Flow-Induced Motions of Multiple Risers

Vortex-induced and galloping vibrations of flexible risers in steady, uniform currents have been investigated. The cross sections consisted of a bundle of pipes tied together to form a so-called multiple production riser, see Fig. 3(b). The tests have been carried out in a wind tunnel at subcritical Reynolds numbers, using spring-mounted sectional models. The tests used the single tube case as a reference case, and the results indicated increased motions for all of the multiple configurations compared to the reference case. For some cases, vortex-induced motions gave the largest excursions, for others galloping. Crude calculations indicate that a typical 400-m depth riser configuration would experience significant galloping motions as well as vortex-induced motions in steady, uniform currents at 0.5 m/s or less.