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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.

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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Signature extension studies

The importance of specific spectral regions to signature extension is explored. In the recent past, the signature extension task was focused on the development of new techniques. Tested techniques are now used to investigate this spectral aspect of the large area survey. Sets of channels were sought which, for a given technique, were the least affected by several sources of variation over four data sets and yet provided good object class separation on each individual data set. Using sets of channels determined as part of this study, signature extension was accomplished between data sets collected over a six-day period and over a range of about 400 kilometers.

Vincent, R. K.↗
NASA NTRS1975

Monitoring crack extension in fracture toughness tests by ultrasonics

An ultrasonic method was used to observe the onset of crack extension and to monitor continued crack growth in fracture toughness specimens during three point bend tests. A 20 MHz transducer was used with commercially available equipment to detect average crack extension less than 0.09 mm. The material tested was a 300-grade maraging steel in the annealed condition. A crack extension resistance curve was developed to demonstrate the usefulness of the ultrasonic method for minimizing the number of tests required to generate such curves.

Klima, S. J.↗
NASA NTRS1974

The ERTS-1 investigation (ER-600). Volume 6: ERTS-1 signature extension analysis, July 1972 - June 1973

Feature classification, spatially and temporally, was extended over the Houston test site area. The Earth Resources Technology Satellite (ERTS-1) multispectral scanner data from August, September, and October 1972, of five widely separated lakes were used as statistical training fields and test sites. Short term temporal (same day to 36 days) and moderately long term spatial (within and between three ERTS multispectral scanner frames) signature extensions have been verified with respect to large relatively homogeneous features. The most significant feature dependent variable affecting spatial and short term extension was water turbidity. Long term signature extension will require a model to compensate or modify the ERTS-1 multispectral scanner data for significant sun angle changes. The presence of atmospheric haze changed the absolute signature but always by approximately the same amount so that the measured water signature was always the same. The normally occurring variations in atmospheric haze conditions had no major effect on the water signatures in this study.

Erb, R. B.↗
NASA NTRS1976

Monitoring crack extension in fracture toughness tests by ultrasonics

An ultrasonic method was used to observe the onset of crack extension and to monitor continued crack growth in fracture toughness specimens during three-point bend tests. A 20-MHz transducer was used with commercially available equipment to detect average crack extension less than 0.09 mm. The material tested was a 300-grade maraging steel in the annealed condition. A crack extension resistance curve was developed to demonstrate the usefulness of the ultrasonic method for minimizing the number of tests required to generate such curves.

Klima, S. J.↗
NASA NTRS1987

Energy dissipation associated with crack extension in an elastic-plastic material

Crack extension in elastic-plastic material involves energy dissipation through the creation of new crack surfaces and additional yielding around the crack front. An analytical procedure, using a two-dimensional elastic-plastic finite element method, was developed to calculate the energy dissipation components during a quasi-static crack extension. The fracture of an isotropic compact specimen was numerically simulated using the critical crack-tip-opening-displacement (CTOD) growth criterion. Two specimen sizes were analyzed for three values of critical CTOD. Results from the analyses showed that the total energy dissipation rate consisted of three components: the crack separation energy rate, the plastic energy dissipation rate, and the residual strain energy rate. All three energy dissipation components and the total energy dissipation rate initially increased with crack extension and finally reached constant values.

Shivakumar, K. N.↗
NASA NTRS1988

Effects of a temperature-dependent rheology on large scale continental extension

The effects of a temperature-dependent rheology on large-scale continental extension are investigated using a thin viscous sheet model. A vertically-averaged rheology is used that is consistent with laboratory experiments on power-law creep of olivine and that depends exponentially on temperature. Results of the calculations depend principally on two parameters: the Peclet number, which describes the relative rates of advection and diffusion of heat, and a dimensionless activation energy, which controls the temperature dependence of the rheology. At short times following the beginning of extension, deformation occurs with negligible change in temperature, so that only small changes in lithospheric strength occur due to attenuation of the lithosphere. However, after a certain critical time interval, thermal diffusion lowers temperatures in the lithosphere, strongly increasing lithospheric strength and slowing the rate of extension. This critical time depends principally on the Peclet number and is short compared with the thermal time constant of the lithosphere. The strength changes cause the locus of high extensional strain rates to shift with time from regions of high strain to regions of low strain. Results of the calculations are compared with observations from the Aegean, where maximum extensional strains are found in the south, near Crete, but maximum present-day strain rates are largest about 300 km further north.

