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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 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Simulation of the prompt energization and transport of radiation belt particles during the March 24, 1991 SSC

We model the rapid (about 1 min) formation of a new electron radiation belt at L about or = 2.5 that resulted from the Storm Sudden Commencement (SSC) of March 24, 1991 as observed by the Combined Release and Radiation Effects Satellite (CRRES) satellite. Guided by the observed electric and magnetic fields, we represent the time-dependent magnetospheric electric field during the SSC by an asymmetric bipolar pulse that is associated with the compression and relaxation of the Earth's magnetic field. We follow the electrons using a relativistic guiding center code. The test-particle simulations show that electrons with energies of a few MeV at L greater than 6 were energized up to 40 MeV and transported to L about or = 2.5 during a fraction of their drift period. The energization process conserves the first adiabatic invariant and is enhanced due to resonance of the electron drift motion with the time-varying electric field. Our simulation results, with an initial W(exp -8) energy flux spectra, reproduce the observed electron drift echoes and show that the interplanetary shock impacted the magnetosphere between 1500 and 1800 MLT.

Li, Xinlin↗
NASA NTRS1985

Analysis of airborne antenna systems using geometrical theory of diffraction and moment method computer codes

Computer codes have been developed to analyze antennas on aircraft and in the presence of scatterers. The purpose of this study is to use these codes to develop accurate computer models of various aircraft and antenna systems. The antenna systems analyzed are a P-3B L-Band antenna, an A-7E UHF relay pod antenna, and traffic advisory antenna system installed on a Bell Long Ranger helicopter. Computer results are compared to measured ones with good agreement. These codes can be used in the design stage of an antenna system to determine the optimum antenna location and save valuable time and costly flight hours.

Hartenstein, Richard G., Jr.↗
NASA NTRS1980

Ozone data and mission sampling analysis

A methodology was developed to analyze discrete data obtained from the global distribution of ozone. Statistical analysis techniques were applied to describe the distribution of data variance in terms of empirical orthogonal functions and components of spherical harmonic models. The effects of uneven data distribution and missing data were considered. Data fill based on the autocorrelation structure of the data is described. Computer coding of the analysis techniques is included.

Robbins, J. L.↗
NASA NTRS1977

Experience with a vectorized general circulation weather model on Star-100

A version of an atmospheric general circulation model was vectorized to run on a CDC STAR 100. The numerical model was coded and run in two different vector languages, CDC and LRLTRAN. A factor of 10 speed improvement over an IBM 360/95 was realized. Efficient use of the STAR machine required some redesigning of algorithms and logic. This precludes the application of vectorizing compilers on the original scalar code to achieve the same results. Vector languages permit a more natural and efficient formulation for such numerical codes.

Soll, D. B.↗
NASA NTRS1981

Development techniques for generic software

In developing the first version of a generic implementation of X.25, Levels 2 and 3, three development techniques are examined: table driven finite state machine implementation, an integrated testing environment, and top down design. A finite state machine (FSM) is a powerful tool for both specifying and implementing protocols. This technique was used in the X.25 specification. A table driven implementation of the FSM was chosen to facilitate changes and simplify coding. The effect that this technique have on program size, speed of execution, coding time, and debugging time are investigated.

Hamilton, R. L.↗
NASA NTRS1982

Modulation techniques

Bandwidth efficient digital modulation techniques, proposed for use on and/or applied to satellite channels, are reviewed. In a survey of recent works on digital modulation techniques, the performance of several schemes operating in various environments are compared. Topics covered include: (1) quadrature phase shift keying; (2) offset - QPSK and MSK; (3) combined modulation and coding; and (4) spectrally efficient modulation techniques.

Schilling, D. L.↗
NASA NTRS1984

An efficient approximate factorization implicit scheme for the equations of gasdynamics

An efficient implicit finite-difference algorithm for the gas dynamic equations utilizing matrix reduction techniques is presented. A significant reduction in arithmetic operations is achieved while maintaining the same favorable stability characteristics and generality found in the Beam and Warming approximate factorization algorithm. Steady-state solutions to the conservative Euler equations in generalized coordinates are obtained for transonic flows about a NACA 0012 airfoil. The theoretical extension of the matrix reduction technique to the full Navier-Stokes equations in Cartesian coordinates is presented in detail. Linear stability, using a Fourier stability analysis, is demonstrated and discussed for the one-dimensional Euler equations. It is shown that the method offers advantages over the conventional Beam and Warming scheme and can retrofit existing Beam and Warming codes with minimal effort.

