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At least 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

Directivity of low frequency solar type III radio bursts

The occurrence rate of type III solar bursts in the frequency range 4.9 MHz to 30 kHz is analyzed as a function of burst intensity and burst arrival direction. We find that (1) the occurrence rate of bursts varies inversely with the 1.5 power of the flux, and (2) the distribution of burst arrival directions at each frequency shows a significantly larger number of bursts observed west of the earth-sun line than east of it. This western excess in occurrence rate appears to be correlated with the direction of the average interplanetary magnetic field, and is interpreted as beaming of the observed burst radiation along the magnetic field direction.

Fitzenreiter, R. J.↗
NASA NTRS1977

Microstructure and composition of InSb-GaSb ingots directionally solidified aboard Skylab

InSb-GaSb solid solution ingots prepared by directional solidification aboard Skylab and on earth consist of twins with (111) twin planes parallel to the direction of solidification and growth directions that lie along 211, 110, or 321 crystallographic directions. Significant fractions of several ingots prepared aboard Skylab were solidified from melts that were not in contact with container walls, resulting in convection driven by surface tension gradients in the melt and corresponding radially-symmetric composition variations in the ingot. In these regions, adjacent twins exhibit marked differences in indium content, indicating a substantial dependence of composition on crystallographic orientation.

Lefever, R. A.↗
NASA NTRS1976

Direction-finding measurements of type III radio bursts out of the ecliptic plane

A series of two-dimensional direction-finding measurements for three type III solar radio bursts is presented which is based on spin-modulation measurements from two satellites (IMP 8 and Hawkeye I) whose spin axes were nearly perpendicular to each other. The two-dimensional direction-finding technique is combined with a model of the solar-wind plasma density in order to provide determinations of type III source locations out of the ecliptic plane as well as information on the three-dimensional structure of the solar magnetic field at radial distances of 0.2 to 1.0 AU from the sun. The direction-finding technique is described in detail, characteristics of the bursts observed by the two satellites are summarized, and the solar-wind model is outlined. The results show that the source locations follow an Archimedean spiral when projected onto the ecliptic plane but usually follow a constant heliocentric latitude perpendicular to that plane. It is also found that measured source sizes are a factor of two larger than the angular sizes of previously reported solar-flare electron emissions, that the spin-modulation factor tends to be largest near the beginning of a type III event, and that the arrival direction of the radiation varies systematically during an event.

Baumback, M. M.↗
NASA NTRS1977

The influence of the directional energy distribution on the nonlinear dispersion relation in a random gravity wave field

The influence of the directional distribution of wave energy on the dispersion relation is calculated numerically using various directional wave spectrum models. The results indicate that the dispersion relation varies both as a function of the directional energy distribution and the direction of propagation of the wave component under consideration. Furthermore, both the mean deviation and the random scatter from the linear approximation increase as the energy spreading decreases. Limited observational data are compared with the theoretical results. The agreement is favorable.

Huang, N. E.↗
NASA NTRS1978

Stereoscopic direction finding analysis of a type III solar radio burst - Evidence for emission at 2f/p-/

Stereoscopic direction finding measurements from the Imp 8, Hawkeye 1, and Helios 2 spacecraft over base line distances of a substantial fraction of an astronomical unit are used to directly determine the three-dimensional trajectory of a type III solar radio burst. By comparing the observed source positions with the direct in situ solar wind plasma density measurements obtained by Helios 1 and 2 near the sun, the relationship of the emission frequency to the local plasma frequency can be determined directly without any modeling assumptions. These comparisons show that the type III radio emission occurs near the second harmonic of the local electron plasma frequency. Other characteristics of the type III radio emission, such as the source size, which can be obtained from this type of analysis, are also discussed.

Gurnett, D. A.↗
NASA NTRS1979

Low-cost directionally-solidified turbine blades, volume 1

A low cost process of manufacturing high stress rupture strength directionally-solidified high pressure turbine blades was successfully developed for the TFE731-3 Turbofan Engine. The basic processing parameters were established using MAR-M 247 and employing the exothermic directional-solidification process in trial castings of turbine blades. Nickel-based alloys were evaluated as directionally-solidified cast blades. A new turbine blade, disk, and associated components were then designed using previously determined material properties. Engine tests were run and the results were analyzed and compared to the originally established goals. The results showed that the stress rupture strength of exothermically heated, directionally-solidified MAR-M 247 turbine blades exceeded program objectives and that the performance and cost reduction goals were achieved.

