Hybrid model testing using pre-offset and asymmetric truncation design for deepwater semi-submersible with highly compliant mooring system

Abstract

The hybrid model testing technique has been widely used for evaluating the safety of deepwater floating systems. In this technique, a full-depth mooring system is equivalently substituted with a truncated model by employing truncation design. However, for a deepwater platform with a highly compliant mooring system, the large offset resulting from harsh environments makes it difficult to realize truncation design. The conventional symmetrically truncated mooring system starts to lose its accuracy. To achieve sufficient equivalence and enlarge the offset limit of the truncated model, a pre-offset and asymmetric truncation design is proposed in this paper for a deepwater semi-submersible system. The feasibility of the technique was first validated by numerical calculations. Thereafter, hybrid model testing was performed successfully for a semi-submersible with a highly compliant mooring system operating in harsh environments. Numerical reconstruction and extrapolation were performed, and the numerical results showed good agreement with experimental results. However, some remarkable discrepancies were observed in vertical motions because of nonlinear effects such as wave impact and the influence of bracings.