Chapter 17 Analytical and Experimental Study of Eddy Current Damper for Vibration Suppression in a Footbridge Structure Wai Kei Ao and Paul Reynolds Abstract Eddy current damping has been extensively developed in recent years and is widely used in the mechanical engineering sector, for example, in railway and turbine braking systems as well as in car vibration control systems. Vibration control approaches for civil engineering structures still usually rely on more traditional approaches, such as viscous and tuned mass dampers. The use of novel Eddy current damping devices has the potential to complement these traditional approaches and is the focus of the work presented here. The Eddy current damper (ECD), which is a kind of electromagnetic induction damper, comprises a permanent magnet, a conductor and framing components. In this study, an ECD is developed and investigated to provide an alternative to viscous dampers that often exhibit undesirable non-linear characteristics arising from friction. Since the moving components of an ECD are not in contact, the influence of friction is negligible. A finite element model is initially used to evaluate the ECD damping properties and employed on a footbridge structure. The finite element and analytical results demonstrate satisfactory augmentation of damping effect under both random and harmonic signal input. Keywords Eddy current damper (ECD) • Permanent magnet • Conductive material • Electromagnetic forces • Method of image 17.1 Introduction The research work described here focuses on improving the vibration serviceability performance of civil engineering structures, for example, buildings, floors and footbridges subjected to different types of dynamic excitation. This is required since increasing problems with vibrations have been observed as a consequence of the increased use of very slender and flexible structures with low inherent damping. Previously, there have been many approaches used to tackle vibration serviceability problems, including passive (e.g. tuned mass dampers (TMD), viscoelastic dampers (VE) and friction dampers), active (e.g. active mass dampers) and semiactive (e.g. magnetorheological dampers) techniques. As an alternative to traditional vibration suppression devices, Eddy current damping (ECD) devices have been proposed to suppress system vibrations in the mechanical sector. The concept of passive ECD is to utilise relative motion between a permanent magnet and a conductor to create a resistance force. For a braking system [1], a cylindrical magnet and conductor plate of arbitrary shape were chosen to provide Eddy current damping according to their relative motion. After that, a simple theoretical study of rectangular magnet and conductor geometry ([2] and [3]) was developed. It included a calculation of induced electrical intensity during the conductive plate passed through a rectangular geometry magnet. Coulomb’s law was used and assumed the magnet had an infinite boundary. A simple example of ECD is shown in [4], which considers the example of a neodymium magnet dropping through a conductive tube. In this example, the magnet is slowed as a result of resistance forces developed by the induced Eddy currents in the tube. This simple model illustrates resistance to motion, which can be used to generate vibration damping via fundamental electromagnetic induction theory. Some other examples have been used in a small scale structure [5] and [6], where a non-contact Eddy current damper was applied to perform vibration suppression on a small scale cantilever beam. These are just some of a large number of previous ECD studies that illustrate the use of this induced resistance force to attenuate vibration. W.K. Ao ( ) • P. Reynolds Vibration Engineering Section, College of Engineering, Mathematics and Physical Sciences, University of Exeter, North Park Road, Exeter EX4 4QF, UK e-mail: wka203@exeter.ac.uk; p.reynolds@exeter.ac.uk © The Society for Experimental Mechanics, Inc. 2017 J. Caicedo, S. Pakzad (eds.), Dynamics of Civil Structures, Volume 2, Conference Proceedings of the Society for Experimental Mechanics Series, DOI 10.1007/978-3-319-54777-0_17 131
RkJQdWJsaXNoZXIy MTMzNzEzMQ==