Sink, L. W.↗
NASA NTRS1978

On phase and ray directions of magnetosonic waves

The behavior of phase speed for 'slow' and 'fast' magnetosonic waves is well documented in the literature. Not so well documented is the behavior of the ray direction and its relation to the phase direction - indeed the ray behavior recorded in most of the standard plasma physics texts has not been found. This situation is rectified, and some of the curiosities associated with the direction of the 'slow' ray relative to the direction of the 'slow' phase wave are indicated. These calculations have been performed as a necessary basis for discussion of phase and ray evolution of magnetosonic waves in differentially shearing plasmas.

Lerche, I.↗
NASA NTRS1978

Directional models for analysis of earth radiation budget measurements

The determination of the radiation heat flux densities at the top of the atmosphere (30 km) for spatial scales ranging from global to regional is necessary for the conversion of satellite irradiance measurements into useful earth radiation budget information. Data reduction algorithms are required which contain assumed directional characteristics of radiation emitted and scattered from the earth-atmosphere system. The directional characteristics are defined by models which express, for a given surface element at the top of the atmosphere, the exiting flux per unit solid angle for each direction out to space as a fraction of the total hemispheric flux exiting the surface element. Both longwave and shortwave directional radiation models are analyzed. It is found that the validity of the Nimbus 2-based limb darkening curves has generally been verified for the longwave data with the exception of the Antarctic snow fields where limb brightening was noticed in the earth radiation budget data.

Suttles, J. T.↗
NASA NTRS1978

Shear rupture of a directionally solidified eutectic gamma/gamma-prime - alpha /Mo/ alloy

Directionally solidified gamma/gamma-prime - alpha (Mo) eutectic alloys are being evaluated for application as advanced aircraft engine turbine blades. Their excellent high-temperature strength is partly due to their directionally aligned microstructure. However, alloys with such directional structures may display low shear strength at 760 C, the operating temperature of advanced blade roots. The objective of this investigation was to determine the shear rupture strength of the gamma/gamma-prime - alpha eutectic alloy and possibly to improve it by microstructural and heat-treatment variations. Bars of gamma/gamma-prime - alpha alloy containing nominally 5.7% Al and 33.5% Mo by weight with balance Ni were directionally solidified at rates between 10 and 100 mm per hour. Materials were solidified in furnaces with thermal gradients at the liquid-solid interface of 250 or 100 C per cm. A limited number of longitudinal shear rupture tests were conducted at 760 C and 207 MPa in the as-solidified and in several heat-treated conditions. It was found that the shear rupture failures are partly transgranular and that resistance to failure is promoted by good fiber alignment and a matrix structure consisting mainly of gamma-prime. Well-aligned as-solidified specimens sustained the shear stress for an average of 81 hours, while cellular material failed in one hour or less.

Harf, F. H.↗
NASA NTRS1979

Effects of fuselage forebody geometry on low-speed lateral-directional characteristics of twin-tail fighter model at high angles of attack

Low-speed, static wind-tunnel tests were conducted to explore the effects of fighter fuselage forebody geometry on lateral-directional characteristics at high angles of attack and to provide data for general design procedures. Effects of eight different forebody configurations and several add-on devices (e.g., nose strakes, boundary-layer trip wires, and nose booms) were investigated. Tests showed that forebody design features such as fineness ratio, cross-sectional shape, and add-on devices can have a significant influence on both lateral-directional and longitudinal aerodynamic stability. Several of the forebodies produced both lateral-directional symmetry and strong favorable changes in lateral-directional stability. However, the same results also indicated that such forebody designs can produce significant reductions in longitudinal stability near maximum lift and can significantly change the influence of other configuration variables. The addition of devices to highly tailored forebody designs also can significantly degrade the stability improvements provided by the clean forebody.

Carr, P. C.↗
NASA NTRS1980

Comparisons between wave directional spectra from SAR and pressure sensor arrays

Simultaneous directional wave measurements were made at Torrey Pines Beach, California, by a synthetic aperture radar (SAR) and a linear array of pressure sensors. The measurements were conducted during the West Coast Experiment in March 1977. Quantitative comparisons of the normalized directional spectra from the two systems were made for wave periods of 6.9-17.0 s. The comparison results were variable but generally showed good agreement of the primary mode of the normalized directional energy. An attempt was made to quantify the physical criteria for good wave imaging in the SAR. A frequency band analysis of wave parameters such as band energy, slope, and orbital velocity did not show good correlation with the directional comparisons. It is noted that absolute values of the wave height spectrum cannot be derived from the SAR images yet and, consequently, no comparisons of absolute energy levels with corresponding array measurements were intended.

