@article{reed_naik_abney_herbert_fine_vadlamannati_morris_taylor_muglia_granlund_et al._2024, title={Experimental Validation of an Iterative Learning-Based Flight Trajectory Optimizer for an Underwater Kite}, volume={32}, ISSN={["1558-0865"]}, url={https://doi.org/10.1109/TCST.2024.3359891}, DOI={10.1109/TCST.2024.3359891}, abstractNote={In this work, we present an iterative learning strategy and experimental validation thereof for optimizing the flight trajectory of an underwater kite. The methodology is adapted to two different power generation configurations. The iterative learning algorithm consists of two main steps, which are executed at each iteration. In the first step, a meta-model is updated using a recursive least squares (RLS) estimate to capture an economic performance index as a function of a set of basis parameters that define the flight trajectory. The second step is an iterative learning update using information from past cycles to update basis parameters at future cycles using a gradient ascent formulation. This algorithm was experimentally validated on a scaled experimental prototype underwater kite system towed behind a test vessel in Lake Norman, North Carolina. Using our experimental system and algorithm, we were able to increase the kite’s mechanical power generation by an average of 24.4% across the tests performed.}, number={4}, journal={IEEE TRANSACTIONS ON CONTROL SYSTEMS TECHNOLOGY}, author={Reed, James and Naik, Kartik and Abney, Andrew and Herbert, Dillon and Fine, Jacob and Vadlamannati, Ashwin and Morris, James and Taylor, Trip and Muglia, Michael and Granlund, Kenneth and et al.}, year={2024}, month={Jul}, pages={1240–1253} }
 @article{reed_abney_mishra_naik_perkins_vermillion_2023, title={Stability and Performance of an Undersea Kite Operating in a Turbulent Flow Field}, volume={31}, ISSN={["1558-0865"]}, DOI={10.1109/TCST.2023.3237614}, abstractNote={In this article, we examine the effects of flow disturbances resulting from turbulence on the dynamic behavior of an underwater energy-harvesting kite system that executes periodic figure-8 flight. Due to the periodic nature of the kite’s operation, we begin by assessing orbital stability using the Floquet analysis and stroboscopic intersection analysis of a Poincaré section, with the former analysis performed on a simplified “unifoil” model and the latter performed on a six-degree-of-freedom (6-DOF)/flexible tether model. With periodic stability established, a frequency-domain analysis based on a linearization about the kite’s path is used to predict the quality of flight path tracking as a function of the turbulence frequency. To validate the accuracy of these simulation-based predictions under flow disturbances, we compare the predictions of the kite’s behavior against the results of small-scale tow testing experiments performed in a controlled pool environment.}, number={4}, journal={IEEE TRANSACTIONS ON CONTROL SYSTEMS TECHNOLOGY}, author={Reed, James and Abney, Andrew and Mishra, Kirti D. and Naik, Kartik and Perkins, Edmon and Vermillion, Chris}, year={2023}, month={Jul}, pages={1663–1678} }
 @article{abney_reed_naik_bryant_herbert_leonard_vadlamannati_mook_beknalkar_alvarez_et al._2022, title={Autonomous Closed-Loop Experimental Characterization and Dynamic Model Validation of a Scaled Underwater Kite}, volume={144}, ISSN={["1528-9028"]}, DOI={10.1115/1.4054141}, abstractNote={Abstract
               This paper presents the closed-loop experimental framework and dynamic model validation for a 1/12-scale underwater kite design. The pool-based tow testing framework described herein, which involves a fully actuated, closed-loop controlled kite and flexible tether, significantly expands upon the capabilities of any previously developed open-source framework for experimental underwater kite characterization. Specifically, the framework has allowed for the validation of three closed-loop flight control strategies, along with a critical comparison between dynamic model predictions and experimental results. In this paper, we provide a detailed presentation of the experimental tow system and kite setup, describe the control algorithms implemented and tested, and quantify the level of agreement between our multi-degree-of-freedom kite dynamic model and experimental data. We also present a sensitivity analysis that helps to identify the most influential parameters to kite performance and further explain the remaining mismatches between the model and data.}, number={7}, journal={JOURNAL OF DYNAMIC SYSTEMS MEASUREMENT AND CONTROL-TRANSACTIONS OF THE ASME}, author={Abney, Andrew and Reed, James and Naik, Kartik and Bryant, Samuel and Herbert, Dillon and Leonard, Zak and Vadlamannati, Ashwin and Mook, Mariah and Beknalkar, Sumedh and Alvarez, Miguel and et al.}, year={2022}, month={Jul} }
 @article{abney_vermillion_2022, title={Drag-Mitigating Dynamic Flight Path Design for an Ultra-Long Tether Underwater Kite}, volume={55}, ISSN={["2405-8963"]}, DOI={10.1016/j.ifacol.2022.11.176}, abstractNote={This paper presents a computational study of an underwater kite operating in an ultra-long tether (ULT) application. Leveraging a dynamic model established in literature, we study the relationship between path shape and tether drag at varying tether lengths in order to develop meaningful insights as to the operation of systems that require ultra-long tethers in order to reach available flow resources. The results are compared to fundamental tether drag relationships developed in the airborne wind energy field, including the multi-airborne wind energy system (MAWES) proposed by Leuthold et al. (2017, 2018). It will be shown that by careful selection of path shape, these fundamental relationships break down in deep-water marine environments, and that high performance rivaling that of the MAWES system can be achieved, without the extra required mechanical complexity.}, number={37}, journal={IFAC PAPERSONLINE}, author={Abney, Andrew and Vermillion, Chris}, year={2022}, pages={151–157} }