A Release-to-Rest Model for Dynamically Installed Anchors: Fid-Bau Portal

A Release-to-Rest Model for Dynamically Installed Anchors

O’Beirne, C. / O’Loughlin, C. D. / Gaudin, C.

Dynamically installed anchors are torpedo-shaped anchors that are installed by dropping them through the ocean such that they self-bury in the soft seabeds typically encountered in deep water. This paper presents and considers field data from reduced scale anchor tests at two sites to validate a new release-to-rest model for dynamically installed anchors. This model extends existing studies by considering the motion of the anchor from the point of release in the water column, modeling the drag resistance that acts on the anchor and its mooring line. Simulations from the model, together with data from the field tests, demonstrate the importance of considering the free-fall in water phase of installation, because the drag developed on the mooring line can be significant for larger release heights, reducing the anchor velocity as it arrives at the seabed by up to 44%. The soil embedment phase of the model also considers drag resistance on the anchor—and optionally on the mooring line—and accounts for the effect of the high anchor velocities on soil strength using a simple power law. Model simulations are shown in the paper to be in very good agreement with the anchor motion data measured in the field tests, resulting in predicted anchor embedments that are in agreement with the field database of over 100 anchor installations to an accuracy of $\pm 10 %$ .