Engineering topics
Publications and source records attributed to Brown, R. A..
Shapes and stability of surface-tension-endowed drops rotating rigidly at fixed angular momentum are calculated by finite-element analysis. A new family of asymmetric two-lobed drop shapes is discovered that branches from, and rejoins, the Pik-Pichak family of symmetric two-lobed shapes. The computations are verified for axisymmetric and symmetric two-lobed drop shape by comparison with previous approximations.
Equilibrium shapes and stability of rotating drops held together by surface tension are found by computer-aided analysis that uses expansions in finite-element basis functions. Shapes are calculated as extrema of appropriate energies. Stability and relative stability are determined from curvatures of the energy surface in the neighborhood of the extremum. Families of axisymmetric, two-, three-, and four-lobed drop shapes are traced systematically. Bifurcation and turning points are located and the principle of exchange of stabilities is tested. The axisymmetric shapes are stable at low rotation rates but lose stability at the bifurcation to two-lobed shapes. Two-lobed drops isolated with constant angular momentum are stable. The results bear on experiments designed to further those of Plateau (1863).
A study of the rotation of Uranus is made generally following the procedures in Paper I. Combining all results, a best estimate of the period was found to be T = 16.16 + or - 0.33 hr. There was no consistent evidence for a latitude dependence of the rotation rate. The value of the period is consistent with recent determinations of the optical oblateness and of the second gravitational moment. A moment of inertia for Uranus is derived which favors theoretical models with volatile-rich envelopes.
The extended atmosphere of the Jupiter system consists of atoms and ions of heavy elements. This material originates on the satellite Io. Energy is lost from the thermal plasma in collisionally excited optical and ultraviolet emission. The juxtaposition of Earth and spacecraft measurements provide insight concerning the underlying processes of particle transport and energy supply.
The paper describes algorithms for equilibrium and steady-state problems with coefficients in the expansions derived by the Galerkin weighted residual method and calculated from the resulting sets of nonlinear algebraic equations by the Newton-Raphson method. Initial approximations are obtained from nearby solutions by continuation techniques as parameters are varied. The Newton-Raphson technique is preferred because the Jacobian of the solution is useful for continuation, for analyzing the stability of solutions, for detecting bifurcation of solution families, and for computing asymptotic estimates of the effects on any solution of small changes in parameters, boundary conditions, and boundary shape.
The design considerations are described which led to the combination of materials used for the MOD-I wind turbine generator rotor and to the fabrication processes which were required to accomplish it. It is noted that the design problem was to create a rotor for a 2500 kW wind turbine generator. The rotor was to consist of two blades, each with a length of 97.5 feet and a weight of less than 21,000 pounds. The spanwise frequency is 1.17-1.45 Hz, and the chordwise frequency 2.80-2.98 Hz. The design life of the blade is 30 years, or 4.35 x 10 to the 8th cycles. The structures of the spars and trailing edges are described, and the adhesive bonding system is discussed.
The surface observations used for direct comparison with Seasat-derived values at fixed locations and as input to analyzed fields of pressure, wind, air and sea temperatures, and surface dew point are discussed. These included measurements made by research vessels participating in the Gulf of Alaska Seasat Experiment (GOASEX) and NOAA research platforms in addition to aircraft observations and reports from the World Weather Watch. The application of these observations in describing the synoptic-scale winds over the ocean is discussed, and the sensitivity of the verification statistics to the type of data (observations from buoys, weather ships, and transient vessels with or without anemometers) is considered. Results of a preliminary comparison of wind fields derived from Seasat-A scatterometer observation with winds specified by several types of platforms are presented.
The Seasat microwave scatterometer was designed to measure, globally and in nearly all weather, wind speed to an accuracy of plus or minus 2 meters per second and wind direction to plus or minus 20 deg in two swaths 500 kilometers wide on either side of the spacecraft. For two operating modes in rain-free conditions, a limited number of comparisons to high-quality surface truth indicates that these specifications may have been met.
The spectrum of Io between 4000 A and 6000 A has been studied at high resolution for new features. None were found. The upper limit to new emissions varies with wavelength from 13 kR to 49 kR.
Photometric spectra of the forbidden S II emission lines at 6716 and 6731 A originating in the Jovian magnetosphere are examined. The summed apparent emission rate in the two sulfur lines is plotted against the central-meridian longitude of Jupiter in System III. It is found that the total sulfur brightness exhibited a distinct minimum when the Jovian magnetic dipole was in the plane defined by the earth-Jupiter vector and the Jovian rotational axis. The observations are shown to be qualitatively consistent with an annular emitting region at the magnetic equator with a thickness of about 1 Jupiter radius and an inner radius of 4 to 5 Jupiter radii. The observations also imply a (logarithmic) characteristic electron density of approximately 3.7 per cu cm and a (logarithmic) average column abundance of about 11.5 per sq cm for singly ionized sulfur.
