Vortex-induced vibration (VIV) and vortex-induced motion (VIM) pose a significant hydrodynamic challenge for offshore risers and platforms respectively. Von Karmen vortex sheets that are periodically shed from bluff bodies induce time-varying lift forces on the body. If the body is not rigid these lift forces can induce significant motion or vibrations, greatly reducing fatigue life. The DeepStar JIP in 2001 contracted Oceanic Consulting Corporation to perform fundamental research into the nature of the forces. A specialized test apparatus was developed to tow a 6 m long segment of a 0.325 m diameter marine riser. A unique feature of the apparatus is its ability to operate in the transcritical regime with Reynolds numbers exceeding 106. The apparatus has two basic modes of operation free VIV and forced VIV and within each of these modes several test variation are possible. In the free mode the test cylinder was mounted on a system of springs and allowed to freely oscillate. In forced mode the cylinder is constrained to follow a sinusoidal motion with prescribed amplitude and frequency. This paper describes the apparatus and illustrates some of the basic results.

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