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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Interactive color graphical postprocessing as a unifying influence in numerical analysis research

The general capabilities and the hardware environment of an interactive color graphical postprocessor for three-dimensional numerical analysis are described as well as the synergistic influence of this aspect of interactive graphics on the research environment. Areas of practical concern include finite element analysis, fracture propagation, surface and framed structures. The interactive color graphical postprocessor, POSTPRO3D, is capable of displaying the scalar, vector, and tensor results of finite difference, finite element, and boundary element analysis. In the case of fatigue cracking in steel crane-rail girders, it was shown that POSTPRO3D offers a high level of flexibility, interactivity and features which minimize response time.

Abel, J. F.↗
NASA NTRS1987

Upstream waves simultaneously observed by ISEE and UKS

Measurements obtained in the solar wind by ISEE-2 and the United Kingdom Subsatellite (UKS) have been examined for observations of upstream waves. These data reveal that the waves in the foreshock region are enhanced at all frequencies from at least 0.003 Hz to 0.5 Hz. The wave spectra generally have a spectral peak, but this peak is usually broad and the peak frequency depends on the position of the spacecraft. Generally, the spectra seen at the two spacecraft are most similar at high frequencies and least similar at low frequencies. The geometry of the interaction is displayed in the plane containing the magnetic field, the solar wind velocity, and the spacecraft location. However, this coordinate system does not order all the observed wave properties. It does not clearly explain or order the handedness of the waves, or their direction of propagation. It is clear that the upstream region is inherently three-dimensional. The position-dependent nature of the upstream waves indicates that comparisons between ground-based measurements and in-situ observations must be undertaken with some caution.

Russell, C. T.↗
NASA NTRS1986

Towards effective interactive three-dimensional colour postprocessing

Recommendations for the development of effective three-dimensional, graphical color postprocessing are made. First, the evaluation of large, complex numerical models demands that a postprocessor be highly interactive. A menu of available functions should be provided and these operations should be performed quickly so that a sense of continuity and spontaneity exists during the post-processing session. Second, an agenda for three-dimensional color postprocessing is proposed. A postprocessor must be versatile with respect to application and basic algorithms must be designed so that they are flexible. A complete selection of tools is necessary to allow arbitrary specification of views, extraction of qualitative information, and access to detailed quantitative and problem information. Finally, full use of advanced display hardware is necessary if interactivity is to be maximized and effective postprocessing of today's numerical simulations is to be achieved.

Bailey, B. C.↗
NASA NTRS1986

Computation of sharp-fin-induced shockwave/turbulent boundary layer interactions

Solutions of the Reynolds-averaged Navier-Stokes equations are presented and are compared with a family of experimental results for the three-dimensional interaction of a sharp-fin-induced shock wave with a turbulent boundary layer. The solutions predict most of the essential features of the flow fields for various shock-wave strengths. However, some features of the measured flow fields, such as secondary separation and size of the largest separated zones were not accurately computed. The computed flow fields, aided by particle tracing techniques, display a prominent vortical structure which can be correlated with the observed surface phenomena.

Horstman, C. C.↗
NASA NTRS1986

Color enhancement of highly correlated images. I - Decorrelation and HSI contrast stretches

Conventional enhancements for the color display of multispectral images are based on independent contrast modifications or 'stretches' of three input images. This approach is not effective if the image channels are highly correlated or if the image histograms are strongly bimodal or more complex. Any of several procedures that tend to 'stretch' color saturation while leaving hue unchanged may better utilize the full range of colors for the display of image information. Two conceptually different enhancements are discussed: the 'decorrelation stretch', based on principal-component (PC) analysis, and the 'stretch' of 'hue' - 'saturation' - intensity (HSI) transformed data. The PC transformation in scene-dependent, but the HSI transformation is invariant. Examples of images enhanced by conventional linear stretches, decorrelation stretch, and by stretches of HSI transformed data are compared. Schematic variation diagrams or two- and three-dimensional histograms are used to illustrate the 'decorrelation stretch' method and the effect of the different enhancements.

Gillespie, Alan R.↗
NASA NTRS1983

Vortices, stability, and turbulence

The transition process between laminar flow to turbulent flow is discussed in terms of a third state of fluid motion, vortical motion that is approximately periodic in space and/or time and displays symmetrical properties. The possibility that the transition from laminar to turbulent flow is accompanied by intermediate vortical states, with turbulence being an instability of the vortical states, is examined, with consideration given to the hypothesis that the turbulent state retains a memory of the vortex structures. Solutions are sought for the Navier-Stokes equations for a viscous liquid in a channel. Instances of inviscid vortical states and the presence of a three-dimensional instability are studied, demonstrating that transition phenomena can be explained qualitatively in terms of vortical state characteristics.

