Penetration of Steel Catenary Riser in Soft Clay Seabed: Finite-Element and Finite-Volume Methods

The penetration of steel catenary risers and other cylindrical objects, such as offshore pipelines or T-bar penetrometers, in a soft clay seabed is of practical importance in deepwater oil and gas development. Finite-element (FE) analyses of these large-deformation problems are computationally very expensive. Water can also play a significant role through development of suction behind the riser. The main objective of the present study is to develop an advanced numerical modeling technique to simulate riser-seabed-water interaction near the touchdown zone. Keeping in mind two critical issues, namely the computational cost and modeling of suction, two different numerical modeling techniques are developed. In the first one, the computational fluid dynamics (CFD) approach is used. The CFD modeling is performed using ANSYS CFX 13.0 software. Among the three different types of CFX models developed in the present study, the subdomain modeling technique is found to be the most efficient. In the second numerical modeling technique, large-deformation FE analyses are performed using the coupled Eulerian-Lagrangian (CEL) approach in Abaqus FE software. The comparison of the results of CFX and CEL shows that CFX can successfully simulate the penetration of the riser or pipeline in soft clay seabed. The main advantages of the present CFX modeling over CEL modeling are (1) the CFX can simulate suctions, and (2) the CFX modeling with a subdomain is computationally very efficient. The analyses compared in this study show that CFX simulations are computationally 10-15 times faster than CEL simulations. (C) 2015 American Society of Civil Engineers.