ABSTRACT

Vortex induced motion of risers in a steady, uniform flow has been investigated experimentally in subcritical flow in a water flume and under critical flow conditions in a high speed cavitations tunnel. Both experimental arrangements provided flexibility in the in-line direction as well as transverse to the flow. Considerable in-line motions were seen in combination with the dominant transverse motions, and the latter were different from those observed in the case where transverse flexibility only was allowed. The tests at critical Reynolds number showed some 80% increase in the average drag coefficient, compared to the results for a fixed cylinder. This is oil much more modest increase than for the subcritical flows where an increase of 2–300% was found. The transverse motion amplitude reached a maximum of almost one diameter, which was slightly smaller than for the subcritical case.

INTRODUCTION

Flow-induced motion of flexibly supported circular cylinders in steady currents is a classical problem, and one that is o∼ great practical significance in many fields. It has been the subject of numerous papers. Though progress has been made and several aspects of the problem are reasonably well understood, there are still very important unresolved questions. For general reference Blevins (1990) or Griffin (1985) may be consulted. The present paper is based on an experimental investigation which was performed as a joint industry project in 1984. A draft of this paper was written in 1985, but it had to be withdrawn from publication at that time. The engineering problem that motivated this investigation was the dynamics of riser lines from the seafloor to floating oil or gas producing platforms in considerable waterdepths, say 300–1000 m. The approach used was model tests of short, spring supported pipe sections in steady flows. The idea was to treat the full length risers as a series of such flexibly supported sections.

This content is only available via PDF.
You can access this article if you purchase or spend a download.