Research On Fish Burst-Coast Swimming Behavior Based On Computer Vision

Fish has been continuously adapted and evolved in the aquatic environment,and has a flexible attitude control ability.The high flexibility of swimming and the high efficiency of tail movement are closely related to its unique propulsion mechanism.People pay more and more attention to the swimming strategy and ecological adaptation behavior of fish,and regard the critical swimming ability of fish as an important evaluation index of swimming ability.However,due to environmental factors and individual differences of species,the determination methods and criteria of fish critical swimming speed are controversial.Traditional measurement methods also affect the comparability and practicability of the research results,which limits its development in related application fields.On this basis,the non-invasive observation characteristics of computer vision technology are compatible with the measurement of fish swimming behavior,which is an indispensable means to study the different swimming modes and propulsion performance of fish.In this paper,the indoor experimental study on the burst-coast swimming behavior of fish with different body length ranges was carried out,and the motion characteristics and propulsion mechanism of this intermittent swimming mode were analyzed by simplifying the physical model and numerical simulation.It provides basic data for the study of quantifying fish swimming ability and the fishway design of water conservancy projects,and further supplements the fish swimming behavior in the determination of fish critical swimming ability.This paper mainly focuses on the following contents:（1）The critical swimming ability test of fish was carried out,and the critical swimming speed indexes of juvenile Spinibarbus sinensis and Puntius titteya were measured by pressure uniform flow field.The quantitative relationship between the body length and the critical swimming speed was obtained:U_crit=0.247·BL^0.57,U_crit=0.355·BL^0.44.（2）Based on the flow rate increasing method,the response characteristics of the sprint-gliding swimming behavior of fish with different body lengths to the flow rate were explored.At the same time,according to the change of the swimming state of the fish,the swimming posture of the experimental fish in the determination process was divided into four categories,which were downstream,countercurrent stationary,top current forward and countercurrent backward.The sprint-gliding swimming behavior of fish was classified into the top current forward state,so as to put forward the attitude conversion frequency of the sprint-gliding swimming behavior and the time proportion of the top current forward state as the judgment index of the critical swimming state of fish,and further improve the judgment mechanism of the critical swimming ability.（3）A simplified two-dimensional model was established by using computer vision technology to extract the motion characteristics of fish,quantify the kinematic parameters of fish burst-coast swimming behavior,including tail swing frequency,tail swing angle and burst-coast distance,and introduce the relationship between burst-coast coefficient coupling.The results showed that the tail swing angle and tail swing frequency of juvenile Spinibarbus sinensis and Puntius titteya with different body lengths were similar,which increased first and then decreased with the increase of flow velocity.The preferred swing tail angle range of burst-coast swimming behavior is 10°～20°,the preferred swing tail frequency is 5～8 times,and the preferred flow rate is 20%～50%of the critical swimming speed.When the burst-coast coefficient is between 1.0 and 4.0,it is of reference significance to quantitatively analyze the intermittent swimming ability of fish.（4）The NACA0012 airfoil is used as the kinematics model of the fish body,and the two-dimensional deformed fish body is numerically simulated by Fluent.The effects of different tail swing frequencies on the swimming speed,resistance and thrust are analyzed.The results show that the swimming speed of the fish increases with the increase of the tail frequency.After the intermittent coasting swimming state is added,the swimming speed fluctuates periodically,and the swimming speed change is an acceleration-deceleration-reacceleration process.The analysis of mechanical properties and propulsion efficiency shows that fish can reduce drag and save energy by actively adjusting swimming posture and using intermittent coasting swimming.Although the swimming speed is reduced,the propulsion efficiency is not significantly reduced.Therefore,when fish do not have the demand for high-speed swimming,energy can be saved by burst-coast swimming.