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Simple, inexpensive apparatus coats semiconductor wafers uniformly with hydrofluoric acid for etching. Apparatus made in part from small commercial electric-fan motor. Features bowl that collects acid. Silicon wafer placed on platform and centered on axis; motor switched on. As wafer spins, drops of hydrofluoric acid applied from syringe. Centrifugal force spreads acid across wafer in fairly uniform sheet.
Activities for the Fall Semester, 1987 focused on investigating the mechanical/electrical properties of wheat seeds and forming various Seed Planting System (SPS) concepts based on those properties. The Electrical Division of the design group was formed to devise an SPS using electrostatic charge fields for seeding operations. Experiments concerning seed separation using electrical induction (rearranging of the charges within the seed) were conducted with promising results. The seeds, when exposed to the high voltage and low current field produced by a Van de Graff generator, were observed to move back and forth between two electrodes. An SPS concept has been developed based on this phenomena, and will be developed throughout the Spring Semester, 1988. The Mechanical Division centered on SPS concepts involving valves, pumps, and fluids to separate and deliver seeds. An SPS idea utilizing the pressure difference caused by air as it rushes out of holes drilled in the wall of a closed container has been formulated and will be considered for future development. Also, a system of seed separation and delivery employing a combination of centrifugal force, friction, and air flow was considered.
With the evolution of advanced composites, the feasibility of designing bearingless rotor systems for high speed, demanding maneuver envelopes, and high aircraft gross weights has become a reality. These systems eliminate the need for hinges and heavily loaded bearings by incorporating a composite flexbeam structure which accommodates flapping, lead-lag, and feathering motions by bending and twisting while reacting full blade centrifugal force. The flight characteristics of a bearingless rotor system are largely dependent on hub design, and the principal element in this type of system is the composite flexbeam. As in any hub design, trade off studies must be performed in order to optimize performance, dynamics (stability), handling qualities, and stresses. However, since the flexbeam structure is the primary component which will determine the balance of these characteristics, its design and fabrication are not straightforward. It was concluded that: pitchcase and snubber damper representations are required in the flexbeam model for proper sizing resulting from dynamic requirements; optimization is necessary for flexbeam design, since it reduces the design iteration time and results in an improved design; and inclusion of multiple flight conditions and their corresponding fatigue allowables is necessary for the optimization procedure.
This volume summarizes the analysis used to assess the structural life of the Space Shuttle Main Engine (SSME) High Pressure Fuel Turbo-Pump (HPFTP) Third Stage Impeller. This analysis was performed in three phases, all using the DIAL finite element code. The first phase was a static stress analysis to determine the mean (non-varying) stress and static margin of safety for the part. The loads involved were steady state pressure and centrifugal force due to spinning. The second phase of the analysis was a modal survey to determine the vibrational modes and natural frequencies of the impeller. The third phase was a dynamic response analysis to determine the alternating component of the stress due to time varying pressure impulses at the outlet (diffuser) side of the impeller. The results of the three phases of the analysis show that the Third Stage Impeller operates very near the upper limits of its capability at full power level (FPL) loading. The static loading alone creates stresses in some areas of the shroud which exceed the yield point of the material. Additional cyclic loading due to the dynamic force could lead to a significant reduction in the life of this part. The cyclic stresses determined in the dynamic response phase of this study are based on an assumption regarding the magnitude of the forcing function.
The integrating matrix technique of computational mechanics is extended to include the effects of concentrated masses. The stability of a flexible rotating beam with discrete masses is analyzed to determine the critical rotational speeds for buckling in the inplane and out-of-plane directions. In this problem, the beam is subjected to compressive centrifugal forces arising from steady rotation about an axis which does not pass through the clamped end of the beam. To determine the eigenvalues from which stability is assessed, the differential equations of motion are solved numerically by combining the extended integrating matrix method with an eigenanalysis. Stability boundaries for a discrete mass representation of a uniform beam are shown to asymptotically approach the stability boundaries for the corresponding continuous mass beam as the number of concentrated masses is increased. An error in the literature is also noted for the discrete mass problem concerning the behavior of the critical rotational speed for inplane buckling as the radius of rotation of the clamped end of the beam is reduced.
Model calculations were performed to describe a mechanism that produces classical nova outbursts on white dwarfs of 1 solar mass or less and for accretion rates of 4 x 10 to the -10th solar mass/yr or greater, i.e., the parameters corresponding to observed data of nova systems. Calculations point to four factors that can induce nuclear runaways of sufficient strength to eject about 0.0001 solar mass at speeds of several hundred to a few thousand km per second, as is observed in classical novae. These are (1) the effects of storage of angular momentum in the star's envelope during the accretion phase; (2) the reduction of centrifugal forces in the star's outer layers during the early nuclear runaway phase, through the inward transport of angular momentum; (3) the inward movement of the zone of peak nuclear burning through the convectively induced shear instability during the runaway phase; and (4) the mixing of original CO stellar matter and H-rich matter, also through the convectively induced shear instability.
