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At least 1,027 records · Page 57
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Solution and sensitivity analysis of a complex transcendental eigenproblem with pairs of real eigenvalues

This paper considers complex transcendental eigenvalue problems where one is interested in pairs of eigenvalues that are restricted to take real values only. Such eigenvalue problems arise in dynamic stability analysis of nonconservative physical systems, i.e., flutter analysis of aeroelastic systems. Some available solution methods are discussed and a new method is presented. Two computational approaches are described for analytical evaluation of the sensitivities of these eigenvalues when they are dependent on other parameters. The algorithms presented are illustrated through examples.

Murthy, Durbha V.↗
NASA NTRS1988

Studies of cryogenic propellant storage and handling for the lunar landing and launch facility (complex 39L)

A brief description of Complex 39L as it is currently conceived is presented. A brief discussion of lunar thermal history is then presented. From this follows a discussion of the current lunar thermal environment which will impact the design of cryogenic storage and handling facilities on the moon. Some previous studies are discussed. A conceptual design of liquid oxygen and hydrogen storage facilities is presented. The essential feature of this facility is that cryogens are to be stored in a number of small tanks which can serve as lander propellant tanks rather than as one large storage vessel. These tanks will be placed under a Fuel Inventory Tent (FIT) for shadow shielding. Methods of dealing with propellant boil-off are discussed. A base case cascade refrigeration system for requirements are such that it seems very feasible to construct a prototype boil-off recovery system in a laboratory environment.

Linsley, Jerald N.↗
NASA NTRS1988

An instrument for measuring the complex permittivity of the Martian top soil

This permittivity measuring instrument measures the resistivity rho and the relative dielectric constant epsilon sub r of the Martian top soil along the path of a rover. This aim is achieved by measuring the real and imaginary parts of the complex permittivity epsilon = epsilon sub r - j epsilon sub i where epsilon sub i = omega epsilon sub o rho/1; epsilon sub 1 is the permittivity of vacuum and omega is a variable angular working frequency. The experimental technique consists in evaluating the mutual, or transfer, impedance of a quadrupolar probe, i.e., in quantifying the influence of the Martian ground on the electrical coupling of two Hertz dipoles. The horizontal and vertical spatial resolutions are of the order of the length and separation of the dipoles, typically 1 to 2 metres. The four-electrode method for measuring the ground resistivity on earth was first applied by Wenner and Schlumberger, but the proposed investigation bears closer resemblance to a similar instrument developed for ground surveying at shallow depth, in connection with archaelogical and pedological research. A quadrupolar probe will provide essential information about the electric properties of the Martian ground and will contribute usefully to the identification of the soil structure and composition in association with other experimental equipment (camera, infra-red detector, gamma and X-ray spectrometers, chemical analyzers, ground temperature probes).

Grard, R.↗
NASA NTRS1989

A survey of intelligent tutoring systems: Implications for complex dynamic systems

An overview of the research in the field of intelligent tutorial systems (ITS) is provided. The various approaches in the design and implementation of ITS are examined and discussed in the context of problem solving in an environment of a complex dynamic system (CDS). Issues pertaining to a CDS and the nature of human problem solving especially in light of a CDS are considered. An overview of the architecture of an ITS is provided as the basis for the in-depth examination of various systems. Finally, the implications for the design and evaluation of an ITS are discussed.

Chu, Rose W.↗
NASA NTRS1989

Generation of unstructured grids and Euler solutions for complex geometries

Algorithms are described for the generation and adaptation of unstructured grids in two and three dimensions, as well as Euler solvers for unstructured grids. The main purpose is to demonstrate how unstructured grids may be employed advantageously for the economic simulation of both geometrically as well as physically complex flow fields.

