Fish Swimming amid Falling Flowers中的中国绘画元素

中国传统文化传播深刻影响了欧美诗人的诗歌创作,如霍华德·奈莫洛夫受中国传统绘画《落花游鱼图》的影响创作了美国现代诗歌Fish Swimming amid Falling Flowers。霍华德·奈莫洛夫受中国传统绘画的影响主要体现在诗歌创作中对物象移用、意境营造、重返自然、诗意栖居、万物相融、和谐共存的哲思。

Experimentation of Fish Swimming Based on Tracking Locomotion Locus

There are many kinds of swimming mode in the fish world, and we investigated two of them, used by cyprinids and bulltrout. In this paper we track the locomotion locus by marks in different flow velocity from 0.2 m·s^-1 to 0.8 m·s^-1. By fit the data above we could find out the locomotion mechanism of the two kinds of fish and generate a mathematical model of fish kine- matics. The cyprinid fish has a greater oscillation period and amplitude compared with the bulltrout, and the bulltrout changes velocity mainly by controlling frequency of oscillation.

Where is the rudder of a fish?:the mechanism of swimming and control of self-propelled fish school

Numerical simulation and control of self- propelled swimming of two- and three-dimensional biomimetic fish school in a viscous flow are investigated. With a parallel computational fluid dynamics package for the two- and three-dimensional moving boundary problem, which combines the adaptive multi-grid finite volume method and the methods of immersed boundary and volume of fluid, it is found that due to the interactions of vortices in the wakes, without proper control, a fish school swim with a given flap- ping rule can not keep the fixed shape of a queue. In order to understand the secret of fish swimming, a new feedback con- trol strategy of fish motion is proposed for the first time, i,e., the locomotion speed is adjusted by the flapping frequency of the caudal, and the direction of swimming is controlled by the swinging of the head of a fish. Results show that with this feedback control strategy, a fish school can keep the good order of a queue in cruising, turning or swimming around circles. This new control strategy, which separates the speed control and direction control, is important in the construction of biomimetic robot fish, with which it greatly simplifies the control devices of a biomimetic robot fish.

Investigation on 3Dt wake flow structures of swimming bionic fish

A bionic experimental platform was designed for the purpose of investigating time accurate three-dimensional flow field, using digital particle image velocimetry （DSPIV）. The wake behind the flapping trail of a robotic fish model was studied at high spatial resolution. The study was performed in a water channel. A robot fish model was designed and built. The model was fixed onto a rigid support frame- work using a cable-supporting method, with twelve stretched wires. The entire tail of the model can perform prescribed motions in two degrees of freedom, mainly in carangiform mode, by driving its afterbody and lunate caudal fin respectively. The DSPIV system was set up to operate in a trans- lational manner, measuring velocity field in a series of parallel slices. Phase locked measurements were repeated for a number of runs, allowing reconstruction of phase average flow field. Vortex structures with phase history of the wake were obtained. The study reveals some new and complex three-dimensional flow structures in the wake of the fish, including ＂reverse hairpin vortex＂ and ＂reverse Karman S-H vortex rings＂, allowing insight into physics of this complex flow.

Research Development on Fish Swimming

Fishes have learned how to achieve outstanding swimming performance through the evolution of hundreds of millions of years,which can provide bio-inspiration for robotic fish design.The premise of designing an excellent robotic fish include fully understanding of fish locomotion mechanism and grasp of the advanced control strategy in robot domain.In this paper,the research development on fish swimming is presented,aiming to offer a reference for the later research.First,the research methods including experimental methods and simulation methods are detailed.Then the current research directions including fish locomotion mechanism,structure and function research and bionic robotic fish are outlined.Fish locomotion mechanism is discussed from three views:macroscopic view to find a unified principle,microscopic view to include muscle activity and intermediate view to study the behaviors of single fish and fish school.Structure and function research is mainly concentrated from three aspects:fin research,lateral line system and body stiffness.Bionic robotic fish research focuses on actuation,materials and motion control.The paper concludes with the future trend that curvature control,machine learning and multiple robotic fish system will play a more important role in this field.Overall,the intensive and comprehensive research on fish swimming will decrease the gap between robotic fish and real fish and contribute to the broad application prospect of robotic fish.

