Alain de Solminihac PhD Researcher ENSTA Bretagne 2 rue Francois Verny
29200 Brest France
alain.de_solminihac@ensta-bretagne.org www.ensta-bretagne.fr
Kite as a Beam – An Analytical 3D Kite Tether Model
Alain de Solminihac1, Alain Nême1, Kostia Roncin1, Jean-Baptiste Leroux1, Christian Jochum1, Yves Parlier2 1ENSTA Bretagne
2beyond the sea R This work is part of the beyond the sea R research
pro-gramme lead by the LBMS laboratory of ENSTA Bretagne in collaboration with the French skipper Yves Parlier. The project attempts to develop a tethered kite system as an auxiliary device to the propulsion of merchant ships. To design new large wings, flow structure interaction and non-linear stiffness must be taken into account. To-day, fully coupled FEM/CFD simulation of a soft struc-ture is possible but still requires too much computational time for design purposes. Nevertheless, Breukels [1] and Bosch [2] developed different structural models consid-ering rigid bodies, springs and, more recently, membrane elements. In this context, the purpose of this study is to consider the kite structure as being only an assembly of equivalent beams to reduce computational time as much as possible.
A kite can be considered as a succession of several el-ementary cells distributed along the span. Each one is composed of a segment of the inflatable leading edge, two lateral battens and the corresponding portion of canopy. From a static point of view, this elementary cell is exposed to a pressure distribution and suspended at its four corner points.
A suitable method is used to reduce the stiffness of each elementary cell to the one of an equivalent beam par-allel to the leading edge. Several nonlinear FEM analy-ses (AbaqusTM) were carried out for each elementary cell
exposed to a homogeneous pressure followed by a set of linear perturbation computations. Consequently, me-chanical properties of equivalent beams (axial, bending,
and torsion stiffness, shear transfer coefficients) and their locations were identified. Thus, a whole kite structure model was built as an assembly of beams connected with rigid bodies as illustrated in the figure.
elementary cell equivalent beam rigid body
This simplified structural model can be coupled with a fluid model, like the 3D lifting line method of Leloup [3] to provide information about kite behaviour.
References:
[1] Breukels J. Schmehl R., Ockels W.: Aeroelastic Simulation of Flex-ible Membrane Wings based on Multibody System Dynamic. In: Air-borne Wind Energy. Springer (2013)
[2] Bosch A., Schmehl R., Tiso P., Rixen D.: Nonlinear Aeroelasticity Flight Dynamics and Control of a Flexible Membrane Traction Kite. In: Airborne Wind Energy. Springer (2013)
[3] Leloup R., Roncin K., Bles G., Leroux J.-B., Jochum C., Parlier Y.: Estimation of the Lift-to-Drag Ratio Using the Lifting Line Method: Application to a Leading Edge Inflatable Kite. In: Airborne Wind En-ergy. Springer (2013)
