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At least 1,099 records · Page 61
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

The Caltech Concurrent Computation Program - Project description

The Caltech Concurrent Computation Program wwhich studies basic issues in computational science is described. The research builds on initial work where novel concurrent hardware, the necessary systems software to use it and twenty significant scientific implementations running on the initial 32, 64, and 128 node hypercube machines have been constructed. A major goal of the program will be to extend this work into new disciplines and more complex algorithms including general packages that decompose arbitrary problems in major application areas. New high-performance concurrent processors with up to 1024-nodes, over a gigabyte of memory and multigigaflop performance are being constructed. The implementations cover a wide range of problems in areas such as high energy and astrophysics, condensed matter, chemical reactions, plasma physics, applied mathematics, geophysics, simulation, CAD for VLSI, graphics and image processing. The products of the research program include the concurrent algorithms, hardware, systems software, and complete program implementations.

Fox, G.↗
NASA NTRS1986

Simultaneous iterations algorithm for general eigenvalue problems on parallel processors

The method of simultaneous iteration with shift is extended to extraction of m-eigenpairs of a general eigenvalue problem of large order n in a parallel processing environment. The algorithm combines the power method and the Jacobi technique, and reduces to performing four basic operations. Parallel implementation of the algorithm is discussed in detail. The analysis accounts for computation and communication costs, and utilizes a parallel processing architecture of the ensemble type. Expressions for the computational efficiency and speedup are defined as a function of the problem and hardware parameters. Selected representative problems exhibit efficiencies ranging from 60 to 98 percent.

Utku, S.↗
NASA NTRS1988

Highly automated transmission-edge mapping

Instrumentation and software are described, which are used to determine maps of properties of materials based on optical transmission spectra. In addition to a Fourier transform spectrometer, the hardware includes an xy-stage containing a small stationary aperture and two computer controlled stepper motors for positioning the sample. This idea has been used for years but this implementation is highly automated compared to those previously described. All mapping has been in the 2-15 micron wavelength range but this is not an inherent limitation of the technique. In this spectral range, useful results may be obtained with apertures as small as 25 microns in diameter. The software is described including the algorithm for obtaining the cut-on wavelength from a semiconductor spectrum. Data from both transverse slices and longitudinal slabs of narrow bandgap alloy semiconductors are shown including composition maps for materials solidified with convex and concave growth interfaces.

Szofran, F. R.↗
NASA NTRS1989

Detailed design of a Ride Quality Augmentation System for commuter aircraft

The design of a Ride Quality Augmentation System (RQAS) for commuter aircraft is documented. The RQAS is designed for a Cessna 402B, an 8 passenger prop twin representative to this class of aircraft. The purpose of the RQAS is the reduction of vertical and lateral accelerations of the aircraft due to atmospheric turbulence by the application of active control. The detailed design of the hardware (the aircraft modifications, the Ride Quality Instrumentation System (RQIS), and the required computer software) is examined. The aircraft modifications, consisting of the dedicated control surfaces and the hydraulic actuation system, were designed at Cessna Aircraft by Kansas University-Flight Research Laboratory. The instrumentation system, which consist of the sensor package, the flight computer, a Data Acquisition System, and the pilot and test engineer control panels, was designed by NASA-Langley. The overall system design and the design of the software, both for flight control algorithms and ground system checkout are detailed. The system performance is predicted from linear simulation results and from power spectral densities of the aircraft response to a Dryden gust. The results indicate that both accelerations are possible.

Suikat, Reiner↗
NASA NTRS1989

Overview of the NASA program in computational structural mechanics

In order to meet the anticipated needs in modeling and analysis of advanced aerospace structures, NASA has developed a program focused on computational structural mechanics. The objective of this program is to advance the state-of-the-art in computational analysis to make accurate analysis of very large and complex structural problems routine. This will be accomplished by emphasizing two key areas: (1) the development of advanced analytical methods, extending beyond traditional approaches and, (2) the exploitation of the newest and most powerful parallel/multiprocessor computers available. Computational testbeds will be developed to serve as technology integrators and to promote/accelerate methodology research and development. An additional, and highly desirable, effect of the Computational Structural Mechanics (CSM) program would be to influence the design of future hardware and software systems to reflect the needs of structural analysis.