Saffman, P. G.↗
NASA NTRS1986

A computer graphics pilot project - Spacecraft mission support with an interactive graphics workstation

The NASA Computer Graphics Pilot Project was undertaken to enhance the quality control, productivity and efficiency of mission support operations at the Goddard Operations Support Computing Facility. The Project evolved into a set of demonstration programs for graphics intensive simulated control room operations, particularly in connection with the complex space missions that began in the 1980s. Complex mission mean more data. Graphic displays are a means to reduce the probabilities of operator errors. Workstations were selected with 1024 x 768 pixel color displays controlled by a custom VLSI chip coupled to an MC68010 chip running UNIX within a shell that permits operations through the medium of mouse-accessed pulldown window menus. The distributed workstations run off a host NAS 8040 computer. Applications of the system for tracking spacecraft orbits and monitoring Shuttle payload handling illustrate the system capabilities, noting the built-in capabilities of shifting the point of view and rotating and zooming in on three-dimensional views of spacecraft.

Hagedorn, John↗
NASA NTRS1981

Stellar convection theory. III - Dynamical coupling of the two convection zones in A-type stars by penetrative motions

The thermal convection occurring over many density scale heights in an A-type star outer envelope, encompassing both the hydrogen and helium convectively unstable zones, is examined by means of anelastic modal equations. The single-mode anelastic equations for such compressible convection display strong overshooting of the motions into adjacent radiative zones, which would preclude diffusive separation of elements in the supposedly quiescent region between the two unstable zones. In addition, the anelastic solutions reveal that the two zones of convective instability are dynamically coupled by the overshooting motions. The two solutions that the nonlinear single-mode equations admit for the same horizontal wavelength are distinguished by the sense of the vertical velocity at the center of the three-dimensional cell. It is suggested that strong horizontal shear flows should be present just below the surface of the star, and that the large-scale motions extending into the stable atmosphere would appear mainly as horizontal flows.

Latour, J.↗
NASA NTRS1973

Biplane roentgen videometric system for dynamic, 60/sec, studies of the shape and size of circulatory structures, particularly the left ventricle.

An operator interactive video system for the measurement of roentgen angiographically outlined structures is described. Left ventricular volume and three-dimensional shapes are calculated from up to 200 pairs of diameters measured from ventriculograms at the rate of 60 pairs of biplane images per second. The accuracy and reproducibility of volumes calculated by the system were established by analysis of roentgenograms of inanimate objects of known volume and by comparison of left ventricular stroke volumes calculated by the system with the stroke volumes calculated by an indicator-dilution technique and an aortic root electromagnetic flowmeter. Computer-generated display of the large amounts of data obtained by the videometry system is described.

Ritman, E. L.↗
NASA NTRS1975

Application of remote sensing to thermal pollution analysis

A comprehensive numerical model development program for near-field thermal plume discharge and far field general circulation in coastal regions is being carried on at the University of Miami Clean Energy Research Institute. The objective of the program is to develop a generalized, three-dimensional, predictive model for thermal pollution studies. Two regions of specific application of the model are the power plants sites at the Biscayne Bay and Hutchinson Island area along the Florida coastline. Remote sensing from aircraft as well as satellites are used in parallel with in situ measurements to provide information needed for the development and verification of the mathematical model. This paper describes the efforts that have been made to identify problems and limitations of the presently available satellite data and to develop methods for enhancing and enlarging thermal infrared displays for mesoscale sea surface temperature measurements.

Hiser, H. W.↗
NASA NTRS1980

V/STOLAND digital avionics system for XV-15 tilt rotor

A digital flight control system for the tilt rotor research aircraft provides sophisticated navigation, guidance, control, display and data acquisition capabilities for performing terminal area navigation, guidance and control research. All functions of the XV-15 V/STOLAND system were demonstrated on the NASA-ARC S-19 simulation facility under a comprehensive dynamic acceptance test. The most noteworthy accomplishments of the system are: (1) automatic configuration control of a tilt-rotor aircraft over the total operating range; (2) total hands-off landing to touchdown on various selectable straight-in glide slopes and on a flight path that includes a two-revolution helix; (3) automatic guidance along a programmed three-dimensional reference flight path; (4) navigation data for the automatic guidance computed on board, based on VOR/DME, TACAN, or MLS navid data; and (5) integration of a large set of functions in a single computer, utilizing 16k words of storage for programs and data.

Liden, S.↗
NASA NTRS1976

A three-dimensional, time-dependent model of Mobile Bay

A three-dimensional, time-variant mathematical model for momentum and mass transport in estuaries was developed and its solution implemented on a digital computer. The mathematical model is based on state and conservation equations applied to turbulent flow of a two-component, incompressible fluid having a free surface. Thus, bouyancy effects caused by density differences between the fresh and salt water, inertia from thare river and tidal currents, and differences in hydrostatic head are taken into account. The conservation equations, which are partial differential equations, are solved numerically by an explicit, one-step finite difference scheme and the solutions displayed numerically and graphically. To test the validity of the model, a specific estuary for which scaled model and experimental field data are available, Mobile Bay, was simulated. Comparisons of velocity, salinity and water level data show that the model is valid and a viable means of simulating the hydrodynamics and mass transport in non-idealized estuaries.

