Swimming velocity of spherical squirmers in a square tube at finite fluid inertia

The three-dimensional lattice Boltzmann method(LBM)is used to simulate the motion of a spherical squirmer in a square tube,and the steady motion velocity of a squirmer with different Reynolds numbers(Re,ranging from 0.1 to 2)and swimming types is investigated and analyzed to better understand the swimming characteristics of microorganisms in different environments.First,as the Reynolds number increases,the effect of the inertial forces becomes significant,disrupting the squirmer's ability to maintain its theoretical velocity.Specifically,as the Reynolds number increases,the structure of the flow field around the squirmer changes,affecting its velocity of motion.Notably,the swimming velocity of the squirmer exhibits a quadratic relationship with the type of swimming and the Reynolds number.Second,the narrow tube exerts a significant inhibitory effect on the squirmer motion.In addition,although chirality does not directly affect the swimming velocity of the squirmer,it can indirectly affect the velocity by changing its motion mode.

Neurogranin as an important regulator in swimming training to improve the spatial memory dysfunction of mice with chronic cerebral hypoperfusion

Background:Vascular cognitive impairment caused by chronic cerebral hypoperfusion(CCH)has become a hot issue worldwide.Aerobic exercise positively contributes to the preservation or restoration of cognitive abilities;however,the specific mechanism has remained inconclusive.And recent studies found that neurogranin(Ng)is a potential biomarker for cognitive impairment.This study aims to investigate the underlying role of Ng in swimming training to improve cognitive impairment.Methods:To test this hypothesis,the clustered regularly interspaced short palindromic repeats(CRISPR)-associated protein 9(Cas9)system was utilized to construct a strain of Ng conditional knockout(Ng cKO)mice,and bilateral common carotid artery stenosis(BCAS)surgery was performed to prepare the model.In Experiment 1,2-month-old male and female transgenic mice were divided into a control group(wild-type littermate,n=9)and a Ng cKO group(n=9).Then,2-month-old male and female C57BL/6 mice were divided into a sham group(C57BL/6,n=12)and a BCAS group(n=12).In Experiment 2,2-month-old male and female mice were divided into a sham group(wild-type littermate,n=12),BCAS group(n=12),swim group(n=12),BCAS+Ng cKO group(n=12),and swim+Ng cKO group(n=12).Then,7 days after BCAS,mice were given swimming training for 5 weeks(1 week for adaptation and 4 weeks for training,5 days a week,60 min a day).After intervention,laser speckle was used to detect cerebral blood perfusion in the mice,and the T maze and Morris water maze were adopted to test their spatial memory.Furthermore,electrophysiology and Western blotting were conducted to record long-term potential and observe the expressions of Ca^(2+)pathway-related proteins,respectively.Immunohistochemistry was applied to analyze the expression of relevant markers in neuronal damage,inflammation,and white matter injury.Results:The figures showed that spatial memory impairment was detected in Ng cKO mice,and a sharp decline of cerebral blood flow and an impairment of progressive spatial memory were observed in BCAS mice.Regular swimming training improved the spatial memory impairment of BCAS mice.This was achieved by preventing long-term potential damage and reversing the decline of Ca^(2+)signal transduction pathway-related proteins.At the same time,the results suggested that swimming also led to improvements in neuronal death,inflammation,and white matter injury induced by CCH.Further study adopted the use of Ng cKO transgenic mice,and the results indicated that the positive effects of swimming training on cognitive impairments,synaptic plasticity,and related pathological changes caused by CCH could be abolished by the knockout of Ng.Conclusion:Swimming training can mediate the expression of Ng to enhance hippocampal synaptic plasticity and improve related pathological changes induced by CCH,thereby ameliorating the spatial memory impairment of vascular cognitive impairment.

