Considerations on the optimal design of semi active magnetorheological dampers

In this paper the optimal semi active control of a system subjected to seismic input is studied. The control algorithm, working in ON-OFF mode, is based on the instantaneous optimal control theory. By taking advantage of this theory, an innovative methodology to obtain global optimal control, that is optimality along the whole seismic event, is proposed in order to surpass the disadvantage of instantaneous control which reaches local optimality only. The control device is a magnetorheological damper, modelled as a Bouc-Wen element in parallel at a viscous element. The variable parameter to be optimized is the input voltage. The time lag of the device is modeled as well. The procedure proposed is applied to a case study representing a four story structure controlled by a semi active bracing which uses a magnetorheological damper. Analyses with several seismic inputs, representing both cases of near and far field earthquakes, are carried out and results obtained with optimal control along the whole seismic event are compared with instantaneous optimal control.