Dynamics of impact-damped continuous systems

Aamir Siddiq Butt, Louisiana Tech University


Experimental and numerical research is conducted to investigate the behavior of impact-damped continuous systems subjected to changes in the damper's parameters. An impact damper belongs to the category of passive damping devices. It has the advantage over other such devices because it can effectively reduce excessive vibrations of flexible structures without a significant change to their design. Numerical and experimental research in the area of impact dampers has been mainly conducted for single- or multi-degree-of-freedom systems. However, since most of the realistic structures are continuous, this dissertation extends the applicability of impact dampers to such systems. During this study, two dampers which were manufactured at Louisiana Tech University were used to conduct experiments at Louisiana Tech University and NASA Johnson Space Center's Vibration and Acoustic Testing Facility. A hollow brass beam with non-classical boundary conditions was used as the test article. In addition, a comprehensive finite element algorithm was developed to model such systems. The parameters considered during this study were the mass of the impacting particle, the gap, the coefficient of restitution which exists between the particle's surfaces and the container's boundary, the location of the damper, and the excitation level. Experimental and numerical results were obtained in the form of time history and frequency response functions. Results indicate that, although an impact damper can be used effectively to reduce excessive vibrations of the system at certain parameters, it may increase the amplitude of the system at other parameters. Therefore, the choice of the parameters to be employed in practical applications is of extreme importance, especially if the damper is to be operated in a hostile environment such as outer space for which maintenance costs are astronomical.