Sonder, Leslie J.↗
NASA NTRS1987

Energy dissipation associated with crack extension in an elastic-plastic material

Crack extension in elastic-plastic material involves energy dissipation through the creation of new crack surfaces and additional yielding around the crack front. An analytical procedure, using a two-dimensional elastic-plastic finite element method, was developed to calculate the energy dissipation components during a quasi-static crack extension. The fracture of an isotropic compact specimen was numerically simulated using the critical crack-tip-opening-displacement (CTOD) growth criterion. Two specimen sizes were analyzed for three values of critical CTOD. Results from the analysis showed that the total energy dissipation rate consisted of three components: the crack separation energy rate, the plastic energy dissipation rate, and the residual strain energy rate. All three energy dissipation components and the total energy dissipation rate initially increased with crack extension and finally reached constant values.

Shivakumar, K. N.↗
NASA NTRS1989

Effects of a temperature-dependent rheology on large-scale continental extension

The effects of a temperature-dependent rheology on large-scale continental extension are investigated using a thin viscous sheet model. A vertically-averaged rheology is used that is consistent with laboratory experiments on power-law creep of olivine and that depends exponentially on temperature. Results of the calculations depend principally on two parameters: the Peclet number, which describes the relative rates of advection and diffusion of heat, and a dimensionless activation energy, which controls the temperature dependence of the rheology. At short times following the beginning of extension, deformation occurs with negligible change in temperature, so that only small changes in lithospheric strength occur due to attenuation of the lithosphere. However, after a certain critical time interval, thermal diffusion lowers temperatures in the lithosphere, strongly increasing lithospheric strength and slowing the rate of extension. This critical time depends principally on the Peclet number and is short compared with the thermal time constant of the lithosphere. The strength changes cause the locus of high extensional strain rates to shift with time from regions of high strain to regions of low strain. Results of the calculations are compared with observations from the Aegean, where maximum extensional strains are found in the south, near Crete, but maximum present-day strain rates are largest about 300 km further north.

Sonder, Leslie J.↗
NASA NTRS1991

Extension-bend-twist coupling behavior of thin-walled advanced composite beams with initial twist

An analytical model is developed for assessing the extension-bend-twist coupling behavior of nonhomogeneous anisotropic beams with initial twist. The model is formulated as a coupled two-dimensional boundary value problem, where the displacement solutions are defined with pretwist-dependent functions that represent the extension, bending, and torsion, and unknown functions that represent local in-plane deformations and out-of-plane cross-section warping. The unknown deformation functions are determined by applying the principle of minimum potential energy to a discretized representation of the cross section. Numerical results are presented that fully verify this approach and illustrate the strong extension-twist coupling behavior present in pretwisted beams with thin-wall laminated composite cross sections as a function of ply angle, initial twist level, and initial twist axis location. Cross-sections analyzed include; thin laminated rectangles with either asymmetric or symmetric ply stacking sequences and a thin-wall single cell D-section composed of a graphite/epoxy woven cloth.

Kosmatka, J. B.↗
NASA NTRS1992

Global correlation of volcanic centers on Venus with uplands and with extension: Influence of mantle convection and altitude

The observed distribution of volcanism on Venus and its associations with geologic and tectonic characteristics are examined for significant global-scale tectonic, mantle, and volcanic influences. We find that volcanic centers are correlated geologically with zones of extension, infrequent in lowland regions, and infrequent in regions with evidence for tectonic shortening. In addition, volcanic centers are significantly concentrated in a broad region at least 10,000 km in diameter between Beta, Alta, and Themis Regiones. This area is nearly hemispheric in scale and coincides spatially with the area of greatest concentration of extensional characteristics. Our analysis suggests that the observed distribution patterns of volcanic centers reflect the regional patterns of extension, the origin of the extension and volcanism are closely related, and the hemispheric scale of both patterns implies a deep-seated origin such as large-scale interior mantle dynamic patterns. However, altitude-dependent effects on both the formation and preservation of volcanic centers could also strongly influence the observed distribution pattern.

