Nonlinear vibration control of long, flexible structures employing inter-modal energy transfer (modal damping)

In the not too distant past, the design philosophy for tall civil structures could be summarized as LARGE MASS-LARGE STIFFNESS. Advances in material science and design technologies provide the means to explore and construct high-reaching, expansive and much lighter-duty geometries requiring not only extensive strength-based engineering but also carefully executed motion-based analysis as such structures are prone to transverse vibrations. Complicating matters, the inherent natural damping properties of such structures are small, leading to drawn out settling times. Motion-based augmentations offer enabling solutions. 'Modal Damping' (MD) exploits damping mechanisms inherent in structures by capitalizing on distinctive dynamic properties existing among the structures vibration modes. An automated, nonlinear control scheme was developed to transfer energy from the fundamental vibration mode, where most vibration energy of the structures of interest resides, to higher order modes where vibration impedance was shown to be more effective. To achieve this objective, MD employs motion control forces self-powered by the redistribution of fundamental mode kinetic energy making the strategy highly efficient. The MD conceptual basis, its dynamic simulation implementation, and the simulation results and analysis are presented herein.