Vibration Transmission Reduction Through Multi-Element Multi-Path Structural Design in Thin Beams and Cylindrical Shells

Abstract

Unwarranted vibrations create adverse effects that can compromise structural integrity, precision and stability. This thesis explores an attenuation technique that rethinks the design of simple lightweight flexible structures, providing an alternative to the current methods of active controllers and heavy damping. Through multi-element/multi-path (MEMP) design, a structure is divided up into several constituent substructures with separate, elastically coupled, wave transmission paths that utilize the inherent dynamics of the system to achieve substantial wide-band reductions in the low frequency range while satisfying constraints on static strength and weight. Attenuation is achieved through several processes acting in concert: different subsystem wave speeds, mixed boundary conditions at end points, interaction through elastic couplings, and stop band behavior. The technique is first introduced into thin beams coupled with discrete axial and torsional springs, resulting in wide-band attenuation and agreement between analytical simulations and experimental studies. MEMP design is then implemented into concentric thin cylindrical shells, providing a more three-dimensional study with axially discrete azimuthally-continuous elastic connectors. By employing a modal decomposition of the governing shell equations, simulations reveal more opportunities for attenuation when subjected to various forcing conditions. Future work examines the effect of MEMP shell design on acoustic scattering reduction.