Physical Modelling of Offshore Service Vessel Motion Influenced by Crane Load
Arndt Hildebrandt, Jannik Meyer (Leibniz Universität Hannover)
The safe execution of offshore crane operations is of high importance in many different aspects for offshore wind turbines (OWT), both in the phases of transport and installation (T&I) and operation and maintenance (O&M) [1]. As the water depths of bottom-fixed OWTs increase and floating OWTs in even deeper water depths are emerging, Jack-Up vessels can hardly satisfy the demands of future OWT needs. Thus, heavy lift vessels / floating installation vessels will become more important.
This trend is emphasized by actions of DEME and Jan de Nul, two of the world’s biggest offshore contractors. Both have ordered one large heavy lift vessel, the Orion (DEME) and the Les Alizés (Jan de Nul). While the Les Alizés is still under construction, the Orion has installed the first monopiles in the North Sea in June 2022 [2].
For these floating crane vessels, not only aerodynamic loads on the crane load, but also wave loads on the vessel and its respective motion, coupled with the crane load, need to be determined with care. To determine these motions in waves with care in simulation tools, these tools need to be validated using experimental data.
Therefore, systematic physical model tests (scale 1:40) of a basic crane vessel with swinging crane load were conducted in the wave flume “Schneiderberg” at the Leibniz University of Hannover. The flume has a length of 110 m and a width of 2.2 m. The tests were conducted at a water depth of 0.85 m. Fresh water with a density of 1000 kg / m³ was used.
As the interaction between swinging crane load and crane vessel depends on the ratio between weight of crane load and weight of crane vessel, different crane loads were investigated, with weight ratios ranging between 1 % and 4 % (Load weight / Empty vessel weight). For smaller ratios, the vessel motion is expected to be independent of the crane load motion. For larger ratios, an influence of the crane load motion on the vessel motion is expected, which will be presented and discussed.
Bibliography
[1] Z. Jiang, Installation of offshore wind turbines: A technical review, Renew. Sustain. Energy Rev. 139 (2021) 110576. https://doi.org/10.1016/j.rser.2020.110576.
[2] DEME Group, DEME’s next generation vessel ‘Orion’ successfully installs first monopile at Arcadis Ost, (2022). https://www.deme-group.com/news/demes-next-generation-vessel-orion-successfully-installs-first-monopile-arcadis-ost (accessed August 5, 2022).
