Mathematical tools help predict capsizing of wave energy devices at open sea

Texas A&M University researchers have developed a new set of analytical tools that can help predict if wave energy devices will capsize in rapidly changing ocean environments.

The tools can help characterize the movements of floating, but anchored wave energy devices. According to the researchers from Texas A&M University, their technique is fast, yet accurate enough to estimate if wave energy devices will turn over in an ever-changing ocean environment.

Jeffrey Falzarano, professor in the Department of Ocean Engineering, said: “Wave energy converters need to take advantage of large wave motions to make electricity. But when a big storm comes, you don’t want big wave, wind and current motions to destroy these devices.

“We have developed much simpler analytical tools to judge the performance of these devices in a dynamic ocean environment without necessitating massive amounts of simulations or physical model tests that take a lot of time to run and are cost-prohibitive”.

For the analysis, Hao Wang, Falzarano’ s graduate student, used a cylindrical wave-energy device. This generic shape allowed the researchers to simplify the problem of prediction and extended their analysis to other wave-energy converters of similar shape. He also considered three mooring configurations.

Wang used two analytical methods, the Markov and Melnikov approaches, to predict the risks of turning over under random excitation.

More specifically, using information from the wave energy device’s geometry, the configuration of the mooring system and tidal wave properties, the methods yield a graph containing an envelope-like region.

Intuitively, if the waves are really big, like during a storm, and the floating vessel escapes this envelope, it will likely turnover, according to Texas A&M University.

“Ships come in a variety of shapes and sizes; tankers, for example, are very different from fishing vessels or other military ships. These different geometries affect the ship’s motion in the water. Similarly, the shape of wave-energy devices can be quite diverse,” said Falzarano.

The researchers noted that although the analytical models were completely different, they yielded almost the same results, validating their merit and accuracy.

They also said that their mathematical approach can be applied to assess the performance of other floating devices, such as floating wind turbines.

“The platform for a floating wind turbine is the same as the one for wave energy devices, and so floating turbines can also pitchpole or turnover if the waves are very high. My group has been leaders in developing methods for predicting ship stability. We’re now looking at applying those approaches to renewable, floating energy devices”, concluded Falzarano.