A TLP for Intermediate Water Depths
During a project supported in part by ETI (Energy Technology Institute) to develop a TLP-type wind turbine support structure, PAFA Consulting Engineers recognised that the convention of tethering a TLP near its keel results in large overturning moments being generated by simultaneous combined actions of wind, wave and current loading.
To prevent these moments causing slack in the tether restraints, tether pretension must be increased and this can only be achieved by an increase in net buoyancy which, generally, results in a significant increase in the size of the underwater part of the structure. In seeking a counter-balancing mechanism, the tether connection points were raised well above the keel of the hull structure so that the moments on the structure below the tether attachments counteracted those above.
The net overturning moments generated by the wave-current and wind loading are reduced significantly enough to enable a far more balanced design to be achieved. This “flower pot” configuration has now been patented, with the generous assistance of ETI, and one form is illustrated here.