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.

半主动减振技术定义为这样一种技术，其中受控动作不直接根据系统的自由度（如主动振动控制的情况）而是根据系统的参数（例如质量，阻尼或刚度）进行操作。

结构系统刚度的循环变化已在先前的几项研究中作为有效的半主动减振方法得到解决。这种想法的建议应用（这里称为刚度调制），范围从简单的弹簧质量系统上的逐步刚度变化到在空气动力载荷下转子叶片上的连续刚度变化。

一般认为半主动系统在能量上是被动的。但是，刚度的变化直接影响系统的弹性势能，并且需要在给定条件下进行外部工作。在大多数情况下，这种能量注入或提取（由负责刚度变化的设备执行，并表示为伪主动效应）通常与半主动效应共存，半主动效应通过重新分配系统中的势能来进行。这样可以更有效地消散它。

这项工作着重于这两种效应之间的区别，这在以前的文献中是不存在的。本文介绍了它们对刚度调制过程参数的依赖性，并重点研究了刚度变化的空间分布。结果表明，局部变化往往会导致较大的半主动振动衰减份额，而空间均一的刚度调制只会产生伪主动效应。