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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 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

A low-cost solar-cell front contact using trapped silver mesh and electrostatic bonding

A new system to provide a contact with a silver mesh trapped between the cell and an encapsulating glass cover is described. Borosilicate glass is joined to the cell by electrostatic bonding during which the glass is deformed around the silver mesh to form a permanent optically coupled integral bond to the cell. The hermetic seal prevents the silver from oxidizing and destroying the electrical contact formed during the bonding process. It is demonstrated that electrostatic glass/silicon bonds have excellent stability under a variety of accelerated environmental tests. Electrostatic bonds to thin films of AL2O3, Ta2O5, and ZrO2 on glass can be used to make antireflective coatings for solar cells manufactured by this process. Test solar cells were manufactured by electrostatic bonding with good curve fill factors and efficiencies of 10 percent.

Landis, Geoffrey A.↗
NASA NTRS1970

Code CUGEL: A code to unfold Ge(Li) spectrometer polyenergetic gamma photon experimental distributions

A FORTRAN code was developed for the Univac 1108 digital computer to unfold lithium-drifted germanium semiconductor spectrometers, polyenergetic gamma photon experimental distributions. It was designed to analyze the combination continuous and monoenergetic gamma radiation field of radioisotope volumetric sources. The code generates the detector system response matrix function and applies it to monoenergetic spectral components discretely and to the continuum iteratively. It corrects for system drift, source decay, background, and detection efficiency. Results are presented in digital form for differential and integrated photon number and energy distributions, and for exposure dose.

Steyn, J. J.↗
NASA NTRS1972

Prediction of unsteady aerodynamic loadings caused by trailing edge control surface motions in subsonic compressible flow: Analysis and results

A theoretical analysis and a computer program have been developed for the prediction of unsteady lifting surface loadings caused by motions of trailing edge control surfaces having sealed gaps. The final form of the downwash integral equation has been formulated by isolating the singularities from the non-singular terms and establishing a preferred solution process to remove and evaluate the downwash discontinuities in a systematic manner. Comparisons of theoretical and experimental pressure data are made for several control surface configurations. The comparisons indicate that reasonably accurate theoretical pressure distributions and generalized forces may be obtained for a wide variety of control surface configurations. Spanwise symmetry or antisymmetry of motion, and up to four control surfaces on each half span can be accommodated.

Rowe, W. S.↗
NASA NTRS1973

Time-split finite-volume method for three-dimensional blunt-body flow

An efficient numerical method for calculating plane, axisymmetric, and fully three-dimensional blunt-body flow is presented. It is a second-order-accurate, time-dependent finite-volume procedure that solves the Euler equations in integral conservation-law form. These equations are written with respect to a Cartesian coordinate system in which an embedded mesh adjusts in time to the motion of the bow shock that is automatically captured as part of the weak solution. With such an adjusting mesh, oscillations in flow properties near the shock are shown to be virtually eliminated. The scheme uses a time-splitting concept that accelerates the convergence appreciably. Comparisons are made between computed and experimental results.

Rizzi, A. W.↗
NASA NTRS1975

Prediction of unsteady aerodynamic loadings caused by leading edge and trailing edge control surface motions in subsonic compressible flow: Analysis and results

A theoretical analysis and computer program was developed for the prediction of unsteady lifting surface loadings caused by motions of leading edge and trailing edge control surfaces having sealed gaps. The final form of the downwash integral equation was formulated by isolating the singularities from the nonsingular terms and using a preferred solution process to remove and evaluate the downwash discontinuities in a systematic manner. Comparisons of theoretical and experimental pressure data are made for several control surface configurations. The comparisons indicate that reasonably accurate theoretical pressure distributions and generalized forces may be obtained for a wide variety of control surface configurations. Spanwise symmetry or antisymmetry of motion, and up to six control surfaces on each half span can be accommodated.

