VIV Hydrodynamic Data Extraction From Field Data

In this paper we extend a methodology to extract a VIV hydrodynamic database from field data to accommodate partially straked cylinders. There are two databases, each consisting of the lift and added mass coefficients as functions of reduced velocity and amplitude of response; the first for the bare part of the riser, and the second for the straked part. The field data can be either in the form of acceleration, strain, or a combination of acceleration and strain time traces, together with the shape of the current profile. First, the program VIVA together with a nominal force database obtained from laboratory hydrodynamic experiments is used in order to get an initial prediction of the riser response under a particular flow profile. The nominal databases are then parameterized and altered in a systematic way until the new VIVA predicted response best matches the measured field response, thus resulting in an optimal database. Examples from the Norwegian Deepwater Program VIV experiments demonstrate the effectiveness of the methodology.