Three-dimensional analysis of drag embedment anchor mooring systems under out of plane loads

Unlike top loaded suction piles or OMNI-Max anchors, drag embedment anchors are usually not designed for out of plane loading on the shackle. Prediction of drag embedment anchor performance under out of plane loading is of interest for mooring engineers. This paper presents an analysis of drag embedment anchor under out of plane loading. This analysis develops a set of three-dimensional reverse catenary equations based on the existing two-dimensional equations. A simplified anchor motion model is proposed to associate the shackle tension orientation with 6 degrees of freedom anchor motion. In this study, the anchor reverse catenary is coupled with the entire mooring leg and therefore the three-dimensional performance of a drag embedment anchor can be associated with the large offset experienced by the moored structure. Some examples are illustrated and compared with drag anchor out of plane tests conducted in Texas A & M University.