Semiactive vibration reduction through stiffness modulation

• Applicant: Professor Dr. Alexander Hasse
• Subject Area: Engineering Design, Machine Elements, Product Development ; Mechanics
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 496813587

Semi-active methods for vibration reduction are usually associated in literature with a good com-promise between active and passive methods. Above all, the comparatively low energy require-ment is often placed in the foreground. The effectiveness (amplitude reduction, avoidance of reso-nances) and the possibilities for application in a wide frequency spectrum or adaptation to differ-ent frequency ranges are on a comparable level to active methods. Vibration reduction by means of cyclic stiffness changes - i.e. changes in the structural stiffness with a similar frequency to the currently prevailing vibration - also falls by definition into the area of semi-active methods, since it involves the modification of a system parameter. However, it must be considered that a change of the stiffness can usually only be achieved with a change of the potential energy and consequently work must be performed. Especially for cyclic change, it is therefore questionable whether such an approach can live up to the ascribed energy efficiency of semiactive methods. In the current state of research, energetic aspects are either not considered or biased due to the use of additional dis-sipative components. An evaluation of the efficiency of cyclic stiffness changes for vibration reduc-tion is therefore still pending. Our own preliminary work has shown that, in particular, the spatial distribution of stiffness chang-es plays a decisive role in the work to be performed. With a homogeneous change of stiffness, am-plitude-reducing effects can be significantly attributed to a negative work of the actuator. With a locally varying stiffness adjustment, on the other hand, energy can not only be extracted from the system, but above all redistributed from the oscillating mode to other modes. This energy redistri-bution has the advantage of making better use of the inherent damping properties of the structure in the higher-frequency region of the energy-absorbing modes. Thus, a large part of the work to be done is omitted and the method shows an efficiency similar to that of classical semiactive methods also under energetic aspects. The long-term goal of the project is to develop a procedure to maximize the semiactive effect (re-distribution of energy to suitable modes) and thus to increase the efficiency of the method for con-tinuous systems. As a mechanism for changing the stiffness, pre-stressing and shape adaptation are considered in particular. However, the temporal and spatial variation of stiffness will be the main focus. These parameters will be analyzed in the proposed project, corresponding laws will be determined and finally design rules and optimization formulations will be established.

• DFG Programme: Research Grants