Pawka, S. S.↗
NASA NTRS1983

Estimating Waveguide Feed Directivity and Spacing

Approximate curves simplify initial steps of antenna design. Maximum achievable directivity exponents plotted as functions of element spacing in wavelengths for equilateral triangular array of rectangular waveguides. Directivities and exponents calculated for circular waveguides, pyramidal horns, and other standard feeds. Designer quickly estimates element spacing necessary to achieve required directivity or directivity achievable.

Rahmat-Samii, Y.↗
NASA NTRS1982

Master list and index to NASA directives

All NASA management directives in force as of August 1, 1982 are listed by major subject headings showing number, effective data, title, responsible office, and distribution code. Delegations of authority in print by that date are listed numerically as well as by the installation or office to which special authority is assigned. Other consolidated lists show all management handbooks, directives applicable to the Jet Propulsion Laboratory, directions published in the Code of Federal Regulations, complementary manuals, and NASA safety standards. Distribution policies and instructions for ordering directives are included.

Source record↗
NASA NTRS1983

A robust Feasible Directions algorithm for design synthesis

A nonlinear optimization algorithm is developed which combines the best features of the Method of Feasible Directions and the Generalized Reduced Gradient Method. This algorithm utilizes the direction-finding sub-problem from the Method of Feasible Directions to find a search direction which is equivalent to that of the Generalized Reduced Gradient Method, but does not require the addition of a large number of slack variables associated with inequality constraints. This method provides a core-efficient algorithm for the solution of optimization problems with a large number of inequality constraints. Further optimization efficiency is derived by introducing the concept of infrequent gradient calculations. In addition, it is found that the sensitivity of the optimum design to changes in the problem parameters can be obtained using this method without the need for second derivatives or Lagrange multipliers. A numerical example is given in order to demonstrate the efficiency of the algorithm and the sensitivity analysis.

Vanderplaats, G. N.↗
NASA NTRS1983

Alternating direction adaptive grid generation

The present investigation is concerned with the development of an alternating direction method which can adaptively resolve numerical solutions involving physical problems by moving the points of a coordinate grid. The alternating direction movement algorithm is applied to adapt a grid to surface data and weights which are given with respect to the grid itself. Attention is given to details concerning the alternating direction method, aspects of algorithmic construction, the choice of weights which controls the coordinate movement and structure, and questions regarding the applications of the alternating direction movement algorithm. On an analytical basis, the method is seen to move points in a nonsingular fashion.

Eiseman, P. R.↗
NASA NTRS1984

Master list and index to NASA directives

All NASA management directives in force as of August 1, 1984 are listed by major subject headings showing number, effective date, title, responsible office, and distribution code. Delegations of authority in print by that date are listed numerically as well as by the installation or office to which special authority is assigned. Other consolidated lists show all management handbooks, directives applicable to the Jet Propulsion Laboratory, directives published in the Code of Federal Regulations, complementary manuals, and NASA safety standards. Distribution policies and instructions for ordering directives are included.

Source record↗
NASA NTRS1984

Crack growth direction in unidirectional off-axis graphite epoxy

An anisotropic elasticity crack tip stress analysis is implemented using three crack extension direction criteria (the normal stress ratio, the tensor polynominal and the strain energy density) to predict the direction of crack extension in unidirectional off axis graphite-epoxy. The theoretical predictions of crack extension direction are then compared with experimental results for 15 deg off axis tensile coupons with center cracks. Specimens of various aspect ratios and crack orientations are analyzed. It is shown that only the normal stress ratio criterion predicts the correct direction of crack growth.

Herakovich, C. T.↗
NASA NTRS1986

Directional handling qualities requirements for nap-of-the-earth tasks

A piloted similator experiment designed to investigate directional axis handling qualities requirements for low-speed and hover tasks conducted by a scout/attack helicopter is described. Included were the directional characteristics of various candidate light helicopter family (LHX) configurations. The test also focused on conventional single main/tail rotor configurations where the first-order effects that contribute to the loss of tail rotor control experienced by the OH-58 series aircraft were modeled. Two types of yaw stability and control augmentation systems were implemented: washed-out yaw rate feedback and shaped control input, and a yaw rate command, heading-hold system. The results of the experiment indicate that rotorcraft configurations with high directional gust sensitivity require more yaw damping to maintain satisfactory handling qualities during nap-of-the-earth (NOE) flying tasks. It was also determined that both yaw damping and control response are critical handling qualities parameters in performing the air-to-air target acquisition and tracking task. The lack of substantial yaw damping and larger values of gust sensitivity increased the possibility of loss of directional control at low airspeeds for the tail rotor configurations.

Bivens, C. C.↗