Review of Structural Strength in the Event of a One-Leg Punch through for a Wind Turbine Installation Vessel

As the demand for eco-friendly energy increases, the offshore wind power generation sector is showing rapid growth. As offshore wind turbines become larger, the need for specialized installation vessels is becoming a more crucial issue. Wind turbine installation vessels (WTIV) require a necessary pre-loading process where the legs and spudcans are penetrated into the seabed to secure stability during installation. Due to these operational characteristics, the installation work can be completed safely when safe pre-loading is finished. Analyzing previous structural collapse accidents investigated by HSE, 53% of them were punch-through problems related to the seabed, which occurred with a high frequency. Therefore, these lead to major accidents, which is a very high-risk problem. In this study, we investigated and analyzed the punch-through accident cases, and a WTIV model with six legs was applied to numerically examine the maximum vertical reaction force variation when punch through occurs for each leg. The maximum vertical reaction force takes place in leg number three when a punch through occurs in leg number five and maximum stress exceeds the allowable criteria in both hull and legs. This requires proper structural reinforcement such as an increase in the thickness and change in the high-yield stress. The key results of this investigation can be used to determine the basic specifications of wind turbine installation vessels, and the reaction force distribution pattern can be used as fundamental data for leg and hull structural design.