Shear‐thinning effects in annular‐orifice viscous fluid dampers

Abstract

Abstract The number of construction projects using viscous fluid dampers for the purpose of seismic energy dissipation has been increasing in recent years. Usually, resisting forces provided by a viscous fluid damper are nonlinearly related to the damper operation velocity. In the current study, the mechanism of the nonlinear behavior is studied. It is found that the fluid shear rate in the orifices of a damper is high enough to cause shear thinning of the fluid, that is, the non‐Newtonian behavior of the fluid must be considered to capture the viscous damper's non‐linearity. Carreau's equation giving the shear‐thinning relationship between fluid viscosity and shear rate is employed in a finite element model. The model is used to calculate the fluid dynamics in viscous dampers and the calculated results successfully explain the nonlinear behavior. Effects of the damper geometry and the fluid viscosity on the damper non‐linearity are also tested and discussed. Again, the trend shown in experimental results can be fully explained by the shear‐thinning concept. In addition, the behavior of a damper operated at ultra high velocity is addressed.