Crumpler, L. S.↗
NASA NTRS1993

Experimental and analytical investigation of dynamic characteristics of extension-twist-coupled composite tubular spars

The results from a study aimed at improving the dynamic and aerodynamic characteristics of composite rotor blades through the use of extension-twist coupling are presented. A set of extension-twist-coupled composite spars was manufactured with four plies of graphite-epoxy cloth prepreg. These spars were noncircular in cross-section design and were therefore subject to warping deformations. Three different cross-sectional geometries were developed: D-shape, square, and flattened ellipse. Three spars of each type were fabricated to assess the degree of repeatability in the manufacturing process of extension-twist-coupled structures. Results from free-free vibration tests of the spars were compared with results from normal modes and frequency analyses of companion shell-finite-element models. Five global modes were identified within the frequency range from 0 to 2000 Hz for each spar. The experimental results for only one D-shape spar could be determined, however, and agreed within 13.8 percent of the analytical results. Frequencies corresponding to the five global modes for the three square spars agreed within 9.5, 11.6, and 8.5 percent of the respective analytical results and for the three elliptical spars agreed within 4.9, 7.7, and 9.6 percent of the respective analytical results.

Lake, Renee C.↗
NASA NTRS1992

An extension of command shaping methods for controlling residual vibration using frequency sampling

The authors present an extension to the impulse shaping technique for commanding machines to move with reduced residual vibration. The extension, called frequency sampling, is a method for generating constraints that are used to obtain shaping sequences which minimize residual vibration in systems such as robots whose resonant frequencies change during motion. The authors present a review of impulse shaping methods, a development of the proposed extension, and a comparison of results of tests conducted on a simple model of the space shuttle robot arm. Frequency shaping provides a method for minimizing the impulse sequence duration required to give the desired insensitivity.

Singer, Neil C.↗
NASA NTRS1993

The FK5 Extension on the FK4 system

This paper reports on the computations necessary to place the FK5 Extension (epoch of place B1950.0) on the B1950.0/FK4 system from its published form and the availability of this version of the catalog. An application of the utility of the new version of the FK5 Extension, to the AGK3U, is given too. This confirms both the system of the AGK3U and the estimated values of its equatorial coordinate and proper motion mean errors. In addition, we have fully exploited the flexibility of the method of infinitely overlapping circles to compute a mean epoch of place/FK4 version of the FK5 Extension which we also make available. These modifications include taking into account the changes induced by the new system of general precession constants, adjusting for the e-terms of aberration, correcting for both the FK5/FK4 equinox offset and motion, and the FK5/FK4 positional and the proper motion systematic differences.

Lattanzi, M. G.↗
NASA NTRS1994

Patterns of brittle deformation under extension on Venus

The development of fractures at regular length scales is a widespread feature of Venusian tectonics. Models of lithospheric deformation under extension based on non-Newtonian viscous flow and brittle-plastic flow develop localized failure at preferred wavelengths that depend on lithospheric thickness and stratification. The characteristic wavelengths seen in rift zones and tessera can therefore provide constraints on crustal and thermal structure. Analytic solutions were obtained for growth rates in infinitesimal perturbations imposed on a one-dimensional, layered rheology. Brittle layers were approximated by perfectly-plastic, uniform strength, overlying ductile layers exhibiting thermally-activated power-law creep. This study investigates the formation of faults under finite amounts of extension, employing a finite-element approach. Our model incorporates non-linear viscous rheology and a Coulomb failure envelope. An initial perturbation in crustal thickness gives rise to necking instabilities. A small amount of velocity weakening serves to localize deformation into planar regions of high strain rate. Such planes are analogous to normal faults seen in terrestrial rift zones. These 'faults' evolve to low angle under finite extension. Fault spacing, orientation and location, and the depth to the brittle-ductile transition, depend in a complex way on lateral variations in crustal thickness. In general, we find that multiple wavelengths of deformation can arise from the interaction of crustal and mantle lithosphere.

