Oscar Curet is an assistant professor at Florida Atlantic University. For the past couple of years, he’s studied the movement of the Knifefish, an animal native to the Amazon River, that uses a long ribbon fin to propel itself through the water and navigate its complex environment. Inspired by it, Oscar Curet along with other researchers from Florida Atlantic University (FAU), created a underwater robot prototype based on blade-like knife fish, composed of 3D-printed materials, 16 motors, and a number of sensors.
The team also recently received a $258,008 grant from the U.S. Navy to equip their prototype with a Volumetric Particle Image Velocity System, or PIV. The system, which uses four cameras synchronized with a laser light to capture currents in three dimensions, will help researchers measure how fluid dynamics interact with the flexible propulsors the team has developed to make underwater vehicles more maneuverable.
“I’m interested in the fluid dynamics of biosystems,” Curet told Digital Trends. “I believe that the kind of flexible structures we see in many types of animal propulsion can transform the way that robots propel and maneuver. The knife fish has a wide range of capabilities. They have a large fin they can manipulate to move forward, backwards, and otherwise generate a big range of rich motions that aren’t seen in many animals.”
“As a engineer, we try to solve problems, and nature has solved some of the problems that we are facing, and one of them is mobility,” Curet said.”If you look at most common submarines, they tend to be very slow motion, they are not highly maneuverable, they need a huge radius of curvature, or they rely on many types of propellers around their body if they want to increase their mobility.”
Nature is a rich source of inspiration for robot development. Millions of years of evolution have endowed biological systems with morphological, neurophysiological, and behavioral features that enable them to survive and thrive in their environments. Bio-inspired robotics is about studying biological systems, and look for the mechanisms that may solve a problem in the engineering field for example biosensors (e.g. eye), bioactuators (e.g. muscle), or biomaterials (e.g. spider silk).
Many countries including the US, Japan and China are involved in research of bio-inspired propulsion systems.
“It was in the oceans that life first evolved and where complex animals have thrived for over 600 million years. Marine animals survive in environments as diverse as tropical coral reefs, polar ice-capped oceans, and the lightless abyssal depths,” says Frank E. Fish from West Chester University and Donna M. Kocak from HARRIS CapRock Communications.
“To deal with the rigors of the marine environment, animals have developed specialized sensory systems (e.g., echolocation, electroreception), mechanisms to deal with pressure (e.g., buoyancy control), strategies to economize on energy (e.g., fusiform body design, schooling, burst-and-glide swimming), armor (e.g., bony scales, mollusk shells), stability mechanisms (e.g., paired and median fins), maneuverability (e.g., flexible bodies, vectored thrust), speed (e.g., high-aspect-ratio oscillatory propulsors, jet propulsion), stealth (e.g., camouflage, low acoustic signature), and use of compliant materials (e.g., collagen, protein rubbers, mucous),” they further write.
Researchers at the University of Texas, Austin looks to fish for Camouflaging
Researchers at the University of Texas, Austin, are studying the remarkable ability of some fishes to hide from plain sight by adjusting to the light in certain angles. They have been funded by Navy with the aim to employ this technology in designing of stealthy submarines. In a paper published this week in Science researchers reports that certain fish use microscopic structures called platelets in their skin cells to scatter polarized light differently depending on the angle which allows the fish to seemingly disappear from their predators. Under the surface of the water, light tends to be polarized, that is all the light waves travel in the same plane.
“Fish have evolved the means to detect polarized light,” said Molly Cummings, professor of integrative biology in the College of Natural Sciences. “Given that, we suggested they’ve probably evolved the means to hide in polarized light. If we can identify that process, then we can improve upon our own camouflage technology for that environment.”
Visual Detection of targets can be through brightness contrast, color contrast or polarization contrast, among them polarization contrast is considered most effective for detection in the open ocean.
In a previous study, the researchers demonstrated in the lab that a fish called the lookdown was able to manipulate polarized light to its advantage. The new study—conducted in the actual ocean, shows lookdowns and other fish that live in the open ocean camouflage themselves this way.
US Navy tests a stealthy “Tuna fish” like swimming robot
In 2014, US Navy tested a UUV (unmanned undersea vehicle) developed by Boston Engineering Corporation’s Advanced Systems Group (ASG) based in Waltham, Massachusetts under grant from Chief of Naval Operations Rapid Innovation Cell, or CRIC.
This four feet long “bio-memetic” undersea vehicle replicates the dynamics of biological fish to move more rapidly, more accurately, and in more challenging areas than other marine solutions. Being propelled by its tail instead of a shaft or propeller helps it remain stealthy and energy efficient. It can accelerate quickly, reaching speeds up to 40 knots. The UUV is currently configured with a lithium ion battery and is engineered so that its front end remains stationary in order to maximize sensor performance.
