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A hydrostatic bearing having two axial grooves on opposite sides of the bearing for breaking the rotational symmetry in the dynamic force coefficients thus reducing the whirl frequency ratio and increasing the damping and stiffness of the hydrostatic bearing.
The detection of the first VIIP case occurred in 2005, and adequate eye outcome measures were available for 31 (67.4%) of the 46 long duration US crewmembers who had flown on the ISS since its first crewed mission in 2000. Therefore, this analysis is limited to a subgroup (22 males and 9 females). A "cardiovascular profile" for each astronaut was compiled by examining twelve individual parameters; eleven of these were preflight variables: systolic blood pressure, pulse pressure, body mass index, percentage body fat, LDL, HDL, triglycerides, use of anti‐lipid medication, fasting serum glucose, and maximal oxygen uptake in ml/kg. Each of these variables was averaged across three preflight annual physical exams. Astronaut age prior to the long duration mission, and inflight salt intake was also included in the analysis. The group of cardiovascular variables for each crew member was compared with seven VIIP eye outcome variables collected during the immediate post‐flight period: anterior-posterior axial length of the globe measured by ultrasound and optical biometry; optic nerve sheath diameter, optic nerve diameter, and optic nerve to sheath ratio‐ each measured by ultrasound and magnetic resonance imaging (MRI), intraocular pressure (IOP), change in manifest refraction, mean retinal nerve fiber layer (RNFL) on optical coherence tomography (OCT), and RNFL of the inferior and superior retinal quadrants. Since most of the VIIP eye outcome measures were added sequentially beginning in 2005, as knowledge of the syndrome improved, data were unavailable for 22.0% of the outcome measurements. To address the missing data, we employed multivariate multiple imputation techniques with predictive mean matching methods to accumulate 200 separate imputed datasets for analysis. We were able to impute data for the 22.0% of missing VIIP eye outcomes. We then applied Rubin's rules for collapsing the statistical results across our 200 multiply imputed data sets to assess the canonical correlation between the eye outcomes and the twelve astronaut cardiovascular variables available for all 31 subjects. Results: A highly significant canonical correlation was observed among the canonical solutions (p<.00001), with an average best canonical correlation of.97. The results suggest a strong association between astronauts' measures of cardiovascular health and the seven eye outcomes of the VIIP syndrome used in this analysis. Furthermore, the "joint test" revealed a significant difference in cardiovascular profile between male and female astronauts (Prob > F = 0.00001). Overall, female astronauts demonstrated a significantly healthier cardiovascular status. Individually, the female astronauts had significantly healthier profiles on seven of twelve cardiovascular variables than the men (p values ranging from <0.0001 to <0.05). Male astronauts did not demonstrate significantly healthier values on any of the twelve cardiovascular variables measured
An investigation was conducted to determine the effectiveness of a free-jet diffuser in reducing the over-all pressure ratios required to operate a free jet with a large air-breathing engine as a test vehicle. Efficient operation of the free jet was determined with and without the considerations required for producing suitable engine-inlet flow conditions. A minimum operating pressure ration of 5.5 was attained with a ratio of nozzle-exit to engine-inlet area of 1.85. Operation of the free jet with unstable engine-inlet flow (buzz) is also included.
The NASA LeRC has begun a program to design, analyze, build, and test a fan stage that can operate with supersonic axial velocities throughout the stage. This report presents the results from the initial experimental evaluation of the supersonic throughflow fan stage. The stage was tested with flows at subsonic and supersonic inlet axial Mach numbers and with rotor speeds at 40 to 100 percent of design speed. Overall performance as well as detailed performance obtained from radially and circumferentially traversing probes downstream of the stator vanes is presented. At the design rotor tip speed of 1500 ft/s and the design Mach number of 2.0, the measured overall pressure ratio was 2.22, and the corresponding adiabatic efficiency was 0.694. Transition from subsonic to supersonic flow was successfully demonstrated at 75, 90, and 100 percent of design speed. In that speed range, the stage 'unstart' (transition from supersonic to subsonic inlet axial conditions) occurred at an inlet axial Mach number of about 1.36, which corresponds to the Mach number at which the stage started.
