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  • 1
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    Enhancements to the GRIDGEN structured grid generation system for internal and external flow applications (1992)
    In:  CASI
    Details
    Publication Date: 2013-08-29
    Description: GRIDGEN is a government domain software package for interactive generation of multiple block grids around general configurations. Though it has been freely available since 1989, it has not been widely embraced by the internal flow community due to a misconception that it was designed for external flow use only. In reality GRIDGEN has always worked for internal flow applications, and GRIDGEN ongoing enhancements are increasing the quality of and efficiency with which grids for external and internal flow problems may be constructed. The software consists of four codes used to perform the four steps of the grid generation process. GRIDBLOCK is first used to decompose the flow domain into a collection of component blocks and then to establish interblock connections and flow solver boundary conditions. GRIDGEN2D is then used to generate surface grids on the outer shell of each component block. GRIDGEN3D generates grid points on the interior of each block, and finally GRIDVUE3D is used to inspect the resulting multiple block grid. Three of these codes (GRIDBLOCK, GRIDGEN2D, and GRIDVUE3D) are highly interactive and graphical in nature, and currently run on Silicon Graphics, Inc., and IBM RS/6000 workstations. The lone batch code (GRIDGEN3D) may be run on any of several Unix based platforms. Surface grid generation in GRIDGEN2D is being improved with the addition of higher order surface definitions (NURBS and parametric surfaces input in IGES format and bicubic surfaces input in PATRAN Neutral File format) and double precision mathematics. In addition, two types of automation have been added to GRIDGEN2D that reduce the learning curve slope for new users and eliminate work for experienced users. Volume grid generation using GRIDGEN3D has been improved via the addition of an advanced hybrid control function formulation that provides both orthogonality and clustering control at the block faces and clustering control on the block interior.
    Keywords: COMPUTER PROGRAMMING AND SOFTWARE
    Type: NASA. Goddard Space Flight Center, Tenth Workshop for Computational Fluid Dynamic Applications in Rocket Propulsion, Part 1; p 543-576
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  • 2
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    Recent enhancements to the GRIDGEN structured grid generation system (1992)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Significant enhancements are being implemented into the GRIDGEN3D, multiple block, structured grid generation software. Automatic, point-to-point, interblock connectivity will be possible through the addition of the domain entity to GRIDBLOCK's block construction process. Also, the unification of GRIDGEN2D and GRIDBLOCK has begun with the addition of edge grid point distribution capability to GRIDBLOCK. The geometric accuracy of surface grids and the ease with which databases may be obtained is being improved by adding support for standard computer-aided design formats (e.g., PATRAN Neutral and IGES files). Finally, volume grid quality was improved through addition of new SOR algorithm features and the new hybrid control function type to GRIDGEN3D.
    Keywords: COMPUTER PROGRAMMING AND SOFTWARE
    Type: NASA. Langley Research Center, Software Surface Modeling and Grid Generation Steering Committee; p 253-271
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  • 3
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    An experimental evaluation of software redundancy as a strategy for improving reliability (1990)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The strategy of using multiple versions of independently developed software as a means to tolerate residual software design faults is suggested by the success of hardware redundancy for tolerating hardware failures. Although, as generally accepted, the independence of hardware failures resulting from physical wearout can lead to substantial increases in reliability for redundant hardware structures, a similar conclusion is not immediate for software. The degree to which design faults are manifested as independent failures determines the effectiveness of redundancy as a method for improving software reliability. Interest in multi-version software centers on whether it provides an adequate measure of increased reliability to warrant its use in critical applications. The effectiveness of multi-version software is studied by comparing estimates of the failure probabilities of these systems with the failure probabilities of single versions. The estimates are obtained under a model of dependent failures and compared with estimates obtained when failures are assumed to be independent. The experimental results are based on twenty versions of an aerospace application developed and certified by sixty programmers from four universities. Descriptions of the application, development and certification processes, and operational evaluation are given together with an analysis of the twenty versions.
    Keywords: COMPUTER PROGRAMMING AND SOFTWARE
    Type: NASA-TM-102613 , NAS 1.15:102613
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  • 4
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    Zebra: A striped network file system (1992)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The design of Zebra, a striped network file system, is presented. Zebra applies ideas from log-structured file system (LFS) and RAID research to network file systems, resulting in a network file system that has scalable performance, uses its servers efficiently even when its applications are using small files, and provides high availability. Zebra stripes file data across multiple servers, so that the file transfer rate is not limited by the performance of a single server. High availability is achieved by maintaining parity information for the file system. If a server fails its contents can be reconstructed using the contents of the remaining servers and the parity information. Zebra differs from existing striped file systems in the way it stripes file data: Zebra does not stripe on a per-file basis; instead it stripes the stream of bytes written by each client. Clients write to the servers in units called stripe fragments, which are analogous to segments in an LFS. Stripe fragments contain file blocks that were written recently, without regard to which file they belong. This method of striping has numerous advantages over per-file striping, including increased server efficiency, efficient parity computation, and elimination of parity update.
