Bistable Nonlinear Energy Sink for Simultaneous Vibration Control and Energy Harvesting in Offshore Wind Turbines

Offshore wind turbines are a big part of the push for renewable energy, capturing wind power out in the ocean. But these massive structures face some real challenges because they are constantly exposed to harsh weather; they are under the relentless forces of wind, waves, and currents, which induce vibrations that can shake the turbines, threaten their safety, lower their efficiency, and drive up maintenance costs. To keep these turbines operating smoothly and safely, it’s essential to mitigate these vibrations. At the same time, those vibrations hold untapped potential: they could be used to generate extra energy right where it’s needed most to power the turbines’ own monitoring systems and sensors, especially in remote places where reliable power isn’t easy to come by. Typically, engineers have relied on devices like tuned mass dampers (TMDs) to keep vibrations in check. TMDs can work well, but they’re usually set to handle a specific frequency range. This is where the problem comes in for offshore turbines, which face constantly changing conditions and, as a result, shifting vibration patterns. When the frequency drifts outside that set range, TMDs become much less effective. And while they absorb energy, they don’t convert it into something useful. That’s a missed opportunity. A recent paper published in Mechanical Systems and Signal Processing, and conducted by Associate Professor Qinlin Cai from Sichuan University, Dr. Yingyu Hua and Professor Songye Zhu from The Hong Kong Polytechnic University together with Associate Professor Xihong Zhang and Dr. Haoran Zuo from the Curtin University, the researchers, took a new approach. They saw the need for a device that could both handle unpredictable vibrations and also capture some of that energy. So, they developed what they call a bistable energy-harvesting track nonlinear energy sink (EHTNES). This device not only helps control vibrations but also turns them into electricity that can be used within the turbine. It’s built to be flexible enough to work across a range of frequencies, perfect for the unpredictable conditions that offshore turbines deal with daily. Their solution brings together a nonlinear energy sink, an electromagnetic damper, and an energy-harvesting circuit. These components allow the device to adapt to changing vibration patterns and simultaneously convert the movement into electricity. They found that EHTNES could manage a wider range of vibrations than traditional dampers. Instead of just swallowing up energy, it actually makes use of it, potentially cutting down the need for other power sources for monitoring equipment.

The research team took an in-depth look at the bistable EHTNES to see if it could handle two jobs at once: reducing vibrations and generating energy. They started by testing the core of the system, a unit combining an electromagnetic damper (EMD) with a buck-boost energy harvesting circuit (EHC). This part of the setup is key because it’s responsible for both dampening vibrations and turning that movement into electricity. To see how well it worked, they built a prototype and put it through a series of controlled vibration tests to monitor how the system performed on both fronts—dampening and energy generation. One of their main findings was that the EHC worked as they’d expected, acting like a stable energy-harvesting resistor. In simpler terms, it was good at converting the vibrations into steady electrical power, which means it could consistently generate energy while reducing the shaking. Even with moderate vibrations, the system maintained a resistance close to 20.2 Ω, which is exactly what they’d hoped for. This stable performance was crucial since it means the EHTNES could deliver reliable vibration control while capturing energy to power small devices. For instance, they found the EMD produced about 9.7 W of damping power, while the energy-harvesting circuit produced 2.3 W of electricity—enough to run sensors or other small electronics inside the turbine. They didn’t stop there. The team also wanted to see how well the EHTNES could handle real-life conditions, so they used it on a 5 MW offshore wind turbine model. They subjected the turbine model to simulated wind and wave forces, just like those it would experience out at sea. They wanted to know if the EHTNES could keep working effectively under the constantly changing conditions that real turbines face. What they found was impressive: the EHTNES was able to adapt and keep working even when the vibration frequencies shifted, thanks to its unique nonlinear design. Unlike traditional vibration control systems, which often struggle when conditions change, the EHTNES kept working smoothly across a range of frequencies. They also compared the EHTNES to a more conventional energy-harvesting tuned mass damper (EHTMD). While the EHTNES was about 10% less effective at controlling vibrations overall, it held up much better under changing frequencies. The traditional EHTMD relies on a narrow frequency range to be effective, so when the conditions shifted, it lost its edge. But the EHTNES remained stable and kept harvesting energy consistently, even as wind and wave conditions fluctuated. This flexibility makes it a strong candidate for offshore environments, where conditions are anything but predictable.

On the energy side, the EHTNES also showed a lot of potential. Depending on wind and wave conditions, it was able to harvest between 30 W and 170 W. While that might sound small compared to a wind turbine’s total output, we believe it’s enough to power onboard sensors or lights within the turbine, helping to make the system more self-sufficient. They were particularly excited about this aspect because it could mean fewer maintenance trips to replace batteries, which is a big deal for offshore turbines. And in extreme weather, the EHTNES could capture even more energy, which opens up more possibilities for powering additional equipment on-site. In the end, the tests also showed that the EHTNES could really help with structural integrity. Under tough conditions, like high winds combined with strong waves, the device cut down vibrations by about 34%. This is crucial for keeping turbines stable and reducing wear and tear on their structures. Overall, these findings show that EHTNES has the potential to do more than just control vibrations. It could help make offshore wind turbines more resilient, reliable, and even partially self-powered in the harsh conditions they face.

This study is truly significant because it takes a fresh approach to solving two key issues for offshore wind turbines: controlling vibrations and harvesting extra energy. By developing the bistable EHTNES, the researchers successfully created a system that can both stabilize turbine structures and capture energy from vibrations that would otherwise be wasted. This dual-purpose capability is especially useful for offshore environments, where reliable power is often hard to come by and the structures constantly face harsh, unpredictable weather. What’s really exciting is that the EHTNES isn’t just limited to wind turbines it could also be used in other large structures like offshore platforms and bridges, which deal with similar forces. In remote locations, where power is scarce and maintenance is a challenge, a device that both controls vibrations and generates energy could be a game-changer. Unlike traditional systems, which are usually only effective within a narrow frequency range, the EHTNES can handle a wide variety of conditions. This makes it perfect for long-term use in offshore wind farms, where reducing maintenance needs is a big deal. Another major benefit of the EHTNES is that it could make offshore infrastructure more self-sufficient by generating power for essential systems like sensors and monitors. This means lower costs in the long run and enhanced safety, since the device could keep these systems running even during extreme weather, when the turbines themselves might need to be shut down. By providing power independently of the grid, the EHTNES could make these wind farms more resilient and reduce the need for costly external power solutions. This research also ties into the bigger picture of making renewable energy systems as efficient as possible. As the world shifts away from fossil fuels, it’s essential to make every watt of energy count. The EHTNES points to a future where renewable energy systems are built to recycle their own energy, not just generate it. This could lead to more multifunctional systems that take on multiple roles—boosting efficiency while also solving other operational challenges. From an engineering perspective, the new study introduces a clever solution to frequency detuning, a common problem with traditional vibration control systems. Devices like tuned mass dampers only work well within a specific frequency range, but the EHTNES’s nonlinear design lets it adapt to a wider range of frequencies and this adaptability could inspire more research into nonlinear systems that can handle complex, real-world conditions, making renewable energy infrastructure even more robust and capable of meeting modern demands.