Vibration Reduction by Stiffness Modulation -- a Theoretical Study

TL;DR

This theoretical study investigates how stiffness modulation can reduce vibrations by distinguishing between semi-active and pseudo-active effects, emphasizing the importance of spatial distribution of stiffness changes for effective vibration control.

Contribution

It provides a novel analysis of the energy effects in stiffness modulation, clarifying the roles of semi-active and pseudo-active effects and their dependence on spatial distribution.

Findings

Localized stiffness changes enhance semi-active vibration attenuation.

Homogeneous stiffness modulation mainly produces pseudo-active effects.

Discrimination between energy redistribution and external energy injection is established.

Abstract

Semi-active vibration reduction techniques are defined as techniques in which controlled actions do not operate directly on the system's degrees of freedom (as in the case of active vibration control) but on the system's parameters, i.e., mass, damping, or stiffness. Cyclic variations in the stiffness of a structural system have been addressed in several previous studies as an effective semi-active vibration reduction method. The proposed applications of this idea, denoted here as stiffness modulation, range from stepwise stiffness variations on a simple spring-mass system to continuous stiffness changes on rotor blades under aerodynamic loads. Semi-active systems are generally claimed to be energetically passive. However, changes in stiffness directly affect the elastic potential energy of the system and require external work under given conditions. In most cases, such injection or extraction of energy (performed by the device in charge of the stiffness variation and denoted as the pseudo-active effect) usually coexists with the semi-active effect, which operates by redistributing the potential energy within the system in such a way that it can be dissipated more efficiently. This work focuses on the discrimination between these two effects, which is absent in previous literature. A first study on their dependence on the process parameters of stiffness modulation is presented here, with emphasis on the spatial distribution of the stiffness changes. It is shown that localized changes tend to result in a larger semi-active share of vibration attenuation, whereas a spatially homogeneous stiffness modulation only generates a pseudo-active effect.