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NASA NTRS1994

NASA geometry data exchange specification for computational fluid dynamics (NASA IGES)

This document specifies a subset of an existing product data exchange specification that is widely used in industry and government. The existing document is called the Initial Graphics Exchange Specification. This document, a subset of IGES, is intended for engineers analyzing product performance using tools such as computational fluid dynamics (CFD) software. This document specifies how to define mathematically and exchange the geometric model of an object. The geometry is represented utilizing nonuniform rational B-splines (NURBS) curves and surfaces. Only surface models are represented; no solid model representation is included. This specification does not include most of the other types of product information available in IGES (e.g., no material properties or surface finish properties) and does not provide all the specific file format details of IGES. The data exchange protocol specified in this document is fully conforming to the American National Standard (ANSI) IGES 5.2.

Blake, Matthew W.↗
NASA NTRS1994

Uncertainty relations as Hilbert space geometry

Precision measurements involve the accurate determination of parameters through repeated measurements of identically prepared experimental setups. For many parameters there is a 'natural' choice for the quantum observable which is expected to give optimal information; and from this observable one can construct an Heinsenberg uncertainty principle (HUP) bound on the precision attainable for the parameter. However, the classical statistics of multiple sampling directly gives us tools to construct bounds for the precision available for the parameters of interest (even when no obvious natural quantum observable exists, such as for phase, or time); it is found that these direct bounds are more restrictive than those of the HUP. The implication is that the natural quantum observables typically do not encode the optimal information (even for observables such as position, and momentum); we show how this can be understood simply in terms of the Hilbert space geometry. Another striking feature of these bounds to parameter uncertainty is that for a large enough number of repetitions of the measurements all V quantum states are 'minimum uncertainty' states - not just Gaussian wave-packets. Thus, these bounds tell us what precision is achievable as well as merely what is allowed.

Braunstein, Samuel L.↗
NASA NTRS1993

Bone geometry, structure and mineral distribution using Dual energy X ray Absorptiometry (DXA)

Dual energy x-ray absorptiometry (DXA) is currently the most widely used method of analyzing regional and whole body changes in bone mineral content (BMC) and areal (g/sq cm) bone mineral density (BMD). However, BMC and BMD do not provide direct measures of long bone geometry, structure, or strength nor do regional measurements detect localized changes in other regions of the same bone. The capabilities of DXA can be enhanced significantly by special processing of pixel BMC data which yields cross-sectional geometric and structural information. We have extended this method of analysis in order to develop non-uniform structural beam models of long bones.

Whalen, Robert↗
NASA NTRS1995

Parametric design and gridding through relational geometry

Relational Geometric Synthesis (RGS) is a new logical framework for building up precise definitions of complex geometric models from points, curves, surfaces and solids. RGS achieves unprecedented design flexibility by supporting a rich variety of useful curve and surface entities. During the design process, many qualitative and quantitative relationships between elementary objects may be captured and retained in a data structure equivalent to a directed graph, such that they can be utilized for automatically updating the complete model geometry following changes in the shape or location of an underlying object. Capture of relationships enables many new possibilities for parametric variations and optimization. Examples are given of panelization applications for submarines, sailing yachts, offshore structures, and propellers.

Letcher, John S., Jr.↗
NASA NTRS1995

Electrically heated tube investigation of cooling channel geometry effects

The results of an experimental investigation on the combined effects of cooling channel aspect ratio and curvature for rocket engines are presented. Symmetrically heated tubes with average heat fluxes up to 1.7 MW/m(exp 2) were used. The coolant was gaseous nitrogen at an inlet temperature of 280 K (500 R) and inlet pressures up to 1.0 x 10(exp 7) N/m(exp 2) (1500 psia). Two different tube geometries were tested: a straight, circular cross-section tube, and an aspect-ratio 10 cross-section tube with a 45 deg bend. The circular tube results are compared to classical models from the literature as validation of the system. The curvature effect data from the curved aspect-ratio 10 tube compare favorably to the empirical equations available in the literature for low aspect ratio tubes. This latter results suggest that thermal stratification of the coolant due to diminished curvature effect mixing may not be an issue for high aspect-ratio cooling channels.

