Extensive resonant vibrations of large civil engineering structures are efficiently damped by the tuned mass absorber. The tuned mass absorber consists of a mass attached to the vibrating structure by a spring and a viscous damper, which are dimensioned such that the absorber counteracts and dissipates the structural resonant motions. However, the vibrations of smaller structures, such as jet engine turbine blades, aircraft wings or satellites may not be mitigated by the tuned mass absorber. Instead, a piezoelectric material, which couples mechanical strains with electric fields, can be glued directly to the vibrating structure whereby the mechanical energy is converted into electrical energy, which is then dissipated in an electric circuit (shunt). When the shunt consists of an inductance and a resistance the piezoelectric absorber functions similarly to the tuned mass absorber, with the resonant motions now counteracted by the movement and dissipation of electric charge. More specifically, the piezoelectric capacitance, shunt inductance and shunt resistance are equivalent to mechanical flexibility, mass and viscous damping, respectively. The optimal shunt design is obtained by considering a modal reduction of the structure, which accurately describes the structure-absorber interaction, when the system vibrates in a targeted resonant vibration mode.
In the present Ph.D. project this interaction is analyzed and it is demonstrated that the optimum shunt tuning can be determined by measuring two dynamic absorber response. The first is the flow of electric current between the short-circuited piezoelectric electrodes, while the second is the voltage between the electrodes, when an infinite electric resistance is inserted. A design procedure for the optimal piezoelectric absorber tuning thereby comprises the gluing of the piezoelectric material to the vibrating structure, the measurement of current and voltage when the structure is excited by a dynamic load and the final tuning of the shunt inductance and resistance with respect to a target vibration mode. Both the inductance and resistance may be designed by passive electronic components, whereby the piezoelectric absorber is stable and effectively mitigates the resonant vibrations of the structure. In the present Ph.D. project the damping of beams and plates are demonstrated by numerical analysis and experiments.
Main supervisor:
Associate Professor Jan Becker Høgsberg, DTU Mechanical Engineering
Co-supervisors:
Professor Steen Krenk, DTU Mechanical Engineering
Professor Ayech Benjeddou, Supméca (Paris & UTC/CNRS Roberval Lab, (Compiègne), France
Examiners:
Associate Professor Jon Juel Thomsen, DTU Mechanical Engineering
Professor Jean-François Deü, Conservatoire national des arts et métiers (Cnam), Paris, France
Professor Stefano Manzoni, Dept. of Mechanical Engineering, Politecnico di Milano, Italy
Chairman:
Senior Researcher Konstantinos Poulios, DTU Mechanical Engineering