Numerical investigation on the effect of anchor modelling on anchor chain-soil interaction for floating offshore wind turbines
International Symposium on Practical Design of Ships and Other Floating Structures (PRADS 2022)
Contribution to Conference
Floating offshore wind turbines (FOWTs) are moored, e.g., by anchor chains connecting the anchorage in the seabed and the floating unit. At various marine foundation infrastructures, erosion has occurred along the anchoring system, reducing soil resistance. This reduction is assumed to be caused by the anchor chain movement. Numerical simulations in 2D investigating anchor chain-seabed interaction only provide limited results. Also, typical catenary forms resulting from the installation process of drag embedment anchors are usually not considered. In this work, a 3D model of an anchor chain is created. This work investigates the changed stress state in the soil and its deformation due to anchor chain ploughing. Furthermore, different methods of modelling the anchor are compared: Modelling the anchor as fixed bearing, as anchor mass in the first chain segment closest to the anchor shackle or in a separate body allowing anchor displacement. The numerical simulations are based on the finite element method (FEM) with the coupled Euler-Lagrange approach (CEL) due to expected large deformations. The anchor chain is modelled ’wished in place’ as an inverse catenary, and the soil is modelled assuming a linear elastic behaviour with Mohr-Coulomb failure criterion. There are significant differences in deformation and in stress distribution in taking anchor mass displacement into account. Both displacement- and force-controlled, the anchor mass was displaced and thus significantly influenced the results. The numerical results show the possibility of better understanding the anchor-chain-soil interaction to ultimately ensure a safer and more economical installation of FOWTs.
floating offshore wind turbine FOWT
offshore foundations, CEL
690: Building, Construction