Loehner, Rainald↗
NASA NTRS1988

Evaluation of Airborne Visible/Infrared Imaging Spectrometer Data of the Mountain Pass, California carbonatite complex

Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) data of the Mountain Pass, California carbonatite complex were examined to evaluate the AVIRIS instrument performance and to explore alternative methods of data calibration. Although signal-to-noise estimates derived from the data indicated that the A, B, and C spectrometers generally met the original instrument design objectives, the S/N performance of the D spectrometer was below expectations. Signal-to-noise values of 20 to 1 or lower were typical of the D spectrometer and several detectors in the D spectrometer array were shown to have poor electronic stability. The AVIRIS data also exhibited periodic noise, and were occasionally subject to abrupt dark current offsets. Despite these limitations, a number of mineral absorption bands, including CO3, Al-OH, and unusual rare earth element bands, were observed for mine areas near the main carbonatite body. To discern these bands, two different calibration procedures were applied to remove atmospheric and solar components from the remote sensing data. The two procedures, referred to as the single spectrum and the flat field calibration methods gave distinctly different results. In principle, the single spectrum method should be more accurate; however, additional fieldwork is needed to rigorously determine the degree of calibration success.

Crowley, James↗
NASA NTRS1988

Accretionary origin for the late Archean Ashuanipi Complex of Canada

The Ashuanipi complex is one of the largest massif granulite terrains of the Canadian Shield. It makes up the eastern end of the 2000 km long, lower-grade, east-west belts of the Archean Superior Province, permitting lithological, age and tectonic correlation. Numerous lithological, geochemical and metamorphic similarities to south Indian granulites suggest common processes and invite comparison of tectonic evolution. The Ashuanipi granulite terrain of the Cannadian Superior Province was studied in detail, and an origin through self-melting of a 55 km thick accretionary wedge seems possible.

Percival, J. A.↗
NASA NTRS1989

A knowledge-based tool for multilevel decomposition of a complex design problem

Although much work has been done in applying artificial intelligence (AI) tools and techniques to problems in different engineering disciplines, only recently has the application of these tools begun to spread to the decomposition of complex design problems. A new tool based on AI techniques has been developed to implement a decomposition scheme suitable for multilevel optimization and display of data in an N x N matrix format.

Rogers, James L.↗
NASA NTRS1989

The organization of perception and action in complex control skills

An attempt was made to describe the perceptual, cognitive, and action processes that account for highly skilled human performance in complex task environments. In order to study such a performance in a controlled setting, a laboratory task was constructed and three experiments were performed using human subjects. A general framework was developed for describing the organization of perceptual, cognitive, and action process.

Miller, Richard A.↗
NASA NTRS1989

A long-range laser velocimeter for the National Full-Scale Aerodynamics Complex: New developments and experimental application

A long-range laser velocimeter (LV) developed for remote operation from within the flow fields of the large wind tunnels of the National Full-Scale Aerodynamics Complex is described. Emphasis is placed on recent improvements in optical hardware as well as recent additions to data acquisition and processing techniques. The system has been upgraded from a dual-beam, single-color LV with focal range to 10 m, to a dual-beam, two-color LV with focal range to 20 m. At the new extended measurement range (between 10 and 20 m), signals are photon-resolved, and a photon correlation technique is applied to acquire and process the LV signals. This technique permits recovery of the velocity probability distributions at a particular measurement location from which the mean components of velocity and the corresponding normal stress components of turbulence are obtained. The method used for data reduction is outlined in detail, and a discussion of measurement accuracy is made. To study the performance of the LV and verify the measurement accuracy, laboratory measurements were made in the flow field of a 10 cm-diameter, 30-m/sec axisymmetric jet. A discussion of the requirements and techniques used to seed the flow is made, and boundary-layer surveys of mean velocity and turbulence intensity of the streamwise component and the component normal to the surface are presented.

