Maneuvering and stability performance of a robotic tuna

The Draper Laboratory Vorticity Control Unmanned Undersea Vehicle(VCUUV) is the first mission-scale, autonomous underwater vehiclethat uses vorticity control propulsion and maneuvering. Builtas a research platform with which to study the energetics andmaneuvering performance of fish-swimming propulsion, the VCUUVis a self-contained free swimming research vehicle which followsthe morphology and kinematics of a yellowfin tuna. The forwardhalf of the vehicle is comprised of a rigid hull which housesbatteries, electronics, ballast and hydraulic power unit. Theaft section is a freely flooded articulated robot tail whichis terminated with a lunate caudal fin. Utilizing experimentallyoptimized body and tail kinematics from the MIT RoboTuna, theVCUUV has demonstrated stable steady swimming speeds up to 1.2m/sec and aggressive maneuvering trajectories with turning ratesup to 75 degrees per second. This paper summarizes the vehiclemaneuvering and stability performance observed in field trialsand compares the results to predicted performance using theoreticaland empirical techniques.     

The function and evolution of the tail streamer in hirundines

The morphology of a bird's tail may result from compromisesbetween aerodynamic efficiency, phylogenetic constraints andselection for non-aerodynamic characteristics, such as mateattraction. A good example of a trait shaped by trade-offsbetween aerodynamic efficiency and reproductive benefits mediatedthrough female preference is the tail streamer of the barn swallow. Here we use a standardized task to measure the impactof manipulated tail streamer lengths on maneuvering flightin the barn swallow and in the sand martin, a closely relatedspecies that lacks a streamer. Our results show that the tailstreamer of the barn swallow has a role in maneuvering flight. However, the outer tail feather is approximately 12 mm (9-20%)longer than the aerodynamic optimum for maneuvering flight.Furthermore, we show that the addition of artificial tail streamersto the sand martin, enhances maneuverability even at smallstreamer lengths, thereby implying that tail streamers mayhave evolved via natural selection for increased flight performance.Our results therefore suggest that initial tail streamer elongationin the barn swallow has a functional explanation in terms of increased aerodynamic performance. However, female choice hasbecome associated with this trait, promoting the developmentof a costly handicap.     

Kinematic Comparison of Forward and Backward Swimming and Maneuvering in a Self-Propelled Sub-Carangiform Robotic Fish

We make a thorough kinematic comparison of forward and backward swimming and maneuvering on a self-propelled robot platform that uses sub-carangifbrm swimming as the primary propulsor. An improved Central Pattern Generator （CPG） model allowing free adjustment of phase relationship and directional bias is employed to achieve flexible swimming and smooth transition. Considering the characteristics of forward swimming in carangiform fish and backward swimming in anguilliform fish, various backward swimming patterns for the sub-carangiform robotic fish are suitably created by reversing the direction of propagating propulsive waves. Through a combined use of the CPG control and closed-loop swimming direction control strategy, flexible and precise turning maneuvers in both forward and backward swimming are implemented and compared. By contrast with forward swimming, backward swimming requires a higher frequency or an increased lateral displacement to reach the same relative swimming speed. Noticeably, the phase difference shows a greater impact on forward swimming than on backward swimming. Our observations also indicate that the robotic fish achieves a larger turning rate in forward maneuvering than in backward maneuvering, yet these two maneuvers display comparable turning precision.     

Kinematics Modeling and Experiments of Pectoral Oscillation Propulsion Robotic Fish

A robotic fish driven by oscillating fins, "Cownose Ray-I", is developed, which is in dorsoventrally flattened shape withouta tail. The robotic fish is composed of a body and two lateral fins. A three-factor kinematic model is established and used in thedesign of a mechanism. By controlling the three kinematic parameters, the robotic fish can accelerate and maneuver. Forwardvelocity is dependent on the largest amplitude and the number of waves in the fins, while the relative contribution of fin beatfrequency to the forward velocity of the robotic fish is different from the usual result. On the other hand, experimental results onmaneuvering show that phase difference has a stronger effect on swerving than the largest amplitude to some extent. In addition,as propulsion waves pass from the trailing edge to the leading edge, the robotic fish attains a backward velocity of 0. 15 m·s^-1.     