Hirschbein, Murray↗
NASA NTRS1989

Design and implementation of a robot control system with traded and shared control capability

Preliminary results are reported from efforts to design and develop a robotic system that will accept and execute commands from either a six-axis teleoperator device or an autonomous planner, or combine the two. Such a system should have both traded as well as shared control capability. A sharing strategy is presented whereby the overall system, while retaining positive features of teleoperated and autonomous operation, loses its individual negative features. A two-tiered shared control architecture is considered here, consisting of a task level and a servo level. Also presented is a computer architecture for the implementation of this system, including a description of the hardware and software.

Hayati, S.↗
NASA NTRS1990

Performance analysis of a generalized concurrent error detection procedure

A general procedure for error detection in complex systems, called the data block capture and analysis monitoring process, is described and analyzed. It is assumed that, in addition to being exposed to potential external fault sources, a complex system will in general always contain embedded hardware and software fault mechanisms which can cause the system to perform incorrect computations and/or produce incorrect output. Thus, in operation, the system continuously moves back and forth between error and no-error states. These external fault sources or internal fault mechanisms are extremely difficult to detect. The data block capture and analysis monitoring process is concerned with detecting deviations from the normal performance of the system, known as errors, which are symptomatic of fault conditions. The process consists of repeatedly recording a fixed amount of data from a set of predetermined observation lines of the system being monitored (i.e., capturing a block of data) and then analyzing the captured block in an attempt to determine whether the system is functioning correctly. The performances of linear, quadratic, and logarithmic data analysis algorithms are rigorously characterized in terms of the probability of correctly detecting an error, the expectation and variance of the number of false alarms per error, and the expectation and variance of the latency in detection of errors. Insight into the nature of the general problem of error detection is obtained.

Blough, Douglas M.↗
NASA NTRS1991

Mechanism test bed. Flexible body model report

The Space Station Mechanism Test Bed is a six degree-of-freedom motion simulation facility used to evaluate docking and berthing hardware mechanisms. A generalized rigid body math model was developed which allowed the computation of vehicle relative motion in six DOF due to forces and moments from mechanism contact, attitude control systems, and gravity. No vehicle size limitations were imposed in the model. The equations of motion were based on Hill's equations for translational motion with respect to a nominal circular earth orbit and Newton-Euler equations for rotational motion. This rigid body model and supporting software were being refined.

Compton, Jimmy↗
NASA NTRS1991

Laser terminal attitude determination via autonomous star tracking

Freespace laser communication systems require an initial spatial acquisition process to coalign the cooperating terminal line of sites (typically to sub-microrad accuracy). The complexity and time required for this process can grow dramatically with the size of the host platform(s) initial uncertainty field-of-view. The feasibility of significantly refining the laser terminal attitude knowledge prior to the initiation of the spatial acquisition process via a preliminary star tracking operation is addressed. It is shown that currently planned laser terminal designs are capable of supporting this star tracking function with minimal hardware augmentation. An analysis of stellar spectral irradiance is presented which enables the computation of the tracking noise equivalent angle versus stellar class and visual magnitude.

Chapman, William↗
NASA NTRS1992

Hazard detection and avoidance sensor for NASA's planetary landers

An optical terrain analysis based sensor system specifically designed for landing hazard detection as required for NASA's autonomous planetary landers is introduced. This optical hazard detection and avoidance (HDA) sensor utilizes an optoelectronic wedge-and-ting (WRD) filter for Fourier transformed feature extraction and an electronic neural network processor for pattern classification. A fully implemented optical HDA sensor would assure safe landing of the planetary landers. Computer simulation results of a successful feasibility study is reported. Future research for hardware system implementation is also provided.

Lau, Brian↗
NASA NTRS1993

Transient Faults in Computer Systems

A powerful technique particularly appropriate for the detection of errors caused by transient faults in computer systems was developed. The technique can be implemented in either software or hardware; the research conducted thus far primarily considered software implementations. The error detection technique developed has the distinct advantage of having provably complete coverage of all errors caused by transient faults that affect the output produced by the execution of a program. In other words, the technique does not have to be tuned to a particular error model to enhance error coverage. Also, the correctness of the technique can be formally verified. The technique uses time and software redundancy. The foundation for an effective, low-overhead, software-based certification trail approach to real-time error detection resulting from transient fault phenomena was developed.

