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At least 1,153 records · Page 64

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NASA NTRS1983

Advances in systems for interactive processing and display of meteorological data

Advances in systems for interactive processing and display of meteorological data are reviewed, with particular attention given to developments in hardware and software, meteorological data base, analysis and display, and systems availability. These developments include inexpensive minicomputers which give the user almost instantaneous results for many types of jobs; image terminals with the capability to enhance, quantify, animate, and compare image and graphical data; accessibility of a large meteorological data base and the capability of merging different types of data; and sophisticated analysis and multidimensional display techniques. Critical problems still to be solved include getting quick access to historical and real time data bases from any system and making it easy to transport software from one system to another.

Hasler, A. F.↗

NASA NTRS1983

Numerical solution of the Navier-Stokes equations for compressible turbulent two/three dimensional flows in the terminal shock region of an inlet/diffuser

The multidimensional, ensemble-averaged, compressible, time-dependent Navier-Stokes equations in conjunction with mixing length turbulence model and shock capturing technique have been used to study the terminal shock type of flows in various flight regimes occurring in a diffuser/inlet model. The numerical scheme for solving the governing equations is based on a linearized block implicit approach and the following high Reynolds number calculations have been carried out: (1) 2-D, steady, subsonic; (2) 2-D, steady, transonic with normal shock, (3) 2-D, steady, supersonic with terminal shock, (4) 2-D, transient process of shock development and (5) 3-D, steady, transonic with normal shock. The numerical results obtained for the 2-D and 3-D transonic shocked flows have been compared with corresponding experimental data; the calculated wall static pressure distributions agree well with the measured data. The predicted transient responses of the flow to externally applied impulsive disturbance are consistent with results obtained via asymptotic analysis.

Liu, N.-S.↗

NASA NTRS1983

Adaptive mesh schemes based on grid speeds

Successful methods for generating solution adaptive grids using grid speeds are reviewed in this paper. The computational mesh is constructed by integrating the grid speeds as opposed to solving a steady grid equation. Advantages and disadvantages for each grid speed scheme are discussed and a number of examples of grids produced with the various schemes are presented. Suggestions are made for the development of new schemes based upon a form of Euler's expansion formula for the grid and the equi-distribution of some parameter over the mesh. Consideration is also given to grid skewness for the multidimensional schemes.

Anderson, D. A.↗

NASA NTRS1983

Computational methods for ideal compressible flow

Conservative dissipative difference schemes for computing one dimensional flow are introduced, and the recognition and representation of flow discontinuities are discussed. Multidimensional methods are outlined. Second order finite volume schemes are introduced. Conversion of difference schemes for a single linear convection equation into schemes for the hyperbolic system of the nonlinear conservation laws of ideal compressible flow is explained. Approximate Riemann solvers are presented. Monotone initial value interpolation; and limiters, switches, and artificial dissipation are considered.

Vanleer, B.↗

NASA NTRS1984

Nonlinear systems approach to control system design

Consider some of the control system design methods for plants with nonlinear dynamics. If the nonlinearity is weak relative to the size of the operating region, then the linear methods apply directly. Fixed-gain design may be feasible even for significant nonlinearities. It may be possible to find a single gain which provides adequate control of the linear models at several perturbation points. If the nonlinearity is restricted to a sector, that fact may be used to obtain a fixed-gain controller. Otherwise, a gain may have to be associated with each perturbation point Pi. A gain schedule K(p(v)) is obtained by connecting the perturbation points by a function, say p(v), of the scheduling parameter v (i.e., speed). When the scheduling parameter must be multidimensional, this approach is difficult; the objective is to develop an easier procedure.

Meyer, G.↗

NASA NTRS1984

A review of internal combustion engine combustion chamber process studies at NASA Lewis Research Center

The performance of internal combustion stratified-charge engines is highly dependent on the in-cylinder fuel-air mixing processes occurring in these engines. Current research concerning the in-cylinder airflow characteristics of rotary and piston engines is presented. Results showing the output of multidimensional models, laser velocimetry measurements and the application of a holographic optical element are described. Models which simulate the four-stroke cycle and seal dynamics of rotary engines are also discussed.

