Design of a flexible chain for winch based point absorbers

DS 91: Proceedings of NordDesign 2018, Linköping, Sweden, 14th - 17th August 2018

Year: 2018
Editor: Ekströmer, Philip; Schütte, Simon and Ölvander, Johan
Author: Andersson, Kjell; Sellgren, Ulf; Hagnestål, Anders
Series: NordDESIGN
Institution: KTH Royal Institute of Technology
ISBN: 978-91-7685-185-2


Wave power is a renewable energy source with a potential to cover up to 10% of the world ́s present energy consumption. It has however been difficult to find a cost effective solution to convert the wave energy into electricity. One significant part of the problem is the harsh marine environment in combination with waves that deliver high forces at low speed. These requirements are challenging for both dimensioning the mechanical structure as well as for an efficient energy conversion. The dimensioning forces strongly depend on the wave power concept, the Wave Energy Converter (WEC)implementation and the actual Power Take-Off (PTO) system. A key issue for making wave power a competitive alternative as a future energy source is to reduce the Levelized Cost Of Energy (LCOE)to a competitive level. Winch Based Point Absorbers (WBPAs) could potentially accomplish this if a key component –a low-cost, durable and efficient winch, can be developed. A crucial part of a winch system is the force transmitting chain or wire that transmits the hydrodynamic wave energy via a winch drum to the generator. In this article we propose a solution with a flexible chain where an elastomeric bearing is used as a means to achieve the relative motion between the links in the chain. With this solution no sliding is present and the motion is achieved as a deformation in the elastomeric bearing. This paper focuses on the design of the links in the chain while the design of the elastomeric bearings is described in more detail in (Andersson, 2018). The link was designed based on two aspects, primarily to maintain minimum number of joints in the chain and the other one was to have a maximum possible relative angle between the links when rolled up over the drum in order to effectively utilize the flexing property of the elastomeric bearing and reduce bending of the links. A detailed strength analysis of the link has been performed as well as topology optimization to increase the strength to weight ratio

Keywords: Wave power, point absorbers, winch, power take-off, elastomeric bearing


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