Hydrodynamics Of Swimming Research Articles

Biomechanics of swimming in developing larval fish.

Most larvae of bony fish are able to swim almost immediately after hatching. Their locomotory system supports several vital functions: fish larvae make fast manoeuvres to escape from predators, aim accurately during suction feeding and may migrate towards suitable future habitats. Owing to their small size and low swimming speed, larval fish operate in the intermediate hydrodynamic regime, which connects the viscous and inertial flow regimes. They experience relatively strong viscous effects at low swimming speeds, and relatively strong inertial effects at their highest speeds. As the larvae grow and increase swimming speed, a shift occurs towards the inertial flow regime. To compensate for size-related limitations on swimming speed, fish larvae exploit high tail beat frequencies at their highest speeds, made possible by their low body inertia and fast neuromuscular system. The shifts in flow regime and body inertia lead to changing functional demands on the locomotory system during larval growth. To reach the reproductive adult stage, the developing larvae need to adjust to and perform the functions necessary for survival. Just after hatching, many fish larvae rely on yolk and need to develop their feeding systems before the yolk is exhausted. Furthermore, the larvae need to develop and continuously adjust their sensory, neural and muscular systems to catch prey and avoid predation. This Review discusses the hydrodynamics of swimming in the intermediate flow regime, the changing functional demands on the locomotory system of the growing and developing larval fish, and the solutions that have evolved to accommodate these demands.

Swimming without a spine: computational modeling and analysis of the swimming hydrodynamics of the Spanish Dancer

Incompressible flow simulations are used to study the swimming of a Spanish Dancer (Hexabranchus sanguineus), a soft-bodied invertebrate marine gastropod that swims by combining body pitching with undulations of its large mantle. A simple model based on a field video is employed as the basis for the model and coupling of the flow with the body acceleration enables us to examine the free swimming of this animal. Simulations indicate propulsive efficiencies up to about 57% and terminal swimming speeds of 1.33 body lengths per cycle. Examination of the effect of body planform on the swimming hydrodynamics suggests that the planform of this animal is likely adapted to enhance its swimming performance.

Numerical investigation of fish exploiting vortices based on the Kármán gaiting model

To understand the mechanism of fish exploiting vortices, this paper, for the first time, employs the Kármán gaiting model to numerically investigate the hydrodynamics of fish swimming in the vortex street. Considering the time-consuming computations during our large-scale simulations, we implement a parallel mesh deformation method based on the radial basis function(RBF) interpolation. Based on simulations over a wide range of controlling parameters, we discuss in detail the efficiency of fish exploiting vortices, the force coefficient and the hydrodynamic interactions between fish and vortices. It is observed that as the phase difference between fish's lateral translation and the shedding vortex changes, the efficiency presents a variation trend opposite to the mean thrust on the fish body; the optimum swimming distance downstream from the cylinder is positively affected by the inlet velocity and the diameter of the cylinder, which is consistent with the experimental results. From the hydrodynamic characteristics in the flow fields, we qualitatively draw a conclusion that the maximum efficiency is obtained when the fish is undulating with the tail flapping towards the center of the vortex, and the optimum distance is gained where vortices are drifting with the slipping mode.

Hot microswimmers

Hot microswimmers are self-propelled Brownian particles that exploit local heating for their directed self-thermophoretic motion. We provide a pedagogical overview of the key physical mechanisms underlying this promising new technology. It covers the hydrodynamics of swimming, thermophoresis and -osmosis, hot Brownian motion, force-free steering, and dedicated experimental and simulation tools to analyze hot Brownian swimmers.

Structure, biomimetics, and fluid dynamics of fish skin surfaces

A overview of the coupling between surface roughness, in the form of scales or denticles, and the hydrodynamics of effective swimming is presented.

Functional morphology and hydrodynamics of backward swimming in bluegill sunfish, Lepomis macrochirus

