Author(s)

JOHN M. NIEDZWECKI & SAM M. FANG

Abstract

An experimental study was conducted to investigate the ability of ribbon fairings to suppress flow-induced vibrations on a long flexible horizontal cylinder. The test matrix included towing the cylinder at various speeds, towing the cylinder in regular waves, and investigating the influence of partial coverage on the response behavior. The test cylinder was 29 m long with a length to diameter (L/D) ratio of ~760. Interior to the tensioned cylinder model were six sets of unequally spaced biaxial accelerometers in a lightly pressurized environment keeping the interior dry. A string potentiometer was externally attached at the center of the model to provide a reference for later displacement estimates based on integration of the acceleration data. The time domain decomposition method (TDD) was used to recover mode shapes, damping characteristics, and modal contribution factors. For the uniform current cases, the findings illustrate that ribbon fairings are effective and provide increased damping when compared with bare cylinders. Partial coverage demonstrates that localized suppression becomes increasingly less effective as the percentage coverage is reduced. The introduction of regular waves to the towed cylinder cases illustrates the ineffectiveness of ribbon fairing to suppress the orbital motions induced by the waves, which is preferable to the amplification typically observed for airfoil fairings.

Keywords

Combined current and regular waves, horizontal flexible towed cylinder, ribbon fairings, time domain decomposition, uniform currents, vortex-induced vibrations