Numerical Simulation of Load Transfer in Mooring Anchor Systems

Abstract

A numerical model for the load transfer mechanism in mooring anchor systems, commonly used in offshore petroleum industry, is presented in this work. Special attention is paid to the mechanical modelling of the contact interaction of the two medium components, namely the soil and the embedded mooring line. Resorting to the 'embedded element concept' [1], a mixed 3D-1D finite element formulation is developed in the context of finite elastoplasticity. A Tresca-like model is used to describe the nonlinear material behaviour of the surrounding soil under undrained conditions, whereas the embedded mooring line regarded as curvilinear bar-like inclusion is assumed to behave elastically with account for geometric nonlinearities. The Mohr-Coulomb model is employed to define the bond-stress and bond-slip relationships at the interface. Nonlinear static and dynamic analyses are performed with a corotational kinematic description in order to include large deformation in the problem [2]. Preliminary results indicate that the main frequencies of the dynamic load applied to the mooring line-soil system are much lower than those of the system itself, thus the overall system may be evaluated disregarding inertial effects. Further simulations based on parametric studies by varying relevant problem parameters are needed to corroborate this result. Moreover, the average load attenuation induced by friction along the soil/mooring line interface for the studied cases is around 25%. Formulation of the interface constitutive behaviour in the context of large strain to address large relative movements between embedded inclusion and surrounding soil is an ongoing task [3]. Parallel implementation of the finite element model with specific data structure storage and iterative solver is currently addressed to handle large 3D computational models.