Energy harvesting from oscillating structures receives a lot of research attention as these applications appear promising for the continuous energy supply of low power devices. Recent studies indicate increased power production of piezoelectric energy harvester configurations undergoing severe nonlinear vibrations, but the obvious drawback is the increased complexity of the coupled electromechanical dynamic response of the harvester. The current study focuses on the development of a robust and accurate numerical tool capable of modelling and design of such systems. This model is used to simulate the electromechanical response of composite strip structures equipped with piezoelectric devices subjected to nonlinear oscillations under compressive loading and near buckling instability conditions. The study is combined with experimental verification studies on a fabricated harvester prototype aiming to validate the numerical tool and to corroborate the electrical voltage generation on the piezoelectric devices. Additionally, a preliminary experimental study is performed to quantify the available electrical energy that is produced from the oscillating structure. Three different harvesting circuits are studied and their energy conversion performance is investigated. Measured results validate the developed numerical tool. Moreover, the increased electrical voltage and charge generation during the geometrically nonlinear oscillations as the prebuckling load increases, increasing also the available electrical power on the circuits, is illustrated numerically and experimentally.
The present paper investigates the nonlinear dynamic electromechanical conversion capability of axially prestressed piezoelectric strips, vibrating under transverse mechanical impulsive forces. A computational structural dynamics framework is adopted, comprising a mixed-field laminate plate theory together with an eight-node coupled plate finite element, that encompass nonlinear effects due to large rotations and initial stresses. The dynamics incorporate all linear and nonlinear coupling terms between mechanical and electric fields, and emphasis is given on the presentation and analysis of nonlinear stiffness and electromechanical coupling terms that affect the electric charge and energy in the piezoelectric devices. The resultant discretized equations of motion are finally linearized and solved using the Newmark implicit time integration scheme in combination with the Newton-Raphson iterative technique. Numerical evaluation cases investigate the nonlinear vibratory response and the electromechanical energy conversion capacity of prestressed vibrating piezoelectric strips excited by transverse impulsive forces. The effect of axial preloading and transverse dynamic loading on both the nonlinear dynamic electromechanical response and electromechanical energy conversion is quantified.