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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 program to compute three-dimensional subsonic unsteady aerodynamic characteristics using the doublet lattic method, L216 (DUBFLX). Volume 1: Engineering and usage

The program input presented consists of configuration geometry, aerodynamic parameters, and modal data; output includes element geometry, pressure difference distributions, integrated aerodynamic coefficients, stability derivatives, generalized aerodynamic forces, and aerodynamic influence coefficient matrices. Optionally, modal data may be input on magnetic file (tape or disk), and certain geometric and aerodynamic output may be saved for subsequent use.

Richard, M.↗
NASA NTRS1980

The quasi-vortex-lattice method for wings with edge vortex separation

The aerodynamic characteristics of wings with leading-edge vortex separation were predicted using a method based on a flow model with free vortex elements which are allowed to merge into a concentrated core. The calculated pressure distribution is more accurate than that predicted by methods with discrete vortex filaments alone. In addition, the computer time is reduced approximately by half.

Pao, J. L.↗
NASA NTRS1980

A vortex-lattice method for the calculation of the nonsteady separated flow over delta wings

An analysis is made of the wake structure and the forces on a delta wing as it undergoes nonsteady motion, wherein the flow separates at the leading edge. Comparisons of these predictions with existing experimental and theoretical data for the nonsteady linear and nonlinear motions indicate good agreement. It was found that the time-dependent, wake-shedding numerical procedure applied here for the wake rollup and the lift force calculation resulted in considerable saving of computer time over methods using the iterative wake rollup procedure. Calculated results for various motions of the delta wing, including the plunging motion, are presented for both the separated and the attached flow cases.

Levin, D.↗
NASA NTRS1980

Investigation of multilayer magnetic domain lattice file

The feasibility of the self structured multilayered bubble domain memory as a mass memory medium for satellite applications is examined. Theoretical considerations of multilayer bubble supporting materials are presented, in addition to the experimental evaluation of current accessed circuitry for various memory functions. The design, fabrication, and test of four device designs is described, and a recommended memory storage area configuration is presented. Memory functions which were demonstrated include the current accessed propagation of bubble domains and stripe domains, pinning of stripe domain ends, generation of single and double bubbles, generation of arrays of coexisting strip and bubble domains in a single garnet layer, and demonstration of different values of the strip out field for single and double bubbles indicating adequate margins for data detection. All functions necessary to develop a multilayer self structured bubble memory device were demonstrated in individual experiments.

Torok, E. J.↗
NASA NTRS1982

Modeling of Large Latticed Surfaces

GEOMLLS program determines dimensions and coordinates of flat segmented triangular surfaces that approximate spherical and paraboloidal surfaces of revolution, where vertexes of triangles lie on true surface. GEOMLLS calculates complete geometry of segmented surface and quantities that measure surface accuracy, such as maximum deviation and root-mean-square deviation from true surface.

Anderson, M. S.↗
NASA NTRS1982

A doublet lattice method for the determination of rotor induced empennage vibration airloads. Analysis description and program documentation

An efficient state-of-the-art method was developed to determine the unteady vibratory airloads produced by the interaction of the main rotor wake with a helicopter empennage. This method was incorporated into a computer program, Rotor Induced Empennage Vibration Analysis (RIEVA). The program requires the main rotor wake position and the strength of the vortices locates near the empennage surfaces. A nonlinear lifting surface analysis is utilized to predict the aerodynamic loads on the empennage surfaces in the presence of these concentrated vortices. The analysis was formulated to include all pertinent effects such as suction of the interacting vortices and the shed vorticity behind the empennage surfaces. The analysis employs a time domain solution. The output of the program consists of chordwise and spanwise airload distributions on the empennage surfaces. The airload distributions are harmonically analyzed and formulated for input into the Coupled Rotor/Airframe Vibration Analysis.

Gangwani, S. T.↗
NASA NTRS1981

Lattice defects in semiconducting Hg/1-x/Cd/x/Te alloys. III - Defect structure of undoped Hg0.6Cd0.4Te

Hall effect measurements were carried out on undoped Hg0.6Cd0.4Te crystals quenched to room temperature subsequent to equilibration at temperatures varying from 450 to 720 C under various partial pressures of Hg. The variation of the hole concentration as a function of the partial pressure of Hg indicates that the native acceptor defects are doubly ionized. Native donor defects are found to be negligible in concentration and the p-type to n-type conversion is shown to be due to residual donors and not due to native donor defects. Thermodynamic constant for the incorporation of the doubly ionized native acceptor defect has been established.

Vydyanath, H. R.↗
NASA NTRS1982

Investigation of multilayer magnetic domain lattice file

A theoretical and experimental investigation determined that current accessed self structured bubble memory devices have the potential of meeting projected data density and speed requirements. Device concepts analyzed include multilayer ferrimagnetic devices where the top layer contains a domain structure which defines the data location and the second contains the data. Current aperture and permalloy assisted current propagation devices were evaluated. Based on the result of this work more detailed device research was initiated. Detailed theoretical and experimental studies indicate that the difference in strip and threshold between a single bubble in the control layer and a double bubble which would exist in both the control layer and data layer is adequate to allow for detection of data. Detailed detector designs were investigated.

Torok, E. J.↗
NASA NTRS1984

The effect of diffusion induced lattice stress on the open-circuit voltage in silicon solar cells

It is demonstrated that diffusion induced stresses in low resistivity silicon solar cells can significantly reduce both the open-circuit voltage and collection efficiency. The degradation mechanism involves stress induced changes in both the minority carrier mobility and the diffusion length. Thermal recovery characteristics indicate that the stresses are relieved at higher temperatures by divacancy flow (silicon self diffusion). The level of residual stress in as-fabricated cells was found to be negligible in the cells tested.

Weizer, V. G.↗
NASA NTRS1984

The effect of diffusion induced lattice stress on the open-circuit voltage in silicon solar cells

It is demonstrated that diffusion induced stresses in low resistivity silicon solar cells can significantly reduce both the open-circuit voltage and collection efficiency. The degradation mechanism involves stress induced changes in both the minority carrier mobility and the diffusion length. Thermal recovery characteristics indicate that the stresses are relieved at higher temperatures by divacancy flow (silicon self diffusion). The level of residual stress in as-fabricated cells was found to be negligible in the cells tested.

Weizer, V. G.↗
NASA NTRS1986

BUNVIS-RG - An exact buckling and vibration program for lattice structures, with repetitive geometry and substructuring options

The exact FORTRAN computer program BUNVIS-RG which uses an exact stiffness matrix method to find eigenvalues and modes of three-dimensional planes, is presented in detail. It is shown that BUNVIS-RG solution times can be predicted fairly accurately from two computer dependent constants, the number of nodes and members in the frame, and the maximum node number difference of any pair of connected nodes. The program's use of repetitive geometry, stayed column substructures and nonuniform member options was found to enhance efficiency and range of application.

Anderson, M. S.↗