SEARCH · Search NASA
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.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Postprocessing system for synthetic-aperture radar (SAR) transforms raw images from natural rotated and distorted SAR reference frame into geocoded images. Images automatically corrected to remove slant-range nonlinearities and Doppler skew. Produces multiple-frame mosaics for large-scale mapping. Does not require tedious manual registration of representative "tie" points in raw SAR imagery with known locations on Earth.
A generalized method for controlling a six degree-of-freedom (DOF) robot and a two DOF positioner used for arc welding operations is described. The welding path is defined in the part reference frame, and robot/positioner joint angles of the equivalent eight DOF serial linkage are determined via an iterative solution. Three algorithms are presented: the first solution controls motion of the eight DOF mechanism such that proper torch motion is achieved while minimizing the sum-of-squares of joint displacements; the second algorithm adds two constraint equations to achieve torch control while maintaining part orientation so that welding occurs in the downhand position; and the third algorithm adds the ability to control the proper orientation of a wire feed mechanism used in gas tungsten arc (GTA) welding operations. A verification of these algorithms is given using ROBOSIM, a NASA developed computer graphic simulation software package design for robot systems development.
Simultaneous Range Differences (SRDs) to Lageos are obtained by dividing the observing stations into pairs with quasi-simultaneous observations. For each of those pairs the station with the least number of observations is identified, and at its observing epochs interpolated ranges for the alternate station are generated. The SRD observables are obtained by subtracting the actually observed laser range of the station having the least number of observations from the interpolated ranges of the alternate station. On the basis of these observables semidynamic single baseline solutions were performed. The aim of these solutions is to further develop and implement the SRD method in the real data environment, to assess its accuracy, its advantages and disadvantages as related to the range dynamic mode methods, when the baselines are the only parameters of interest. Baselines, using simultaneous laser range observations to Lageos, were also estimated through the purely geometric method. These baselines formed the standards the standards of comparison in the accuracy assessment of the SRD method when compared to that of the range dynamic mode methods. On the basis of this comparison it was concluded that for baselines of regional extent the SRD method is very effective, efficient, and at least as accurate as the range dynamic mode methods, and that on the basis of a simple orbital modeling and a limited orbit adjustment. The SRD method is insensitive to the inconsistencies affecting the terrestrial reference frame and simultaneous adjustment of the Earth Rotation Parameters (ERPs) is not necessary.
Finite-difference and finite-volume formulations are analyzed in order to clear up the confusion concerning their application to the numerical solution of conservation laws. A new coordinate-free formulation of systems of conservation laws is developed, which clearly distinguishes the role of physical vectors from that of algebraic vectors which characterize the system. The analysis considers general types of equations--potential, Euler, and Navier-Stokes. Three-dimensional unsteady flows with time-varying grids are described using a single, consistent nomeclature for both formulations. Grid motion due to a non-inertial reference frame as well as flow adaptation is covered. In comparing the two formulations, it is found useful to distinguish between differences in numerical methods and differences in grid definition. The former plays a role for non-Cartesian grids, and results in only cosmetic differences in the manner in which geometric terms are handled. The differences in grid definition for the two formulations is found to be more important, since it affects the manner in which boundary conditions, zonal procedures, and grid singularities are handled at computational boundaries. The proper interpretation of strong and weak conservation-law forms for quasi-one-dimensional and axisymmetric flows is brought out.
Work on plate motions published in 1983-1986 and in early 1987 is reviewed. Models for these motions, including global ones for driving forces and local ones for subduction history and back-arc spreading, are addressed. The problem of reference frames, both hotspot and paleomagnetic, is discussed. The assessment of errors in plate motion studies is reviewed.
The filtering of the satellite range and range-rate measurements from single channel sequential Global Positioning System receivers is usually done with an extended Kalman filter which has state variables defined in terms of an orthogonal navigation reference frame. An attractive suboptimal alternative is range-domain filtering, in which the individual satellite measurements are filtered separately before they are combined for the navigation solution. The main advantages of range-domain filtering are decreased processing and storage requirements and simplified tuning. Several range filter mechanization alternatives are presented, along with an innovative approach for combining the filtered range-domain quantities to determine the navigation state estimate. In addition, a method is outlined for incorporating measurements from auxiliary sensors such as altimeters into the navigation state estimation scheme similarly to the satellite measurements. A method is also described for incorporating inertial measurements into the navigation state estimator as a process driver.
