Static behaviours and collision onset criterion of two adjacent vertical risers

This study aims to investigate the static behaviours of two risers and establish the generalised dual-riser collision onset criterion (COC). The dual-riser model is developed based on the vector form intrinsic finite element method where the Blevins wake model is used to consider the wake effects. The governing equations including a virtual damping force are solved by the central difference method to obtain the static behaviours of risers. Then, the effects of initial spacing, top tension factor and current velocity on the static behaviours of two vertical risers arranged tandem are investigated. Further, the dual-riser COC is established with three non-dimensional parameters by linear-regression analysis. The results show that a larger top tension factor of the upstream riser and a smaller that of the downstream riser is a more effective combination to avoid collisions. The dual-riser COC can be described by a linear function of non-dimensional parameters.