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At least 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Algorithms and programming tools for image processing on the MPP, part 2

A number of algorithms were developed for image warping and pyramid image filtering. Techniques were investigated for the parallel processing of a large number of independent irregular shaped regions on the MPP. In addition some utilities for dealing with very long vectors and for sorting were developed. Documentation pages for the algorithms which are available for distribution are given. The performance of the MPP for a number of basic data manipulations was determined. From these results it is possible to predict the efficiency of the MPP for a number of algorithms and applications. The Parallel Pascal development system, which is a portable programming environment for the MPP, was improved and better documentation including a tutorial was written. This environment allows programs for the MPP to be developed on any conventional computer system; it consists of a set of system programs and a library of general purpose Parallel Pascal functions. The algorithms were tested on the MPP and a presentation on the development system was made to the MPP users group. The UNIX version of the Parallel Pascal System was distributed to a number of new sites.

Reeves, Anthony P.↗
NASA NTRS1985

Thermal blanket insulation for advanced space transportation systems

The feasibility of weaving Nextel ceramic and Nicalon silicon carbide yarns into integrally woven, three dimensional fluted core fabrics was demonstrated. Parallel face fabrics joined with woven fabric ribs to form triangular cross section flutes between the faces were woven into three single and one double layer configuration. High warp yarn density in the double layer configuration caused considerable yarn breakage during weaving. The flutes of all four fabrics were filled with mandrels made from Q-Fiber Felt and FRCI-20-12 to form candidate insulation panels for advanced Space Transportation Systems. Procedures for preparing and inserting the mandrels were developed. Recommendations are made on investigating alternate methods for filling the flutes with insulation, and for improving the weaving of these types of fabrics.

Pusch, Richard H.↗
NASA NTRS1986

The relationship of the large-scale solar field to the interplanetary magnetic field - What will Ulysses find?

Using photospheric magnetic field observations obtained at the Stanford Wilcox Solar Observatory, results from a potential field model for the present solar cycle are given, and qualitative predictions of the IMF that Ulysses may encounter are presented. Results indicate that the IMF consists of large regions of opposite polarity separated by a neutral sheet (NS) (extended to at least 50 deg) and a four-sector structure near solar minimum (produced by small quadripolar NS warps). The latitudinal extent of the NS increases following minimum and the structure near maximum includes multiple NSs, while a simplified IMF is found during the declining phase.

Hoeksema, J. T.↗
NASA NTRS1987

Nonlinear beam kinematics by decomposition of the rotation tensor

A simple matrix expression is obtained for the strain components of a beam in which the displacements and rotations are large. The only restrictions are on the magnitudes of the strain and of the local rotation, a newly-identified kinematical quantity. The local rotation is defined as the change of orientation of material elements relative to the change of orientation of the beam reference triad. The vectors and tensors in the theory are resolved along orthogonal triads of base vectors centered along the undeformed and deformed beam reference axes, so Cartesian tensor notation is used. Although a curvilinear coordinate system is natural to the beam problem, the complications usually associated with its use are circumvented. Local rotations appear explicitly in the resulting strain expressions, facilitating the treatment of beams with both open and closed cross sections in applications of the theory. The theory is used to obtain the kinematical relations for coupled bending, torsion, extension, shear deformation, and warping of an initially curved and twisted beam.

Danielson, D. A.↗
NASA NTRS1986

Remote sensing of chlorophyll concentrations in the northern Gulf of Mexico

During a 17 month period (November 1978 - March 1980), phytoplankton pigment concentrations were remotely sensed in the northern Gulf of Mexico using the Coastal Zone Color Scanner (CZCS). A total of 29 CZCS orbits were processed into pigment (chlorophyll a + phaeopigments) images and then geometrically warped to a Mercator projection. A correction factor of 1.67 was applied to the pigment concentrations to correct for the tendency of the standard fluorometric method to underestimate chlorophyll a concentrations. The spatial and temporal distributions of pigment fronts were quite variable during this time series. Constant features observed throughout the pigment imagery were the entrainment of coastal waters offshore. The most extensive entrainments occurred during intrusions of the Loop Current. For the 17 month survey, the mean HPLC-corrected pigment concentration was 3.30 + or - 1.45 mg/cu m.

Trees, Charles C.↗
NASA NTRS1987

A simple and efficient shear-flexible plate bending element

A shear-flexible triangular element formulation, which utilizes an assumed quadratic displacement potential energy approach and is numerically integrated using Gauss quadrature, is presented. The Reissner/Mindlin hypothesis of constant cross-sectional warping is directly applied to the three-dimensional elasticity theory to obtain a moderately thick-plate theory or constant shear-angle theory (CST), wherein the middle surface is no longer considered to be the reference surface and the two rotations are replaced by the two in-plane displacements as nodal variables. The resulting finite-element possesses 18 degrees of freedom (DOF). Numerical results are obtained for two different numerical integration schemes and a wide range of meshes and span-to-thickness ratios. These, when compared with available exact, series or finite-element solutions, demonstrate accuracy and rapid convergence characteristics of the present element. This is especially true in the case of thin to very thin plates, when the present element, used in conjunction with the reduced integration scheme, outperforms its counterpart, based on discrete Kirchhoff constraint theory (DKT).

