Aerodynamic Instabilities of Thin-walled Structures for Driving Novel Energy Harvesters - Numerical Simulation Method, Physical Effects and Analytical Model

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Aeroelastic phenomena such as flutter are of major relevance for the design of light engineering structures such as aircraft wings and bridges. These line-like structures have cross sections that approximately retain their shape and they are designed not to flutter. In contrast, novel concepts of energy harvesting are based on extracting energy from aeroelastically unstable thin-walled structures that undergo bending. These are designed to have a low flutter onset wind speed and they exhibit large cross sectional deformations. Important factors influencing the dynamic response of these elements are atmospheric turbulence and geometric nonlinearities. Parameters of interest in the context of practical applications are onset wind speed, extractable energy and structural demand. In order to study the underlying fluid-structure interaction mechanisms of such and many other similar structures in detail, to quantify the important parameters influencing the behaviour and to facilitate an optimisation of the system, analysis models are required. Here, a numerical simulation method on the basis of Vortex Particle Methods (VPM) shall be developed, which couples a geometrically nonlinear structural dynamics Finite Element formulation with a new extension of the Boundary Element Method of the VPM, thus accounting for large deformations of the solid interface geometry. Further, recent developments for modelling atmospheric turbulence shall be applied, in order to be able to account for the gustiness of the natural wind. The method will be developed and implemented in a generalised manner that allows the application to other problems such as light roof structures. Here, the concept of a new electromagnetic energy harvester shall be used as a reference object. Prototype models will be tested in the wind tunnel in order to validate the simulation methods. The dynamic response of the structure will be measured in detail during the tests. The numerical model will then be used to quantify relevant aspects with regard to efficiency of and structural demand on the harvester. Finally, a new analytical model for the quantification of the self-induced fluid dynamic forces on thin-walled structures shall be developed, which extends the concept of Scanlan Derivatives. This model would allow simplified analytical stability analyses and facilitate studies of parameters influencing the system behaviour.