Nonlinear mechanical model of a fluid inerter

Dynamic vibration control devices provided with inertance, such as Tuned Inerter Dampers, Tuned Mass Damper Inerters or Tuned Liquid Column Damper Inerters, have been shown in numerous numerical studies to have superior vibration mitigation performance compared to conventional devices, such as Tuned Mass Dampers. One possible way to produce this inertance effect is by means of a moving fluid. In this study, the dynamic performance of such a fluid inerter is analyzed experimentally. The considered small-scale prototype consists of a hydraulic cylinder, and the inertance is generated by the flow of the working fluid in an external channel attached to the cylinder itself. In a first step, the dry configuration, i.e. without fluid, is investigated, revealing a nonlinear dissipation force. In a corresponding mechanical model, this force is represented by a variant of the well-known Stribeck effect. Subsequent experiments on the complete configuration, i.e. with fluid, reveal a further nonlinear effect. This effect is attributed to the compressibility of the working fluid as well as air trapped in the channel. Once the parameters of the mechanical model are retrieved, comparative studies are carried out. These show a remarkable agreement between numerical and experimental outcomes, thus enabling the mechanical model to be used in dynamic vibration control devices, as stated above.