Modelling of thrust generated by oscillation caudal fin of underwater bionic robot

A simplified model of the thrust force is proposed based on a caudal fin oscillation of an underwater bionic robot. The caudal fin oscillation is generalized by cen- tral pattern generators （CPGs）. In this model, the drag coefficient and lift coefficient are the two critical parameters which are obtained by the digital particle image velocimetry （DPIV） and the force transducer experiment. Numerical simulation and physical experi- ments have been performed to verify this dynamic model.

RNA-seq analysis of a zebrafish caudal fin cell line in response to infection with spring viraemia of carp virus

A cell line,termed ZFIN,was established from the caudal fin of zebrafish and was shown to be susceptible to spring viremia of carp virus(SVCV).The ZFIN cells are epithelial like cells and have a moderate plasmid transfection efficiency of 13.9%.Using an RNA-seq approach,differentially expressed genes(DEGs)regulated by SVCV were identified.Infection of SVCV gave rise to 3931 DEGs and up-regulated DEGs were mostly enriched into the biological regulation and cellular processes,among which pathways for the type I interferon signaling and the response to exogenous dsRNA were the top two GO terms.Several KEGG signaling pathways including TLR signaling pathway,RLR receptor signaling pathway,cytosolic DNA-sensing pathway,NLR signaling pathway,cytokine-cytokine receptor interaction and ferroptosis were significantly enriched.Antiviral genes including ifnφ1,isg15 and mx were significantly up-regulated.In addition,key DEGs involved in autophagy were identified.The results indicate that the ZFIN cell line provides a useful in vitro tool for study on the gene functions and cellular responses to viral infection in fish.

NUMERICAL AND EXPERIMENTAL STUDIES OF INFLUENCE OF THE CAUDAL FIN SHAPE ON THE PROPULSION PERFORMANCE OF A FLAPPING CAUDAL FIN

This article presents a comprehensive study of the effects of the caudal fin shape on the propulsion performance of a candal fin in harmonic heaving and pitching. A numerical simulation based on an unsteady panel method was carried out to analyze the hydrodynamic performance of flapping caudal fins of three shapes （the whale caudal fin with the largest projected area, the dolphin caudal fin with the median projected area, and the tuna caudal fin with the smallest projected area）. Then, a series of hydrodynamic experiments for three caudal fin shapes were performed. Both computational and experimental results indicate that the tuna caudal fin produces the highest efficiency. However the mean thrust coefficient of the tuna caudal fin is the smallest. It is found that although the mean thrust coefficient for the tuna caudal fin is not large, the input power of the tuna caudal fin is also quite small. So the tuna caudal fin achieves a high efficiency.

NUMERICAL SIMULATION OF THE HYDRODYNAMIC PERFORMANCE OF AN UNSYMMETRICAL FLAPPING CAUDAL FIN

A comprehensive numerical simulation of the hydrodynamic performance of a caudal fin with unsymmetric flapping motion is carried out. The unsymmetrical motion is induced by adding a pitch bias or a heave bias. A numerical simulation program based on the unsteady panel method is developed to simulate the hydrodynamics of an unsymmetrical flapping caudal fin. A CFD code based on Navier-Stokes equations is used to analyze the flow field. Computational results of both the panel method and the CFD method indicate that the hydrodynamics are greatly affected by the pitch bias and the heave bias. The mean lateral force coefficient is not zero as in contrast with the symmetrical flapping motion. By increasing the pitch bias angle, the mean thrust force coefficient is reduced rapidly. By adding a heave bias, the hydrodynamic coefficients are separated as two parts： in one part, the amplitude is the heave amplitude plus the bias and in the other part, it is the heave amplitude minus the bias. Analysis of the flow field shows that the vortex distribution is not symmetrical, which generates the non-zero mean lateral force coefficient.

EXPERIMENT ON THE CHARACTERISTICS OF 3-D VORTEX RING BEHIND A FLEXIBLE OSCILLATING CAUDAL FIN

A test for the wake vortex of a flexible oscillating caudal fin is carried out with Digital Particle Image Velocimetry （DPIV）, and the variation of vortex distance and the vorticity in the range of oscillating frequency from 0.704 Hz to 1.17 Hz are analyzed. It is found that with the increase of the oscillating frequency, the vortex distance decreases and the peak of the vorticity increases, When the Strouhal number is smaller than 0.49, a larger thrust component is obtained. The distribution of the velocity circulation and the vortex distance in the different spanwise section of the caudal fin are given, and then the dimension of the vortex ring is determined. The radius of the vortex ring is 79.3 mm and the average velocity circulation is 28152.9 mm2/s at the oscillating frequency of 0.835 Hz. The model of 3-D vortex ring chain of flexible oscillating caudal fin is constructed based on the information of wake vortex field. Finally, an effective analysis method is provided for establishing the relationship of oscillating parameters for the caudal fin and the wake structure and the intrinsic mechanism of efficient fish swimming is investigated.