Fish Swim Bladder-Derived Porous Carbon for Defluoridation at Potable Water pH

The levels of fluoride in various ground water sources in East Africa are above the World Health Organization upper limit of 1.5 mg/L. Research on diverse defluoridation technologies has proven that adsorption stands out as an affordable, efficient, and facile technology. Fish swim bladder-derived porous carbon (FBPC) activated by KOH and surface oxidized by nitric acid was successfully investigated as an adsorbent for defluoridation at portable water pH. The FBPC was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS). Batch methods were used to study physiochemical parameters viz., initial fluoride concentration, temperature, adsorbate dosage, contact time and pH. Freundlich, Temkin, Langmuir and Dubinin-Radushkevich isotherms were plotted and analyzed to understand the adsorption process. Bangham, Weber Morris, pseudo first and second-order models were used to elucidate the kinetics of adsorption. Optimal conditions for fluoride removal were found to be: pH of 6, FBPC adsorbent dose of 5.0 g/L and contact time of 50 min. Flouride adsorption followed pseudo second-order kinetic model and Langmuir isotherm best describes the adsorption process.

Computational analysis of fluid-structure interaction in case of fish swimming in the vortex street

The fluid-structure interaction (FSI) in case of fish swimming in the vortex street is investigated by numerical simulations. The vortex street is generated by a D-section cylinder. A 2-D fish model is placed on the downstream centerline of the bluff cylinder at a distance of 4 diameters away from the center of the cylinder. To simulate the fish body undulation and movement, the moving mesh is generated by a coupling approach based on the radial basis function and the overset grid technology. The Navier-Stokes equation in the arbitrary Lagrangian-Eulerian form is solved by coupling with the kinematics equation. Three cases are investigated: in a stationary position without deformation, a passive locomotion without deformation, and an active deformation based on the Kármán gait model. The results indicate that the fish body is acted by an alternating force and moment when it is located in the centerline of the vortex street. Furthermore, the fish could extract sufficient kinetic energy to overcome the drag under suitable conditions even when it keeps rigid and out of the suction zone. When the fish body undulates based on the Kármán gait model, the interaction is evidently shown between the fish body and the vortices. The theoretical analysis demonstrates that the lateral force and the moment acting on the fish body vary in a cosine formula, with the lateral translation and the body rotation as a result. This study focuses on the behavior of the fish body in the bluff cylinder wake and reproduces some phenomena observed in the experiments. Besides, the Kármán gait model is also theoretically analyzed, for the further exploration of the FSI mechanism in case of fish swimming.

Numerical Simulation of a Three-Dimensional Fish-like Body Swimming with Finlets

The swimming of a 3Dfish-like bodywith finlets is numerically investigated at Re=1000(the Reynolds number is based on the uniform upstream flow and the length of the fish-like body).The finlets are simply modeled as thin rigid rectangular plates that undulate with the body.The wake structures and the flow around the caudal peduncle are studied.The finlets redirect the local flow across the caudal peduncle but the vortical structures in the wake are almost not affected by the finlets.Improvement of hydrodynamic performance has not been found in the simulation based on this simple model.The present numerical result is in agreement with that of the work of Nauen and Lauder[J.Exp.Biol.,204(2001),pp.2251-2263]and partially supports the hypothesis ofWebb[Bull.Fish.Res.Bd.Can.,190(1975),pp.1-159].

Flow hydrodynamics drive effective fish attraction behaviour into slotted fishway entrances

Effective fishways rely on attracting fish,utilising the natural rheotactic behaviour of fish to orient into an attraction flow near the entrance.Despite the critical importance of attraction,understanding of the hydrodynamics of vertical slot entrances in relation to fish behaviour remains poor.Herein,hydrodynamic measurements of flows at slotted fishway entrances were experimented with two different designs,two velocities,three water depths,and two fish species,silver perch(Bidyanus bidyanus)and Australian bass(Percalates novemaculeata).Fish behaviours were tracked in relation to hydrodynamic measures of three-dimensional velocity and turbulent kinetic energy(TKE).There were distinct differences in the attraction flow between entrance designs,irrespective of velocity and water depth.A plain slotted entrance produced a more symmetric flow in the centre of the flume,causing fish to approach the entrance by skirting the core of the attraction jet flow and areas of high turbulence.In contrast,streamlined slotted entrance design resulted in an asymmetric attraction flow which guided fish along the wingwall towards the slotted entrance,improving attraction for both species.There were clear patterns in swimming trajectories for silver perch,swimming along the sidewalls of the observation zone towards the entrance,but Australian bass were less predictable,using random routes on their way to the slotted entrance.Both species preferred areas of low turbulence(TKE<0.02 m^(2)/s^(2)).This work has important implications for design of vertical slotted entrance systems.

