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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 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Refined Transistor Model For Simulation Of SEU

Equivalent base resistance added. Theoretical study develops equations for parameters of Gummel-Poon model of bipolar junction transistor: includes saturation current, amplification factors, charging times, knee currents, capacitances, and resistances. Portion of study concerned with base region goes beyond Gummel-Poon analysis to provide more complete understanding of transistor behavior. Extended theory useful in simulation of single-event upset (SEU) caused in logic circuits by cosmic rays or other ionizing radiation.

Zoutendyk, John A.↗
NASA NTRS1987

Refining image segmentation by polygon skeletonization

A skeletonization algorithm was encoded and applied to a test data set of land-use polygons taken from a USGS digital land use dataset at 1:250,000. The distance transform produced by this method was instrumental in the description of the shape, size, and level of generalization of the outlines of the polygons. A comparison of the topology of skeletons for forested wetlands and lakes indicated that some distinction based solely upon the shape properties of the areas is possible, and may be of use in an intelligent automated land cover classification system.

Clarke, Keith C.↗
NASA NTRS1988

Preparation of multistage zone-refined materials for thermochemical standards

This paper describes the steps of a two-step zone purification procedure for completed minicells filled with ultrahigh-purity succinonitrile (SCN) in which the CNS is under its own vapor pressure. The solid-liquid equilibrium, as determined by melting and freezing point measurements, is therefore considered to be a realization of the triple-point. The freezing-point plateaus measured at a variety of bath temperatures demonstrated both the fundamental reproducibility of the measurement for a given sample and the lack of dependence of that measurement on the bath temperature which controls the freezing rate. The measurement reproducibility and the sample consistency indicate that the method described is indeed suitable for the preparation of pure material which can be used for the purposes of thermistor and thermometer calibration at 58.0796 + or - 0.0015 C.

Rubinstein, E.↗
NASA NTRS1988

Refining, revising, augmenting, compiling and developing computer assisted instruction K-12 aerospace materials for implementation in NASA spacelink electronic information system

The NASA Spacelink is an electronic information service operated by the Marshall Space Flight Center. The Spacelink contains extensive NASA news and educational resources that can be accessed by a computer and modem. Updates and information are provided on: current NASA news; aeronautics; space exploration: before the Shuttle; space exploration: the Shuttle and beyond; NASA installations; NASA educational services; materials for classroom use; and space program spinoffs.

Blake, Jean A.↗
NASA NTRS1989

Development and refinement of test bed simulations

Lewis Research Center of NASA, with support from Rocketdyne, was engaged in non-real time computer simulation effort for the Space Station Freedom Electric Power System (EPS) EASY5, a simulation package, is used as the primary tool for this activity. Early in the design of the EPS, two test beds were set up at Lewis. The Integrated Test Bed (ITB), that combines and upgrades these test beds, is in the planning stage. The test beds are designed to functionally represent many of the components of the EPS and their interconnections. The simulation effort is primarily directed towards these test beds. Model verification is performed using test bed data.

Dravid, Narayan V.↗
NASA NTRS1989

Refinements in a viscoplastic model

A thermodynamically admissible theory of viscoplasticity with two internal variables (a back stress and a drag strength) is presented. Six material functions characterize a specific viscoplastic model. In the pursuit of compromise between accuracy and simplicity, a model is developed that is a hybrid of two existing viscoplastic models. A limited number of applications of the model to Al, Cu, and Ni are presented. A novel implicit integration method is also discussed. Applications are made to obtain solutions using this viscoplastic model.

Freed, A. D.↗
NASA NTRS1989

Grid refinement studies of turbine rotor-stator interaction

Results from a three-dimensional, time-accurate Navier-Stokes simulation of rotor-stator interaction in an axial turbine stage are presented. The present study uses a fine grid in the spanwise direction to better resolve endwall and tip cllearance effects and complements coarse-grid calculations that were reported earlier. A realistic turbine stage with 22 stator vanes and 28 rotor blades is simulated as a single-stator, single-rotor airfoil combination with the stator geometry modified to properly account for blockage effects. This is in contrast to the earlier coarse-grid calculations where the rotor geometry was modified. The improved grid resolution and the unmodified rotor geometry result in a more accurate simulation of the flow field, particularly in the rotor channel where the interaction effects are more severe. The numerical results are compared to experimental data wherever possible and to earlier calculations.

Madavan, N. K.↗
NASA NTRS1989

Viscous-inviscid interaction and local grid refinement via truncation error injection

A methodology is presented which makes it possible to decouple a complex problem having multiple disparate length scales into problems of single length scale so that they can be solved more efficiently on a computer. The method is applied to a viscous transonic flow over an airfoil. It is found that accurate prediction of the flow over an airfoil can be obtained by solving the Euler equations on a relatively coarse global grid with viscous effects computed separately on a boundary-layer type grid and injected into the global grid solution as a combination of vorticity and trucation error.

