Floating single-lift installation of WTGs equipped with C1 Wedge Connection

Abstract

This master thesis proposes a method for assessment of the allowable sea states for the single-lift installation of a Wind Turbine Generator (WTG) with a Quick Connection System (QCS) on a bottom-founded support structure with focus on the landing (mating) operation. The thesis also determines the operability of this installation and examines how it could be optimised.

Due to an increase of WTG size, the current lifting height of state-of-the-art floating Heavy Lift Vessels (HLVs) is insufficient to lift the WTG components to the required installation height. To overcome this limitation, and to further reduce installation time, new installation techniques are being developed. The single-lift installation methodology; where the WTG is lifted at the bottom of the WTG and just above the combined Centre of Gravity, in combination with the C1 Wedge Connection; a newly developed connection with a high ULS and FLS strength and large installation tolerances, forms a promising setup for dual crane HLVs. The Quick Connection System (QCS) of the C1 Wedge Connection can create a temporary connection able to provide sufficient restoring moment, required to keep the WTG upright. In this thesis the operability of a floating single-lift installation of a WTG with a QCS is determined and optimised. The performance of the QCS is compared to alternative connections and design improvements for the operation are proposed.

Two computer simulation models are built and compared, where-after the most promising model is expanded and further developed. This OrcaFlex model includes wave and wind loading in in-plane directions (3 Degree of Freedom directions). Nine critical events and limiting parameters are identified, containing motion limits of the WTG and QCS limits.

The results show that the operability for the base case (no Heave Compensation and strict limiting parameters) is negligible. In all cases assessed, the time required to activate the QCS turned out to be the governing limit. If heave compensation is incorporated and some parameters are altered (e.g. increasing the allowed WTG rotation or the maximum C1 Wedge Connection gap between the flanges) the operability can be increased to become feasible for wave peak periods up to Tp < 9s and significant wave heights Hs < 2m. In this optimised situation the activation of the QCS is the governing installation activity, with respect to the load transfer phase situation. Here, a minimum of 16 QCS Wedges are required for the load transfer phase and the pre-activation load transfer should be around 20% of the WTG static weight. For Hs < 1.4m, the mating operation was found to be feasible without a QCS. Here, it should be noted that optimal wind loading was assumed, and zero DP drift is incorporated.

It is recommended to expand the model to include all 6 DOF directions to verify if these results are still valid for non-optimal wind loading conditions. Furthermore, with these results, a study could be set up to determine the economic feasibility of this installation methodology. Such a study is essential as the economic viability determines the adoption of the technology.