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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 757 records · Page 42
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Optical Matrix.Matrix Multiplier

Proposed apparatus for optical multiplication of two matrices based on Stanford optical vector.matrix multiplier. Does not require redundant representation of one of matrices. Because apparatus performs multiplication in fully parallel manner, incorporated as subsystem into large optical-processing system. Optical matrix.matrix multiplier processes inputs in fully parallel fashion, without redundant matrix images or ancillary intermediate electronic processing.

Gheen, Gregory↗
NASA NTRS1989

Optical systems for digit-serial computation

High-accuracy optical systems for implementing digit-serial computations are discussed which incorporate parallelism and carry-free addition to achieve high processing speed. Employing on-line arithmetic, parallel calculations can be performed by the concurrent execution of operations. The algorithms are shown to be problem invariant and step invariant. Architectures using optical bistable devices and optical interconnects are discussed which can implement digit-serial addition, subtraction, multiplication, and division algorithms via the present approach.

Perlee, Caroline J.↗
NASA NTRS1990

Reflectivities of uniform and broken stratiform clouds: An update

The reflectivities of uniform and broken stratiform clouds obtained from the NOAA-9 and NOAA-10 overpasses collected during the FIRE Marine Stratocumulus Intensive Field Observations (IFO) were compared, and these reflectivities were compared with those obtained through radiative transfer calculation performed for plane-parallel cloud models. The objective was to determine the extent to which plane-parallel radiative transfer calculations could reproduce the reflectivities observed for uniform clouds and to determine the extent to which finite cloud effects cause broken clouds to reflect differently than uniform clouds. The latter study is to provide guidance in the parameterization of finite cloud effects in general circulation climate models as well as to assess the ability of plane-parallel theory, which is used by ISCCP to retrieve cloud properties, to treat the reflectivities of broken clouds. Some results from this study were reported at the last FIRE Science Team meeting and some were reported elsewhere (Coakley and Briegleb, 1989). Improvements since the previous reports include: (1) the analysis of additional satellite passes, and (2) a modification to the analysis which helps to show the significance of the differences in reflectivities for uniform and broken clouds.

Coakley, James A., Jr.↗
NASA NTRS1991

An efficient massively parallel Euler solver for unstructured grids

A data parallel mesh-vertex upwind finite-volume scheme for solving the Euler equations on triangular unstructured meshes is described. A novel vertex-based partitioning of the problem is introduced which minimizes the computation and communication costs associated with distributing the computation to the processors of a massively parallel computer. Finally, the performance of this unstructured computation on 8K processors of the Connection Machine CM-2 is compared with one processor of a Cray-YMP. The experiments show that 8K processors of the CM-2 achieve approximately 70 percent of the performance of one processor of the Cray-YMP on the unstructured mesh computations described here.

Hammond, Steven W.↗
NASA NTRS1991

Note on unit tangent vector computation for homotopy curve tracking on a hypercube

Probability-one homotopy methods are a class of methods for solving nonlinear systems of equations that are globally convergent from an arbitrary starting point. The essence of all such algorithms is the construction of an appropriate homotopy map and subsequent tracking of some smooth curve in the zero set of the homotopy map. Tracking a homotopy curve involves finding the unit tangent vector at different points along the zero curve, which amounts to calculating the kernel of the n x (n + 1) Jacobian matrix. While computing the tangent vector is just one part of the curve tracking algorithm, it can require a significant percentage of the total tracking time. This note presents computational results showing the performance of several different parallel orthogonal factorization/triangular system solving algorithms for the tangent vector computation on a hypercube.

