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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 703 records · Page 39
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Digital interface for bi-directional communication between a computer and a peripheral device

For transmission of data from the computer to the peripheral, the computer initially clears a flipflop which provides a select signal to a multiplexer. A data available signal or data strobe signal is produced while tht data is being provided to the interface. Setting of the flipflop causes a gate to provide to the peripherial a signal indicating that the interface has data available for transmission. The peripheral provides an acknowledge or strobe signal to transfer the data to the peripheral. For transmission of data from the peripheral to the computer, the computer presents the initially cleared flipflop. A data request signal from the peripheral indicates that the peripheral has data available for transmission to the computer. An acknowledge signal indicates that the interface is ready to receive data from the peripheral and to strobe that data into the interface.

Bond, H. H., Jr.↗
NASA NTRS1984

Computational aerodynamics and artificial intelligence

The general principles of artificial intelligence are reviewed and speculations are made concerning how knowledge based systems can accelerate the process of acquiring new knowledge in aerodynamics, how computational fluid dynamics may use expert systems, and how expert systems may speed the design and development process. In addition, the anatomy of an idealized expert system called AERODYNAMICIST is discussed. Resource requirements for using artificial intelligence in computational fluid dynamics and aerodynamics are examined. Three main conclusions are presented. First, there are two related aspects of computational aerodynamics: reasoning and calculating. Second, a substantial portion of reasoning can be achieved with artificial intelligence. It offers the opportunity of using computers as reasoning machines to set the stage for efficient calculating. Third, expert systems are likely to be new assets of institutions involved in aeronautics for various tasks of computational aerodynamics.

Mehta, U. B.↗
NASA NTRS1984

Computer Aided Modeling and Post Processing with NASTRAN Analysis

Computer aided engineering systems are invaluable tools in performing NASTRAN finite element analysis. These techniques are implemented in both the pre-processing and post-processing phases of the NASTRAN analysis. The finite element model development, or pre-processing phase, was automated with a computer aided modeling program called Supertabl, and the review and interpretation of the results of the NASTRAN analysis, or post-processing phase, was automated with a computer aided plotting program called Output Display. An intermediate program, Nasplot, which was developed in-house, has also helped to cut down on the model checkout time and reduce errors in the model. An interface has been established between the finite element computer aided engineering system and the Learjet computer aided design system whereby data can be transferred back and forth between the two. These systems have significantly improved productivity and the ability to perform NASTRAN analysis in response to product development requests.

Boroughs, R. R.↗
NASA NTRS1984

An emulator for minimizing computer resources for finite element analysis

A computer code, SCOPE, has been developed for predicting the computer resources required for a given analysis code, computer hardware, and structural problem. The cost of running the code is a small fraction (about 3 percent) of the cost of performing the actual analysis. However, its accuracy in predicting the CPU and I/O resources depends intrinsically on the accuracy of calibration data that must be developed once for the computer hardware and the finite element analysis code of interest. Testing of the SCOPE code on the AMDAHL 470 V/8 computer and the ELAS finite element analysis program indicated small I/O errors (3.2 percent), larger CPU errors (17.8 percent), and negligible total errors (1.5 percent).

Melosh, R.↗
NASA NTRS1984

Computational aerodynamics and artificial intelligence

Some aspects of artificial intelligence are considered and questions are speculated on, including how knowledge-based systems can accelerate the process of acquiring new knowledge in aerodynamics, how computational fluid dynamics may use 'expert' systems and how expert systems may speed the design and development process. The anatomy of an idealized expert system called AERODYNAMICIST is discussed. Resource requirements are examined for using artificial intelligence in computational fluid dynamics and aerodynamics. Considering two of the essentials of computational aerodynamics - reasoniing and calculating - it is believed that a substantial part of the reasoning can be achieved with artificial intelligence, with computers being used as reasoning machines to set the stage for calculating. Expert systems will probably be new assets of institutions involved in aeronautics for various tasks of computational aerodynamics.

Kutler, P.↗
NASA NTRS1984

Application of concurrent processing to structural dynamic response computations

Described are the experiences gained from solving for the dynamic response of two simple structures on an experimental Multiple Instruction Multiple Data (MIMD) computer called the finite element machine. Introduced are MIMD computing concepts, describing how the concurrent algorithmic techniques implemented and giving results for the two example problems. The results show computational speedups of up to 7.83 using eight of the finite element machine processors and indicate that significant computational speedups are possible for large order structural computations.

