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At least 955 records · Page 53
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Tectonic implications of the microearthquake seismicity and fault plane solutions in southern Peru

Because the contortion in the seismic zone in southern Peru is aligned approximately parallel to the direction of relative plate motion, rather than perpendicular to the coast of Peru, the position of the contortion need not migrate with respect to the overriding South American plate as the Nazca plate subducts beneath it, and the flow in the surrounding asthenosphere could be in a steady state. In addition, the position of the contortion defines the northern boundary of the volcanic arc in southern Peru. The inference that a wedge of asthenospheric material must overlie the downgoing slab for subduction-related volcanism to occur is thereby strengthened.

Grange, F.↗
NASA NTRS1984

A tomographic image of mantle structure beneath southern California

The variations in seismic structure beneath southern California were determined by using a tomographic method of inversion on teleseismic P delays recorded with the Southern California Array. The inversion reveals two prominent features beneath the region. The first is a thin, vertical wedge directly beneath the Transverse Ranges that is 2-3 percent faster than the surrounding region. This feature deepens to the east, attaining a maximum depth of about 250 km beneath the San Bernardino Mountains. The second feature is a major zone of low velocity material that is 2-4 percent slow under the Salton Trough rift valley, extending to a depth of about 125 km. Two possible explanations for the spatial association of the Transverse Ranges with the velocity anomaly below are lithospheric subduction or small-scale sublithospheric convection in the region of the Big Bend of the San Andreas Fault. The low velocity anomaly beneath the Salton Trough is consistent with convective upwelling there.

Humphreys, E.↗
NASA NTRS1986

Improved Numerical Evaluation Method for Elliptic Integrals

Two modifications to Bartky's method for numerical evaluation of complete elliptic integrals increase rate of convergence and eliminate loss of accuracy due to roundoff errors. Other integrals (nonelliptic) evaluated by manipulating integrand into form F(R)/R required for evaluation by this method. Improved method used to map upper half of complex plane conformally onto interior or exterior of round-nosed wedges of various angles.

Rossow, V. J.↗
NASA NTRS1984

Local stability analysis for a planar shock wave

A procedure to study the local stability of planar shock waves is presented. The procedure is applied to a Rankine-Hugoniot shock in a divergent/convergent nozzle, to an isentropic shock in a divergent/convergent nozzle, and to Rankine-Hugoniot shocks attached to wedges and cones. It is shown that for each case, the equation governing the shock motion is equivalent to the damped harmonic oscillator equation.

Salas, M. D.↗
NASA NTRS1985

Stress intensity factor in a tapered specimen

The general problem of a tapered specimen containing an edge crack is formulated in terms of a system of singular integral equations. The equations are solved and the stress intensity factor is calculated for a compact and for a slender tapered specimen, the latter simulating the double cantilever beam. The results are obtained primarily for a pair of concentrated forces and for crack surface wedge forces. The stress intensity factors are also obtained for a long strip under uniform tension which contains inclined edge cracks.

Xue-Hui, L.↗
NASA NTRS1985

Distribution and Properties of Large Symmetric Knobs on Mars

Knobby terrain on Mars exists in a variety of forms from small closely spaced hills to widely separated large massifs. Fractional areal distributions of knobby terrain range from over 49% of the sampled area in regions of chaotic terrain to less than 5% along the cratered highland boundary in Amenthes and Aeolis. All symmetric knobs with long dimensions greater than or equal to 10 km were identified, mapped, and classified by shape. The spatial and dimensional distributions and shape characteristics of these features are discussed. The most common shape is elliptical: 79% of the knobs fall into this category, 11% were circular or round, 6% were triangular or wedge-shaped and the remaining 4% other shapes. All types show a roughly similar trend of rapidly decreasing number with increasing size, such that overall less than 10% of the knobs are larger than 20 km in long dimension. Circular knobs show the steepest fall-off in numbers with increasing diameter. Triangular knobs have a broader maximum with more than 65% falling in the 10 to 14 km range.

