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At least 577 records · Page 32

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NASA NTRS1988

Small engine components test facility turbine testing cell

NASA Lewis Research Center has designed and constructed a new state-of-the-art test facility. This facility, called the Small Engine Components Test Facility (SECTF), is used to test gas turbines and compressors at conditions similar to actual engine conditions. The SECTF is comprised of two separate facilities - a turbine test cell and a compressor test cell. The paper will describe the turbine test cell. The capabilities of the facility make it unique - no other facility of its kind is capable of combining its pressure, speed, and temperature ranges. Turbine inlet air ranges up to 9 atm (125 psig). The turbine exhaust pressure ranges from 0.15 atm (2 psia) to atmospheric pressure. Turbine inlet air temperatures range from ambient to 700 K (1260 deg R). The controllable speed of the turbine rotor ranges from 4000 to 60,000 rpm and the maximum power absorbed by the facility dynamometer is 1250 hp. The data acquisition system scans up to 2000 channels/sec. This paper will discuss in detail the capabilities of the facility, overall facility design, instrumentation used in the facility, and the data acquisition system. Actual research data is not discussed.

Nowlin, Brent C.↗

NASA NTRS1988

Flaw characterization in structural ceramics using scanning laser acoustic microscopy

The ability of scanning laser acoustic microscopy (SLAM) to characterize artifically seeded voids in sintered silicon nitride structural ceramic specimens was investigated. The voids ranged from 20 to 430 microns in diameter and were embedded up to 2 mm beneath the surface of the specimens. Probability of detection was determined as a function of void depth and size. Trigonometric relationships and Airy's diffraction theory were used to obtain predictions of void depth and size from acoustic diffraction patterns produced by the voids. Agreement was observed between actual and predicted void depths. However, predicted void diameters were generally much greater than actual diameters. Precise diameter predictions are difficult to obtain because of measurement uncertainty and the limitations of the 100 MHz SLAM applied to typical ceramic specimens.

Roth, Don J.↗

NASA NTRS1988

The Shuttle Imaging Radar B (SIR-B) experiment report

The primary objective of the SIR-B experiment was to acquire multiple-incidence-angle radar imagery of a variety of Earth's surfaces to better understand the effects of imaging geometry on radar backscatter. A complementary objective was to map extensive regions of particular interest. Under these broad objectives, many specific scientific experiments were defined by the 43 SIR-B Science Team members, including studies in the area of geology, vegetation, radar penetration, oceanography, image analysis, and calibration technique development. Approximately 20 percent of the planned digital data were collected, meeting 40 percent of the scientific objectives. This report is an overview of the SIR-B experiment and includes the science investigations, hardware design, mission scenario, mission operations, events of the actual missions, astronaut participation, data products (including auxiliary data), calibrations, and a summary of the actual coverage. Also included are several image samples.

Cimino, Jo Bea↗

NASA NTRS1988

Internal temperature gradient of alloy semiconductor melts from interrupted growth experiments

Interrupted growth experiments on Hg(0.8)Cd(0.2)Se alloys were performed in an attempt to estimate the actual internal temperature gradient in the melt during directional solidification. The results have been analyzed in terms of a theoretical model which assumes an axial composition profile characteristic of diffusion controlled solute redistribution during growth. A comparison of the calculated and measured values suggests a reduction in the applied (empty furnace) temperature gradient by about a factor of three. Values of the interface segregation coefficient (k) determined from the phase diagram, predict values of solute concentration build up in the solid during growth interruptions which are inconsistent with measured results. It appears that the k values used tend to underestimate the actual k values for higher alloy compositions and overestimate k for the lower alloy compositions.

Andrews, R. N.↗

NASA NTRS1988

Small engine components test facility turbine testing cell

Nowlin, Brent C.↗

NASA NTRS1988

Experimental investigation of control/display augmentation effects in a compensatory tracking task

The effects of control/display augmentation on human performance and workload have been investigated for closed-loop, continuous-tracking tasks by a real-time, man-in-the-loop simulation study. The experimental results obtained indicate that only limited improvement in actual tracking performance is obtainable through display augmentation alone; with a very high level of display augmentation, tracking error will actually deteriorate. Tracking performance improves when status information is furnished for reasonable levels of display quickening; again, very high quickening levels lead to tracking error deterioration due to the incompatibility between the status information and the quickened signal.