Chaudhuri, Reaz A.↗
NASA NTRS1988

Consistent linearization of the element-independent corotational formulation for the structural analysis of general shells

A consistent linearization is provided for the element-dependent corotational formulation, providing the proper first and second variation of the strain energy. As a result, the warping problem that has plagued flat elements has been overcome, with beneficial effects carried over to linear solutions. True Newton quadratic convergence has been restored to the Structural Analysis of General Shells (STAGS) code for conservative loading using the full corotational implementation. Some implications for general finite element analysis are discussed, including what effect the automatic frame invariance provided by this work might have on the development of new, improved elements.

Rankin, C. C.↗
NASA NTRS1988

Analytical approximation of a distorted reflector surface defined by a discrete set of points

Reflector antennas on Earth orbiting spacecrafts generally cannot be described analytically. The reflector surface is subjected to a large temperature fluctuation and gradients, and is thus warped from its true geometrical shape. Aside from distortion by thermal stresses, reflector surfaces are often purposely shaped to minimize phase aberrations and scanning losses. To analyze distorted reflector antennas defined by discrete surface points, a numerical technique must be applied to compute an interpolatory surface passing through a grid of discrete points. In this paper, the distorted reflector surface points are approximated by two analytical components: an undistorted surface component and a surface error component. The undistorted surface component is a best fit paraboloid polynomial for the given set of points and the surface error component is a Fourier series expansion of the deviation of the actual surface points, from the best fit paraboloid. By applying the numerical technique to approximate the surface normals of the distorted reflector surface, the induced surface current can be obtained using physical optics technique. These surface currents are integrated to find the far field radiation pattern.

Acosta, Roberto J.↗
NASA NTRS1987

Characteristics of inhomogeneous coupled cylindrical striplines

Using conformal transformation, closed-form expressions for the even and odd mode impedances of inhomogeneous coupled cylindrical striplines are presented. It is shown that the analysis can be extended for the calculation of characteristics of coupled cylindrical microstrip lines. The analysis can also be extended to reveal the effects of warping due to environmental changes on an otherwise planar structure.

Reddy, C. J.↗
NASA NTRS1987

Stress concentration around a part-through hole weakening a laminated plates

A quasi-three-dimensional-elasticity type theory, based on the assumptions of transverse inextensibility and layerwise constant shear-angle, is presented, in the context of an assumed quadratic displacement potential energy approach, for analyzing an edge-loaded laminated plate weakened by the presence of a part-through hole. Numerical results, obtained using the C-deg-type triangular finite element, indicate the existence of severe cross-sectional warping in the vicinity of the hole and plate boundaries. Furthermore, the three-dimensional nature of the stress concentration factor in the neighborhood of the hole boundary is clearly exhibited. Besides, very high stress concentration factors are found in the layer weakened by the part-through hole. The numerical results presented should serve as bench-mark solutions for future comparisons.

Chaudhuri, Reaz A.↗
NASA NTRS1988

Evolution of inclined galactic gas disks. I - A cloud-fluid approach

In this paper, numerical models are developed to follow the time-dependent behavior of inclined gas disks in nonspherical galaxies. Differential equations are developed which describe the time rate of change of the orbits of mass elements composing a thin, smoothly warping and twisting gas disk. These equations include multiple moments due to the nonsphericity of the galactic mass distribution, Coriolis effects arising from determination of orbits in a reference frame which tumbles with the surface figure of the galaxy, and viscous forces arising from cloud-cloud collisions. A cloud-fluid approach is used in determining the viscous forces. Physical arguments are used to determine the maximum permissible local value of the coefficient of kinematic viscosity. For small initial inclinations, analytic expressions are obtained for the inclination as a function of time and for the settling time, and the features of the solution are discussed.

Steiman-Cameron, Thomas Y.↗
NASA NTRS1988

Characteristics of broadside coupled cylindrical striplines

This letter presents a method for calculating the even and odd mode impedances of broadside coupled cylindrical stiplines using the conformal mapping technique. Closed form expressions are presented for calculating the even and odd mode characteristic impedances. The data for even and odd mode impedances are presented. The analysis can also be extended to warped broadside coupled striplines.