Ransom, J.↗
NASA NTRS1984

Research in applied mathematics, numerical analysis, and computer science

Research conducted at the Institute for Computer Applications in Science and Engineering (ICASE) in applied mathematics, numerical analysis, and computer science is summarized and abstracts of published reports are presented. The major categories of the ICASE research program are: (1) numerical methods, with particular emphasis on the development and analysis of basic numerical algorithms; (2) control and parameter identification; (3) computational problems in engineering and the physical sciences, particularly fluid dynamics, acoustics, and structural analysis; and (4) computer systems and software, especially vector and parallel computers.

Source record↗
NASA NTRS1985

Exploiting parallel computing with limited program changes using a network of microcomputers

Network computing and multiprocessor computers are two discernible trends in parallel processing. The computational behavior of an iterative distributed process in which some subtasks are completed later than others because of an imbalance in computational requirements is of significant interest. The effects of asynchronus processing was studied. A small existing program was converted to perform finite element analysis by distributing substructure analysis over a network of four Apple IIe microcomputers connected to a shared disk, simulating a parallel computer. The substructure analysis uses an iterative, fully stressed, structural resizing procedure. A framework of beams divided into three substructures is used as the finite element model. The effects of asynchronous processing on the convergence of the design variables are determined by not resizing particular substructures on various iterations.

Rogers, J. L., Jr.↗
NASA NTRS1985

Reliability models for dataflow computer systems

The demands for concurrent operation within a computer system and the representation of parallelism in programming languages have yielded a new form of program representation known as data flow (DENN 74, DENN 75, TREL 82a). A new model based on data flow principles for parallel computations and parallel computer systems is presented. Necessary conditions for liveness and deadlock freeness in data flow graphs are derived. The data flow graph is used as a model to represent asynchronous concurrent computer architectures including data flow computers.

Kavi, K. M.↗
NASA NTRS1985

System enhancements of Mesoscale Analysis and Space Sensor (MASS) computer system

The interactive information processing for the mesoscale analysis and space sensor (MASS) program is reported. The development and implementation of new spaceborne remote sensing technology to observe and measure atmospheric processes is described. The space measurements and conventional observational data are processed together to gain an improved understanding of the mesoscale structure and dynamical evolution of the atmosphere relative to cloud development and precipitation processes. A Research Computer System consisting of three primary computers was developed (HP-1000F, Perkin-Elmer 3250, and Harris/6) which provides a wide range of capabilities for processing and displaying interactively large volumes of remote sensing data. The development of a MASS data base management and analysis system on the HP-1000F computer and extending these capabilities by integration with the Perkin-Elmer and Harris/6 computers using the MSFC's Apple III microcomputer workstations is described. The objectives are: to design hardware enhancements for computer integration and to provide data conversion and transfer between machines.

Hickey, J. S.↗
NASA NTRS1985

A new taxonomy for distributed computer systems based upon operating system structure

Characteristics of the resource structure found in the operating system are considered as a mechanism for classifying distributed computer systems. Since the operating system resources, themselves, are too diversified to provide a consistent classification, the structure upon which resources are built and shared are examined. The location and control character of this indivisibility provides the taxonomy for separating uniprocessors, computer networks, network computers (fully distributed processing systems or decentralized computers) and algorithm and/or data control multiprocessors. The taxonomy is important because it divides machines into a classification that is relevant or important to the client and not the hardware architect. It also defines the character of the kernel O/S structure needed for future computer systems. What constitutes an operating system for a fully distributed processor is discussed in detail.

Foudriat, E. C.↗
NASA NTRS1985

Computation of unsteady transonic aerodynamics with steady state fixed by truncation error injection

A novel technique is introduced for efficient computations of unsteady transonic aerodynamics. The steady flow corresponding to body shape is maintained by truncation error injection while the perturbed unsteady flows corresponding to unsteady body motions are being computed. This allows the use of different grids comparable to the characteristic length scales of the steady and unsteady flows and, hence, allows efficient computation of the unsteady perturbations. An example of typical unsteady computation of flow over a supercritical airfoil shows that substantial savings in computation time and storage without loss of solution accuracy can easily be achieved. This technique is easy to apply and requires very few changes to existing codes.

