Abstract
This paper reports the results from three-dimensional dynamic finite-element analysis undertaken to provide insight into the behaviour of OMNI-Max™ anchors during dynamic installation in non-homogeneous clay. The large-deformation finite-element analyses were carried out using the coupled Eulerian–Lagrangian approach, modifying the simple elastic–perfectly plastic Tresca soil model to allow strain softening, and incorporate strain-rate dependency of the shear strength using the Herschel–Bulkley model. The results were validated against field data prior to undertaking a detailed parametric study, exploring the relevant range of parameters in terms of anchor mass, impact velocity and soil strength. To predict the embedment depth in the field, an improved rational analytical embedment model, based on the total energy method, was proposed, with the large-deformation finite-element data used to calibrate the model.
Highlights
Installed anchors (DIAs) are the most recent generation of anchoring systems for mooring floating facilities for deep water oil and gas developments
Validation against field data The large-deformation finite-element (LDFE) results were validated against field data reported by Zimmerman et al (2009) and Shelton et al (2011), as noted in the second section of this paper (‘Reported data from field installation’)
An LDFE analysis was carried out using vi 1⁄4 19 m/s and su,ref 1⁄4 2·4 þ 1·1z kPa (η 1⁄4 1·0; β 1⁄4 0·1; γref 1⁄4 0·1 sÀ1; δrem 1⁄4 1/St 1⁄4 1/3; ξ95 1⁄4 20)
Summary
Installed anchors (DIAs) are the most recent generation of anchoring systems for mooring floating facilities for deep water oil and gas developments. The anchor is released from a specified height above the seabed. This allows the anchor to gain velocity as it falls freely through the water column before impacting the seafloor and embedding into the sediments. Torpedo anchors are rocket-shaped, typically consist of a long shaft, with the loading point (or padeye) attached at the top, and may feature up to four relatively small fins at the trailing edge (Brandão et al, 2006; Lieng et al, 2010). OMNI-MaxTM anchors feature three large fins with intermittent discontinuity to accommodate an arm that transfers the loading point nearer to the head of the anchor (Zimmerman et al, 2009; Nie & Shelton, 2011; Shelton et al, 2011)
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