Session: Structural Design-2

Paper Number: 165255

165255 - Comparison of a Semi-Submersible and Tension Leg Platform FOWTs in Extreme Irish Atlantic Waters 

Abstract: 

As the nearshore zone becomes saturated with fixed bottom offshore wind in an effort to achieve short-term energy targets, the focus on harnessing wind energy in deeper waters utilising floating offshore wind turbines(FOWT) is increasing. The exclusive economic zone of Ireland extends into the worlds greatest wind resource, figure 1. A key challenge of deploying in the Irish Atlantic is the harsh metocean climate including the some of largest waves ever recorded. The performance of floating wind turbines has yet to be proven in such challenging conditions. 

Presently, there are a range of floating wind turbine platform systems being proposed including semi-submersible, tension leg platforms and spar legs. These technologies are in various stages of development, with a series of reference turbine models available for numerical analysis. In this study the performance of two such systems, a 15MW Semi-Submersible FOWT and a 15MW tension leg platform are assessed. Utilising a coupled finite element analysis model, the performance of each system is examined over a range of metocean conditions. These conditions gathered from real wave buoy data represent recent storms incident of the Irish coast featuring waves up-to 30m in height, Figure 2.

The motions of the FOWTs in 6 degrees of freedom, are calculated and compared as well as key structural loading parameters including tower based moments and fairlead tensions, Figure 3. This comparative analysis of FOWTS in extreme Atlantic conditions has not previously been undertaken and as such provides there first indicator of the advantages and disadvantages of Semi submersible systems over tension leg platform in real extreme conditions. The magnitude of loads simulated during this study provides designers  with an indication of the range of mooring arrangement, type and  anchors required for installation in deep Irish Atlantic waters.

 

Figures 1 Irish Exclusive Economic Zone

 

Figure 2. Water Surface elevation recorded at offshore  wave buoys in Irish Atlantic waters

 

 

 

 

 

 

 

 

 

Figure 3 Structural output from FEA model for storm conditions.

Presenting Author: Arman Aghaei University College Cork

Presenting Author Biography: A lecturer in structural engineering, with 20 years’ experience in coastal and offshore engineering research, design and construction. A Chartered member of Engineers Irelands, NSAI Ocean Energy Committee member and IEA TCP57 Offshore wind Code Comparison(OC7) and TCP 12Ocean Energy Systems representative. He is the director of the Structural and Hydro Environmental Dynamics group in UCC and leads a team of postdoctoral and PhD researchers across a range of themes. His research is focused on offshore wind modelling and monitoring, marine renewable energy and in particular the impact of wave slamming on fixed and floating structures.

His research is focused on structural health monitoring, dynamic structural analysis and offshore renewable energy. Since 2020, Michael has secured over €1million in research funding through a variety funding sources including SFI, GSI, SEAI, from the EC and the US DOE as well as Industry. Michaels current research projects includes the Horizon Europe WEDUSEA project and GSI funded GEOBim. Dr O'Shea is currently supervising PhD students in Structural health monitoring and Subsea superconductors.

Authors:

Arman Aghaei University College Cork
Gregorio Iglesias University College Cork
Tom Doyle Dublin Offshore
Michael O'Shea University College Cork