Garg, Sanjay↗

NASA NTRS1988

A possible explanation for the inconsistency between the Giotto grain mass distribution and ground-based observations

Giotto measured the in situ Halley dust grain mass distribution with 2 instruments, Particle Impact Analyzer and Dust Impact Detection System (DIDSY), as well as the total intercepted mass from the deceleration of the spacecraft (Giotto Radio-Science Experiment, GRE). Ground based observations made shortly before encounter have fluxes much higher than would be predicted from Giotto data. It is concluded that Giotto DIDSY and GRE data represent observations of dust originating from a narrow track along the nucleus. They are consistent with ground based data, if assumptions are made about the level of activity along this track. The actual size distribution that should be used for modeling of the whole coma should not include the large mass excess actually observed by Giotto. Extrapolation of the small grain data should be used, since for these grains the velocity dispersion is low and temporal changes at the nucleus would not affect the shape of the mass distribution.

Perry, C. H.↗

NASA NTRS1988

Utilizing remote sensing of thematic mapper data to improve our understanding of estuarine processes and their influence on the productivity of estuarine-dependent fisheries

The continuing disintegration of the coastal marshes of Louisiana is one of the major environmental problems of the nation. The problem of marsh loss in Louisiana is relevant to fishery management because Louisiana leads the nation in landings of fishery products, and most of the landed species are dependent upon estuaries and their associated tidal marshes. In evaluating the potential effect of marshland loss on fisheries, the first two critical factors to consider are: whether land-water interface in actual disintegrating marshes is currently increasing or decreasing, and the magnitude of the change. In the present study, LANDSAT Thematic Mapper (TM) data covering specific marshes in coastal Louisiana were used to test conclusions from the Browder et al (1984) model with regard to the stage in disintegration at which maximum interface occurs; to further explore the relationship between maximum interface and the pattern of distribution of land and water suggested by the model; and to determine the direction and degree of change in land-water interface in relation to land loss in actual marshes.

Browder, Joan A.↗

NASA NTRS1988

Design of an expert system for estimating the cost of new knowledge in high energy astrophysics

The High Energy Astrophysics Costing Tool (HEACT) is a combined Expert System/Numerical Simulation to evaluate sensors and experiments proposed for space platforms in order to determine their expected performance and to assess the amount and quality of scientific information likely to be gathered by such experiments. The end product of this tool will be both a cost estimate for the experiment package as deployed and also an estimate of the amount of new scientific knowledge (both new data and reductions in the uncertainties of previous measurements) which would result from the actual deployment and operation of that experiment package. The numerical simulation part of HEACT will contain components to: (1) calculate the high energy signatures of both actual and proposed classes of astrophysical objects, and (2) model the response and resolution of the candidate sensors for observing those objects. The rule based part of the HEACT will be based on knowledge in the areas of experiment design, instrument selection, and system integration developed from experience with existing high energy astrophysics observatories, both orbiting and lofted by rockets or balloons. This paper presents mainly results from the design of the rule-based part of HEACT. It focuses on the structure of the rules and the structures used to represent the knowledge related to the design and integration of such experiments. Methods for integrating the results from numerical simulations into the expert system will also be discussed.

Bosworth, Edward L., Jr.↗

NASA NTRS1989

Operational implications of a cloud model simulation of space shuttle exhaust clouds in different atmospheric conditions

A three-dimensional cloud model was used to characterize the dominant influence of the environment on the Space Shuttle exhaust cloud. The model was modified to accept the actual heat and moisture from rocket exhausts and deluge water as initial conditions. An upper-air sounding determined the ambient atmosphere in which the cloud would grow. The model was validated by comparing simulated clouds with observed clouds from four actual Shuttle launches. Results are discussed with operational weather forecasters in mind. The model successfully produced clouds with dimensions, rise, decay, liquid water contents, and vertical motion fields very similar to observed clouds whose dimensions were calculated from 16 mm film frames. Once validated, the model was used in a number of different atmospheric conditions ranging from very unstable to very stable. Wind shear strongly affected the appearance of both the ground cloud and vertical column cloud. The ambient low-level atmospheric moisture governed the amount of cloud water in model clouds. Some dry atmospheres produced little or no cloud water. An empirical forecast technique for Shuttle cloud rise is presented and differences between natural atmospheric convection and exhaust clouds are discussed.

