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In this article, nonlinear dynamics tools are employed to quantify the ability of pendulum harvesters to recover energy from the sea waves. The versatility of pendulum harvesters is highlighted, as it is shown that devices can be scaled to produce a usable energy from 6 W to 10 kW. Several aspects of the pendulum's dynamics having a key influence on power generation are discussed by means of bifurcation diagrams, parameter spaces and basins of attraction. Parameter ranges that minimize the need for a control action are identified, and an explanation is provided on why tilting the pendulum's plane of rotation improves power generation. A practical mathematical model of the parametric pendulum is formulated for such purpose. This model incorporates the possibility of accounting an arbitrary number of concentric masses, while allowing a simple and direct correlation between dimensionless approaches and the myriad possible physical configurations of the system.

The dynamic response of a thin-walled beam with a breathing crack is studied by employing a refined one-dimensional model introduced for such purpose. It is shown that, due to the nonlinearity of breathing, some effects take place which are impossible by using a completely open crack model. Even with the simplest of sinusoidal excitations, the system under study reveals a rich and complex dynamics. Some of the topics emphasized in the article are self-excitation of harmonic resonances, period doubling and the presence of quasi-periodic motion. Furthermore, the possibility of chaotic vibrations is analyzed.

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