Research on Vortex Induced Motion of a Deep Draft Semisubmersible with Four Rectangular Columns

摘要

In recent years, Vortex Induced Motion (VIM) of floating structuressuch as Spar, Semi-submersible, TLP, etc, has proved to be a veryrelevant subject for the design of mooring and riser systems. The DeepDraft Semi-submersible (DDS) is a typical multi-column floater. Withlonger exciting length than the conventional Semi-submersible’s, itshows obvious VIM phenomenon. Furthermore, its VIM characteristicsare more complicated compared to Spar platform because of the flowinterference between columns.The model test of a DDS with four rectangular columns and fourpontoons is carried out in a towing tank to study its VIM response. The6-DOF motions are measured under different current directions andvelocities. Conclusions about the DDS’s VIM characteristics are drawnfrom the model test. It is shown that a DDS may experience significantVIM in the transverse and in-line direction and its amplitude is stronglydependent not only on the current directions but also on the reducedvelocity Ur regularly. The lock-in range is defined as 6