Schock, H. J.↗

NASA NTRS1984

Aggregating available soil water holding capacity data for crop yield models

The total amount of water available to plants that is held against gravity in a soil is usually estimated as the amount present at -0.03 MPa average water potential minus the amount present at -1.5 MPa water potential. This value, designated available water-holding capacity (AWHC), is a very important soil characteristic that is strongly and positively correlated to the inherent productivity of soils. In various applications, including assessing soil moisture status over large areas, it is necessary to group soil types or series as to their productivity. Current methods to classify AWHC of soils consider only total capacity of soil profiles and thus may group together soils which differ greatly in AWHC as a function of depth in the profile. A general approach for evaluating quantitatively the multidimensional nature of AWHC in soils is described. Data for 902 soil profiles, representing 184 soil series, in Indiana were obtained from the Soil Characterization Laboratory at Purdue University. The AWHC for each of ten 150-mm layers in each soil was established, based on soil texture and parent material. A multivariate clustering procedure was used to classify each soil profile into one of 4, 8, or 12 classes based upon ten-dimensional AWHC values. The optimum number of classes depends on the range of AWHC in the population of oil profiles analyzed and on the sensitivity of a crop to differences in distribution of water within the soil profile.

Seubert, C. E.↗

NASA NTRS1984

Storage, retrieval, and analysis of ST data

Space Telescope can generate multidimensional image data, very similar in nature to data produced with microdensitometers. An overview is presented of the ST science ground system between carrying out the observations and the interactive analysis of preprocessed data. The ground system elements used in data archival and retrieval are described and operational procedures are discussed. Emphasis is given to aspects of the ground system that are relevant to the science user and to general principles of system software development in a production environment. While the system being developed uses relatively conservative concepts for the launch baseline, concepts were developed to enhance the ground system. This includes networking, remote access, and the utilization of alternate data storage technologies.

Albrecht, R.↗

NASA NTRS1984

A practical adaptive-grid method for complex fluid-flow problems

A practical solution, adaptive-grid method utilizing a tension and torsion spring analogy is proposed for multidimensional fluid flow problems. The tension spring, which connects adjacent grid points to each other, controls grid spacings. The torsion spring, which is attached to each grid node, controls inclinations of coordinate lines and grid skewness. A marching procedure was used that results in a simple tridiagonal system of equations at each coordinate line to determine grid-point distribution. Multidirectional adaptation is achieved by successive applications of one-dimensional adaptation. Examples of applications for axisymmetric afterbody flow fields and two dimensional transonic airfoil flow fields are shown.

Nakahashi, K.↗

NASA NTRS1983

An analysis of the processing requirements of a complex perceptual-motor task

Current concerns in the assessment of mental workload are discussed, and the event-related brain potential (ERP) is introduced as a promising mental-workload index. Subjects participated in a series of studies in which they were required to perform a target acquisition task while also covertly counting either auditory or visual probes. The effects of several task-difficulty manipulations on the P300 component of the ERP elicited by the counted stimulus probes were investigated. With sufficiently practiced subjects the amplitude of the P300 was found to decrease with increases in task difficulty. The second experiment also provided evidence that the P300 is selectively sensitive to task-relevant attributes. A third experiment demonstrated a convergence in the amplitude of the P300s elicited in the simple and difficult versions of the tracking task. The amplitude of the P300 was also found to covary with the measures of tracking performance. The results of the series of three experiments illustrate the sensitivity of the P300 to the processing requirements of a complex target acquisition task. The findings are discussed in terms of the multidimensional nature of processing resources.

Kramer, A. F.↗

NASA NTRS1984

Protostellar formation in rotating interstellar clouds. IV Nonisothermal collapse

Radiative transfer in the Eddington approximation is included in a multidimensional, self-gravitational, hydrodynamical computer code. Details of the numerical solution and thermodynamic relations are given. Comparison calculations with previous spherically symmetrical models of protostellar collapse are used to validate the basic approach and the artifices which allow the explicit hydrodynamics code to follow the accretion of gas onto a quasi-equilibrium core. A series of axisymmetric models is used to investigate the importance of rotation in collapsing clouds, as the initial amount of angular momentum is lowered, with an emphasis on the possible formation of rings. Rings readily form even in the nonisothermal regime except for very low initial angular momenta; even these clouds may experience ring formation prior to reaching stellar densities. The models imply that other effects (such as gravitational torques or turbulent viscosity) may be necesary to avoid binary formation and thus result in a presolar nebula consistent with the assumptions of either Safronov or Cameron.

