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Biomimetic Unmanned Underwater Vehicle (BUUV) use Biomimetics for design of innovative propulsion systems

Unmanned underwater vehicles (UUVs), also known as underwater drones, are submersible vehicles that can navigate their way through various water systems with or without human intervention. Typically, UUVs fall into two categories, remotely operated underwater vehicles, or autonomous underwater vehicles.

 

Traditional underwater propulsion systems, such as screw-type axial propellors, convert torque into thrust; in other words, power from an engine turns the propellers and generates force by moving the flow of water downward and behind the blade.

 

Autonomous underwater vehicles (AUVs) are playing an ever-growing role in modern subocean operations, generating a demand for faster, more manoeuvrable designs capable of deployments of increasingly longer durations. In order to meet these demands, vehicle developers have been looking to biological aquatic animals for inspiration.

 

Nature is a rich source of inspiration for robot development. 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).

 

Therefore, biomimetic systems that transform UUVs to BUUVs are attracting significant attention as they demonstrate higher propulsion efficiency, enhanced maneuverability, and quieter actuation than conventional UUVs equipped with axial propellors.

 

Navies are also interested in biomimetic systems for developing more efficient propulsion systems, stealthy submarines, UUV (unmanned undersea vehicle) and improved military armor. Many countries including the US, Japan, India and China are involved in research of bio-inspired  systems.

 

Engineers have been able to mimic their behavior by constructing robotic imitations, with some considerable success. One of the best-known examples is Robotuna, an eight link tendon- and pulley-driven, whose external shape has the form of a bluefin tuna, capable of emulating the swimming motion of a live tuna. This project evolved into the Ghostswimmer, a prototype Navy vehicle that swims by manipulating its dorsal (back), pectoral (chest), and caudal (tail) fins.

 

Biomimetic underwater propulsion

For thrust, most modern human-designed propulsors utilize some sort of continuous rotation (think propellers), which is not a motion natural to biology. Fish and mammals such as dolphins and whales use fins and flukes to propel themselves in combined pitching and heaving motions, turtles use a paddling motion, while squid eject jets of fluid.

 

Animals have shown us that there are many more kinds of underwater locomotion, potentially offering unique benefits to robots. After evolving for millions of years, fish and cetaceans have developed fast efficient locomotion techniques, with levels of manoeuvrability that far outperform conventional engineered marine locomotion systems.

 

For example, Jellyfishes in nature propel themselves through their surroundings by radially expanding and contracting their bell-shaped bodies to push water behind them, which is called jet propulsion. As a source of inspiration, aquatic creatures such as fish, cetaceans, and jellyfish could inspire innovative designs to improve the ways that manmade systems operate in and interact with aquatic environments. Such vehicles have the potential to uncover new mission capabilities and improve maneuverability, efficiency, and speed.

 

In steady swimming, where there is no acceleration or deceleration, the thrust produced by the propulsive system is balanced exactly by the drag on the vehicle, in the time-average. For underwater vehicles, the drag force has two major components: the friction drag due to the viscous shear stresses acting on the surface of the vehicle, and the pressure, or form, drag due to the pressure losses in the wake. For streamlined vehicles, such as those shaped like fish, the viscous drag component tends to dominate, whereas for bluff bodies, exemplified by more boxy shapes, the form drag dominates.

 

We find that there are four major sources of thrust: (1) drag-based thrust, (2) lift-based thrust, (3) added mass forces, and (4) momentum injection. Drag is the force acting opposite to the direction of motion of the body, lift is the force produced normal to the direction of motion, added mass forces are due to the inertia of the water that is put in motion by the body, and momentum injection is the force produced by jetting fluid from the body, as used by squid and jellyfish.

 

In general, we can identify four major types of swimmers:

Oscillatory: these animals propel themselves primarily using a semi-rigid caudal fin or fluke that is oscillated periodically. Examples include salmon, tuna, and dolphin.
Undulatory: these animals utilize a traveling wave along their body or propulsive fins to push fluid backward. Examples include eels, lampreys, and rays.
Pulsatile: these animals periodically “inhale” a volume of water and then discharge it impulsively as a jet, producing thrust in the direction opposite the jet. Examples
include jellyfish, squid, and some mollusks.
Drag-based: these animals force a bluff body such as a rigid flipper through the water to generate thrust by reaction. Examples include humans, turtles, and ducks.

