On the design of electromechanical vibration isolators and energy harvesters

Author(s)

Willian Minnemann Kuhnert

• Document type: Doctoral Thesis
• Press: Bauru. 2020-10-05.
• Institution: Universidade Estadual Paulista (Unesp). Faculdade de Engenharia. Bauru
• Defense date: 2020-09-03
• Advisor: Paulo José Paupitz Gonçalves; Andrea Cammarano

Abstract

Conventional vibration isolators have been used for a long time to isolate a receiver from a source of disturbance and probably the most popular application are in vehicle suspensions, which are essentially composed by spring and damper elements. The damper element is responsible for converting the mechanical energy, originated by the external disturbances, into heat during the damping process. The idea of recovering part of this energy has become an attractive topic among researchers in the last decades and the energy harvesting process became a hot topic. Usually, the energy harvesting requires the use of electromechanical systems and much work has been done in the field. Among the alternatives to realize the energy harvesting is the electromagnetic damping, which is a phenomena that the literature lacks, somehow, detailed information on its behavior, focusing more on building and testing new electromechanical devices rather than understanding the phenomena itself. In this context, a study was performed on the replacement of the damper element by electrical circuits coupled to the mechanical system through a permanent magnet and coil transducer, or in short: electromagnetic shunt dampers. The goals were to understand the effects of the electromagnetic damping on the electromechanical systems by providing design expressions for several conditions considering the linear systems, and lastly to understand the effects of introducing hardening and softening nonlinear behavior to the system stiffness and analyze its pros and cons regarding the dynamics, and the vibration isolation and energy harvesting capabilities compared to the linear systems. Different electrical circuits were considered to study the linear systems, and free and forced vibration cases were studied to obtain the critical damping and optimal damping that reduce the maximum peak in the frequency response function under Den Hartog's methodology. The optimal damping for white noise excitation and the energy harvesting optimal conditions were obtained using standard differentiation procedures. The results for the linear system coupled to one of the studied electrical circuits were validated experimentally, presenting a good agreement between numerical and experimental data regarding the frequency response functions. Furthermore, the nonlinear stiffness was introduced to the electromechanical systems, and the study was performed by computing backbones, bifurcation diagrams and basins of attraction through the use of numerical continuation and integration, and harmonic balance methods. The design equations were obtained and tabulated for ease of reference, and the main conclusions were that the damper element can be fully replaced by an electromagnetic damper; the coupled electrical circuit greatly influences the dynamics of the system, even introducing the relaxation effect; that the softening nonlinearity can enhance vibration isolation; that hardening can be used for broadening the band of energy harvesters through the tuning on the isolated responses encountered and; that the same isolated responses are a risk for vibration isolation as the excitation frequency and/or nonlinearity severity increases. (AU)

• FAPESP's process: 16/17083-4 - Exploiting Nonlinearities for Energy and Comfort Optimization in Electromechanical Vehicle Suspension Systems
• Grantee: Willian Minnemann Kuhnert
• Support Opportunities: Scholarships in Brazil - Doctorate