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At least 541 records · Page 30
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Design of structures for optimum geometry

A method is presented for configuration optimization of finite element structures, given a reasonable initial geometry. The objective is to minimize weight or cost. Design variables include geometric as well as member sizing parameters. The number of elements and joints, and the element-joint relationships are prescribed and are not changed during the optimization process. However, the joint locations are changed. The structure is assumed to be linearly elastic and may be statically indeterminate. Multiple loading conditions are allowed. Constraints include limits on stiffness as well as strength. The method is demonstrated with application to truss design, subject to minimum size, strength, buckling, and displacement constraints. Major design improvements are achieved through configurations changes.

Vanderplaats, G. N.↗
NASA NTRS1978

High speed cylindrical roller bearing analysis, SKF computer program CYBEAN. Volume 2: User's manual

The CYBEAN (Cylindrical Bearing Analysis) was created to detail radially loaded, aligned and misaligned cylindrical roller bearing performance under a variety of operating conditions. Emphasis was placed on detailing the effects of high speed, preload and system thermal coupling. Roller tilt, skew, radial, circumferential and axial displacement as well as flange contact were considered. Variable housing and flexible out-of-round outer ring geometries, and both steady state and time transient temperature calculations were enabled. The complete range of elastohydrodynamic contact considerations, employing full and partial film conditions were treated in the computation of raceway and flange contacts. Input and output architectures containing guidelines for use and a sample execution are detailed.

Kleckner, R. J.↗
NASA NTRS1981

High speed cylindrical roller bearing analysis. SKF computer program CYBEAN. Volume 2: User's manual

CYBEAN (CYlindrical BEaring ANalysis) was created to detail radially loaded, aligned and misaligned cylindrical roller bearing performance under a variety of operating conditions. Emphasis was placed on detailing the effects of high speed, preload and system thermal coupling. Roller tilt, skew, radial, circumferential and axial displacement as well as flange contact were considered. Variable housing and flexible out-of-round outer ring geometries, and both steady state and time transient temperature calculations were enabled. The complete range of elastohydrodynamic contact considerations, employing full and partial film conditions were treated in the computation of raceway and flange contacts. The practical and correct implementation of CYBEAN is discussed. The capability to execute the program at four different levels of complexity was included. In addition, the program was updated to properly direct roller-to-raceway contact load vectors automatically in those cases where roller or ring profiles have small radii of curvature. Input and output architectures containing guidelines for use and two sample executions are detailed.

Dyba, G. J.↗
NASA NTRS1986

Computer aided derivation of equations for composite mechanics problems and finite element analyses

Explicit equations are derived for analysis of multilayered fiber composites and for finite element analyses. The equations are obtained using a symbolic program and tested for various composite properties as well as for different fiber orientations. In order to analyze multilayered fiber composite structures, a variable thickness finite element is formulated. Examples of an airfoil geometry, simulated in a form of a cantilevered beam with various fiber orientations are studied.

Sarigul, N.↗
NASA NTRS1993

Computing Shapes Of Cascade Diffuser Blades

Computer program generates sizes and shapes of cascade-type blades for use in axial or radial turbomachine diffusers. Generates shapes of blades rapidly, incorporating extensive cascade data to determine optimum incidence and deviation angle for blade design based on 65-series data base of National Advisory Commission for Aeronautics and Astronautics (NACA). Allows great variability in blade profile through input variables. Also provides for design of three-dimensional blades by allowing variable blade stacking. Enables designer to obtain computed blade-geometry data in various forms: as input for blade-loading analysis; as input for quasi-three-dimensional analysis of flow; or as points for transfer to computer-aided design.