Motion Control and Motion Coordination of Bionic Robotic Fish： A Review

Fish＇s outstanding motion and coordination performance make it an excellent source of inspiration for scientists and engineers aiming to design and control next-generation autonomous underwater vehicles within the framework of bionics. This paper offers a general review of the current status of bionic robotic fish, with particular emphasis on the hydrodynamic modeling and testing, kinematic modeling and control, learning and optimization, as well as motion coordination control. Among these aspects, representative studies based on ideas and concepts inspired from fish motion and coordination are discussed. At last, the major challenges and the future research directions are addressed in the context of integration of various research streams from ichthyologic, hydrodynamic, mechanical, electronic, control, and artificial intelligence. Further development of bionic robotic fish can be utilized to execute some specific missions in complex underwater environments, where operations are unsafe or impractical for divers or conventional underwater vehicles.

A NUMERICAL STUDY ON A SIMPLIFIED TAIL MODEL FOR TURNING FISH IN C-START

Most freshwater fish are good at turning manoeuvres. A simulated fish tail model was numerically investigated and discussed in detail. This study deals with unsteady forces and moment exerted on the fish tail-fin in an initial sideways stroke and a subsequent return stroke motion, and visualizes the flow fields and vortex structures, in order to explore the flow control mechanism of the typical turning motion of fish. Further discussion on fluid dynamic consequences corresponding to two different bending forms of fish tail-fins in its C-start is given. The two-dimensional unsteady incompressible Navier-Stokes equations are solved with a developed pseudo-compressibility method to simulate the flow around the fish tail-fin. The computed results and the comparison with experiments indicate that （1） fish performs a turning motion of its body using the impulsive moment produced by the to-and-fro stroke, and each stage of the process exhibits its specific hydrodynamic characteristic, （2） fishes adopt two forms of tail-tip bend （single bend and double bend） to accomplish a C-start turning manoeuvre, in dependence of their physical situations and natural environments, （3） fish can control its turning motion by modulating some key kinematic parameters.

ANALYSIS OF HYDRODYNAMICS FOR TWO-DIMENSIONAL FLOW AROUND WAVING PLATES

Hydrodynamic characteristics for two-dimensional flow around a waving plate are investigated. Under large Reynolds number approximation, the flow is assumed to be a combination of the outer potential flow and a thin vortex layer, which consists of a boundary layer and a shed free shear layer. A nonlinear mathematical formulation for describing the outer unsteady potential flow coupled with an unsteady boundary layer equation for the inner viscous flow adjacent to the waving plate is developed. A semi-analytical method with a nonlinear Kutta condition imposed at the trailing edge is used to solve the velocity field of the outer flow and the evolution of wake vortex induced by a large-amplitude waving plate. The unsteady boundary layer equation is solved by extending Pohlhausen＇s method to its unsteady counterpart. The thrust and viscous drag coefficients, propulsive efficiency, and the pattern of wake vortex sheet are discussed.

A NUMERICAL STUDY ON MECHANISM OF S-STARTS OF NORTHERN PIKE (ESOX LUCIUS)

Northern pike is regarded as a specialist in swimming acceleration. The force production mechanism of northern pike, Esox lucius, during its predation S-starts was numerically studied in this article. The problem was reasonably simplified to a loose-coupling problem of fish swimming dynamics and hydrodynamics just in the swimming direction. The approach involved the simulation of the flow by solving the two-dimensional unsteady incompressible Navier-Stokes equations and decribing the fish motion dynamics based on Newton＇s Second Law. Visualizations of flow fields and vortex structures were performed. The results show that the large acceleration is obtained mainly in the first undulatory cycle in which the amplitude increases. In the second cycle, a couple of vortices are generated and induce a jet. In the third cycle, the jet is strengthened by the mergence of the vortices in the same direction. Through discussing the effects of various controllable factors on the swimming performance, it is found that the actual locomotion mode of the northern pike in nature is just the best choice.

Hydrodynamic scaling law in undulatory braking locomotion

Flow over a fish-like airfoil is numerically investigated to elaborate the hydrodynamics of the undulatory braking locomotion for an elongated eel-like body or long-based fin. For undulation with low frequency, we find that boundary layer separation occurs in a parameter region with wakes in which two vortex pairs are formed per undulatory period. The physical mechanism of separation is governed by the slip(the ratio of swimming-to-body-wave speed), and the critical value of the slip in an inertial flow regime is approximately 4/3 rather than 1, which is independent of steepness(or amplitude). The relationship between pressure drag and relative velocity(between phase speed and free stream velocity) changes from linear to quadratic, corresponding to two different flow structures;this happens due to boundary layer separation, and the piecewise scaling relationship between pressure drag and relative velocity is explicitly clarified. Considering the viscosity effects, the separation criterion and the scaling relationship in the case of an undulatory brake are both synthetically modified using the Reynolds number, with all the required parameters clearly expressed. The results of this study provide physical insight into understanding the flow structures and hydrodynamics of the undulatory braking locomotion, which has instructional significance to brake design.