High-intensity swimming alleviates nociception and neuroinflammation in a mouse model of chronic postischemia pain by activating the resolvin E1-chemerin receptor 23 axis in the spinal cord

Physical exe rcise effectively alleviates chronic pain associated with complex regional pain syndrome type-Ⅰ.However,the mechanism of exe rcise-induced analgesia has not been clarified.Recent studies have shown that the specialized pro-resolving lipid mediator resolvin E1 promotes relief of pathologic pain by binding to chemerin receptor 23 in the nervous system.However,whether the resolvin E1-chemerin receptor 23 axis is involved in exercise-induced analgesia in complex regional pain syndrome type-Ⅰ has not been demonstrated.In the present study,a mouse model of chronic post-ischemia pain was established to mimic complex regional pain syndrome type-Ⅰ and subjected to an intervention involving swimming at different intensities.Chronic pain was reduced only in mice that engaged in high-intensity swimming.The resolvin E1-chemerin receptor 23 axis was clearly downregulated in the spinal cord of mice with chronic pain,while high-intensity swimming restored expression of resolvin E1 and chemerin receptor 23.Finally,shRNA-mediated silencing of chemerin receptor 23in the spinal cord reve rsed the analgesic effect of high-intensity swimming exercise on chronic post-ischemic pain and the anti-inflammato ry pola rization of microglia in the dorsal horn of the spinal cord.These findings suggest that high-intensity swimming can decrease chronic pain via the endogenous resolvin E1-chemerin receptor 23 axis in the spinal cord.

Adaptive Swimming of Underwater Snake-like Robot in Different Underwater Environment

Hydrodynamic force is an important factor that affects the performance of underwater vehicle.Adapting to the current underwater environment by changing its shape is an important feature of underwater snake-like robots(USLR).An experiment was implemented to verify the swimming along the straight line of USLR.A simulation platform is also established for the analysis of the swimming of USLR.To figure out adaptive swimming of USLR to different underwater environments,the relationships between CPG parameters and maximum swimming speed have been discussed,and the switching between different swimming modes has been implemented.

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。

Solumbra技术和SWIM技术治疗脑卒中的疗效对比

目的评估Solumbra技术和SWIM技术治疗急性缺血性脑卒中(acute ischemic stroke,AIS)的有效性与安全性。方法回顾性分析191例AIS病例资料,根据手术方式分为Solumbra组(n=97)和SWIM组(n=94)。应用倾向性评分匹配法(propensity score matching,PSM)将两组患者按1∶1配比。对比匹配后两组患者临床相关指标、术后不同时间点美国国立卫生院卒中量表(the National Institutes of Health Stroke Scale,NIHSS)评分、侧支循环改善情况及并发症发生率。结果经PSM匹配,有50对患者匹配成功。Solumbra组患者取栓>2次占比与住院时间均高于SWIM组,预后良好占比低于SWIM组(P<0.05)。Solumbra组患者术后7d及术后2周NIHSS评分均低于SWIM组(P<0.05)。并发症发生率Solumbra组为20.00%,SWIM组为38.00%,Solumbra组低于SWIM组(P<0.05)。结论Solumbra技术和SWIM技术取栓治疗各有优势,临床可充分结合患者实际病情,针对性选择取栓方式。

World Class Elite Breaststrokers Downward Kick EMG Muscle Activity of the Gluteus Maximus, Quadriceps Femoris, Hamstring, Gastrocnemius Medialis, Rectus Abdominal, and Erector Spinae

This study analyzed the difference between using a downward breaststroke kick and a horizontal breaststroke kick in a sample of world class elite swimmers.We compared average muscle activity of the gluteus maximus,quadriceps femoris(vastus medialis and rectus femoris),hamstring/long head of the biceps femoris,gastrocnemius medialis,rectus abdominal,and erector spinae when using the downward breaststroke kick technique.We find that when this sample of swimmers utilized the downward breaststroke kick,max speed and velocity per stroke increased,measured by 12,788 EMG samples,where the results are highly correlated to duration of the aerodynamic buoyant force in breaststroke kick technique.The increases in performance observed from measuring the world class elite swimmers is highly correlated to the duration of the kick aerodynamic buoyant force.Among this sample of elite swimmers,the longer a swimmer demonstrates a buoyant force breaststroke kick,the lower the time in a 100 breaststroke.

