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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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

A university teaching simulation facility

An experimental telerobotics (TR) simulation is described suitable for studying human operator (HO) performance. Simple manipulator pick-and-place and tracking tasks allowed quantitative comparison of a number of calligraphic display viewing conditions. A number of control modes could be compared in this TR simulation, including displacement, rate, and acceleratory control using position and force joysticks. A homeomorphic controller turned out to be no better than joysticks; the adaptive properties of the HO can apparently permit quite good control over a variety of controller configurations and control modes. Training by optimal control example seemed helpful in preliminary experiments.

Stark, Lawrence↗
NASA NTRS1989

CSM parallel structural methods research

Parallel structural methods, research team activities, advanced architecture computers for parallel computational structural mechanics (CSM) research, the FLEX/32 multicomputer, a parallel structural analyses testbed, blade-stiffened aluminum panel with a circular cutout and the dynamic characteristics of a 60 meter, 54-bay, 3-longeron deployable truss beam are among the topics discussed.

Storaasli, Olaf O.↗
NASA NTRS1989

Parallel-vector solution of large-scale structural analysis problems on supercomputers

A direct linear equation solution method based on the Choleski factorization procedure is presented which exploits both parallel and vector features of supercomputers. The new equation solver is described, and its performance is evaluated by solving structural analysis problems on three high-performance computers. The method has been implemented using Force, a generic parallel FORTRAN language.

Storaasli, Olaf O.↗
NASA NTRS1990

A parallel-vector algorithm for rapid structural analysis on high-performance computers

A fast, accurate Choleski method for the solution of symmetric systems of linear equations is presented. This direct method is based on a variable-band storage scheme and takes advantage of column heights to reduce the number of operations in the Choleski factorization. The method employs parallel computation in the outermost DO-loop and vector computation via the 'loop unrolling' technique in the innermost DO-loop. The method avoids computations with zeros outside the column heights, and as an option, zeros inside the band. The close relationship between Choleski and Gauss elimination methods is examined. The minor changes required to convert the Choleski code to a Gauss code to solve non-positive-definite symmetric systems of equations are identified. The results for two large-scale structural analyses performed on supercomputers, demonstrate the accuracy and speed of the method.

Storaasli, Olaf O.↗
NASA NTRS1991

Protection of electrical and electronic equipment against lightning indirect effects on the Airbus A340 wing

The provisions applied to the Airbus A340 wing wiring against lightning indirect effects are presented. The construction and installation of the wiring's shielding systems are described, and the analysis and tests performed to determine the effectiveness of the measures taken are discussed. A first evaluation of the results of the theoretical analysis together with the provisional results of tests indicate a sufficient safety margin between required and achieved protection levels.

Spiller, Olaf↗
NASA NTRS1991

Far-ultraviolet mapping of the Cygnus Loop with the Voyager 2 Ultraviolet Spectrometer

FUV maps of the Cygnus Loop made using spectroscopic data from the Voyager 2 Ultraviolet Spectrometer are presented. Emission line features at about 980 and about 1035 A dominate the 500-1700 A spectra of the Cygnus Loop as observed with Voyager. Maps were generated in the light of these two features. The 980 and 1035 A maps are compared with X-ray and optical images of the Cygnus Loop that have been sampled in the same manner. From this comparison it is clear that the 980 A feature arises mainly from regions of bright optical emission, whereas the 1035 A emission more closely resembles the X-ray emission. This general impression can be confirmed by inspection of the spectra as a function of position. Spectra extracted from positions corresponding to the primary shock front show the 1035 A feature to be relatively strong, while the 980 A feature is brighter when substantial optical emission is present within the aperture.

Blair, William P.↗
NASA NTRS1991

Discovery of a fast radiative shock wave in the Cygnus Loop using the Hopkins Ultraviolet Telescope

Observations of the far-ultraviolet spectrum of a bright radiative filament on the eastern edge of the Cygnus Loop supernova remnant are described which were made through the Hopkins Ultraviolet Telescope aboard the Astro-1 Space Shuttle mission in December 1990. Observations include strong emission lines of C III 977, N III 991, and O VI 032, 1038 and many fainter lines. A comparison of this spectrum with shock model calculations indicates that the emission at this position in the Cygnus Loop is dominated by 170 km/s shock wave.

