The design and analysis of wind turbine installation vessels poses specific challenges that DNV GL - Software’s Sesam GeniE is well suited to cope with.
The development of an increasing number of offshore wind farms across the globe is creating a marked growth in demand for installation and service vessels. Currently, the wind turbine installation vessel market is still a niche market, The increasing number of wind turbine installation vessel newbuilds signifies that this current niche market but it is becoming steadily more important. There are currently 25 wind turbine installation vessels in operation globally, and an additional 11 in production. DNV GL - Software’s Sesam GeniE design and analysis software is fit for purpose to the market, and has a strong potential for increased market shares in this area.
Senior engineer Mathias Sørhaug at Technical Advisory Services in DNV GL uses Sesam GeniE for analysis on a current newbuild. Although wind turbine installation vessels have many parallels to jack-ups, there are certain challenges concerning the analysis of these vessels.
“For efficient operations the vessels are designed for speeds around 10-12 knots. This requires a ship shaped hull much more slender than a conventional jack-up,” says Sørhaug. With four or six legs (as opposed to three for jack-ups), the pre-load condition causes extensive global bending moments and shear forces in the hull structure that have to be considered during the structural design of the hull. Thus the hull is modelled using shell and beam elements to pick up both global and local responses. The final capacity check is performed using the Puls yield and buckling calculations that are integrated in GeniE.
“The great benefit with using Sesam GeniE is that we from one common model can run all wave load and structural analysis,” says Sørhaug. “The integration of the wave load analysis and structural analysis saves a lot of effort compared to other tools where data and results must be transferred between different programs and models. It is not only a great timesaver, but also keeps the user in control of the analysis and limits potential error sources. In total, it is an excellent tool for a wide range of analyses,” he says.
The ship currently under design will be able to install offshore wind turbines in waters up to 45 meters deep. For transit conditions the hull strength is evaluated according to the ship rules using Nauticus Hull. Due to the protruding heavy legs the vessels have different motion characteristics than traditional ships. “We will perform a direct wave load analysis in Sesam HydroD to calculate more realistic motions and accelerations,” says Sørhaug. “Since the vessel can have up to 6,500 tonnes of windmill turbines and rotors on deck during transport it is crucial to have realistic accelerations as input to the local strength assessment,” he says.
DNV GL’s goal is to positively impact development toward a low carbon economy as a world leader in risk management services to the cleaner energy industries. DNV GL - Software is working toward this goal by expanding the functionality of its Sesam program to include support for both fixed and floating wind installations.
Author: Kaia Means