An adaptive pneumatic system for the attenuation of random vibrations

Adaptive suspensions can modify their filtering capacity to better accommodate excitations with different characteristics. The modification of stiffness (and, to a certain extent, damping) is particularly simple in pneumatic systems. The authors have proposed, modeled, analyzed, validated and tested a pneumatic suspension (composed of an air spring, an auxiliary tank and several connecting pipes) the transfer function of which can be modified simply by routing the air flow through the desired pipe. The method has been successfully tested in the case of unbalanced machinery. Procedures to estimate the input frequency have also been proposed for more general cases, but the question remains as to whether the adaptive scheme could be useful in the case of random excitations composed of a sizable range of frequencies. The focus of the work presented in this paper is to shed some light on this question. To this end, a suspension prototype is subjected to random inputs where the frequency content is tuned to increase the relative ‘weight’ of low frequencies, high frequencies or intermediate frequencies. The responses obtained using three different passive configurations, as well as an adaptive approach that can continuously choose among all three, are simulated, tested and compared. It will be shown that adaptation can minimize the root mean square displacement of the random response even in cases where there is significant overlap in the frequency content of the different types of input.