Tran, Ken↗
NASA NTRS1994

Fatigue analysis of multiple site damage at a row of holes in a wide panel

This paper is concerned with predicting the fatigue life of unstiffened panels which contain multiple site damage (MSD). The initial damage consists of through-the-thickness cracks emanating from a row of holes in the center of a finite width panel. A fracture mechanics analysis has been developed to predict the growth, interaction, and coalescence of the various cracks which propagate in the panel. A strain-life analysis incorporating Neuber's rule for notches, and Miner's rule for cumulative damage, is also employed to predict crack initiation for holes without initial cracking. This analysis is compared with the results of a series of fatigue tests on 2024-T3 aluminum panels, and is shown to do an excellent job of predicting the influence of MSD on the fatigue life of nine inch wide specimens. Having established confidence in the ability to analyze the influence of MSD on fatigue life, a parametric study is conducted to examine the influence of various MSD scenarios in an unstiffened panel. The numerical study considered 135 cases in all, with the parametric variables being the applied cyclic stress level, the lead crack geometry, and the number and location of MSD cracks. The numerical analysis provides details for the manner in which lead cracks and MSD cracks grow and coalesce leading to final failure. The results indicate that MSD located adjacent to lead cracks is the most damaging configuration, while for cases without lead cracks, MSD clusters which are not separated by uncracked holes are most damaging.

Buhler, Kimberley↗
NASA NTRS1996

Calculation of Turbulent Subsonic Diffuser Flows Using the NPARC Navier-Stokes Code

Axisymmetric subsonic diffuser flows were calculated with the NPARC Navier-Stokes code in order to determine the effects various code features have on the flow solutions. The code features examined in this work were turbulence models and boundary conditions. Four turbulence models available in NPARC were used: the Baldwin-Lomax algebraic model, the Baldwin-Barth one-equation model, and the Chien kappa-epsilon and Wilcox kappa-omega two-equation models. The three boundary conditions examined were the free boundary, the mass flux boundary and the subsonic outflow with variable static pressure. In addition to boundary condition type, the geometry downstream of the diffuser was varied to see if upstream influences were present. The NPARC results are compared with experimental data and recommendations are given for using NPARC to compute similar flows.

Dudek, J. C.↗
NASA NTRS2003

Probabilistic Evaluation of Blade Impact Damage

The response to high velocity impact of a composite blade is probabilistically evaluated. The evaluation is focused on quantifying probabilistically the effects of uncertainties (scatter) in the variables that describe the impact, the blade make-up (geometry and material), the blade response (displacements, strains, stresses, frequencies), the blade residual strength after impact, and the blade damage tolerance. The results of probabilistic evaluations results are in terms of probability cumulative distribution functions and probabilistic sensitivities. Results show that the blade has relatively low damage tolerance at 0.999 probability of structural failure and substantial at 0.01 probability.

Chamis, C. C.↗
NASA NTRS2004

FUSE Observations of the Bright, Eclipsing Nova-like Cataclysmic Variable, UX UMa (FUSE 2000)

This was a project to study the disk and wind of the eclipsing nova-like variable UX UMa, in order to better define the wind geometry of the system, including the nature of the transition region between the disk photosphere and the supersonic wind. We proposed to use phase resolved spectroscopy of the system, taking advantage of the fact that UX UMa is an eclipsing system, to isolate different regions of the wind and to use a Monte Carlo radiative transfer code to simulate the spectra through the eclipse.

Long, Knox↗
NASA NTRS2007

More on the Possible Composition of the Meridiani Hematite-Rich Concretions

Elsewhere in these proceedings, Schneider et al. discuss compositional constraints on hematite-rich spherule (blueberry) formation at Meridiani Planum. Schneider et al. provide the background for work done to date to understand the composition and mineralogy of the spherules and devise a test of possible concretion growth processes. They also report the results of area analyses of spherules in targets analyzed with the Alpha Particle X-ray Spectrometer (APXS) and test several possible models for included components other than hematite. In this abstract, we use the compositional trends for spherule-rich targets to compute possible elemental compositions of the spherules. This approach differs from that of, which also used a determination of the area of spherules in APXS targets, coupled with a correction for the radial acceptance function, to try to un-mix the compositions directly, using 2 and 3-component models and mass balance. That approach contained a fair amount of uncertainty owing to problems associated with irregular and heterogeneous target geometry, unknown composition of non-spherule lithic components, and variable dust coatings on spherules. Since then, Opportunity has analyzed additional spherule-rich targets, and the compositional trends so obtained permit a more direct assessment of the data.

