Design method for high-force electrorheological dampers
Electrorheological (ER) materials are suspensions of polarizable particles in a dielectrically strong suspension. When a strong (kV mm-1) electric field is applied to ER materials, their visco-elastic and, more importantly, yielding properties increase by orders of magnitude. While Newtonian viscous stresses are relatively field independent, dissipative forces in ER dampers are adjusted by varying the field-dependent yield stress. By varying the ratio of the flow-rate-independent yield stresses to Newtonian viscous stresses, ER dampers may be designed to match the requirements of a wide range of applications. In many cases, it is desirable for the ER damper to not only have high force capacities in a compact geometry, but also have a large range of controllable forces. A class of ER dampers is analysed and illustrated in this paper. The analysis of these device configurations is completed in closed form by virtue of a linear approximation to the non-Newtonian ER Poiseuille flow equation. These dampers feature multiple concentric cylindrical ducts which can be interconnected in parallel, in series or in combinations thereof. The hydraulic connectivity of the ducts determines, to a great extent, the force-velocity relationship of the device. Within overall size constraints, a tradeoff between the field-controllable force range and force magnitude is controlled by the format of the ducts. Other design variables considered in this paper are the across-flow dimension of the ducts and the number of ducts. Designs are evaluated based on force capacity, range of field-dependent forces, electrical energy requirements and response time. The effects of pre-yield elasticity and particle concentration inhomogeneity are also addressed. Numerical examples focus on a large-scale damper which requires a very modest amount of external energy (kJ), yet can regulate very large forces (200 kN) and can modify its force by a factor of ten or more within milliseconds.
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