Design of a Novel Robotic Fish Structure Utilizing PVC Gel Actuators

In this research work, it has been designed a bionic robot fish structure, can swim underwater. The active compact body is powered by eight sets of symmetric PVC gel actuators with a caudal fin. The robot’s 200 mm-long, fish structure design incorporates a 55.52 angle to optimize the fish dynamics movement. It’s a fast and smooth operation and can swim. The robot can swim fast and quietly by using the right positions and the appropriate actuators on PVC gel actuators. This design entails a unique architecture that enables the robot to move safely and unobtrusively at the same time, which makes it suitable equipment for different exploration and surveillance missions in the water with speed and silent operation as the foremost concern.

Cancer risk assessment from exposure to trihalomethanes in tap water and swimming pool water

We investigated the concentration of trihalomethanes （THMs） in tap water and swimming pool water in the area of the Nakhon Path- om Municipality during the period April 2005-March 2006. The concentrations of total THMs, chloroform, bromodichloromethane, dibromochloromethane and bromoform in tap water were 12.70-41.74, 6.72-29.19, 1.12-11.75, 0.63-3.55 and 0.08-3.40 μg/L, respectively, whereas those in swimming pool water were 26.15-65.09, 9.50-36.97, 8.90-18.01, 5.19-22.78 and ND-6.56 μg/L, respectively. It implied that the concentration of THMs in swimming pool water was higher than those in tap water, particularly, brominated-THMs. Both tap water and swimming pool water contained concentrations of total THMs below the standards of the World Health Organization （WHO）, European Union （EU） and the United States Environmental Protection Agency （USEPA） phase Ⅰ, but 1 out of 60 tap water samples and 60 out of 72 swimming pool water samples contained those over the Standard of the USEPA phase Ⅱ. From the two cases of cancer risk assessment including Case Ⅰ Non-Swimmer and Case Ⅱ Swimmer, assessment of cancer risk of nonswimmers from exposure to THMs at the highest and the average concentrations was 4.43×10^-5 and 2.19×10^-5, respectively, which can be classified as acceptable risk according to the Standard of USEPA. Assessment of cancer risk of swimmers from exposure to THMs at the highest and the average concentrations was 1.47×10^-3 and 7.99×10^-4, respectively, which can be classified as unacceptable risk and needs to be improved. Risk of THMs exposure from swimming was 93.9%-94.2% of the total risk. Cancer risk of THMs concluded from various routes in descending order was： skin exposure while swimming, gastro-intestinal exposure from tap water intake, and skin exposure to tap water and gastro-intestinal exposure while swimming. Cancer risk from skin exposure while swimming was 94.18% of the total cancer risk.

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.

Effects of different dietary lipid sources on growth performance and tissue fatty acid composition of juvenile swimming crab Portunus trituberculatus

This study was conducted to evaluate the effects of dietary lipid sources on the growth performance and fatty acid composition of the swimming crab, P ortunus trituberculatus. Four isonitrogenous and isoenergetic experimental diets were formulated to contain four separate lipid sources, including fish, soybean, rapeseed, and linseed oils(FO, SO, RO, and LO, respectively). With three replicates of 18 crabs each for each diet, crabs(initial body weight, 17.00 ±0.09 g) were fed twice daily for 8 weeks. There were no significant differences among these groups in terms of weight gain, specific growth rate, and hepatosomatic index. However, the RO groups' survival rate was significantly lower than FO groups. The feed conversion and protein efficiency ratios of RO groups were poorer than other groups. The proximate compositions of whole body and hepatopancreas were significantly affected by these dietary treatments. Tissue fatty acid composition mainly reflected dietary fatty acid compositions. Crabs fed FO diets exhibited significantly higher arachidonic, eicosapentaenoic, and docosahexaenoic acid contents in muscle and hepatopancreas compared with VO crabs. Linoleic, oleic, and linolenic acids in muscle and hepatopancreas were the highest in the SO, RO, and LO groups, respectively. The present study suggested that SO and LO could substitute for FO in fishmeal-based diets for swimming crabs, without affecting growth performance and survival.

