ABSTRACT

Tow tests have been conducted on flexible circular cylinders at supevaitical Reynolds numbers in water. The tests were conducted at the Naval Surface Warfare Center's David Taylor Model Basin in Carderock, Maryland. Measurements were made of both drag and acceleration (due to vortex-induced vibration) of the cylinder. An ABS pipe was used to achieve Reynolds numbers ranging from about 2 × l05 to 6 × l0−5, and a 5–9/16-in. diameter PVC pipe was used to achieve Reynolds numbers ranging from about 6 × 105 to 1.5 × 106. Tests were also conducted with aluminum inserts (strongbacks), made to fit just inside the test cylinders, in order to obtain stationary (rigid) cylinder drag measurements for comparison purposes. The test results for (relatively) smooth cylinders are presented in this paper.

INTRODUCTION

Vortex-induced vibration (VIV) of cylindrical structures is a fairly well-known phenomenon that can cause fatigue failure and/or excessive drag on a structure. In the ocean, many cylindrical structures are potentially subject to VIV from ocean currents. These structures include cables, risers, tendons, mooring lines and the huh of a spartype structure. One of the important parameters affecting VIV is known as the Reynolds number. The Reynolds number is defined as Re = V'D/v, where: V is the relative velocity of the flowing fluid that the cylinder experiences; D is the cylinder outside diameter, and v is the kinematic viscosity of the fluid. Since the Reynolds number is proportional to both diameter and velocity, testing at Reynolds numbers that correspond to those of a prototype structure in which the velocity and diameter are often large (e.g., driIling risers with buoyancy and spar hulls in high currents), is quite difficult, especially in water where the associated forces are very large.

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