Reddy, C. Jagadeswara↗
NASA NTRS1988

An optical study of stars and dust in the Andromeda galaxy

The distribution of light in M 31 is characterized on the basis of the UBVR surface photometry reported by Walterbos and Kennicutt (1987). The results of the data analysis are presented in extensive graphs, maps, and tables and discussed in detail, considering the outer disk regions, the decomposition into bulge and disk, the global disk and bulge colors, and dust and gas in two spiral arms. Principal findings examined include: (1) position-angle changes at radial distances beyond about 18 kpc (consistent with SW disk warping); (2) a bulge profile well described by an r exp 1/4 power law; (3) a bulge contribution to total light of about 40 percent; (4) increasing blueness in the outer disk (color gradient 0.02 mag/kpc in B-R); (5) an extinction law similar to that for the Galaxy; and (6) a significant correlation between dust and H I distributions.

Walterbos, R. A. M.↗
NASA NTRS1988

The Titan-1:0 nodal bending wave in Saturn's Ring C

The most prominent oscillatory feature observed in the Voyager 1 radio occultation of Saturn's rings is identified as a one-armed spiral bending wave excited by Titan's-1:0 nodal inner vertical resonance. Ring particles in a bending wave move in coherently inclined orbits, warping the local mean plane of the rings. The Titan-1:0 wave is the only known bending wave that propagates outward, away from Saturn, and the only spiral wave yet observed in which the wave pattern rotates opposite to the orbital direction of the ring particles. It is also the first bending wave identified in ring C. Modeling the observed feature with existing bending wave theory gives a surface mass density of about 0.4 g/sq cm outside the wave region and a local ring thickness of less than about 5 meters, and suggests that surface mass density is not constant in the wave region.

Rosen, Paul A.↗
NASA NTRS1988

Analysis of coupled cylindrical striplines filled with multilayered dielectrics

A method of analysis for coupled cylindrical striplines filled with multilayered dielectrics is presented that uses a variational technique in the space domain. Coupled-mode analysis is presented for the case of a pair of coupled circular arc strips arbitrarily located between cylindrical ground planes filled with multilayered dielectrics. An even- and odd-mode approach is used for the analysis of shielded cylindrically curved edge-coupled pairs of broad-side parallel strips (broad-side, edge-coupled cylindrical striplines). The effect of environmental changes on an otherwise planar structure is also studied by extending the present analysis to cylindrically warped coupled striplines.

Reddy, C. Jagadeswara↗
NASA NTRS1988

A high heat flux experiment for verification of thermostructural analysis

A major concern in advancing the state of the art technologies for hypersonic vehicles is the development of an aeropropulsion system capable of handling the high heat fluxes during flight. The leading edges of such systems must not only tolerate the maximum heating rates, but must also minimize distortions to the flow field due to excessive blunting and/or thermal warping of the compression surface to achieve the high inlet performance required. A combined analytical and experimental effort to study the aerothermodynamic loads on actively cooled structures for hypersonic applications was established. A hydrogen/oxygen rocket engine was modified to establish a high enthalpy high heat flux environment. The facility provides heat flux levels from about 200 up to 10000 Btu/sq ft/sec. Cross flow and parallel flow regeneratively cooled model can be tested and analyzed by using cooling fluids of water and hydrogen. Results are presented of the experiment and the characteristics of the Hot Gas Test Facility. The predicted temperature results of the cross flow model are compared with the experimental data on the first monolithic specimens and are found to be in good agreement. Thermal stress analysis results are also presented.

Gladden, Herbert J.↗
NASA NTRS1989

Automatic voice recognition using traditional and artificial neural network approaches

The main objective of this research is to develop an algorithm for isolated-word recognition. This research is focused on digital signal analysis rather than linguistic analysis of speech. Features extraction is carried out by applying a Linear Predictive Coding (LPC) algorithm with order of 10. Continuous-word and speaker independent recognition will be considered in future study after accomplishing this isolated word research. To examine the similarity between the reference and the training sets, two approaches are explored. The first is implementing traditional pattern recognition techniques where a dynamic time warping algorithm is applied to align the two sets and calculate the probability of matching by measuring the Euclidean distance between the two sets. The second is implementing a backpropagation artificial neural net model with three layers as the pattern classifier. The adaptation rule implemented in this network is the generalized least mean square (LMS) rule. The first approach has been accomplished. A vocabulary of 50 words was selected and tested. The accuracy of the algorithm was found to be around 85 percent. The second approach is in progress at the present time.

Botros, Nazeih M.↗
NASA NTRS1988

Structural evolution of the Kolar Schist Belt, South India

The structural evolution of the Kolar Schist Belt was discussed. Evidence was described from structures in the ferrigenous quartzite within the schist belt for two periods of nearly coaxial isoclinal folding attributable to E-W compression. This folding was followed by collapse of the F sub 1/F sub 2 folds, forming open F sub 3 folds with NNE-SSW axes. Finally, a period of N-S shortening caused a broad warping of the earlier N-S trending fold axes. There is evidence within the gneisses for shearing produced by similar, nearly E-W compression.

Mukhopahyay, Dilip K.↗