Vortex-Induced Vibration and Coincident Current Velocity Profiles for a Deepwater Drilling Riser

Abstract

The objective of this study is to use full-scale field data on current velocities and riser motions to better understand the behavior of deepwater drilling risers. The data are comprised of riser accelerations and coincident current velocity profiles from the monitoring of vortex-induced vibration (VIV) of a drilling riser located at a 1000 m water depth site. Proper orthogonal decomposition (POD), an efficient numerical technique for characterizing the spatial coherence in a random field, is employed here to identify energetic current profiles. The accuracy resulting from the use of only a limited number of the most important POD modes is studied by comparing measured current velocity profiles with those reconstructed based on a reduced-order truncation. In addition to studying current velocity profiles, riser acceleration data from this deepwater drilling riser are also analyzed. In order to analyze the VIV response of this riser, in-line and cross-flow motions in different data segments are studied. Again, empirical POD procedures are employed—this time to derive energetic spatial vibration modes defining the riser motion. Importantly, these modes are identified without the need for either an analytical/computational model of the riser or any physical dimensions and material properties; instead, they are derived exclusively using the field data. Relationships between riser response and coincident current velocity profiles are investigated, especially for those data segments associated with observed lock-in response.