Neumann, G. A.↗
NASA NTRS1961

Transonic Investigation of Aerodynamic Characteristics of a Swept-Wing Fighter-Airplane Model with Leading-Edge Droop in Combination with Outboard Chord-Extensions and Notches

An investigation of the effects of several wing leading-edge modifications on the aerodynamic characteristics of a 45 degree swept-wing fighter-airplane model has been conducted in the Langley 16-foot transonic tunnel at low and high lifting conditions at Mach numbers from 0.85 to 1.03. The investigation included the determination of the effect on longitudinal stability and performance characteristics of wing leading-edge and chord-extension droops of 60 and 20 degrees chord-extension overhangs of 0.075c and 0.15c (where c inboard end of the 0.075c chord-extension to depths of 0.075c and 0.l25c, and indention of the model fuselage to conform partially to the supersonic area rule for a Mach number of 1.20. Lift, drag, and pitching-moment data were obtained for configurations with the tail on and off. Comparisons of data obtained from the present model with data from a configuration with leading-edge slats are included. Generally, the model wing modifications provided only slight improvements of the airplane longitudinal stability characteristics, but did substantially reduce the airplane drag coefficients at moderate and high lifting conditions.

Whitcomb, Charles F.↗
NASA NTRS1993

Wall extensibility: its nature, measurement and relationship to plant cell growth

Expansive growth of plant cells is controlled principally by processes that loosen the wall and enable it to expand irreversibly. The central role of wall relaxation for cell expansion is reviewed. The most common methods for assessing the extension properties of plant cell walls ( wall extensibility') are described, categorized and assessed critically. What emerges are three fundamentally different approaches which test growing cells for their ability (a) to enlarge at different values of turgor, (b) to induce wall relaxation, and (c) to deform elastically or plastically in response to an applied tensile force. Analogous methods with isolated walls are similarly reviewed. The results of these different assays are related to the nature of plant cell growth and pertinent biophysical theory. I argue that the extensibilities' measured by these assays are fundamentally different from one another and that some are more pertinent to growth than others.

Review, Academic↗
NASA NTRS1947

Effect of Slot-Entry Skirt Extensions on Aerodynamic Characteristics of a Wing Section of the XB-36 Airplane Equipped with a Double Slotted Flap

An investigation was made in the Langley two-dimensional low-turbulence tunnel on a wing section for the XB-36 airplane equipped with a double slotted flap to determine the effect on lift and drag of various slot-entry skirt extension. A skirt extension of 0.787 deg. was found to provide the best combination of high maximum lift with flap deflected and law drag with flap retracted. The data showed that the maximum lift at intermediate (20 deg. to 45 deg.) flap deflections was lowered considerably by the slot-entry extension; but at high flap deflections the effect was small. An increase in Reynolds number from 2.4 million to 6.0 million increased the maximum.lift coefficient at a flap deflection of 55 deg. from 3.12 to 3.30 and from 1.18 to 1.40 for the flap retracted condition, but did not greatly affect the maximum lift coefficient for intermediate flap deflections. The flap and fore flap load data indicated that the maximum lift coefficients at high flap deflections are limited by a breakdown in the flow over the .flaps.

Cahill, Jones F.↗
NASA NTRS2013

Extension of a Kinetic Approach to Chemical Reactions to Electronic Energy Levels and Reactions Involving Charged Species With Application to DSMC Simulations

The ability to compute rarefied, ionized hypersonic flows is becoming more important as missions such as Earth reentry, landing high mass payloads on Mars, and the exploration of the outer planets and their satellites are being considered. Recently introduced molecular-level chemistry models that predict equilibrium and nonequilibrium reaction rates using only kinetic theory and fundamental molecular properties are extended in the current work to include electronic energy level transitions and reactions involving charged particles. These extensions are shown to agree favorably with reported transition and reaction rates from the literature for nearequilibrium conditions. Also, the extensions are applied to the second flight of the Project FIRE flight experiment at 1634 seconds with a Knudsen number of 0.001 at an altitude of 76.4 km. In order to accomplish this, NASA's direct simulation Monte Carlo code DAC was rewritten to include the ability to simulate charge-neutral ionized flows, take advantage of the recently introduced chemistry model, and to include the extensions presented in this work. The 1634 second data point was chosen for comparisons to be made in order to include a CFD solution. The Knudsen number at this point in time is such that the DSMC simulations are still tractable and the CFD computations are at the edge of what is considered valid because, although near-transitional, the flow is still considered to be continuum. It is shown that the inclusion of electronic energy levels in the DSMC simulation is necessary for flows of this nature and is required for comparison to the CFD solution. The flow field solutions are also post-processed by the nonequilibrium radiation code HARA to compute the radiative portion of the heating and is then compared to the total heating measured in flight.

Liechty, Derek S.↗