Many studies have investigated the mass outflows generated when a planar shock transits an imperfect (“defected”) metal surface, where the defects are symmetric triangular or sinusoidal grooves. Yet a fundamental question remains unanswered: how does the quantity of outflow mass and its maximum velocity vary as a function of the groove cross-sectional aspect ratio? We identify two sets of missing experiments that must be addressed to answer the question. The aspect ratio (groove depth over width) is equivalently represented by θ, the cross sectional half angle, or by η 0 k, the amplitude multiplied by an effective wavenumber. Low θ (high η 0 k) grooves comprise the first set of missing experiments, which are necessary to determine the validity of theoretical predictions of the nonlinear regime (η 0 k ≥ 1, θ < 57.5°). The second set of missing experiments are those in which the volume of the groove (or equivalently, the axial cross-sectional area) has been held constant as θ or η 0 k are varied. Such experiments are necessary to independently measure the effects of variations in groove volume and groove aspect ratio on the resulting jets.
Outer casing blowing and bleeding and undistorted inlet flow for improved performance of high aspect ratio transonic rotor
Many studies have investigated the mass outflows generated when a planar shock transits an imperfect (“defected”) metal surface, where the defects are symmetric triangular or sinusoidal grooves. Yet a fundamental question remains unanswered: how does the quantity of outflow mass and its maximum velocity vary as a function of the groove cross-sectional aspect ratio? We identify two sets of missing experiments that must be addressed to answer the question. The aspect ratio (groove depth over width) is equivalently represented by θ, the cross-sectional half angle, or by η 0 k, the amplitude multiplied by an effective wavenumber. Low θ (high η 0 k) grooves comprise the first set of missing experiments, which are necessary to determine the validity of theoretical predictions of the nonlinear regime (η 0 k ≥ 1, θ < 57.5°). The second set of missing experiments are those in which the volume of the groove (or equivalently, the axial cross-sectional area) has been held constant as θ or η 0 k are varied. Such experiments are necessary to independently measure the effects of variations in groove volume and groove aspect ratio on the resulting jets.
In order to clarify under what conditions two-dimensional theoretical models can realistically account for the actual growth rate distribution in horizontal CVD reactors, a systematic numerical study was performed, and the results were compared with published experimental data for the MOCVD of gallium arsenide. Three models of increasing complexity were studied. It is shown that two-dimensional models can produce realistic predictions only for reactors with large width-to-height (aspect) ratios, that are operated at subcritical Rayleigh number,i.e., under dominant forced flow conditions. But even then, depending on the carrier gas, thermal (Soret) diffusion must be included in the model. Furthermore, velocity corrections for finite aspect ratios must be made, and buoyancy effects can be significant in the entrance region. On the other hand, the results are relatively insensitive to axial diffusion, temperature dependence of transport properties (versus averaged properties), and an assumed Poiseuille velocity profile (versus a rigorous solution of the velocity field). Yet, boundary layer approximations are prone to give unrealistic results at the low Reynolds numbers typical for CVD operations.
An experimental gas turbine was operated over a range of blade-jet speed ratios, total pressure ratios, and inlet total pressures at a constant inlet temperature of 800 R. Peak over-all efficiencies were obtained at blade-jet speed ratios from 0.525 to 0.575 for all runs. The variation in peak efficiency with inlet pressure and pressure ratio was of small magnitude for the conditions investigated.
Ground based and ISS (International Space Station) exercise research have shown that axial loading via two-point loading at the shoulders and load quality (i.e. consistent load and at least 1:1 concentric to eccentric ratio) are extremely important to optimize musculoskeletal adaptations to resistance exercise. The Advanced Resistance Exercise Device (ARED) is on ISS now and is the "state of the art" for resistance exercise capabilities in microgravity; however, the ARED is far too large and power consuming for exploration vehicles. The single cable exercise device design selected for MPCV (Multi-Purpose Crew Vehicle), does not readily allow for the two-point loading at the shoulders.
Detailed interference force and pressure data were obtained on a representative wing-body nacelle combination at Mach numbers of 0.9 to 1.4. The model consisted of a delta wing-body aerodynamic force model with four independently supported nacelles located beneath the wing-body combination. The primary variables examined included Mach number, angle of attack, nacelle position, and nacelle mass flow ratio. Four different configurations were tested to identify various interference forces and pressures on each component; these included tests of the isolated nacelle, the isolated wing-body combination, the four nacelles as a unit, and the total wing-body-nacelle combination. Nacelle axial location, relative to both the wing-body combination and to each other, was the most important variable in determining the net interference among the components. The overall interference effects were found to be essentially constant over the operating angle-of-attack range of the configuration, and nearly independent of nacelle mass flow ratio.
