Floriane’s feedback on the first year of thesis
During the elaboration of the subject, it was decided to implement a non-linear mechanism in the resonator.
Nonlinear vibration absorbers, also called Nonlinear Energy Sinks (NES), are characterized by a nonlinear stiffness. The absorber’s movement is no longer proportional to the exerted force. The relation at play can for example be cubic: F=k1.x+k3.x3. With this phenomenon, the NES can automatically synchronize with the structure’s oscillations. Designing piezoelectric resonators with a nonlinear stiffness would allow us to obtain performances similar to a NES and to increase their frequency robustness. Non-linear piezoelectric resonators could operate at the structures’ natural frequency even if it evolves. The thesis’ technical objective is to establish the different design rules for piezoelectric NES.
Because of this nonlinearity, NES are sensitive to the amplitude of the solicitation, i.e. to the applied strength magnitude, and should be correctly designed according to this amplitude level. Damping appears as a critical parameter which needs to be perfectly adjusted, however mechanical damping is sparsely predictable and adjustable. By adding piezoelectric elements and a shunt, it would be possible to modify the behavior of the system. Electrical components affect the mechanical components’ dynamics and vice versa thanks to the electromechanical conversion at play. Adding a resistor inside the shunt would induce an electric damping. The total damping value could then equal the optimal value by adjusting the resistor value.
The first months of the thesis were dedicated to the assimilation of the analytical methodologies used to study NES. Performance indicators were defined to compare their responses with conventional TMDs. Different optimization methods based on these indicators are currently under study to determine the resonators’ optimal factors. These results will then be used to design a prototype.