Modified centrifugal barrel-finishing machine imparts desired residual compressive stresses to "fir trees" of turbine blades. Centrifugal forces generate compressive stresses, which are transmitted to turbine blades through abrasive slurries in which suspended. Eliminates need for shot peening, rounding of edges and burrs caused by shot peening and, consequently, need for mass finishing operations to remove burrs. Improves surface finish of "fir trees".
Goertler vortices arise in laminar boundary layers along concave walls due to an imbalance between pressure and centrifugal forces. In advanced laminar-flow control (LFC) supercritical airfoil designs, boundary-layer suction is primarily used to control Tollmien-Schlichting instability and cross-flow vortices in the concave region near the leading edge of the airfoil lower surface. The concave region itself is comprised of a number of linear segments positioned to limit the total growth of Goertler vortices. Such an approach is based on physical reasonings but rigorous theoretical justification or experimental evidence to support such an approach does not exist. An experimental project was initiated at NASA Langley to verify this concept. In the first phase of the project an experiment was conducted on an airfoil whose concave region has a continuous curvature distribution. Some results of this experiment were previously reported and significant features are summarized.
Space Station and satellite reservicing will require the ability to vent gas on orbit from liquid supply or storage tanks and to gage liquid quantity under microgravity conditions. In zero gravity, (zero-g) the vortex vent is capable of venting gas from a tank of liquid containing gas randomly distributed as bubbles. The concept uses a spinning impeller to create centrifugal force inside a vortex tube within a tank. This creates a gas pocket and forces the liquid through a venturi and back into the tank. Gas is then vented from the gas pocket through a liquid detector and then out through an exhaust port. If the liquid detector senses liquid in the vent line, the fluid is directed to the low-pressure port on the venturi and is returned to the tank. The advantages of this system is that it has no rotating seals and is compatible with most corrosive and cryogenic fluids. A prototype was designed and built at the NASA Johnson Space Center and flown on the KC-135 zero-g aircraft. During these test flights, where microgravity conditions are obtained for up to 30 sec, the prototype demonstrated that less than 0.10 percent of the volume of fluid vented was liquid when the tank was half full of liquid. The pressure volume temperature (PVT) gaging system is used in conjunction with the vortex vent to calculate the amount of liquid remaining in a tank under microgravity conditions. The PVT gaging system is used in conjunction with the vortex vent to gage liquid quantity in zero or low gravity. The system consists of a gas compressor, accumulator, and temperature and pressure instrumentation. To measure the liquid in a tank a small amount of gas is vented from the tank to the compressor and compressed into the accumulator. Pressure and temperature in the tank and accumulator are measured before and after the gas transfer occurs. Knowing the total volume of the tank, the volume of the accumulator, the volume of the intermediate lines, and initial and final pressures and temperatures, the mass of the gas leaving the tank is equated to the mass of the gas entering the accumulator. The volume of liquid remaining in the tank is calculated using the ideal gas law.
A method is developed for predicting three-dimensional turbulent boundary layers occurring in internal flows, including rotor blades of turbomachinery. These boundary layers are complex, turbulent, and are subject to Coriolis and centrifugal forces. The algebraic Reynolds stress model (ARSM) developed in this paper satisfies the realizability conditions exactly and captures the changes in turbulenet structure arising from curvature and rotation. The prediction of pressure driven secondary flow agrees well with the data and all the three turbulent models (k-e, algebraic eddy viscosity, and ARSM) show the same level of agreement. The prediction of boundary layer on rotor blades shows much better agreement with the ARSM. It is essential to employ the higher order models to capture the effects of rotation and curvature and three-dimensional boundary layers in turbomachinery.
A model combining the internal magnetic field with a self-consistent model of the Jovian magnetodisc was fitted to the Voyager 1 Jovian magnetic field data by means of a generalized inverse technique. The model parameters included the internal field spherical harmonic coefficients as well as with parameters describing the plasma distribution in the magnetosphere. Assuming that the pressure in the middle and outer magnetosphere is related to the unit flux tube volume V through PV exp gamma = const, the model fit yielded a value of 0.88 for gamma. If the hot (30 keV) plasma is transported adiabatically inward under the interchange instability triggered by centrifugal force of the heavy torus ions, losses are not sufficient to account for such a low value of gamma beyond L = 10. Closer to the planet, as the outer edge of the Io plasma torus is approached, PV exp gamma is found to decrease inward, as expected from the particle measurements, which identified an inner boundary of the particle fluxes in that region. With the present stage of the development of magnetodisc models, secular variations of the internal field still remain difficult to estimate.
