Automated acoustic intensity measurements and the effect of gear tooth profile on noise

Acoustic intensity measurements were made at NASA Lewis Research Center on a spur gear test apparatus. The measurements were obtained with the Robotic Acoustic Intensity Measurement System developed by Cleveland State University. This system provided dense spatial positioning, and was calibrated against a high quality acoustic intensity system. The measured gear noise compared gearsets having two different tooth profiles. The tests evaluated the sound field of the different gears for two speeds and three loads. The experimental results showed that gear tooth profile had a major effect on measured noise. Load and speed were found to have an effect on noise also

Forced Rossby waves in a basin with a meridional barrier and bottom friction

The forced, linear, Rossby wave solution for a barotropic fluid in a square basin on a b plane containing a thin, continuous but pierced meridional barrier is examined. The forcing is zonally localized and vorticity is removed through bottom friction. The forcing is applied east of the barrier and is periodic in time. To the north and south of the barrier there are small gaps of equal width d separating the barrier from the basin walls. The value of the stream function on the walls of the basin is zero while the value of the stream function on the barrier, CI , is a function of time, the forcing structure and the forcing frequency. CI is determined by an application of Kelvin’s theorem on a contour about the barrier and its value gives the flux between the two sub-basins that are formed by the barrier. The variance of the stream function is explored as a function of the forcing frequency for different meridional structures of the forcing. We investigate symmetric, antisymmetric, and asymmetric forcings about the mid-latitude of the basin. Peaks in the variance occur at frequencies where the solution is dominated by a full basin or sub-basin mode. It was found that modes which were antisymmetric about the mid-latitude could not propagate past the barrier, while modes which were symmetric about the mid-latitude always had some propagation past the barrier. For the case of eastern sub-basin modes which are symmetric about the mid-latitude this propagation is minute. The sensitivity of the solutions to bottom friction is also discussed. As friction is increased, the peaks in the variance become broader and begin to merge. At sufficiently high values of bottom friction a combination of modes, rather than one single mode, dominates the solution at a peak frequency

Competing Alignments of Nematic Liquid Crystals on Square Patterned Substrates

A theoretical analysis is presented of a nematic liquid crystal confined between substrates pat- terned with squares that promote vertical and planar alignment. Two approaches are used to eluci- date the behavior across a wide range of length scales: Monte Carlo simulation of hard particles and Frank-Oseen continuum theory. Both approaches predict bistable degenerate azimuthal alignment in the bulk along the edges of the squares; the continuum calculation additionally reveals the possi- bility of an anchoring transition to diagonal alignment if the polar anchoring energy associated with the pattern is sufficiently weak. Unlike the striped systems previously analyzed, the Monte Carlo simulations suggest that there is no "bridging" transition for sufficiently thin cells. The extent to which these geometrically patterned systems resemble topographically patterned substrates, such as square wells, is also discussed.Comment: 11 pages, 12 figure