Suspension-type tuned mass dampers with varying pendulum length to dissipate energy

In this paper, an optimal energy dissipation control algorithm is applied into a semi-active suspension-type tuned mass damper (SA-STMD) to suppress excessive vibration by means of variable pendulum length. The SA-STMD mechanism consists of a mass block, a suspension rope, and a movable fulcrum that can be a short tube driven by a linear motor to vertically move along the suspension rope. As the fulcrum goes up, the pendulum length is extended, resulting in a smaller stiffness of the SA-STMD, and vice versa. Accordingly, the restoring force in the SA-STMD can be adjusted by varying the fulcrum positions. In the case where the energy dissipation ability by the original STMDs is insufficient, the movable fulcrum in the SA-STMD system can compensate the STMDs for stiffness according to the proposed optimal energy dissipation control algorithm to provide controllable restoring forces. The controllable restoring forces are designed to act as viscous dampers that can make up for the lack of energy dissipation capacity. The numerical results from the time domain and frequency domain analyses show that the proposed approach utilizing the optimal energy dissipation control algorithm to adjust the pendulum length can induce controllable restoring forces with a butterfly-shaped hysteresis loop, supplying a sufficient energy dissipation capacity to reduce responses to the unexpectedly large external vibration. Another potential benefit is cost reduction because of use of a less number of conventional viscous dampers in the STMD system.