Researchers at the Fraunhofer Institute for Ceramic Technologies and Systems IKTS in Dresden have successfully tested in-house developed sensor rings designed to monitor the condition of wind turbine foundations at offshore wind farms.
Working together with staff from Baltic Taucher in Rostock, the researchers successfully demonstrated the viability of the process in an on-site trial at the Baltic 1 offshore wind farm.
For this trial, they made a crack measuring 0.9 millimeters in width, 45 millimeters in length, and 7 millimeters in depth in a branched metal pipe, and lowered it to the bottom of the Baltic Sea at a depth of 18 meters.
The trial was a success, siad Fraunhofer, as not only was the system able to locate the crack with excellent precision, but it even determined its length, height and depth.
Researchers are hopeful that the system will be certified and ready for robotic operation in approximately five years. Their goal is to sustainably ensure a long service life for the wind turbines while supporting the transition to new energy sources.
“We have developed a sensor ring that simplifies these measurements and will allow them to be performed automatically in the future,” said Andreas Schnabel, project manager at the IKTS.
“The heart of the system is the sensor ring, which is placed around the weld and remains there for the entire service life of the wind turbine.”
This ring is composed of numerous sensor elements arranged like a string of pearls, with spaces of five to seven centimeters between them. To take the measurements, the diver first connects a battery-powered handheld device to the interface port on the ring and then begins the analysis with the press of a button. In the future, this task will be performed by the robot, and the task of cleaning the area using high pressure will no longer be needed, Fraunhofer IKTS said.
Each of the sensor elements takes its turn in functioning as an actuator. The sensor hits the weld with ultrasound waves, which then permeate the entire structure. If there is a crack somewhere, the waves will be reflected back from the damaged area, while passing unobstructed through the intact areas. The other sensors detect these signals, and in this way they can hone in on the damaged areas.
The next sensor then takes its turn as an actuator: it transfers the data via cable connection to the handheld reader, whose data is transferred to a PC. As a result, the researchers receive data similar to that of a CT scanner at a doctor’s office. The end user, or in this case the inspector of the offshore wind farm, receives an image of the weld with damaged areas color-coded according to severity.
Researchers will be presenting the system for this at Hannover Messe from April 25 to 29, 2016.