Beyond the Sea project team (from left to right): Christian Jochum, Nedeleg Bigi, Morgan Behrel, Guy Leblanc, Damien Grelon, Yves Parlier and Richard Leloup, at ENSTA Bretagne (15 December 2017)
Beyond the Sea⃝R project by Yves Parlier
Antoine Morvan
Research Fellow ENSTA Bretagne
Institut de Recherche Dupuy de Lôme 2 Rue François Verny
29200 Brest France
antoine.morvan@ensta-bretagne.org www.ensta-bretagne.org
A Fast Simulation Tool for Ships Towed by Kites:
Assessment of Propulsion Efficiency
Antoine Morvan, Nedeleg Bigi, Jean-Baptiste Leroux, Christian Jochum
IRDL ENSTA-Bretagne CNRS FRE 3744 Over the past decades, more and more research
pro-grams are developing innovative and green propulsion systems for maritime transportation. This is also the ap-plication background of the present work, which aims at reducing the consumption of container ships by an al-ternative propulsion technique. In his pioneering work, Duckworth [1] proposed kite propulsion. Podeur et al. [2] confirmed the potential of this technique to achieve significant fuel savings. However, the assessment of the possible risk entailed in the towing of a ship by a kite has not been studied consistently. Existing literature ref-erences consider static equilibrium [3]. The dynamic in-teraction between a ship and a kite has been studied by Bigi [4]. The main objective of the present work is to pre-cise the dynamic effects on the ship and the kite operabil-ity for a realistic sea and wind environment. To achieve this, a unified seakeeping/manoeuvring numerical code is used by updating the equation of motions with the forces generated by the kite [5]. A zero mass model is used for the kite, assuming that the tethers are straight and inelastic. The aerodynamic lift coefficient and the lift-to-drag ratio are functions of the yaw turning rate of the kite. Two types of simulation are considered: firstly, the ship in calm water and, secondly, the ship subjected to regu-lar Airy wave for varying parameters such as wave ampli-tude, wind force, tether length and ship heading. The re-sults show that the kite is more affected by the dynamic motion than the ship (see figure). Indeed, a lock-in phe-nomenon between the wave frequency of encounter and the first harmonic of the kite is clearly demonstrated. A dimensional analysis is provided in order to identify this phenomenon prior to simulation.
ωk1kite first harmonic frequency, ∆σkkite wind load amplitude, ∆φsheel amplitude,Lttether length for a kite areaAw=500 m2, true wind speedUtw=12.5 m/s, wind direction βtw=45◦, a wave en-counter frequency ωe=0.285 rad/s.
References:
[1] D. Duckworth: The Application of Elevated Sails (Kites) for Fuel Saving Auxiliary Propulsion of Commercial Vessels. Journal of Wind Energy and Industrial Aerodynamics, n◦12, pp. 75-97 (1983) [2] V. Podeur, D. Merdrignac, M. Behrel, K. Roncin, C. Jochum, Y. Par-lier et P. Renaud: Simulation de voyage au long cours pour le cal-cul d’économies de carburant : Application á la propulsion par cerf-volant, in 15e Journèes de l’Hydrodynamique, Brest, France (2016) [3] J. Wellicome and S. Wilkinson: Ship Propulsive Kites: An Initial Study, University of Southampton (1984)
[4] N. Bigi: Investigation of The Dynamic Motions and Operability of a Ship Towed by Kite. PhD Thesis, University of Western Brittany, Brest (2017)
[5] N. Bigi, J.-B. Leroux, K. Roncin, A. Nême, C. Jochum, Y. Parlier: Ship Towed By Kite In Waves ś A Strongly Coupled System, The 4th International Conference on Innovation in High Performance Sail-ing Yachts, Lorient (2017)