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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 1,297 records · Page 72
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

Gravity-gradient measurements down to approximately 100-km height by means of long-tethered satellites

Long-tethered satellite systems for Shuttle flights would make measurements of the earth's gravitational field possible to a spatial resolution approaching 100 km. For instance, a subsatellite carrying a gravity gradiometer could be made to orbit at a height of 110 km by means of a 110-km tether tied to the Shuttle in a 220-km orbit. Even with an overall instrument sensitivity as poor as 1 Eotvos unit (e.u.), it would be possible to measure spatial wavelengths of approximately 600 to 700 km (i.e., harmonics of 80th to 70th degree). Also, a system of two satellites (one of which could be the Shuttle orbiter or one of its payloads) connected by a tether a few tens of kilometers long could provide a simple and sensitive means of detecting gravity anomalies characterized by wavelengths of a few hundred kilometers. In this system, the observable would be the mechanical tension on the tether, and a sensitivity up to 0.01 e.u. could be attained, provided the two satellites are tracked from the ground with sufficient accuracy.

Colombo, G.↗
NASA NTRS1976

The diffusion approximation. An application to radiative transfer in clouds

It is shown how the radiative transfer equation reduces to the diffusion equation. To keep the mathematics as simple as possible, the approximation is applied to a cylindrical cloud of radius R and height h. The diffusion equation separates in cylindrical coordinates and, in a sample calculation, the solution is evaluated for a range of cloud radii with cloud heights of 0.5 km and 1.0 km. The simplicity of the method and the speed with which solutions are obtained give it potential as a tool with which to study the effects of finite-sized clouds on the albedo of the earth-atmosphere system.

Arduini, R. F.↗
NASA NTRS1976

Numerical and approximate solution of the high Reynolds number small separation problem

Several possible methods of solving the small separation problem at high Reynolds number are investigated. In addition to using analytical methods, there are several numerical approaches which are used. High Reynolds number laminar two dimensional problems are used for simplicity. A brief discussion is given of the finite difference methods since these methods are discussed in detail. Most of the emphasis is placed on developing an approximate integral method. As a model problem the supersonic compression ramp problem is chosen since several numerical solutions along with experimental data are available. The techniques discussed are modified and applied to other similar type wall geometries.

Davis, R. T.↗
NASA NTRS1976

Longitudinal aerodynamic characteristics of 45 deg swept wings at Mach approximately 0

Wind tunnel tests were conducted in the Langley 7 x 10 foot wind tunnel at Mach numbers less than 0.20 and at Reynolds numbers less than 3.74 million. The effect of the aft area on the 45 deg swept wing longitudinal aerodynamic characteristics at low subsonic speeds and at an angle of attack range from approximately -2 deg to 28 deg was studied. The data are presented without analysis.

Lamar, J. E.↗
NASA NTRS1976

Wave refraction diagrams for the Baltimore Canyon region of the mid-Atlantic continental shelf computed by using three bottom topography approximation techniques

The Langley Research Center and Virginia Institute of Marine Science wave refraction computer model was applied to the Baltimore Canyon region of the mid-Atlantic continental shelf. Wave refraction diagrams for a wide range of normally expected wave periods and directions were computed by using three bottom topography approximation techniques: quadratic least squares, cubic least squares, and constrained bicubic interpolation. Mathematical or physical interpretation of certain features appearing in the computed diagrams is discussed.

Poole, L. R.↗
NASA NTRS1977

Implicit approximate-factorization schemes for the efficient solution of steady transonic flow problems

Implicit approximate-factorization algorithms (AF) are developed for the solution of steady-state transonic flow problems. The performance of the AF solution method is evaluated relative to that of the standard solution method for transonic flow problems, successive line over-relaxation (SLOR). Both methods are applied to the solution of the nonlinear, two-dimensional transonic small-disturbance equation. Results indicate that the AF method requires substantially less computer time than SLOR to solve the nonlinear finite-difference matrix equation for a transonic flow field. This increase in computational efficiency is achieved with no appreciable increase in computer storage or coding complexity.

Ballhaus, W. F.↗
NASA NTRS1977

The application of the Routh approximation method to turbofan engine models

The Routh approximation technique is applied in the frequency domain to a 16th order state variable turbofan engine model. The results obtained motivate the extension of the frequency domain formulation of the Routh method to the time domain to handle the state variable formulation directly. The time domain formulation is derived, and a characterization, which specifies all possible Routh similarity transformations, is given. The characterization is computed by the solution of two eigenvalue eigenvector problems. The application of the time domain Routh technique to the state variable engine model is described, and some results are given.