Most teleost fishes, like the bluegill sunfish Lepomis macrochirus, have multiple flexible fins that are used as modifiable control surfaces. This helps to make fish highly maneuverable, permitting behaviors like reversing direction of motion and swimming backwards without having to rotate body position. To answer the question of how fish swim backwards we used high–speed videography and electromyography to determine the kinematics and muscle activity necessary to produce reverse-direction propulsion in four bluegill sunfish. We found that, in contrast to slow forward swimming, low-speed backward swimming is a multi-fin behavior, utilizing the pectoral, dorsal, anal, and caudal fins. The pectoral fins alternate beats, each fin broadly flaring on the outstroke and feathered on the instroke. The dorsal fin and dorsal portion of the caudal fin move out of phase as do the anal fin and ventral portion of the caudal fin. Electromyography of muscles in the pectoral, dorsal, anal, and caudal fins demonstrated bilateral activation when these fins changed direction, suggesting that fins are stiffened at this time. In addition to backward propulsion by the pectoral fins, particle image velocimetry revealed that the dorsal and anal fins are capable of producing reverse momentum jets to propel the fish backward. Because teleost fishes are statically unstable, locomotion at slow speeds requires precise fin control to adequately balance torques produced about the center of mass. Therefore, the kinematics of backward swimming may be the result of compensation for rolling, pitching, and yawning instability. We suggest that asymmetric pectoral fin activity with feathering during adduction balances rolling instability. The ventral to dorsal undulatory wave on the caudal fin controls pitch instability and yaw instability encountered from pectoral-driven backward locomotion. Thrust generation from the dorsal and anal fins decreases the destabilizing effect of the long moment arm of the tail in backward swimming. Thus, backward locomotion at slow speed is not simply the reverse of slow forward swimming.

Hydrodynamics of swimming in stingrays: numerical simulations and the role of the leading-edge vortex

Stingrays, in contrast with many other aquatic animals, have flattened disk-shaped bodies with expanded pectoral ‘wings’, which are used for locomotion in water. To discover the key features of stingray locomotion, large-eddy simulations of a self-propelled stingray, modelled closely after the freshwater stingray,Potamotrygon orbignyi, are performed. The stingray’s body motion was prescribed based on three-dimensional experimental measurement of wing and body kinematics in live stingrays at two different swimming speeds of 1.5 and$2.5L~\text{s}^{-1}$($L$is the disk length of the stingray). The swimming speeds predicted by the self-propelled simulations were within 12 % of the nominal swimming speeds in the experiments. It was found that the fast-swimming stingray (Reynolds number$Re=23\,000$and Strouhal number$St=0.27$) is approximately 12 % more efficient than the slow-swimming one ($Re=13\,500$,$St=0.34$). This is related to the wake of the fast- and slow-swimming stingrays, which was visualized along with the pressure on the stingray’s body. A horseshoe vortex was discovered to be present at the anterior margin of the stingray, creating a low-pressure region that enhances thrust for both fast and slow swimming speeds. Furthermore, it was found that a leading-edge vortex (LEV) on the pectoral disk of swimming stingrays generates a low-pressure region in the fast-swimming stingray, whereas the low- and high-pressure regions in the slow-swimming one are in the back half of the wing and not close to any vortical structures. The undulatory motion creates thrust by accelerating the adjacent fluid (the added-mass mechanism), which is maximized in the back of the wing because of higher undulations and velocities in the back. However, the thrust enhancement by the LEV occurs in the front portion of the wing. By computing the forces on the front half and the back half of the wing, it was found that the contribution of the back half of the wing to thrust in a slow-swimming stingray is several-fold higher than in the fast-swimming one. This indicates that the LEV enhances thrust in fast-swimming stingrays and improves the efficiency of swimming.

The three-dimensional hydrodynamics of thunniform swimming under self-propulsion

This paper presents the hydrodynamics of thunniform swimming under self-propulsion as the body and caudal fin kinematic behaviors are systematically varied. The swimmer is a three-dimensional (3D) tuna-like flexible model with prescribed kinematics of thunniform mode. Simulations are carried out for various body behaviors by varying the wave frequency f and the tail amplitude Ap and for various caudal fin behaviors by varying the maximum angle of attack αmax and the phase difference φ. The results show that the swimming velocity as well as the propulsive efficiency is an increasing function of both f and Ap, but their trend with αmax and φ is found to be not monotonic. Specially, for peak swimming velocity generation, αmax occurs at 20–30°, and φ ranges from 60° to 75°, while for peak efficiency, αmax is 20–30° and φ nears 90°. The wake structure formed by the swimmer is single row wake consisting of a series of disconnected vortex rings that are resembled by sickle-like shape vortices. As φ increases, the tail of the sickle-shape vortices is shortening gradually while the head is stretching. As αmax increases, the aligned sickle-like vortices have almost identical shape with each other, but the wake strength is reducing gradually.

