A novel analytical investigation of magneto-rheological (MR) fluids in squeezing flows is performed and the results are validated with experimental test data. The squeeze flow of MR fluids has recently been of great interest to researchers. This is due to the large force capacity of MR fluids in squeeze mode compared to other modes (valve and shear modes), which makes the squeeze mode appropriate for a wide variety of applications such as impact dampers and engine mounts. Tested MR fluids were capable of providing a large range of controllable force along a short stroke in squeeze mode. A mathematical model was developed using perturbation techniques to predict closed-form solutions for velocity field, shear rate distribution, pressure distribution and squeeze force. Therefore, the obtained solutions greatly help with the design process of intelligent devices that use MR fluids in squeeze mode. The mathematical model also reduces the need for complicated and computationally expensive numerical simulations. The analytical results are validated by performing experimental tests on a novel MR device called an 'MR pouch' in an MR squeeze mode rheometer, both designed and built at CVeSS.

A new controller is introduced in this paper as a novel method for active vibration suppression in flexible structures. The hybrid positive feedback (HPF) uses a second-and a first-order compensator that are fed by the displacement and velocity feedbacks, respectively. Parallel pairs of the HPF controller are implemented when suppression in multimode condition is issued. Since the controller uses two gains for each pair of the actuator/sensor patch for each mode, a suitable gain optimization method has to be used to ensure the optimum performance. To this end, H 2 and H ∞ optimization approaches are utilized. For validation purposes, the controller is verified numerically and experimentally for vibration control of a cantilever beam. System identification is performed, then closed-loop system responses to simultaneous multimode and swept frequency excitations are obtained. According to the results, the HPF controller has a superior performance compared to the conventional method of positive position feedback. Vibration displacement amplitudes were reduced by more than 85% relative to the uncontrolled state. The best performance was achieved by the H 2 -optimized HPF, as the net value for vibration displacement amplitude reduction in the multimode condition was 90% of the uncontrolled amplitude.

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This paper provides a comparison between two different energy harvesting circuits for a piezoelectric flag subjected to uniform flow. Between two circuits tested, one is Simple Resistive Load, and the other one is the standard AC-DC circuit. To experimentally investigate these circuits, the piezoelectric flag output voltage has been studied under various wind speeds in a wind tunnel. The simple resistive load circuit provides an alternating voltage, and not a DC voltage. The standard AC-DC circuit is used to convert the AC voltage into a DC voltage; however, the power dropped as a result of the voltage drop across the forward-biased diodes.

A piezoelectric flag is modeled as a membrane for energy harvesting purposes. The tension, pressure, piezoelectric material, and external force are introduced and employed in the model. In this model, the tension is caused by gravity, the piezoelectric material, and the fluid flow. The pressure acting on the flag consists of a non-circulatory and a circulatory component. Additionally, an external force is modeled to ensure that the pressure acting on the system does not dissipate. To model the system, Hamilton’s principle is employed to find differential equation of motion. In this study, the flag is vertically oriented. This is to ensure the flag does not droop, which would greatly complicate the effect of gravity. In studying the free response, it is found that the Bessel function of the first kind describes the flag. Lastly, Galerkin’s method is applied to the system. This allows for the deflection and the voltage produced by the flag to be found. It is found that the presented model reasonably predicts both the deflection and voltage of the piezoelectric flag.