School of Mechanical Engineering Dr. Lea Beilkin
School of Mechanical Engineering Seminar
Wednesday, December 19, 2018 at 14:00
Wolfson Building of Mechanical Engineering, Room 206
ACTIVE CONTROL OF WAVE PROPAGATION IN SYSTEMS.
APPLICATION TO STRUCTURAL VIBRATION, POWER GRIDS
AND MECHANICAL METAMATERIALS
Lea Beilkin
Post-doctoral researcher
Active-Adaptive Control Lab
Department of Mechanical Engineering
Massachusetts Institute of Technology
Wave propagation is central to diverse fields of engineering, and its control might be essential to enable flawless operation of existing processes, as well as for design of new ones. In this talk I will discuss the application of control theory through a dedicated fractional order frequency domain approach, to active manipulation of wave propagation processes in systems. In particular, I will present three examples. The first is vibration suppression in mechanical flexible structures, for which the approach is employed as active rigidization of the structures through their boundaries. The second is swing oscillation damping in electric power grids for flawless power transmission. Treating the power disturbances as electro-mechanical waves, the approach is utilized to suppress those waves using minimal concentrated actuation. The results also lead to a methodology of active uni-directional wave generation in the interior of general waveguides, enabling the design of active wave absorbers without any physical boundaries present. The third is the emerging area of acoustic/mechanical metamaterials, which are engineered structures supporting unconventional wave propagation phenomena. I will discuss the design of active mechanical metamaterials, in which the essential underlying mechanism is feedback control. The control system is implemented only via external actuation, i.e. by using a periodic distribution of actuators attached to the host structure (the representative example is a beam in axial vibration) and activated by a proper control logic. The embedded feedback system generates desired combinations of effective wave characteristics (constitutive parameters), but leaves the properties of the host structure unchanged when the transducers are inactive. The fractional order approach turns out to be the key element in the active metamaterial control design, as the associated model explicitly exhibits the dynamic constitutive parameters, dispersion function and impedance. The resulting metamaterial is tunable and reconfigurable in real time, as it is capable of obtaining a variety of conditions for the same operating frequency, including negative effective mass for wave propagation suppression, zero stiffness and negative mass for total wave blocking, zero mass and infinite stiffness for rigid body motion or double negative parameters for backward wave propagation.