SEARCH · Search NASA

Results for “triangularity”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,783 records · Page 99

All sources NASA NTRS DOE OSTI

NASA NTRS1988

A fine grid finite element computation of two-dimensional high Reynolds number flows

A velocity-pressure-integrated mixed-interpolation Galerkin finite-element computation of the Navier-Stokes equations using the grids is presented. The velocity variables are interpolated using complete quadratic shape functions, and the pressure was interpolated using linear shape functions defined on a triangular element which is contained inside the quadratic element for velocity variables. Comprehensive computational results for a cavity flow at Reynolds number Re = 400-10,000 and a laminar backward-facing step flow at Re = 100-900 are presented. Many high-Re flows involve convection-dominated motion as well as diffusion-dominated motion in the flow domain. The computational results for both of the fluid motions compared favorably with high-accuracy finite-difference computational results and/or experimental data.

Kim, Sang-Wook↗

NASA NTRS1989

Fiber-Optic Sensor Would Detect Movements Of Shaft

Fiber-optic sensor senses both rotational speed and axial displacement of shaft in motor, pump, or other rotating machine. Does not require magnetic materials, notches, or grooves in shaft. Required modification of shaft is etching or plating surface to make ring black around half circumference and reflective around other half along short length at one end or some other convenient location. Triangular bundle of sending and receiving optical fibers aimed at black/reflective ring on shaft. Frequency and amplitude of output pulses of fiber-optic probe indicates rotational frequency and axial position of shaft.

Roschak, Edmund J.↗

NASA NTRS1988

Focal region fields of distorted reflectors

The problem of the focal region fields scattered by an arbitrary surface reflector under uniform plane wave illumination is solved. The physical optics (PO) approximation is used to calculate the current induced on the reflector. The surface of the reflector is described by a number of triangular domain-wise 5th degree bivariate polynomials. A 2-dimensional Gaussian quadrature is employed to numerically evaluate the integral expressions of the scattered fields. No Freshnel or Fraunhofer zone approximations are made. The relation of the focal fields problem to surface compensation techniques and other applications are mentioned. Several examples of distorted parabolic reflectors are presented. The computer code developed is included, together with instructions on its usage.

Buris, N. E.↗

NASA NTRS1988

The structure of red-infrared scattergrams of semivegetated landscapes

A physically based linear stochastic geometric canopy soil reflectance model is presented for characterizing spatial variability of semivegetated landscapes at subpixel and regional scales. Landscapes are conceptualized as stochastic geometric surfaces, incorporating not only the variability in geometric elements, but also the variability in vegetation and soil background reflectance which can be important in some scenes. The model is used to investigate several possible mechanisms which contribute to the often observed characteristic triangular shape of red-infrared scattergrams of semivegetated landscapes. Scattergrams of simulated and semivegetated scenes are analyzed with respect to the scales of the satellite pixel and subpixel components. Analysis of actual aerial radiometric data of a pecan orchard is presented in comparison with ground observations as preliminary confirmation of the theoretical results.

Jasinski, Michael F.↗

NASA NTRS1988

Algebraic turbulence models for the computation of two-dimensional high speed flows using unstructured grids

The incorporation of algebraic turbulence models in a solver for the 2-D compressible Navier-Stokes equations using triangular grids is described. A practical way to use the Cebeci Smith model, and to modify it in separated regions is proposed. The ability of the model to predict high speed, perfect gas boundary layers is investigated from a numerical point of view.

Rostand, Philippe↗

NASA NTRS1989

Application of a lower-upper implicit scheme and an interactive grid generation for turbomachinery flow field simulations

A finite-volume lower-upper (LU) implicit scheme is used to simulate an inviscid flow in a tubine cascade. This approximate factorization scheme requires only the inversion of sparse lower and upper triangular matrices, which can be done efficiently without extensive storage. As an implicit scheme it allows a large time step to reach the steady state. An interactive grid generation program (TURBO), which is being developed, is used to generate grids. This program uses the control point form of algebraic grid generation which uses a sparse collection of control points from which the shape and position of coordinate curves can be adjusted. A distinct advantage of TURBO compared with other grid generation programs is that it allows the easy change of local mesh structure without affecting the grid outside the domain of independence. Sample grids are generated by TURBO for a compressor rotor blade and a turbine cascade. The turbine cascade flow is simulated by using the LU implicit scheme on the grid generated by TURBO.

Choo, Yung K.↗

NASA NTRS1988

Growth of GaAs crystals from the melt in a partially confined configuration

The experimental approach was directed along two main goals: (1) the implementation of an approach to melt growth in a partially confined configuration; and (2) the investigation of point defect interaction and electronic characteristics as related to thermal treatment following solidification and stoichiometry. Significant progress was made along both fronts. Crystal growth of GaAs in triangular ampuls was already carried out successfully and consistent with the model. In fact, pronounced surface tension phenomena which cannot be observed in ordinary confinement system were identified and should premit the assessment of Maragoni effects prior to space processing. Regarding thermal treatment, it was discovered that the rate of cooling from elevated temperatures is primarily responsible for a whole class of defect interactions affecting the electronic characteristics of GaAs and that stoichiometry plays a critical role in the quality of GaAs.