Shape optimization of the caudal fin of the three-dimensional self-propelled swimming fish

Shape optimization of the caudal fin of the three-dimensional self-propelled swimming fish,to increase the swimming efficiency and the swimming speed and control the motion direction more easily,is investigated by combining optimization algorithms,unsteady computational fluid dynamics and dynamic control in this study.The 3D computational fluid dynamics package contains the immersed boundary method,volume of fluid method,the adaptive multi-grid finite volume method and the control strategy of fish swimming.Through shape optimizations of various swimming speeds,the results show that the optimal caudal fins of different swimming modes are not exactly the same shape.However,the optimal fish of high swimming speed,whose caudal fin shape is similar to the crescent,also have higher efficiency and better maneuverability than the other optimal bionic fish at low and moderate swimming speeds.Finally,the mechanisms of vorticity creation of different optimal bionic fish are studied by using boundary vorticity-flux theory,and three-dimensional wake structures of self-propelled swimming of these fish are comparatively analyzed.The study of vortex dynamics reveals the nature of efficient swimming of the 3D bionic fish with the lunate caudal fin.

Using spanwise flexibility of caudal fin to improve swimming performance for small fishlike robots

This paper examines the beneficial effects of the spanwise flexibility of the caudal fin for the improvement of the swimming performance for small fishlike robots. A virtual swimmer is adopted for controlled numerical experiments by varying the spanwise flexible trajectories and the spanwise flexible size of the caudal fin while keeping the body kinematics fixed. 3-D Navier-Stokes equations are used to compute the viscous flow over the robot. Elliptical, parabolic and hyperbola trajectories are chosen to describe the spanwise flexible profile of the caudal fin. According to the sign（positive or negative） of the phase difference of the swinging motion, the spanwise flexibility can be divided into the fin surface of ＂bow＂ and the fin surface of ＂scoop＂. It is observed that for both the fin surface of ＂bow＂ and the fin surface of ＂scoop＂, the spanwise elliptical trajectory has the optimal swimming velocity, thrust, lateral force, and efficiency. With comparisons, using the flexible caudal fin with the fin surface of ＂bow＂, the lateral force and the power consumption can be reduced effectively and the swimming stability can be increased while reducing little the swimming velocity and thrust. Meanwhile, using the flexible caudal fin with the fin surface of ＂scoop＂ can greatly improve the swimming velocity, thrust, and efficiency while increasing part of the lateral force and the power consumption. Three-dimensional flow structures clearly indicate the evolution process around the swimming robot. It is suggested that the fish, the dolphin, and other aquatic animals may benefit their hydrodynamic performance by the spanwise flexibility of the caudal fin.

The effects of caudal fin deformation on the hydrodynamics of thunniform swimming under self-propulsion

To investigate the effects of the caudal fin deformation on the hydrodynamic performance of the self-propelled thunniform swimming,we perform fluid-body interaction simulations for a tuna-like swimmer with thunniform kinematics.The 3-D vortices are visualized to reveal the role of the leading-edge vortex(LEV)in the thrust generation.By comparing the swimming velocity of the swimmer with different caudal fin flexure amplitudes fa,it is shown that the acceleration in the starting stage of the swimmer increases with the increase of fa,but its cruising velocity decreases.The results indicate that the caudal fin deformation is beneficial to the fast start but not to the fast cruising of the swimmer.During the entire swimming process,the undulation amplitudes of the lateral velocity and the yawing angular velocity decrease as fa increases.It is found that the formation of an attached LEV on the caudal fin is responsible for generating the low-pressure region on the surface of the caudal fin,which contributes to the thrust.Furthermore,the caudal fin deformation can delay the LEV shedding from the caudal fin,extending the duration of the low pressure on the caudal fin,which will cause the caudal fin to generate a drag-type force over a time period in one swimming cycle and reduce the cruising speed of the swimmer.

