A state-switched absorber (SSA) is a device that is capable of switching between discrete stiffnesses, thus it is able to instantaneously switch between resonance frequencies. The state-switched absorber is essentially a passive vibration absorber between switch events; however, at each switch event the SSA instantly 'retunes' its natural frequency and maintains that frequency until the next switch event. The SSA has shown improved performance over classical tuned vibration absorbers at reducing the vibration in a base system. This paper considers the optimization of the state-switched absorber applied to a continuous vibrating system. The objective function to be minimized in the state-switching system is the average kinetic energy of the base to which the absorber is attached. Due to the discrete nature of the switch events of the SSA, this objective function is discontinuous as a function of tuning parameters, such as frequency and attachment location. Because of the discontinuities in the objective function, classical gradient-based optimization techniques cannot be employed. To avoid the problem of discontinuities in the objective function, a heuristic approach will be utilized to optimize the state-switched absorber. The optimized performance of the state-switched absorber will be compared to that of an optimized classical tuned vibration absorber. For the entire range of forcing frequencies considered, an SSA has improved performance over a TVA.
This paper considers the optimization of the performance of a state-switched absorber (SSA) in controlling the vibration of a continuous beam. A state-switched absorber has the capability to instantaneously change its stiffness, which allows the absorber to 'retune' to a new natural frequency instantaneously. Between each 'retuning', or switch event, the SSA is essentially a passive device, tuned to the resonance frequency of its current state. With proper switching logic, the SSA shows improved performance in vibration control as compared to classical passive devices when the excitation contains more than one frequency component. The SSA considered here is capable of switching between only two discrete stiffnesses. A direct search algorithm is employed for optimization of the absorber's location along the beam as well as the two tuning frequencies needed to achieve the best performance of the state-switched absorber. Several two-frequency component point excitations are considered at a few locations along the beam and over a range of frequencies. The optimized performance of the state-switched absorber is compared to the optimized performance of a classical tuned vibration absorber (TVA) for each forcing case.
A state-switched device is conceptually capable of instantaneously changing its mass, stiffness, or damping. Such a device will exhibit different dynamical response properties (modes and resonance frequencies) depending on its current state. A state-switched vibration absorber exploits the state-switching concept for the purposes of enhanced vibration suppression. Between each state switch, it is fundamentally a passive vibration absorber, but one which exhibits a different tuning frequency for each possible state. A state-switched vibration absorber therefore has a greater effective bandwidth than a classical passive absorber. This paper considers the role of damping in the state-switching concept for a simple one-degree of freedom system and for a two-degree of freedom system. Certain values of damping in the system improve performance, while other values hinder the performance of the state-switched absorber, as compared to classical absorbers. The predicted performance of the system also depends upon the particular damping model used, such as proportional, viscous, or modal damping. Damping values also affect the frequency of switch events that occur during the response of the system. In general, a state-switched absorber with optimized damping is more effective at vibration suppression as compared to a classical vibration absorber with optimized damping.
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