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At least 847 records · Page 47

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NASA NTRS1991

Stacking-sequence optimization for buckling of laminated plates by integer programming

Integer-programming formulations for the design of symmetric and balanced laminated plates under biaxial compression are presented. Both maximization of buckling load for given total thickness, and the minimization of total thickness subject to a buckling constraint are formulated. The design variables that define the stacking sequence of the laminate are zero-one integers. It is shown that the formulation results in a linear optimization problem that can be solved on readily aviable software. Constraints on the stacking sequence such as a limit on the number of contiguous plies of the same orientation and limits on in-plane stiffnesses are easily accommodated. Examples are presented for graphite-epoxy plates under uniaxial and biaxial compression using a commercial software package based on the branch-and-bound algorithm.

Haftka, Raphael T.↗

NASA NTRS1990

Simulation of capacitor charging power supplies

By neglecting losses and other nonidealities, the authors were able to derive a simple single-loop equivalent circuit for each mode of operation of the series resonant converter. From these equivalent circuits, a good approximation of the current and voltages within the converter was obtained, despite the simplified approach taken. It is pointed out that designers of capacitor charging power supplies can utilize this approach in deciding what type of control strategy is needed to obtain a desired characteristic. Once the basic topology of the power supply has been determined, a detailed simulation could be implemented using one of the general-purpose software packages available.

Newton, S. R.↗

NASA NTRS1991

Experiments with conjugate gradient algorithms for homotopy curve tracking

There are algorithms for finding zeros or fixed points of nonlinear systems of equations that are globally convergent for almost all starting points, i.e., with probability one. The essence of all such algorithms is the construction of an appropriate homotopy map and then tracking some smooth curve in the zero set of this homotopy map. HOMPACK is a mathematical software package implementing globally convergent homotopy algorithms with three different techniques for tracking a homotopy zero curve, and has separate routines for dense and sparse Jacobian matrices. The HOMPACK algorithms for sparse Jacobian matrices use a preconditioned conjugate gradient algorithm for the computation of the kernel of the homotopy Jacobian matrix, a required linear algebra step for homotopy curve tracking. Here, variants of the conjugate gradient algorithm are implemented in the context of homotopy curve tracking and compared with Craig's preconditioned conjugate gradient method used in HOMPACK. The test problems used include actual large scale, sparse structural mechanics problems.

Irani, Kashmira M.↗

NASA NTRS1990

Interactive numerical flow visualization using stream surfaces

Particle traces and ribbons are often used to depict the structure of three-dimensional flowfields, but images produced using these models can be ambiguous. Stream surfaces offer a more visually intuitive method for the depiction of flowfields, but interactive response is needed to allow the user to place surfaces which reveal the essential features of a given flowfield. FLORA, a software package which supports the interactive calculation and display of stream surfaces on silicon graphics workstations, is described. Alternative methods for the integration of particle traces are examined, and calculation through computational space is found to provide rapid results with accuracy adequate for most purposes. Rapid calculation of traces is teamed with progressive refinement of appoximated surfaces. An initial approximation provides immediate user feedback, and subsequent improvement of the surface ensures that the final image is an accurate representation of the flowfield.

Hultquist, J. P. M.↗

NASA NTRS1991

Interactive design of hypersonic waverider geometries

The paper deals with an inverse design code utilizing the method of oscillating cones; the code integrated into an interactive graphics software package allows manipulation of both the exit-plane shock profile and leading edge of the vehicle. Another interactive feature of the system is the ability to vary freestream conditions and reevaluate the governing conditions. The development of the oscillating cones is shown on five classes each of which is chosen to demonstrate an aspect of improved design flexibility over previous studies. Results are evaluated using a robust flow solver, insuring that the shock shapes specified in the design process are recovered. It is pointed out that the expanded range of waverider geometries that may be generated using the oscillating cones technique may provide insight into visually oriented optimization parameters such as volumetric efficiency and practical planform.

Center, K. B.↗

NASA NTRS1992

Analyzing Satellite Images Of The Ocean

PC-SEAPAK is user-interactive software package specifically developed for analysis of data from satellites in oceanographic research. Program used to process and interpret data obtained from Nimbus-7/Coastal Zone Color Scanner (CZCS) and NOAA Advanced Very High Resolution Radiometer (AVHRR). PC-SEAPAK copyrighted product with all copyright vested in National Aeronautics and Space Administration.