Goble, Brian D.↗
NASA NTRS1989

A few remarks concerning several refined theories of anisotropic composite laminated plates

An analysis and comparison of several shear deformable bending theories of composite laminated anisotropic plates currently encountered in the field literature are given in this paper. Although apparently different, it is shown in a unitary way, that these theories constitute in fact only different formulations of a single theory, generically designated to as the moderately thick plate theory. Their connection with the first order transverse shear deformation theory is also emphasized and some conclusions concerning its shortcomings and field applicability are presented.

Librescu, L.↗
NASA NTRS1990

Additional measurements and a refined analysis of the millimeter- and submillimeter-wave spectrum of methanol

A total of 414 previously unobserved millimeter- and submillimeter-wave transitions of (C-12)H3OH through J = 10 and v(t) = 2 are assigned. These data and previous measured spectral transitions are combined and fitted by a modified internal axis method (IAM) treatment in which the A and E substates are treated separately and a wide variety of new rotational-torsional interaction terms are employed. The modified IAM treatment reduces the overall rms deviation of the fits to the level of experimental accuracy. The resultant spectroscopic constants allow for the accurate prediction of 569 additional transitions through J = 12 or less.

Anderson, Todd↗
NASA NTRS1989

Development and refinement of test bed simulations

Lewis Research Center of NASA, with support from Rocketdyne, has engaged in a nonreal-time computer simulation effort for the Space Station Freedom Electric Power System (EPS). EASYS, a simulation package, is used as the primary tool for this activity. Early in the design of the EPS, two test beds were set up at Lewis. The Integrated Test Bed (ITB) that combines and upgrades these test beds is in the planning stage. The test beds are designed to functionally represent many of the components of the EPS and their interconnections. The simulation effort is primarily directed towards these test beds. Model verification is performed using test bed data.

Dravid, N. V.↗
NASA NTRS1991

Computation Of Flow In A Turbine Stage On A Refined Grid

Finer grid yields more accurate results. Report describes numerical simulation of flow in axial-turbine stage, showing interactions between rotor- and stator-airfoil rows. Complements earlier three-dimensional, time-accurate Navier-Stokes numerical simulation.

Madavan, N. K.↗
NASA NTRS1989

TOPEX microwave radiometer system calibration - Refining the SMMR heritage

A modified version of the Scanning multichannel Microwave Radiometer (SMMR) will be used for wet tropospheric path-delay corrections to the TOPEX/POSEIDON radar altimeter measurements. A number of the sources of calibration problems encountered by SMMR onboard the Seasat and Nimbus-7 platforms have been identified, and appropriate corrections have been attempted. Calibration hardware corrections include a more representative modeling of the microwave losses and reflections, and a reduction in the thermal gradients expected across this hardware through the use of radomes and sun shades and the choice of pertinent orbit parameters. Antenna calibration corrections include a postlaunch fine tuning of the antenna pattern correction algorithm to accommodate small errors in the prelaunch antenna pattern measurements. This is accomplished by overpasses of ground-based, upward-looking water vapor radiometers. An absolute calibration accuracy of 1.0 K or less is anticipated.

Ruf, Christopher S.↗
NASA NTRS1991

Light scattering by nonspherical particles - A refinement to the coupled-dipole method

In the coupled-dipole method, an arbitrary particle is modeled as an array of N polarizable subunits, each of which gives rise to only electric dipole radiation. The Clausius-Mosotti relation is widely used to calculate the polarizability of the subunits that correspond to the dielectric function of the particle that the array represents. The Clausius-Mosotti relation is replaced here with an exact expression for the electric dipole polarizability, and improvement is found in extinction calculations for spheres as compared with Mie theory. Near a Froehlich frequency the coupled-dipole method yields extinction cross sections for spheres and spheroids that compare favorably with the continuous distribution of ellipsoids method and measured values.

Dungey, Clifton E.↗
NASA NTRS1990

On refined theories of composite laminates

A review of the developments in the displacement-based theories of plates is presented. It is shown that many of the third-order theories reported in the literature are based on the same or equivalent displacement field, and thus lead to the same results. A strain-consistent third-order theory is presented, which contains most existing third-order plate theories as special cases. The layer-wise laminate plate theory proposed is also reviewed. The accuracy of the theories is evaluated by comparing the numerical solutions with those of the three-dimensional elasticity theory.

Reddy, J. N.↗
NASA NTRS1991

Interface conditions for domain decomposition with radical grid refinement

Interface conditions for coupling the domains in a physically motivated domain decomposition method are discussed. The domain decomposition is based on an asymptotic-induced method for the numerical solution of hyperbolic conservation laws with small viscosity. The method consists of multiple stages. The first stage is to obtain a first approximation using a first-order method, such as the Godunov scheme. Subsequent stages of the method involve solving internal-layer problem via a domain decomposition. The method is derived and justified via singular perturbation techniques.

Scroggs, Jeffrey S.↗