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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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Algorithms and software for solving finite element equations on serial and parallel architectures

The primary objective was to compare the performance of state-of-the-art techniques for solving sparse systems with those that are currently available in the Computational Structural Mechanics (MSC) testbed. One of the first tasks was to become familiar with the structure of the testbed, and to install some or all of the SPARSPAK package in the testbed. A brief overview of the CSM Testbed software and its usage is presented. An overview of the sparse matrix research for the Testbed currently employed in the CSM Testbed is given. An interface which was designed and implemented as a research tool for installing and appraising new matrix processors in the CSM Testbed is described. The results of numerical experiments performed in solving a set of testbed demonstration problems using the processor SPK and other experimental processors are contained.

Chu, Eleanor↗
NASA NTRS1989

Algorithms and software for solving finite element equations on serial and parallel architectures

Over the past 15 years numerous new techniques have been developed for solving systems of equations and eigenvalue problems arising in finite element computations. A package called SPARSPAK has been developed by the author and his co-workers which exploits these new methods. The broad objective of this research project is to incorporate some of this software in the Computational Structural Mechanics (CSM) testbed, and to extend the techniques for use on multiprocessor architectures.

George, Alan↗
NASA NTRS1990

Serial Escape System For Aircraft Crews

Emergency escape system for aircraft and aerospace vehicles ejects up to seven crewmembers, one by one, within 120 s. Intended for emergencies in which disabled craft still in stable flight at no more than 220 kn (113 m/s) equivalent airspeed and sinking no faster than 110 ft/s (33.5 m/s) at altitudes up to 50,000 ft (15.2 km). Ejection rockets load themselves from magazine after each crewmember ejected. Jumpmaster queues other crewmembers and helps them position themselves on egress ramp. Rockets pull crewmembers clear of aircraft structure. Provides orderly, controlled exit and avoids ditching at sea or landing in rough terrain.

Wood, Kenneth E.↗
NASA NTRS1990

General-Purpose Serial Interface For Remote Control

Computer controls remote television camera. General-purpose controller developed to serve as interface between host computer and pan/tilt/zoom/focus functions on series of automated video cameras. Interface port based on 8251 programmable communications-interface circuit configured for tristated outputs, and connects controller system to any host computer with RS-232 input/output (I/O) port. Accepts byte-coded data from host, compares them with prestored codes in read-only memory (ROM), and closes or opens appropriate switches. Six output ports control opening and closing of as many as 48 switches. Operator controls remote television camera by speaking commands, in system including general-purpose controller.

Busquets, Anthony M.↗
NASA NTRS1989

Preliminary study of a serial-parallel redundant manipulator

The manipulator design discussed here results from the examination of some of the reasons why redundancy is necessary in general purpose manipulation systems. A spherical joint design actuated in-parallel, having the many advantages of parallel actuation, is described. In addition, the benefits of using redundant actuators are discussed and illustrated in the design by the elimination of loci of singularities from the usable workspace with the addition of only one actuator. Finally, what is known by the authors about space robotics requirements is summarized and the relevance of the proposed design matched against these requirements. The design problems outlined here are viewed as much from the mechanical engineering aspect as from concerns arising from the control and the programming of manipulators.

Hayward, Vincent↗
NASA NTRS1991

Linear and circular digital spectral analysis of serial data

Two methods of digital spectral analysis of unevenly sampled data are developed and illustrated here. One method uses a linear function of time (or space), the other uses circular functions. The circular method turns out to be essentially equivalent to a least-squares sine-wave analysis. The linear, anharmonic method uses only the field of real numbers and elementary algebraic operations, and hence it can be made computationally very fast and accurate. Both methods are very general, properly handling all kinds of time series ranging from simple series consisting only of the times of events to complicated series consisting of pulses with long duty cycles. The two methods are here applied to the analysis of annual mean relative sunspot numbers.

Stothers, Richard B.↗
NASA NTRS1991

New dynamic FET logic and serial memory circuits for VLSI GaAs technology

The complexity of GaAs field effect transistor (FET) very large scale integration (VLSI) circuits is limited by the maximum power dissipation while the uniformity of the device parameters determines the functional yield. In this work, digital GaAs FET circuits are presented that eliminate the DC power dissipation and reduce the area to 50% of that of the conventional static circuits. Its larger tolerance to device parameter variations results in higher functional yield.

Eldin, A. G.↗
NASA NTRS1994

A comparative study of serial and parallel aeroelastic computations of wings

A procedure for computing the aeroelasticity of wings on parallel multiple-instruction, multiple-data (MIMD) computers is presented. In this procedure, fluids are modeled using Euler equations, and structures are modeled using modal or finite element equations. The procedure is designed in such a way that each discipline can be developed and maintained independently by using a domain decomposition approach. In the present parallel procedure, each computational domain is scalable. A parallel integration scheme is used to compute aeroelastic responses by solving fluid and structural equations concurrently. The computational efficiency issues of parallel integration of both fluid and structural equations are investigated in detail. This approach, which reduces the total computational time by a factor of almost 2, is demonstrated for a typical aeroelastic wing by using various numbers of processors on the Intel iPSC/860.

Byun, Chansup↗
NASA NTRS1994

On extending parallelism to serial simulators

This paper describes an approach to discrete event simulation modeling that appears to be effective for developing portable and efficient parallel execution of models of large distributed systems and communication networks. In this approach, the modeler develops submodels using an existing sequential simulation modeling tool, using the full expressive power of the tool. A set of modeling language extensions permit automatically synchronized communication between submodels; however, the automation requires that any such communication must take a nonzero amount off simulation time. Within this modeling paradigm, a variety of conservative synchronization protocols can transparently support conservative execution of submodels on potentially different processors. A specific implementation of this approach, U.P.S. (Utilitarian Parallel Simulator), is described, along with performance results on the Intel Paragon.