Effect of Dissolved Oxygen on Swimming Ability andPhysiological Response to Swimming Fatigue ofWhiteleg Shrimp （Litopenaeus vannamet3

The swimming endurance of whiteleg shrimp （Litopenaeus vannamei, 87.66 mm±0.25 mm, 7.73 g±0.06 g） was exam-ined at various concentrations of dissolved oxygen （DO, 1.9, 3.8, 6.8 and 13.6mgL-1） in a swimming channel against one of the fiveflow velocities （vb v2, v3, v4 and vs）. Metabolite contents in the plasma, hepatopancreas and pleopods muscle of the shrimp werequantified before and after swimming fatigue. The results revealed that the swimming speed and DO concentration were significantfactors that affected the swimming endurance ofL. vannamei. The relationship between swimming endurance and swimming speedat various DO concentrations can be described by the power model （vtb= a）. The relationship between DO concentration （mgL-l） e 9000and the swimming ability index （SAI）, defined as SAI= ∫9000vdt （cm）, can be described as SAI=27.947DO0.137 （R2=0.9312）. Thelevel of DO concentration directly affected the physiology of shrimp, and exposure to low concentrations of DO led to the increasesin lactate and energetic substrate content in the shrimp. In responding to the low DO concentration at 1.9 mg L-1 and the swimmingstress, L. vannamei exhibited a mix of aerobic and anaerobic metabolism to satisfy the energetic demand, mainly characterized by theutilization of total protein and glycogen and the production of lactate and glucose. Fatigue from swimming led to severe loss ofplasma triglyceride at Vl, v2, and v3 with 1.9mgL-1DO, and at V1 with 3.8, 6.8 and 13.6mgL-1 DO, whereas the plasma glucose con-tent increased significantly at v3, v4 and v5 with 3.8 and 6.8mgL-1 DO, and at v5 with 13.6mgL-1 DO. The plasma total protein andhepatopancreas glycogen were highly depleted in shrimp by swimming fatigue at various DO concentrations, whereas the plasmalactate accumulated at high levels after swimming fatigue at different velocities. These results were of particular value to under-standing the locomotory ability of whiteleg shrimp and its physiological changes, further contributing to the improvement of captureand rearing technique.

Cold water swimming pretreatment reduces cognitive deficits in a rat model of traumatic brain injury

A moderate stress such as cold water swimming can raise the tolerance of the body to potentially injurious events. However, little is known about the mechanism of beneficial effects induced by moderate stress. In this study, we used a classic rat model of traumatic brain injury to test the hypothesis that cold water swimming preconditioning improved the recovery of cognitive functions and explored the mechanisms. Results showed that after traumatic brain injury, pre-conditioned rats（cold water swimming for 3 minutes at 4℃） spent a significantly higher percent of times in the goal quadrant of cold water swim, and escape latencies were shorter than for non-pretreated rats. The number of circulating endothelial progenitor cells was significantly higher in pre-conditioned rats than those without pretreatment at 0, 3, 6 and 24 hours after traumatic brain injury. Immunohistochemical staining and Von Willebrand factor staining demonstrated that the number of CD34~＋ stem cells and new blood vessels in the injured hippocampus tissue increased significantly in pre-conditioned rats. These data suggest that pretreatment with cold water swimming could promote the proliferation of endothelial progenitor cells and angiogenesis in the peripheral blood and hippocampus. It also ameliorated cognitive deficits caused by experimental traumatic brain injury.

