Active control of cables by axial support motion

Active control of a slightly sagged cable using actuator motion in the cable axial direction is studied. Two active control schemes are proposed: (i) active stiffness control and (ii) active sag-induced force control. They are verified experimentally, and good agreement between experiments and predictions is shown. Next, using the direct method of Liapunov, a stable control scheme to control multimodal response of a cable is proposed. An uncontrollable motion is identified as a circular swirling motion of the cable that is formed by two closely spaced antisymmetric modes. The simulation results show that the controller suppresses free vibration of a cable efficiently whenever the cable motion is controllable and stops when uncontrollable. It is observed that control spillovers occur but their effects are not significant. The vibration energy of the multimodal response of a cable under random excitation is shown to be reduced effectively by the proposed control scheme.