We investigate the dynamics of the buoyancy-driven rise of a bubble inside a viscoplastic material when it is subjected to an acoustic pressure field. To this end, we develop a simplified model based on the Lagrangian formalism assuming a pulsating bubble with a spherical shape. Moreover, to account for the effects of a deformable bubble, we also perform detailed two-dimensional axisymmetric simulations. Qualitative agreement is found between the simplified approach and the detailed numerical simulations. Our results reveal that the acoustic excitation enhances the mobility of the bubble, by increasing the size of the yielded region that surrounds the bubble, thereby decreasing the effective viscosity of the liquid and accelerating the motion of the bubble. This effect is significantly more pronounced at the resonance frequency, and it is shown that bubble motion takes place even for Bingham numbers (Bn) that can be orders of magnitude higher than the critical Bn for bubble entrapment in the case of a static pressure field.

This paper presents the optimization of the design of a railway wheel in terms of the wheel's sound power levels emission, with respect to its geometrical properties. To this end, a simplified finite element method (FEM) model of the wheel was employed, that did not include the interaction of the wheel and rail or the influence of the braking system that is assembled on the wheel. The objective of the optimization method was to find a design of the selected railway wheel, which without the use of damping or tuning devices, emits less vibration/noise compared to the original design. The optimization method used, was based on genetic algorithms (GAs). GAs are a robust optimization method that performs regardless of the optimization problem. The GA-based optimization method that is presented in this paper, utilized ANSYS running in batch mode for the calculation of the objective function values of the population of each generation.

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