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Nondimensional Herschel—Bulkley Analysis of Magnetorheological and Electrorheological Dampers

Smart Structures Laboratory, Alfred Gessow Rotorcraft Center Deptartment of Aerospace Engineering, University of Maryland, College Park, MD 20742 USA, wereley{at}umd.edu

Quasisteady modeling of linear stroke flow mode magnetorheological (MR) (or electrorheological (ER)) dampers has focused primarily on the utilization of the Bingham-plastic constitutive model to assess performance metrics such as damping capacity. In such Bingham-plastic MR (or ER) flows, the variable yield stress of the fluid, _y, is activated by applying magnetic (or electric) field. The Bingham-plastic model assumes that the material is in either (1) a pre-yield condition where the local shear stress is less than the yield stress, <_y, or (2) a post-yield condition, where the local shear stress is greater than the yield stress, > _y, so that the material flows with a constant post-yield viscosity. The objective of this study is to analyze the damping capacity of such a controllable MR or ER damper in the situation when the field dependent fluid exhibits post-yield shear thinning or thickening behavior, that is, the post-yield viscosity is a function of shear rate. A Herschel—Bulkley model with a field dependent yield stress is proposed, and the impact of shear rate dependent viscosity on damping capacity is assessed. Key analysis results — velocity profile, pre-yield thickness, and damping coefficient — are presented in a nondimensional formulation that is consistent with prior results for the Bingham-plastic analysis. The nondimensional analysis formulated here clearly establishes the Bingham number as the independent variable for assessing flow mode damper performance.

Key Words: magnetorheology • magnetorheological fluids • electrorheology • electrorheological fluids • Bingham-plastic • Herschel-Bulkley • shear thinning • shear thickening • magnetorheological damper • electrorheological damper • Bingham number.

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