Barth, T. J.↗
NASA NTRS1984

Interactive Finite Elements for General Engine Dynamics Analysis

General nonlinear finite element codes were adapted for the purpose of analyzing the dynamics of gas turbine engines. In particular, this adaptation required the development of a squeeze-film damper element software package and its implantation into a representative current generation code. The ADINA code was selected because of prior use of it and familiarity with its internal structure and logic. This objective was met and the results indicate that such use of general purpose codes is viable alternative to specialized codes for general dynamics analysis of engines.

Adams, M. L.↗
NASA NTRS1985

Analytical determination of propeller performance degradation due to ice accretion

It is pointed out that ice accretion on aircraft produces an adverse effect on aircraft performance in terms of decreased lift and increased drag of the lifting surface. Ice on the surface of a propeller may also cause a decrease in thrust, increase in the required power, and a resultant decrease in propeller efficiency. During the past years, a number of attempts have been made to analyze the effects of ice accretion on both fixed wings and propellers. The present investigation is concerned with the development of a single user-oriented computer code which makes it possible to calculate propeller performance degradation due to ice accretion for specified flight conditions, atmospheric conditions, and propeller geometry. This development is based on a combination of several of the codes and correlations considered in earlier studies.

Miller, T. L.↗
NASA NTRS1987

ICAN: Integrated Composites Analyzer

Program calculates macromechanical, micromechanical, and related environmental effects. Computer code ICAN developed to carry out comprehensive linear analyses of multilayered fiber composites. Contains essential features required to design structural components made from fiber composites. Code in FORTRAN IV.

Chamis, Christos C.↗
NASA NTRS1987

A simplified procedure for correcting both errors and erasures of a Reed-Solomon code using the Euclidean algorithm

It is well known that the Euclidean algorithm or its equivalent, continued fractions, can be used to find the error locator polynomial and the error evaluator polynomial in Berlekamp's key equation needed to decode a Reed-Solomon (RS) code. A simplified procedure is developed and proved to correct erasures as well as errors by replacing the initial condition of the Euclidean algorithm by the erasure locator polynomial and the Forney syndrome polynomial. By this means, the errata locator polynomial and the errata evaluator polynomial can be obtained, simultaneously and simply, by the Euclidean algorithm only. With this improved technique the complexity of time domain RS decoders for correcting both errors and erasures is reduced substantially from previous approaches. As a consequence, decoders for correcting both errors and erasures of RS codes can be made more modular, regular, simple, and naturally suitable for both VLSI and software implementation. An example illustrating this modified decoding procedure is given for a (15, 9) RS code.

Truong, T. K.↗
NASA NTRS1988

A transonic-small-disturbance wing design methodology

An automated transonic design code has been developed which modifies an initial airfoil or wing in order to generate a specified pressure distribution. The design method uses an iterative approach that alternates between a potential-flow analysis and a design algorithm that relates changes in surface pressure to changes in geometry. The analysis code solves an extended small-disturbance potential-flow equation and can model a fuselage, pylons, nacelles, and a winglet in addition to the wing. A two-dimensional option is available for airfoil analysis and design. Several two- and three-dimensional test cases illustrate the capabilities of the design code.

Phillips, Pamela S.↗
NASA NTRS1988

OEXP Analysis Tools Workshop

This publication summarizes the software needs and available analysis tools presented at the OEXP Analysis Tools Workshop held at the NASA Langley Research Center, Hampton, Virginia on June 21 to 22, 1988. The objective of the workshop was to identify available spacecraft system (and subsystem) analysis and engineering design tools, and mission planning and analysis software that could be used for various NASA Office of Exploration (code Z) studies, specifically lunar and Mars missions.

Garrett, L. Bernard↗
NASA NTRS1989

Probabilistic constitutive relationships for material strength degradation models

In the present probabilistic methodology for the strength of aerospace propulsion system structural components subjected to such environmentally-induced primitive variables as loading stresses, high temperature, chemical corrosion, and radiation, time is encompassed as an interacting element, allowing the projection of creep and fatigue effects. A probabilistic constitutive equation is postulated to account for the degradation of strength due to these primitive variables which may be calibrated by an appropriately curve-fitted least-squares multiple regression of experimental data. The resulting probabilistic constitutive equation is embodied in the PROMISS code for aerospace propulsion component random strength determination.

Boyce, L.↗
NASA NTRS1989

Measured and predicted aerodynamic heating on a cylinder in wake of AFE configuration at incidence

Thin-film resistance gages were used to measure cylinder surface heat-transfer rates in the near wake of the Aeroassist Flight Experiment vehicle configuration, while surface-streamline directions were ascertained by the oil-flow techniques under the same configuration and test conditions. Both heat transfer distributions and flow over the entire cylinder surface were influenced by impingement of that portion of the free shear layer originating at the forebody shoulder in the upper symmetry plane. Heating rate distributions predicted with a Navier-Stokes solver computer code were in general agreement with measurements.

Wells, William L.↗