Boss, A. P.↗

NASA NTRS1984

A review of internal combustion engine combustion chamber process studies at NASA Lewis Research Center

Schock, H. J.↗

NASA NTRS1985

Technical support for creating an artificial intelligence system for feature extraction and experimental design

Techniques for classifying objects into groups or clases go under many different names including, most commonly, cluster analysis. Mathematically, the general problem is to find a best mapping of objects into an index set consisting of class identifiers. When an a priori grouping of objects exists, the process of deriving the classification rules from samples of classified objects is known as discrimination. When such rules are applied to objects of unknown class, the process is denoted classification. The specific problem addressed involves the group classification of a set of objects that are each associated with a series of measurements (ratio, interval, ordinal, or nominal levels of measurement). Each measurement produces one variable in a multidimensional variable space. Cluster analysis techniques are reviewed and methods for incuding geographic location, distance measures, and spatial pattern (distribution) as parameters in clustering are examined. For the case of patterning, measures of spatial autocorrelation are discussed in terms of the kind of data (nominal, ordinal, or interval scaled) to which they may be applied.

Glick, B. J.↗

NASA NTRS1984

Atmospheric frontal zone studies

The research supported by this contract and directed Activities in the inversion and interpretation of data produced by the Nimbus-7 scanning multichannel microwave radiometer (SMMR) are reported. There were five principal subjects: (1) modeling of the emissivity of foam patches on the ocean surface; (2) inversion of radiometric data by a multidimensional algorithm; (3) an operational water vapor retrieval algorithm; (4) inference of Antarctic firm accumulation rates; and (5) inference of water vapor over the Arctic sea ice.

Staelin, D. H.↗

NASA NTRS1985

An algorithm for computing the number of distinct spectral vectors in thematic mapper data

A computationally efficient method was developed to compute the number of distinct spectral vectors and their frequency of occurrence in Landsat-4 Thematic Mapper (TM) data. The algorithm first partitions the image into spectrally disjoint subsets and then computes the frequency distribution of distinct spectral vectors within each subset from a multidimensional histogram. The overall frequency distribution is tabulated by accumulating the results from each subset. The number of distinct spectral vectors could be used as a measure of potential storage compaction of alternate data representations for data compression, or as a measure of information content in the comparison of spectral band combinations and/or spatial resolutions for an image. Results from processing three 512 x 512 pixel Landsat-4 TM images and one Landsat-4 Multispectral Scanner (MSS) image are presented as examples. An algorithm for computing the frequency distribution of distinct spectral vectors in MSS data is given in the Appendix.

Wharton, S. W.↗

NASA NTRS1983

The elemental and isotopic composition of quiet time low energy cosmic rays

Isotopic abundances during several periods of solar quiet times are derived from multidimensional analysis of double dE/dX modes made with two 150 micron dE detectors and a 3000 micron stopping E detector. The spectra of the low-energy cosmic rays suggest that all the primary species of elements exhibit flux enhancements. The flux increases of 5-12 MeV/N for C, Mg, Si, and Fe are different from the anomalous components and may result from solar contamination of the quiet time data or from interplanetary acceleration processes. They may be anomalous components (ACR), although to a lesser extent than He, N, O, and Ne. The isotopic data indicate that the ACR component is predominantly N-14, O-16, and Ne-20. The isotopic compositions require that the ACRs have traversed a very limited amount of material, suggesting a local origin for them.

Smith, B.↗

NASA NTRS1983

The use of multisensor images for Earth Science applications

The use of more than one remote sensing technique is particularly important for Earth Science applications because of the compositional and textural information derivable from the images. The ability to simultaneously analyze images acquired by different sensors requires coregistration of the multisensor image data sets. In order to insure pixel to pixel registration in areas of high relief, images must be rectified to eliminate topographic distortions. Coregistered images can be analyzed using a variety of multidimensional techniques and the acquired knowledge of topographic effects in the images can be used in photogeologic interpretations.

Evans, D.↗

NASA NTRS1985

Two dimensional and axisymmetric heat transfer results with the CSCM upwind implicit algorithm

The single level conservative supra characteristic method (CSCM-S) is an upwind implicit method that is very robust and in a single level relaxation format makes efficient use of computer resources, and is very rapidly convergent. These factors render the unconditionally stable algorithm a useful compromise between Parabolized Navier-Stokes methods and two level linearized implicit time dependent methods and, thus, the method is very attractive for multidimensional Navier-Stokes problems. In this paper the heat transfer prediction capabilities of the CSCM schemes for flat plate, nozzle, blunt cone and bluff body flows are reported for the first time. Results are compared with available experimental heat transfer measurements.

Bardina, J.↗