Rowe, W. S.↗
NASA NTRS1976

A new method for solving problems of sound radiation from a duct for the case of low Mach number

A method for rapidly solving duct end-plane impedance problems is presented which is based on deriving a form of the Helmholtz integral formula expressing the normal derivative of the acoustic pressure at a boundary point. A set of integral expressions is obtained by satisfying the existing boundary conditions and then solved using a general collocation method. The results obtained for the Levine-Schwinger (1948) problem agree well with the exact values. In the case of a duct flow having a temperature mismatch with the surroundings, the results show an increase in the magnitude of the reflection coefficient for the case of a cold core, and a decrease in its value for the case of a hot core, as compared with the case of exhaust into a uniform medium. A phase change of between pi/2 and pi is nearly always achieved, which indicates the tendency towards maintaining a constant pressure at the exit plane. The method can easily be extended to arbitrary duct shapes as long as they are axisymmetric.

Wahbah, M. M.↗
NASA NTRS1976

Lifting surface theory for rectangular wings

A new incompressible lifting-surface theory is developed for thin rectangular wings. The solution requires the downwash equation to be in the form of Cauchy-type integrals. Lan's method is employed for the chordwise integrals since it properly accounts for the leading-edge singularity, Cauchy singularity and Kutta condition. The Cauchy singularity in the spanwise integral is also accounted for by using the midpoint trapezoidal rule and theory of Chebychev polynomials. The resulting matrix equation, formed by satisfying the boundary condition at control points, is simpler and quicker to compute than other lifting surface theories. Solutions were found to converge with only a small number of control points and to compare favorably with results from other methods.

Dejarnette, F. R.↗
NASA NTRS1977

Statistical properties of the sound and source fields of an axisymmetric jet

It is shown, by measurements and analysis, that the sound field radiated from subsonic jets as well as the source field are statistically axially symmetric at lower frequencies. In this range, the source field behaves like a line-quadrupole. The sources are coherent with respect to phase and compact with respect to acoustic wavelength. The results are developed in terms of correlation, coherence, and phase. A new and simpler form of the source integral is obtained in the range where the phases are linear functions of frequency through symmetry, translation, and rotation of the axis.

Maestrello, L.↗
NASA NTRS1971

Temperature compensated current source

A current source was designed which is substantially independent of variations of temperature. The current source may be made either to have a linear dependence upon changes of temperature or, by the simple addition of a resistor, may be made substantially independent of temperature variations. Since the current source consists only of transistors of one conductivity type and resistors, it is ideally suited for manufacture in the form of a monolithic integrated circuit.

Breuer, D. R.↗
NASA NTRS1980

Technique for mounting pyroelectric detector arrays

Technique is developed at Langley Research Center for mounting pyroelectric detector arrays on silicon integrated circuits. Procedure incorporates normal silicon integrated-circuit technology to form quasi-free mounts for detector arrays. Advantages of technique include lower cost, better image registration, and improved reliability.

Breckenridge, R. A.↗
NASA NTRS1980

Design, evaluation and test of an electronic, multivariable control for the F100 turbofan engine

A digital, multivariable control design procedure for the F100 turbofan engine is described. The controller is based on locally linear synthesis techniques using linear, quadratic regulator design methods. The control structure uses an explicit model reference form with proportional and integral feedback near a nominal trajectory. Modeling issues, design procedures for the control law and the estimation of poorly measured variables are presented.

Skira, C. A.↗
NASA NTRS1980

Uncontrolled dynamics of the Skylab vehicle - Comparison of simulation, theory and flight data

When the final Skylab mission was completed in 1974, the onboard systems were used to maneuver the vehicle to a gravity gradient equilibrium attitude and were then shut down. Parked in this storage attitude, the vehicle was left undisturbed until March 1978 when contact was reestablished and the control systems were reactivated. During the intervening four years, the vehicle was subjected to subtle environmental torques which caused the vehicle to gradually progress from its initial stable state to a very dynamic condition just prior to the resumption of control. The paper deals with the dynamics of this process, including the analyses and simulations which were made to explain the motion and enable the planning of the reactivation process. The complementary roles of both numerical integration and closed-form analysis are demonstrated. Flight data obtained in the spring of 1978 are presented which support the analytical and simulation results.