It is shown that proton beams, often observed upstream of the earth's bow shock and associated with the generation of low-frequency hydromagnetic fluctuations, are also capable of generating whistler waves. The waves can be excited by an instability driven by two-temperature streaming Maxwellian proton distributions which have T (perpendicular)/T(parallel) much greater than 1. It can also be excited by gyrating proton beam distributions. These distributions generate whistler waves with frequencies ranging from 10 to 100 times the proton cyclotron frequency (in the solar wind reference frame) and provide another mechanism for generating the '1-Hz' waves often seen in the earth's foreshock.
In this paper, numerical models are developed to follow the time-dependent behavior of inclined gas disks in nonspherical galaxies. Differential equations are developed which describe the time rate of change of the orbits of mass elements composing a thin, smoothly warping and twisting gas disk. These equations include multiple moments due to the nonsphericity of the galactic mass distribution, Coriolis effects arising from determination of orbits in a reference frame which tumbles with the surface figure of the galaxy, and viscous forces arising from cloud-cloud collisions. A cloud-fluid approach is used in determining the viscous forces. Physical arguments are used to determine the maximum permissible local value of the coefficient of kinematic viscosity. For small initial inclinations, analytic expressions are obtained for the inclination as a function of time and for the settling time, and the features of the solution are discussed.
The behavior of collisionless hydromagnetic shocks in interplanetary space is considered analytically, with a focus on relations, implicit in the governing Rankine-Hugoniot equations, involving the magnetic field (B) and the plasma velocity (V). A moving reference frame aligned with the shock is employed, and expressions are derived which make it possible (1) to determine the speed of a shock of arbitrary orientation from upstream and downstream measurements of B and V; (2) to characterize the change in flow direction as the plasma crosses the shock in terms of the plasma beta, the Mach number, and the angle between the upstream field and the shock normal; and (3) to infer the third component of the upstream-downstream velocity jump from B and two-dimensional V measurements. These expressions are applied to ISEE-3 data on an interplanetary shock on April 5, 1979, and the results are presented in tables.
The invariance of constitutive equations in continuum mechanics is examined from a basic theoretical standpoint. It is demonstrated the constitutive equations which are not form invariant under arbitrary translational accelerations of the reference frame are in violation of the Einstein equivalane principle. Furthermore, by making use of an analysis based on statistical mechanics, it is argued that any frame-dependent terms in constitutive equations must arise from the intrinsic spin tensor and are negligible provided that the ratio of microscopic to macroscopic time scales is extremely small. The consistency of these results with existing constitutive theories is discussed in detail along with possible avenues of future research.
Using Voyager images, layer thickness variations in the flow around Jupiter's Great Red Spot (GRS) and White Oval BC were investigated by treating potential vorticity as a conserved tracer. Fluid trajectories around the GRS and the White Oval BC were calculated assuming the flow to be frictionless, adiabatic, hydrostatic, and steady in the reference frame of the vortex. The data obtained constitute a useful diagnostic which will help to differentiate between models of Jovian vortices. Implications of the observations were studied in the context of a one-layer quasi-geostrophic model in which a thin upper weather layer, which contains the vortex, is supported hydrostatically by a much deeper lower layer.
An astrometric radio reference frame has been determined from intercontinental dual-frequency radio interferometric measurements. These measurements were carried out on a regular basis during 1978-1985 between NASA's Deep Space Network stations in California, Spain, and Australia. Analysis of 6800 pairs of delay and delay-rate observations made during 51 sessions produced estimates of 1300 parameters. The most significant of these are geophysical quantities and positions of extragalactic sources. The source catalog resulting from this analysis includes 106 sources fairly uniformly distributed over the celestial sphere, north of -45 deg declination. Almost all of the resulting source positions have formal uncertainties between 0.5 and 3 milliarcseconds (mas), with rms values of 2 mas in both angular coordinates. Internal consistency checks, as well as comparisons with independently determined source catalogs of comparable quality, indicate that relative source coordinates determined by VLBI contain systematic errors at the level of 1 to 2 mas.
The migration of bubbles or drops in a rotating liquid-filled sphere was observed under a variety of experimental conditions, and the trajectory, final equilibrium position, and shape were compared with results of analysis. It was found that small migrating bubbles or drops were spherical and, under the quasi-steady conditions employed, behaved in a predictable manner. Large migrating bubbles were nonspherical yet still behaved predictably except when close to the sphere wall. At low rotation rates, the final equilibrium position was offset from the rotation axis and stationary in the rotating liquid relative to a laboratory (inertial) reference frame. One of the bubble migration experiments was accomplished in the near-free-fall environment provided by the NASA KC-135 flight program. At higher rotation rates and under zero gravity conditions where the rotation axis is the final equilibrium position, the shape was reasonably predictable.
