Experiments on vibration absorption using energy sinks
(Color online) A primary mass that consists of a steel block in an air bearing and a set of pendulums that act as an energy sink.
Response of the primary mass in Fig. 1 with (dark) and without (gray) the attached pendulums. Each figure corresponds to a different uncoupled natural frequency of the primary structure obtained by using springs that have different stiffness. The differences in the decay of free vibration amplitude result from the different loss factors associated with each spring pair. In each figure represents the loss factor of the primary alone, and represents the loss factor of the primary with the attached oscillators. In each case the mass ratio is 9% and the frequency distribution of the pendulums is unchanged, ranging between 0.58 and . (a) , (b) , (c) , (d) , (e) , (f) , (g) , (h) .
(Color online) Snapshots of pendulums following an initial displacement provided to the primary mass. During the initial periodic energy exchange between the primary, pendulums maintain a coherent wave-like configuration (left) and after a time when energy is retained mostly by the pendulums.
(Color online) Oscillators attached to the same primary structure shown in Fig. 1 through a light-weight superstructure built on it. Each oscillator consists of a small mass attached to a steel wire that permits adjustment of its natural frequency by changing the position of the mass on the wire. The figures show sets of 24, 40, and 69 oscillators.
Impulse response of the block (left) without the attached oscillators and that of an individual oscillator shown in Fig. 5 .
(Color online) Response of the primary structure (block) with a set of 40 oscillators all with the same natural frequency, effectively reducing the system freedom to two degrees. In each case the uncoupled natural frequency of the block is . From top the oscillators have a constant frequency of , 4.08, and as indicated by the arrows. The response in time domain shows the expected beats.
(Color online) Response of the same system shown in Fig. 6 but with linear and optimum frequency distributions. In both cases the vibration amplitude of the block is reduced significantly. The optimum distribution (right) further reduces the response and spreads the energy over a larger set of frequencies.
(Color online) A primary structure that consists of two beams connected in a T-configuration. Attached thin beams act as a set of oscillators vibrating at their fundamental frequencies, which follow an optimum distribution. Impulse excitation is applied at the point indicated by the arrow.
(Color online) A comparison of the response of the primary structure shown in Fig. 9 without (a) and with (b)–(d) the attached oscillators. In (c) and (d), the fundamental frequency of the primary structure coincides with the lowest and the highest value in the frequency band of the oscillators, respectively. In both (a) and (b), the primary natural frequency is . The comparison clearly shows the effects of the attached thin beams.
(Color online) A comparison of the response of the primary structure shown in Fig. 9 with and without the attached oscillators. The presence of thin beam oscillators spreads the energy over their frequency band, reducing the amplitude of the primary significantly.
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