Author(s)

S. M. FANG & J. M. NIEDZWECKI

Abstract

Cables and various subsea product flow-lines are often subjected to flow-induced vibrations as a consequence of wave or wave and current flow excitation. An experimental study that explores the comparative suppression effectiveness of airfoil and ribbon fairings is presented. In the experimental investigation, an instrumented tensioned 29 m horizontal composite cylinder with a length to diameter ratio of 760 is subjected to a range of uniform current and combined current and regular wave conditions. In the analysis of the cross-flow response amplitude ratios, modal parameters, such as mode shape, damping ratio were extracted. The analytical procedures were performed using a modified time domain decomposition technique. The analysis illustrated the amplified response behavior for bare cylinders, and illustrated that full coverage by airfoil and ribbon fairings could effectively suppress flow-induced vibrations in current only conditions, but both fairings were ineffective when regular wave conditions were superimposed on the uniform current conditions, even though the airfoil provided larger damping than ribbon fairings. Under combined wave and current conditions, the response behavior of either suppression device was found to be insensitive to coverage densities.

Keywords

Airfoil fairing, combined loads of current and waves, coverage density, flow-induced vibration, ribbon fairing, Time domain decomposition, vortex-induced vibration