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The aim of this paper is to highlight and identify the influencing parameters of the nonlinear behavior of highly deformable structures. Therefore, as an example, a large deformable square frame consisting of four slender members of equal length has been investigated experimentally. Based on highly resolving measurements using the digital image correlation method (DIC), the inverse problem of nonlinear system identification has been solved by an automatic parameter identification algorithm. For this purpose, a numerical model is set up with a beam finite element model using the absolute nodal coordinate formulation (ANCF), which enables the modeling of geometrical and possible material nonlinearities. The influencing parameters as well as the system properties have been determined by using a genetic optimization algorithm. The impact of the main influencing parameter is carved out by an included sensitivity study. The final model with automatically identified parameters shows high agreement with the experimental setup. With this approach the influences and nonlinearities, e.g. material parameters, rigid behavior, real boundary conditions, etc., come up to surface leading to a deeper understanding of the structural behavior of the system itself. Therefore, the present approach can be utilized for further investigations of nonstandard structures undergoing large deformations. [ABSTRACT FROM AUTHOR]

To suppress vibration and noise of mechanical structures piezoelectric ceramics play an increasing role as effective, simple and light-weighted damping devices as they are suitable for sensing and actuating. Out of the various piezoelectric damping methods this paper compares mode based active control strategies to passive shunt damping for thin plates. Therefore, a new approach for the optimal placement of the piezoelectric sensors/actuators, or more general transducers, is proposed after intense theoretical investigations based on the Kirchhoff kinematical hypotheses of plates; in particular, modal and nilpotent transducers are discussed in detail. Based on the proposed distribution a discrete design for modal transducers is implemented, tested and verified on an experimental setup. For active control the modal sensors clearly identify the eigenmodes, whereas the modal actuators impose distributed eigenstrains in order to reduce the transverse plate vibrations. In contrast to the modal control, passive shunt damping works without requiting additional actuators or auxiliary power and can therefore act as an autonomous system, but it is less effective compensating the flexible vibrations. Exemplarily, an acryl glass plate disturbed by an arbitrary force initialized by a loudspeaker is investigated. Comparing the different methods their specific advantages are highlighted and a significant broadband reduction of the vibrations of up to -20dB is obtained. [ABSTRACT FROM AUTHOR]

Subject of the present work is the stability control of beam-type structures under a compressive force. Main scope of this article is to increase the critical buckling load by means of active feedback control. The compressive force is applied with the help of a cable which is fixed at the tip of the free end and passes through a point at the fixation of the beam. The structural displacement of the column is controlled by a constant gain feedback algorithm, with strain sensors used as input and piezoelectric actuators. A consistent theoretical formulation of this nonconservative system based on the Bernoulli–Euler beam theory is presented. The formulation takes into account the complete mechatronic system, including the influence of the controller with discrete strain measurements as well as distributed piezoelectric patches. The analytical results are compared to numerical simulations. The influence of the controller on the buckling load, the appearance of flutter instability and the limits of the controller’s operation range are highlighted. [ABSTRACT FROM PUBLISHER]

In this paper the influencing factors of the nonlinear behavior of a highly deformable square frame are aimed to highlight and identify. Therefore, in a first step a square frame consisting of four slender members of equal length has been investigated experimentally. Subsequently to these investigations, a numerical model is set up with a beam finite element model, which is based on the absolute nodal coordinate formulation (ANCF), including geometrical and possible material nonlinearities. The influencing factors as well as the system properties are identified by using a genetic optimization algorithm. The final results show that the highly nonlinear behavior of the square frame can be reproduced accurately in case the nonlinear characteristics of the joints are taken into account carefully. The numerical model combined with the system parameter identification can be utilized for further numerical investigations of non-standard structures undergoing large deformations. (© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]