Frey, H.↗
NASA NTRS1985

Fault Offsets and Lateral Crustal Movement on Europa

Structural evidence is presented for tension cracking associated with strike slip faulting and crustal movement in the bright ice covered Galilean satellite Europa. The structure and morphology of wedge shaped bands argues that they formed as a result of the rotation and lateral displacement of crustal units bounded by near vertical faults penetrating through the brittle crustal layer. The significant rotation and lateral motion of crustal blocks near the anti-jove point on Europa, without graben formation, also argues that the lithosphere in the fractured area is mechanically decoupled from the solid silicate interior, by either warm ice at depth or liquid water. Ice at depth and at a large fraction of its melting temperature is expected to behave as a fluid over geologically short time intervals due to its extremely low viscosity relative to the cold, brittle ice near the surface. One proposed convection mechanism is thus considered unlikely as it would be difficult to transmit internal stress through a decoupling layer to the surface.

Schenk, P. M.↗
NASA NTRS1985

Geology of the Ganymede Quadrangle Jg7

The western half of Ganymede quadrangle Jg7 is covered by Voyager 2 images with resolution of .5 to 5 km/pixel. The imaged area includes dark terrain in the north underlying the southeastern part of Galileo Regio, and light terrain in the south underlying the southeastern extension of Uruk Sulcus. Several slivers and wedges of dark terrain occur within the light areas. Numerous craters are present, as well as three large palimsests (crater scars with little topographic expression) in the dark terrain and a basin in the light terrain. The boundary between dark and light materials on the south side of Galileo Regio is locally marked by a scarp that faces the light terrain. The scarp truncates several craters. The truncation and rotation of structures suggest that light material grew at the expense of dark material, and that the destruction, except for minor pivoting, was essentially in situ. The composition and structural properties of the palimsests and craters are examined.

Lucchitta, B. K.↗
NASA NTRS1985

Aircraft rotor blade with passive tuned tab

A structure for reducing vibratory airloading in a rotor blade with a leading edge and a trailing edge includes a cut out portion at the trailing edge. A substantially wedge shaped cross section, inertially deflectable tab, also with a leading edge and a trailing edge is pivotally mounted in the cut out portion. The trailing edge of the tab may move above and below the rotor blade. A torsion strap applies force against the tab when the trailing edge of the tab is above and below the rotor blade. A restraining member is slidably movable along the torsion strap to vary torsional biasing force supplied by the torsion bar to the tab. A plurality of movable weights positioned between plates vary a center of gravity of the tab. Skin of the tab is formed from unidirectional graphite and fiberglass layers. Sliders coupled with a pinned degree of freedom at rod eliminate bending of tab under edgewise blade deflection.

Campbell, T. G.↗
NASA NTRS1985

Aerodynamic characteristics of a distinct wing-body configuration at Mach 6: Experiment, theory, and the hypersonic isolation principle

An experimental investigation has been conducted to determine the effect of wing leading edge sweep and wing translation on the aerodynamic characteristics of a wing body configuration at a free stream Mach number of about 6 and Reynolds number (based on body length) of 17.9 x 10 to the 6th power. Seven wings with leading edge sweep angles from -20 deg to 60 deg were tested on a common body over an angle of attack range from -12 deg to 10 deg. All wings had a common span, aspect ratio, taper ratio, planform area, and thickness ratio. Wings were translated longitudinally on the body to make tests possible with the total and exposed mean aerodynamic chords located at a fixed body station. Aerodynamic forces were found to be independent of wing sweep and translation, and pitching moments were constant when the exposed wing mean aerodynamic chord was located at a fixed body station. Thus, the Hypersonic Isolation Principle was verified. Theory applied with tangent wedge pressures on the wing and tangent cone pressures on the body provided excellent predictions of aerodynamic force coefficients but poor estimates of moment coefficients.

Penland, J. A.↗
NASA NTRS1985

Unsteady flow in a supersonic cascade with two in-passage shocks

A model for a supersonic blade row with two in-passage shock waves is developed. It accounts for three-dimensional effects in real flows by using an altered blade shape in a two-dimensional cascade. There is enough flexibility in the choice of blade shape to accommodate a desired entrance angle, exit angle, boundary-layer thickness and stage pressure ratio at a given entrance Mach number. The model divides the mean flow into regions of uniform or one-dimensional flow in which the solutions for the unsteady flow may be formed successively. The analysis makes use of previous solutions for unsteady flow in cascades and over an oscillation wedge. Six flow conditions are chosen in the range of parameters for which the two-shock model is valid for studies of flutter in torsion and bending. It is found, in keeping with previous results from a single-shock model, that in each case there is increasing instability with decreasing frequency.