 

Oscillatory and undulatory swimmers make up a large fraction of the aquatic life synonymous with high swimming speed and efficiency, and so they have become the focus of propulsion inspiration.

 

It is not surprising that different swimmers show differences in their performance characteristics such as typical swimming speed (normalized by body length) and cost of transport. The cost of transport quantifies the energy efficiency of transporting an animal or vehicle from one place to another. In biology, it is often expressed as the distance traveled per unit energy cost (similar to miles per gallon). Despite large differences in size and swimming mechanisms, we see that most organisms swim between 0.5 and 1.5 body lengths per second. This is a typical cruising speed, and the maximum swimming speed can be very different among different swimmer types. However, drag-based swimmers have a notably higher cost of transport than the others. This makes sense, as most drag-based swimmers do not necessarily solely live in water, and many have evolved to also walk or fly.

 

A team of researchers in Poland has developed a novel energy-saving propulsion system design for a biomimetic unmanned underwater vehicle (BUUV)

Biomimetic systems may be designed to move like a fish, turtle, seal, or other marine animals which undulate to generate propulsion by pushing water against passing waves. However, the impact of tail oscillation on the fluid flow around a hull may result in vortices and thus necessitates the study of the FSI and the vortex structures.

 

Furthermore, existing BUUV designs often have many moving parts that couple rigid and flexible forms which result in a complex structure not without its flaws: “This type of construction is difficult to control, expensive and increases the risk of flooding the electronic components inside,” explains Dr. Paweł Piskur at the Faculty of Mechanical and Electrical Engineering, Polish Naval Academy, Gdynia, Poland.

 

The novel biomimetic propulsion systems the researchers have designed incorporate two fins fitted to a drive mechanism with fewer moving parts and components than existing models. “The movement of both fins outwards is simply an auxiliary movement that allows the specified values of the maximum angular deflection of the fins regarding the longitudinal axis of symmetry to be obtained, which is required to begin the work movement, says Piskur.

 

The fins work by driving the fins inwards and pushing the water outwards in opposition to the body of the BUUV, and then return to the start position with a force reduction generated by a positional shift: “During the movement, the fins alter their position from the vertical to the horizontal plane. This reduces the hydrodynamic drag of the fins during outside movement and, as a result, the drag of underwater vehicles,” explains Piskur.

 

The objective of this system is to address some of the challenges associated with present biomimetic models by reducing the number of design and control variables to demonstrate the difference between an innovative propulsion system and an undulating system. “Increasing the velocity of the fins during thrust generation while decreasing the velocity of the fins during the returning movement should result in even better efficiency,” says Piskur.

 

The propulsion system demonstrated higher thrust capabilities and improved net efficiency for low-speed movement, thereby ensuring the biomimetic nature of the movement. The team state that further tests will be conducted to evaluate the impact of a body on the novel propulsion system design as well as incorporating an additional joint and flexible fins to accommodate various styles of movement.

 

US Navy tests a stealthy “Tuna fish” like swimming robot in 2014

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.

 

 A robot fish is helping the Navy improve underwater movement reported in Sep 2016

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  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.”

 

In May 2018, University of California reported Transparent eel-like soft robot can swim underwater without propulsion

The engineers and marine biologists at the University of California  have developed transparent eel-like robot that  uses artificial muscles filled with water to propel itself . The foot-long robot, which is connected to an electronics board that remains on the surface, is also virtually transparent. The bot, described in the journal Science Robotics, is an important step towards a future when soft robots can swim in the ocean alongside fish and invertebrates without disturbing or harming them. Today, most underwater vehicles designed to observe marine life are rigid and submarine-like and powered by electric motors with noisy propellers, researchers said.

 

“Instead of propellers, our robot uses soft artificial muscles to move like an eel underwater without making any sound,” said Caleb Christianson, a PhD student at the University of California San Diego. One key innovation was using the salt water in which the robot swims to help generate the electrical forces that propel it. The bot is equipped with cables that apply voltage to both the salt water surrounding it and to pouches of water inside of its artificial muscles.\ The robot’s electronics then deliver negative charges in the water just outside of the robot and positive charges inside of the robot that activate the muscles.

