Studies of the performance of particle dampers attached to a two-degrees-of-freedom system under random excitation

This paper presents an investigation of the performance of particle dampers attached to a two-degrees-of-freedom system, using the discrete-element method. Correlation functions, the amount of dissipated energy due to impact and friction, and the concept of ''effective momentum exchange'' are shown to be suitable ways of interpreting the physics involved in the behavior of particle dampers. Using three different types of excitation, the optimum operating regions are determined, within which particles move in a plug flow pattern and correlation functions decay fast, while the dissipated energy and the effective momentum exchange are large compared with inefficient operating conditions. The paper also evaluates the effects of many system parameters (such as the mass ratio, coefficient of restitution, excitation levels, damping ratio of the primary system, container dimensions and shape, number of particles, and the coefficient of friction), using high-fidelity simulations. It is shown that: increasing the mass ratio can improve the damper's effectiveness, but only up to a certain level; applying particles with a high value of the coefficient of restitution can result in a broader range of acceptable response levels; friction has a complex influence on particle dampers in a generally detrimental form; a lightly-damped primary system can achieve a considerable reduction in its response with a small weight penalty; and that a cylindrical-shaped container provides a higher level of effectiveness than a rectangular-shaped one. Finally, the behavior of the particle damper is compared to a multi-unit impact damper to enhance the understanding of the two passive control devices, and it is shown that a particle damper is more robust when considering arbitrary levels of excitation in different directions.