A Tuned Mass Damper Design Based on Eddy Current Damping

Abstract

All dynamic structures encounter vibration during their operation. A structure experiences the vibration load in an amplified manner at structure’s natural frequencies. If the amplitude of vibration load is high enough, this may damage the structure. Tuned mass dampers (TMD’s) are one of the passive vibration control methods to prevent mechanical failure. A TMD, which has good applicability in space applications, is designed in this study. Reliability is chosen as the key concept of the design since the TMD is going to operate at space, where maintenance is not an option. A literature survey is carried out to find the best concept for the application. It is found that a passively controlled classical TMD with eddy current damping (ECD) mechanism is the best candidate for the application. In ECD, a permanent magnet which moves in proximity of a conductive material creates eddy currents within the conductor. These eddy currents create electromagnetic force on the magnet and this force tries to counter act to the motion of the magnet. Therefore, damping is achieved which is analogues to the viscous damping. ECD is created by placing a permanent magnet inside of a conductive tube in this thesis. After the system architecture of the damping mechanism is determined, analytical model of the TMD is prepared. This model consists of mass, damping coefficient and stiffness of the TMD. It is found in the literature that as the frequency of the excitation increases, damping coefficient of the ECD decreases. This phenomenon is called as the skin effect. A dynamic damping coefficient model which includes the skin effect is found. Although the effect of the skin effect on the ECD is known, it seems that there is no detailed study related to couple the skin effect with the damping coefficient in a scenario where a magnet is moving inside of a conductive tube. In order to observe the effect of the TMD, a test structure is required in which the dynamic characteristics around its natural frequency are to be controlled. This structure is chosen to be a simple cantilever beam which has a rectangular cross section. Fundamental natural frequency of this cantilever beam is chosen to be controlled. Analytical model of this cantilever beam is prepared. Then, coupling of the TMD and cantilever beam is modeled to simulate the assembly of the TMD to the cantilever beam. Afterwards, response of this system is modeled. In order to observe the effects of the TMD, response of the cantilever beam alone is also modeled. These responses are modeled under a harmonic sweep forcing excitation. The design of the TMD is optimized to have maximum ECD possible. After the design of the TMD, two dedicated experimental setups are designed to measure steady-state damping coefficient and the system response. It is shown that the experimental results are found to be consistent with respect to theoretical results. Therefore, it can be concluded that a TMD based on ECD was successfully designed, analyzed and tested.