Abstracts Engineering

The effectiveness of particle dampers under centrifugal loads

by Daniel Nicolaas Johannes Els

Thesis (PhD (Mechanical and Mechatronic Engineering)) – University of Stellenbosch, 2009. The main research objective of this dissertation was to determine the performance parameters of particle dampers (PDs) under centrifugal loads. A test bench was developed consisting of a rotating cantilever beam with a PD at the tip. Equal mass containers with di erent depths, filled with a range of uniform sized steel ball bearings, were used as PDs. For all the tests, the total PD mass was identical. During operation the tip of the beam was displaced, and after release, the beam could vibrate freely. The decay in the vibratory motion of the tip of the beam was measured over a range of centrifugal loads. The experiments were duplicated numerically with a discrete element method (DEM) model, calibrated against the experimental data. This model could then be used for a more in-depth investigation of phenomena occurring when PDs are under centrifugal loads. From the data analysis, it can be concluded that there are two zones of damping, one with a high and one with a low damping factor. These damping zones depend on the ratio between the peak vibration acceleration and the centrifugal loading. Each zone has a limit in terms of the centrifugal loading beyond which the PD cannot function if the vibration amplitude is fixed. In the high damping zone, it was found that the excitation state of the particles was high enough for the system vibration frequency to change. In the low damping zone, there is only limited motion between the particles. The main parameters that influence the performance of the PDs are the friction between the particles themselves and with the container, the PD length/diameter aspect ratio, and the particle size. An important finding is that a PD with less layers (increase in particle size) will still function at a higher centrifugal load compared to one with a smaller number number of layers.