Gatos, Harry C.↗

NASA NTRS1989

A reduced version of the NMC DERF 2 data set

The National Meterological Center (NMC) Dynamical Extended Range Forecast (DERF 2) data represents a major computational effort to better ascertain the potential for extended range forecasts and to develop a strategy for performing operational extended range forecasts using dynamical models. A major stumbling block for using this data has been the sheer volume of data that must be processed to perform even simple calculations. The product of the data reduction described is a manageable data set that fits comfortably on five magnetic tapes or on one compact disc. The document outlines the data reduction process of the second phase of DERF data. It contains the description of the fields and the resolution of both the original and final fields. In order to assist the users of this data set, maps of selected fields, using both the original truncation at rhomboidal 30 and the truncation of the final data at triangular 20, are displayed.

Schubert, Siegfried↗

NASA NTRS1987

Development of tailorable advanced blanket insulation for advanced space transportation systems

Two items of Tailorable Advanced Blanket Insulation (TABI) for Advanced Space Transportation Systems were produced. The first consisted of flat panels made from integrally woven, 3-D fluted core having parallel fabric faces and connecting ribs of Nicalon silicon carbide yarns. The triangular cross section of the flutes were filled with mandrels of processed Q-Fiber Felt. Forty panels were prepared with only minimal problems, mostly resulting from the unavailability of insulation with the proper density. Rigidizing the fluted fabric prior to inserting the insulation reduced the production time. The procedures for producing the fabric, insulation mandrels, and TABI panels are described. The second item was an effort to determine the feasibility of producing contoured TABI shapes from gores cut from flat, insulated fluted core panels. Two gores of integrally woven fluted core and single ply fabric (ICAS) were insulated and joined into a large spherical shape employing a tadpole insulator at the mating edges. The fluted core segment of each ICAS consisted of an Astroquartz face fabric and Nicalon face and rib fabrics, while the single ply fabric segment was Nicalon. Further development will be required. The success of fabricating this assembly indicates that this concept may be feasible for certain types of space insulation requirements. The procedures developed for weaving the ICAS, joining the gores, and coating certain areas of the fabrics are presented.

Calamito, Dominic P.↗

NASA NTRS1989

Design sensitivity analysis of boundary element substructures

The ability to reduce or condense a three-dimensional model exactly, and then iterate on this reduced size model representing the parts of the design that are allowed to change in an optimization loop is discussed. The discussion presents the results obtained from an ongoing research effort to exploit the concept of substructuring within the structural shape optimization context using a Boundary Element Analysis (BEA) formulation. The first part contains a formulation for the exact condensation of portions of the overall boundary element model designated as substructures. The use of reduced boundary element models in shape optimization requires that structural sensitivity analysis can be performed. A reduced sensitivity analysis formulation is then presented that allows for the calculation of structural response sensitivities of both the substructured (reduced) and unsubstructured parts of the model. It is shown that this approach produces significant computational economy in the design sensitivity analysis and reanalysis process by facilitating the block triangular factorization and forward reduction and backward substitution of smaller matrices. The implementatior of this formulation is discussed and timings and accuracies of representative test cases presented.

Kane, James H.↗

NASA NTRS1989

Scaling results for the Liquid Sheet Radiator (LSR)

Surface tension forces at the edges of a thin liquid (approx. 100 micrometers) sheet flow result in a triangularly shaped sheet. Such a geometry is ideal for an external flow radiator. The experimental investigation of such sheet flows was extended to large sheets (width = W = 23.5 cm, length = L approx. = 3.5 m). Experimental L/W results are greater than the calculated results. However, more experimental results are necessary for a complete comparison. The calculated emissivity of a sheet of Dow-Corning 705 silicone oil, which is a low temperature (300 to 400K) candidate for a liquid sheet radiator (LSR), is greater than .8 for sheet thicknesses greater than 100 micrometers.

Chubb, Donald L.↗

NASA NTRS1989

Pactruss support structure for precision segmented reflectors

The application of the Pactruss deployable structure to the support of large paraboloidal reflectors of very high precision was studied. The Pactruss concept, originally conceived for the Space Station truss, is shown to be suitable for use in a triangular arrangement to support a reflector surface composed of hexagonal reflector panels. A hybrid of Pactruss structural and deployable single-fold beams is shown to accommodate a center body. A minor alteration in the geometry is in order to avoid lockup during deployment. To assess the capability of the hybrid Pactruss structure, an example truss supporting a full-scale (20 meter diameter) infrared telescope was analyzed for static and dynamic performance. A truss structure weighing 800 kilograms gave adequate support to a reflector surface weighing 3,000 kilograms.