Jolliff, B. L.↗
NASA NTRS2020

Evaluation of Packing_3D Code for Design of Variable-Depth, Bent-Chamber Acoustic Liners

Increases in the bypass ratio for commercial aircraft engines have caused the broadband fan noise component to become dominant. As a result, there is a need to develop improved acoustic liners suitable for absorption of this fan noise over a wide frequency range, preferably up to at least two octaves. Variable depth liners with bent chambers and three-dimensional geometries present one way to achieve this goal, however, they can be difficult and time-consuming to design due to their complexity and volume constraints. A packing code, called Packing3D, has been developed that automatically designs the chamber configurations of such liners once the chamber dimensions and volume constraints are known. The code uses a randomized trial and error approach to place each chamber in a representation of the liner sample, then returns a colored diagram and sufficient information for the liner sample to be fabricated. For evaluation, the code is used to design four liner samples of varying levels of complexity. These samples are tested with and without a mesh facesheet in the NASA Langley Normal Incidence Tube, and the results are compared to predictions computed in COMSOL. The results indicate that the packing code is able to quickly design samples that are predictable, achieve the desired absorption spectrum, fit the given constraints, and are able to be built. This code is flexible, lends itself to optimization, and allows samples to be designed quickly, accurately, and efficiently.

Marinova, Miroslava M.↗
NASA NTRSDate not supplied

Relationships Between Variability in the Stratospheric Polar Vortex, Upper Tropospheric Jets, Tropopauses, and UTLS Ozone

The impacts of stratospheric polar vortex variations on upper troposphere / lower stratosphere (UTLS) circulation and composition are not well understood. We use stratospheric polar vortex geometry / strength diagnostics combined with characterisation of tropopauses and UTLS jets to show links between stratospheric polar vortex variability and regional variations in UTLS jet and tropopause characteristics. Polar vortex diagnostics are from Characterization and Analysis of Vortex Evolution using Algorithms for Region Tracking (CAVE-ART), while UTLS diagnostics are from JEt and Tropopause Products for Analysis and Characterization (JETPAC). We will present results showing UTLS jet and tropopause characteristics for strong and weak stratospheric vortex states (defined using vortex-focused metrics that are less dependent on geometry and position than commonly used diagnostics), as well as regional variations in correlations between CAVE-ART and JETPAC diagnostics. Furthermore, we will focus on preliminary results extending the stratospheric vortex, UTLS jet, and tropopause relationships to assess their impacts on regional ozone variations diagnosed from the M2-SCREAM (MERRA-2 Stratospheric Composition Reanalysis of Aura Microwave Limb Sounder) composition reanalysis.

Gloria Manney↗
NASA NTRS1994

Geometry and physical conditions in the stellar wind of AG Carinae

AG Carinae is one of the prototypes of the class of Luminous Blue Variables (LBVs). Since 1990 the star has continuously brightened in its visual continuum. We report on a multi-instrument and -wavelength observing campaign to monitor the current activity phase of AG Car. Ground-based photometry, polarimetry, spectroscopy, and space-ultraviolet spectroscopy and spectropolarimetry have been obtained. From the variability of the polarization at ultraviolet and optical wavelengths we detect significant intrinsic polarization. P(sub int) greater than or equal to 0.5% is a large value for a hot, luminous star, suggesting departure from spherical symmetry in the wind of AG Car. The intrinsic polarization is variable on a timescale of 2 months or less. The measured ultraviolet polarization (intrinsic + interstellar) dropped to 0.5% in 1992 May and returned to 1% in 1992 July. The results are interpreted in terms of a variable outflow with a density enhancement in the equatorial plane. A similar model was suggested for the related object R127 in the Large Magellanic Cloud (LMC). This geometry is reminiscent of the large-scale morphology of the gas nebula and dust 'jet' surrounding AG Car. It is therefore likely that physical conditions close to the stellar surface are responsible for the geometry of the spatially resolved circumstellar material around AG Car. Despite the drastic change of the photospheric conditions, the mass-loss rate did not increase. We find no evidence for a positive correlation between wind density and stellar radius. This makes models that explain the radius increase by opacity effects in the outflow unlikely. The mechanism responsible for the temperature and radius variations is still unknown but most likely has its origin in subphotospheric regions.

