In deep water offshore, mooring systems can contribute significantly to the total cost of the system. Whilst this may not be such a compelling issue with the offshore oil and gas industry where profit is very large, it is vital factor for FOWTs where accomplishing a cost effective and profitable system is the one of the main challenges facing developers. As installed capacity increases and shallow water near shore sites are exhausted, projects will need to be developed further from shore and in deeper water, which will pose greater technical challenges and constrain efforts to reduce costs. There are a number of floating wind concepts currently under development, but there is no clear favourite at this stage with regard to which concept is most likely to be deployed at industrial scale in the future as other ideas are being proposed and investigated.
In terms of technology development of floating offshore wind turbine, it is essential to have a clear understanding about the structure behaviour in harsh environment as well as to consider a sustainable, reliable, and cost effective mooring and anchor system. This means, it is important to demonstrate how the mooring, anchoring and cabling elements of the system can be utilized aim for improving levelized cost of energy (LCOE) and the lifecycle of the wind farm. Therefore, there is a need for improved understanding of those factors to drive towards large scale development.
This project concentrates on developing reliable methods to solve the static and dynamic response of mooring lines to examine how this knowledge transfers into the design of mooring system in terms of technical requirements and guidelines on design and construction of positioning mooring system.
This study will use realistic met-ocean data (wave, wind, current and geotechnical) which represents shallow and deep water sites suitable for wind farms of more than 100 floating wind turbines. In order to develop the innovative technologies required to reduce the cost, experiences from industries leading this concept can be adapted for establishing a base case design of a FOWT. The key elements of the mooring system include catenary and semi taut mooring lines with disconnecting ability, top loaded suction piles and tensioning mooring line at anchor to investigate the coupled dynamics of the mooring and platform dynamics. Better estimation of extreme forces and the distribution of fatigue loads will enable to find more realistic, and thereby more economic safety factors that meet an acceptable probability of failure.
The following presents a short summary of the new and innovative aspects addressed in the course of this project.
- Numerical investigation of different types of 10MW FOWT system dynamic behaviour in irregular wave conditions, facing unsteady wind by applying combined aerodynamics, hydrodynamic, current forces on the system. Coupled analysis will be conducted for a range of operating conditions and to evaluate system safety in survival conditions.
- Identify optimised mooring configurations for FOWT through a thorough investigation of various key aspects such as material properties, mooring layout and anchor properties and their influence on the fatigue life of key components.
- Investigate symmetric and asymmetric mooring systems to evaluate critical safety aspects in case of failure, especially for closely spaced arrays and in case of anchor sharing.
- Apply analytical methods of FOWT design optimization with the aim to study the detailed influence of various design constraints (eigenfrequency, extreme load and fatigue load constraints) on the structural design and the performance optimization procedure.
- Conduct an experimental model test of a 10MW FOWT complete system including unsteady wind, irregular wave and current forces.