Mcclain, Charles R.↗

NASA NTRS1992

Vortex-Blob Simulation Of Two-Dimensional Flows

Software package includes two programs: KPD12 and KPD12P. Both programs use vortex-blob method to simulate flow around solid bodies. KPD12 treats unbounded domain, while KPD12P treats domain having periodicity in one direction. Main advantage, ability to handle situations involving arbitrary shapes, including multiple bodies. User supplies only points on solid boundaries; no grid. Source code in Cray FORTRAN.

Spalart, Philippe↗

NASA NTRS1992

Program Aids Design Of Fluid-Circulating Systems

Computer Aided Systems Engineering and Analysis (CASE/A) program is interactive software tool for trade study and analysis, designed to increase productivity during all phases of systems engineering. Graphics-based command-driven software package provides user-friendly computing environment in which engineer analyzes performance and interface characteristics of ECLS/ATC system. Useful during all phases of spacecraft-design program, from initial conceptual design trade studies to actual flight, including pre-flight prediction and in-flight analysis of anomalies. Written in FORTRAN 77.

Bacskay, Allen↗

NASA NTRS1992

Software For Animated Graphics

Graphics Animation System (GAS) software package serves as easy-to-use, menu-driven program providing fast, simple viewing capabilities as well as more-complex features for rendering and animation in computational fluid dynamics (CFD). Displays two- and three-dimensional objects along with computed data and records animation sequences on video digital disk, videotape, and 16-mm film. Written in C.

Merritt, F.↗

NASA NTRS1992

Software For Computing Selected Functions

Technical memorandum presents collection of software packages in Ada implementing mathematical functions used in science and engineering. Provides programmer with function support in Pascal and FORTRAN, plus support for extended-precision arithmetic and complex arithmetic. Valuable for testing new computers, writing computer code, or developing new computer integrated circuits.

Grant, David C.↗

NASA NTRS1992

Reformatting Data From X-Ray Photoelectron Spectroscopy

ASCITOVG program for IBM PC-series computers creates files in binary format from columns of numbers in American National Standard Code for Information Interchange (ASCII) format. Files suitable for DEC PDP-11/73 computer under Micro-RSX operating system running the VGS-5000 Enhanced Data Processing (EDP) software package which analyzes data with color graphics display, speeding up analysis compared with batch job processing. Written in FORTRAN.

Abel, P. B.↗

NASA NTRS1991

LV software support for supersonic flow analysis

During 1991, the software developed allowed an operator to configure and checkout the TSI, Inc. laser velocimeter (LV) system prior to a run. This setup procedure established the operating conditions for the TSI MI-990 multichannel interface and the RMR-1989 rotating machinery resolver. In addition to initializing the instruments, the software package provides a means of specifying LV calibration constants, controlling the sampling process, and identifying the test parameters.

Bell, William A.↗

NASA NTRS1991

Vibroacoustic Payload Environment Prediction System (VAPEPS): VAPEPS management center remote access guide

A Vibroacoustic Payload Environment Prediction System (VAPEPS) Management Center was established at the JPL. The center utilizes the VAPEPS software package to manage a data base of Space Shuttle and expendable launch vehicle payload flight and ground test data. Remote terminal access over telephone lines to the computer system, where the program resides, was established to provide the payload community a convenient means of querying the global VAPEPS data base. This guide describes the functions of the VAPEPS Management Center and contains instructions for utilizing the resources of the center.

Fernandez, J. P.↗

NASA NTRS1991

Computational modelling of polymers

Polymeric materials and polymer/graphite composites show a very diverse range of material properties, many of which make them attractive candidates for a variety of high performance engineering applications. Their properties are ultimately determined largely by their chemical structure, and the conditions under which they are processed. It is the aim of computational chemistry to be able to simulate candidate polymers on a computer, and determine what their likely material properties will be. A number of commercially available software packages purport to predict the material properties of samples, given the chemical structures of their constituent molecules. One such system, Cerius, has been in use at LaRC. It is comprised of a number of modules, each of which performs a different kind of calculation on a molecule in the programs workspace. Particularly, interest is in evaluating the suitability of this program to aid in the study of microcrystalline polymeric materials. One of the first model systems examined was benzophenone. The results of this investigation are discussed.

