Magnetic effect in viscosity of magnetorheological fluids

Piezoelectric bimorph as a high-sensitivity viscosity resonant sensor to test the anisotropy of magnetorheological fluid

In this paper, we present a device which is very sensitive for small changes in the viscosity of the investigated fluid. The main part of the device is a piezo-electric bimorph which consists of the brass shim with two piezo-ceramic layers on the opposite sides. One of them is responsible for generating vibrations, whereas the second one is meant to measure system response which is produced by the damping properties of the surrounding fluid. During the experiment, the cylindrical bar is forced to move by the series of sinusoidal waves with different frequencies and at constant amplitudes. The probe is immersed in the fluid and then the amplitude vs frequency and phase vs frequency curves are obtained. Next, one can determine the viscosity according to a proper mathematical model. The resonant frequency is related to the damping coefficient which depends on the viscosity of the surrender fluid and immersion depth of the probe. The coefficients necessary for calculating viscosity are obtained by fitting the resonance curve to the amplitude vs frequency data obtained from the experiment. The device has been applied to study the anisotropy of magnetorheological fluids. The weak anisotropy of viscosity has been observed. The highest value of viscosity was observed in the case of viscosity measurement in the direction orthogonal to the magnetic field and the lowest in the direction parallel to the magnetic field.

One-way sound propagation via spatio-temporal modulation of magnetorheological fluid

This manuscript details the possibility of achieving one-way sound propagation using a smart fluid such as magnetorheological fluid (MRF) by subjecting it to a spatio-temporally varying magnetic field. The local speed of sound in MRF is dependent on applied magnetic field as demonstrated in several experimental works and this property of MRF has been leveraged, in this work, to induce one-way bandgaps. Initially, a general wave equation pertaining to fluid with space-and-time-varying material properties was derived. Assuming plane wave propagation in one dimension, an approximate Floquet solution was imposed and the dispersion relationship was obtained. A comprehensive finite element analysis was conducted and good agreement was noted between the numerical and theoretical dispersion relations. It was concluded that space-time periodic modulation of fluid density and local sound speed is necessary to induce asymmetry in the band diagram around the ω axis. The feasibility of real-world implementation using MRF has been discussed. A parametric study detailing the effect of viscosity on the one-way bandgaps has been undertaken. It was found that one-way bandgaps formed at relatively lower frequencies are more robust to viscous corruption. A real-world implementation may be feasible if the viscosity of MRF is less than 3000 Pa-s.

Active Control of a Small-Scale Wind Turbine Blade Containing Magnetorheological Fluid

This research study proposes a new active control structure to suppress vibrations of a small-scale wind turbine blade filled with magnetorheological (MR) fluid and actuated by an electromagnet. The aluminum blade structure is manufactured using the SH3055 (Bergey Windpower Co. Inc., Norman, OK, USA) code numbered airfoil which is designed for use on small wind turbines. A dynamic interaction model between the MR fluid and the electromagnetic actuator is constructed to obtain a force relation. A detailed characterization study is presented for the proposed actuator to understand the nonlinear behavior of the electromagnetic force. A norm based multi-objective H₂/H_∞ controller is designed using the model of the elastic blade element. The H₂/H_∞ controller is experimentally implemented under the impact and steady state aerodynamic load conditions. The results of experiments show that the MR fluid- electromagnetic actuator is effective for suppressing vibrations of the blade structure.