Blair, William P.↗
NASA NTRS1990

A parallel-vector algorithm for rapid structural analysis on high-performance computers

A fast, accurate Choleski method for the solution of symmetric systems of linear equations is presented. This direct method is based on a variable-band storage scheme and takes advantage of column heights to reduce the number of operations in the Choleski factorization. The method employs parallel computation in the outermost DO-loop and vector computation via the loop unrolling technique in the innermost DO-loop. The method avoids computations with zeros outside the column heights, and as an option, zeros inside the band. The close relationship between Choleski and Gauss elimination methods is examined. The minor changes required to convert the Choleski code to a Gauss code to solve non-positive-definite symmetric systems of equations are identified. The results for two large scale structural analyses performed on supercomputers, demonstrate the accuracy and speed of the method.

Storaasli, Olaf O.↗
NASA NTRS1991

Parallel Methods on Large-Scale Structural Analysis and Physics Applications; Symposium, Hampton, VA, Feb. 5, 6, 1991, Selected Papers

Recent advances in parallel methods and algorithms integrated into large-scale codes are presented. Consideration is given to problem decomposition (substructuring), efficient matrix solution algorithms for shared memory architectures, dynamic and transient analysis algorithms for shared memory architectures, and algorithms for distributed and massively parallel architectures. Particular attention is given to partitioning of unstructured problems for parallel processing, parallel-vector computation for linear-structural analysis and nonlinear unconstraint optimization problems, a parallel-vector equation solver for unsymmetric matrices on supercomputers, parallel nonlinear finite element dynamic response, multigrid algorithms for solving structural mechanics problems on supercomputers, structural analysis on massively parallel computers, explicit finite element methods with contact-impact on SIMD computers, and the impact of mapping and sparsity on parallelized finite element method modules.

Storaasli, Olaf O.↗
NASA NTRS1992

A multiwavelength study of the supernova remnant N49 in the Large Magellanic Cloud

The 2.5-m du Pont telescope at Las Campanas, the IUE, and archival high-resolution imager X-ray data from the Einstein Observatory are used to present a detailed imaging and spectroscopic study of the SNR N49 in the LMC. The asymmetry of the optical image and the relatively high X-ray and optical luminosity of this remnant both arise from its interaction with an extended dense cloud to the southeast seen in CO emission. The optical spectra reveal clear evidence of reddening variations on spatial scales as small as about 2 arcsec over the face of the SNR. UV line emission is associated primarily with the bright optical filaments, and the total luminosity of N49 is measured in several optical and UV lines. A combined analysis of IUE and optical spectra indicates a range of radiative shock velocities. Implications for the interstellar medium surrounding N49 are discussed.

Vancura, Olaf↗
NASA NTRS1993

Parallel-Vector Algorithm For Rapid Structural Anlysis

New algorithm developed to overcome deficiency of skyline storage scheme by use of variable-band storage scheme. Exploits both parallel and vector capabilities of modern high-performance computers. Gives engineers and designers opportunity to include more design variables and constraints during optimization of structures. Enables use of more refined finite-element meshes to obtain improved understanding of complex behaviors of aerospace structures leading to better, safer designs. Not only attractive for current supercomputers but also for next generation of shared-memory supercomputers.

Agarwal, Tarun R.↗
NASA NTRS1992

Far-ultraviolet observations of the Crab Nebula using the Hopkins Ultraviolet Telescope

Observations of the FUV spectrum of the central portion of the Crab Nebula SNR using the Hopkins Ultraviolet Telescope (HUT) aboard the Astro-1 space shuttle mission in December 1990 are reported. The C IV 1549-A emission line shows two resolved components representing the front and back sides of the shell expanding at roughly +/- 1100 km/s. The He II 1640-A emission line shows only a blueshifted component corresponding to the near side of the shell. The HUT observation is compared to optical emission-line imagery and to archival IUE observations. This comparison indicates that a distribution emission component, consisting of either a number of individually faint filaments or a diffuse component, produces the bulk of the emission seen by HUT. A grid of photoionization models for the Crab Nebula filaments is calculated to infer the range of limits. The differing UV line ratios observed for these components indicates that varying carbon and/or He abundances are present in the observed material.

