Efficient response recovery procedures for detailed design of jacket foundations

Abstract eng:
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 forcecontrolled 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 governing, 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.

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