Research On Numerical Simulation Of Deep Water Riser Collision

Top tensioned risers and steel catenary risers are deemed as key equipments for deep water oil and gas exploitation with the development of tensioned leg platform and spar. Deep water risers are subject to platform motions and complicated environmental loads, mismatches of dynamic behaviors among adjacent risers may cause collision between them, this will influence the ultimate strength of the riser and may even result in damage to the structure integrity. Hence, new challenges arise for investigation of riser collision behavior. This paper summarizes a study of collision behaviors of TTRs and SCRs based on national "863"project including riser collision mechanism, global and local numerical analysis of riser collision, the riser collision behavior from aspects of collision type, deformation and energy absorption are described.Based on the excitation mechanism of riser collision, the numerical simulation of TTRs collision and SCRs collision are carried out respectively with marine riser dynamics program OrcaFlex. Statistics information like impact position, impact duration, impact angle and impact velocity are obtained. Besides, time history of impact force and stress are achieved. Major work of this part is to investigate the influence of the various riser factors on the collision process which for TTR is riser spacing, top tension, current profile, TLP motion; for SCR is riser spacing, hanging angle, flexible joint stiffness, soil friction coefficient, current profile and TLP motion.Based on the global numerical simulation, this paper presents more detailed research on local riser collision. Two processes are set up to simulate the collision behavior completely, the bending process in pre-collision and post-collision phase. An "Involved length" method is adopted to define the contact area. This part mainly focuses on the assessment of the influence of the bending deformation to the collision results. Meanwhile, different collision results such as impact force, deformation of riser pipe cross-section have been got under different impact angles, providing some basic suggestions and reference for anti-collision measurements.