Effects of demi-hull separation ratios on motion responses of tidal current turbines-loaded catamaran

Abstract

Catamaran has recently been a choice to support a typical vertical axis turbine in floating tidal current energy conversion system. However, motion responses associated with the catamaran can reduce the turbines efficiency. The possibility to overcome this problem is to change the catamaran parameter by varying and simulating the demi-hull separations to have lower motion responses. This simulation was undertaken by Computational Fluid Dynamic (CFD) using potential flow analysis. Cases of demi-hull separation were considered, with ratios of demi-hull separation (S) to the breadth of demi-hull (B), S⁄B of 3.45, 4.95, 6.45, 7.2 and 7.95. In order to compare to the previous works in the literature, the regular wave was set with wave height of 0.8 m. Furthermore, the analysis was carried out by irregular waves with significant wave height, Hs, of about 0.09 to 1.5 m and the wave period, T, of about 1.5 to 6 s or corresponding to the wave frequency, w, of about 1.1 to 4.2 rad/s. The wave spectrum was derived from the equation of the International Towing Tank Conference (ITTC). For the case of turbines-loaded catamaran under consideration, the new finding is that the least significant amplitude response can be satisfied at the ratio S⁄B of 7.2. This study indicates that selecting a right choice of demi-hull separation ratio could contribute in reducing motion responses of the tidal current turbines-loaded catamaran.