Swimming Movements Research Articles

Reinforcement learning control for the swimming motions of a beaver-like, single-legged robot based on biological inspiration

Complex hydrodynamic modeling and analysis are considered as stumbling blocks in the motion study of underwater bionic robots. In recent years, reinforcement learning techniques have been applied for robot motion control in unknown environments. However, robots may act in an unconventional or dangerous manner during the learning process. These actions increase the training difficulty and decrease the training efficiency. In this study, a biological-inspired reinforcement learning control method is proposed. It realizes the self-learning movement policy of the robot with discretized swimming motions of a beaver without the need to establish motion models, such as hydrodynamics, of underwater robots. The biological-inspired model further reduces the robot’s ineffective movements during the reinforcement learning and improves training efficiency. The experiment results verify the environmental adaptation and self-learning ability of the proposed robot platform and proves the effectiveness of the reinforcement learning control method for robotic swimming based on biological inspiration. This study’s findings provide new ideas for the motion control of underwater bionic robots and further promote the application of artificial intelligence in underwater robots.

The Effect of the Swimmer's Trunk Oscillation on Dolphin Kick Performance Using a Computational Method with Multi-Body Motion: A Case Study.

The effect of a specific Chinese swimmer’s trunk oscillation on dolphin kick was investigated in order to optimize competitive swimming movement. Using a numerical simulation method based on multi-body motion, different swimmer’s trunk oscillation during a dolphin kick was analyzed. The simulation was conducted using 3D incompressible Navier–Stokes equations and renormalization group k-ε turbulence model, combined with the Volume of Fluid method to capture the water surface. The simulation’s results were evaluated by comparing them with experimental data and with previous studies. The net streamwise forces, mean swimming velocity, and joint moments were also investigated. There was a positive correlation between the mean swimming velocity and the amplitudes of the swimmer’s trunk oscillation, where the Pearson correlation coefficient was 0.986 and the selected model was statistically significant (p < 0.05). In addition, as the mean swimming velocity increased from 1.42 m/s in Variant 1 to 2 m/s in Variant 5, the maximum positive moments of joints increased by about 24.7% for the ankles, 27.4% for the knees, −3.9% for the hips, and 5.8% for the upper waist, whereas the maximum negative moments of joints increased by about 64.5% for the ankles, 28.1% for the knees, 23.1% for the hips, and 10.1% for the upper waist. The relationship between the trunk oscillation and the vortices was also investigated. Therefore, it is recommended that swimmers should try to increase the amplitudes of trunk oscillation to increase their swimming velocity. In order to achieve this goal, swimmers should increase strength training for the ankles, knees, and upper waist during the upkick. Moreover, extra strength training is warranted for the ankles, knees, hips, and upper waist during the downkick.

Unsteady chiral swimmer and its response to a chemical gradient

Unsteadiness occurs in the motion of swimmers while they start from rest or escape from a predator, or attack prey. In this paper, we study the behaviour of an unsteady chiral swimmer, with a prescribed surface slip velocity, in the low-Reynolds-number regime, and its response to an external chemical gradient. In the first part, by solving the unsteady Stokes equation, we calculate the migration velocity ( $\boldsymbol {U}$ ), rotation rate ( $\boldsymbol {\varOmega }$ ) and flow field of the unsteady swimmer in a closed form. We compare these results with some previously known results in appropriate limits. In the second part, we investigate the response of the unsteady chiral swimmer to an external chemical gradient, which can influence the swimmer's surface slip velocity. Consequently, the swimmer either steers towards the source of the chemical gradient or moves away from it, depending on the strengths of $\boldsymbol {U}$ and $\boldsymbol {\varOmega }$ , and the corresponding angle ( $\chi$ ) between them. Interestingly, the swimmer swims in a closed orbit in the vicinity of the chemical target, depending on the strengths of $\boldsymbol {\varOmega }$ and $\chi$ . We present a complete state diagram representing the successful, unsuccessful and orbital states for various strengths of $\boldsymbol {\varOmega }$ and $\chi$ . This study is useful to understand the unsteady propulsion of ciliated microorganisms and their response to external gradients.

Pirarucu larviculture in green water provides heavier fish and modulates locomotor activity

ABSTRACT The green water technique uses microalgae in the water of indoor larviculture, providing a darker environment to favor fish growth, welfare and health. We evaluated growth performance and locomotor activity after light exposure of pirarucu (Arapaima gigas) larvae reared in green or clear water. During one test, pirarucu larvae (3.6 ± 0.3 cm; 0.36 ± 0.1 g) were reared in 50-L circular tanks (n = 3 per treatment, 50 larvae per tank) in a static system containing green water [microalgae (w3algae; Bernaqua® 10 g m-3) added] or clear water (control). Fish weaning was achieved by co-feeding with Artemia nauplii and microdiets for seven days until full microdiet substitution. Larvae were biometrically evaluated on days 10, 17 and 24 to assess growth performance. In a second test, the locomotor activity of the larvae was analyzed before and after light exposure (1400 ± 60 lx) for 48 h according to an ethogram. After 24 days, the larvae reared in the green water were significantly heavier than those from the clear water, and displayed significantly fewer circular swimming movements. Body cortisol increased in both groups after light exposure. The microalgae provided an additional food source for larvae, with positive impact on growth until day 17 of larviculture. Green water can be a strategy to achieve better results in pirarucu larviculture, especially during and up to 10 days after the co-feeding period.