Blair, William P.↗
NASA NTRS1992

Spectroscopy of a Balmer-dominated filament in the Cygnus Loop with the Hopkins Ultraviolet Telescope

A fair UV spectrum of a nonradiative filament in the Cygnus Loop covering the wavelength range 830-1860 A at 3.5-A resolution was obtained using the Hopkins Ultraviolet Telescope (HUT) on the Astro-1 space shuttle mission. Nonradiative shock models which include a more sophisticated treatment of Lyman line transfer are calculated. It is found that the HUT spectrum can be explained in terms of a shock with velocity 175-185 km/s propagating into a low-density medium. This shock velocity can be reconciled with the 135-km/s width of the broad component of H-alpha in this filament if equilibration of the postshock electron and ion temperatures proceeds much more rapidly than Coulomb equilibration time scales. The time required for a 180-km/s shock to develop a partial recombination zone is short, about 200 yr if n is approximately equal to 2/cu cm. This suggests that the shock is decelerating as it encounters denser material. The current analysis patently favors rapid equilibration of electrons and ions behind the shock.

Long, Knox S.↗
NASA NTRS1992

Far-ultraviolet observations of the supernova remnant N49 using the Hopkins Ultraviolet Telescope

The Hopkins Ultraviolet Telescope has been used to obtain the first sub-Lyman-alpha spectrum of an extragalactic SNR, N49, in the LMC. Emission from O VI 1032, 1038 has been detected in this spectral region. The measured fluxes of C IV, semiforbidden O IV, and O VI and the upper limit on N V provide stringent limits on the shocks responsible for the bulk of the O VI production. O VI cannot originate in the shocks with velocities of 140 km/s or less because the postshock temperature is not high enough. The nonradiative main blast wave cannot account for the brightness of the observed O VI emission. The majority of the O VI must originate in an optically faint system of shocks with velocities of 190-270 km/s and preshock densities of 20-40 cu cm. The emission from such high-velocity shocks is dominated by O VI.

Vancura, Olaf↗
NASA NTRS1993

Computational mechanics analysis tools for parallel-vector supercomputers

Computational algorithms for structural analysis on parallel-vector supercomputers are reviewed. These parallel algorithms, developed by the authors, are for the assembly of structural equations, 'out-of-core' strategies for linear equation solution, massively distributed-memory equation solution, unsymmetric equation solution, general eigensolution, geometrically nonlinear finite element analysis, design sensitivity analysis for structural dynamics, optimization search analysis and domain decomposition. The source code for many of these algorithms is available.

Storaasli, Olaf O.↗
NASA NTRS1993

Application of jet-shear-layer mixing and effervescent atomization to the development of a low-NO(x) combustor

An investigation was conducted to develop appropriate technologies for a low-NO(x), liquid-fueled combustor. The combustor incorporates an effervescent atomizer used to inject fuel into a premixing duct. Only a fraction of the combustion air is used in the premixing process to avoid autoignition and flashback problems. This fuel-rich mixture is introduced into the remaining combustion air by a rapid jet-shear-layer-mixing process involving radial fuel-air jets impinging on axial air jets in the primary combustion zone. Computational analysis was used to provide a better understanding of the fluid dynamics that occur in jet-shear-layer mixing and to facilitate a parametric analysis appropriate to the design of an optimum low-NO(x) combustor. A number of combustor configurations were studied to assess the key combustor technologies and to validate the modeling code. The results from the experimental testing and computational analysis indicate a low-NO(x) potential for the jet-shear-layer combustor. Key parameters found to affect NO(x) emissions are the primary combustion zone fuel-air ratio, the number of axial and radial jets, the aspect ratio and radial location of the axial air jets, and the radial jet inlet hole diameter. Each of these key parameters exhibits a low-NO(x) point from which an optimized combustor was developed. Using the parametric analysis, NO(x) emissions were reduced by a factor of 3 as compared with the emissions from conventional, liquid-fueled combustors operating at cruise conditions. Further development promises even lower NO(x) with high combustion efficiency.

Colantonio, Renato Olaf↗