The airborne wind energy (AWE) technology aims to utilise tethered wings to harvest wind energy at altitudes conventional wind turbines cannot reach. There are two distinct methods to harvest airborne wind energy: onboard and ground-based generation. The onboard generation is achieved through flying fast manoeuvres driving propellers attached to the tethered wing, while the generated electricity is conducted through the tether. On the other hand, the ground-based generation utilises the tether tension of the kite to unwind it from a drum, driving a generator. When the tether is fully extended, it is reeled in by the generator, which consumes energy. Since the traction phase is a lot longer and produces a lot more electricity than electricity needed in the reel-in phase the net energy of such a cycle is positive. SkySails Power is one of the leading companies developing a ground-based AWE generator driven by a large ram-air kite. This thesis describes the development of a methodology for simulating their wing.@en

We present a multidisciplinary design optimization method for the profile and structural reinforcement layout of a ram‐air kite rib. The aim is to minimize the structural elastic energy and to maximize the traction power of a ram‐air kite used for airborne wind energy generation. Because of the large deformations occurring during flight, a fluid‐structure interaction (FSI) routine is included in the optimization, which determines the actual deformed rib geometry and its corresponding aerodynamic characteristics. A qualitative comparison between FSI inclusion and exclusion in the optimization is given. Discrepancies in airfoil profile and structural layout are observed.@en

We present a computationally efficient steady-state solution method to model the aeroelastic deformation of a ram-air kite for airborne wind energy applications. The kite’s weight in comparison to the aerodynamic forces is small which justifies a quasi-steady analysis, neglecting gravitational and inertial force effects [1]. The approach is suitable to efficiently determine the deformed configuration of a ram-air kite for design and optimization purposes as found in [2]. Because of the expected large deformations and changes in the flow field, fluid-structure interaction has to be taken into account in the analysis. @en

We investigate inflatable kites made of membranes such as ram-air [1] and leading edge inflatable [2] kites. The kites are very flexible and therefore exhibit a strong coupling between fluid and structure. An accurate aerodynamic model is essential to design kites which are aerodynamically efficient and of high steering capability@en

Ram-air kites are made of thin coated woven fabric and are attractive for the airborne wind energy industry due to their low weight and easy storage ability. The aerodynamic load is transferred from the top canopy through the ribs into the bridle system causing high stresses on the ribs. In order to spread the load as equally as possible, reinforcements are added on the ribs which also sustain the airfoil shape. The most common reinforcement strategy is to simply sewadditional fabric onto highly stressed locations of the ribs. For the kite designer one of the challenges is to find a balance between the right amount and orientation of reinforcements, and the extra weight added to the structure. In this study the layout of a rib reinforcement used in ramair kites is expressed as an optimization problem. The objective is to find an optimum reinforcement layout such that the deformation of the rib is minimized. Also, the force fromthe kite acting onthe tether is included into the expression and should be maximized, leading to a multidisciplinary optimization (MDO). For simplicity, the optimization is initially done in a twodimensional analysis of the flow and structure. To obtain the aerodynamic pressure acting on the rib the panel method software XFOIL [1] is utilized. The resultant deformations are computed with the finite elementmethod which takes the position of the reinforcements into account, augmenting the element’s stiffness based on [2]. Finally the optimum layout is found with a gradient based optimization method. The optimization is easily extendable to 3D which will eventually yield a more realistic load case acting on the rib structure due three-dimensional floweffects. Also the inflated kite structure in three dimensions behaves considerably different due to the curvature of the canopy. @en