Hydrodynamics study of dolphin’s self-yaw motion realized by spanwise flexibility of caudal fin

The hydrodynamic performance of the virtual underwater vehicle under self-yaw is investigated numerically in this paper,we aim to explore the fluid laws behind this plane motion achieved by the bionic flexibility,especially the spanwise flexibility of the caudal fin.The kinematics of the chordwise flexible body and the spanwise flexible caudal fin are explored through dynamic mesh technology and user-defined functions(UDF).The 3-D Navier-Stokes equations are applied to simulate the viscid fluid surrounding the bionic dolphin.The study focuses on quantitative problems about the fluid dynamics behind the specific motion law,including speed of movement,energy loss and working efficiency.The current results show that the self-yaw can be composed of two motions,autonomous propulsion and active steering.In addition,the degree of the flexible caudal fin can produce different yaw effects.The chordwise phase differenceФis dominant in the propulsion function,while the spanwise phase differenceδhas a more noticeable effect on the steering function.The pressure distribution on the surface of the dolphin and the wake vortex generated in the flow field reasonably reveal the evolution of self-yaw.It properly turns out that the dolphin can combine the spanwise flexible caudal fin and the chordwise flexible body to achieve self-yaw motion.

Topology Optimization of the Caudal Fin of the Three-Dimensional Self-Propelled Swimming Fish

Based on the boundary vorticity-flux theory,topology optimization of the caudal fin of the three-dimensional self-propelled swimming fish is investigated by combining unsteady computational fluid dynamics with moving boundary and topology optimization algorithms in this study.The objective functional of topology optimization is the function of swimming efficiency,swimming speed and motion direction control.The optimal caudal fin,whose topology is different from that of the natural fish caudal fin,make the 3D bionic fish achieve higher swimming efficiency,faster swimming speed and better maneuverability.The boundary vorticity-flux on the body surface of the 3D fish before and after optimization reveals the mechanism of high performance swimming of the topology optimization bionic fish.The comparative analysis between the swimming performance of the 3D topology optimization bionic fish and the 3D lunate tail bionic fish is also carried out,and the wake structures of two types of bionic fish show the physical nature that the swimming performance of the 3D topology optimization bionic fish is significantly better than the 3D lunate tail bionic fish.

Principle and Experimental Verification of Caudal-fin-type Piezoelectric-stack Pump with Variable-cross-section Oscillating Vibrator

In the traditional flow-resistance-differential (FRD) type valve-less piezoelectric pump, the generated outflow and pressure are discontinuous because of the inherent periodicity and fluctuation of the pump. To overcome these drawbacks, utilizing the bending vibration of piezoelectric bimorph to drive fluid was conducted. However, our investigation on the current status of this piezoelectric bimorph pump shows that larger driving force and vibration amplitude are required for fluid pumping; the pumping can be realized through the centrifugal force; and the mechanism of fluid pumping is no longer further studied. Based on these cases, the paper designed a piezoelectric-stack pump with variable-cross-section oscillating (VCSO) vibrator by imitating the swing of the caudal-fin of tuna, and the pump is neither the rotating type nor the volumetric type according to the taxonomy. The interaction between the oscillating vibrator and the fluid parcel is firstly analyzed from the viewpoint of momentum conservation, and the analytical expression of pump flow rate is obtained. Then the modal and harmonic response analyses on the vibrator immerged in water are carried out. From the analyses the first two orders resonance frequencies are 832 Hz and 1 939 Hz, respectively, and the peak value of the tip amplitude is 0.6 mm. Laser Doppler vibrometer is used to measure both the frequency and vibration amplitude, and the determined first two orders resonance frequencies are 617 Hz and 1 356 Hz, respectively. The measured tip amplitude reaches to the peak value of 0.3 mm. At last, experimental measurement for the flow rates with different driving frequencies is conducted. The results show that the flow rate can reach 560 mL/min at 1 370 Hz when the pump runs under the backpressure of 30 mm water column. And the flow rate is as much as 560% of that of experiment results carried out by researchers from Brazil. The proposed pump innovates in both theory and taxonomy; in addition, the pump overcomes the drawbacks such as large flow fluctuation and low flow rate in the traditional FRD type pumps, which will help to broaden the application of the valve-less piezoelectric pump.

