Deepwater anchors, such as drag anchors and gravity installed anchors, are widely adopted and play an important role in mooring systems for deep waters. With the development of new concepts and technologies in the field of deepwater mooring, the kinematic behavior of deepwater anchors in the seabed becomes more complicated, which brings great challenges to existing analytical methods. Therefore, it is significant to develop a rational mechanical model which can precisely describe comprehensive anchor behaviors in the seabed, such as penetration of drag anchors and non-catastrophic behavior of OMNI-Max anchors which is a new type of diving (embedding) gravity installed anchor. In the present work, comprehensive anchor behaviors in the seabed are considered to be the combination of keying and translating (including pullout and diving), whose mechanical models are respectively established with the limit equilibrium theory. The "least-force principle" which can be regarded as the failure mechanism of deepwater anchors is proposed not only to determine the translating direction and the rotation center of the anchor, but also to serve as the criteria to decide when keying and translating will occur. With the developed analytical model, comprehensive anchor behaviors are reasonably described and the anchor trajectory can then be obtained. To examine the present model, a comparative study of drag anchor installation is performed, and a generally good agreement is obtained. Then, the present model is used to simulate the non-catastrophic behavior of OMNI-Max anchors. The present work demonstrates that comprehensive anchor behaviors of different anchors can be easily and reasonably predicted by the analytical model, which is a convenient tool for better understanding the kinematic behavior of deepwater anchors in the seabed.
Through the exploitation of oil and gas in deep waters, sufficiently effective and reliable mooring systems have become increasingly popular in offshore engineering, which makes the need for the development of the anchor systems more pressing. Due to better performance both in capacity and installation, drag anchors and gravity installed anchors are attractive options. However, there are still problems in reasonably describing the comprehensive anchor behaviors in the seabed. On the one hand, the geometry of the anchor becomes more complex to meet the need for the engineering, which makes the anchor behaviors more complicated; on the other hand, people are lack of recognition of the anchor-soil interaction mechanism, which bring great challenges to develop a rational analytical method to describe comprehensive anchor behaviors, especially the anchor trajectory in the seabed.
