Finite Element Analysis of Composite Mooring Tensioner Springs in Wave Energy Converters

Abstract Floating structures are widely used in the offshore oil and gas industry, in deep-sea wind farms, and ocean wave energy converters, where fixed-bottom designs are often uneconomical due to the water depth. The traditional way of positioning a floating platform is using a catenary mooring system. The mooring tensioner is a critical component of a mooring system and is responsible for station-keeping during different ocean wave conditions. Statistically, a disproportionate amount of offshore floating structure incidents can be attributed to premature mooring failures [1]. Therefore, a new concept of a taut leg mooring system that utilises a fibre-reinforced polymer (FRP) mooring tensioner will be introduced in this paper. FRP mooring tensioners not only can be used for station-keeping of offshore structures but also can be used for wave energy harvesting. This is due to its advantages compared to metal tensioners, such as corrosion resistance, high specific strain energy, and the ability to tailor the spring constant without changing the overall dimensions. In this paper, the operation envelope of the FRP mooring tensioner in a Wave Energy Converter (WEC) will be investigated through simulation. By doing a simulation, this paper will discuss the estimated amount of energy stored by the mooring tensioners made with different materials at the same torque. The analysis shows that UD S2 glass/epoxy mooring tensioners can store significantly more energy than a metal spring made with spring steel at the same wave conditions, and therefore generators inside the Power Take-Off (PTO) unities can convert more stored mechanical energy into electricity. This FRP mooring tensioner not only can be used in WECs, but also can be used in offshore oil, gas, offshore wind, and aquaculture industries. The generated electricity can power auxiliary equipment, such as feeding barges in the aquaculture industry. In the case of the wind farm industry, the FRP mooring tensioners integrated PTO systems can be the wave energy converter component of wind-wave multi-purpose renewable energy generation systems.