Numerical simulation of a centrifuge test related to the interaction between an ice feature and an offshore pipeline

Abstract

Ice features present one of the major obstacles to offshore development in the Arctic and Atlantic regions of Canada. Ice features have been observed to interact with the see floor creating scour features (Clark et al., 1986). In particular, when an ice feature is driven by environmental forces into the shallow water, ice scouring of the seabed may cause a danger to bottom installations such as submarine pipelines. In the present study, the ice-scour event in a centrifuge test is simulated by using PLAXIS and ADINA finite element programs. The centrifuge test data reported by (Lach et al., 1993; Yang and Poorooshasb, 1997) and the input data in their numerical study are utilized in the present work. In numerical analysis, geometric and material nonlinearities are considered. Two dimensional and three dimensional finite element models are used to calculate the stresses and deformations in the seabed soils, the deflections of the pipe, and the stresses acting on the pipe. In order to establish the validity of the finite element calculations, the experimental results and the numerical results are compared. The importance of using interface elements between the soil and the ice feature is also investigated. The FE predictions are reasonably close to the centrifuge test data. The displacements of the pipe in 3-D model are smaller than those predicted by 2-D model due to the three dimensional effects. Bending and torsion of the pipe along its long axis can only be calculated in 3-D FE analysis. Using the interface elements in the numerical analysis helps to obtain a better agreement between the calculated and measured values. In addition, convergence problems are reduced.