Effects of salinity on survival,feeding behavior and growth of the juvenile swimming crab,Portunus trituberculatus(Miers,1876)

Effect of salinity on survival,feeding behavior and growth of juvenile swimming crab P ortunus trituberculatus was investigated under 5 salinity levels of 5,10,20,30 and 40. The results show that the crab juveniles fed 2 or 3 times at the salinity 20 and 30,each lasted for about 25 minutes,for a total feeding time of 73.2±22.65 minutes per day. At these salinities,there were significantly higher in the frequency of feeding and in total feeding time than those at lower salinities of 5 and 10. All crab juveniles moulted when reared at a salinity of 20 during the 5 days duration of the experiment,which is significantly higher than those at other salinities. All juveniles survived at salinity 20,and the survivorship was not significantly different from that at 30,but was signif icantly higher than those at other salinities. The crab juveniles reared at a salinity of 20 had the highest value of food ration of 0.190 8±0.011 3 g/g BW,average body weight gain of 0.796±0.128 g,gain rate of 87%–96%,and food conversion ratio of 1.20±0.09. There was no significant difference in the values found between 20 and 30 but these values were significantly lower than that at the other salinities( P> 0.05). Highest activities of digestive enzymes(Amylase,Protease,Lipase) and lowest activities of protective enzymes(SOD,PO,CAT) were also obtained on crab juveniles reared at salinity of 20.

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.

Orbitofrontal cortex action of 5-hydroxytryptamine and its receptor in an acute forced swimming stress-induced depression model

BACKGROUND： The orbitofrontal cortex （OFC） is a brain region closely associated with emotion. 5-hydroxytryptamine （5-HT） has been shown to be involved in human depression. OBJECTIVE： To investigate OFC actions and mechanisms of 5-HT and 5-HT1A receptor （5-HT1AR） in stress-induced depression.DESIGN, TIME AND SETTING： A randomized, controlled, animal experiment was performed at Laboratory of Neurobiology, College of Life Science, Shaanxi Normal University between May 2006 and March 2008. MATERIALS： 5-HT, p-chlorophenylalanine （PCPA, an inhibitor to tryptophan hydroxylase） and spiperone （5-HT1AR antagonist） were provided by Sigma, USA; rabbit anti-rat 5-HT1AR antibody was provided by Tianjin Haoyang Biological Manufacture. METHODS： A total of 40 male Sprague Dawley rats, aged 3 months, were randomly divided into five groups： control, model, 5-HT, spiperone ＋ 5-HT, and PCPA, with 8 rats in each group. Except for control group, rats in the other four groups were used to establish depression models by forced swimming for 15 minutes. At 30 minutes before forced swimming test, 0.5 pL of 5-HT （12.5 pg/pL）, PCPA （20 pg/pL）, spiperone （1.3 pg/pL） ＋ 5-HT （12.5 pg/pL, 10 minutes later）, and saline were respectively injected into the OFC of 5-HT, PCPA, spiperone ＋ 5-HT, and model groups, respectively. The control group received a saline microinjection into the OFC.MAIN OUTCOME MEASURES： Forced swimming and open field tests were employed to measure animal behaviors, and immunohistochemistry was used to analyze 5-HT1AR expression in the OFC, cingulate cortex, and piriform cortex. RESULTS： （1） Compared with the model group, 5-HT microinjection into the OFC prominently reduced immobility time in the forced swimming test and rearing in open field test （P 〈 0.05）; locomotion and grooming in open field test were increased, although there was no significance （P 〉 0.05）. Furthermore, following PCPA microinjection into the OFC （PCPA ＋ forced swimming stress）, immobility time in forced swimming test increased dramatically （P〈 0.01）, locomotion and rearing in open field test declined （P〈 0.05 and P 〈 0.01, respectively）. Compared with the 5-HT group, 5-HT1AR antagonist （spiperone ＋ 5-HT ＋ forced swimming stress） increased immobility time in forced swimming test （P 〈 0.01）, but decreased locomotion, rearing, and grooming in open field test. （2） Forced swimming stress markedly elevated 5-HT1AR expression in OFC, cingulate cortex, and piriform cortex （P〈 0.05 or P〈 0.01）. CONCLUSION： 5-HT improved stress-induced depression, and 5-HT anti-depression effects are primarily achieved via 5-HT1AR. Stress-induced up regulation of 5-HT1AR expression might be a compensatory mechanism for decreased 5-HT expression.

