Drilling and production risers experiencing vortex-induced-vibrations (VIV) may adversely impact operations in two ways: by increasing deflection due to amplified drag and causing structural fatigue damage due to VIV induced dynamic stresses. Complex hydrodynamic mechanisms controlling correlation length and force dependence on motion and frequency of response are major obstacles in predicting the VIV response, except for a limited number of cases for which extensive experimental calibrations were carried out. A pragmatic VIV analysis methodology has been developed based on correlation length measurements, and riser specific experimental tests to establish basic CD and CL databases for realistic riser configurations with auxiliary lines and buoyancy modules. Correlation length properties are established using flow visualization methods, in particular Digital Particle Image Velocimetry (DPIV), which allows whole-field quantitative information on the velocity and vorticity fields to be obtained. Identification of the role of two basic VIV mechanisms, the formation of braid vortices and the impact of vortex splitting, has provided a robust correlation length model. A VIV analysis program has evolved from these experimental tests in conjunction with extensive research in structural and hydrodynamic riser responses.
Pragmatic riser VIV analysis
1999
8 Seiten, 12 Quellen
Conference paper
English