Waves Group supports Sarens with Design and Heavy Lift Engineering in the Installation of Fryslan Nearshore Wind Farm

Waves Group’s engineering team supported Sarens in the concept design and engineering of a large floating platform which was used for the construction and installation of the Fryslan nearshore wind farm project. The Fryslan wind farm is a unique project located in the IJsselmeer lake in the Netherlands, characterised by its shallow water and limited access via narrow locks.  The 380MW wind farm, which is expected to start operating this year, will consist of 89 turbines with an energy generating capacity of 4.3MW. This is corresponding to the consumption of some 500,000 households.

We were first contacted by Sarens in summer 2019 to assess the feasibility of the large platform. The concept relied on assembling four barges, linking them by beams overarching the four decks, to provide a work area wide enough to support all the equipment including a 1250T crane, whilst maintaining a shallow draught required for the offshore installation. The whole facility was to be held in position and stabilised during critical lifts by spuds.

A hydrostatic model of the deck was built to assess the stability against well-known criteria (IMO and DNVGL), but also location specific ones suitable for European Inland Waterways. We undertook motions analyses to provide Sarens with accelerations at key locations such as the tip of the crane to assess the deformation of the boom, as well as at the sea-fastening locations, to ensure the crane would be well secured during transportation to site and operations.

As the design progressed, a detailed model of the deck was produced using OrcaFlex, an industry standard software, able to handle multiple vessels joined, subject to complex environmental conditions. We provided bending moment and shear force on the beams connecting the four barges, motions, and accelerations at various locations on deck and along the length of the crane boom and finally loads generated on the spuds by the environmental conditions (current, wind and waves) to maintain the deck in position. A mooring analysis was also performed, should the deck be brought to a sheltered location and moored during a storm. The video below shows the design in OrcaFlex.

By assembling four of their barges, a large deck 63m x 49m was provided by Sarens, allowing the draught during installation to remain in the 2.0 – 2.5m range. The monopiles weighed up to 250T for a length of 39m thus requiring the use of a tall crane for the lift and installation. During the monopile installation, the deck was maintained in place using spuds driven in the seabed.

To drive the monopile in the seabed, a hydraulic hammer was used, and detailed hydrodynamic analyses were performed to calculate the rigging loads but also the maximum excursion of the hammer once held in the air during the hammering operation. Alongside the main analysis, the influence of a range of factors was investigated including soil model properties and location specific wave and wind profiles.

This study developed over 18 months leading into detailed advanced engineering culminating in the construction of the deck by Sarens and the successful installation of 89 monopiles in the IJsselmeer by Van Oord in late 2020.

Wave Group is proud to have been part of the project, providing advanced hydrodynamic analysis and technical support. The concept design of the large platform assisted Sarens to deliver the project on schedule.  The successful delivery of the project reinforces our engineering expertise and capabilities. Our team of Naval Architects and Structural Engineers have the technical expertise to support your project from the concept through to installation using industry standard software and advanced modelling techniques.

For further information about our engineering and consultancy services please email mail@waves-group.co.uk, or contact us on our 24- hr emergency response number +44 (0) 20 7083 7266.

Image: Sarens