Establishment of a biomimetic device based on tri-layer polymer actuators--propulsion fins

We propose to use bending type tri-layer polymer actuators as propulsion fins for a biomimetic device consisting of a rigid body, like a box fish having a carapace, and paired fins running through the rigid body, like a fish having pectoral fins. The fins or polymer bending actuators can be considered as individually controlled flexible membranes. Each fin is activated with sinusoidal inputs such that there is a phase lag between the movements of successive fins to create enough thrust force for propulsion. Eight fins with 0.125 aspect ratio have been used along both sides of the rigid body to move the device in the direction perpendicular to the longitudinal axis of the body. The designed device with the paired fins was successfully tested, moving in an organic solution consisting of solvent, propylene carbonate (PC), and electrolyte. The design procedure outlined in this study is offered as a guide to making functional devices based on polymer actuators and sensors.     

Research on the Swing of the Body of Two-Joint Robot Fish

The disadvantages caused by the swing of a fish body were analyzed. The coordinate system of a two-joint robot fish was built. The hydrodynamic analysis of robot fish was developed. The dynamic simulation of a two-joint robot fish was carried out with the ADAMS software. The relationship between the swing of fish body and the mass distribution of robot fish, the relationship between the swing of fish body and the swing frequency of tail, were gained. The impact of the swing of fish body on the kinematic parameters of tail fin was analyzed. Three methods to restrain the swing of fish body were presented and discussed.     

Computational hydrodynamics of animal swimming: boundary element method and three-dimensional vortex wake structure.

The slender body theory, lifting surface theories, and more recently panel methods and Navier-Stokes solvers have been used to study the hydrodynamics of fish swimming. This paper presents progress on swimming hydrodynamics using a boundary integral equation method (or boundary element method) based on potential flow model. The unsteady three-dimensional BEM code 3DynaFS that we developed and used is able to model realistic body geometries, arbitrary movements, and resulting wake evolution. Pressure distribution over the body surface, vorticity in the wake, and the velocity field around the body can be computed. The structure and dynamic behavior of the vortex wakes generated by the swimming body are responsible for the underlying fluid dynamic mechanisms to realize the high-efficiency propulsion and high-agility maneuvering. Three-dimensional vortex wake structures are not well known, although two-dimensional structures termed 'reverse Karman Vortex Street' have been observed and studied. In this paper, simulations about a swimming saithe (Pollachius virens) using our BEM code have demonstrated that undulatory swimming reduces three-dimensional effects due to substantially weakened tail tip vortex, resulting in a reverse Karman Vortex Street as the major flow pattern in the three-dimensional wake of an undulating swimming fish.     

Dynamic Modeling and Experiment of a Fish Robot with a Flexible Tail Fin

This paper presents the dynamic modeling of a flexible tail for a robotic fish. For this purpose firstly, the flexible tail was simplified as a slewing beam actuated by a driving moment. The governing equation of the flexible tail was derived by using the Euler-Bernoulli theory. In this equation, the resistive forces were estimated as a term analogous to viscous damping. Then, the modal analysis method was applied in order to derive an analytical solution of the governing equation, by which the relationship between the driving moment and the lateral movement of the flexible tail was described. Finally, simulations and experiments were carried out and the results were compared to verify the accuracy of the dynamic model. It was proved that the dynamic model of a fish robot with a flexible tail fin well explains the real behavior of robotic fish in underwater environment.     