It can function autonomously, but can also be remotely controlled by an operator via a 500 ft tether, long enough to inspect ship hulls and send information up through the cable.
It’s engineered to carry a range of interchangeable payloads from acoustic sensors to underwater cameras and can support a variety of tactical missions. The robot fish could be used for a range of missions, including undersea mine detection or prolonged surveillance of ships, ports and submarines. It is also capable of operating in high viscosity fluids such as crude oil, which could make it a valuable tool for off-shore drilling operations.
3D-Printed Fish Scales May Improve Military Armor
Researchers at MIT are studying some of the sturdiest forms of animal armor, particularly fish scales, and designing gear that matches the flexibility, comfort and durability found in the natural world using3D printing.
“We want to understand how the scales interact with each other to provide mobility, but then also how the scales, at a global level, provide structure, rigidity and flexibility at the same time,” Swati Varshney, a graduate student at MIT, told LiveScience.
Chinese Researchers developed bio-inspired transformable robotic fin
Chinese researchers are aiming to develop bio-inspired unmanned underwater vehicles with a very high swimming performance.
Fish swim by oscillating their pectoral fins forwards and backwards in a cyclic motion such that their geometric parameters and aspect ratios change according to how fast or slow a fish wants to swim; these complex motions result in a complicated hydrodynamic response.
Researchers from Department of Precision Machinery and Precision Instrumentation, University of Science and Technology of China, are studying how the dynamic change in the shape of a fin improves the underwater propulsion of bio-inspired mechanism. They have designed a novel transformable robotic fin to investigate how this change in shape affects the hydrodynamic forces acting on the fin.
This robotic fin has a multi-link frame and a flexible surface skin where changes in shape are activated by a purpose designed multi-link mechanism driven by a transformation motor. A drag platform has been designed to study the performance of this variable robotic fin. Numerous experiments were carried out to determine how various controlling modes affect the thrust capability of this fin.
The kinematic parameters associated with this robotic fin include the oscillating frequency and amplitude, and the drag velocity. The fin has four modes to control the cyclic motion; these were also investigated in combination with the variable kinematic parameters. The results will help us understand the locomotion performance of this transformable robotic fin. Note that different controlling modes influence the propulsive performance of this robotic fin, which means its propulsive performance can be optimized in a changing environment by adapting its shape.
Indian Institute of Technology-Madras developing super-efficient propellers
Scientists at Indian Institute of Technology-Madras are developing finlike blades, inspired by animals like penguins, turtles and fish, which can be super-efficient propellers and whiplash-like rudders. These blades respond faster to commands and their dual functions mean they can turn on a dime and save on fuel consumption. The bio-inspired propulsion systems can be used in ships remotely, underwater and in aerial vehicles as well.
Just like aquatic animals that navigate without a ripple on the water’s surface, these systems can steer a vessel underwater without creating a disturbance — making them hard to detect. IIT-M’s department of ocean engineering P Krishnankutty says aquatic animals make use of a variety of propulsion systems but the IIT-M team focused particularly on penguins and fish, which have better hydrodynamics and cause less disturbance.
Research scholar M N Praveen Babu said the penguin-inspired system has two fins that use the pressure difference between the upper and the lower surface of the fins to generate propulsion, rotating and swinging to move forward. “The other system inspired by fish has two side fins near to the fore end (where the pectoral fins of a fish are) and a tail fin,” Babu said. “Both the pectoral and tail fins help propel and manoeuvre but the tailfins give larger thrust.” The researchers tested propulsion and rudder systems on ship models in two different sizes at varying speeds. “We tested several parameters including selfpropulsion, thrust force, flapping amplitude, flapping frequency, forward speed, lift and drag,” Babu
said. “Certain devices, we found, had an efficiency of 80% when compared to an average of 65%.
Highly Maneuverable Robotic Fish Based on Biological Principles and Biomimetic Materials
This project, Sponsored by Office of Naval Research aims to develop highly maneuverable and efficient robotic fish by advancing biomimetic actuation and sensing materials, and by designing and controlling the robotic fish based on biological principles.
The research is concentrated on
Biomimetic actuation. “Inspired by fins of living fish, we are developing flexible artificial fins capable of complex 3D deformations based on electroactive polymers, seeking fundamental understanding of electro-mechano-hydrodynamics in fin-fluid interactions, and investigating biologically inspired maneuvering and propulsion strategies for biomimetic pectoral and caudal fins.”
Bioinspired flow sensing. “We are interested in developing micro flow sensors through novel microfabrication processes, characterizing and modeling the sensory response in a variety of flow conditions that are of biological and engineering interest, and exploring the use of arrays of such sensors as an artificial lateral line system for robotic fish.”
Feedback flow control. “We will investigate artificial lateral line-based feedback control of biomimetic fins to achieve maneuvers and schooling behaviors of robotic fish.”