Effectiveness of oscillating mass damper system in the protection of rigid blocks under impulsive excitation

In this paper the effects of a mass damper on the rocking motion of a non-symmetric rigid block, subject to one-sine pulse type excitation, is investigated. The damper is modelled as a single degree of freedom oscillating mass, running at the top of the block and connected to it by a linear visco-elastic device. The equations of rocking motion, the uplift and the impact conditions are derived and the results are obtained by numerical integration of these equations. An extensive parametric analysis is performed, by taking fixed the geometrical characteristics of the block. The frequency and the amplitude of the excitation, the mass ratio and the period of the oscillating mass are taken as variable parameters in the analyses. The main objective of the study is to understand if it is possible to find the optimal properties of the oscillating mass, capable to make more difficult the overturning of the body. The results show that the presence of the mass damper, if correctly designed, leads to a general improvement of the response of the system. Curves providing the optimum value of the characteristics of the mass damper versus the parameters characterizing the excitation, are finally obtained.