Hydraulic Experiments and Numerical Analysis of Large Pile Suspended on Crane Vessel

In the construction of monopile offshore wind power foundations, it is important to understand the motion characteristics of vessels and piles for construction planning, especially when a large diameter pile is installed by a large crane vessel in open sea. However, there are few examples of detailed studies on the motion of long and heavy objects such as monopiles. In this study, to investigate the characteristics of the motion of a large monopile and a vessel, the hydraulic model experiments were conducted. For regular and irregular waves, the motion was observed in the cases that the pile is in air and semi-submerged conditions. The results showed that the motion response of the suspended pile depended on the motion of vessel, especially on the natural period of vessel oscillation. It was confirmed that the motion of the pile was in an oscillatory mode of rotational motion with the top and bottom of the pile fluctuating in opposite phase, and the movement of the top of the pile in the semi-submerged condition was greater than that in the air. It was also confirmed that the response of the pile varied depending on the vessel motion and the vessel motion itself was also affected by the suspended load. Furthermore, a numerical simulation was conducted using the motion analysis software OrcaFlex, and the simulated results showed good agreement with the experimental results.