Engineering designs in the ocean environment often involve bodies with thin or plate-like appendages. These are used as devices to inhibit flow-induced vibrations, enhance directional stability, increase damping, or reduce excessive wave-induced motion. These phenomena all share the common characteristics that flow separation is important. An overview is given of the treatment of these physically similar problems, with the use of a recently developed viscous-fluid solver called the Free-Surface Random-Vortex Method (FSRVM). This is an efficient nonlinear formulation that can include surface-wave effects and reproduce inviscid-fluid results if the latter is desired. Vortex-induced vibration (VIV) of risers, roll-damping of bilge keels, free decay of a Floating Production Storage and Offloading (FPSO) barge are considered as examples. Comparisons with experiments are made where available. Limitations and outlook are discussed.
Bodies with finned geometry are of importance in a wide range of engineering problems. A well-known application is the installation of a \splitter plate " behind a circular cylinder in steady ow. This inhibits the formation of the Karman vortex street, thus reducing the magnitude of the oscillatory transverse loading. The classical experiments of Roshko (1955) documented that a plate length of significant, threshold size was required to achieve this purpose. Vortex-induced vibrations (VIV) of cylindrical structures has long known to be a problematic issue in offshore engineering. The fatigue life of cables, marine risers, or pipelines is greatly reduced if unwanted oscillations are strong enough to induce significant cyclic stresses. To reduce the magnitude of the design load, it is not unusual to have strakes or ribbons installed. This can lead to a design trade-off. The subject literature on VIV is rich, particularly in relation to experimental data, but it is only recently that modeling of such phenomena based on first principles is beginning to emerge