Chakraborty, A.↗
NASA NTRS1993

Cycle life status of SAFT VOS nickel-cadmium cells

The SAFT prismatic VOS Ni-Cd cells have been flown in geosynchronous orbit since 1977 and in low earth orbit since 1983. Parallel cycling tests are performed by several space agencies in order to determine the cycle life for a wide range of temperature and depth of discharge (DOD). In low Earth orbit (LEO), the ELAN program is conducted on 24 Ah cells by CNES and ESA at the European Battery Test Center at temperatures ranging from 0 to 27 C and DOD from 10 to 40 percent. Data are presented up to 37,000 cycles. One pack (X-80) has achieved 49,000 cycles at 10 C and 23 percent DOD. The geosynchronous orbit simulation of a high DOD test is conducted by ESA on 3 batteries at 10 C and 70, 90, and 100 percent DOD. Thirty-one eclipse seasons are completed, and no signs of degradation have been found. The Air Force test at CRANE on 24 Ah and 40 Ah cells at 20 C and 80 percent DOD has achieved 19 shadow periods. Life expectancy is discussed. The VOS cell technology could be used for the following: (1) in geosynchronous conditions--15 yrs at 10-15 C and 80 percent DOD; and (2) in low earth orbit--10 yrs at 5-15 C and 25-30 percent DOD.

Goualard, Jacques↗
NASA NTRS1991

The MSFC space station/space operations mechanism test bed

The Space Station/Space Operations Mechanism Test Bed consists of the following: a hydraulically driven, computer controlled Six Degree-of-Freedom Motion System (6DOF); a six degree-of-freedom force and moment sensor; remote driving stations with computer generated or live TV graphics; and a parallel digital processor that performs calculations to support the real time simulation. The function of the Mechanism Test Bed is to test docking and berthing mechanisms for Space Station Freedom and other orbiting space vehicles in a real time, hardware-in-the-loop simulation environment. Typically, the docking and berthing mechanisms are composed of two mating components, one for each vehicle. In the facility, one component is attached to the motion system, while the other component is mounted to the force/moment sensor fixed in the support structure above the 6DOF. The six components of the contact forces/moments acting on the test article and its mating component are measured by the force/moment sensor.

Sutton, William G.↗
NASA NTRS1992

Parallel fault-tolerant robot control

A shared memory multiprocessor architecture is used to develop a parallel fault-tolerant robot controller. Several versions of the robot controller are developed and compared. A robot simulation is also developed for control observation. Comparison of a serial version of the controller and a parallel version without fault tolerance showed the speedup possible with the coarse-grained parallelism currently employed. The performance degradation due to the addition of processor fault tolerance was demonstrated by comparison of these controllers with their fault-tolerant versions. Comparison of the more fault-tolerant controller with the lower-level fault-tolerant controller showed how varying the amount of redundant data affects performance. The results demonstrate the trade-off between speed performance and processor fault tolerance.

Hamilton, D. L.↗
NASA NTRS1993

Neurocomputing strategies in decomposition based structural design

The present paper explores the applicability of neurocomputing strategies in decomposition based structural optimization problems. It is shown that the modeling capability of a backpropagation neural network can be used to detect weak couplings in a system, and to effectively decompose it into smaller, more tractable, subsystems. When such partitioning of a design space is possible, parallel optimization can be performed in each subsystem, with a penalty term added to its objective function to account for constraint violations in all other subsystems. Dependencies among subsystems are represented in terms of global design variables, and a neural network is used to map the relations between these variables and all subsystem constraints. A vector quantization technique, referred to as a z-Network, can effectively be used for this purpose. The approach is illustrated with applications to minimum weight sizing of truss structures with multiple design constraints.

Szewczyk, Z.↗
NASA NTRS1993

Abundance inhomogeneities and atmospheric structure in CN-bimodal globular cluster giants

It has been suggested by several authors that the sodium and aluminum abundance variations correlating with CN-band strength, frequently observed in CN-bimodal globular cluster giants, could be spurious manifestations of different temperature structures in the 'CN-strong' and 'CN-weak' stars, caused by different molecular line blanketing related to the C, N, and O trio. For stellar parameters generally appropriate to giants in the intermediate metallicity CN-bimodal cluster M4, we demonstrate through new model atmosphere calculations, employing opacity sampling and spherical geometry, that the observed abundance anomalies cannot be the result of atmospheric temperature structure. Our results using spherical geometry are compared to identical calculations performed with plane-parallel geometry: the effects of atmospheric extension on derived abundances for all lines considered amount to less than 0.1 dex.

