Research at Nobelwind: Project overview
Cedric Vanden Haute1, Christof Devriendt
,3, Wout Weijtjens2
,3, Gert De Sitter2
1Parkwind NV., Brussels, Belgium, 2Vrije Universiteit Brussel, Brussels, Belgium, 3OWI-lab, Brussels, Belgium, 424SEA BVBA, Brussels, Belgium
Nobelwind is the newest offshore wind farm off the coast of Belgium. In a continued effort to optimize future offshore wind farms Parkwind and OWI-lab have started a new research project at the Nobelwind site with the support of the Flemish government. In the project Nobelwind have teamed up with industry partners 24SEA and COM&SENS to improve the knowledge on offshore wind turbines.
As part of the research project Nobelwind three wind turbine monopiles have been instrumented with optical strain gauges over the entire length of the monopile, pore water pressure and earth pressure sensors and inclinometers at specific locations subsoil. With this innovative set-up the project aims to better understand the dynamics subsoil, and validate new design methodologies, aiming to improve future designs. In addition, the sensors subsoil will be used to validate the concept of virtual sensing below the mudline, where strains over the entire substructure are predicted using accelerometers on the tower.
Moreover, Nobelwind is the first Belgian offshore wind farm that uses a bolted connection instead of the classic grouted connection. This novel approach has still many unknowns that will be targeted by instrumenting selected turbines with intelligent bolts of which the loads in the bolt can be monitored continuously. Results will shed a light on the evolutions of the loads in the very large bolts of offshore wind turbines.
The project aims to solve several questions relevant to the design of future offshore wind turbines. By heavily instrumenting three wind turbines in the farm with sensors going beneath the soil the stresses in the monopile sub-soil on an operational wind-turbine will directly be measured over a long term. Prior to the installation of the substructures the monopiles were instrumented by experts in the field of geotechnics (TU Braunschweig) and optical fiber measurement technology (COM&SENS). 24SEA installs all the sensors above the soil e.g. accelerometers, inclinometers, strain gauges and provides all data acquisition systems and manages the remote access, data transfer, data storage and performs the basic data processing. The above sensor set-up will yield relevant results to improve design of future wind farms.
All results will be processed by OWI-lab which has built up a strong experience in the processing and interpretation of structural measurements on offshore wind turbines.
As the project has only recently kicked-off this contribution will mainly focus on the intended goals of the project and the measurement setup designed to answer the research questions. These questions are :
- Can the dynamics sub-soil be modelled better than current design practice?
- Is virtual sensing applicable to strains sub-soil?
- Are the loads in the bolts accurately set in design? And how do these loads evolve over time?
In addition this contribution will analyze and discuss the first results of the measurement setup.
The research project Nobelwind will operate a truly unique monitoring system in an academic environment. With a large number of sensors installed sub-soil a new window on the loads on the foundation will be opened for research. In addition for the first time the loads inside the bolts at the TP-Monopile interface will be monitored and a new light will be shed on the loads in these new connectors.
The open research questions for Nobelwind are discussed in depth. Readers will learn about an innovative set-up installed at three wind turbines and how this will answer some of the open questions. The main research effort is towards loads on the foundation of offshore wind turbines and how this can be modelled more accurately in the future. In addition the concept of virtual sensing will be discussed and validated on the new set-up at Nobelwind. In the future the concept of virtual sensing can eliminate the necessity of sensors sub-soil to determine the stress histories of the foundation.
In addition the research project Nobelwind also aims to improve the understanding of the loads and load histories in the bolted connection currently employed at Nobelwind.