be briefly reviewed.

Bainum, P. M.↗
NASA NTRS1982

The Clark Lake Teepee-Tee telescope

A new, fully steerable, decametric array for radio astronomy has been built at the Clark Lake Radio Observatory near Borrego Springs, California. This array is a 'T' of 720 conical spiral (teepee-shape) antennas, 3.0 km by 1.8 km. It is capable of operating between 15 and 125 MHz but has best sensitivity in the 25 to 75 MHz range. Both its operating frequency and beam position are adjustable in about 1 msec. A 1024-channel digital correlator has been built and attached to the array. This permits the simultaneous measurement of the complex visibility functions on 512 interferometer baselines between various portions of the array. After Fourier transformation these visibility data yield a 32 x 32 resolution element picture of the area of sky under observation, with frequency-dependent angular resolution ranging from 20 to 2.7 arcsec and a sensitivity of 1 Jy per beam. This system is described, and some initial observations are presented.

Erickson, W. C.↗
NASA NTRS1984

A model of asynchronous iterative algorithms for solving large, sparse, linear systems

Solving large, sparse, linear systems of equations is one of the fundamental problems in large scale scientific and engineering computation. A model of a general class of asynchronous, iterative solution methods for linear systems is developed. In the model, the system is solved by creating several cooperating tasks that each compute a portion of the solution vector. This model is then analyzed to determine the expected intertask data transfer and task computational complexity as functions of the number of tasks. Based on the analysis, recommendations for task partitioning are made. These recommendations are a function of the sparseness of the linear system, its structure (i.e., randomly sparse or banded), and dimension.

Reed, D. A.↗
NASA NTRS1983

Microwave holographic surface measurement of the Tidbinbilla 64-m antenna

The use of a holographic technique for accurately measuring the surface figure of the Tidbinbilla (Canberra, Australia) 64-m antenna is described. Described by Bennet et al. (1976) and Scott and Ryle (1977), the technique consists of measuring the complex far-field response of the antenna at a single frequency using a terrestrial, satellite-borne or celestial radiation source of small angular diameter. This two-dimensional pattern is then Fourier transformed to yield the complex illumination function across the antenna aperture; antenna surface deviations are manifested as phase fluctuations in this function. The speed and low cost of using the technique are real advantages where observing schedules with the telescopes are heavily subscribed. For the 64-m antenna, the unweighted rms surface deviation is found to be about 1.8 mm; when weighted by the radial amplitude taper it is about 1.1 mm. Two earlier estimates by other methods had yielded tolerances of about 1.2 mm rms and 1.1 mm rms. It is planned to use the technique to survey the 22-m antennas of the Australian Telescope accurate to approximately 0.1 mm rms near 10 Ghz.

Rahmat-Samii, Y.↗
NASA NTRS1985

Spectral properties of water ice and contaminants

For remote sensing studies of ices in the solar system, it is important to understand the optical properties of water ice, and mixtures of ice and particulate materials. The present paper has the objective to review the current understanding of the spectral properties of ice, and mixtures of ice and particulates. The review is to provide a basis for the understanding of the remote sensing of ice. It is found that reflectance spectra of ice-soil intimate mixtures are complex, nonlinear functions of the optical and physical properties of the components which comprise the surface.

Lucey, P. G.↗
NASA NTRS1985

Autoionization: Recent developments and applications

Among the topics discussed are: theory of resonance and autoionization of two-electron atoms and ions; projection and quasi-projection operators for electron impact resonances on many-electron atomic targets; and hole projection methods for calculating Feshbach resonances and inner-shell vacancies. Consideration is also given to: complex stabilization methods; complex coordinate and complex basis function calculations; and the variational principle. The application of autoionization calculations to solar and astrophysical plasma diagnostics is also discussed in detail.

Temkin, A.↗