Vortex Shedding from a Vibrating Cable with Attached Spherical Bodies in a Linear Shear Flow.
Abstract
Marine cables often comprise an integral part of a larger structural system, such as an offshore drilling platform. They are also used to support marker buoys, as well as anchored or towed instrument arrays. Consequently, the resonant flow-induced oscillations of these cables, caused by vortex shedding, are extremely undesirable because of the associated damaging phenomena. The present study, which employs hot wire anemometry as the principal investigative tool, was undertaken to examine the behavior in the near wake of a flexible, helically wound, high aspect ratio (L/d = 107) marine cable in a linear shear flow (steepness parameter beta = 0.0053) at centerline Reynolds numbers between 2.0 x 1000 < or = Rec 4.2 x 1000. Particular attention was paid to lock-on or 'synchronization' related changes associated with uniform and sheared flow past the cable when it was forced to vibrate in the first mode. The study was extended to include an analysis of the effects on vortex shedding synchronization phenomena generated by placing spherical bluff bodies along the cable span. The frequency and reduced velocity boundaries of the lock-on regions, for both the cable and sphere-cable combination, as a function of vibration amplitude up to a/d = 0.322, were measured, plotted and analyzed. The critical reduced velocity of the vibrating was Ur* = 5.50, and for the sphere- cable combination Ur* = 3.39. A sudden increase in the vortex formation length in the near wake of the vibrating cable occurred during perfect synchronization (Ur* = 5.50). Shortly thereafter, the formation length returned to stationary cable values.
Document Details
- Document Type
- Technical Report
- Publication Date
- Oct 27, 1982
- Accession Number
- ADA120586
Entities
People
- R. D. Peltzer
Organizations
- United States Naval Research Laboratory