Meyer, Michael L.↗
NASA NTRS1994

Minimizing systematic errors from atmospheric multiple scattering and satellite viewing geometry in coastal zone color scanner level IIA imagery

Water-leaving radiances and phytoplankton pigment concentrations are calculated from coastal zone color scanner (CZCS) radiance measurements by removing atmospheric Rayleigh and aerosol radiances from the total radiance signal measured at the satellite. The single greatest source of error in CZCS atmospheric correction algorithms in the assumption that these Rayleigh and aerosol radiances are separable. Multiple-scattering interactions between Rayleigh and aerosol components cause systematic errors in calculated aerosol radiances, and the magnitude of these errors is dependent on aerosol type and optical depth and on satellite viewing geometry. A technique was developed which extends the results of previous radiative transfer modeling by Gordon and Castano to predict the magnitude of these systematic errors for simulated CZCS orbital passes in which the ocean is viewed through a modeled, physically realistic atmosphere. The simulated image mathematically duplicates the exact satellite, Sun, and pixel locations of an actual CZCS image. Errors in the aerosol radiance at 443 nm are calculated for a range of aerosol optical depths. When pixels in the simulated image exceed an error threshhold, the corresponding pixels in the actual CZCS image are flagged and excluded from further analysis or from use in image compositing or compilation of pigment concentration databases. Studies based on time series analyses or compositing of CZCS imagery which do not address Rayleigh-aerosol multiple scattering should be interpreted cautiously, since the fundamental assumption used in their atmospheric correction algorithm is flawed.

Martin, D. L.↗
NASA NTRS1994

Spectropolarimetry of Nova Cygni 1992: Evidence for an asymmetric geometry

We present the first study of the spectropolarimetric evolution of a fast neon nova from outburst through the decline of the light curve, showing the initial presence and gradual disappearance of intrinsic linear polarization. The observations of Nova Cygni 1992 were obtained at the Pine Bluff Observatory of the University of Wisconsin from 1992 March through 1993 May. The emission lines and the continuum show quite different linear polarization behaviors, with the line emission essentially unpolarized and the continuum showing intrinsic polarization. The data provide evidence for an asymmetric geometry in the initial explosion and evidence for clumping in the subsequent nova ejecta.

Bjorkman, K. S.↗
NASA NTRS1994

Small-scale cosmic microwave background anisotropies as probe of the geometry of the universe

We perform detailed calculations of cosmic microwave background (CMB) anisotropies in a cold dark matter (CDM)-dominated open universe with primordial adiabatic density perturbations for a variety of reionization histories. The CMB anisotropies depend primarily on the geometry of the universe, which in a matter-dominated universe is determined by Omega and the optical depth to the surface of last scattering. In particular, the location on the primary Doppler peak depends primarily on Omega and is fairly insensitive to the other unknown parameters, such as Omega(sub b), h, Lambda, and the shape of the power spectrum. Therefore, if the primordial density perturbations are adiabatic, measurements of CMB anisotropies on small scales may be used to determine Omega.

Kamionkowski, Marc↗
NASA NTRS1994

Geometry of thin liquid sheet flows

Incompresible, thin sheet flows have been of research interest for many years. Those studies were mainly concerned with the stability of the flow in a surrounding gas. Squire was the first to carry out a linear, invicid stability analysis of sheet flow in air and compare the results with experiment. Dombrowski and Fraser did an experimental study of the disintegration of sheet flows using several viscous liquids. They also detected the formulation of holes in their sheet flows. Hagerty and Shea carried out an inviscid stability analysis and calculated growth rates with experimental values. They compared their calculated growth rates with experimental values. Taylor studied extensively the stability of thin liquid sheets both theoretically and experimentally. He showed that thin sheets in a vacuum are stable. Brown experimentally investigated thin liquid sheet flows as a method of application of thin films. Clark and Dumbrowski carried out second-order stability analysis for invicid sheet flows. Lin introduced viscosity into the linear stability analysis of thin sheet flows in a vacuum. Mansour and Chigier conducted an experimental study of the breakup of a sheet flow surrounded by high-speed air. Lin et al. did a linear stability analysis that included viscosity and a surrounding gas. Rangel and Sirignano carried out both a linear and nonlinear invisid stability analysis that applies for any density ratio between the sheet liquid and the surrounding gas. Now there is renewed interest in sheet flows because of their possible application as low mass radiating surfaces. The objective of this study is to investigate the fluid dynamics of sheet flows that are of interest for a space radiator system. Analytical expressions that govern the sheet geometry are compared with experimental results. Since a space radiator will operate in a vacuum, the analysis does not include any drag force on the sheet flow.

