Active vibration control of a mounting bracket for automotive gearboxes

The aim of this paper is to investigate the use of active vibration control in automotive gearboxes mounting brackets to reduce tonal disturbances. A combination of piezoelectric accelerometers and an internally preloaded piezo stack actuator is used to counteract their unbalanced caused vibrations. Initially, a numerical modal analysis was carried out to identify the normal modes in the frequency range of interest. The piezo stack was simulated by a ROD element and its effect numerically characterized. The upper and lower faces of the stack were mechanically coupled with the bracket structure, whereas the active control strategy involved the relative displacement of two opposite points of the bracket. To this aim, dedicated interfaces were designed to integrate the stack into the mounting bracket. In order to control the vibrations in correspondence of the second bending mode (1599.4Hz), the primary disturbance, simulated by a shaker, was modelled in the frequency domain using a white noise signal. A narrow window of 20Hz was initially selected as the control system domain. Then, this frequency range has been made gradually wider around the resonance peak, in order to optimize the control effect, and then extended up to 80 Hz when undesired effects occurred. Primary and secondary control plants were firstly numerically fitted from the measured responses and excitations using system identification techniques, and then used for the active controller design and simulations

Feasibility study for a tonal vibration control system of a mounting bracket for automotive gearboxes

A conceptual design of an active device able to attenuate the tonal vibrations of a mounting bracket for automotive gearboxes is addressed in this paper. A preloaded piezo stack actuator is used to counteract the unbalanced vibrations of the component by monitoring its operational deformations. Firstly, a numerical modal analysis is carried out to characterize the normal modes in the frequency range of interest. The piezo stack is simulated by a rod element and its effect is numerically characterized. The upper and lower faces of the stack are mechanically coupled with the bracket structure, whereas the active control deals with the relative displacement of two points of the bracket. The primary disturbance was simulated by a shaker to control the vibrations in correspondence of the second bending mode (around 1.6 kHz). A 20 Hz narrow band was additionally selected as the control window. Then, this frequency range was enlarged around the resonance peak in order to optimize the control effect, till 80 Hz to investigate the resulting effects. Finally, focus is given to the structural damping by assessing its impact on the control forces and phases to cancel the deformation along the contact direction. The description of the experimental results concludes this work by generally confirming the numerical expectations

Response of a mixed grass prairie to an extreme precipitation event

Citation: Concilio, A. L., Prevey, J. S., Omasta, P., O'Connor, J., Nippert, J. B., & Seastedt, T. R. (2015). Response of a mixed grass prairie to an extreme precipitation event. Ecosphere, 6(10), 12. doi:10.1890/es15-00073.1Although much research has been conducted to measure vegetation response to directional shifts in climate change drivers, we know less about how plant communities will respond to extreme events. Here, we evaluate the response of a grassland community to an unprecedented 43 cm rainfall event that occurred in the Front Range of Colorado in September, 2013 using vegetation plots that had been monitored for response to simulated precipitation changes since 2011. This rain caused soils to stay at or above field capacity for multiple days, and much of the seed bank germinated following the early autumn event. Annual introduced grasses, especially cheatgrass (Bromus tectorum), and several introduced forbs demonstrated strong positive increases in cover the following growing season. Native cool season grasses and native forbs showed limited changes in absolute cover despite continued high soil water availability, while native warm season grasses increased in cover the following summer. Treatments that previously altered the amounts and seasonality of rainfall during the 2011-2013 interval showed legacy effects impacting cover responses of introduced species and warm-season native grasses. Resin bag estimates of inorganic nitrogen flux resulting from the event indicated twice as much nitrogen movement compared to any previous collections during the 2011-2013 interval. Nitrogen additions to a subset of plots made in spring of 2014 demonstrated that the relative cover of introduced species could be further increased with additional soil nitrogen. Collectively, these results support the contention that extreme precipitation events can favor species already benefiting from other environmental change drivers

Function space topologies between the uniform topology and the Whitney topology

n/

topologizing homeomorphism groups

This paper surveys topologies, called admissible group topologies, of the full group of self-homeomorphisms of a Tychonoff space , which yield continuity of both the group operations and at the same time provide continuity of the evaluation function or, in other words, make the evaluation function a group action of on . By means of a compact extension procedure, beyond local compactness and in two essentially different cases of rim-compactness, we show that the complete upper-semilattice of all admissible group topologies on admits a least element, that can be described simply as a set-open topology and contemporaneously as a uniform topology. But, then, carrying on another efficient way to produce admissible group topologies in substitution of, or in parallel with, the compact extension procedure, we show that rim-compactness is not a necessary condition for the existence of the least admissible group topology. Finally, we give necessary and sufficient conditions for the topology of uniform convergence on the bounded sets of a local proximity space to be an admissible group topology. Also, we cite that local compactness of is not a necessary condition for the compact-open topology to be an admissible group topology of

Proximal convergence

Suppose X is a topological space and Y a proximity space , fn L C f (Leader Convergence) iff for each A in X, B in Y, f(A) near B implies eventually fn (A) is near B. L.C. is a generalization of U. C. (Uniform Convergence). In this paper we study L. C. and various generalizations and prove analogues of the classical results of Arzelà, Dini and others

Numerical and experimental transition results evaluation for a morphing wing and aileron system

A new wing-tip concept with morphing upper surface and interchangeable conventional and morphing ailerons was designed, manufactured, bench and wind tunnel tested. The development of this wing tip model was performed in the frame of an international CRIAQ project, and the purpose was to demonstrate the wing upper surface and aileron morphing capabilities in improving the wing tip aerodynamic performances. During numerical optimization with ‘in-house’ genetic algorithm software, and during wind tunnel experimental tests, it was demonstrated that the air flow laminarity over the wing skin was promoted, and the laminar flow was extended with up to 9% of the chord. Drag coefficient reduction of up to 9% was obtained when the morphing aileron was introduced