Masson, Gerald M.↗
NASA NTRS1996

GPS Monitor Station Upgrade Program at the Naval Research Laboratory

One of the measurements made by the Global Positioning System (GPS) monitor stations is to measure the continuous pseudo-range of all the passing GPS satellites. The pseudo-range contains GPS and monitor station clock errors as well as GPS satellite navigation errors. Currently the time at the GPS monitor station is obtained from the GPS constellation and has an inherent inaccuracy as a result. Improved timing accuracy at the GPS monitoring stations will improve GPS performance. The US Naval Research Laboratory (NRL) is developing hardware and software for the GPS monitor station upgrade program to improve the monitor station clock accuracy. This upgrade will allow a method independent of the GPS satellite constellation of measuring and correcting monitor station time to US Naval Observatory (USNO) time. THe hardware consists of a high performance atomic cesium frequency standard (CFS) and a computer which is used to ensemble the CFS with the two CFS's currently located at the monitor station by use of a dual-mixer system. The dual-mixer system achieves phase measurements between the high-performance CFS and the existing monitor station CFS's to within 400 femtoseconds. Time transfer between USNO and a given monitor station is achieved via a two way satellite time transfer modem. The computer at the monitor station disciplines the CFS based on a comparison of one pulse per second sent from the master site at USNO. The monitor station computer is also used to perform housekeeping functions, as well as recording the health status of all three CFS's. This information is sent to the USNO through the time transfer modem. Laboratory time synchronization results in the sub nanosecond range have been observed and the ability to maintain the monitor station CFS frequency to within 3.0 x 10 (sup minus 14) of the master site at USNO.

Galysh, Ivan J.↗
NASA NTRS1997

Development of a Telescoping Vaned Exhaust Nozzle for the ASTOVL LiftFan(Trademark) Application

A discussion on the development of a Telescoping, Vaned, Exhaust Nozzle (TEVEN) is presented. This nozzle was challenged to meet the thrust vectoring requirements of an Advanced Short Takeoff and Vertical Landing (ASTOVL) aircraft. The nozzle underwent a development process from concepts to detail design using computational flow analyses and from subscale performance verification tests to full-scale hardware design. The LiftFan(Trademark) nozzle is capable of providing a pitch vector range of about 80 degrees from up to 20 degrees forward to 60 degrees aft. In addition, a set of post exit yaw doors provide +/- 10 degrees yaw while maintaining a relatively high performance at all operating conditions. Further, the nozzle is axially compact, to be stowable in very short length (LJD less than 0.3), while efficiently converging the upstream nozzle flow from an annular cross section to a "D" shape at the nozzle exit. The discussion includes a review of various nozzle concepts, viscous flow analyses, and results from 1/3 scale nozzle model tests conducted at NASA LeRC Powered Lift Facility (PLF) in 1994.

Sokhey, Jack S.↗
NASA NTRS1999

Unmanned Vehicle Guidance Using Video Camera/Vehicle Model

A video guidance sensor (VGS) system has flown on both STS-87 and STS-95 to validate a single camera/target concept for vehicle navigation. The main part of the image algorithm was the subtraction of two consecutive images using software. For a nominal size image of 256 x 256 pixels this subtraction can take a large portion of the time between successive frames in standard rate video leaving very little time for other computations. The purpose of this project was to integrate the software subtraction into hardware to speed up the subtraction process and allow for more complex algorithms to be performed, both in hardware and software.

Sutherland, T.↗
NASA NTRS2001

High-Speed Observer: Automated Streak Detection in SSME Plumes

A high frame rate digital video camera installed on test stands at Stennis Space Center has been used to capture images of Space Shuttle main engine plumes during test. These plume images are processed in real time to detect and differentiate anomalous plume events occurring during a time interval on the order of 5 msec. Such speed yields near instantaneous availability of information concerning the state of the hardware. This information can be monitored by the test conductor or by other computer systems, such as the integrated health monitoring system processors, for possible test shutdown before occurrence of a catastrophic engine failure.

Rieckoff, T. J.↗
NASA NTRS2004

DSP Implementation of the Retinex Image Enhancement Algorithm

The Retinex is a general-purpose image enhancement algorithm that is used to produce good visual representations of scenes. It performs a non-linear spatial/spectral transform that synthesizes strong local contrast enhancement and color constancy. A real-time, video frame rate implementation of the Retinex is required to meet the needs of various potential users. Retinex processing contains a relatively large number of complex computations, thus to achieve real-time performance using current technologies requires specialized hardware and software. In this paper we discuss the design and development of a digital signal processor (DSP) implementation of the Retinex. The target processor is a Texas Instruments TMS320C6711 floating point DSP. NTSC video is captured using a dedicated frame-grabber card, Retinex processed, and displayed on a standard monitor. We discuss the optimizations used to achieve real-time performance of the Retinex and also describe our future plans on using alternative architectures.

Hines, Glenn↗