Vibration characteristics of marine riser groups considering the coupled action of cross-flow and in-line

Abstract

Fluid-induced vibration (FIV) prediction is an important prerequisite work in wear and fatigue analysis of multi-wellhead marine risers in deepwater operation condition. A two-way fluid-structure coupling method (CFD/CSD) is used to establish a numerical model vibration of the marine riser groups, taking into account the interaction between two physical fields of fluid-structure, the combined effects of ocean eddy-induced force and wave-induced force. The model is solved numerically by ANSYS Workbench and Fluent software and verified preliminarily by a classical example in literature in which considering vibration response of a single riser. The effects of number, spacing, and arrangement of risers on the vibration response characteristics of marine riser groups are analyzed by established mode. It is found that with the increase of the number of risers, the vibration of the front risers is mainly cross-flow (CF), while the vibration of the rear risers is mainly in-line (IL). Therefore, the influence of incoming flow should be taken into account in the front risers, and the disturbance of wake should be taken into account in the rear risers. With the increase of the distance between risers, the interaction between risers groups affects CF and IL. The critical spacing of the interaction is between 3.5D and 4D. The arrangement of marine risers mainly affects the CF vibration of risers, especially the upstream and downstream risers. The research results can provide theoretical support for the design and vibration control of multi-wellhead marine risers.