Design and Implementation of Paired Pectoral Fins Locomotion of Labriform Fish Applied to a Fish Robot

In present,there are increasing interests in the research on mechanical and control system of underwater vehicles.These ongoing research efforts are motivated by more pervasive applications of such vehicles including seabed oil and gas explorations, scientific deep ocean surveys,military purposes,ecological and water environmental studies,and also entertainments. However,the performance of underwater vehicles with screw type propellers is not prospective in terms of its efficiency and maneuverability.The main weaknesses of this kind of propellers are the production of vortices and sudden generation of thrust forces which make the control of the position and motion difficult. On the other hand,fishes and other aquatic animals are efficient swimmers,posses high maneuverability,are able to follow trajectories,can efficiently stabilize themselves in currents and surges,create less wakes than currently used underwater vehicle, and also have a noiseless propulsion.The fish's locomotion mechanism is mainly controlled by its caudal fin and paired pectoral fins.They are classified into Body and/or Caudal Fin(BCF)and Median and/or paired Pectoral Fins(MPF).The study of highly efficient swimming mechanisms of fish can inspire a better underwater vehicles thruster design and its mechanism. There are few studies on underwater vehicles or fish robots using paired pectoral fins as thruster.The work presented in this paper represents a contribution in this area covering study,design and implementation of locomotion mechanisms of paired pectoral fins in a fish robot.The performance and viability of the biomimetic method for underwater vehicles are highlighted through in-water experiment of a robotic fish.

First Recorded Account of a White Shark Agonistic Pectoral Fin Depression Behavior at Guadalupe Island, Mexico

An agonistic display by a white shark was observed and photographed during a cage dive at Guadalupe Island in November 2015. Exhibiting exaggerated pectoral fin depression, agonistic behaviors have been previously observed and described in several shark species. This account may be the first record of a white shark in close proximity to a caged diver, exhibiting strong pectoral fin depression significantly dipped, in the mid-agonistic display. Such displays should be considered as aggressive and potentially life-threatening by those using the ocean for recreational or professional purposes.

Effect of Active–Passive Deformation on the Thrust by the Pectoral Fins of Bionic Manta Robot

Bionic manta underwater vehicles will play an essential role in future oceans and can perform tasks,such as long-duration reconnaissance and exploration,due to their efficient propulsion.The manta wings’deformation is evident during the swimming process.To improve the propulsion performance of the unmanned submersible,the study of the deformation into the bionic pectoral fin is necessary.In this research,we designed and fabricated a flexible bionic pectoral fin,which is based on the Fin Ray®effect with active and passive deformation(APD)capability.The APD fin was actively controlled by two servo motors and could be passively deformed to variable degrees.The APD fin was moved at 0.5 Hz beat frequency,and the propulsive performance was experimentally verified of the bionic pectoral fins equipped with different extents of deformation.These results showed that the pectoral fin with active–passive deformed capabilities could achieve similar natural biological deformation in the wingspan direction.The average thrust(T)under the optimal wingspan deformation is 61.5%higher than the traditional passive deformed pectoral fins.The obtained results shed light on the design and optimization of the bionic pectoral fins to improve the propulsive performance of unmanned underwater vehicles(UUV).

HYDRODYNAMIC STUDY ON A PECTORAL FIN ROWING MODEL OF A FISH

Fish pectoral fin movement involves primarily a drag-based and a lift-based mechanisms to produce thrust. A numerical study on a pectoral fin rowing propulsion model based on the drag-based mechanism is presented in this article. The propulsive mechanism of the pectoral fin rowing model is related with the voriticity and pressure in the flow field. The relationship between the thrust and kinematic parameters and the wake-captured problem are analyzed. It is shown that a high thrust is produced in the power stroke, mainly due to the backward translation acceleration, the anticlockwise angular acceleration and the absence of stall in the uniform translation. Moreover, the flow control mechanism and the effect of dynamic flexible deformation are further analyzed. To properly choose controllable factors and adopt an appropriate dynamic deformation can improve the propulsive performance.

Experimental and Numerical Study on Pectoral-Fin Propulsive System

Generally the underwater bio-robots take the tail fin as propulsor, and combined with pectoral fin they can manoeuvre agilely and control their position and movement at will. In nature, a lot of fishes realize to suspend itself in water to go forward and to move back up by the pectoral fin moving complexly. So that it is significant theoretically and valuable for practical application to investigate the propulsive principle and hydrodynamic performance of pectoral fin, and find the method utilizing the pectoral fin to manoeuvre the underwater bio-robot agilely. In this paper, a two degree of freedom （DoF） motion model is established for a rigid pectoral fin, and the hydrodynamic performances of the pectoral fin are studied by use of the pectoral fin propulsive experimental platform developed by Harbin Engineering University, simultaneously the hydrodynamic performance of the pectoral fin is analyzed when some parameters change. Then, through the secondary development of FLUENT （CFD code） software, the hydrodynamic performances of rigid pectoral fin in viscous flows are calculated and the results are compared with the latest experimental results. The research in this paper will provide the theoretical reference for the design of the manoeuvring system imitating pectoral fin, at the same time will become the foundation for the development of the small underwater bio-robot.

