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O&M tools integrating accurate structural health in offshore energy

Periodic Reporting for period 2 - WATEREYE (O&M tools integrating accurate structural health in offshore energy)

Reporting period: 2021-05-01 to 2022-10-31

The highest critical cost related to Operation and Maintenance (O&M) in offshore wind turbines is caused by structural failures that mainly occur due to corrosion. The WATEREYE project aims to reduce O&M cost, by developing a solution to monitor corrosion in the structure level that will allow predictive maintenance, with the objective of preventing major failures or even a breakdown. This objective will be reached through monitoring critical points of Wind Turbines (WT), analysing the data to generate a diagnosis and a prognosis maintenance strategy.
WATEREYE addresses the whole study of corrosion and its consequences in the different parts of a WT structure. The project develops a monitoring system capable of remotely estimating the corrosion. In addition, WATEREYE has developed technologies for data analytics, modelling, and diagnosis for WT as well as Wind Farm (WF) O&M advanced control strategies. These technologies will contribute to significant OPEX reductions and to improve the efficiency and profitability of offshore energy resources.
The most significant achievements reached during the project are:
WP1 represents the starting point of WATEREYE project with the definition of the project framework and general system requirements to be developed during the project. For this purpose, a study on corrosion and its effect on the relevant parts of the wind turbine structure has been carried out, allowing the identification the main challenges that corrosion brings to marine structures. External steel surfaces in the atmospheric and splash zones shall be protected by coating systems. Thus, not only structural steel but also protective coatings are defined clarifying the requirements of the WATEREYE solution. Finally, two scenarios (Canary Islands and Scotland East Coast) were selected as test cases. The main purpose of these sites is to be used as example in the validation and testing phase.
WP2 is focused on the design of the physical components of the WATEREYE solution composed by fixed sensor nodes, a mobile node, a drone, a Drone Docking Station and the WATEREYE Computer. The monitoring system was designed and validated in a relevant environment. After the final validation, we can say that the system is capable of remotely estimating the wall thickness losses due to corrosion and the intra-day corrosion rate. This will be useful to reduce the maintenance costs of the atmospheric and splash zones of offshore wind turbines. Corrosion is a relative slow process. It takes a long time (years in general) to induce corrosion on coated steel samples in field tests. Hence, accelerated laboratory testing was needed to produce corroded sampled within the project period. Both non-corroded and corroded, coated and bare steel samples in different thicknesses were produced with the aim of characterizing appropriately the ultrasound sensor nodes to get higher precision. On the other hand, high efforts were done to design a robust drone-based platform able to position accurately the sensor head on the wall.
The main goal of WP3 is to develop algorithms and software tools for ensuring integral intelligent processing of the inspection data generated both by the novel smart sensors developed in WP2 and by the data coming from WTs to optimise the O&M of a single WT. A corrosion prognosis methodology was designed by incorporating a corrosion model and a corrosion indicator extracted from the ultrasound signal. Moreover, a load reduction control algorithm was developed for offshore turbine tower to mitigate the loads. A Weather Research and Forecasting was designed to simulate the weather and turbine operating conditions. The system level data was used by the decision support tool at turbine level, which allowed calculation and scheduling of stochastically economically optimal commissioning actions.
The WATEREYE wind farm management tools developed in WP4 are part of the overall solution with the objective to reduce O&M costs by extending the lifetime of offshore wind turbines. The focus of WATEREYE lies on the protection of turbine towers from failure by preventing both corrosion and material fatigue from progressing. A tool for probabilistic analysis of turbine dynamics in the frequency domain was developed as well as a module of farm-scale turbulence that supports computationally efficient multiscale stochastic simulations in the time domain. Moreover, a control framework was developed that calculates the accumulated damage depending on environmental conditions and the wind farm control. The damage estimate feeds into the method for optimal O&M planning that considers potential power gains in the long and short term, power losses due to derating or shut down, maintenance costs as well as the weather forecast when scheduling maintenance tasks. These tools can be used both for retrofitting existing wind turbines and in novel system developments.
Due to the unavailability to conduct the validation inside a real wind turbine tower, it was decided to build in WP5 a steel structure to simulate a wind turbine tower in a “realistic and feasible way”. Therefore, the final validation took place inside the hangar of PLOCAN’s offshore platform, using this steel tower as the main element to which the system was attached. The WATEREYE monitoring solution was validated both at lab scale in Sint-Truiden (Belgium) and in relevant environment at the PLOCAN’s offshore platform in Gran Canaria (Spain). Therefore, it can be concluded that the validation of the WATEREYE monitoring system has been successfully conducted.
The WATEREYE system is an integral solution which will allow the WF operators to autonomously monitor the structural health of their offshore assets in real-time as well as to accurately predict their RUL with a final goal of optimizing the schedule of operation and maintenance at WF level.
The most significant WATEREYE outcomes that present a clear progress beyond the state of the art are:
● The monitoring solution aims to detect early-stage defects on the tower walls without any human intervention deploying several fixed sensor nodes on the tower wall and one ultrasound node integrated into a drone. The high precision obtained by the ultrasound-based sensor nodes allows to estimate a high reliable intra-day corrosion rate and to enhance the estimation of the RUL of the tower structure done by the corrosion models and the prognostics tool.
● Nowadays drones use satellite navigation for positioning and control. However, for indoors applications this is not available. To create a reliable indoor positioning system, a combination of small sensors is used to form a robust and precise means to navigate inside offshore structures.
● Development of Fault Tolerant Control (FTC) algorithms of individual WT considering structural health status prediction. The WT FTC algorithms are developed for load reduction and power optimization.
● Two probabilistic analysis tools contribute to a better understanding of how the uncertainties affect the estimated remaining useful lifetime and the performance of optimal WF control algorithms and maintenance scheduling.
● WF control that prioritizes power tracking while mitigating damage will be relevant in the future when wind farms have to support the stability of the power grid with more renewable energy plants connected.
In WATEREYE, WF control and O&M scheduling frameworks are linked.