Drake, Jeremy J.↗
NASA NTRS1993

Approximate optimal guidance for the advanced launch system

A real-time guidance scheme for the problem of maximizing the payload into orbit subject to the equations of motion for a rocket over a spherical, non-rotating earth is presented. An approximate optimal launch guidance law is developed based upon an asymptotic expansion of the Hamilton - Jacobi - Bellman or dynamic programming equation. The expansion is performed in terms of a small parameter, which is used to separate the dynamics of the problem into primary and perturbation dynamics. For the zeroth-order problem the small parameter is set to zero and a closed-form solution to the zeroth-order expansion term of Hamilton - Jacobi - Bellman equation is obtained. Higher-order terms of the expansion include the effects of the neglected perturbation dynamics. These higher-order terms are determined from the solution of first-order linear partial differential equations requiring only the evaluation of quadratures. This technique is preferred as a real-time, on-line guidance scheme to alternative numerical iterative optimization schemes because of the unreliable convergence properties of these iterative guidance schemes and because the quadratures needed for the approximate optimal guidance law can be performed rapidly and by parallel processing. Even if the approximate solution is not nearly optimal, when using this technique the zeroth-order solution always provides a path which satisfies the terminal constraints. Results for two-degree-of-freedom simulations are presented for the simplified problem of flight in the equatorial plane and compared to the guidance scheme generated by the shooting method which is an iterative second-order technique.

Feeley, T. S.↗
NASA NTRS1995

The relation of scalability and execution time

Scalability has been used extensively as a de facto performance criterion for evaluating parallel algorithms and architectures. However, for many, scalability has theoretical interests only since it does not reveal execution time. In this paper, the relation between scalability and execution time is carefully studied. Results show that the isospeed scalability well characterizes the variation of execution time: smaller scalability leads to larger execution time, the same scalability leads to the same execution time, etc. Three algorithms from scientific computing are implemented on an Intel Paragon and an IBM SP2 parallel computer. Experimental and theoretical results show that scalability is an important, distinct metric for parallel and distributed systems, and may be as important as execution time in a scalable parallel and distributed environment.

Sun, Xian-He↗
NASA NTRS1996

A Comparison of Lifting-Line and CFD Methods with Flight Test Data from a Research Puma Helicopter

Four lifting-line methods were compared with flight test data from a research Puma helicopter and the accuracy assessed over a wide range of flight speeds. Hybrid Computational Fluid Dynamics (CFD) methods were also examined for two high-speed conditions. A parallel analytical effort was performed with the lifting-line methods to assess the effects of modeling assumptions and this provided insight into the adequacy of these methods for load predictions.

Bousman, William G.↗
NASA NTRS1996

A Conforming Multigrid Method for the Pure Traction Problem of Linear Elasticity: Mixed Formulation

A multigrid method using conforming P-1 finite element is developed for the two-dimensional pure traction boundary value problem of linear elasticity. The convergence is uniform even as the material becomes nearly incompressible. A heuristic argument for acceleration of the multigrid method is discussed as well. Numerical results with and without this acceleration as well as performance estimates on a parallel computer are included.

Lee, Chang-Ock↗
NASA NTRS1999

Compute as Fast as the Engineers Can Think! ULTRAFAST COMPUTING TEAM FINAL REPORT

This report documents findings and recommendations by the Ultrafast Computing Team (UCT). In the period 10-12/98, UCT reviewed design case scenarios for a supersonic transport and a reusable launch vehicle to derive computing requirements necessary for support of a design process with efficiency so radically improved that human thought rather than the computer paces the process. Assessment of the present computing capability against the above requirements indicated a need for further improvement in computing speed by several orders of magnitude to reduce time to solution from tens of hours to seconds in major applications. Evaluation of the trends in computer technology revealed a potential to attain the postulated improvement by further increases of single processor performance combined with massively parallel processing in a heterogeneous environment. However, utilization of massively parallel processing to its full capability will require redevelopment of the engineering analysis and optimization methods, including invention of new paradigms. To that end UCT recommends initiation of a new activity at LaRC called Computational Engineering for development of new methods and tools geared to the new computer architectures in disciplines, their coordination, and validation and benefit demonstration through applications.