 

The electrical charges cause the muscles to bend, generating the robot’s undulating swimming motion. The charges are located just outside the robot’s surface and carry very little current so they are safe for nearby marine life. “Our biggest breakthrough was the idea of using the environment as part of our design,” said Michael T Tolley, a professor UC San Diego. “There will be more steps to creating an efficient, practical, untethered eel robot, but at this point we have proven that it is possible,” said Tolley.

Royal Navy  exploring future Submarine Designs Like Robot Fish reported in August 2017

The Royal Navy has unveiled new futuristic submarine design concepts inspired by fish, eels, and other deep sea dwellers. The whole project was created to mark the 100th anniversary of the launch of the USS Nautilus, the world’s first nuclear-powered submarine.

 

The new Nautilus, as envisioned by young designers and engineers from technology nonprofit UKNEST, looks like a cross between a manta ray and a whale. Like an actual fish, flexible wingtips facilitate the vessel’s steering. A selection of drones accompany the mothership for defence and attack purposes. Just like the Nautilus, they take inspiration from nature.

 

The Eel, an Unmanned Underwater Vehicle, is an autonomous drone launched from the weapons bay of the Nautilus. Its organic design not only makes for efficient underwater movement, but also helps it camouflage into the surrounding environment. Flying Fish swarm drones, complete with fins, replace traditional missiles and torpedoes. “They would operate in the two most challenging regions for sensors to detect threats—the highly unpredictable sea surface and noisy layer under the sea surface,” UKNEST explains.

 

“It is no longer sufficient for Britannia to rule the waves,” UKNEST chair Tony Graham says. “Tomorrow the Royal Navy must aspire to dominate the deepest oceans.” Commander Peter Pipkin, fleet robotics officer, concurs. “The underwater battle space is a hugely challenging environment and it’s predicted to remain so for a long time yet.”

Chinese Researchers develop a novel robotic jellyfish able to perform 3-D jet propulsion and maneuvers reported in August 2019

Contrary to the prevailing view that jellyfishes are described as inefficient swimmers, jellyfishes have been proven to be one of the most energetically efficient swimmers. That is, it has been shown that jellyfish-like swimming will have a remarkable propulsive advantage if low-energy propulsion is demanded. Therefore, the movements of jellyfish have attracted significant interest over the past decade in the context of bioinspired underwater vehicles. Recently, researchers from Institute of Automation, Chinese Academy of Sciences in Beijing, China successfully developed a novel robotic jellyfish able to perform three-dimensional jellyfish-like propulsion and maneuvers based on a reinforcement learning-based method.

 

Combining the latest advancements in mechatronic design, materials, electronics, and control methods, researchers are making an integrated effort to develop smart actuators to fabricate various robotic jellyfishes. In general, such robotic jellyfishes are often tethered and much slower in speed in comparison with the kind actuated by conventional electric motors. Most existing robotic jellyfishes cannot freely adjust their three-axis attitude, which has an adverse effect on free-swimming propulsion and plausible applications.

 

To solve this problem, the research group led by Prof. Junzhi Yu from the Institute of Automation, Chinese Academy of Sciences, has investigated how a bioinspired motor-driven jellyfish-like robotic system capable of 3-D motion is designed and controlled.

 

The designed robotic jellyfish are modeled after Aurelia aurita (commonly termed moon jellyfish), which has a relatively large displacement and is especially suited for use with large load capacity. It is about 138 mm high and weighs about 8.2 kg. The robotic jellyfish is hemispherical in shape and consists of a bell-shaped rigid head, a cylindroid main cavity, four separate six-bar linkage mechanisms, and a soft rubber skin. To enhance the maneuverability of the robotic jellyfish, a barycenter adjustment mechanism assembled inside the cavity is introduced. Through adjusting two clump weights in vertical or horizontal direction or in a combination of the two, attitude regulation is achieved.

 

“It is very hard to establish a precise dynamic model for jellyfish-like swimming, since it is a highly nonlinear, strong coupling, and time-varying system,” said by Prof. Junzhi Yu. “Parametric uncertainties and external disturbances in dynamic aquatic environments, at the same time, cause difficulty in deriving control laws by solving the inverse kinematics problem.” Therefore, a reinforcement learning based closed-loop attitude control method is proposed for the robotic jellyfish, which can solve optimal decision control problem through direct interaction with the environment, particularly without the need for dynamic modeling.

