Performance enhancement of floating raft system by exploiting geometric nonlinearity and motion constraint in vibration isolators

This paper proposes a nonlinear vibration isolator with hybrid passive elements to mitigate the vibration transmission in floating raft systems. The proposed isolator employs a combination of a geometrically nonlinear linkage mechanism, an inerter, and a motion constraint. Analytical and numerical methods are applied to determine the responses. Given the presence of multiple transmission paths and excitations, power flow indices serve as primary metrics for performance assessment. The results show that the constraint can prevent the folding problem of the linkage mechanism. This, in turn, provides 1) flexibility in the parameter design to achieve quasi-zero dynamic stiffness and 2) protection for geometrically nonlinear systems under extreme operating conditions. The proposed element introduces an anti-peak into the response and power transmission curves, effectively shifting the resonance peaks to lower frequencies. The desired low-frequency isolation performance can be achieved through a coordinated parameter design. This would provide an ultralow response as well as force and energy transmission near the original resonant peaks of the linear system. Furthermore, the proposed design exhibits enhanced performance across diverse operational conditions including multiple frequency excitations and varying mass ratios and forcing amplitudes. These observations demonstrate the potential of utilizing hybrid nonlinear elements in ocean engineering applications.