Dynamic nonlinear aeroelastic model of a kite for power generation

This paper presents a numerical modeling approach for the flight dynamics and deformation of tethered inflatable wings, which are central components of many contemporary airborne wind energy systems. A geometrically nonlinear finite element framework is used to describe the large quasi-static deformations caused by changing bridle line geometry and by varying aerodynamic loading. The effect of the external flow is described in terms of discrete pressure distributions for the different wing sections. The empirical model takes into account the shape parameters of chord length, camber, and thickness per section, and it is derived by fitting precomputed data from computational fluid dynamic analysis. To reduce computation times, local dynamic deformation phenomena are neglected. For each integration time step, the steady aerodynamic loading is determined first and then used to update the static equilibrium shape of the wing. This static aeroelastic model is embedded in a dynamic system model that includes the tether, bridle lines, and kite control unit. The iterative approach can accurately describe bending and torsion of the wing, which contribute to the aerodynamic steering moments. The presented approach is complemented with a flight controller and used to simulate figure-eight flight maneuvers of a leading-edge inflatable tube kite used for traction power generation.