Biedron, R. T.↗
NASA NTRS2001

Computational Analyses of Propulsion Aeroacoustics for Mixed Flow Nozzle Pylon Installation at Takeoff

A CFD analyses is presented for a set of baseline and noise suppression mixed flow nozzles with and without a pylon installation. The five model configurations are as follows; a baselinecore/fan dual-stream nozzle with an external plug, a chevron mixer nozzle with a peak on the symmetry plane with external plug, both of the above nozzles with an installed bifurcatingpylon and lastly a clocked chevron mixer nozzle such that a trough is aligned with the center of the pylon. The fluid flow is simulated by solving the asymptotically steady, compressible, Reynolds-averaged Navier-Stokes equations using an implicit, up-wind, flux-difference splitting finite volume scheme and standard two equation k-epsilon turbulence model with a linear stress representation. All computations are performed using the multiblock, parallel, structuredcode PAB3D. Results indicate that the clocked chevron with pylon case achieves the most optimal levels of average and peak turbulence kinetic energy and vorticity and therefore is expected to be the quietest of the five configurations tested. Further study is required to refine expressions which are indicative of noise and mate these with rigorous noise prediction models.

Massey, Steven J.↗
NASA NTRS2002

Battery Reinitialization of the Photovoltaic Module of the International Space Station

The photovoltaic (PV) module on the International Space Station (ISS) has been operating since November 2000 and supporting electric power demands of the ISS and its crew of three. The PV module contains photovoltaic arrays that convert solar energy to electrical power and an integrated equipment assembly (IEA) that houses electrical hardware and batteries for electric power regulation and storage. Each PV module contains two independent power channels for fault tolerance. Each power channel contains three batteries in parallel to meet its performance requirements and for fault tolerance. Each battery consists of 76 Ni-Hydrogen (Ni-H2) cells in series. These 76 cells are contained in two orbital replaceable units (ORU) that are connected in series. On-orbit data are monitored and trended to ensure that all hardware is operating normally. Review of on-orbit data showed that while five batteries are operating very well, one is showing signs of mismatched ORUs. The cell pressure in the two ORUs differs by an amount that exceeds the recommended range. The reason for this abnormal behavior may be that the two ORUs have different use history. An assessment was performed and it was determined that capacity of this battery would be limited by the lower pressure ORU. Steps are being taken to reduce this pressure differential before battery capacity drops to the point of affecting its ability to meet performance requirements. As a first step, a battery reinitialization procedure was developed to reduce this pressure differential. The procedure was successfully carried out on-orbit and the pressure differential was reduced to the recommended range. This paper describes the battery performance and the consequences of mismatched ORUs that make a battery. The paper also describes the reinitialization procedure, how it was performed on orbit, and battery performance after the reinitialization. On-orbit data monitoring and trending is an ongoing activity and it will continue as ISS assembly progresses.

Hajela, Gyan↗
NASA NTRS2002

Research in Computational Astrobiology

We present results from several projects in the new field of computational astrobiology, which is devoted to advancing our understanding of the origin, evolution and distribution of life in the Universe using theoretical and computational tools. We have developed a procedure for calculating long-range effects in molecular dynamics using a plane wave expansion of the electrostatic potential. This method is expected to be highly efficient for simulating biological systems on massively parallel supercomputers. We have perform genomics analysis on a family of actin binding proteins. We have performed quantum mechanical calculations on carbon nanotubes and nucleic acids, which simulations will allow us to investigate possible sources of organic material on the early earth. Finally, we have developed a model of protobiological chemistry using neural networks.

Chaban, Galina↗