Semi-active vibration control of space truss structures by friction damper for maximization of modal damping ratio

A semi-active control approach using a dry friction damper is presented to reduce transient vibrations of a space truss structure. The control target is to maximize an equivalent damping ratio of the lowest bending mode, which is considered most dominant in its transient vibrations. The key concept is to represent the equivalent damping ratio of a typical 1 degree of freedom (dof) system with a friction mechanism in terms of the normal force and vibration amplitude and, subsequently, to control the normal force for maximization of the equivalent damping ratio as the amplitude decreases. The 1-dof approach is extended to a multi-dof truss model by modal transformation based on FE formulations and properties of the friction damper indentified experimentally. In the extended approach, the normal force can be explicitly obtained in terms of modal parameters and estimated amplitude of the modal displacement. This is a major difference from many other researches, which require numerical optimizations for design of control parameters. Effectiveness of the proposed control technique is shown through numerical simulations and experiments in terms of the settling time and damping ratio of the first mode, in which the results are compared with those by passive and bang–bang control.