Chubb, Donald L.↗
NASA NTRS1994

Topography and subduction geometry in the central Andes: Clues to the mechanics of a noncollisional orogen

The central Andeean orogen between 12 deg and 32 deg S latitude exhibits a high degree of spatial order: principally an extraordinary bilateral symmetry that is common to the Earth's surface, the underlying Wadati-Benioff zone, and the Nazca/South America plate kinematics, which has been stable since the mid-Tertiary. This spatial order must reflect the physical mechanisms of mountain building in this noncollisional orogen. The shapes of the topography and subduction zone can be reduced to symmetric and antisummeric components relative to any verical symmetry plane; the particular plaen which minimizes the antisymmetry (and maximizes the symmetry) is well resolved and is essentially coincident with the stable Euler equator of Nacza/South America relative motion since the mid-Tertiary. That the topography, subduction geometry, and persistent mid-Tertiary plate kinematics share common spatial and geometric elements suggests that he distribution of topography in this orogen depends strongly on the dynamics of subduction. Other factors that might affect the topography and underlying tectonics, such as climate and inherited strutura fabric, which have different spatial characterisitcs, must be of less significance at a continental scale. Furthermore, the small components of asymmetry among the various elements of the orogen appear to be mutually relate in a simple way; it is possible that this coupled asymmetry is associated with a late Teriary change in plate kinematics. These observations suggest that there is a close connection between plate tectonics and the form of the Earth's surface in this noncollisional setting. It follows hta the distribution of topography near convergent plate boundaries may provide a powerful constraing for understanding the dynamics of subduction.

Gephart, John W.↗
NASA NTRS1995

Geometry and pulse profiles of x-ray pulsars: Asymmetric relativistic fits to 4U1538 - 52 and vela x-1

Model calculation of inhomogenuous magnetized neutron star atmospheres are used to analyze the phase-dependent spectra of 4U 1538-52 and Vela X-1 taking into account general relativistic effects. A chi (exp 2) fitting procedure is used on the Ginga data for these objects to determine the geometry and the magnetic structure of the polar caps, as well as their size and location on the surface of the stars. Other parameters determined by the fit are the masses and radii of neutron stars, the accretion rates, and the rotation and magnetic inclination angles including an azimuthal offset to reproduce the asymmetry of the pulse shapes. We find that general relativistic effects play a significant role in determining the derived cap sizes, the fluxes, and the observational appearance of the pulses. There is evidence that the polar caps are unequal and nonantipodal, suggesting either an off-center or bent magnetic axis, or a strong nondipole component. The magnetic field structure is approximated by a two-component model. The rotation axes are inferred to be moderately close to the mean magnetic axes and seen at large inclinations with respect to the line of sight.

Bulik, T.↗
NASA NTRS1995

Design geometry and design/off-design performance computer codes for compressors and turbines

This report summarizes some NASA Lewis (i.e., government owned) computer codes capable of being used for airbreathing propulsion system studies to determine the design geometry and to predict the design/off-design performance of compressors and turbines. These are not CFD codes; velocity-diagram energy and continuity computations are performed fore and aft of the blade rows using meanline, spanline, or streamline analyses. Losses are provided by empirical methods. Both axial-flow and radial-flow configurations are included.

Glassman, Arthur J.↗
NASA NTRS1995

Self consistent MHD modeling of the solar wind from coronal holes with distinct geometries

Utilizing an iterative scheme, a self-consistent axisymmetric MHD model for the solar wind has been developed. We use this model to evaluate the properties of the solar wind issuing from the open polar coronal hole regions of the Sun, during solar minimum. We explore the variation of solar wind parameters across the extent of the hole and we investigate how these variations are affected by the geometry of the hole and the strength of the field at the coronal base.

Stewart, G. A.↗
NASA NTRS1993

Efficient Three-Dimensional Direct Simulation Monte Carlo for Complex Geometry Problems

The simulation of flowfields in the transition flow regime is notoriously difficult with high demands on computer resources (CPU time and storage) and user expertise/labor. This paper describes a new, efficient code which has been developed to simulate high Knudsen number flowfields in three dimensions about bodies of arbitrarily complex geometry. The algorithm has been tested over a wide range of conditions, from free molecular to near-continuum flow regimes, for slender and blunt bodies, for re-entry vehicles and spacecraft. A series of validation tests have been conducted using both wind-tunnel measurements and flight data.