The experimental part of the turbine heat transfer subproject consists of six large experiments, which are highlighted in this overview, and three of somewhat more modest scope. One of the initial efforts was the stator airfoil heat transfer program. The non-film cooled and the showerhead film cooled data have already been reported. The gill region film cooling effort is currently underway. The investigation of secondary flows in a 90 deg curved duct, was completed. The first phase examined flows with a relatively thin inlet boundary layer and low free stream turbulence. The second phase studied a thicker inlet boundary layer and higher free stream turbulence. A comparison of analytical and experimental cross flow velocity vectors is shown for the 60 deg plane. Two experiments were also conducted in the high pressure facility. One examined full coverage film cooled vanes, and the other, advanced instrumentation. The other three large experimental efforts were conducted in a rotation reference frame. An experiment to obtain gas path airfoil heat transfer coefficients in the large, low speed turbine was completed. Single-stage data with both high and low-inlet turbulence were taken. The second phase examined a one and one-half stage turbine and focused on the second vane row. Under phase 3 aerodynamic quantities such as interrow time-averaged and rms values of velocity, flow angle, inlet turbulence, and surface pressure distribution were measured.
One of the difficulties in determining constituent trends from the ER-2 flight data is the large amount of day to day variability generated by the motion of the polar vortex. To reduce this variability, the observations have been transformed into the conservative (Lagrangian) reference frames consisting of the coordinate pairs, potential temperature (PT) and potential vorticity (PV), or PT and N2O. The requirement of only two independent coordinates rests on the assumption that constituent distributions and their chemical processes are nearly zonal in that coordinate system. Flight data is used everywhere for these transformation except for potential vorticity. Potential vorticity is determined from level flight segments, and NMC PV values during flight dives and takeoffs are combined with flight data in a smooth fashion.
The Pioneer Venus Orbiter Neutral Mass Spectrometer (ONMS) has observed fast O(+) ions with an energy exceeding 40 eV in the spacecraft reference frame. The orbit of the spacecraft is nearly polar with periapsis near the equator. The ONMS is mounted at an angle to the spin axis which, in turn, is perpendicular to the ecliptic plane. From the spin modulated data the direction of the ion flow in that plane can be determined. Data from the first 11 diurnal cycles (orbits 1 to 2475) are vector averaged in order to display the general flow pattern. Plots of the averaged data are presented. On the dayside and near the terminators, where fast O(+) is observed near the ionopause, the directions are more or less parallel to the planet's surface with evidence of an asymmetry about the Sun-Venus line. On the nightside below 2000 km and near the equator there is a preferred dawn to dusk direction while at higher altitudes (lower solar zenith angles and higher latitudes) the flow direction is more antisunward. The averaged flux for this time period is 8x10 to the 5th/sq cm/s with a maximum of 5x10 to the 8th.
The very long baseline interferometry (VLBI) measurements made in the western U.S. since 1979 as part of the NASA Crustal Dynamics Project provide discrete samples of the temporal and spatial deformation field. The interpretation of the VLBI-derived rates of deformation requires an examination of geologic information and more densely sampled ground-based geodetic data. In the first two of three related studies, triangulation and trilateration data measured on two regional networks, one in the central Mojave Desert and one in the Coast Ranges east of the San Andreas fault, have been processed. At the spatial scales spanned by these local geodetic networks, auxiliary geologic and geophysical data have been utilized to examine the relation between measured incremental strain and the accommodation of strain seen in local geological structures, strain release in earthquakes, and principal stress directions inferred from in situ measurements. In a third study, the geocentric position vectors from a set of 77 VLBI experiments beginning in October 1982 have been used to estimate the tangential rate of change of station positions in the western U.S. in a North-America-Fixed reference frame.
The wave equation for an object in arbitrary motion is investigated analytically using a BEM approach, and practical applications to potential flows of compressible fluids around aircraft wings and helicopter rotors are considered. The treatment accounts for arbitrary combined rotational and translational motion of the reference frame and for the wake motion. The numerical implementation as a computer algorithm is demonstrated on problems with prescribed and free wakes, the former in compressible flows and the latter for incompressible flows; results are presented graphically and briefly characterized.