Braun, W. H.↗
NASA NTRS1984

A geometric analysis of surface deformation - Implications for the tectonic evolution of Ganymede

The identification of various types of surface deformation of Ganymede by a geometric study of the furrow system and an analysis of circularity of impact craters is addressed. The hypothesis that the furrow system was initially concentric and that the present configuration of the furrows provides a measure of lateral motion of dark terrain is tested by determining the present centers of the furrow system in several dark terrain blocks and observing the amount of deformation in bright terrain regions which separate these blocks. An upper scale limit is placed on the amount of extension associated with bright terrain formation by using the deviation from circularity of impact craters to calculate the strain field around wedge-shaped regions of bright terrain. Penetrative deformation in Ganymede's lithosphere is identified by examining the circularity of impact craters in dark terrain.

Zuber, M. T.↗
NASA NTRS1984

Fizeau wavemeter for pulsed laser wavelength measurement

A Fizeau wavelength meter optimized for use with pulsed laser sources has been developed and characterized which demonstrates a CW resolution better than 2 parts in 10 to the 7th and a pulsed resolution better than 1 part in 10 to the 6th. The static optical design is based on a Fizeau wedge interferometer, which together with spatial filtering and collimating optics is used to produce a pattern of parallel fringes which is imaged on a linear photodiode array and analyzed by a minicomputer. A series of CW and pulsed measurements of various narrowband laser sources are described, and particular difficulties involved in pulsed laser measurements with the wavemeter are examined.

Morris, M. B.↗
NASA NTRS1985

Transient motion of hypersonic vehicles including time history effects

An analytic method is developed for calculating the transient pitching motion of a wedge in hypersonic flow, taking into account fully the interaction between its motion and the unsteady air flow passing it. The effects of past motion history on the present state of motion are shown to be caused by the wave reflection from the bow shock. In the Newtonian limit they are equivalent to that of an added moment of inertia. The time history effects generally tend to decrease the damping, rendering the oscillatory motion more persistent. Numerical examples are given.

Hui, W. H.↗
NASA NTRS1985

Electronic readout systems for microchannel plates

The modes of operation of position-sensitive electronic readout systems which use high-gain microchannel plate (MCP) electron multipliers are described, and their performance characteristics, along with those of the MCP, are compared. Among the structures presented are the wedge-and-strip, Codacon, and multilayer coincidence-anode MAMA (Multimode Microchannel Array) arrays. Spatial resolution of 25 x 25 sq microns (coincidence anode arrays) is achieved with an array format of 256 x 1024 pixels. On the basis of the performance data it is concluded that the readout systems using only conducting electrodes offer the best performance characteristics.

Timothy, J. G.↗
NASA NTRS1984

Ultrasonic probing of the fracture process zone in rock using surface waves

A microcrack process zone is frequently suggested to accompany macrofractures in rock and play an important role in the resistance to fracture propagation. Attenuation of surface waves propagating through mode I fractures in wedge-loaded double-cantilever beam specimens of Westerly granite has been recorded in an attempt to characterize the structure of the fracture process zone. The ultrasonic measurements do not support the generally accepted model of a macroscopic fracture that incrementally propagates with the accompaniment of a cloud of microcracks. Instead, fractures in Westerly granite appear to form as gradually separating surfaces within a zone having a width of a few millimeters and a length of several tens of millimeters. A fracture process zone of this size would necessitate the use of meter-sized specimens in order for linear elastic fracture mechanics to be applicable.

Swanson, P. L.↗
NASA NTRS1985

Adaptive mesh solution for supersonic conical flow in a rectilinear inlet

Solutions for the inviscid and viscous supersonic conical flow in a complete rectilinear inlet consisting of four planes intersecting at arbitrary wedge and sweep angles are obtained. To compute the flow on a specially constructed mesh, a three-dimensional flow solver ARC3D is used. It is shown that a single-pass mesh re-adaptation procedure can be used to obtain improved shock capture without the necessity of modifying the flow code, provided that the flow solver works in curvilinear coordinates and is restartable. Results computed by the method show good agreement with experimental measurements and previous calculations.

Kerlick, G. D.↗