    Keywords: COMPUTER PROGRAMMING AND SOFTWARE
    Type: NASA-CR-192912 , NAS 1.26:192912 , UCB/CSD-92/683 , USENIX Workshop on File Systems; May 01, 1992; Berkeley, CA; United States
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  • 5
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    Analysis of faults detected in a large-scale multi-version software development experiment (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: In a multiversion software experiment, twenty programs were built to the same specification of an inertial navigation problem. The programs were then subjected to a three-phase testing and debugging process: an acceptance test, a certification test, and an operational test. Less than 20 percent of the faults discovered during the certification and operational testing were nonunique, i.e., the same or very similar faults would be found in more than one program. However, some of these common faults spanned as many as half of the versions. Faults discovered during the certification testing were due to specification errors and ambiguities, inadequate programmer background knowledge, insufficient programming experience, incomplete analysis, and insufficient acceptance testing. Faults discovered during the operational testing were of a more subtle nature, and were mostly due to various programmer knowledge defects and incomplete analysis errors. Techniques that might have prevented the observed faults are discussed.
    Keywords: COMPUTER PROGRAMMING AND SOFTWARE
    Type: IEEE/AIAA/NASA Digital Avionics Systems Conference; Oct 15, 1990 - Oct 18, 1990; Virginia Beach, VA; United States
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  • 6
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    Incorporation of a hierarchical grid component structure into GRIDGEN (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The underlying framework of the GRIDGEN multiple block grid generation system has been refined so that grid components are now stored within a hierarchical data structure. This restructuring has enhanced the usability of the software by allowing grids to be generated on a more intuitive level. This new framework also provides a means by which the multiple block system can be edited at most any level in the grid generation process. Editing tools are currently being added to GRIDGEN so that a change to the grid can be propagated backward and forward in the data hierarchy. The new data structure, the editing tools, and other recent GRIDGEN improvements are described in this paper.
    Keywords: COMPUTER PROGRAMMING AND SOFTWARE
    Type: AIAA PAPER 93-0429 , AIAA, Aerospace Sciences Meeting and Exhibit; Jan 11, 1993 - Jan 14, 1993; Reno, NV; United States|; 12 p.
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  • 7
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    An experimental evaluation of software redundancy as a strategy for improving reliability (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: The strategy of using multiple versions of independently developed software as a means to tolerate residual software design faults is suggested by the success of hardware redundancy for tolerating hardware failires. Although, as generally accepted, the independence of hardware failures resulting from physical wearout can lead to substantial increases in reliability for redundant hardware structures, a similar conclusion is not immediate for software. The degree to which design faults are manifested as independent failures determines the effectiveness of redundancy as a method for improving software reliability. Interest in multi-version software centers on whether it provides an adequate measure of increased reliability to warrant its use in critical applications. The effectiveness of multi-version software is studied by comparing estimates of the failure probabilities of these systems with the failure probabilities of single versions. The estimates are obtained under a model of dependent failures and compared with the estimates obtained when failures are assumed to be independent. The experimental results are based on twenty versions of an aerospace application developed and certified by sixty programmers from four universities. Descriptions of the application, development and certifications processes, and operational evaluation are given together with an analysis of the twenty versions.
    Keywords: COMPUTER PROGRAMMING AND SOFTWARE
    Type: IEEE Transactions on Software Engineering (ISSN 0098-5589); 17; 692-702
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  • 8
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    Examples of finite element mesh generation using SDRC IDEAS (1990)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: IDEAS (Integrated Design Engineering Analysis Software) offers a comprehensive package for mechanical design engineers. Due to its multifaceted capabilities, however, it can be manipulated to serve the needs of electrical engineers, also. IDEAS can be used to perform the following tasks: system modeling, system assembly, kinematics, finite element pre/post processing, finite element solution, system dynamics, drafting, test data analysis, and project relational database.
    Keywords: COMPUTER PROGRAMMING AND SOFTWARE
    Type: NASA-CR-186962 , NAS 1.26:186962 , UMICH-025921-16-T
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  • 9
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    Lessons learned from Space Shuttle flight software and Mission Control software (1991)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: The techniques utilized by NASA to manage risk in the development and operations of flight software and Mission Control Center software for the Space Shuttle are reviewed. Particular attention is given to independent software in the backup flight system, structured requirements and design techniques, multiple levels of testing in development and production, independent testing following production, and independence of development and production, and the Mission Control Center model for Real Time Data System project.
    Keywords: COMPUTER PROGRAMMING AND SOFTWARE
    Type: In: The management of aerospace software; Proceedings of the Conference, London, United Kingdom, June 6, 1991 (A93-18713 05-61); p. 2.1-2.7.
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  • 10
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    Accumulated approximation: A new method for structural optimization by iterative improvement (1990)
    In:  CASI
    Details
    Publication Date: 2004-12-04
    Description: A new method for the solution of non-linear mathematical programming problems in the field of structural optimization is presented. It is an iterative scheme which for each iteration refines the approximation of objective and constraint functions by accumulating the function values of previously visited design points. The method has proven to be competitive for a number of well-known examples of which one is presented here. Furthermore because of the accumulation strategy, the method produces convergence even when the sensitivity analysis is inaccurate.
    Keywords: COMPUTER PROGRAMMING AND SOFTWARE
    Type: NASA. Langley Research Center, The Third Air Force(NASA Symposium on Recent Advances in Multidisciplinary Analysis and Optimization; p 253-258
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