Evaluation of Touch Down Point Displacement of Cable Catenary Risers Under Random Wave

Marine risers are the main components of the drilling and extraction of oil and gas in the offshore platforms. Hence the study of the riser lines under the specific environmental and loading conditions is mandatory to achieve optimal design of offshore oil platform. Future production of oil and gas will to a large extent take place in water depths that exceed 1000 m. The movement of floating and semi-submersible rig causes the stress and displacement of the Touch Down Point (TDP) in marine risers. Therefore, determining the exact movement of TDP is an important parameter to approximate the behavior of the riser. Also, it can be used to investigate the phenomenon of fatigue and corrosion caused by movements of risers in the touch down zone. In this paper, a riser cable catenary on soft clay in 1000 m depth of water is modeled using the commercial software OrcaFlex. The dynamic response of the riser is investigated. A fully 3D non-linear time domain finite element with a robust meshing technique has been applied to simulate the arbitrarily large deflections of the flexible from the initial configuration. A simple lumped mass element is used which greatly simplifies the mathematical formulation and allows quick and efficient development of the program to include additional force terms and constraints on the system. Analytical equations governing the motion of the cable catenary riser is used to compare the numerical results. The displacement and curvature of the riser is determined in the TDP.