Swimming of motile gyrotactic microorganisms and suspension of nanoparticles in a rheological Jeffery fluid with Newtonian heating along elastic surface

Bioconvection plays an inevitable role in introducing sustainable and environment-friendly fuel cell technologies.Bio-mathematical modelling of such designs needs continuous refinements to achieve strong agreements in experimental and computational results.Actually,microorganisms transport a miscellaneous palette of ingredients in manufacturing industrial goods particularly in fertilizer industries.Heat transfer characteristics of molecular structure are measured by a physical phenomenon which is allied with the transpiration of heat within matter.Motivated by bioinspired fuel cells involved in near-surface flow phenomena,in the present article,we examine the transverse swimming of motile gyrotactic microorganisms numerically in a rheological Jeffery fluid near a stretching wall.The leading physical model is converted in a nonlinear system of ODEs through proper similarity alterations.A numerical technique called shooting method with R-K Fehlberg is applied via mathematical software and graphical presentations are obtained.The influence of all relative physical constraints on velocity,temperature,concentration,and volume fraction of gyrotactic microorganisms is expressed geometrically.It is found that heat and mass flux at the surface as well as density of motile microorganism’s declines for Brownian motion and thermophoresis parameter.Comparison in tabular form is made with existing literature to validate the results for limiting cases with convective boundary conditions.

Bio-inspired Actuating System for Swimming Using Shape Memory Alloy Composites

The paper addresses the designs of a caudal peduncle actuator, which is able to furnish a thrust for swimming of a robotic fish. The caudal peduncle actuator is based on concepts of ferromagnetic shape memory alloy （FSMA） composite and hybrid mechanism that can provide a fast response and a strong thrust. The caudal peduncle actuator was inspired by Scomber Scombrus which utilises thunniform mode swimming, which is the most efficient locomotion mode evolved in the aquatic environment, where the thrust is generated by the lift-based method, allowing high cruising speeds to be maintained for a long period of time. The morphology of an average size Scomber Scombrus （length in 310 mm） was investigated, and a 1：1 scale caudal peduncle actuator prototype was modelled and fabricated. The propulsive wave characteristics of the fish at steady speeds were employed as initial design objectives. Some key design parameters are investigated, i.e. aspect ratio （AR） （AR = 3.49）, Reynolds number （Re = 429 649）, reduced frequency （σ = 1.03）, Strouhal number （St = 0.306） and the maximum strain of the bent tail was estimated at ε = 1.11% which is in the range of superelasticity. The experimental test of the actuator was carried out in a water tank. By applying 7 V and 2.5 A, the actuator can reach the tip-to-tip rotational angle of 85° at 4 Hz.

Unsteady bio-fluid dynamics in flying and swimming

Flying and swimming in nature present sophisticated and exciting ventures in biomimetics, which seeks sustainable solutions and solves practical problems by emulating nature＇s time-tested patterns, functions, and strategies. Bio-fluids in insect and bird flight, as well as in fish swimming are highly dynamic and unsteady; however, they have been studied mostly with a focus on the phenomena associated with a body or wings moving in a steady flow. Characterized by unsteady wing flapping and body undulation, fluid-structure interactions, flexible wings and bodies, turbulent environments, and complex maneuver, bio-fluid dynamics normally have challenges associated with low Reynolds number regime and high unsteadiness in modeling and analysis of flow physics. In this article, we review and highlight recent advances in unsteady bio-fluid dynamics in terms of leading-edge vortices, passive mechanisms in flexible wings and hinges, flapping flight in unsteady environments, and micro-structured aerodynamics in flapping flight, as well as undulatory swimming, flapping-fin hydrodynamics, body–fin interac-tion, C-start and maneuvering, swimming in turbulence,collective swimming, and micro-structured hydrodynamics in swimming. We further give a perspective outlook on future challenges and tasks of several key issues of the field.