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 ANALYSIS AND SIMULATION OF A SWIMMING BIONIC ROBOT TUNA

A dynamic model for undulatory locomotion was proposed to study the swimming mechanism of a developed bionic robot tuna. On the basis of inviscid hydrodynamics and rigid-body dynamics, the momentum and propulsive force required for propelling the swimming robot tuna’s flexible body was calculated. By solving the established dynamic equations and efficiency formula, the swimming velocity and propulsive efficiency of the bionic robot tuna were obtained. The relationship between the kinematic parameters of the robot tuna’s body curve and the hydrodynamic performances was established and discussed after hydrodynamic simulations. The results presented in this article can be used to increase the swimming speed, propulsive thrust, and the efficiency of underwater vehicles effectively.     

两种手姿态在不同攻角下划水的数值模拟

该文旨在用计算流体力学（CFD）的方法研究游泳推进问题,建立了手掌和前臂的联接模型,并生成3D非结构网格，计算了两种不同手姿态：并拢和张开在不同来流速度和攻角下的推进阻力和推进升力，并结合计算结果进行了流场分析，研究了两种手姿态对推进效率的影响。结果表明，在各个攻角状态下，手并拢划水均能获得更高的推进效率。     

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.     

蝌蚪模型并列游动的数值研究

该文通过数值求解雷诺平均N-S方程,对高雷诺数下蝌蚪模型同相位和反相位并排游动进行了数值研究,揭示了并列蝌蚪群游的流动机制。研究表明,非流线型的蝌蚪并列群游与流线型的鱼体不同。蝌蚪同相位并列游动时,总推力比单独游动时低,尽管能量消耗有所增加但推进效率更高;蝌蚪反相位并列游动时,总推力比单独游动时低,但比同相位并列游动时高,间距很近时消耗的能量会显著增加,而推进效率依然提高。蝌蚪的钝体头部产生的涡在群游时有利于增加推力。     

Effects of obstacles and flow velocity on locomotory behavior in juvenile,silver carp,Hypophthalmichthys molitrix

We currently have only a minimal understanding of energy‐saving strategies of fish in unsteady flows. In this study, we found that obstacle shape can affect swimming ability of fish: our results suggested that a half cylinder improved critical swimming speed of silver carp (Hypophthalmichthys molitrix) compared with swimming downstream of a full cylinder, square tube or for free‐flow conditions. We also discovered how silver carp alter their locomotory behavior in response to turbulent flow caused by varying flow velocities around obstacles. At a flow velocity of 1 BL/s (body length per second), the fish spent similar percentages of time between holding station and moving forward behind the half cylinder: their motions resembled freestream swimming behavior. The greatest percentage of time spent downstream of the half cylinder occurred at a flow velocity of 5 BL/s. Fish were unstable and displayed irregular body motions with large lateral displacement at 5 BL/s. However, the fish held station for a long time and moved forward steadily behind the half cylinder at 3 BL/s. In holding station behind the half cylinder, fish maintained constant tail‐beat frequency and tail‐ beat amplitude when flow velocity was increased from 1 to 3 BL/s. In moving forward behind the half cylinder, fish increased tail‐beat frequency and tail‐beat amplitude while maintaining constant ground swimming speed, swimming acceleration and ground stride when flow velocity was increased from 3 to 5 BL/s. Moreover, fish positioned their snouts in a small area approximately 1–3 BL downstream from the half cylinder at 3 BL/s. These behaviors support the hypothesis that turbulence behind a half cylinder was a suitable location for fish to conserve energy at 3 BL/s. Our results indicate that the combined effect of obstacles and flow velocity influence fish locomotory behavior, and some combinations may be beneficial to fish energy expenditure swimming in unsteady flow.     

