Design of a Floating Spar Wind Platform with an Integrated Substructure and Tower
Authors: Sherman Mailys , Sablok Anil , Kopsov Igor , Chen Liyong 
Published: April 2019

The proposed concept relates to modifying the construction/assembly method to reduce the cost and schedule of a floating Spar wind platform. Detailed analysis was performed and execution plan developed to quantify the benefits of integrating the tower and the substructure at the construction yard in a horizontal position compared to installing the tower by lifting while the wind platform is floating vertically.

Current offshore wind turbines are typically assembled by lifting and bolting standard onshore towers and wind turbine generators (WGT) onto a purpose designed floater. The concept presented here proposes to integrate the tower section and the floater at the fabrication yard while in horizontal position.

During an internal Research and Development study of a floater with a long cylindrical design, like a Classic/Cell Spar, the Construction method was developed following which each phase of marine operations was carefully analyzed and compared with the conventional execution plan used to construct and assemble a floating Spar Wind platform. The equipment normally included in the Tower were investigated with the vendors for feasibility to be transported in a horizontal position.

The Construction and Assembly method can be used for more efficient execution of future Spar and other floating structure type Wind Platforms.

It was proven that:

The integrated structure can withstand the loads during loadout/launching from the yard and float off,

The integrated structure can handle the loads during a horizontal tow for transport from the fabrication yard to the inshore assembly site. Bending moments and shear forces were confirmed within acceptable limits.

The integrated structure can withstand loads during upending, from the horizontal to vertical position,

The integrated structure can handle the hydrostatic pressure should partial submergence be required for lift height during mating of the WTG.

Overview of Tower integrated Wind floater

Positions of openings in the hull, for handling water ballast for upending, solid ballast and water deballast following upending, need to be considered.

Overall construction and assembly schedule was found to be efficient and added benefit to the concept.

This integrated method creates the following two main advantages:

It removes the challenges of the mating interface flange between the floater and the tower. This flange can prove costly. It also has limitations in term of size and load capacity that could potentially impact future development. The welding solution can accommodate a wider range of diameters, hence wider range of rotor dimensions.

It simplifies mating operations and makes the mating schedule more efficient. It allows the use of smaller floating cranes for mating, as systems can be partially submerged to limit the lift height during mating. It reduces and simplifies the infrastructure spread required for mating operations.

This proposed solution offers an opportunity to simplify project execution, reduce cost and interface risks, and open the doors to larger structure design optimization.