 

Finally, the proposal of the reinforcement learning based attitude control method makes autonomous attitude regulation possible. “In comparison with most of the other robotic jellyfish, the built robot displays a high order of structure flexibility and yaw maneuverability,” Points out Yu. He also stressed that this self-propelled robotic jellyfish with 3-D motion has great implications for bioinspired design of jet propulsion system with great agility

 

Chinese Researchers developed  bio-inspired transformable robotic fin reported in 2016

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.

 

A jet-powered squid robot that can leap out of the water reported in June 2019

This “squid-like aquatic-aerial vehicle” from Beihang University in China is modeled after flying squids. Real squids, in addition to being tasty, propel themselves using water jets, and these jets are powerful enough that some squids can not only jump out of the water, but actually achieve controlled flight for a brief period by continuing to jet while in the air. The flight phase is extended through the use of fins as arms and wings to generate a little bit of lift. Real squids use this multimodal propulsion to escape predators, and it’s also much faster—a squid can double its normal swimming speed while in the air, flying at up to 50 body lengths per second.

The squid robot is powered primarily by compressed air, which it stores in a cylinder in its nose (do squids have noses?). The fins and arms are controlled by pneumatic actuators. When the robot wants to move through the water, it opens a value to release a modest amount of compressed air; releasing the air all at once generates enough thrust to fire the robot squid completely out of the water.

 

The robot squid can travel between 10 and 20 meters by jumping, whereas using its jet underwater will take it just 10 meters. At the moment, the squid can only fire its jet once, but the researchers plan to replace the compressed air with something a bit denser, like liquid CO2, which will allow for extended operation and multiple jumps. There’s also plenty of work to do with using the fins for dynamic control, which the researchers say will “reveal the superiority of the natural flying squid movement.”

 

In Sep 2021, Chinese researchers tested a new drone in the South China Sea that resembles a manta ray.

In Sep 2021, Chinese researchers also tested a new undersea drone shaped like a manta ray, in what appears to be its first open water test in the South China Sea. Utilizing a type of bio-inspired design, the drone—created by a university with strong ties to the Chinese military—uses the manta ray’s shape to help it efficiently glide through the water.

 

The unnamed UUV is modeled on the “shape and motion” of a manta ray, and can “flap its wings and slide underwater” like a real ray, per Xinhua. It explains that the rays are the ocean’s “most efficient swimmers,” and ​​are known for “high propulsion efficiency, high mobility and stability, low noise and large load capacity.” The drone weighs 1,036 pounds and can dive to a depth of 3,362 feet.

 

Undersea authority H.I. Sutton told Popular Mechanics that the ray design, while range-efficient, may not be the most quiet choice. Biomimicking drones which use a lot of servos to move the ‘fin’ may not be as stealthy as a traditional propeller.” “Biomimicking uncrewed underwater vehicles are an area of research in several countries, not least because of their military potential. Vessels which look and move like a fish of some sort may be more stealthy, particularly if creeping into an event harbor.”

 

The drone combines range, payload, and natural camouflage, making it an ideal candidate to spy on other countries in the Paracel Islands, and other island chains in the South China Sea. Manta rays are also native to the region, preferring warmer equatorial waters, so the presence of a manta ray-shaped object might not set off any alarms. All the while, this particular “manta ray” could be mapping the sea floor near the naval bases of other countries, infiltrating military facilities, or collecting radio and electronic signals for later analysis.

 

Another clue that the drone is destined for military use is the developer, Northwestern Polytechnical University (NWPU). It’s described by the U.S. government as a “​​Chinese military university that is heavily involved in military research and works closely with the People’s Liberation Army on the advancement of its military capabilities.”

 

A robotic scallop that moves just like the real thing reported in June 2019

RoboScallop, a “bivalve inspired swimming robot,” comes from EPFL’s Reconfigurable Robotics Laboratory, headed by Jamie Paik. Real scallops, in addition to being tasty, propel themselves by opening and closing their shells to generate jets of water out of their backsides. By repetitively opening their shells slowly and then closing quickly, scallops can generate forward thrust in a way that’s completely internal to their bodies. Relative to things like fins or spinning propellers, a scallop is simple and robust, especially as you scale down or start looking at large swarms of robots. The EPFL researchers describe their robotic scallop as representing “a unique combination of robust to hazards or sustained use, safe in delicate environments, and simple by design.”