Effect of head swing motion on hydrodynamic performance of fishlike robot propulsion

This paper studies the effect of the head swing motion on the fishlike robot swimming performance numerically.Two critical parameters are employed in describing the kinematics of the head swing: the leading edge amplitude of the head and the trailing edge amplitude of the head.Three-dimensional Navier-Stokes equations are used to compute the viscous flow over the robot.The user-defined functions and the dynamic mesh technology are used to simulate the fishlike swimming with the head swing motion.The results reveal that it is of great benefit for the fish to improve the thrust and also the propulsive efficiency by increasing the two amplitudes properly.Superior hydrodynamic performance can be achieved at the leading edge amplitudes of 0.05L( L is the fish length) and the trailing edge amplitudes of 0.08 L.The unsteady flow fields clearly indicate the evolution process of the flow structures along the swimming fish.Thrust-indicative flow structures with two pairs of pressure cores in a uniform mode are generated in the superior performance case with an appropriate head swing,rather than with one pair of pressure cores in the case of no head swing.The findings suggest that the swimming biological device design may improve its hydrodynamic performance through the head swing motion.     

异齿裂腹鱼通过鱼道内流速障碍能力及行为

鱼类通过流速障碍能力是鱼道设计的主要生态指标,目前国内外主要使用封闭游泳水槽进行鱼类各种游泳速度指标及游泳行为研究,其水流流态及鱼类游泳行为与鱼类通过鱼道的实际状态有较大的差距,有必要结合鱼类游泳速度指标来探索能够更加准确量化鱼类通过鱼道流场的游泳能力测试方法。首先,在封闭游泳水槽中通过速度递增法测得异齿裂腹鱼临界游泳速度(101.01±20.86 cm/s)和突进游泳速度(196.94±21.80 cm/s);然后,以临界游泳速度和藏木水电站鱼道竖缝流速(110.00 cm/s)为参考,通过在开放游泳水槽内加不同束窄梯形体,形成类竖缝式鱼道的鱼类自主游泳能力测试水槽,开展两种底坡条件下4级短竖缝(工况1和工况2竖缝流速为101.55±14.87 cm/s、114.63±24.28 cm/s,竖缝顺水流长度均为40 cm)和单级长竖缝(工况3竖缝流速为137.45±17.63 cm/s、竖缝顺水流长度为160 cm)下试验鱼通过流速障碍能力和行为研究。试验结果表明:工况1、工况2下试验鱼通过4级竖缝成功率分别为82.05%、84.62%,通过流速大于临界游泳速度的竖缝时,持续爆发游泳时间为0.52±0.34 s;工况3下93.33%试验鱼以209.43±21.76 cm/s游泳速度成功通过单级长竖缝;3种工况下试验鱼通过流速大于临界游泳速度的竖缝时,以与突进游泳速度无显著性差异(P0.05)的恒定游泳速度(214.01±30.64 cm/s)上溯。鱼类游泳轨迹与流场耦合分析表明:鱼类上溯所需时间及路径长度与其选择的游泳路径密切相关,试验鱼通过借助回流区同向水流推动,增加上溯效率。本文研究方法及研究结论可为鱼道设计、改造、评价提供依据。     

NUMERICAL STUDY ON PROPULSIVE PERFORMANCE OF FISH-LIKE SWIMMING FOILS

1. INTRODUCTION The study of the movement of fishes can be very informative in exploring mechanisms of unsteady flow control because movements in fish is a result of many millions of years of evolutionary optimization. Previous studies have shed light on …     

NUMERICAL STUDIES ON LOCOMOTION PERFROMANCE OF FISHLIKE TAIL FINS

Flapping plates of typical fishlike tail shapes are simulated to investigate their locomotion performance using the multi-block Lattice Boltzmann Method (LBM) and Immersed Boundary (IB) method. Numerical results show that fishlike forked configurations have better locomotion performance compared with unforked plates. Based on our results, the caudal fin in carangiform mode has greater thrust, and the lunate tail fin in thunniform mode has higher efficiency. These findings are qualitatively consistent with biological observations of fish swimming. Analysis of wake topology shows that the wake of the forked plate consists of a chain of alternating reverse horseshoe-like vortical structures. These structures induce a backward jet and generate a positive thrust. Moreover, this backward jet has a more favorable direction compared with that behind an unforked plate.     

LATTICE BOLTZMANN SIMULATIONS OF TRIAGULAR CAVITY FLOW AND FREE-SURFACE PROBLEMS

The Lattice Boltzmann Method (LBM) was investigated to solve triangular cavity flow and free-surface problems in hydraulic dynamics. Some cases of triangular cavity flow and backward step flow were simulated to show the efficiency and stability of this method. Two-dimensional partial dam breaking problem and the propagation and diffraction of dam-break wave around rectangular and circular cylinder were numerically studied successfully. Excellent agreement was obtained between numerical predictions and available results.     

