Neutrally reinforced holes in symmetrically laminated plates

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76616/1/AIAA-46360-396.pd

Investigation of Reynolds Stresses in a 3D Idealized Urban Area Using Large Eddy Simulation

High resolution, large eddy simulation (LES) of neutral flow through an array of cubes has been conducted with periodic boundary conditions in lateral and longitudinal directions. In this paper, we first describe the model formulation and validate the simulation by comparing the mean flow and turbulence statistics with wind-tunnel experimental data from a cube array of buildings. The LES model is then used to investigate the physical mechanisms that lead to the low turbulent stresses that have been reported in the lower half of the urban canopy layer. To do this, the urban boundary layer is conceptually broken down into three distinct regions: (a) the urban roughness sub-layer, (b) street channels (roads with axis aligned with mean wind direction aloft) and (c) street canyons (roads with axis normal to the mean wind direction aloft). The distribution of the Reynolds stresses differ significantly amongst these regions and we hypothesize that the low stresses in the lower half of the canopy can been attributed to the temporary unstable of the above mentioned regions at different periods of time. In a complex urban area, these regions can be observed intermittently at the same physical location, thus, stresses with opposite signs have the potential to cancel each other and on average yield a low magnitude. In this paper, mean turbulence statistics and spectra from high resolution LES have been analyzed for these scenarios and the results have been interpreted within the context of the proposed idealized flow regions

Generalized conductance sum rule in atomic break junctions

When an atomic-size break junction is mechanically stretched, the total conductance of the contact remains approximately constant over a wide range of elongations, although at the same time the transmissions of the individual channels (valence orbitals of the junction atom) undergo strong variations. We propose a microscopic explanation of this phenomenon, based on Coulomb correlation effects between electrons in valence orbitals of the junction atom. The resulting approximate conductance quantization is closely related to the Friedel sum rule.Comment: 4 pages, 1 figure, appears in Proceedings of the NATO Advanced Research Workshop ``Size dependent magnetic scattering'', Pecs, Hungary, May 28 - June 1, 200

Large-eddy simulation of spectral coherence in a wind turbine wake

This work is mainly dedicated to the study of the characteristics of spectral coherence of turbulence fluctuations in wind turbine wakes. A computational fluid dynamics (CFD) code has been implemented using a large-eddy simulation (LES) approach, which is thought to be conceptually more suitable for studying the turbulence evolution in a wind turbine wake. Comparisons with experimental data from the Nørrekær Enge II Windfarm, in Denmark, and with an analytical model proposed by Panofsky and Dutton have been performed, and the results are found to be in reasonable agreement with both

Thermo-Mixed Hydrodynamics of Piston Compression Ring Conjunction

The final publication is available at http://link.springer.com.A new method, comprising Navier-Stokes equations, Rayleigh-Plesset volume fraction equation, an analytical control-volume thermal mixed approach and asperity interactions is reported. The method is employed for prediction of lubricant flow and assessment of friction in the compression ring-cylinder liner conjunction. The results are compared with Reynolds-based laminar flow with Elrod cavitation algorithm. Good conformance is observed for medium load intensity part of the engine cycle. At lighter loads and higher sliding velocity, the new method shows more complex fluid flow, possessing layered flow characteristics on account of pressure and temperature gradient into the depth of the lubricant film, which leads to a cavitation region with vapour content at varied volume fractions. Predictions also conform well to experimental measurements reported by other authors

Sinonasal pathology and headaches

Primary headaches or other chronic headaches can be triggered by sinonasal pathologies, or variations within the sinonasal tract. Establishing a cause and effect relationship between certain sinonasal conditions and chronic headaches can justify sinonasal surgery for the relief of headaches and provide considerable relief to a subgroup of patients with chronic headaches resistant to medical treatment. A prospective study on 204 patients undergoing sinonasal surgery for an apperent symptomatic sinonasal pathology was conducted to determine the incidence and types of headaches in sinonasal patients preoperatively, the presence of potential sinonasal triggering mechanisms, and postoperative headache relief when such triggers are removed. The relationship between potential triggers and postoperative relief is analysed to determine a possible link. Headache was a major complaint in 50% of these patients and the overall incidence of primary type headaches was 25.5% (52 of 204 patients). Postoperatively, 83.4% of the patients expressed improvement of the headaches (85/102). High scores of preoperative Sinonasal Headache Quotient (SNHQ), obtained through a general questionnaire and endoscopic/radiologic work up seems to correlate well with postoperative relief of headaches (p<0.0001), as well as a well defined lesion site and an ipsilateral pain localization (P<0.02). A detailed sinonasal analysis of chronic headache patients may help identify a subgroup with potential sinonasal triggers and these patients may experience considerable relief of headache following surgery