Drafting mechanisms between a dolphin mother and calf

We numerically study the drafting mechanisms between a dolphin mother and her calf swimming near the free surface. Formation locomotion between the cetacean mother-calf pair provides a way for the mother to assist the calf in its locomotion. Depending on the age and size of the calf, it swims at neonate, echelon, and infant positions. At each position, the effects of the calf’s size, swimming speed, proximity to the free surface and the formation pattern are investigated and the optimal configurations predicted by the model based on the swimming hydrodynamics are compared with previous observations. It is shown that the neonate position is the optimal formation for controlling the separation of the calf, and the echelon position is the most hydrodynamically efficient position in transferring the thrust force from the mother to the calf. The infant position, on the other hand, avoids the energy loss due to wave generation so that it improves the self-propulsion performance of an older calf.

Bio-inspired Flow Sensing and Prediction for Fish-like Undulating Locomotion: A CFD-aided Approach

Feedback flow information is of significance to enable underwater locomotion controllers with higher adaptability and efficiency within varying environments. Inspired from fish sensing their external flow via near-body pressure, a computational scheme is proposed and developed in this paper. In conjunction with the scheme, Computational Fluid Dynamics (CFD) is employed to study the bio-inspired fish swimming hydrodynamics. The spatial distribution and temporal variation of the near-body pressure of fish are studied over the whole computational domain. Furthermore, a filtering algorithm is designed and implemented to fuse near-body pressure of one or multiple points for the estimation on the external flow. The simulation results demonstrate that the proposed computational scheme and its corresponding algorithm are both effective to predict the inlet flow velocity by using near-body pressure at distributed spatial points.

From video to computation of biological fluid–structure interaction problems

This work deals with the techniques necessary to obtain a purely Eulerian procedure to conduct CFD simulations of biological systems with moving boundary flow phenomena. Eulerian approaches obviate difficulties associated with mesh generation to describe or fit flow meshes to body surfaces. The challenges associated with constructing embedded boundary information, body motions and applying boundary conditions on the moving bodies for flow computation are addressed in the work. The overall approach is applied to the study of a fluid–structure interaction problem, i.e., the hydrodynamics of swimming of an American eel, where the motion of the eel is derived from video imaging. It is shown that some first-blush approaches do not work, and therefore, careful consideration of appropriate techniques to connect moving images to flow simulations is necessary and forms the main contribution of the paper. A combination of level set-based active contour segmentation with optical flow and image morphing is shown to enable the image-to-computation process.

Quantitative wake analysis of a freely swimming fish using 3D synthetic aperture PIV

Synthetic aperture PIV (SAPIV) is used to quantitatively analyze the wake behind a giant danio (Danio aequipinnatus) swimming freely in a seeded quiescent tank. The experiment is designed with minimal constraints on animal behavior to ensure that natural swimming occurs. The fish exhibits forward swimming and turning behaviors at speeds between 0.9 and 1.5 body lengths/second. Results show clearly isolated and linked vortex rings in the wake structure, as well as the thrust jet coming off of a visual hull reconstruction of the fish body. As a benchmark for quantitative analysis of volumetric PIV data, the vortex circulation and impulse are computed using methods consistent with those applied to planar PIV data. Volumetric momentum analysis frameworks are discussed for linked and asymmetric vortex structures, laying a foundation for further volumetric studies of swimming hydrodynamics with SAPIV. Additionally, a novel weighted refocusing method is presented as an improvement to SAPIV reconstruction.

Modelling the mechanics and hydrodynamics of swimming E. coli.

The swimming properties of an E. coli-type model bacterium are investigated by mesoscale hydrodynamic simulations, combining molecular dynamics simulations of the bacterium with the multiparticle particle collision dynamics method for the embedding fluid. The bacterium is composed of a spherocylindrical body with attached helical flagella, built up from discrete particles for an efficient coupling with the fluid. We measure the hydrodynamic friction coefficients of the bacterium and find quantitative agreement with experimental results of swimming E. coli. The flow field of the bacterium shows a force-dipole-like pattern in the swimming plane and two vortices perpendicular to its swimming direction arising from counterrotation of the cell body and the flagella. By comparison with the flow field of a force dipole and rotlet dipole, we extract the force-dipole and rotlet-dipole strengths for the bacterium and find that counterrotation of the cell body and the flagella is essential for describing the near-field hydrodynamics of the bacterium.

Modelling Swimming Hydrodynamics to Enhance Performance

Swimming assessment is one of the most complex but outstanding and fascinating topics in biomechanics. Computational fluid dynamics (CFD) methodology is one of the different methods that have been applied in swimming research to observe and understand water movements around the human body and its application to improve swimming

The hydrodynamics of swimming at intermediate Reynolds numbers in the water boatman (Corixidae).