The effect of enhancement devices on flow boiling heat transfer in coolant channels, which are heated either from the top side or uniformly was studied. Studies are completed of the variations in the local (axial and circumferential) and mean heat transfer coefficients in horizontal, top-heated coolant channels with smooth walls and internal heat transfer enhancement devices. The working fluid is freon-11. The objectives are to: (1) examine the variations in both the mean and local (axial and circumferential) heat transfer coefficients for a circular coolant channel with either smooth walls or with both a twisted tape and spiral finned walls; (2) examine the effect of channel diameter (and the length-to-diameter aspect ratio) variations for the smooth wall channel; and (3) develop and improved data reduction analysis. The case of the top-heated, horizontal flow channel with smooth wall (1.37 cm inside diameter, and 122 cm heated length) was completed. The data were reduced using a preliminary analysis based on the heated hydraulic diameter. Preliminary examination of the local heat transfer coefficient variations indicated that there are significant axial and circumferential variations. However, it appears that the circumferential variation is more significant than the axial ones. In some cases, the circumferential variations were as much as a factor of ten. The axial variations rarely exceeded a factor of three.
Here, this work is motivated by the desire to devise an internal pressure test that can mimic a displacement-controlled loading scenario and demonstrate how to apply the multiaxial stress and strain data from the test to develop an elastic/plastic constitutive model for a thin-walled tubular component. This is achieved by conducting simultaneous measurements of tangential and axial strain during the pressure test and integrating these strain measures into a feedback loop with the pressure controller. It is shown how data from such a test can be used to develop a large mechanical property data set relevant to biaxial loading conditions. The data obtained have high confidence evidenced by their low variability and alignment with other literature studies. Additionally, data from these internal pressure tests combined with full-tube axial tensile tests allow for the derivation of the Hill anisotropic yield function. The developed Hill yield function is validated by comparing the plastic strain ratios from the full-tube tension tests and by comparing the predicted yield stress in the tangential direction with measured values from ring tension tests in a previous study.
The use of concrete in fatigue critical structures, such as wind turbine towers, has necessitated the replacement of simplistic (and therefore insufficient) fatigue design recommendations with more accurate and advanced fatigue models that can consider a greater complexity of stress states and materials. As the first part of a multistage test series, an experimental investigation was conducted to determine the fatigue life of concrete subjected to axial compressive fatigue loading, focusing on the relatively high-cycle fatigue domain. Here, a wide range of values for maximum stress levels and stress ratios were considered. The experimental results were compared against existing predictive models, and the most applicable model was identified. Concrete strain and stiffness behavior during fatigue loading were also investigated and reported. Based on the observed behavior, a hypothesis for identifying the impending occurrence of fatigue failure, based on the monotonic stress-strain curve, is examined.
Analysis, design, fabrication, and test activities were conducted to develop additional technology needed for application of filament-wound fiberglass struts to cryogenic flight tankage. It was conclusively verified that monocoque cylinder or ogive struts are optimum or near-optimum for the range of lengths and loads studied, that a higher strength-to-weight ratio can be achieved for fiberglass struts than for any metallic struts, and that integrally-wrapped metallic end fittings can be used to achieve axial load transfer without reliance on bond strength or mechanical fasteners.
An axial flow compressor has been tested with water droplet ingestion under a variety of conditions. The results illustrate the manner in which the compressor pressure ratio, efficiency and surging characteristics are affected. A model for estimating the performance of a compressor during water ingestion has been developed and the predictions obtained compare favorably with the test results. It is then shown that with respect to five droplet-associated nonlinearly-interacting processes (namely, droplet-blade interactions, blade performance changes, centrifugal action, heat and mass transfer processes and droplet break-up), the initial water content and centrifugal action play the most dominant roles.
An axisymmetric liquid bridge is subjected to an axial temperature gradient. Thermal variations in surface tension drive a motion that is described using lubrication theory for slender bridges. At leading order in aspect ratio, a class of similarity solutions is obtained valid in the core region away from the endwalls of the bridge. These solutions describe the flows, temperature fields, and interfacial shapes of bridges that may sustain substantial interfacial deflections.
An aerodynamic investigation of a slender pointed parabolic body of revolution was conducted at Mach number of 1.92 with and without the effects of an annular supersonic jet exhausting from the base. Measurements with the jet inoperative were made of lift, drag, pitching moment, base pressures, and radial and axial pressures. With the jet in operation, pressure measurements were made over the rear of the body with the primary variables being angle of attack, ratio of jet velocity to stream velocity, and ratio of pressure at jet exit to stream pressure.