This study compares the results of an analytical and a numerical model simulating the coupled motion of crane vessel and crane load in regular waves. The analytical model is a frequency domain model, which uses hydrodynamic input data from a Boundary Element Method solver (i.e., Ansys AQWA). The numerical model is a time domain model (i.e., Orcina OrcaFlex). Its ship motion computation also bases on Boundary Element Method results. Additionally, the validation dataset from physical model tests is presented. In this validation dataset, different load masses are used to estimate the influence of increasing crane load on the vessel motion. Light lift and heavy lift conditions (according to DNV-RP-H103) are investigated. Nonlinear motions are observed close to the natural period of the crane pendulum. These nonlinearities cannot be resembled by the analytical model, while the nonlinear time domain model shows good agreement. Nonetheless, the linear analytical model and the nonlinear numerical model agree well with regard to the general influence of the coupled crane mass on the vessel motion.


The decarbonization of our energy systems is an integral part of the joint international efforts to reduce green house gas emissions and limit climate change and global warming. Offshore wind energy will have to play an important role in this decarbonization, and a great number of offshore wind energy turbines (OWTs) will have to be installed in the coming years and decades to reach the aforementioned goals. Additionally, the size of a single OWT is continuously increasing, and it is projected to keep increasing in the future. As shallow water installation sites for OWTs are scarce, the future turbines will have to be installed in deeper water depths. Floating OWTs can be one solution for the deep water sites. In addition to floating turbines, also bottom-fixed OWTs on large foundations ("offshore megastructures", (Schuster et al., 2021)) are developed to reach water depths of 50 m and more.

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