The fluid forces that govern propulsion determine the speed and energetic cost of swimming. These hydrodynamics are scale dependent and it is unclear what forces matter to the tremendous diversity of aquatic animals that are between a millimeter and a centimeter in length. Animals at this scale generally operate within the regime of intermediate Reynolds numbers, where both viscous and inertial fluid forces have the potential to play a role in propulsion. The present study aimed to resolve which forces create thrust and drag in the paddling of the water boatman (Corixidae), an animal that spans much of the intermediate regime (10<Re<200). By measuring the force generated by tethered water boatmen, we found that thrust is generated primarily by drag on the paddling appendages, with a negligible contribution from the acceleration reaction force. Based on these findings, we developed a forward-dynamic model of propulsion in free swimming that accurately predicted changes in the body's center of mass over time. For both tethered and free swimming, we used non-linear optimization algorithms to determine the force coefficients that best matched our measurements. With this approach, the drag coefficients on the body and paddle were found to be up to three times greater than on static structures in fully developed flow at the same Reynolds numbers. This is likely a partial consequence of unsteady interactions between the paddles or between the paddles and the body. In addition, the maximum values for these coefficients were inversely related to the Reynolds number, which suggests that viscous forces additionally play an important role in the hydrodynamics of small water boatmen. This understanding for the major forces that operate at intermediate Reynolds numbers offers a basis for interpreting the mechanics, energetics and functional morphology of swimming in many small aquatic animals.

Swimming near the substrate: a simple robotic model of stingray locomotion

Studies of aquatic locomotion typically assume that organisms move through unbounded fluid. However, benthic fishes swim close to the substrate and will experience significant ground effects, which will be greatest for fishes with wide spans such as benthic batoids and flatfishes. Ground effects on fixed-wing flight are well understood, but these models are insufficient to describe the dynamic interactions between substrates and undulating, oscillating fish. Live fish alter their swimming behavior in ground effect, complicating comparisons of near-ground and freestream swimming performance. In this study, a simple, stingray-inspired physical model offers insights into ground effects on undulatory swimmers, contrasting the self-propelled swimming speed, power requirements, and hydrodynamics of fins swimming with fixed kinematics near and far from a solid boundary. Contrary to findings for gliding birds and other fixed-wing fliers, ground effect does not necessarily enhance the performance of undulating fins. Under most kinematic conditions, fins do not swim faster in ground effect, power requirements increase, and the cost of transport can increase by up to 10%. The influence of ground effect varies with kinematics, suggesting that benthic fish might modulate their swimming behavior to minimize locomotor penalties and incur benefits from swimming near a substrate.

1D06 胴体の波打ち運動と胸びれの羽ばたき運動の位相差による稚魚遊泳推進性能への影響(OS10-2:生物の遊泳と飛翔(2))

1D06 胴体の波打ち運動と胸びれの羽ばたき運動の位相差による稚魚遊泳推進性能への影響(OS10-2:生物の遊泳と飛翔(2))

Influence of a postural change of the swimmer's head in hydrodynamic performances using 3D CFD

This study deals with recent researches undertaken by the authors in the field of hydrodynamics of human swimming. The aim of this numerical study was to investigate the flow around the entire swimmer's body. The results presented in this article focus on the combination of a 3D computational fluid dynamics code and the use of the k–ω turbulence model, in the range of Reynolds numbers representative of a swimming level varying from national to international competition. Emphasis is placed on the influence of a postural change of the swimmer's head in hydrodynamic performances, which is directly related to the reduction of overall drag. These results confirm and complete those, less accurate, of a preliminary 2D study recently published by the authors and allow the authors to optimise the swimmer's head position in underwater swimming.

Dolphin-like Swimming Modeling for a Biomimetic Amphibious Robot

AbstractThis paper focuses on a dolphin-like swimming hydrodynamics problem for a biomimetic amphibious robot capable of both fish- and dolphin-like swimming modes. A Lagrangian reduction has been established in terms of rigid-body dynamics. For robust gait control, a central pattern generator-based approach is incorporated into the model serving as explicit joint angle control. Consequently, a simultaneous kinematics and dynamics system has been established to investigate the dolphin-like swimming. The rough comparisons between fish-and dolphin-like propulsion are very promising, which verify the effectiveness of the proposed model and further provide an insight into more efficient underwater propulsor.

Modelling Swimming Hydrodynamics to Enhance Performance~!2009-07-05~!2009-11-01~!2010-04-20~!

Modelling Swimming Hydrodynamics to Enhance Performance~!2009-07-05~!2009-11-01~!2010-04-20~!