Multi-resonant TVA formed by a tree of deflated composite beams with core structured fabrics

This paper presents a study on a multi-resonant tuneable vibration absorber for the control of flexural vibrations of thin structures in a low frequency band where the response is characterized by distinct lightly damped resonances of low order flexural modes. The absorber is formed by a tree of deflated composite beams made by a core structured fabric wrapped on a plastic skin. The beams have increasingly smaller length and are fixed in the middle on a mast that works as a base-post and vacuum-junction too. The fabric in each beam is made by a lattice of interlocked truss-like rigid particles. The uniform pressure exerted by the deflated skin forces the particles to jam such that the fabric moves from its natural fluid-like state to a solid state whose rigidity depends on the confining pressure exerted by the skin. Hence, each beam is characterized by a fundamental flapping vibration mode whose response resembles that of a classical mass-spring-damper vibration absorber and can be suitably tuned by adjusting the level of vacuum. The paper first analyses the working principles of single-beam and three-beams absorbers with respect to their vibration transmissibility and base impedance frequency response functions. Then, it presents the vibration control generated by the single-beam and the three-beams absorbers tuned to minimise the resonant responses of a single or three low order flexural modes of a thin plate. The paper shows that the operational frequency of each beam-absorber can be suitably adapted in a band of 8 Hz by varying the vacuum pressure in a 5–80 kPa range. Also, it shows that the single-beam or multi-beams absorbers reduce the resonant response of the target flexural modes by 10–20 dB.