Influence of mass on the efficiency and dynamics of single-sided and double-sided vibro-impact nonlinear energy sinks

This paper studies the efficiency of the asymmetric single-side and symmetric double-sided vibro-impact nonlinear energy sinks (SSVI NES and DSVI NES), that is, vibro-impact dampers, in mitigating unwanted vibrations of the heavy primary structure (PS) to which these dampers are attached. The dynamic behavior of this vibro-impact system is also investigated. The damper efficiency and system behavior are studied for dampers with four different masses, as optimization is carried out for other damper parameters at a predetermined mass. The effect of the damper mass changing on its efficiency and system dynamic behavior is shown. The dampers with different masses and optimal design exhibit similar high efficiency in mitigating the PS vibrations, but the optimal design of the dampers with lower mass has unusual parameters, namely the huge clearance and small damping coefficient. The SSVI NES hits not only the obstacle hardwired to the PS but also the PS directly. From this point of view, it can be considered as double-sided DSVI NES only asymmetric. The DSVI NES hits the left and right obstacles rigidly connected with PS. The regions of bilateral impacts are narrow and located near the resonant frequency of the exciting force. In the rest of the frequency range, the SSVI NES makes unilateral direct impacts on the PS; the DSVI NES performs shockless motion without any impacts and operates in this frequency range as a linear damper without any nonlinearity. The numerous numerical tests were able to show the system dynamics with 36 different dampers, namely for four masses, for two damper types for each mass, and for several variants of the optimal damper design. The optimal design is not unique; it can have many variants, since there is a lot of damper parameter sets that provide similar mitigation of the main structure vibrations. Therefore, optimization procedure itself does not and cannot give an unambiguous result, allows for great arbitrariness in its execution and requires great experience and skill from the performer.