Experimental Investigation On Vortex Induced Motions of Truss SPARS Available to Purchase

With the successful application of spars in offshore oil and gas industry, one of the critical issues related to a spar design, the Vortex- Induced Motions (VIM), has attracted significant attention among offshore engineers. It's difficult to accurately predict the VIM responses with CFD due to insufficient understanding of the mechanism, the influence of structural configuration, the complexity of the real sea states, as well as the limitations of CFD tools. Until now, model test is still the most reliable and effective method to carry out quantitative study of VIM in order to exam the influence of the parameters such as the dimensionless amplitude; vibrating and shedding frequencies; and the reduced velocity. The 1:60 scale Truss Spar model tests have been conducted in deepwater offshore basin at State Key Laboratory of Ocean Engineering (SKLOE). The Truss Spar model consists of a hard tank with removable helical strakes, a truss section and a square soft tank. Model tests were carried out with truncated mooring system. Uniform current profiles are generated by the current generating system. In this paper, the trajectories of Truss Spar with and without helical strakes were recorded and analyzed. The heading of the model was varied from 90 to 180 degrees. The reduced velocity was from 5 to 10 and Reynolds number ranges from 1E05 to 2E05. "Figure 8" was clearly observed in the Truss Spar without strakes, while semi-circular figure was found in the strake case. Strakes suppressed VIM at all headings. The 50% decrease in amplitude for Truss Spar with strakes at the reduced velocity 8 indicates the efficiency of helical strakes on the VIM suppression. And it was found that the 120 degree heading with strakes is more effective compare to 90 and 180 degree current headings.