Fung, K.-Y.↗
NASA NTRS1986

The SIMRAND 1 computer program: Simulation of research and development projects

The SIMRAND I Computer Program (Version 5.0 x 0.3) written in Microsoft FORTRAN for the IBM PC microcomputer and its compatibles is described. The SIMRAND I Computer Program comprises eleven modules-a main routine and ten subroutines. Two additional files are used at compile time; one inserts the system or task equations into the source code, while the other inserts the dimension statements and common blocks. The SIMRAND I Computer Program can be run on most microcomputers or mainframe computers with only minor modifications to the computer code.

Miles, R. F., Jr.↗
NASA NTRS1984

Numerical computation of viscous flow around bodies and wings moving at supersonic speeds

Research in aerodynamics is discussed. The development of equilibrium air curve fits; computation of hypersonic rarefield leading edge flows; computation of 2-D and 3-D blunt body laminar flows with an impinging shock; development of a two-dimensional or axisymmetric real gas blunt body code; a study of an over-relaxation procedure forthe MacCormack finite-difference scheme; computation of 2-D blunt body turbulent flows with an impinging shock; computation of supersonic viscous flow over delta wings at high angles of attack; and computation of the Space Shuttle Orbiter flowfield are discussed.

Tannehill, J. C.↗
NASA NTRS1985

Orbits: Computer simulation

In rotating machinery dynamics an orbit (Lissajous curve) represents the dynamic path of the shaft centerline motion during shaft rotation and resulting precession. The orbit can be observed with an oscilloscope connected to XY promixity probes. The orbits can also be simulated by a computer. The software for HP computer simulates orbits for two cases: (1) Symmetric orbit with four frequency components with different radial amplitudes and relative phase angles; and (2) Nonsymmetric orbit with two frequency components with two different vertical/horizontal amplitudes and two different relative phase angles. Each orbit carries a Keyphasor mark (one-per-turn reference). The frequencies, amplitudes, and phase angles, as well as number of time steps for orbit computation, have to be chosen and introduced to the computer by the user. The orbit graphs can be observed on the computer screen.

Muszynska, A.↗
NASA NTRS1986

Computation of separated flow on a ramp using the space marching conservative supra-characteristics method

Steady, hypersonic viscous flows over compression corners with streamwise separation have been computed using the space marching Conservative Supra-Characteristics Method (CSCM-S) of Lombard. The CSCM-S method permits stable space marching of the parabolized Navier-Stokes (PNS) equations through large separated flow regions. The present method has been used to compute surface pressure, heat transfer, and skin friction coefficients for two compression corner cases studied experimentally by Holden and Moselle. The computed results compare favorably with previous Navier-Stokes results and the experimental data. The present method has also been compared with the conventional Beam-Warming scheme for solving the PNS equations. Comparison are made for accuracy, computer time, and computer storage.

Stookesberry, D. C.↗
NASA NTRS1986

A nonlinear substructuring method for concurrent processing computers

This paper proposes a method, based on substructuring, to solve nonlinear structural analysis problems on multiprocessor computers. Background information is given on the use of substructuring in large-scale finite element programs and computational time distributions for the major components for an example nonlinear finite element analysis are discussed. Implementation of the substructuring method on a typical multiprocessor computer is described and estimates are made of expected reductions in computation times based on nonlinear substructuring results obtained on a single processor computer.

Storaasli, O. O.↗
NASA NTRS1986

Computation of multi-dimensional viscous supersonic flow

A method has been developed for two- and three-dimensional computations of viscous supersonic jet flows interacting with an external flow. The approach employs a reduced form of the Navier-Stokes equations which allows solution as an initial-boundary value problem in space, using an efficient noniterative forward marching algorithm. Numerical instability associated with forward marching algorithms for flows with embedded subsonic regions is avoided by approximation of the reduced form of the Navier-Stokes equations in the subsonic regions of the boundary layers. Supersonic and subsonic portions of the flow field are simultaneously calculated by a consistently split linearized block implicit computational algorithm. The results of computations for a series of test cases associated with supersonic jet flow is presented and compared with other calculations for axisymmetric cases. Demonstration calculations indicate that the computational technique has great promise as a tool for calculating a wide range of supersonic flow problems including jet flow. Finally, a User's Manual is presented for the computer code used to perform the calculations.

Buggeln, R. C.↗