Reinath, Michael S.↗
NASA NTRS1988

Large molecular-cloud complexes

The properties of the large molecular cloud complexes in the solar vicinity and in the inner Galaxy are summarized. Particular attention is paid to the stability of the clouds against the tidal field of the Galaxy, associated clouds of warm atomic hydrogen gas and star formation in the clouds. The linewidth-size relation is discussed and the possibility that it is an artifact of the blending of unrelated clouds at different distances is raised.

Blitz, L.↗
NASA NTRS1988

Spectra of van der Waals complexes (dimers) with applications to planetary atmospheres

Spectral features observed in the atmosphere of Titan by the Voyager IR experiment have been attributed to weakly bound complexes of N2 and H2, dominant and minor constituents, respectively. The abundance of H2-N2 dimers there was computed. Current calculations include quantitative spectral line positions and intensities for N2-Ar and CO2-CO2 relating to Titan and Earth, and to Mars and Venus, respectively. This work suggests applications to spectra of planetary atmospheres obtained in spacecraft missions.

Fox, Kenneth↗
NASA NTRS1988

Reliability analysis of large, complex systems using ASSIST

The SURE reliability analysis program is discussed as well as the ASSIST model generation program. It is found that semi-Markov modeling using model reduction strategies with the ASSIST program can be used to accurately solve problems at least as complex as other reliability analysis tools can solve. Moreover, semi-Markov analysis provides the flexibility needed for modeling realistic fault-tolerant systems.

Johnson, Sally C.↗
NASA NTRS1988

One-level modeling for diagnosing surface winds over complex terrain. II - Applicability to short-range forecasting

The Alpert and Getenio (1988) modification of the Mass and Dempsey (1985) one-level sigma-surface model was used to study four synoptic events that included two winter cases (a Cyprus low and a Siberian high) and two summer cases. Results of statistical verification showed that the model is not only capable of diagnosing many details of surface mesoscale flow, but might also be useful for various applications which require operative short-range prediction of the diurnal changes of high-resolution surface flow over complex terrain, for example, in locating wildland fires, determining the dispersion of air pollutants, and predicting changes in wind energy or of surface wind for low-level air flights.

Alpert, P.↗
NASA NTRS1989

A patched-grid algorithm for complex configurations directed towards the F-18 aircraft

A patched-grid algorithm for the analysis of complex configurations with an implicit, upwind-biased Navier-Stokes solver is presented. Results from both a spatial-flux and a time-flux conservation approach to patching across zonal boundaries are presented. A generalized coordinate transformation with a biquadratic geometric element is used at the zonal interface in order to treat highly stretched viscous grids and arbitrarily-shaped zonal boundaries. Applications are made to the F-18 forebody-strake configuration at subsonic, high-alpha conditions. Computed surface flow patterns compare well with ground-based and flight-test results; the large effect of Reynolds number on the forebody flowfield is shown.

Thomas, James L.↗
NASA NTRS1989

Analysis and visualization of complex unsteady three-dimensional flows

Flow field animation is the natural choice as a tool in the analysis of the numerical simulations of complex unsteady three-dimensional flows. The PLOT4D extension of the widely used PLOT3D code to allow the interactive animation of a broad range of flow variables was developed and is presented. To allow direct comparison with unsteady experimental smoke and dye flow visualization, the code STREAKER was developed to produce time accurate streaklines. Considerations regarding the development of PLOT4D and STREAKER, and example results are presented.

Van Dalsem, William R.↗
NASA NTRS1988

Robustness with real parametric and structured complex uncertainty

The problem of robust stability and performance in feedback control systems with n real (possibly related) uncertain parameters and structured unmodeled dynamics (the latter taking the form of m complex blocks dynamic uncertainties) is considered. A robustness margin rm is defined with respect to such model uncertainty structure and an algorithm is developed to compute it. Robust stability and performance are characterized in terms of r sub m or the structured singular value mu. An iterative procedure using the above algorithm is given to compute tight bounds on k sub m and mu. These bounds are exact for the case m = 3 or less.

Pena, Ricardo S. Sanchez↗