RoboScallop is safe to handle even while it’s operating, although a gentle nibbling is possible if you get too handsy with it. Since the robot sucks water in and then jets it out immediately, the design is resistant to fouling, which can be a significant problem in marine environments. The RoboScallop prototype weighs 65 grams, and tops out at a brisk 16 centimeters per second, while clapping (that’s the actual technical) at just over 2.5 Hz. While RoboScallop doesn’t yet steer, real scallops can change direction by jetting out more water on one side than the other, and RoboScallop should be able to do this as well. The researchers also suggest that RoboScallop itself could even double as a gripper, which as far as I know, is not something that real scallops can do.

 

Indian Institute of Technology-Madras developing super-efficient propellers reported in Jan 2017

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%.

Learning from fish and flags to inform new propulsion strategies reported in April 2020

From the vibrations of the rear-view mirror just as your car reaches precisely 70 miles per hour to a building that collapses when, in an earthquake, it begins to vibrate at a specific frequency, there is untapped energy that could be harnessed for propulsion. In recent research, Andres J.Goza, found relationships between frequencies and the passive dynamics at play when vehicles move in air or water toward a better understanding of how to use these forces to enhance performance. According to Goza, assistant professor in the Department of Aerospace Engineering at the University of Illinois at Urbana-Champaign, his work is an effort to seek new bio-inspired propulsion strategies.

 

“Fish swim very efficiently and birds can fly very efficiently, so how can we use those observations to inform real paradigm shifts in the locomotion strategies that we engineer,” he said. “For example, the wing of a bird and the tail of a fish are flexible and when these animals fly or swim, the air and water around them induce passive motion. “Another example is when air blows past a flag, making it flap, it affects the air motion around it,” Goza said. “If we can understand this fluid-structure interaction or fluid-structure coupling at a very basic level, could we use it to design aircraft and submarines with a very different kind of locomotion?” Goza said the speed of the air or water flow around the vehicle and the density of the materials they are made from play a role, both in the resonance and in the passively induced motion.

 

“Scientists have understood, outside of this fluid-structure interaction context, that there’s a profound response when you excite a structure or system at its resonant frequency,” Goza said. “But what role do these passive dynamics play, and can we tune the structural properties so that the resonant frequency of your system is somehow meaningfully tied to the flow—that is, to the motion that you’re prescribing?” One sticking point in this research was that the standard definition of resonant frequency assumed that the structure was in a vacuum. “But it’s not; it’s in fluid and the fluid affects what that resonance frequency is,” Goza said. Consequently, step one was to define a notion of resonance that incorporates the effect of the fluid. “One of the big contributions of this research was unambiguously defining this resonant frequency, and then confirming that over a wide range of different parameters we actually see performance benefits near this resonant frequency,” he said. “Namely, if the structure flaps or moves at a certain frequency within this flow, it leads to an improvement in thrust.”

 

Goza said the larger heave amplitude computations are more reflective of fish swimming. The results indicated that at these larger amplitudes, both resonant and non-resonant mechanisms played a role. “Resonance is defined in terms of super small undulations, but we understand that fish are actually swimming at large amplitudes,” Goza said. “We bridged the gap between defining what resonance means in this small amplitude setting when there’s a fluid present, but also embracing the fact that fish undergo much larger emotions. We established connections to results in the small amplitude case, finding that performance benefits persist near resonance even at large amplitudes that are actually relevant to biological propulsion.”

 

Depending on the regime, Goza said, the peak thrust is near this resonant frequency associated with small amplitude. “The key is, as you move to these large amplitudes, resonance continues to play a predominant role. We found that the small linear amplitude notion of resonance was appropriate for predicting and understanding these peaks and thrust in the majority of cases. “If this passive motion can be useful in locomotion, it can reduce the amount of energy put into the system,” Goza said. “We can harness these passive dynamics and let them do the propulsion for us.” Goza said one of the next phases of this research will be to look at modern active materials that can be tuned to have the right resonant frequency to induce passive dynamics with the desired output.

 

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.”

 

 

References and Resources also include:

https://www.popularmechanics.com/military/research/a37530309/chinas-newest-drone-looks-and-swims-like-a-manta-ray/

https://www.azom.com/news.aspx?newsID=57700

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