Merrill, W. C.↗
NASA NTRS1977

Observations on approximate integrations

A class of integration strategies is explored that fall in between the two extremes of symbolic integration and numerical quadrature, which are, respectively, aimed at the computer generation of answers in the form of exact expressions and numerical values. The theoretical advances in symbolic integration are discussed. Three major contexts of applications with attendant case studies, four possible types of strategies for approximate integration are examined. The feasibility and adequacy (or inadequancy) of MACSYMA for implementing these strategies are considered.

Ng, E. W.↗
NASA NTRS1976

An approximate spin design criterion for monoplanes, 1 May 1939

An approximate empirical criterion, based on the projected side area and the mass distribution of the airplane, was formulated. The British results were analyzed and applied to American designs. A simpler design criterion, based solely on the type and the dimensions of the tail, was developed; it is useful in a rapid estimation of whether a new design is likely to comply with the minimum requirements for safety in spinning.

Seidman, O.↗
NASA NTRS1977

Multimodal far-field acoustic radiation pattern: An approximate equation

The far-field sound radiation theory for a circular duct was studied for both single mode and multimodal inputs. The investigation was intended to develop a method to determine the acoustic power produced by turbofans as a function of mode cut-off ratio. With reasonable simplifying assumptions the single mode radiation pattern was shown to be reducible to a function of mode cut-off ratio only. With modal cut-off ratio as the dominant variable, multimodal radiation patterns can be reduced to a simple explicit expression. This approximate expression provides excellent agreement with an exact calculation of the sound radiation pattern using equal acoustic power per mode.

Rice, E. J.↗
NASA NTRS1977

Electron-impact excitation of carbon and silicon in the distorted-wave approximation

The 3P to 1D electron-impact excitation cross section within the ground configuration of both neutral carbon and silicon is calculated in the distorted-wave approximation of the two-state Hartree-Fock coupled equations. An essential element of the present treatment is that orthogonality to core orbitals is not assumed in deriving equations for the scattering orbitals. A local adiabatic polarization potential is also added to the distorted-wave equations. Both elements are necessary in getting good agreement with close-coupling results for carbon to low impacting energies. The agreement is sufficiently good that predictions for silicon should be accurate to within a factor of 2.

Pindzola, M. S.↗
NASA NTRS1976

On the computational cost of approximating and recognizing noise-perturbed straight lines and quadratic arcs in the plane

Recognition of underlying straight lines and quadratic arcs in line drawings, and approximation of very noisy data by such line/curve segments, is addressed as a subproblem of the more general problem of optimum recognition of complicated line/curve drawings. Some specific algorithms are presented with extensions and interpretations for more complicated applications, and a data generation model is developed for the problem. Data are generated as a perturbation of a single underlying straight line or an elliptic or hyperbolic arc. Recursive estimation techniques, minimization of central processing unit time, decision making with controlled error probabilities, and modeling and recognition of pictures consisting of noisy curves are dealt with. Applications envisaged include: picture data compression, contour line representation in maps, intelligent data searches, and ballistic missile decoy tracking.

Cooper, D. B.↗
NASA NTRS1977

Remarks on entropy production in the one-dimensional approximation to unsteady flow in combustion chambers

The treatment of unsteady flows in a combustion chamber is discussed. As an example a rocket motor is considered, where material enters through a lateral boundary with its stagnation enthalpy different from the average speed. The equations of motion for unsteady flow within a one-dimensional approximation are analyzed, and the production of entropy is deduced. In the equations, the term representing the dissipative processes are identified by constructing a representation for the production of entropy.

Culick, F. E. C.↗
NASA NTRS1977

Electron-impact excitation of O III in the distorted-wave approximation

The 3P - 1D electron-impact excitation cross section within the ground configuration of doubly ionized oxygen is calculated in the distorted-wave approximation. An essential element of the present treatment is that orthogonality is not assumed between core and scattering orbitals of the same angular symmetry. Resonance structures are included through the use of quantum-defect theory. Near threshold the effect of an isolated autoionization resonance in the dominant 2D(0) partial wave is found to be important, in agreement with previous close-coupling results.

Pindzola, M. S.↗
NASA NTRS1977

Approximate method for calculating free vibrations of a large-wind-turbine tower structure

A set of ordinary differential equations were derived for a simplified structural dynamic lumped-mass model of a typical large-wind-turbine tower structure. Dunkerley's equation was used to arrive at a solution for the fundamental natural frequencies of the tower in bending and torsion. The ERDA-NASA 100-kW wind turbine tower structure was modeled, and the fundamental frequencies were determined by the simplified method described. The approximate fundamental natural frequencies for the tower agree within 18 percent with test data and predictions analyzed.

Das, S. C.↗
NASA NTRS1978

Approximate analytic solutions for the optical pumping of fluorescent dyes

A general technique for solving a system of rate equations describing the interaction of an electromagnetic field and a molecular system is presented. The method is used to obtain approximate time-dependent solutions for the upper-level population of fluorescent dyes in the presence of a pump field.

Lawandy, N. M.↗