不同流速对鲫鱼推进效率影响的数值研究

鱼类趋流性的试验和鱼类游动的数值模拟是当前研究的两个热点,大多数鱼类不仅有趋流特性而且还能高效节能的向前推进,开展鱼类趋流性与推进效率关系的研究既能完善鱼类推进机理理论,也能在鱼道设计时提高其过鱼效率。本文以鲫鱼在不同恒定流速中的实测游泳数据为依据,利用计算流体力学软件flow-3d对鱼类波状摆动进行数值模拟,建立鲫鱼游动的数值计算模型,研究在不同流速下鲫鱼完成一个运动周期后所对应的推进效率。结果表明,随着流速的增大鱼的推进效率呈现出先增大后减小的变化趋势,当流速条件为0.5 m/s时对应的鱼类推进效率值最大,也是推进效率随流速变化的转折点。该研究获得了鲫鱼在顶流运动状态下鱼类推进效率与流速条件之间的相关关系。     

仿自然通道及鱼道池室结构布置研究

为了提高仿自然通道及鱼道设计水平,以某水电站仿自然通道工程为案例,根据其过鱼需求,提出了池室结构布置方案,并通过数值模拟及物理模型试验对其平面及三维池室流态进行了分析。结果表明:通过在仿自然通道或鱼道内部采用收缩段、侧壁设置消能墩、底部辅以条形消能墩的新型结构可使池室内部流场实现纵向分层和横向分区,可供不同游泳能力的鱼类通过。该池室结构在流速流态控制等方面较普通仿自然通道和技术型鱼道均具有优势,适合多种鱼类通过,具有推广价值。     

Short-term Water Mass Movements in Lake Michigan: Implications for Larval Fish Transport

Water mass movement within the Great Lakes may rapidly transport fish larvae from favorable nursery areas to less favorable habitats, thereby affecting recruitment success. During 2001 and 2002, we released satellite-tracked drifting buoys in eastern Lake Michigan to follow discrete water masses, and used ichthyoplankton nets to repeatedly sample larval fish within these water masses. Observed nearshore water currents were highly variable in both direction and velocity. Current velocities far exceeded potential larval fish swimming speeds, suggesting that currents can potentially rapidly advect fish larvae throughout the lake. Evidence suggests that while paired drifters released during 2002 were able to track relatively small alewife (Alosa pseudoharengus) and yellow perch (Perca flavescens) larvae within an alongshore coastal current, paired drifters released during 2001 failed to track larger alewife larvae when flow was more offshore and highly variable. These results are consistent with the decorrelation scales associated with alongshore and offshore transport.     

Swimming behavior of crucian carp in an open channel with sudden expansion

The sudden‐expansion effect created by natural and man‐made structures such as unsubmerged boulders, spur dikes, and culvert structures is common in open channels. Migratory fishes may use the heterogeneous flow generated by sudden expansion to their benefit, to select habitats for balancing energy expenditure or for maximizing predation opportunities. This study explores the swimming behavior of three size classes of crucian carp in response to hydrodynamic characteristics in an experimental open channel with sudden expansion. The flow field was characterized using particle image velocimetry (PIV) measurements and featured a recirculation zone in the vicinity of the expansion. Based on the classification of the swimming trajectory, four specific swimming behaviours (SSBs) were utilized by crucian carp during migration. With increasing flow velocity, fish spent more time in the recirculation zone. Residence time in the recirculation zone was inversely correlated with fish body length. Due to the advantage in providing shelter from challenging heterogeneous hydraulic conditions, the recirculation zone was preferred by crucian carp, especially the smaller ones, indicating the importance of energy conservation in habitat occupation. These findings confirm that the recirculation zone generated by sudden expansion may be beneficial to the upstream passage of fish and in habitat restoration.     