Nicol, David↗
NASA NTRS2001

Tools to Rapidly and Effectively Parallelise Serial FORTRAN Codes Using Either MPI or OpenMP

Significant progress has been made in hardware and software technologies, as a result the use of efficient standard message passing communication calls in parallel application codes has greatly assisted in reducing execution times. In addition, the introduction of OpenMP, an industrial standard for shared memory programming with directives addresses the issue of portability and also provides a means to deliver respectable performance. In general however, the manual parallelisation of a user's application code using either message passing or directives is still a very costly and error-prone process.

Jin, Hao-Qiang↗
NASA NTRS2001

Chip for CCSDS Compatible Serial Data Streams

A configurable service processor for telemetry ground stations is totally implemented in VLSI/ASIC hardware and finds use in spacecraft systems and other communications systems that operate according to CCSDS and CCSDS-like protocols. The service processor performs the traditional functions of data extraction at very high data and packet rates.

Jason T Dowling↗
NASA NTRS1999

Three-dimensional segmentation of luminal and adventitial borders in serial intravascular ultrasound images

Intravascular ultrasound (IVUS) provides exact anatomy of arteries, allowing accurate quantitative analysis. Automated segmentation of IVUS images is a prerequisite for routine quantitative analyses. We present a new three-dimensional (3D) segmentation technique, called active surface segmentation, which detects luminal and adventitial borders in IVUS pullback examinations of coronary arteries. The technique was validated against expert tracings by computing correlation coefficients (range 0.83-0.97) and William's index values (range 0.37-0.66). The technique was statistically accurate, robust to image artifacts, and capable of segmenting a large number of images rapidly. Active surface segmentation enabled geometrically accurate 3D reconstruction and visualization of coronary arteries and volumetric measurements.

NASA Discipline Cardiopulmonary↗
NASA NTRS2005

A Survey of Singular Value Decomposition Methods and Performance Comparison of Some Available Serial Codes

This contractor report describes a performance comparison of available alternative complete Singular Value Decomposition (SVD) methods and implementations which are suitable for incorporation into point spread function deconvolution algorithms. The report also presents a survey of alternative algorithms, including partial SVD's special case SVD's, and others developed for concurrent processing systems.

Plassman, Gerald E.↗
NASA NTRS2006

Time Serial Analysis of the Induced LEO Environment within the ISS 6A

Anisotropies in the low Earth orbit (LEO) radiation environment were found to influence the thermoluminescence detectors (TLD) dose within the (International Space Station) ISS 7A Service Module. Subsequently, anisotropic environmental models with improved dynamic time extrapolation have been developed including westward and northern drifts using AP8 Min & Max as estimates of the historic spatial distribution of trapped protons in the 1965 and 1970 era, respectively. In addition, a directional dependent geomagnetic cutoff model was derived for geomagnetic field configurations from the 1945 to 2020 time frame. A dynamic neutron albedo model based on our atmospheric radiation studies has likewise been required to explain LEO neutron measurements. The simultaneous measurements of dose and dose rate using four Liulin instruments at various locations in the US LAB and Node 1 has experimentally demonstrated anisotropic effects in ISS 6A and are used herein to evaluate the adequacy of these revised environmental models.

Wilson, John W.↗
NASA NTRS1992

Serial data transmission between redundant channels

Data is communicated between redundant channels formatted in blocks having an initial command word followed by a destination code, starting address and a variable number of data words including a word count. The blocks are transmitted between each channel and all of the channels over cross-channel data links, each channel receiving the data blocks and determining the validity thereof by counting the number of data words received and comparing that number to the word count transmitted for that block. An interrupt signal indicative of invalidity of a block is provided in the event of a miscompare. A stop address is generated for each block received for storage at the start address. A memory address is generated for each valid word received for storage in sequence starting immediately after the start address. The next block received has its start address placed immediately at the end of the previously received block.

Tulpule, Bhalchandra R.↗
NASA NTRS2010

Measurement Techniques for Transmit Source Clock Jitter for Weak Serial RF Links

Techniques for filtering clock jitter measurements are developed, in the context of controlling data modulation jitter on an RF carrier to accommodate low signal-to-noise ratio thresholds of high-performance error correction codes. Measurement artifacts from sampling are considered, and a tutorial on interpretation of direct readings is included.

Lansdowne, Chatwin A.↗
NASA NTRS2012

Ka-Band Waveguide Three-Way Serial Combiner for MMIC Amplifiers

In this innovation, the three-way combiner consists internally of two branch-line hybrids that are connected in series by a short length of waveguide. Each branch-line hybrid is designed to combine input signals that are in phase with an amplitude ratio of two. The combiner is constructed in an E-plane split-block arrangement and is precision machined from blocks of aluminum with standard WR-28 waveguide ports. The port impedances of the combiner are matched to that of a standard WR-28 waveguide. The component parts include the power combiner and the MMIC (monolithic microwave integrated circuit) power amplifiers (PAs). The three-way series power combiner is a six-port device. For basic operation, power that enters ports 3, 5, and 6 is combined in phase and appears at port 1. Ports 2 and 4 are isolated ports. The application of the three-way combiner for combining three PAs with unequal output powers was demonstrated. NASA requires narrow-band solid-state power amplifiers (SSPAs) at Ka-band frequencies with output power in the range of 3 to 5 W for radio or gravity science experiments. In addition, NASA also requires wideband, high-efficiency SSPAs at Ka-band frequencies with output power in the range of 5 to 15 W for high-data-rate communications from deep space to Earth. The three-way power combiner is designed to operate over the frequency band of 31.8 to 32.3 GHz, which is NASA s deep-space frequency band.

Wintucky, Edwin G.↗