Modelling and analysis of rotary airborne wind energy systems : a tensile rotary power transmission design

Airborne wind energy is a novel form of wind power. Through the use of lightweight wings and tethers it aims to access locations out of reach to current wind harvesting devices, at a lower cost and with a lower impact on the environment. There are multiple airborne wind energy systems currently under development, one group of these, referred to as rotary systems, use multiple wings networked together to form rotors. This thesis presents an analysis on the design and operation of rotary systems, with a particular focus on the power transmission from the airborne components down to the ground. There are various power transmission methods used for rotary systems, among them tensile rotary power transmission uses multiple networked tethers held apart by a small number of rigid components to transfer torque from a flying rotor down to a ground station. The aim of this research is to improve the design and operation of rotary airborne wind energy systems that incorporate tensile rotary power transmission, and to assess system performance based on mathematical modelling and test data. It focuses on the Daisy Kite system design, a rotary system, being developed by Windswept and Interesting. Included in this thesis work is the development of three mathematical representations to support systematic analysis and design improvement. The first representation, a steady state model, is used to analyse rotary system design. The second and third models are dynamic representations of varying complexity. Also included is an experimental campaign conducted on the Daisy Kite in collaboration with Windswept and Interesting. Field tests are carried out on nine different Daisy Kite prototypes at their test site on the Isle of Lewis, Scotland. Measured data is collected for the various prototype designs under different operating conditions. The measured data is used to assess the reliability of the three mathematical representations. This allows the models to be validated and compared to one another in terms of their accuracy and computational efficiency. During the experimental campaign several design and operational improvements are made that increase the power output and lead to more reliable operation. The mathematical representations are used to identify key design factors and to optimise rotary system design. Improved understanding and design of the rotary airborne wind energy system has been achieved through this holistic investigation.Airborne wind energy is a novel form of wind power. Through the use of lightweight wings and tethers it aims to access locations out of reach to current wind harvesting devices, at a lower cost and with a lower impact on the environment. There are multiple airborne wind energy systems currently under development, one group of these, referred to as rotary systems, use multiple wings networked together to form rotors. This thesis presents an analysis on the design and operation of rotary systems, with a particular focus on the power transmission from the airborne components down to the ground. There are various power transmission methods used for rotary systems, among them tensile rotary power transmission uses multiple networked tethers held apart by a small number of rigid components to transfer torque from a flying rotor down to a ground station. The aim of this research is to improve the design and operation of rotary airborne wind energy systems that incorporate tensile rotary power transmission, and to assess system performance based on mathematical modelling and test data. It focuses on the Daisy Kite system design, a rotary system, being developed by Windswept and Interesting. Included in this thesis work is the development of three mathematical representations to support systematic analysis and design improvement. The first representation, a steady state model, is used to analyse rotary system design. The second and third models are dynamic representations of varying complexity. Also included is an experimental campaign conducted on the Daisy Kite in collaboration with Windswept and Interesting. Field tests are carried out on nine different Daisy Kite prototypes at their test site on the Isle of Lewis, Scotland. Measured data is collected for the various prototype designs under different operating conditions. The measured data is used to assess the reliability of the three mathematical representations. This allows the models to be validated and compared to one another in terms of their accuracy and computational efficiency. During the experimental campaign several design and operational improvements are made that increase the power output and lead to more reliable operation. The mathematical representations are used to identify key design factors and to optimise rotary system design. Improved understanding and design of the rotary airborne wind energy system has been achieved through this holistic investigation