Celarier, Edward A.↗

NASA NTRS1991

Comparison of different fractal dimension measuring algorithms for RE-TM M-O films

Noise in magneto-optical recording devices is discussed. In general, it appears that either the divider technique or amplitude spectrum technique may be used interchangeably to measure the fractal dimension (D) in the domain wall structure of ideal images. However, some caveats must be observed for best results. The divider technique is attractive for its simplicity and relatively modest computation requirements. However, it is sensitive to noise, in that noise pixels that touch the domain boundary are interpreted as being part of the boundary, skewing the measurement. Also, it is not useful in measuring nucleation-dominated films or domains that have significant amounts of structure within the interior of the domain wall. The amplitude spectrum method is more complex, and less intuitive than the divider method, and somewhat more expensive to implement computationally. However, since the camera noise tends to be white, the noise can be avoided in the measurement of D by avoiding that portion of the curve that is flat (due to the white noise) when the least squares line is fit to the plot. Also, many image processing software packages include a Fast Fourier Transformation (FFT) facility, while the user will most likely have to write his own edge extraction routine for the divider method. The amplitude spectrum method is a true two dimensional technique that probes the interior of the domain wall, and in fact, can measure arbitrary clusters of domains. It can also be used to measure grey-level images, further reducing processing steps needed to threshold the image.

Bernacki, Bruce E.↗

NASA NTRS1991

Technical Requirements Analysis and Control Systems (TRACS) Initial Operating Capability (IOC) documentation

The Technical Requirements Analysis and Control Systems (TRACS) software package is described. TRACS offers supplemental tools for the analysis, control, and interchange of project requirements. This package provides the fundamental capability to analyze and control requirements, serves a focal point for project requirements, and integrates a system that supports efficient and consistent operations. TRACS uses relational data base technology (ORACLE) in a stand alone or in a distributed environment that can be used to coordinate the activities required to support a project through its entire life cycle. TRACS uses a set of keyword and mouse driven screens (HyperCard) which imposes adherence through a controlled user interface. The user interface provides an interactive capability to interrogate the data base and to display or print project requirement information. TRACS has a limited report capability, but can be extended with PostScript conventions.

Hammond, Dana P.↗

NASA NTRS1992

Graphical workstation capability for reliability modeling

In addition to computational capabilities, software tools for estimating the reliability of fault-tolerant digital computer systems must also provide a means of interfacing with the user. Described here is the new graphical interface capability of the hybrid automated reliability predictor (HARP), a software package that implements advanced reliability modeling techniques. The graphics oriented (GO) module provides the user with a graphical language for modeling system failure modes through the selection of various fault-tree gates, including sequence-dependency gates, or by a Markov chain. By using this graphical input language, a fault tree becomes a convenient notation for describing a system. In accounting for any sequence dependencies, HARP converts the fault-tree notation to a complex stochastic process that is reduced to a Markov chain, which it can then solve for system reliability. The graphics capability is available for use on an IBM-compatible PC, a Sun, and a VAX workstation. The GO module is written in the C programming language and uses the graphical kernal system (GKS) standard for graphics implementation. The PC, VAX, and Sun versions of the HARP GO module are currently in beta-testing stages.

Bavuso, Salvatore J.↗

NASA NTRS1992

ISE: An Integrated Search Environment. The manual

Integrated Search Environment (ISE), a software package that implements hierarchical searches with meta-control, is described in this manual. ISE is a collection of problem-independent routines to support solving searches. Mainly, these routines are core routines for solving a search problem and they handle the control of searches and maintain the statistics related to searches. By separating the problem-dependent and problem-independent components in ISE, new search methods based on a combination of existing methods can be developed by coding a single master control program. Further, new applications solved by searches can be developed by coding the problem-dependent parts and reusing the problem-independent parts already developed. Potential users of ISE are designers of new application solvers and new search algorithms, and users of experimental application solvers and search algorithms. The ISE is designed to be user-friendly and information rich. In this manual, the organization of ISE is described and several experiments carried out on ISE are also described.

Chu, Lon-Chan↗