Towards the Anchoring of Marine Hydrokinetic Energy Devices: Three-Dimensional Discrete Element Method Simulations of Interface Shear

Abstract

Interfaces between soils and structures are common in engineering practice. Physical experiments and numerical analyses have been used to explore interface shear behavior. A numerical model based on the discrete element method (DEM) is presented to simulate the three-dimensional granular-continuum interface shear behavior between soil and (e.g.) an anchor for a marine hydrokinetic (MHK) energy device when the anchor is subjected to a constant axial load and embedded into sandy marine sediments. These MHK devices rely upon seafloor anchors and compliant mooring systems to maintain their station, but without retarding the motion being converted to electricity. The capacity of these anchors is a significant design parameter for the entire MHK system. Anchor self-weight and soil-anchor interface shear forces provide holding capacity for the MHK device. Numerous factors will influence the pullout capacity of an anchor, including anchor type and seabed properties—and particularly, how those two components interact to manifest as interface friction. This interface friction is difficult to measure in-situ and thus, robust numerical models are necessary for system simulation and design. The effects of anchor friction are considered. Anchor surface roughness and asperity angle are defined as functions of mean grain size, consistent with prior definitions of counterface roughness from the literature. Fabric evolution at the sediment-anchor interface is investigated and the micromechanics of strain softening are discussed, though not quantified.