Bistable Attachment Research Articles

Vibration control of a pre-twisted rotating beam with nonlinear bi-stable attachments

The influence of the nonlinear bi-stable attachment on the vibration suppression of a pre-twisted rotating cantilever beam is investigated in this study. The kinetic and potential energies of the system, comprising a pre-twisted rotating Euler–Bernoulli beam and the nonlinear bi-stable attachments, are obtained, and the equations of motion are derived using the Rayleigh–Ritz method. The natural frequencies and mode shapes of the beam (without the attachments) obtained using the present formulation are validated with the results obtained from Ansys. Subsequently, the flapwise vibration control of the pre-twisted rotating beam subjected to a base excitation is studied. A parametric study is performed for various amplitudes of base excitation, rotational speeds, and the number and position of the bi-stable attachments. Results show significant vibration suppression capabilities of the nonlinear attachments, and hence the proposed system could potentially be used for rotating beam-type structures such as wind turbine blades.

High frequency characterization of a sweeping jet actuator

Sweeping jets are an emerging type of actuators that have gained interest due to their potential use in flow control applications. The working principle of these devices is based on the bi-stable attachment of a jet to adjacent walls. They are able to produce unsteady blowing within a wide range of operating frequencies. Nevertheless, the state of art shows a lack of space-time characterization of these actuators for high sweeping frequencies. This paper presents a conditional approach that reconstructs the spatial dynamic response of sweeping jets for sweeping frequencies above 500 Hz. The time-dependent velocity is measured with two single-hot-wire sensors: a reference one placed at the edge of the exit nozzle, and a flying one. The method is then tested to characterize the flow at the exit nozzle of an in-house sweeping jet actuator with 1 mm space resolution, and 50 μs time resolution. These measurements are performed with a sweeping frequency of 639 Hz. Overall this paper demonstrates that the conditional approach is very useful for understanding the physics of flow control actuators.

A Disturbance Cancellation Perspective on Vibration Control Using a Bistable Snap-Through Attachment

One approach to vibration control is to apply a force to a primary structure that opposes the excitation, effectively canceling the external disturbance. A familiar passive example of this approach is the linear-tuned mass absorber. In this spirit, the utility of a bistable attachment for attenuating vibrations, especially in terms of the high-orbit, snap-through dynamic, is investigated using the harmonic balance method and experiments. Analyses demonstrate the fundamental harmonic snap-through dynamic, having commensurate frequency with the single-frequency harmonic excitation, may generate adverse constructive forces that substantially reinforce the applied excitation, primarily at lower frequencies. However, both analyses and experiments indicate that such high-orbit dynamics may be largely destabilized by increased bistable attachment damping. Destructive forces, which substantially oppose the excitation, are unique in that they lead to a form of vibration attenuation analogous to strictly adding damping to the host structure, leaving its spectral characteristics largely unaltered. The experiments verify the analytical findings and also uncover nonlinear dynamics not predicted by the analysis, which render similar attenuation effects.