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The Technical University of Denmark is recognized inter-nationally as a leading university in technical and natural sciences.
With climate change as the accelerating factor, there is a major focus on renewable energy in Denmark. Department of Wind Energy, Technical University of Denmark (DTU Wind Energy) and the ReliaBlade project tackle the goals established by the Danish policies on climate change migration by helping the development of wind turbines with engineering insights. Kim Branner is a senior researcher and Head of Section at the DTU Wind Energy department as well as project manager for the ReliaBlade project.
Branner designed ship propellers 30 years ago as a master thesis student and for the last 18 years worked with wind energy research. He and his DTU Wind Energy team study the dynamics of wind turbine blades, designing wind turbine blades, testing wind turbine blades and working with various tools around them to develop methods to understand blade strength and fatigue life.
Offshore turbines are not readily visible or heard easily but are positioned where wind is most prevalent. Assessing offshore turbines is a major challenge, necessitating an obvious need for a better way to monitor them for maintenance purposes. That’s where the ReliaBlade project comes in.
ReliaBlade is a Danish-German joint research project aimed at developing and demonstrating techniques to create a unique digital twin for each individual wind turbine blade, taking into account its specific defects and imperfections. Digitalizing the entire process is paramount. This is readily apparent in the use of high-precision scanning, non-destructive testing (NDT) tools, advanced image processing techniques and multi-scale modeling of blades. The digital twin tracks not only a blade’s current condition but can also be used to predict the rotor blade’s future state as damages first appear and grow through its entire lifecycle.
“The ReliaBlade utilizes a comprehensive digital twin to monitor turbines and make wind turbine blades more reliable. That‘s why it‘s called ReliaBlade,” says Branner. “The focus is to make wind turbine blades more reliable by using a digital twin. That was one of the ideas of establishing this project.”
The ReliaBlade projects aims to ensure blades last longer without human interaction or other unforeseen problems. By using a digital twin and sensor technologies in the process of building the blades, DTU Wind Energy can develop condition monitoring systems that monitor the structure and can alert wind turbine owners of potential problems or damage developing in the blade. This allows the wind turbine owner to either change how they operate the turbine or make a repair decision before the issue becomes too critical. And go offshore to make necessary repairs, ideally in the summer.
“With the monitoring systems that can come with a digital twin, you have an opportunity to intervene before it becomes a problem and therefore make these structures more reliable,” says Branner.
The manufacturing of test blades in a research environment allows you to produce the blade with modern instrumentation and detailed process monitoring and feed the data back into the blade modeling to predict the damage behavior in the full-scale tests conducted with innovative test methods.
The DTU Wind Energy team is partnering with Siemens Digital Industries Software. As part of this collaboration, DTU Wind Energy uses Simcenter™ software to develop a comprehensive digital twin of the wind turbine for the ReliaBlade project. The ReliaBlade digital platform features blade design for the digital product, blade and component manufacturing as well as material properties and effects of defects for digital manufacturing and finally sub-component testing and full-scale blade testing for digital performance.
Simcenter is a part of the Xcelerator™ portfolio, a comprehensive and integrated portfolio of software and services from Siemens Digital Industries Software.
“We chose Siemens Digital Industries Software as a partner because they have experience working with digital twin technology in other industries and possess a wide branch of software that can support this development,” says Branner. “And it’s not used so much in the wind energy industry. Some companies have worked with a digital twin for the bearings and gears in the drive train of the turbine, but not for blades. That’s unique and of course, an interesting area for us as we work with blades and test blades.
“But it’s also a very challenging area because those are some of the most highly loaded structures. It’s also a challenge because the goal is it should last 20, 30 years, running on a turbine every day in all kinds of weather. It’s a hostile environment out at sea. So it’s really challenging to build the systems that are robust and can work in practice.”
DTU Wind Energy performed physical testing in Simcenter Testlab™ software, 1D simulation in Simcenter Amesim™ software and virtual channels in Simcenter Testlab Neo software.
For blade testing, DTU Wind Energy uses experimental structural dynamics to identify the blade. This includes experimental modal analysis, operational modal analysis and strain-based operational modal analysis. In addition, DTU Wind Energy incorporated 3D finite element (FE) simulation and correlation with the test.
Free-free geometry was the baseline for all ReliaBlade tests and featured 124 measurement points. Strain-based operational modal analysis is a combination of strain gauges and speckle pattern for digital image correlation (DIC) measurements. Strain-based operational modal analysis features four different force levels (1.50kN, 2.17kN, 2.65kN, 3.17kN), 76 strain gauges along 12 sections and 200Hz sampling frequency.
Simcenter Testlab was used for structural dynamics identification, validation of numerical models, vibration-based damage detection and model-based system testing.
Digital platform development aided in the automation of the modal model estimation, Internet of Things (IoT) data transfer to IBM® Cloud, virtual sensors and model-based system testing and test and simulation integration.
The results of the ReliaBlade project shows DTU Wind Energy how it can apply developed digital twin architecture from the full mockup to the full-scale blade. DTU Wind Energy also works on how it can embed machine learning methods, perform automated model updating and use vibration-based structural health monitoring in the ReliaBlade project.
“Working with Simcenter is a great way, I think, to develop the vision for this project,” says Branner.
The Technical University of Denmark imagines a future where when a blade leaves the factory, it’s not just the physical blade, but it comes with a digital twin.
Blades are unique and they all have small imperfections or deviations that occur in the manufacturing process. Engineers need to consider all of the material properties, as they can be slightly different. The ReliaBlade project works with scanning technologies to take these imperfections into account and include them in the blade’s unique digital twin.
By applying sensors to the blade, they can monitor what happens to the blade during its lifetime. Real-life damage to the blades is monitored in the lab by loading the blades with exciters and then measured with sensors to detect the cumulative dam-age over time. This information is used to update the individual digital twin accordingly. In this way, a blade’s digital twin can always represent the true state of the physical blade.
With this optimized digital twin, it is possible to make further decisions with insight. When there comes a time that a blade needs repair, its digital twin can be used to simulate different repair methods, and from that, one could decide which particular repair option is best for the damage. One could also use the digital twin to make decisions on how to operate the turbine so the damage does not grow or propagate.