Zak, J. A.↗

NASA NTRS1989

A cloud model simulation of space shuttle exhaust clouds in different atmospheric conditions

A three-dimensional cloud model was used to characterize the dominant influence of the environment on the Space Shuttle exhaust cloud. The model was modified to accept the actual heat and moisture from rocket exhausts and deluge water as initial conditions. An upper-air sounding determined the ambient atmosphere in which the cloud could grow. The model was validated by comparing simulated clouds with observed clouds from four actual Shuttle launches. The model successfully produced clouds with dimensions, rise, decay, liquid water contents and vertical motion fields very similar to observed clouds whose dimensions were calculated from 16 mm film frames. Once validated, the model was used in a number of different atmospheric conditions ranging from very unstable to very stable. In moist, unstable atmospheres simulated clouds rose to about 3.5 km in the first 4 to 8 minutes then decayed. Liquid water contents ranged from 0.3 to 1.0 g kg-1 mixing ratios and vertical motions were from 2 to 10 ms-1. An inversion served both to reduce entrainment (and erosion) at the top and to prevent continued cloud rise. Even in the most unstable atmospheres, the ground cloud did not rise beyond 4 km and in stable atmospheres with strong low level inversions the cloud could be trapped below 500 m. Wind shear strongly affected the appearance of both the ground cloud and vertical column cloud. The ambient low-level atmospheric moisture governed the amount of cloud water in model clouds. Some dry atmospheres produced little or no cloud water. One case of a simulated TITAN rocket explosion is also discussed.

Chen, C.↗

NASA NTRS1989

Computer simulation of a pilot in V/STOL aircraft control loops

The objective was to develop a computerized adaptive pilot model for the computer model of the research aircraft, the Harrier II AV-8B V/STOL with special emphasis on propulsion control. In fact, two versions of the adaptive pilot are given. The first, simply called the Adaptive Control Model (ACM) of a pilot includes a parameter estimation algorithm for the parameters of the aircraft and an adaption scheme based on the root locus of the poles of the pilot controlled aircraft. The second, called the Optimal Control Model of the pilot (OCM), includes an adaption algorithm and an optimal control algorithm. These computer simulations were developed as a part of the ongoing research program in pilot model simulation supported by NASA Lewis from April 1, 1985 to August 30, 1986 under NASA Grant NAG 3-606 and from September 1, 1986 through November 30, 1988 under NASA Grant NAG 3-729. Once installed, these pilot models permitted the computer simulation of the pilot model to close all of the control loops normally closed by a pilot actually manipulating the control variables. The current version of this has permitted a baseline comparison of various qualitative and quantitative performance indices for propulsion control, the control loops and the work load on the pilot. Actual data for an aircraft flown by a human pilot furnished by NASA was compared to the outputs furnished by the computerized pilot and found to be favorable.

Vogt, William G.↗

NASA NTRS1989

Improved performance in NASTRAN (R)

Three areas of improvement in COSMIC/NASTRAN, 1989 release, were incorporated recently that make the analysis program run faster on large problems. Actual log files and actual timings on a few test samples that were run on IBM, CDC, VAX, and CRAY computers were compiled. The speed improvement is proportional to the problem size and number of continuation cards. Vectorizing certain operations in BANDIT, makes BANDIT run twice as fast in some large problems using structural elements with many node points. BANDIT is a built-in NASTRAN processor that optimizes the structural matrix bandwidth. The VAX matrix packing routine BLDPK was modified so that it is now packing a column of a matrix 3 to 9 times faster. The denser and bigger the matrix, the greater is the speed improvement. This improvement makes a host of routines and modules that involve matrix operation run significantly faster, and saves disc space for dense matrices. A UNIX version, converted from 1988 COSMIC/NASTRAN, was tested successfully on a Silicon Graphics computer using the UNIX V Operating System, with Berkeley 4.3 Extensions. The Utility Modules INPUTT5 and OUTPUT5 were expanded to handle table data, as well as matrices. Both INPUTT5 and OUTPUT5 are general input/output modules that read and write FORTRAN files with or without format. More user informative messages are echoed from PARAMR, PARAMD, and SCALAR modules to ensure proper data values and data types being handled. Two new Utility Modules, GINOFILE and DATABASE, were written for the 1989 release. Seven rigid elements are added to COSMIC/NASTRAN. They are: CRROD, CRBAR, CRTRPLT, CRBE1, CRBE2, CRBE3, and CRSPLINE.

