The force production physics and the flow control mechanism of fish fast C-start are studied numerically and theoretically by using a tail-flapping model.The problem is simplified to a 2-D foil that rotates rapidly to...The force production physics and the flow control mechanism of fish fast C-start are studied numerically and theoretically by using a tail-flapping model.The problem is simplified to a 2-D foil that rotates rapidly to and fro on one side about its fixed leading edge in water medium.The study involves the simulation of the flow by solving the two-dimensional unsteady incompressible Navier- Stokes equations and employing a theoretical analytic modeling approach.Firstly,reasonable thrust magnitude and its time history are obtained and checked by fitting predicted results coming from these two approaches.Next,the flow fields and vortex structures are given,and the propulsive mechanism is interpreted.The results show that the induction of vortex distributions near the trailing edge of the tail are important in the time-averaged thrust generation,though the added inertial effect plays an important role in producing an instant large thrust especially in the first stage.Furthermore,dynamic and energetic effects of some kinematic controlling factors are discussed.For enhancing the time- averaged thrust but keeping a favorable ratio of it to time-averaged input power within the limitations of muscle ability,it is recommended to have a larger deflection amplitude in a limited time interval and with no time delay between the to-and-fro strokes.展开更多
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 a...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.展开更多
When faced with danger,pufferfish react with both a fast-start escape response and inflation behavior.The neural basis of these stress responses in the pufferfish has not been described.The present study reveals that ...When faced with danger,pufferfish react with both a fast-start escape response and inflation behavior.The neural basis of these stress responses in the pufferfish has not been described.The present study reveals that during inflation behavior,the buccal cavity expands and compresses as a pump to control the direction of water flow and draws water in and out.The inflation involves a series of major anatomical modifications of the head.The greatly enlarged first branchiostegal ray and its associated hyohyoideus abductor muscle are the key mechanisms responsible for this behavior.The nerve branch innervating the hyohyoideus abductor muscle is highly developed,and its central origin at the motor nucleus of the VIIth cranial nerve was revealed by tract-tracing using the carbocyanine dye DiI.The central connections from its origin were found to be several motor nuclei in the medulla and the spinal cord,the nuclei of cranial nerve III and IV in the mesencephalon,and the pretectalis superficialis and periventricular preoptic nuclei in the diencephalon.Both the sympathetic cells and the parvocellular part of the periventricular preoptic nucleus might play a neuro-endocrine role in the rapid movement of the buccal cavity during puffing behavior in this species of pufferfish.The central circuit revealed by this study is hypothesized to mediate the C-start escape behavior and puffing behavior.展开更多
文摘The force production physics and the flow control mechanism of fish fast C-start are studied numerically and theoretically by using a tail-flapping model.The problem is simplified to a 2-D foil that rotates rapidly to and fro on one side about its fixed leading edge in water medium.The study involves the simulation of the flow by solving the two-dimensional unsteady incompressible Navier- Stokes equations and employing a theoretical analytic modeling approach.Firstly,reasonable thrust magnitude and its time history are obtained and checked by fitting predicted results coming from these two approaches.Next,the flow fields and vortex structures are given,and the propulsive mechanism is interpreted.The results show that the induction of vortex distributions near the trailing edge of the tail are important in the time-averaged thrust generation,though the added inertial effect plays an important role in producing an instant large thrust especially in the first stage.Furthermore,dynamic and energetic effects of some kinematic controlling factors are discussed.For enhancing the time- averaged thrust but keeping a favorable ratio of it to time-averaged input power within the limitations of muscle ability,it is recommended to have a larger deflection amplitude in a limited time interval and with no time delay between the to-and-fro strokes.
基金Project supported by the National Natural Science Fourndation of China(Grant No:10332040) and the Innovation Project of the Chinese Acadeny of Sciences (Grant No:KJCX-SW-L04).
文摘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.
基金supported by the National Natural Science Foundation of China(No.30970365).
文摘When faced with danger,pufferfish react with both a fast-start escape response and inflation behavior.The neural basis of these stress responses in the pufferfish has not been described.The present study reveals that during inflation behavior,the buccal cavity expands and compresses as a pump to control the direction of water flow and draws water in and out.The inflation involves a series of major anatomical modifications of the head.The greatly enlarged first branchiostegal ray and its associated hyohyoideus abductor muscle are the key mechanisms responsible for this behavior.The nerve branch innervating the hyohyoideus abductor muscle is highly developed,and its central origin at the motor nucleus of the VIIth cranial nerve was revealed by tract-tracing using the carbocyanine dye DiI.The central connections from its origin were found to be several motor nuclei in the medulla and the spinal cord,the nuclei of cranial nerve III and IV in the mesencephalon,and the pretectalis superficialis and periventricular preoptic nuclei in the diencephalon.Both the sympathetic cells and the parvocellular part of the periventricular preoptic nucleus might play a neuro-endocrine role in the rapid movement of the buccal cavity during puffing behavior in this species of pufferfish.The central circuit revealed by this study is hypothesized to mediate the C-start escape behavior and puffing behavior.
