A novel semi-passive morphing airfoil concept based on variable bending-twist coupling induced by adaptive shear center location and torsional stiffness is presented. Numerical parametric studies and upscaling show that the concept relying on smart materials permits effective twist control while offering the potential of being lightweight and energy efficient. By means of an experimental characterization of an adaptive beam and a scaled adaptive wing structure, effectiveness and producibility of the structural concept are demonstrated.

This paper aims at an analytical and numerical analysis of a bistable Duffing equation. One purpose lies in the identification of suitable oscillations for a robust energy harvesting device, i.e. a system that is well suited for a broad bandwidth excitation. A map is constructed illustrating the dependence of the harvested energy on the predominant oscillation type. It shows that inter-well oscillations lead to the highest energy harvest compared to intra-well and cross-well oscillations under harmonic excitation. The determination of the critical excitation parameters necessary to maintain inter-well oscillations is essential for the design of bistable energy harvesters. Therefore, investigations are made to attain an analytical description of the inter-well oscillation region. On this basis, a design criterion is derived for nonlinear energy harvesters.

In this contribution we investigate a bistable energy harvester with regard to its optimal impedance load. A bistable energy harvester exhibits three different types of oscillation: Single-well (about a stable equilibrium), cross-well (between the wells) and inter-well (about the unstable equilibrium). The occurring oscillation type depends, for instance, on the excitation parameters and the initial conditions. It has already been observed ( [1]) that the optimal impedance, which allows to maximize the power output, varies for each oscillation type. In our investigations we complement these findings with analytical and numerical calculations. For our analysis we examine the non-dimensionalized coupled equations of a bistable energy harvester.