Within the next years, thousands of wind turbines in Europe are getting to the end of their certification period, and it’s necessary to assess whether they are durable enough to go on producing electricity and have their certificate renewed.

But how do you test if the delicate parts of a turbine that is placed 60-80 meters above ground can withstand heavy storms for the next 20 years? And can you assess the durability of a whole park of several wind turbines if you know that some of them are either fatigued or getting to the end of their lifetime certificate?

Usually, lifetime assessment is done by adding measurement equipment to the turbines and the assessment is combined with visual inspections. Another option is hybrid testing, where a physical test of critical parts of the turbine is linked to a mathematical simulation of the movements during a storm to assess the system level dynamics.

“You split a full wind turbine into something virtual and something physical. The virtual part is simulated in a computer while the physical part is tested in a laboratory. Then you let them talk together, explains PhD student Frederik Nordtorp Kristiansen, Department of Civil and Architectural Engineering, Aarhus University.

Data and models of wind turbines are confidential

But to create that mathematical simulation, you need data about the turbine and the parts, and those data are typically confidential and as manufacturers compete to develop the best and most powerful designs, they are reluctant to share computational models with external experimental facilities.

Now there is a new solution for conducting the tests, which is an outcome from the project Demonstration of lifetime extension (DLTE), funded by the Danish Department of Energi.

“In cooperation with the test bench experts at R&D Test Systems, we have succeeded with a new platform that combines physical testing and computer simulation of how a storm will affect the structure based on data about the wind turbine – but without sharing the models with test facilities.

“In this solution, the tests can be done in different locations, exchanging data via a close circuit on the internet, so manufacturers can collaborate with external test facilities while maintaining the confidentiality of their computational models, says Frederik Nordtorp Kristiansen, who is working on the DLTE project.

Principle used to test how buildings move during earthquakes

The Hybrid Testing principle has been used for many years in seismic engineering. To test a building under seismic excitation – an earthquake – for instance one of the walls is tested while simulating its interaction with the rest of the building.

The researchers applied the principle for wind turbines – more specifically the pitch bearings, which rotates the blade to catch more or less wind.

“This is a complex structure, as the flexibility needed for rotation conflicts the strength required to transfer the wind loads to the hub and generate energy. It is one of the critical components - the sore spots of the wind turbine,” says Frederik Nordtorp Kristiansen.

“In the project group, we generated a numerical simulation of the wind turbine in Aarhus. The pitch bearing was tested on a physical test bench at Force Technology’s test facility in Munkebo. And they then interacted. The simulation sends a force to the test bench and received data on the displacement back. Like this, you could actually simulate how it would behave in a 50-year storm”, he explains.

Cyber-secure and industrial-secret-friendly communication

Besides seismic engineering, hybrid testing has been used for a long time in other sectors. For instance, hybrid testing in closed circuits is very mature in automotives, where experience as well as budgets are way heavier than in the wind turbine industry.

“We created a secure communication for the wind turbine industry, that is cyber secure and “industrial-secret-friendly” because you can avoid showing your experiment and still share the simulations. Everyone can have their own assets. The assets talk to each other over the internet. But no one has access to each other’s assets, says Giuseppe Abbiati, Associate Professor and Head of the Structural Engineering Section at the Department of Civil and Architectural Engineering at Aarhus University.

“The wind turbine park is getting older, so the certification body must issue an extension and with the testing techniques available today, it is not obvious to say yes or no. The overall motivation of this project was to find a solution to enable the certification body to put an “approved” stamp on the parks. We developed a model, that may be the solution, and in other projects we work to develop it further and make it faster, says Giuseppe Abbiati.

  For LinkedIn:

Can older wind turbines withstand future storms?

Researchers at Aarhus University have developed a new hybrid testing platform that combines physical experiments with digital simulations of extreme weather conditions. The goal is to make it possible to assess whether aging wind turbines are still robust enough to continue producing electricity – and have their certification renewed.

The solution was developed in collaboration with R&D Test Systems as part of the Demonstration of Lifetime Extension (DLTE) project, funded by the Danish Energy Agency. It enables testing of turbine components without sharing sensitive data – a key concern in a competitive and confidentiality-driven industry.

 “We connect a physical test in the lab with a virtual model of a storm. This allows us to analyze how the entire turbine responds – without requiring the manufacturer to share their computational models,” explains PhD student Frederik Nordtorp Kristiansen from the Department of Civil and Architectural Engineering.

With thousands of European turbines nearing the end of their certification period, this method could become a vital tool in the green transition.

#WindEnergy #Research #GreenTransition #HybridTesting #AarhusUniversity #DLTE #EnergyTechnology