Abstract Summary
Earthquakes, strong wind or human activity are examples of potential sources of vibrations that might cause damage to structural elements or human discomfort in slender structures. To control vibrations, the mitigation effect of well-known passive control systems such as Tuned Mass Dampers (TMDs) can be used. Nevertheless, the effectiveness of TMDs strongly depends on their mass. With this in mind, the development of innovative auxiliary devices and arrange-ments that can improve the performance of mass-dependent control systems has been a flourishing research area in civil and mechanical engineering in recent years. In this regard, the so-called inerter can be exploited to fictitiously increase the mass of the structure to which it is connected, allowing a mass amplification effect without any physical addition. The most common types are rack and pinion inerters, ball screw inerters, and fluid inerters. The latter are easier to design and develop and can be adapted to implement different damper arrangements, especially for larger civil structures with very low maintenance requirements. In addition, parasitic effects such as backlash and ratcheting are less pronounced than in the mechanical alternatives. For these reasons, the present study aims to identify the dynamic properties of a fluid inerter. To this end, a test campaign is conducted to reveal the actual behaviour of this device, focusing on the effects of its nonlinearities. The prototype consists of a hydraulic cylinder in which the inerter effect is achieved by the flow of the working fluid through an external channel. In the first step, the dry configuration, i.e., without fluid, is investigated, revealing nonlinearity due to the friction of the piston. While simplified models such as Coulomb friction without velocity-dependence of the friction force fail to reproduce the experimental data, a model based on the Stribeck effect successfully captures the dissipation force caused by friction. Subsequent experiments on the complete configuration, i.e., with fluid, reveal further nonlinear effects due to the compressibility of the working fluid and the air trapped in the external channel. An accurate mechanical model of the device is determined and its efficiency is demonstrated by means of comparative studies. The nonlinear layout provides a more realistic numerical prediction than a common linear model and can be implemented in several structural control device configurations. Finally, the experimentally generated inertance shows the large potential of fluid inerters when used for vibration control in civil structures.
