Frequency Scaling of Physical Model Tests on Tensile Loaded Suction Buckets by Finite Element Analysis-Paper

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The study investigates how to scale physical model tests of suction bucket foundations subjected to tensile loading, a critical issue for offshore wind turbine jackets. Although 1g tests allow detailed measurements and better representation of grain size and skirt thickness than centrifuge tests, their low stress levels limit direct extrapolation to full scale.<br /><br />The authors conducted 30 model tests in sand, varying bucket dimensions, embedment, displacement rates, and cyclic loading conditions. They used the results to calibrate and validate a coupled hydro-mechanical finite element (FE) model, then enlarged the simulated foundations to prototype dimensions.<br /><br />Tests showed that drained tensile resistance depends on installation method, embedment, and size. Under partially drained conditions, faster displacement rates produced greater resistance and negative pore-pressure differentials; model size and aspect ratio also mattered. The FE model generally reproduced test behaviour adequately, though it tended to overestimate frictional resistance and somewhat underestimate negative pore pressure.<br /><br />For cyclic loading, the validated model was used to identify prototype frequencies that produced displacement accumulation equivalent to that in the physical tests. For the investigated geometric scale of approximately 1:15.7, the model-to-prototype frequency ratios ranged from about 11.75 to 14.50 and increased with load magnitude. This indicates that frequency scaling is load-dependent and cannot be captured fully by simple scaling laws.<br /><br />The simulations suggest that some tensile loads—even those briefly exceeding drained resistance—may be acceptable, provided they do not recur too soon or persist too long. The study demonstrates FE-based scaling as a practical way to interpret model tests, while noting that further testing is needed to establish general scaling relations and that interaction between tensile and compressive loads was not considered.

Keywords

suction bucket foundations

tensile loading

offshore wind turbine jackets

physical model tests

finite element model

drained tensile resistance

partially drained conditions

negative pore pressure

cyclic loading

frequency scaling