Pitts, F. H.↗
NASA NTRS1984

Three-dimensional ray tracing of the Jovian magnetosphere in the low-frequency range

Three-dimensional ray tracing of the Jovian DAM emission has been performed utilizing the O-4 magnetic field model (Acuna and Ness, 1979) and a realistic plasma model. Minimal assumptions about the emission mechanism have been made that include radiation in the right-hand extraordinary mode, propagating nearly perpendicular to the field line at source points located just above the RX cutoff frequency along Io flux tubes. Ray tracing has been performed in the frequency range from 2-35 MHz from successive Io flux tubes separated by ten degrees of central meridian longitude for a full circumference of northern hemisphere sources. The results show unusual complexity in model arc spectra that is displayed in a constant Io phase format with many similarities to the Voyager PRA data. The results suggest much of the variation in observed DAM spectral features is a result of propagation effects rather than emission process differences.

Menietti, J. D.↗
NASA NTRS1984

STARS: A general-purpose finite element computer program for analysis of engineering structures

STARS (Structural Analysis Routines) is primarily an interactive, graphics-oriented, finite-element computer program for analyzing the static, stability, free vibration, and dynamic responses of damped and undamped structures, including rotating systems. The element library consists of one-dimensional (1-D) line elements, two-dimensional (2-D) triangular and quadrilateral shell elements, and three-dimensional (3-D) tetrahedral and hexahedral solid elements. These elements enable the solution of structural problems that include truss, beam, space frame, plane, plate, shell, and solid structures, or any combination thereof. Zero, finite, and interdependent deflection boundary conditions can be implemented by the program. The associated dynamic response analysis capability provides for initial deformation and velocity inputs, whereas the transient excitation may be either forces or accelerations. An effective in-core or out-of-core solution strategy is automatically employed by the program, depending on the size of the problem. Data input may be at random within a data set, and the program offers certain automatic data-generation features. Input data are formatted as an optimal combination of free and fixed formats. Interactive graphics capabilities enable convenient display of nodal deformations, mode shapes, and element stresses.

Gupta, K. K.↗
NASA NTRS1977

Real-time manned simulation of advanced terminal area guidance concepts for short-haul operations

A real-time simulation was conducted of three-dimensional area navigation and four-dimensional area navigation equipped (STOL) aircraft operating in a high-density terminal area traffic environment. The objectives were to examine the effects of 3D RNAV and 4D RNAV equipped aircraft on the terminal area traffic efficiency, and to examine the performance of an air traffic control system concept and associated controller display proposed for use with advanced RNAV systems. Three types of STOL aircraft were simulated each with different performance capabilities. System performance was measured in both the 4D mode and in a 3D mode; the 3D mode, used as a baseline, was simply the 4D mode less any time specification. The results show that communications workload in the 4D mode was reduced by about 35 percent compared to the 3D, while 35 percent more traffic was handled with the 4D. Aircraft holding time in the 4D mode was only 30 percent of that required in the 3D mode. In addition, the orderliness of traffic was improved significantly in the 4D mode.

Tobias, L.↗
NASA NTRS1980

Computation of three-dimensional viscous flows with the Navier-Stokes equations

The paper presents computations of three-dimensional viscous flows generated with the General Interpolation Method/STAR code based on the time-averaged Navier-Stokes equations. Calculations are presented for three viscous flow problems, and a two dimensional nozzle-exhaust shear flow case is solved and compared to an inviscid slip-line code. This nozzle-exhaust flow case is then extended to three dimensions and the steady solution displayed at pressure contours in the cross planes. The third problem consists of a simulated two-dimensional aircraft inlet flow which includes calculation of the 'spillage' flow and a shock wave/boundary layer interaction in the nozzle.

Spradley, L. W.↗
NASA NTRS1981

Predictor symbology in computer-generated pictorial displays

The display under investigation, is a tunnel display for the four-dimensional commercial aircraft approach-to-landing under instrument flight rules. It is investigated whether more complex predictive information such as a three-dimensional perspective vehicle symbol, predicting the future vehicle position as well as future vehicle attitude angles, contributes to a better system response, and suitable predictor laws for the predictor motions, are formulated. Methods for utilizing the predictor symbol in controlling the forward velocity of the aircraft in four-dimensional approaches, are investigated. The simulator tests show, that the complex perspective vehicle symbol yields improved damping in the lateral response as compared to a flat two-dimensional predictor cross, but yields generally larger vertical deviations. Methods of using the predictor symbol in controlling the forward velocity of the vehicle are shown to be effective. The tunnel display with superimposed perspective vehicle symbol yields very satisfactory results and pilot acceptance in the lateral control but is found to be unsatisfactory in the vertical control, as a result of too large vertical path-angle deviations.

Grunwald, A. J.↗