基于CFD的仿生水动力学数值计算方法及其验证

鱼类经过长期的进化与自然选择,有着优异的水中游动能力,鱼类借助尾鳍能够进行快速高效的定向游动和快速启动/机动,借助胸鳍能够进行前进、后退和灵活的转向。本文基于计算流体力学(CFD)方法,给出适用于求解鱼类尾鳍/胸鳍的刚性运动以及身体躯干的柔性运动的网格划分策略,对仿生尾鳍、仿生胸鳍和仿生鱼在均匀来流中的水动力性能以及仿生鱼在静水中的自主游动进行数值计算。结果表明:基于CFD方法,采用结构与非结构混合的网格划分策略,应用动网格方法能够对仿生鱼的各类鳍及身体躯干的刚性或柔性运动进行有效的模拟,通过与实验结果进行对比,验证了对水动力性能求解的有效性。数值计算方法和验证算例对仿生水动力学的研究具有一定的理论参考意义。

尾鳍摆动推进水动力与流动涡结构特征分析

作为BCF(body-caudalfin)推进模式中的典型代表,金枪鱼游动快,是重要的仿生研究对象之一。本文基于弹性光顺模型和局部网格重构模型动网格技术,建立仿金枪鱼尾鳍摆动推进流场RANS数值计算及涡结构提取分析方法,通过网格无关性验证,并与其它研究结果的比较验证数值计算方法的有效性。对尾鳍摆动推进过程中主要涡结构的产生与演化研究表明,尾鳍摆动推进水动力由St数主控,尾流中环状涡结构呈“之”形交错分布,并且随着St数增加,涡结构逐渐从单列演变成双列,推力系数逐渐增大。

鱼类自主游动推进机理与游动性能二维数值模拟研究

推进机理及游动性能研究对鱼类洄游通道建设具有重要意义。利用计算流体动力学方法结合重叠网格技术,通过编译控制鱼体摆动的UDF程序,对二维鱼类自主游动进行模拟,分析鱼体压力场分布及反卡门涡街结构演化过程与参数变化情况,开展不同摆尾频率、摆尾幅度、鱼体体形及尾鳍尺寸等参数下鱼类游动性能及鱼体受力的变化情况,揭示鱼类自主游动过程中的游动机理。研究结果表明:(1)鱼体尾鳍周期性往复摆动下漩涡脱落形成反卡门涡街,是鱼体前进推力的主要来源,且随着摆尾频率、摆尾幅度的增加,鱼体尾部涡街长度、涡街强度逐渐增加,而摆尾幅度对涡街宽度的影响较大;(2)随着摆尾频率、摆尾幅度的增加,纵向平均合力系数和最大侧向力系数均增大,使得鱼类获得较大的游动速度,但摆尾频率改变时平均合力系数和游动速度的增加更为明显,摆尾幅度改变时最大侧向力系数的增加更为明显;(3)随着体宽指数的增加,纵向平均合力系数逐渐减小,需克服的游动阻力增加,使得鱼类游动速度逐渐减小,而最大侧向力系数逐渐增加;(4)随着尾鳍指数的增加,纵向平均合力系数和最大侧向力系数均增大,使得鱼类游动速度逐渐增大。研究成果可为鱼类生境恢复营造提供支撑。

柔性尾鳍的形状对仿生机器鱼水动力学特性的影响研究

研究了仿生机器鱼不同形状柔性尾鳍的水动力学特性。根据仿生学观测结果,研制了4种形状的仿生机器鱼尾鳍,通过开展水动力学实验,对比分析了尾鳍外形、结构、材料和运动参数对水动力学参数的影响。结果表明,增大尾鳍的摆角幅度和摆动频率有利于提高推进力,但会引起游动的不稳定性;柔性强的新月形尾鳍具有较好的推进性能;展弦比越小的无鳍条尾鳍,高频游动性能越好,鳍条会降低尾鳍的高频游动性能。

鱼类叉状尾鳍效率转捩点水动力性能研究

鲔科鱼类具有较高的游动速度和游动效率,因此成为了仿生机器鱼的理想生物原型。为了研究鲔科鱼类叉状尾鳍效率转捩点的水动力特征,针对推力和功耗的源项进行重点分析。尾鳍模型采用了相同的表面面积、展弦比和叉长。为了统一尾鳍形状的尺度,采用扫掠角用于表征不同的叉状尾鳍平面结构。研究发现鲔科鱼类尾鳍扫掠角的增加弱化了尾鳍的有效面积,导致了尾鳍摆动时推动流体向下游运动而受到的反作用力降低,因此尾鳍的推进能力也会随之衰退。另外,扫掠角的增加也引起了前缘涡强度的增加和前缘涡的发展,从而造成了更大的涡增推力。然而,过分增加扫掠角尽管存在功耗下降的优势,但也引起推力和水动力效率的下降,特别是对于高斯特劳哈尔数的情况。通过对推力的源项进行分析发现扫掠角对附加质量力和涡增推力存在相反的作用机制。

