<p>Vibration isolation often involves inertially coupled systems that are tuned to provide antiresonance at a specific target frequency, independent of the isolated mass. The oscillation of the auxiliary inertia cancels the stiffness induced in spring structures in discrete dynamic systems, thus allowing for a complete reduction of force or displacement transmissibility to the isolated body. This paper investigates antiresonance in continuous dynamic systems consisting of beam networks with inherent inertial coupling. As a proof of concept, an analytical transfer function model is developed to predict the isolation behavior of a cantilever beam with a tip mass. The analytical results are validated with an experimental study whereby the shear force is recorded at the root of a cantilever beam with a tip mass that is subject to harmonic point force excitation. The experimental results show that the root shear response at the first isolation frequency is reduced by 79% after the addition of a tip mass equivalent to 230% of the beam mass. Extensions to multi-beam isolator networks are discussed, whereby a beam network is tuned to provide isolation at different frequencies with different types of input. It is shown that the isolation forces generated by the oscillation of the auxiliary mass, as well as the stiffness of the beam network are both linear with the number of beams, thus allowing for superposition to be applied to increase or decrease the isolation as well as the stiffness. Using the method of superposition allows for the stiffness and the isolation forces to increase or decrease with no effect on the natural frequencies of the structure. The analytical model is also used to quantify the vibration behavior of the beam network for two different tuning methods. Tuning each beam to provide root shear force isolation at a specific single frequency results in complete isolation if the damping is negligible. On the other hand, tuning the beams to have different isolation frequencies would allow for partial isolation over a specific frequency range, thus the structure will have a reduced dynamic stiffness over a specific range of frequencies. Furthermore, a nondimensional analytical model is developed and used to show the effect of various parameters such as beam length, position of the input, and tip mass. Nondimensional design graphs are developed and used as a guideline for specific beam-based tuning and structure-based tuning. The results of this study are then used to discuss the utility of beam network structures in helicopter and engine vibration isolation applications.</p>

Vibration Isolation in Continuous Beam Networks

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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