A numerical prediction model for the global collision behavior of marine risers

Abstract

This study develops a precise and efficient numerical model for predicting the global collision behavior of marine risers. Considering the combined effects of currents, random waves, top motions, and hydrodynamic interference, a dual-riser mechanical model is developed using the vector form intrinsic finite element (VFIFE) method. The point-value modeling method overcomes the limitations of displacement governing equations, eliminating the need for displacement constraint and stiffness matrix modification in the collision region. The issue of collision discontinuity is addressed using path elements. A two-stage collision detection strategy and an adaptive detection interval function, along with a self-developed collision detection algorithm, enhance efficiency without compromising accuracy. Additionally, the collision detection criteria are refined to avoid "pseudo-collisions." Upon detecting a riser collision, a rigid-body collision model is employed between collision path elements to correct riser element "penetration," thereby obtaining the true collision response. The model's accuracy is validated against ABAQUS results and is applied to analyze the global collision response of a tandem top-tensioned riser system. The results show that this model substantially improves calculation efficiency. Riser collisions are nearly line-line contacts and affect the downstream riser more than upstream riser. These collisions impact velocity response more than displacement. Normal collision velocities are much higher than tangential ones.