Operability Analysis of Monopile Lowering Operation Using Different Numerical Approaches

Offshore installation operations require careful planning in the design phase to minimize associated risks. This study addresses numerical modeling and time-domain simulations of the lowering operation during installation of a monopile (MP) for offshore wind turbine (OWT) using a heavy lift vessel (HLV). The purpose is to apply different numerical approaches to obtain the allowable sea states and to assess the operability. Four critical factors regarding the numerical modeling approaches for the coupled HLV–MP lowering process are studied. Those factors include wave short-crestedness, shielding effects from the HLV, radiation damping from the MP, and the nonstationarity of the process. The influence of each factor on the allowable sea states and operability is assessed. A large number of time-domain simulations are performed, considering random waves, to derive the allowable sea states. The results indicate that, although the radiation damping from the MP is secondary, it is essential to consider the other features. The study can be used as a reference for the numerical modeling of relevant offshore operations