Experimental and Numerical Study of Penguin Mode Flapping Foil Propulsion System for Ships

The use of biomimetic tandem flapping foils for ships and underwater vehicles is considered as a unique and interesting concept in the area of marine propulsion.The flapping wings can be used as a thrust producing,stabilizer and control devices which has both propulsion and maneuvering applications for marine vehicles.In the present study,the hydrodynamic performance of a pair of flexible flapping foils resembling penguin flippers is studied.A ship model of 3 m in length is fitted with a pair of counter flapping foils at its bottom mid-ship region.Model tests are carried out in a towing tank to estimate the propulsive performance of flapping foils in bollard and self propulsion modes.The same tests are performed in a numerical environment using a Computational Fluid Dynamics (CFD) software.The numerical and experimental results show reasonably good agreement in both bollard pull and self propulsion trials.The numerical studies are carried out on flexible flapping hydrofoil in unsteady conditions using moving unstructured grids.The efficiency and force coefficients of the flexible flapping foils are determined and presented as a function of Strouhal number.     

CFD Simulation of Fish-like Body Moving in Viscous Liquid

The study of fish-like bodies moving in liquid is an interesting and challenging research subject in the fields of biolocomotion and biomimetics. Typically the effect of tail oscillation on fluid flow around such a body is highly unsteady, generating vortices and requiring detailed analysis of fluid-structure interactions. An understanding of the complexities of such flows is of interest not only to biologists but also to engineers interested in developing vehicles capable of emulating the high performance of fish propulsion and manoeuvring. In the present study, a computational fluid dynamic （CFD） simulation of a three-dimensional biomimetic fish-like body has been developed to investigate the fluid flows around this body when moving in a viscous liquid. A parametric analysis of the variables that affect the flow surrounding the body is presented, along with flow visualisations, in an attempt to quantify and qualify the effect that these variables have on the performance of the body. The analysis provided by the unsteady transient simulation of a fish-like body has allowed the flow surrounding a fish-like body undergoing periodic oscillations to be studied. The simulation produces a motion of the tail in the （x, y） plane, with the tail oscillating as a rigid body in the form of a sinusoidal wave.     

Why do electric fishes swim backwards? An hypothesis based on gymnotiform foraging behavior interpreted through sensory constraints

Synopsis Fishes producing high-frequency wavelike electrical discharges maintain a relatively rigid body axis and swim forwards and backwards with equal ease. Using stop-action videotape filming we have observed the gymnotiform Apteronotus albifrons feeding on zooplankton and oligochaete annelids. Here it is reported that reverse swimming is characteristic of two foraging behaviors: searching for prey and assessing it. In assessing a potential prey item, fish typically scan it from tail to head by swimming backwards, then ingest it after a short forward lunge. A scan in the opposite direction-from head to tail by forward swimming-would have the prey located near the tail and out of position for the final lunge. Food choice experiments indicate that these electrosensing fish feed equally well, and take larger rather than smaller zooplankton, under light and dark conditions. Furthermore, electric fish take normal (light) colored and darkened prey (Daphnia) in a 50: 50 ratio under both dark and light conditions. These results are consistent with the interpretation that electrosensory cues are being used to detect zooplankton and other prey. Together, our observations support Lissmann's (1958, 1974) and Lissmann & Machin's (1958) assertion that backwards swimming is a component of a locomotory pattern guided by the constraints produced by an active electrical sense.     

The fish tail as a derivation from axial musculoskeletal anatomy: an integrative analysis of functional morphology

The adult morphology of the tail varies greatly among extant fishes despite sharing both ontogenetic similarities and the functional need to propel the body through a fluid medium. Both sharks (Chondrichthyes) and ray-finned fishes (Actinopterygii) control caudal fin musculature independently of axial body myomere activity to modify the stiffness and shape of their tails. For example, sharks and bony fishes possess different structural elements and muscles and move their tails in different ways, resulting in different locomotory hydrodynamic effects and a range of performance variables including speed and maneuverability. The stiffness of the heterocercal, lobate tail of the shark can be modulated during the tail beat resulting in nearly continuous thrust production. In contrast, the highly flexible tail of ray-finned fishes can be manipulated into many different shape conformations enabling increased maneuverability for these fishes. Consequently, the developmental, morphological, and functional derivation of the tail from the axial trunk has resulted in a diversity of form, the attributes of which may be of ecological and evolutionary significance.     

