Heerema Marine Contractors has completed the first sea test of a new method of assembling and installing XXL wind turbines on board a dynamically positioned (DP) floating vessel.
The method was tested in the Dutch North Sea aboard the giant semi-submersible crane ship Sleipnir.
Heerema carried out the demonstration project, known as the floating offshore installation of XXL wind turbines (FOX), in collaboration with DOT and Delft University of Technology (TU Delft) to collect operational data and test installation methods and times.
This demonstration project was supported by the Dutch Ministry of Economic Affairs and Climate Policy and Eneco. The partners worked with a wide range of subcontractors who supported this test, including Heerema Engineering Solutions, F&B Group, Harco Heavy Lifting, Ampelmann, Sif and CAPE Holland.
The method
The offshore wind industry is expected to produce 228 GW by 2030, enough to power more than 68 million homes. To achieve these goals, offshore wind turbines are gradually increasing in size and are intended to be installed in remote locations and at deeper water depths. Due to these market developments, Heerema has strategically developed the new method of assembling rotor nacelles (RNA) for the next generation of wind turbines.
The biggest technical challenge when using a floating installation vessel is the relative movement between the vessel’s crane and the geostatic foundation of the offshore structure. A specific point of attention within the RNA method is the installation of the blades, which has been identified as the most critical part of the installation of turbines at sea for any vessel. To meet these challenges, Heerema has developed the Guided Root Positioning Tool, known as GREPT. This in-house developed blade assembly tool enables safe and efficient handling and installation of blades at sea.
The development of Heerema’s RNA method has continued over the past two years and has been extensively tested at the Leiden Office based simulation center in Heerema. This offshore test put the method into practice for the first time at the Prinses Amalia wind farm in Eneco, the Netherlands. The test results will be used to further improve the RNA method within the Simulation Center.
CEO of Heerema Koos-Jan van Brouwershaven noted: “Testing our new method of installing RNA at sea is an important step in our ambition to provide the solutions customers need for the next generation of offshore wind generators. This project is another demonstration example of our offshore methods which have been developed in our simulation center.
Sliding joint test
In addition to Heerema’s RNA installation project, the offshore scope included testing of DOT’s Slip Joint connection. Typically, wind turbine generators use bolted flange-to-flange connections between the following parts, installed offshore using multiple elevators.
The Slip Joint, on the other hand, is an alternative connection between an offshore wind turbine and its foundation. It works and looks like two upside down paper cups stacked on top of each other. The connection is based on friction, where the weight ensures a firm and stable connection. Installation is done by simply sliding the two parts over each other without the use of grout or bolts. This simple mechanism helps reduce material, equipment and personnel costs while allowing for shorter installation time, Heerema said.
Two separate Slip Joint links were used during the FOX project: connecting the lower tower of the wind turbine to the foundation of the monopile and connecting the nacelle to the upper tower. In addition, a sliding joint based overboard attachment was used to transport the entire tower section safely and to be able to transfer the load to the ship’s crane in a controlled and efficient manner.
Operations at sea
During the sea trial, Heerema assembled the entire wind turbine on board, which included installing the blades using the GREPT. After that, the tower was installed on a pre-installed monopile using the DOT slip joint connection. The single lift RNA was installed using a slip joint connection and also subsequently with a flange to flange connection. Once the test project was finalized, the wind generator was dismantled and the monopile removed using a Vibro lifting tool.
During operations, researchers from TU Delft were on board to collect a unique dataset of more than 15 million data points, gathered by more than a dozen specially designed motion tracking sensors. . These data will be analyzed by TU Delft to develop knowledge and validate methods for the installation of the next generation of offshore wind farms.
Vibro lifting tool
The monopile used was installed in 2018 as part of a previous test project known as SJOR. The SJOR project was the first time that a Vibro Lifting Tool was used with a Dynamic Positioning (DP) vessel for the installation of a monopile without the use of a gripping frame or the like. This time the process was reversed to perform the monopile removal.
During the withdrawal, the scope of the test continued with extensive research undertaken in collaboration with Heerema Engineering Solutions and CAPE Holland. This action included a series of tests that were performed while reinstalling the monopile and again safely removing the structure before transferring it to the Sleipnir bridge. These tests provide valuable data that can be used to demonstrate the feasibility of installing monopiles without the need for gripping frames due to the capabilities of Heerema’s DP vessels and the Vibro lifting tool.
