RIVERSIDE, CA – A team of mechanical engineers at the University of California, Riverside (UCR) has unlocked a key secret to how stingrays maintain stability while swimming near the ocean floor. Their findings, published this week in the Journal of the Royal Society Interface, challenge previous assumptions about lift and could lead to significant advancements in underwater robotics and vehicle design.

The research centers around a meticulously crafted robotic fin designed to mimic the undulating movements of benthic rays – those that inhabit shallow waters. Unexpected results from tests in a specialized water tunnel revealed that these rays don’t simply glide; they actively counteract a downward force by subtly adjusting their fin angles.

The Elegant Efficiency of Ray Locomotion

For decades, scientists have been captivated by the graceful movements of rays. Unlike many fish that rely on powerful tail movements for propulsion, rays employ a unique undulating motion that appears remarkably energy-efficient. This efficiency stems from their ability to recycle energy from the surrounding water, minimizing the brute force required for movement. Swimming in this manner allows them to conserve energy, crucial for navigating their often-challenging environments.

However, the mechanics of this efficiency weren’t fully understood, particularly when it came to rays inhabiting different depths. Massive manta rays and other pelagic species, which frequent the open ocean, utilize a flapping motion to stay afloat. Benthic rays, like the common stingray, face a different challenge: maintaining position near the seafloor where downward forces are more pronounced.

UCR mechanical engineer Yuanhang Zhu and his team hypothesized that the differing environments dictated distinct swimming strategies. To test this, they constructed a 9.5-millimeter-thick robotic fin from silicone rubber and a large water tunnel to simulate ocean currents. The goal was to observe how physical forces impacted fin movement and, crucially, lift.

What they discovered was counterintuitive. Instead of experiencing increased lift near the simulated seafloor, the robotic fin was pulled downward. This unexpected result prompted the team to make subtle adjustments, ultimately finding that tilting the fin upward by just a few degrees counteracted the downward force. This suggests that stingrays naturally swim with a slight upward fin angle, a detail previously unknown.

“This wasn’t what we expected,” Zhu said in a UCR blog post. “Instead of gaining extra lift near the ground, the rays were pulled downward.”

This discovery has significant implications for the design of underwater vehicles. By mimicking the subtle fin adjustments of stingrays, engineers can create robots that are more stable, energy-efficient, and capable of navigating complex underwater environments.

But the inspiration doesn’t stop there. Researchers are already exploring how to apply these principles to create stealthier underwater vehicles. Could we see submarines that move with the silent grace of a ray? It’s a distinct possibility.

What other secrets might the natural world hold for the future of robotics? And how can we better leverage biomimicry to solve complex engineering challenges?

From Bio-Inspired Robots to Next-Gen Vehicles

The quest to replicate ray-like locomotion in robotics isn’t new. In 2018, UCLA engineers unveiled a 10-millimeter-long tissue-based robot constructed from heart cells and flexible electrodes. Even more remarkably, Harvard researchers created a biohybrid robot in 2017 powered by rat muscles and propelled by light-triggered propulsion.

Beyond these biohybrid approaches, engineers at the University of Washington are actively investigating how stingray swimming techniques can be integrated into next-generation underwater vehicles. The goal is to develop platforms that are not only more energy-efficient but also quieter than conventional submarines and remotely operated vehicles (ROVs). This is particularly crucial for applications like marine research, environmental monitoring, and even national security.

The natural world continues to serve as an unparalleled source of inspiration for engineers and scientists. As we deepen our understanding of biological systems, we unlock new possibilities for innovation and technological advancement. The Oxford Robotics Institute is another leading research center exploring biomimetic robotics, demonstrating the global interest in this field.

Frequently Asked Questions About Stingray Swimming