Efficient response recovery procedures for detailed design of jacket foundations

Two efficient system reduction procedures for detailed design of jacket foundations by post-processing of aero-elastic simulation results based on reduced structural models (superelements) are presented. It is illustrated that the full foundation response can be accurately recovered either via a force-controlled approach where the interface forces from the coupled aero-elastic simulations are applied to the non-reduced jacket model along with synchronized hydrodynamic wave loads in a dynamic time simulation, or by direct expansion via the superelement reduction basis. The procedures are illustrated on a coupled aero-elastic model represented by the NREL 5 MW reference wind turbine founded on a comprehensive, high-fidelity jacket model with hydrodynamics defined in Ramboll’s in-house offshore structural analysis program, ROSAP. The performances of both the force-controlled method and the direct expansion approach are compared for superelements based on the Guyan method, the Craig-Bampton method and an augmented Craig-Bampton method. It is shown that the Craig-Bampton method is superior to the Guyan method for dynamic problems irrespective of the recovery method. In particular for cases where wave loads are govern-ing, application of the direct expansion approach calls for the Augmented Craig-Bampton method in order to accurately capture the details of the hydrodynamic loading. It is shown that a compact, yet accurate reduction basis can be obtained by replacing some of the fixed interface modes with load dependent residual vectors.