Development of a rotary fluid inerter with negative stiffness and variable damping characteristics

As a single-port, two-terminal device, the inerter generates inertance proportional to the relative acceleration between its two terminals, delivering forces aligned with the direction of the relative motion and exhibiting a negative stiffness feature. The helical-tube fluid inerter generates inertance via the fluid motion in the helical tube outside the device. However, only linear fluid inerters have been reported to date, with the rotary ones remaining unexplored. To address this gap, this study reports a novel rotary fluid inerter. By integrating a magnetorheological unit, the inerter can deliver variable damping characteristics in addition to its negative stiffness feature. Conversely, such integration also resolves the limitation of magnetorheological devices in outputting forces in the same direction of the relative motion, thereby enhancing their vibration attenuation performance. To validate the proposed concept, a prototype rotary fluid inerter was designed, fabricated, and tested. The experiment results confirm that the device exhibits negative stiffness and variable damping characteristics. Additionally, a phenomenological model is established based on the test results to describe the characteristics of the inerter, and its parameters are identified using MATLAB/Simulink. The good alignment between the simulated and experimental results validates the effectiveness and precision of the proposed model in describing the behavior of the proposed rotary fluid inerter. The development of this variable damping rotary fluid inerter enhances the capabilities of variable damping devices as well as diversifies the category of inerters.