Eddy current damping has been widely applied in mechanical engineering; however, its adaptation for civil engineering applications remains rather limited due to its low density of energy dissipation. This study presents the development of a new type of eddy current damper and theoretical and experimental characterization of its damping properties. In addition to rectangular permanent magnets and conductive plate, both primary back iron and secondary back iron are considered in the proposed eddy current damper, which represents an improved design over previous configurations. The analytical method based on the charge model of permanent magnets is extended to simulate the extra damping effect of the primary back iron and secondary back iron, and the magnet field and damping properties of the dampers are evaluated analytically. The use of a back iron in the proposed damper is shown to increase the damping coefficients by a factor of up to 5. The analytical results are compared with those obtained with the finite-element analysis in terms of accuracy in magnetic field distributions, eddy current distributions, and damping coefficients. The linear assumption, which implies the damping force is linearly proportional to velocity in the analytical model, is also examined for different motional velocities and relative permeability of the permanent magnet. It is shown that the linear damping assumption in the analytical model is only valid for a limited range of low velocity, and this velocity range can be increased by reducing the thickness or conductivity of the conductive plate. In addition, a modification is needed for the analytical model if the relative permeability of the permanent magnet significantly deviates from the assumed value of 1.0. Finally, the accuracy of the analytical model and the finite-element model is verified by experiment of a prototype damper mounted in a laboratory steel frame.

Undesirable vibrations occurring in undersea pipeline structures due to ocean currents may shorten the lifecycle of pipeline structures and even lead to their failure. Therefore, it is desirable to find a feasible and effective device to suppress the subsea vibration. Eddy current tuned mass damper (ECTMD), which employs the damping force generated by the relative movement of a non-magnetic conductive metal (such as copper or aluminum) through a magnetic field, is demonstrated to be an efficient way in structural vibration control. However, the feasibility and effectiveness of ECTMD in a seawater environment has not been reported on before. In this paper, an experiment is conducted to validate the feasibility of an eddy current damper in a seawater environment. A submerged pipeline is used as the controlled structure to experimentally study the effectiveness of ECTMD. The dynamic properties of the submerged pipeline are obtained from dynamic tests and the finite element method (FEM). The optimum design of TMD with a linear spring-damper element for a damped primary structure is carried out through numerical optimization procedures and is used to determine the optimal frequency tuning ratio and damping ratio of ECTMD. In addition, the performance of ECTMD to control the submerged pipeline model is respectively studied in free vibration case and forced vibration case. The results show that the damping provided by eddy current in a seawater environment is only slightly varied compared to that in an air environment. With the optimal ECTMD control, vibration response of the submerged pipeline is significantly decreased.