大坝泄水对鱼类洄游能力的影响研究

大坝的建设将天然河道分隔成上、下两个环境单元,改变了河道的流量、流速和水位等水文要素,使原有的水力条件及生态环境都发生了变化,对鱼类的洄游、繁殖和生长等都产生较大影响。以江河湖泊常见鱼种—成年鲤为研究对象,以0.02 m~3/s为基础流量,按照0.01 m~3/s的流量递增进行大坝泄水模拟实验;采用声学信号监测技术监测成年鲤在不同泄水量下的洄游能力及游泳轨迹,分析不同泄水量的河道流场并与鱼类游泳轨迹进行拟合,研究不同流速对鱼类洄游能力的影响。结果表明:成年鲤的洄游距离、游泳速度随着河道流速增大而逐渐减小,成年鲤洄游开始出现困难、开始出现逆流后退以及无法洄游时河道流速分别为0.42,0.48 m/s和0.62 m/s;泄水量每增加一个0.01 m~3/s流量梯度,成年鲤洄游距离约减少1.5 m,说明随着河道流速增大鱼类洄游轨迹变化是一个逐渐收敛的过程。大坝泄水过程同时还会造成氮气和氧气过饱和、改变水体温度和浊度从而对鱼类生存环境、繁殖及鱼类资源造成影响。     

Propulsive performance of a passively flapping plate in a uniform flow

Propulsive performance of a passively flapping plate in a uniform viscous flow has been studied numerically by means of a multiblock lattice Boltzmann method. The passively flapping plate is modeled by a rigid plate with a torsion spring acting about the pivot at the leading-edge of the plate, which is called a lumped-torsional-flexibility model. When the leading-edge is forced to take a vertical oscillation, the plate pitches passively due to the fluid-plate interaction. Based on our numerical simulations, various fundamental mechanisms dictating the propulsive performance, including the forces on the plate, power consumption, propulsive efficiency and vortical structures, have been studied. It is found that the torsional flexibility of the passively pitching plate can improve the propulsive performance. The results obtained in this study provide some physical insights into the understanding of the propulsive behaviors of swimming and flying animals.     

Effect of a vertical half cylinder on swimming of silver carp,Hypophthalmichthys molitrix: Implications for microhabitat restoration and fishway design

In recent years, the relationship between hydraulics associated with the substrate and fish swimming behaviour has become increasingly important to the design of microhabitat around substrates for river restoration. To better understand the hydraulics associated with substrate on fish swimming, we studied the effects of a vertical half cylinder (hereafter, cylinder) on the critical swimming speed of juvenile silver carp (Hypophthalmichthys molitrix). Absolute and relative critical swimming speeds of fish in the flow field of the cylinder were significantly increased compared with those swimming in free flow. In addition, the amplitude of fish head and tail oscillations were significantly greater in flows created by the half cylinder. This study highlights the importance of roughness elements in stream microhabitat restoration and, possibly, for fishway design.     

Swimming behaviour and ascent paths of brook trout in a corrugated culvert

Culverts may restrict fish movements under some hydraulic conditions such as shallow flow depths or high velocities. Although swimming capacity imposes limits to passage performance, behaviour also plays an important role in the ability of fish to overcome velocity barriers. Corrugated metal culverts are characterized by unsteady flow and existence of low‐velocity zones, which can improve passage success. Here, we describe swimming behaviour and ascent paths of 148 wild brook trout in a 1.5‐m section of a corrugated metal culvert located in Raquette Stream, Québec, Canada. Five passage trials were conducted in mid‐August, corresponding to specific mean cross‐sectional flow velocities ranging from 0.30 to 0.63 m/s. Fish were individually introduced to the culvert and their movements recorded with a camera located above the water. Lateral and longitudinal positions were recorded at a rate of 3 Hz in order to identify ascent paths. These positions were related to the distribution of flow depths and velocities in the culvert. Brook trout selected flow velocities from 0.2 to 0.5 m/s during their ascents, which corresponded to the available flow velocities in the culvert at the low‐flow conditions. This however resulted in the use of low‐velocity zones at higher flows, mainly located along the walls of the culvert. Some fish also used the corrugations for sheltering, although the behaviour was marginal and did not occur at the highest flow condition. This study improves knowledge on fish behaviour during culvert ascents, which is an important aspect for developing reliable and accurate estimates of fish passage ability.     

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.