Drag anchor is the most extensively applied mooring device in ocean engineering. Most researchers assume the shear strength of seabed increase linearly with depth. However, some in-situ investigations suggest the shear strength is non-linear or piece wisely linear with depth. In this paper, Coupled Eulerian-Lagrangian technique is employed to investigate the anchor embedment. The non-linear shear strength is accomplished by implementing a subroutine to ABAQUS. A simulated repose angle tests are conducted as verifications of deformation. The simulated anchor trajectory is compared with the tested results. Results show that a non-linear model can provide more precise predictions of a trajectory.
Drag anchor is a part of the offshore mooring system. Because of its excellent bearing capacity, it is applied to the mooring systems of almost all the ships and the majority of oil and gas platforms. During the installation process, the anchor vertically penetrates at first. Then, the anchor shank rotates to a certain angle and be locked. With the traction of the anchor chain, the anchor continues to penetrate the seabed until it finally reaches the ultimate embedment depth.
Severe damage will be caused if the anchor strikes or hooks with the subsea pipelines or production facilities. This kind of damage is called anchor damage. From 1956 to 2015, 87% of mooring accidents that occurred were caused by dragging anchors. In the total pipeline damages caused by human activities, more than 30% of accidents were caused by dragging anchor (Guoguang, 1992). Accurate predictions of anchor trajectory can effectively avoid anchor damages. Therefore, the positioning problemis significant in the engineering applications of drag anchor.
Due to the number of influential factors, the complex engineering environment of anchor installation can hardly be reproduced in laboratories. Numerical simulation researches are appropriate methods for investigating these kinds of engineering problems.
CEL (Coupled Eulerian and Lagrangian) method is a hybrid FE method that combines pure Eulerian method with Lagrangian analysis (Benson, 1992). In CEL analysis, objects which largely deform during the simulation are composed of Euler grids. Objects that interact with Euler bodies are defined as Lagrangian bodies. CEL method has been widely used in the investigations of the interaction between the foundation of marine engineering and the seabed. Qiu (2011) conducted a benchmark test which had small deformation conditions by traditional FEM method and CEL method respectively. The reliability of the CEL method in geotechnical engineering analysis was verified through this benchmark test. Qiu (2011) applied the CEL method to simulate the installation of the suctional pile shoe on the sandy seabed covered by loose clay. Puker (2012) used CEL method to investigate the installation of FDP pile foundation. Besides the applications in foundation investigations, CEL method is also an effective method for PSI researches. Dutta (2015) applied the CEL method into the researches of the circumferential displacement of partially buried pipelines that bore vertical loads. The deformation of the surrounding seabed was also investigated in Dutta’s paper. (Dutta, Hawlader and Phillips, 2015).