Long descending commissural V0v neurons ensure coordinated swimming movements along the body axis in larval zebrafish

Developmental maturation occurs in slow swimming behavior in larval zebrafish; older larvae acquire the ability to perform slow swimming while keeping their head stable in the yaw dimension. A class of long-distance descending commissural excitatory V0v neurons, called MCoD neurons, are known to develop in a later phase of neurogenesis, and participate in slow swimming in older larvae. We hypothesized that these MCoD neurons play a role in coordinating the activities of trunk muscles in the diagonal dimension (e.g., the rostral left and the caudal right) to produce the S-shaped swimming form that contributes to the stability of the head. Here, we show that MCoD neurons do indeed play this role. In larvae in which MCoD neurons were laser-ablated, the swimming body form often adopted a one-sided (C-shaped) bend with reduced appearance of the normal S-shaped bend. With this change in swimming form, the MCoD-ablated larvae exhibited a greater degree of head yaw displacement during slow swimming. In mice, the long-distance descending commissural V0v neurons have been implicated in diagonal interlimb coordination during walking. Together with this, our study suggests that the long-distance descending commissural V0v neurons form an evolutionarily conserved pathway in the spinal locomotor circuits that coordinates the movements of the diagonal body/limb muscles.

Jet-driven viscous locomotion of confined thermoresponsive microgels

We consider the dynamics of micro-sized, asymmetrically coated thermoresponsive hydrogel ribbons (microgels) under periodic heating and cooling in the confined space between two planar surfaces. As the result of the temperature changes, the volume and, thus, the shape of the slender microgel change, which leads to repeated cycles of bending and elastic relaxation, and to net locomotion. Small devices designed for biomimetic locomotion need to exploit flows that are not symmetric in time (non-reciprocal) to escape the constraints of the scallop theorem and undergo net motion. Unlike other biological slender swimmers, the non-reciprocal bending of the gel centerline is not sufficient here to explain for the overall swimming motion. We show instead that the swimming of the gel results from the flux of water periodically emanating from (or entering) the gel itself due to its shrinking (or swelling). The associated flows induce viscous stresses that lead to a net propulsive force on the gel. We derive a theoretical model for this hypothesis of jet-driven propulsion, which leads to excellent agreement with our experiments.

Experimental Research on the Coupling Relationship between Fishtail Stiffness and Undulatory Frequency

Fish can swim in a variety of states. For example, they look flexible and perform low-frequency undulatory locomotion when cruising, but they seem very powerful and stiff and perform high-frequency undulatory when hunting. In the process of changing the motion state, the stiffness of the fish body affects the swimming performance of the fish. In this article, we imitated the change of stiffness by superimposing rubber sheets and used experimental methods to test its swimming performance under different swing frequencies. A series of rubber fish tails were made according to the analysis of the swimming movement of real fish, providing different stiffness values and changing the curves of the body. In the prototype experiments, the base of the fish tail was fixed to a platform via a force sensor, which can oscillate at various speeds, so that the fish tail was able to swing and the thrust could be tested at different frequencies. According to the experimental results, we found that with the change of the swing frequency, there were different optimal stiffnesses that could make the thrust reach the maximum value, and with the increase of stiffness, the envelope interval of the swing curve gradually widened, the amplitude increased, and the hysteresis of the tail fin relative to the end decreased.

The Consistency of Gastropod Identified Neurons Distinguishes Intra-Individual Plasticity From Inter-Individual Variability in Neural Circuits.

Gastropod mollusks are known for their large, individually identifiable neurons, which are amenable to long-term intracellular recordings that can be repeated from animal to animal. The constancy of individual neurons can help distinguish state-dependent or temporal variation within an individual from actual variability between individual animals. Investigations into the circuitry underlying rhythmic swimming movements of the gastropod species, Tritonia exsulans and Pleurobranchaea californica have uncovered intra- and inter-individual variability in synaptic connectivity and serotonergic neuromodulation. Tritonia has a reliably evoked escape swim behavior that is produced by a central pattern generator (CPG) composed of a small number of identifiable neurons. There is apparent individual variability in some of the connections between neurons that is inconsequential for the production of the swim behavior under normal conditions, but determines whether that individual can swim following a neural lesion. Serotonergic neuromodulation of synaptic strength intrinsic to the CPG creates neural circuit plasticity within an individual and contributes to reorganization of the network during recovery from injury and during learning. In Pleurobranchaea, variability over time in the modulatory actions of serotonin and in expression of serotonin receptor genes in an identified neuron directly reflects variation in swimming behavior. Tracking behavior and electrophysiology over hours to days was necessary to identify the functional consequences of these intra-individual, time-dependent variations. This work demonstrates the importance of unambiguous neuron identification, properly assessing the animal and network states, and tracking behavior and physiology over time to distinguish plasticity within the same animal at different times from variability across individual animals.