NUMERICAL SIMULATION OF FISH SWIMMING WITH RIGID PECTORAL FINS

The numerical simulation of the self-propelled motion of a fish with a pair of rigid pectoral fins is presented.A Navier-Stokes equation solver incorporating with the multi-block and overset grid method is developed to deal with the multi-body and moving body problems.The lift-based swimming mode is selected for the fin motion.In the lift-based swimming mode,the fin can generate great thrust and at the same time have no generation of lift force.It can be found when a pair of rigid pectoral fins generates the hydrodynamic moment,it may also generate a lateral force opposite to the centripetal direction,which has adverse effect on the turn motion of the fish.Furthermore,the periodic vortex structure generation and shedding,and their effects on the generation of hydrodynamic force are also demonstrated in this article.

Fluid dynamics of a self-propelled biomimetic underwater vehicle with pectoral fins

Fluid dynamics of a self-propelled biomimetic underwater vehicle(BUV)with pectoral fins is investigated by an immersed boundary(IB)method.Typically,the BUV with a pair of pectoral fins starts from rest and attains a constant mean velocity as the mean longitudinal force is zero.The capability and accuracy of the IB method to deal with the interaction between the fluid and complex moving body are firstly validated.Then we carry out a parametric study to understand the effect of key governing parameters on the dynamic response of the BUV.It is found that with the increase of motion frequency or rolling amplitude,the pectoral fin propulsors can induce larger forward velocity so that the BUV takes less time to attain its stable periodic swimming state.Although the pectoral fin is a very complicated lifting surface,a linear relationship between forward Reynolds number(final swimming velocity is used as velocity scale)and frequency Reynolds number(product of motion frequency and fin chord length is used as velocity scale)can be established when the frequency Reynolds number is above a critical value.A linear relationship between forward Reynolds number and rolling amplitude is also found within the studied range of rolling amplitude.Furthermore,a small-density-ratio BUV is sensitive to the surrounding flow with more rapid evolution process of self-propulsion.Whereas,BUV with a large density ratio is more stable.The implications of the hydrodynamic analysis on the bio-inspired engineering design of BUV with pectoral fins are also discussed.

Range extension of Lepidocephalichthys alkaia （Teleostei： Cobitidae） and notes on its sexual dimorphism

The natural distributional range of the cobitid loach Lepidocephalichthys alkaia is extended into Yunnan Province, China. The modified sexually dimorphic pectoral fin in males of L. alkaia is described.

Design and Experiment on a Biomimetic Robotic Fish Inspired by Freshwater Stingray

Freshwater stingrays undulate their flexible disc-like pectoral fins to perform cruising, manoeuvring, and other motions. This undulatory propulsion has a higher propulsive efficiency and more precise manoeuvrability than most other species at low swimming velocity. In the current study, a new robotic fish inspired by the freshwater stingray was developed and tested. First, the morphology and kinematic patterns of the freshwater stingray were presented. A kinematic model of the pectoral fin was established based on several assumptions. Then a robotic stingray with an undulatory pectoral fin was designed and developed. Experiments were conducted to investigate the effects of various fin actuation parameters on its linear swimming velocity and the forces generated by the robotic stingray. The controllable fin parameters include oscillation frequency, wave number, maximal angular deflection of the fin rays, and the amplitude pattern of the pectoral fin. The experimental results indicate that the developed prototype is able to generate adequate thrust for self-propulsion. Linear swimming velocity and surge force increase rapidly with oscillation frequency, angular deflection, and wave number. A maximum velocity of 4.3 cm.s 1 （nearly 0.18 Body Lengths per second （BL·s-1）） and a maximum surge force of 102 mN are achieved at an oscillation frequency of 0.5 Hz, a wave number of 1, a maximum angular deflection of 30°, and an equal amplitude pattern. The sway force of the robotic fish fluctuates around 0 mN. The heave force varies with wave number and reaches its minimum at a wave number of 1.

NUMERICAL SIMULATION OF BATOID LOCOMOTION

The hydrodynamics of batoid swimming motions is investigated using the three-dimensional simulation of a self-propelled body in still water. The kinematics of batoid swimming is characterized by large amplitude undulations of the pectoral fins while the middle part of the body remains straight. The majority of the thrust is generated by pectoral fins. Linear and quadratic amplitude variations are used for the pectoral fins in analyzing the locomotion of the batoid. Navier-Stokes equations are used to solve the unsteady fluid flow. A user defined function and a dynamic mesh method are applied to track the batoid locomotion. The mean swimming velocities of 1.6 BL/s and 1.3 BL/s are achieved, respectively, with thrust coefficients of 0.13 in and 0.095 in the dynamical simulation, where BL/s is the body length per second. The maximum propulsive efficiency 19% is achieved when the frequency of the undulation is 2.2 Hz in both amplitude variations.

Video tracking method for three-dimen-sional measurement of a free-swimming fish

A video system for tracking a free-swimming fish two-dimensionally is introduced in this paper. The tracking is accomplished by simultaneously taking images from the ventral view and the lateral view of the fish with two CCD cameras mounted on two computer-controlled and mutually orthogonal translation stages. By processing the images recorded during tracking,three-dimensional kinematic parameters of the tail and pectoral fin of the fish in forward,backward and turning swimming modes are obtained.