PO050

Numerical simulation of lifting operations using floating crane for installation and maintenance of floating offshore wind turbines

Sho Oh 1 ,2, Tomoaki Utsunomiya2, Kota Saeki2
1ClassNK, Tokyo, Japan, 2Kyushu University, Fukuoka, Japan

Abstract

Although jack-up vessels are commonly used for the marine operations for bottom-fixed offshore wind turbines, floating cranes will become the choice in most cases for installation and maintenance operations for floating offshore wind turbines which are usually located in deep waters. However, the problem with the marine operation using floating cranes is that the vessel motions are easily affected by external environments, which gives the marine operation both the risk of accidents caused by unexpected behavior of the system and the limitation of installation time caused by the small weather window accounting for the uncertainties. In order to find solutions to this problem and lower the risk and cost of marine operations using floating cranes, accurate prediction of their motions during the operation under wind and waves is important. In this study, numerical simulations are conducted for the lifting operations using floating cranes, which is one of the operations that are affected by external wind and wave conditions most. The analysis was performed using two numerical tools with different theoretical back ground; MOSES and ADAMS. First, the motion of the floating crane and the lifted object during the operation were evaluated for various external conditions. Then, by comparing the results from the two methods, the difference in both the simulated results and the resulting estimated weather limitations were discussed.

Method

The motion of the crane vessel and the lifted object during the lifting operations are simulated using two numerical tools. MOSES is an analysis tool for marine operations based on Finite Element Method, and is widely used in the Oil & Gas industry. Meanwhile ADAMS is a numerical solver for Multi-body dynamics systems which is more suitable when the simulated system undergoes large displacement. The models of the crane vessel and the lifted object were determined from the previously conducted marine operation for wind turbines. Using the two numerical tools, the behavior of the floating crane and the lifted object during the lifting operation were analyzed for various wind and wave conditions.

Results

Using MOSES and ADAMS, the motion of the floating crane and the lifted object during the lifting operations were evaluated. The characteristics of the motion of the vessel and the object were discussed for the wind only conditions, wave only conditions and combined wind and wave conditions based on the time series, statistics and spectrum of the simulated results. By comparing the results from the two numerical tools with different theoretical backgrounds, the differences of the simulated motions are assessed and their impacts on the estimated weather criteria for the targeted floating crane are discussed.

Conclusions

In this study, the motion of the floating crane system during lifting operations under various environmental conditions are evaluated using two numerical tools with different theoretical background. The characteristics of the motion of the floating crane and the lifted object were evaluated for wind only, wave only and combined wind and wave conditions, and their sensitivity to external conditions are concluded. By comparing the results from the two tools, the impacts of the difference in theoretical background on the simulated motions and the resulting estimated weather criteria are also concluded.

Objectives

The delegates will learn about the marine operation using floating cranes from the numerical simulation point of view. The information about the simulation tool, modelling procedure, the sensitivity of vessel motions to external conditions, and the dependence of the simulated results on different numerical tools will be provided. The content will mainly help the constructors and insurance companies for their future works in planning of the installation and maintenance for floating offshore wind projects, and the risk assessments for marine operations.