Leitherer, Claus↗
NASA NTRS1993

Aerodynamic configuration design using response surface methodology analysis

An investigation has been conducted to determine a set of optimal design parameters for a single-stage-to-orbit reentry vehicle. Several configuration geometry parameters which had a large impact on the entry vehicle flying characteristics were selected as design variables: the fuselage fineness ratio, the nose to body length ratio, the nose camber value, the wing planform area scale factor, and the wing location. The optimal geometry parameter values were chosen using a response surface methodology (RSM) technique which allowed for a minimum dry weight configuration design that met a set of aerodynamic performance constraints on the landing speed, and on the subsonic, supersonic, and hypersonic trim and stability levels. The RSM technique utilized, specifically the central composite design method, is presented, along with the general vehicle conceptual design process. Results are presented for an optimized configuration along with several design trade cases.

Engelund, Walter C.↗
NASA NTRS1979

Dayside merging and cusp geometry

Geometrical considerations are presented to show that dayside magnetic merging when constrained to act only where the fields are antiparallel results in lines of merging that converge at the polar cusps. An important consequence of this geometry is that no accelerated flows are predicted across the dayside magnetopause. Acceleration owing to merging acts in opposition to the magnetosheath flow at the merging point and produces the variably directed, slower-than-magnetosheath flows observed in the entry layer. Another consequence of the merging geometry is that much of the time closed field lines constitute the subsolar region of the magnetopause. The manner in which the polar cap convection patterns predicted by the proposed geometry change as the interplanetary field is rotated through 360 deg provides a unifying description of how the observed single circular vortex and the crescent-shaped double vortex patterns mutually evolve under the influence of a single operating principle.

Crooker, N. U.↗
NASA NTRS1972

A 30-cm diameter bombardment thruster with a variable magnetic baffle

Variable magnetic baffles were used to allow a change in baffle geometry to improve thruster performance and stability. Test results are presented. Thruster performance characteristics were analyzed to show how magnetic baffle field strength can improve performance at a fixed beam current, as well as increase the range of ion beam current for throttling.

Bechtel, R. T.↗
NASA NTRS1984

A new method for acoustic containerless processing of materials

The development of an acoustic positioner, which uses only one acoustic mode in chambers of rectangular, cylindrical, and spherical geometries, for high-temperature containerless processing of materials in space is described. The objective of the single-mode positioner is to develop sufficient acoustic forces to stably localize and manipulate molten materials. In order to attain this goal the transducer power, energy transfer medium, and chamber geometry and dimensions need to be optimized. The use of a variable frequency compression driver or solid-state piezoelectric transducer to optimize these properties is investigated; it is determined that a solid-state transducer would be most applicable for optimizing the positioner. The positioning capabilities of this single-mode positioner are discussed. The dependence of the acoustic forces on temperature and ambient pressure is studied. The development of a levitator to process a molten sample at 1500 C in the space environment using the cylindrical (011) mode is illustrated.

Barmatz, M.↗
NASA NTRS1990

Zoom Vision System For Robotic Welding

Rugged zoom lens subsystem proposed for use in along-the-torch vision system of robotic welder. Enables system to adapt, via simple mechanical adjustments, to gas cups of different lengths, electrodes of different protrusions, and/or different distances between end of electrode and workpiece. Unnecessary to change optical components to accommodate changes in geometry. Easy to calibrate with respect to object in view. Provides variable focus and variable magnification.

Gilbert, Jeffrey L.↗