147,826 research outputs found
Recommended from our members
Measured displacement coefficients of an adjustable hydrodynamic journal rotor bearing
In simulating a proposed machine tool grinding wheel design, a bearing system comprised a stationary spindle or shaft with fluid film bearings supporting a belt driven rotor. Two hydrodynamic bearings acted in parallel, and built into the shaft were the means to effect continuous pro-active adjustments to their performance characteristics during operation, irrespective of load, speed and other running conditions. The design is outlined, as is a specially constructed test rig for evaluating it. A method for determining the combined displacement coefficients is given which used an incremental load technique with dedicated axis system selection. Observations are given on the bearingsā performance characteristics. The effects of the adjustments on rotor eccentricity are shown, along with the ability to maintain a given rotor eccentricity, including zero, irrespective of load and changes in load. Results of measured rotor displacements and displacement coefficients are also given showing that the bearing exhibited high stiffness at zero load and eccentricity, and that stiffness could be changed by adjustment if required, thereby ātuningā the system rotordynamics behaviour. Comparisons are made with results of othersā work on the measured displacement coefficients of a conventional type of tilting pad bearing. An approach to uncertainty estimation of measured data is included
Modelling heat transfer through a novel design of rotary kiln
A novel form of rotary kiln has been developed which confers advantages over conventional designs. Details are given of the main features of the kiln, along with an approach used to study its heat transfer characteristics when hot processing waste products into a lightweight synthetic aggregate for recycling in building materials. Computer aided finite element modelling was used to predict temperature profiles and heat fluxes involving non-linear properties of the exterior insulation materials and internal radiation effects. Observations are given comparing predicted temperatures for two different cross sectional shapes and with those measured in practice on a prototype novel kiln. Observations are also given on the methods of approach to the modelling
Generalization of the Calogero-Cohn Bound on the Number of Bound States
It is shown that for the Calogero-Cohn type upper bounds on the number of
bound states of a negative spherically symmetric potential , in each
angular momentum state, that is, bounds containing only the integral
, the condition is not necessary,
and can be replaced by the less stringent condition , which allows oscillations in the potential. The
constants in the bounds are accordingly modified, depend on and , and
tend to the standard value for .Comment: 1 page. Correctly formatted version (replaces previous version
Helical Magnetic Fields from Inflation
We analyze the generation of seed magnetic fields during de Sitter inflation
considering a non-invariant conformal term in the electromagnetic Lagrangian of
the form , where
is a pseudoscalar function of a non-trivial background field .
In particular, we consider a toy model, that could be realized owing to the
coupling between the photon and either a (tachyonic) massive pseudoscalar field
and a massless pseudoscalar field non-minimally coupled to gravity, where
follows a simple power-law behavior during
inflation, while it is negligibly small subsequently. Here, is a positive
dimensionless constant, the wavenumber, the conformal time, and
a real positive number. We find that only when and astrophysically interesting fields can be produced as
excitation of the vacuum, and that they are maximally helical.Comment: 17 pages, 1 figure, subsection IIc and references added; accepted for
publication in IJMP
Measurement and Analysis of Terminal Shock Oscillation and Buffet Forcing Functions on a Launch Vehicle Payload Fairing
The buffet loads on a launch vehicle payload shroud can be impacted by the unsteadiness associated with a terminal shock at high subsonic speeds. At these conditions, flow accelerates to supersonic speeds on the nose of the payload fairing and is terminated by a normal shock on the cylindrical section downstream of the nose cone/cylinder shoulder. The location of the terminal shock and associated separated boundary layer is affected by the freestream Mach number, Reynolds number, and the pitch/yaw of the launch vehicle. Furthermore, even when the freestream conditions and vehicle attitude are constant, this terminal shock oscillates on the surface of the vehicle. The time-varying surface pressure associated with the terminal shock results in unsteady aerodynamic loads that may interact with vehicle structural dynamic modes and the guidance and control of the vehicle. Buffet testing of a 3-percent scale rigid buffet model of a launch vehicle cargo configuration with a tangent-ogive payload shroud was conducted in 2012 and in 2016. Initial buffet forcing functions (BFFs) utilized a coarse pressure sensor distribution on the vehicle surface in which a single longitudinal station with eight sensors observed the terminal shock environment at Mach 0.90. An examination of these circumferential pressures reveal large impulse-like pressure fluctuations and an asymmetry in pressure when the vehicle is at a nonzeroangle of attack that result in high BFFs. Revisions to the shock integration region were made based on computational fluid dynamics and shadowgraph video of shock motion to better represent the BFFs and reduce the high loads resulting from this environment. To more clearly understand this terminal shock environment, a second wind tunnel test was conducted with a dense distribution of 256 sensors at the terminal shock location. These sensor arrays presents a unique opportunity to observe the unsteady terminal shock environment and to characterize the impact of various integration schemes on the BFFs. This paper presents a summary of the development of BFFs for this terminal shock and a detailed analyses of shock region pressure coefficients, coherence, BFFs, shock location time histories, and power spectral density to help guide development of BFFs for other launch vehicle test and analysis programs
Targeted deep surveys of high Galactic latitude HI with the GBT
Over 800 sq. deg. of high Galactic latitude sky have been mapped at 21 cm
with the Robert C. Byrd Green Bank Telescope (GBT). An improved knowledge of
the telescope's beam characteristics has allowed us to reliably map not only
regions of high column density, but also such regions as ELAIS N1, a targeted
Spitzer field, which have very low HI column density. The additional fields we
have observed cover a cross-section of dynamically and chemically interesting
regions as indicated by the presence of intermediate/high velocity gas and/or
anomalous far-IR (dust) colour.Comment: 7 pages, 5 figures. To appear in "The Dynamic ISM: A celebration of
the Canadian Galactic Plane Survey" ASP Conference Serie
STATE-LEVEL ANALYSIS OF NATIONAL BEEF POLICY: THE USE OF STATE ECONOMETRIC MODELS
Interest has grown in analyzing the impact of national imports of foreign beef on state agricultural sectors. In this study, an interfaced Hawaiian-national model is simulated for a change in national beef imports. Hawaiian and national impacts demonstrate wide variation in both sign and magnitude. Usefulness of state models is emphasized for situations where state impacts of national policies are of interest.Agricultural and Food Policy,
Exploitation of ERTS-1 imagery utilizing snow enhancement techniques
Photogeological analysis of ERTS-simulation and ERTS-1 imagery of snowcovered terrain within the ERAP Feather River site and within the New England (ERTS) test area provided new fracture detail which does not appear on available geological maps. Comparative analysis of snowfree ERTS-1 images has demonstrated that MSS Bands 5 and 7 supply the greatest amount of geological fracture detail. Interpretation of the first snow-covered ERTS-1 images in correlation with ground snow depth data indicates that a heavy blanket of snow (more than 9 inches) accentuates major structural features while a light "dusting", (less than 1 inch) accentuates more subtle topographic expressions. An effective mail-based method for acquiring timely ground-truth (snowdepth) information was established and provides a ready correlation of fracture detail with snow depth so as to establish the working limits of the technique. The method is both efficient and inexpensive compared with the cost of similarly scaled direct field observations
- ā¦