Thermal maps of Venus on 16 days during a span of 43 days just before inferior conjunction were obtained during 1973-1974 and are described. The research represents a first step towards the goal of using ground-based observations to determine the time and space scales of dynamical events taking place in the Venus clouds. The described average limb darkening differs from that reported by Ingersoll and Orton (1974). Real day-to-day changes in limb darkening, one occasion of a 4-day repetition of a thermal anomaly, solar-related anomalies, and a southern hemisphere solar-related disturbance are discussed.
The rotation rate of Uranus is investigated by measuring the tilts of reflected Fraunhofer lines observed through a slit spectrograph. The data obtained are corrected for the effect of astronomical seeing, and the data-reduction procedures are outlined in detail. Observations are discussed which indicate that the planet's pole of rotation is parallel to the pole of its satellites' orbits and that Uranus may not rotate as a solid body. A rotational period of 15.57 + or - 0.80 hr is derived for northern midlatitudes on Uranus by adopting a planetary diameter of 51,800 + or - 600 km. Possible sources of small systematic errors are briefly considered.
A simple model of Jupiter's S II emission nebula is developed on the basis of a complete treatment of electron-impact excitation of sulfur ions. Forbidden line emission from S II ions excited by electron collisions in the Jovian nebula is analyzed, and existing observations are interpreted using a simple model of an S II nebula which is uniform in depth. The results show that the depth of the nebula is 300,000 to 600,000 km, the electron density is about 3160 per cu cm, the electron temperature is approximately 25,000 K, and the S II concentration is roughly 79 ions per cu cm. It is noted that these plasma conditions are quite different from those reported for the same region on the basis of Pioneer 10 data, indicating that the S II nebula is a sporadic event. Io is suggested as the source of the sulfur.
The paper outlines current understanding of phenomena associated with Io's atmosphere and optical emissions, along with a review of their relationships. The discussion covers the sodium D-line emission from Io, the ultraviolet emission observed from Pioneer 10, other optical emission lines, and future observational work on Io's line emission. Analysis of Io's ionosphere indicates that the atmosphere may be cooler than the observed sodium and that the exobase probably stands well above Io's surface. Also discussed is Io as a source of hydrogen and as a source of sodium. The observed electron profiles and the constraints provided by the emission cloud are consistent with two models of Io's neutral atmosphere. In the first model, hydrogen is supplied by dissociation of ammonia, whereas proton charge exchange is the primary source of hydrogen in the second model. Both models have the common feature that meteoritic impact or sputtering of the surface provides a source for sodium.
A computer simulation program which models a commercial short-haul aircraft operating in the civil air system was developed. The purpose of the program is to evaluate the effect of a given aircraft avionics capability on the ability of the aircraft to perform on-time carrier operations. The program outputs consist primarily of those quantities which can be used to determine direct operating costs. These include: (1) schedule reliability or delays, (2) repairs/replacements, (3) fuel consumption, and (4) cancellations. More comprehensive models of the terminal area environment were added and a simulation of an existing airline operation was conducted to obtain a form of model verification. The capability of the program to provide comparative results (sensitivity analysis) was then demonstrated by modifying the aircraft avionics capability for additional computer simulations.
A short-takeoff and landing (STOL) systems simulation model has been developed and implemented in a computer code (known as STOL OPS) which permits evaluation of the operation of a STOL aircraft and its avionics in a commercial airline operating environment. STOL OPS concentrated on the avionics functions of navigation, guidance, control, communication, hazard aviodance, and systems management. External world factors influencing the operation of the STOL aircraft include each airport and its geometry, air traffic at each airport, air traffic control equipment and procedures, weather (including winds and visibility), and the flight path between each airport served by the route. The development of the STOL OPS program provides NASA a set of computer programs which can be used for detailed analysis of a STOL aircraft and its avionics and permit establishment of system requirements as a function of airline mission performance goals.
Gas operated release mechanism releases load by fluid pressure to provide positive action quick release. Method can be used with large loads and is useful in repetitive cycling functions where shear pins and similar devices would be cumbersome.
Stochastic control system design methodology noting applications to ASW, law enforcement, document retrieval and autopilots