Rault, Didier F. G.↗
NASA NTRS1996

Effect of Dust Coagulation Dynamics on the Geometry of Aggregates

Master equation gives a more fundamental description of stochastic coagulation processes rather than popular Smoluchowski's equation. In order to examine the effect of the dynamics on the geometry of resulting aggregates, we study Master equation with a rigorous Monte Carlo algorithm. It is found that Cluster-Cluster aggregation model is a good approximation of orderly growth and the aggregates have fluffy structures with a fractal dimension approx. 2. A scaling analysis of Smoluchowski's equation also supports this conclusion.

Nakamura, R.↗
NASA NTRS1994

Geometry and Unoccupied Electronic States of Ba and BaO on W(001)

A study aimed at understanding the geometrical and electronic properties of barium and oxygen coadsorbed on the tungsten(001) surface has been carried out by means of work-function measurements (Delta-phi), Auger-electron spectroscopy, low-energy electron diffraction, inverse photoelectron spectroscopy, and relativistic-electronic-structure calculations. A report of the experimental measurements and a comparison with theoretical results from embedded-cluster-model calculations are presented. Our experimental studies show that the work function of the W(001) surface (phi = 4.63 eV) is lowered to approximately 2.3-2.4 eV by coadsorption of 1 ML of Ba and O regardless of the order of deposition of these two species. The technique of IPS in the isochromat mode was used to determine the unoccupied electronic-energy band structure for ordered c (2 X 2) Ba and O layers on W(001). Several spectral features are observed above the Fermi level (E(F)), which we assign to transitions into Ba and W d-states. The measured two-dimensional electronic band structure is independent of the order of Ba and O deposition. Using embedded-cluster-model calculations, we investigated two possible adsorption configurations of an ordered c(2 X 2) adlayer of Ba and O on W(001): 'tilted,' where Ba and O are placed on alternate fourfold-hollow sites, and 'upright,' where the adsorbed atoms lay above the same site with Ba outer-most. The calculated densities of states for the tilted geometry show distinct peaks above E(F) originating from Ba and W d-orbitals and are in good agreement with the experimental results.

Lamouri, A.↗
NASA NTRS1997

Reactive Hydrodynamics in Rotating Spherical and Cylindrical Geometry

In turbulent spray combustion among many complex interactions between local flow structures called turbulent eddies and droplets are those associated with rotation of droplets. In general, for a complete statistical description of turbulent sprays, consideration of at least four degrees of freedom respectively associated with translational, rotational, vibrational (pulsational), and internal motions of the droplet are needed. Clearly the interactions between all degrees of freedom of the droplets and those for the gaseous background field will be exceedingly complex. For example, one type of interaction between the translational and the rotational velocity of droplets results in droplet helicity, H(d) = w(d).v(d), the significance of which in turbulent spray combustion is yet to be recognized. The role of droplet rotation in turbulent spray combustion modeling and its impact on the evaporation of liquid fuel droplets was recently investigated. Also, the impact of rotation on combustion of solid particles such as is encountered in pulverized coal combustion has been emphasized. The problem of viscous flow around a rotating sphere discussed above also occurs in other areas of physical sciences such as astrophysics and geophysics. Consequently, the subject has been addressed in many classical as well as more recent investigations. According to these investigations, the rotation of a rigid sphere in an otherwise quiescent, unconfined environment results in the motion of the fluid towards the poles. The polar flows from the northern and southern hemispheres move along helical trajectories towards the equatorial plane. Eventually, the polar flows collide at the equatorial plane, thus producing a sheet of rotating fluid that is radially ejected outward on this plane. Therefore, a droplet induces a strained flow field as a result of its rotation. Since the spatial extent of equatorial jets could easily exceed many droplet diameters, interactions between neighboring droplets are enhanced as a result of their rotation. Also, the equatorial jet substantially alters the spherical geometry of the diffusion flame surface that surrounds a rotating droplet. The objective of the research is to gain more knowledge about the hydrodynamics within and around rotating spherical and cylindrical body of fluid, and the behavior of diffusion or premixed flame surfaces that could surround such symmetric body of rotating fluid.

Sohrab, Siavash H.↗