Numerical simulations of the load on an embedded anchor from a taut mooring system

© Copyright 2016 by the International Society of Offshore and Polar Engineers (ISOPE).With the oil and gas exploration stepping into deeper water, taut mooring systems have become a popular solution for station keeping. However, the inclination angle at the anchor point in a taut mooring system may reach up to 40 degree from horizontal, which brings significant uplift load to the offshore foundation. In this scenario, embedded anchors, such as suction anchor, dynamically-embedded plate/torpedo anchor and drag anchors, are always employed to provide adequate holding capacity. The pad-eye of these anchors is designed at a certain depth into the mudline, which causes interaction between the soil and the embedded mooring line. The interaction is complex and introduces challenges in predicting the mooring load acting on the anchor. The present study proposes a dynamic method to predict anchor load caused by the motion of the floating platform. Soil resistance is calculated instantaneously by a simple and robust model. Based on the proposed method, sensitivity studies were conducted to investigate the influence of the oscillation amplitude and period on the anchor load. It is concluded that the maximum anchor load is more sensitive to the oscillation amplitude rather than the period, meaning that for the conditions considered, a dynamic analysis is not required.