Vortex-Induced Vibrations of Marine Cables and Structures.
Abstract
The dynamic analysis of marine structures and cable systems has become increasingly important in order to predict stress distributions and operational lifetimes in hostile ocean environments. This is largely because the amplitudes of vortex-induced vibration for a cylindrical structure such as a riser or pipeline in water are an order of magnitude greater than for a similar structure in air. The small mass ratio (structure to displace fluid) in water produces small values of the reduced damping which in turn result in the relatively large limiting vibration amplitudes shown in this report. Risers, platform mooring cables and other long, slender structures often are subjected to spanwise nonuniform shear currents. The response of long cylinders in non-uniform flows cannot be predicted accurately in many cases using existing methods which were originally developed for uniform flows. There is a limited base of data available for current shear effects from both laboratory and field experiments. However, it is possible from these results to make reasonable engineering estimates of the level and extent of vortex-induced vibrations in shear currents. Several examples are given to illustrate these estimates. The vortex-induced hydrodynamic drag forces on vibrating structures in water are amplified substantially above the corresponding case of a structure at rest. This drag amplification has been measured in several extensive experiments and reaches 250 percent at the largest amplitudes of crossflow displacement. The available experimental results for circular cylindrical members are summarized and put to use in several example calculations. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- Jun 19, 1985
- Accession Number
- ADA157481
Entities
People
- O. M. Griffin
Organizations
- United States Naval Research Laboratory