The scaling of locomotor performance in predator-prey encounters: from fish to killer whales.

During predator-prey encounters, a high locomotor performance in unsteady manoeuvres (i.e. acceleration, turning) is desirable for both predators and prey. While speed increases with size in fish and other aquatic vertebrates in continuous swimming, the speed achieved within a given time, a relevant parameter in predator-prey encounters, is size independent. In addition, most parameters indicating high performance in unsteady swimming decrease with size. Both theoretical considerations and data on acceleration suggest a decrease with body size. Small turning radii and high turning rates are indices of maneuverability in space and in time, respectively. Maneuverability decreases with body length, as minimum turning radii and maximum turning rates increase and decrease with body length, respectively. In addition, the scaling of linear performance in fish locomotion may be modulated by turning behaviour, which is an essential component of the escape response. In angelfish, for example, the speed of large fish is inversely related to their turning angle, i.e. fish escaping at large turning angles show lower speed than fish escaping at small turning angles. The scaling of unsteady locomotor performance makes it difficult for large aquatic vertebrates to capture elusive prey by using whole-body attacks, since the overall maneuverability and acceleration of small prey is likely to be superior to that of large predators. Feeding strategies in vertebrate predators can be related to the predator-prey length ratios. At prey-predator ratios higher than approximately 10(-2), vertebrate predators are particulate feeders, while at smaller ratios, they tend to be filter feeders. At intermediate ratios, large aquatic predators may use a variety of feeding methods that aid, or do not involve, whole body attacks. Among these are bubble curtains used by humpback whales to trap fish schools, and tail-slapping of fish by delphinids. Tail slapping by killer whales is discussed as an example of these strategies. The speed and acceleration achieved by the flukes of killer whales during tail slaps are higher and comparable, respectively, to those that can be expected in their prey, making tail-slapping an effective predator behaviour.     

Dynamic Modeling of a Non-Uniform Flexible Tail for a Robotic Fish

In this paper, a non-uniform flexible tail of a fish robot was presented and the dynamic model was developed. In this model, the non-uniform flexible tail was modeled by a rotary slender beam. The hydrodynamics forces, including the reactive force and resistive force, were analyzed in order to derive the governing equation. This equation is a fourth-order in space and second-order in time Partial Differential Equation (PDE) of the lateral movement function. The coefficients of this PDE were not constants because of the non-uniform beams, so they were approximated by exponential functions in order to obtain an analytical solution. This solution describes the lateral movement of the flexible tail as a function of material, geometrical and actuator properties. Experiments were then carried out and compared to simulations. It was proved that the proposed model is suitable for predicting the real behavior of fish robots.     

Multifunctional DNA-based biomemory device consisting of ssDNA/Cu heterolayers

In the present study, we developed a novel DNA-based biomemory device that was comprised of ssDNA/Cu heterolayers on Au electrodes. As a conducting material, a thiol-modified single strand DNA (26 bp) was designed and immobilized on the Au electrode without the need for any linker material. Cu(2+) ions, which acted as the active site, were then chemically absorbed on the external structure of ssDNA through electrostatic interactions. The presence of the fabricated ssDNA/Cu heterolayer was confirmed by surface plasmon resonance (SPR) spectroscopy and Raman spectroscopy. Cyclic voltammetry experiments were carried out to investigate the redox properties of ssDNA/Cu hybrids to obtain the oxidation and reduction potential. Based on measured oxidation and reduction potential, a ROM-type, 3-state type, and WORM type DNA memory functions were demonstrated by chronoamperometry (CA) and open circuit potential amperometry (OCPA). This proposed device acts and operates the memory function very well. In the near future, DNA based biomemory device in this study could provide the alternative to the inorganic electronic device when molecular scaled immobilization control and signal measurement are achieved.     