Hedgepeth, John M.↗

NASA NTRS1989

Calculation of turbulence-driven secondary motion in ducts with arbitrary cross section

Calculation methods for turbulent duct flows are generalized for ducts with arbitrary cross-sections. The irregular physical geometry is transformed into a regular one in computational space, and the flow equations are solved with a finite-volume numerical procedure. The turbulent stresses are calculated with an algebraic stress model derived by simplifying model transport equations for the individual Reynolds stresses. Two variants of such a model are considered. These procedures enable the prediction of both the turbulence-driven secondary flow and the anisotropy of the Reynolds stresses, in contrast to some of the earlier calculation methods. Model predictions are compared to experimental data for developed flow in triangular duct, trapezoidal duct and a rod-bundle geometry. The correct trends are predicted, and the quantitative agreement is mostly fair. The simpler variant of the algebraic stress model procured better agreement with the measured data.

Demuren, A. O.↗

NASA NTRS1989

A torus bifurcation theorem with symmetry

Hopf bifurcation in the presence of symmetry, in situations where the normal form equations decouple into phase/amplitude equations is described. A theorem showing that in general such degeneracies are expected to lead to secondary torus bifurcations is proved. By applying this theorem to the case of degenerate Hopf bifurcation with triangular symmetry it is proved that in codimension two there exist regions of parameter space where two branches of asymptotically stable two-tori coexist but where no stable periodic solutions are present. Although a theory was not derived for degenerate Hopf bifurcations in the presence of symmetry, examples are presented that would have to be accounted for by any such general theory.

Vangils, S. A.↗

NASA NTRS1988

Finite element Euler computations in three dimensions

A two-step explicit FEM solution algorithm for the three-dimensional compressible Euler and Navier-Stokes equations based on unstructured triangular and tetrahedral grids is described and demonstrated. The method represents an extension and refinement of the algorithms presented by Loehner et al. (1984 and 1985), Peraire et al. (1987), and Morgan et al. (1987). The formulation and numerical implementation are outlined; the mesh generation, data structures, and adaptive remeshing are explained; and results for a two-dimensional airfoil, a three-dimensional engine air intake, a B747 in landing configuration, and a generic fighter aircraft are presented in extensive graphics and discussed in detail.

Peraire, Jaime↗

NASA NTRS1988

Thermal distortion analysis of the Space Station solar dynamic concentrator

A method was developed to evaluate the thermal distortion of the Space Station Solar Dynamic Concentrator and the effects of thermal distortion on concentrator optical performance. The analytical method includes generating temperature distributions with TRASYS and SINDA models, interfacing the SINDA results with the SINDA-NASTRAN Interface Program (SNIP), calculating thermal distortion with a NASTRAN/PATRAN finite element model, and providing flux distribution maps within the receiver with the ray tracing OFFSET program. Temperature distributions, thermally induced slope errors, and flux distribution maps within the receiver are discussed. Results during a typical orbit indicate that temperatures of the hexagonal panels and triangular facets range between -18 and 99 C (-1 to 210 F), facet rotations are less than 0.2 mrad, and a change in facet radius due to thermal flattening is less than 5 percent. The predicted power loss with thermal distortion effects was less than 0.3 percent. The thermal distortion of the Solar Dynamic concentrator has negligible effect on the flux distribution within the receiver cavity.

Trudell, Jeffery J.↗

NASA NTRS1988

Ray tracing optical analysis of offset solar collector for Space Station solar dynamic system

OFFSET, a detailed ray tracing computer code, was developed at NASA Lewis Research Center to model the offset solar collector for the Space Station solar dynamic electric power system. This model traces rays from 50 points on the face of the sun to 10 points on each of the 456 collector facets. The triangular facets are modeled with spherical, parabolic, or toroidal reflective surface contour and surface slope errors. The rays are then traced through the receiver aperture to the walls of the receiver. Images of the collector and of the sun within the receiver produced by this code provide insight into the collector receiver interface. Flux distribution on the receiver walls, plotted by this code, is improved by a combination of changes to aperture location and receiver tilt angle. Power loss by spillage at the receiver aperture is computed and is considerably reduced by using toroidal facets.

Jefferies, Kent S.↗

NASA NTRS1988

Growth of GaAs from a free surface melt under controlled arsenic pressure in a partially confined configuration

A partially confined configuration for the growth of GaAs from melt in space was developed, consisting of a triangular prism containing the seed crystal and source material in the form of a rod. It is suggested that the configuration overcomes two obstacles in the growth of GaAs in space: total confinement in a quartz crucible and lack of arsenic pressure control. Ground tests of the configuration show that it is capable of crystal growth in space and is useful for studying the growth of GaAs from a free-surface melt on earth. The resulting chemical composition, electrical property variations, and phenomenological models to account for the results are presented.

Gatos, H. C.↗