This paper reviews the fundamental physical properties of gravitational and centrifugal forces, describes the physiological changes that result from long-term exposure to the nearly gravity-free environment of space, and explores the nature of these changes. The paper then cites currently employed and advanced techniques that can be used to prevent some of these changes. Following this review, the paper examines the potential use of artificial gravity as the ultimate technique to maintain terrestrial levels of physiological functioning in space, and indicates some of the critical studies that must be conducted and some of the trade-offs that must be made before artificial gravity can intelligently be used for long duration spaceflight.
In the present numerical model for calculating H(+) and O(+) ion densities, fluxes, and temperatures, as well as the temperature of electrons, on a convecting magnetic field line, the one-dimensional fluid equations are solved along a field line path extending from 100-km altitude into the magnetotail. The evolution of O(+) and H(+) densities is calculated on field lines convecting over the polar cap. The results obtained indicate that centrifugal force is effective in accelerating ionospheric H(+) plasma outward into the magnetotail, while the 'smothering' effect of the H(+) plasma, on top of the O(+) plasma, prevents any ejection of the latter as long as its scale height is smaller than that of the H(+) plasma.
Tapered strap provides more torque than parallel one. Report describes theoretical and experimental-investigation of simplified model of tension/torsion strap. Proposed for use in helicopter rotor blade to hold otherwise freely pitching blade tip inward against centrifugal force and to apply torque about pitch axis to regulate pitching motions of tip. Intended to improve aerodynamic performances of rotors and to reduce vibrations.
The optimization of trajectories for coplaner, aeroassisted orbital transfer (AOT) from a high Earth orbit (HEO) to a low Earth orbit (LEO) is examined. In particular, HEO can be a geosynchronous Earth orbit (GEO). It is assumed that the initial and final orbits are circular, that the gravitational field is central and is governed by the inverse square law, and that two impulses are employed, one at HEO exit and one at LEO entry. During the atmospheric pass, the trajectory is controlled via the lift coefficient in such a way that the total characteristic velocity is minimized. First, an ideal optimal trajectory is determined analytically for lift coefficient unbounded. This trajectory is called grazing trajectory, because the atmospheric pass is made by flying at constant altitude along the edge of the atmosphere until the excess velocity is depleted. For the grazing trajectory, the lift coefficient varies in such a way that the lift, the centrifugal force due to the Earth's curvature, the weight, and the Coriolis force due to the Earth's rotation are in static balance. Also, the grazing trajectory minimizes the total characteristic velocity and simultaneously nearly minimizes the peak values of the altitude drop, dynamic pressure, and heating rate. Next, starting from the grazing trajectory results, a real optimal trajectory is determined numerically for the lift coefficient bounded from both below and above. This trajectory is characterized by atmospheric penetration with the smallest possible entry angle, followed by flight at the lift coefficient lower bound. Consistently with the grazing trajectory behavior, the real optimal trajectory minimizes the total characteristic velocity and simultaneously nearly minimizes the peak values of the altitude drop, the dynamic pressure, and the heating rate.
The factors that affect the interchange instability of the earth's plasmapause are investigated using an extension of Richmond's (1973) procedure based on computing individual particle motions. The effects of particle inertia, centrifugal force, and gravity are estimated. A general differential equation is derived for the time variation of the perturbation potential characterizing an electrostatic ripple with no field-aligned potential drop, which can be solved as an eigenvalue problem to find the linear growth rate. Approximate analytic solutions to this equation were obtained from which it was deduced that the interchange instability is caused by the sharp change in plasma pressure at the plasmapause; its growth rate is limited by ionospheric conductivity and, for very short wavelengths, by the inertia of the magnetospheric particles.
The physical behavior of superfluid and normal fluid helium II is discussed. It is shown that the centrifugal force due to a rotating container can never separate the superfluid from the normal fluid helium in a large rotating cylindrical spacecraft. A classical approach is appropriate for treating superfluid and normal fluid cryogenic helium as a mixture without separation in a large rotating cylinder in a spacecraft propellant systems.
A method is developed for predicting the behavior of three-dimensional, turbulent boundary layers occurring in internal flows, including those on turbomachinery rotor blades. These boundary layers are complex, turbulent, and subject to Coriolis and centrifugal forces. The major thrust of this paper is the development and use of an algebraic Reynolds stress model (ARSM) that captures the changes in turbulent flow structure arising from curvature, rotation, and three dimensionality. The prediction of pressure-driven secondary flow agrees well with the measured data, and all three turbulence models (k-epsilon, algebraic eddy viscosity, and ARSM) show the same level of agreement. The prediction of boundary-layer development on rotor blades shows much better agreement with measurements with the ARSM. It is essential to employ higher-order turbulence models to capture the effects of rotation, curvature, and three dimensionality on boundary layers in turbomachinery.