The tubercles on humpback whales' flippers: application of bio-inspired technology

The humpback whale (Megaptera novaeangliae) is exceptional among the large baleen whales in its ability to undertake aquabatic maneuvers to catch prey. Humpback whales utilize extremely mobile, wing-like flippers for banking and turning. Large rounded tubercles along the leading edge of the flipper are morphological structures that are unique in nature. The tubercles on the leading edge act as passive-flow control devices that improve performance and maneuverability of the flipper. Experimental analysis of finite wing models has demonstrated that the presence of tubercles produces a delay in the angle of attack until stall, thereby increasing maximum lift and decreasing drag. Possible fluid-dynamic mechanisms for improved performance include delay of stall through generation of a vortex and modification of the boundary layer, and increase in effective span by reduction of both spanwise flow and strength of the tip vortex. The tubercles provide a bio-inspired design that has commercial viability for wing-like structures. Control of passive flow has the advantages of eliminating complex, costly, high-maintenance, and heavy control mechanisms, while improving performance for lifting bodies in air and water. The tubercles on the leading edge can be applied to the design of watercraft, aircraft, ventilation fans, and windmills.     

The bacteriophage T4 DNA injection machine

The tail of bacteriophage T4 consists of a contractile sheath surrounding a rigid tube and terminating in a multiprotein baseplate, to which the long and short tail fibers of the phage are attached. Upon binding of the fibers to their cell receptors, the baseplate undergoes a large conformational switch, which initiates sheath contraction and culminates in transfer of the phage DNA from the capsid into the host cell through the tail tube. The baseplate has a dome-shaped sixfold-symmetric structure, which is stabilized by a garland of six short tail fibers, running around the periphery of the dome. In the center of the dome, there is a membrane-puncturing device, containing three lysozyme domains, which disrupts the intermembrane peptidoglycan layer during infection.     

Vorticity Control in Fish-like Propulsion and Maneuvering

Vorticity control is employed by marine animals to enhance performancein maneuvering and propulsion. Studies on fish-like robots andexperimental apparatus modelling rigid and flexible fins providesome of the basic mechanisms employed for controlling vorticity.     

Dynamics Modeling and Simulation of a Bionic Swim Bladder System in Underwater Robotics

While considering that fish could suspend themselves under water and could enhance their mobility by adjusting its swim bladder, we have carried out research on a bionic swim bladder system in underwater robotics, which could amend the underwater robotics' static balance and controllability conditions even if the depth of water changes. First, this paper introduces the bio-swim bladder's structure and function. Second, it works out the dynamic model of the bionic swim bladder, and then it analyses the dynamic characteristic and effect of the bionic swim bladder system with the software Matlab/simulink. Finally, considering about the nonlinear relationship of the parameters in the model, this paper brings forward a dual-speed control method, which could make the effect of the bionic swim bladder non-coupling. The result of the simulation reveals that the bionic swim bladder could change the buoyancy and centroid distribution of the underwater robotics effectively and independently, bringing it into a balance state, under which the control and maneuverability could be enhanced.     

A food web based hypothesis for the survival vs. weight relationship of rainbow trout in an experimental stream study with bleached kraft mill effluent

A series of experimental streams studies carried out with biologically treated bleached kraft mill effluent (BKME) and rainbow trout Oncorhynchus mykiss included a variety of fish health parameters. There was a pattern of larger but fewer fish in BKME exposed streams. To determine if reduced fish numbers was a detrimental effect, we examined the relationship between number and weight for control and BKME exposed streams for the 9‐month effluent exposures of 1.3–5.1% v/v. A regression analysis indicated that fish numbers decreased at a similar rate for corresponding fish size in both control and BKME‐exposed streams. A dose‐response relationship for effluent and fish number was not found, indicating that reduced fish number was not a direct expression of toxicity. The factors which induced BKME‐exposed fish populations to tend toward fewer but larger fish were not determined but are hypothesized to relate to BKME food web stimulation, a related enhancement in trout growth, and a corresponding reduction in fish number.