基于RBF神经网络滑模控制的双尾鳍机器鱼

为了开展水下探测,设计了一种双尾鳍水下机器鱼。由于其存在模型参数不确定性和复杂水波干扰,为了得到较好的控制效果,建立了带有参数不确定因子的动力学模型,并在此基础上设计了径向基函数(RBF)神经网络滑模控制器。利用Lyapunov函数证明了控制系统的稳定性。仿真结果表明:与传统的PID控制器相比,所设计的RBF神经网络滑模控制器对双尾鳍水下机器鱼模型参数变化不敏感,控制精度高,鲁棒性强。该方法为今后鳍驱动式水下机器人的设计及应用提供了参考。

宽口裂腹鱼尾鳍细胞系的建立及其应用

宽口裂腹鱼为塔里木河水系的特有物种。为建立其尾鳍细胞系,笔者采用组织块法和胰酶消化法相结合,分别用含胎牛血清的DME/F12培养基体外培养尾鳍组织。初步建立宽口裂腹鱼尾鳍细胞系,细胞传代培养至45代。细胞呈悬浮生长,最适培养液为DME/F12,最适胎牛血清质量分数为20%,最适温度为25℃。第10代细胞的群体倍增时间为24.94 h,细胞呈“S”型生长。第6代细胞液氮冷冻保存180 d后复苏,经台盼蓝染色计数,(88.72±0.99)%的宽口裂腹鱼尾鳍细胞系具有活性,复苏后增殖速度快,可正常传代。细菌、真菌、支原体的鉴定未发现污染。第10代细胞线粒体16S rRNA基因测序结果与GenBank中基因序列做一致性对比,宽口裂腹鱼尾鳍细胞系与NC036933.1的一致率达99.91%,从分子水平证明,宽口裂腹鱼尾鳍细胞系来自宽口裂腹鱼。NaCl质量分数为8‰时,宽口裂腹鱼尾鳍细胞系的相对增殖率最高;NaHCO3质量浓度为7 g/L时,宽口裂腹鱼尾鳍细胞系的相对增殖率最高;宽口裂腹鱼尾鳍细胞系的相对增殖率随盐碱度增加呈先升后降趋势。

仿生机器鱼胸尾鳍联动水动力学性能分析

针对尾鳍摆动仿生机器鱼游动迟缓、姿态不稳定的问题,文中提出一种胸尾鳍联动的仿生机器鱼,实现了仿生机器鱼外部轮廓、内部布局设计,提出了仿生机器鱼运动控制系统,为仿真和实验提供硬件基础;改进了仿生机器鱼运动学模型,提出了水动力学仿真中鱼体轮廓改变的运动函数;基于仿生机器鱼游动水动力学仿真分析,得到最优运动参数以及最优运动参数下的应力、流速、涡情况;采用仿真最优胸尾鳍运动幅度结果,改变胸尾鳍运动频率,设计实验研究了仿生机器鱼游动水动力学性能。仿真结果表明,以尾鳍摆动幅度72 mm、胸鳍转动角度水平正负45°、胸尾鳍运动频率均为3 Hz等运动参数进行仿真,无胸鳍辅助游动的推进力为2 N,有胸鳍辅助游动的推进力为2.6 N;实验分析结果表明,以最佳运动参数实验,无胸鳍辅助游动的推进力为1.57 N,有胸鳍辅助游动的推进力为2.57 N。仿真和实验均说明,有胸鳍辅助鱼体游动的推进力更大。

基于双向流固耦合仿真的新月形尾鳍水动力学特性研究

以新月形仿生机器鱼尾鳍为研究对象,基于双向流固耦合仿真技术,研究了新月形仿生机器鱼尾鳍的结构参数和运动参数对其水动力学参数的影响关系。结果表明:增大尾鳍摆角幅度和摆动频率有利于提高推进力,同时也带来了游动的不稳定性;相比于等厚度柔性尾鳍,变厚度柔性尾鳍具有更好的推进性能,符合真实鱼类尾鳍结构特征;柔性大面积新月形尾鳍的推进性能最优。