September 2020

30 HYDRAULICS & PNEUMATICS September 2020 www.hpmag.co.uk HYDRAULICS According to industry reports, each year one out of every 200 wind turbine blades fail. Those failures pose a two-fold concern for turbine owners. First, when a blade fails, there’s unplanned downtime and potential insurance issues. Second, how can blade manufacturers and turbine owners and operators feel confident that the blades on their turbine are tested adequately? Researchers at the Technical University of Denmark (DTU) Large Scale Facility, part of Department of Wind Energy and the Villum Centre for Advanced Structural and Material Testing (CASMaT), believe they have answers. The test facility, built by the Danish Building and Property Agency, opened in 2017 on the DTU Risø campus. Scientists at the facility focus on developing new, advanced test methods to gain a better understanding of failure in large structures. DTU works with the wind energy industry conducting research projects funded partly by government grants and with money from leading global turbine manufacturers. Prior to 2017, DTU had a vision to develop a facility with the capability to test large-scale blades and other industrial components to help manufacturers reliably and efficiently replicate field conditions. DTU solicited proposals from engineers who could design a building and equipment capable of running advanced testing methods and research about the strength and fatigue behaviour of large structures when exposed to complex loading. After soliciting proposals and securing funding from the Danish government, DTU picked Moog in the UK and its technical partners TA Savery and Qualter Hall for the project. Design and installation Moog’s knowledge of closed loop servo control and actuation helped it create a testing facility underpinned by a digital closed loop control system and application software. To provide DTU testing flexibility, Moog and its partners designed and installed test equipment to be used with the three test stands, which are part of the original building design and construction and designed to take 15m, 25m and 45m blade sizes. Moog engineers carried out the installation and commissioning of the suite of test equipment and provided training and ongoing support for DTU staff. Key role of hydraulics The Moog scope of supply for the three blade test stands included the hydraulic power plant and distribution network, six hydraulic winches for the static test and a combination of eight Mass Resonance Exciter (MRE) and linear actuator assemblies for dynamic test work. The solution also included all pipe work, hosing and actuation devices, control system electronics and application software. In designing the facility’s equipment, Moog gave DTU the latitude to conduct an array of tests. For example, if researchers wanted to use a test bay to conduct a dynamic test on a blade, the hydraulic system would accommodate wide pressure fluctuations. If the next test required a static one with winches, DTU could set the hydraulics to meet a very- low flow. Designing the winch assemblies, the team partnered with UK based Qualter Hall. This project included discussions about the type of rope, safety factors and mounting a hydraulic manifold on the winches, so DTU researchers can angle the winches depending on a configuration of 2, 4 or 6 load points. Competing blade-testing designs use enormous towers with winches that facility managers move with a fork truck for static testing sidewise. DTU’s winches load the blade vertically, so researchers can perform a static test to extreme loads with six winches loading a blade at six positions, while pulling the test specimen toward the floor and mimicking an extreme wind load experienced in a 100-year storm. The tip of a blade in the DTU facility can move up to 14 meters, while the root of the blade moves a few centimetres. DTU wanted a facility wherein gravity and the test direction were the same. The advantage to testing a blade vertically versus sidewise with a tower is that with the latter configuration, researchers have a tower that will bend during a test; this makes it difficult to control load position as well as taking up a lot of facility space, even when not in use. Actuator designs from the aircraft industry In designing the actuation for the MRE, Moog included hydraulic actuator designs it had used for the aircraft industry. Within the MRE is a standard Moog actuator building block that excites the blade. The weight of the MRE was also of concern to DTU because similar devices manufactured by test houses included manifolds and piping that added mass. Working with DTU, Moog created a control manifold made from high-strength aircraft aluminium that DTU could mount anywhere. Full support “For every customer, with these types of systems, we seek to engage in a service level agreement, support package, preventive maintenance and tech support,” says Kevin Cherrett, business segment manager for systems and services with Moog’s Industrial Solutions & Services group. “Our definition of tech support is not just a one-off exercise; we’ll be with DTU for the duration of the use of the equipment.” Another example of how Moog continues to support DTU’s work is via a project in which researchers hope to see what the future holds for a working wind turbine blade. By developing sensors to embed in a blade, DTU wants to know if it can predict damage. “Moog’s technology is helping with this because we will embed sensors in test blades with built-in defects and monitor how the damage grows,” says Dr Kim Branner, senior research scientist and head of the Structural Design & Testing Team for DTU Wind Energy. “The Moog exciters will put realistic loads on the blades.” Branner sees the project helping blade makers build better blades but also creating a digitised twin of each blade that a wind farm operator could use to model what a blade’s future state might look like. If all goes according to plan, someday a wind farm control centre could predict a blade fail before it happens. info.moog.co.uk/bladetest8 Moog takes blade testing to the extreme