Buchanan, H. J.↗
NASA NTRS1982

Petrogenesis of light and dark portions of the Leighton gas-rich chondritic breccia

Individual dark fractions of the Leighton chondritic breccia are all enriched in volatile/mobile trace elements. Concentrations of the most highly volatile/mobile elements correlate with degree of equilibration, as expressed by compositional variability for silicates. Individual light clasts in the same meteorite are equilibrated and generally volatile-poor, except for enrichments in Rb and Cs. These alkali elements may have been redistributed by feldspar formation during metamorphism. Enrichments of other trace elements in dark portions may have been caused by mobilization during metamorphism in the parent body interior and deposition in the cooler surface layers. An alternative model involves accretional mixing of a diverse compositional population of primitive H group materials to form dark materials. Subsequent integration of light and dark materials was accomplished by impacts into a regolith.

Mcsween, H. Y., Jr.↗
NASA NTRS1983

The human as supervisor in automated systems

This hierarchical approach to information display forces the development of a set of human oriented system models which will guide the design of the displays. If the appropriate information is provided at the appropriate time, it is likely that less information will be displayed at any given time, and the quality of the displayed information will require less operator effort to integrate into an assimilatable form. A problem with contemporary control rooms is that there is too much information for an operator to be able to assimilate quickly, easily, and accurately. It is suggested that necessary direction for research in the area of automated control room design is to develop displays which provide active decision aiding for the modern controller. Displays are needed which provide information compatible with the operator's current internal model, filter out irrelevant information, and summarize and condense lower level information.

Mitchell, C. M.↗
NASA NTRS1984

A method for computing the kernel of the downwash integral equation for arbitrary complex frequencies

For the design of active controls to stabilize flight vehicles, which requires the use of unsteady aerodynamics that are valid for arbitrary complex frequencies, algorithms are derived for evaluating the nonelementary part of the kernel of the integral equation that relates unsteady pressure to downwash. This part of the kernel is separated into an infinite limit integral that is evaluated using Bessel and Struve functions and into a finite limit integral that is expanded in series and integrated termwise in closed form. The developed series expansions gave reliable answers for all complex reduced frequencies and executed faster than exponential approximations for many pressure stations.

Desmarais, R. N.↗
NASA NTRS1984

Thermal shock in a circumferentially cracked hollow cylinder with cladding

An theoretical analysis is presented which demonstrates the effect of cladding on the thermal resistance of a circumferentially cracked hollow cylinder. The cladding is assumed to be bonded to the inner wall of the hollow cylinder. The axisymmetric circumferential crack may be either embedded in the cylinder wall or may be an edge crack which passes through the clad and opens into the inner wall of the hollow cylinder. The problem is formulated mathematically and a solution is found which is in the form of a single integral equation. The integral equation is solved numerically and yields estimates of transient temperature distributions, thermal stresses in the uncracked cylinder, and stress intensity factors as a function of time for various cladding thickness to cylinder wall thickness ratios. It is shown that yielding of the clad under certain conditions can result in a reduction in the magnitude of the stress intensity factor for the crack tip in the elastic base material.

Nied, H. F.↗
NASA NTRS1983

Planar dynamics of a uniform beam with rigid bodies affixed to the ends

The planar dynamics of a uniform elastic beam subject to a variety of geometric and natural boundary conditions and external excitations were analyzed. The beams are inextensible and capable of small transverse bending deformations only. Classical beam vibration eigenvalue problems for a cantilever with tip mass, a cantilever with tip body and an unconstrained beam with rigid bodies at each are examined. The characteristic equations, eigenfunctions and orthogonality relations for each are derived. The forced vibration of a cantilever with tip body subject to base acceleration is analyzed. The exact solution of the governing nonhomogeneous partial differential equation with time dependent boundary conditions is presented and compared with a Rayleigh-Ritz approximate solution. The arbitrary planar motion of an elastic beam with rigid bodies at the ends is addressed. Equations of motion are derived for two modal expansions of the beam deflection. The motion equations are cast in a first order form suitable for numerical integration. Selected FORTRAN programs are provided.

Storch, J.↗