Chan, Gordon C.↗

NASA NTRS1988

Method and system for monitoring and displaying engine performance parameters

The invention is believed a major improvement that will have a broad application in governmental and commercial aviation. It provides a dynamic method and system for monitoring and simultaneously displaying in easily scanned form the available, predicted, and actual thrust of a jet aircraft engine under actual operating conditions. The available and predicted thrusts are based on the performance of a functional model of the aircraft engine under the same operating conditions. Other critical performance parameters of the aircraft engine and functional model are generated and compared, the differences in value being simultaneously displayed in conjunction with the displayed thrust values. Thus, the displayed information permits the pilot to make power adjustments directly while keeping him aware of total performance at a glance of a single display panel.

Abbott, Terence S.↗

NASA NTRS1988

High level intelligent control of telerobotics systems

A high level robot command language is proposed for the autonomous mode of an advanced telerobotics system and a predictive display mechanism for the teleoperational model. It is believed that any such system will involve some mixture of these two modes, since, although artificial intelligence can facilitate significant autonomy, a system that can resort to teleoperation will always have the advantage. The high level command language will allow humans to give the robot instructions in a very natural manner. The robot will then analyze these instructions to infer meaning so that is can translate the task into lower level executable primitives. If, however, the robot is unable to perform the task autonomously, it will switch to the teleoperational mode. The time delay between control movement and actual robot movement has always been a problem in teleoperations. The remote operator may not actually see (via a monitor) the results of high actions for several seconds. A computer generated predictive display system is proposed whereby the operator can see a real-time model of the robot's environment and the delayed video picture on the monitor at the same time.

Mckee, James↗

NASA NTRS1988

A Rayleigh-Ritz approach to structural parameter identification

This paper is concerned with the identification of parameter distributions in large space structures. The formulation is based on a Rayleigh-Ritz type approach working with the actual displacement at a given number of points in the structure. The parameter distributions are expanded in terms of known admissible functions multiplied by unknown coefficients, and the identification process reduces to the determination of these coefficients. The procedure uses a perturbation approach, beginning with a postulated set of parameters and iterating to the actual values in an incremental fashion.

Meirovitch, L.↗

NASA NTRS1988

Robot geometry calibration

Autonomous robot task execution requires that the end effector of the robot be positioned accurately relative to a reference world-coordinate frame. The authors present a complete formulation to identify the actual robot geometric parameters. The method applies to any serial link manipulator with arbitrary order and combination of revolute and prismatic joints. A method is also presented to solve the inverse kinematic of the actual robot model which usually is not a so-called simple robot. Experimental results performed by utilizing a PUMA 560 with simple measurement hardware are presented. As a result of this calibration a precision move command is designed and integrated into a robot language, RCCL, and used in the NASA Telerobot Testbed.

Hayati, Samad↗

NASA NTRS1988

Minimizing the total harmonic distortion for a 3 kW, 20 kHz ac to dc converter using SPICE

This paper describes the SPICE model of a transformer-rectified-filter (TRF) circuit and the Micro-CAP (Microcomputer Circuit Analysis Program) model and their application. The models were used to develop an actual circuit with reduced input current THD. The SPICE analysis consistently predicted the THD improvements in actual circuits as various designs were attempted. In an effort to predict and verify load regulation, the incorporation of saturable inductor models significantly improved the fidelity of the TRF circuit output voltage.

Lollar, Louis F.↗