PLAT-O #2 is a subsea floating tidal energy generator. A scaled-down physical model of this device was tested at FloWave in steady axial currents of up to 6.2 m/s (full-scale). The platform’s motion and mooring tensions were measured to validate a tank-scale numerical model in ProteusDS. In currents above 3.5 m/s (full-scale) the platform with turbines was observed to squat in an arc motion about the upstream lines to a stable lower depth, to balance the forces of drag, thrust, net buoyancy and lift.
Hydrodynamic characteristics of the platform are derived from these experiments to aid the model calibration. A significant downward lift towards the bed is observed when the platform (with turbines) pitches bow-up to the flow. The downward lift acts to lower upstream line tensions but encourages the squatting motion. The platform’s drag coefficient is observed to reduce with the tank flow, by up to 15% at 1.24 m/s (critical, Re ≈ 2×105) relative to the value at 0.40 m/s (sub-critical, Re ≈ 5×104).
Representing the downward lift and the Reynolds-dependent drag in the numerical model resulted in accurate predictions of mooring tensions (< 5%) and motion (< 1 standard deviation). Further work includes: a wave-current validation, the flume-testing of the platform for more comprehensive lift and drag characteristics; the optimisation of the mooring geometry to control squatting, and CFD studies to predict lift in the sea.