Gyrotactic cluster formation of bottom-heavy squirmers

Squirmers that are bottom-heavy experience a torque that aligns them along the vertical so that they swim upwards. In a suspension of many squirmers, they also interact hydrodynamically via flow fields that are initiated by their swimming motion and by gravity. Swimming under the combined action of flow field vorticity and gravitational torque is called gyrotaxis. Using the method of multi-particle collision dynamics, we perform hydrodynamic simulations of a many-squirmer system floating above the bottom surface. Due to gyrotaxis they exhibit pronounced cluster formation with increasing gravitational torque. The clusters are more volatile at low values but compactify to smaller clusters at larger torques. The mean distance between clusters is mainly controlled by the gravitational torque and not the global density. Furthermore, we observe that neutral squirmers form clusters more easily, whereas pullers require larger gravitational torques due to their additional force-dipole flow fields. We do not observe clustering for pusher squirmers. Adding a rotlet dipole to the squirmer flow field induces swirling clusters. At high gravitational strengths, the hydrodynamic interactions with the no-slip boundary create an additional vertical alignment for neutral squirmers, which also supports cluster formation.

SODIUM FLUORIDE DISTRESSES CHROMATOPHORE INTEGRITY AND BEHAVIOUR OF GUPPY, POECILIA RETICULATA PETERS

The present study was undertaken to investigate the toxicological effect of uoride (as NaF) on chromatophores in skin of larvivorous sh, Poecilia reticulata Peters after chronic exposure. Guppy is supposed to be amongst the most colourpolymorphic vertebrates in the animal kingdom. Fish were exposed to three sub-lethal concentrations of Sodium uoride viz. lowest (5.75 ppm), lower intermediate (7.18 ppm) and higher intermediate (9.58 ppm), which were selected on the basis of 96 hrs. LC value of 115 ppm. 50 Anomalous behavioral alterations observed in NaF intoxicated sh were restlessness, erratic swimming movement, periodic surface to bottom movement, recurrent surfacing activity, loss of equilibrium, amplied gulping and increased opercular activity were pragmatically seen. Signicant variation in colouration was observed in all the experimental groups as compared to control. The melanophores showed notable pigment aggregation state and/or pigment dispersion state. Structurally, melanophores were distinguished into three types viz., reticulate, stellate and punctuate. The severity in distortion of structure and number of chromatophore increased with increasing concentrations of uoride. Several distortions in morphology and even functional integrity of chromatophores when compared with the control group were observed, for instance, rupture of pigment cells accompanied by breakage in dendritic processes, conversion of one type of chromatophore into another type, augmentation and detachment between adjacent chromatophores, variation in number with complete loss of cellular activity. The derangement in structural integrity was observed to be dose dependent and increased with increasing concentrations of Sodium uoride, thus making the sh unt for survival. The attractive pigmentation of the male Guppy sh was abridged making them less attractive for their mate thus affecting reproductive potential of the sh.

Underwater sensing and warming E-textiles with reversible liquid metal electronics

Emerging underwater exploration suggests the need for subaqueous E-textiles. Large-deformation signal feedback for swimming motions and body thermal protection against hypothermia are urgently desirable. Here, underwater-usable E-textiles with remarkable sensing and electrothermal behaviors are introduced, which are composed of stretchable core-sheath fibers based on liquid metal fabricated via a coaxial wet-spinning strategy. The fibers possess outstanding specific resistance (∼0.05 Ω·cm−1) and robust sensing detection range for both strain (∼600% elongation) and pressure (∼30 MPa), as well as a quick response time (30 ms). Meanwhile, the fabricated E-textiles present excellent low-power-driving electrothermal performance (1.5 W, ∼50 °C) even at underwater conditions. Remarkably, the conducting liquid metal circuit can be well reversed even after being entirely broken out of the sensing ranges. For proof of concept, an underwater glove integrating motion sensing, visual danger warning and hypothermia prevention is exhibited, which has potential for application in underwater exploration.

Interaction of Active Janus Colloids with Tracers.

Understanding the motion of artificial active swimmers in complex surroundings, such as a dense bath of passive particulate matter, is essential for their successful utilization as cargo (drug) carriers and sensors or for medical imaging, under microscopic domains. In this study, we experimentally investigated the motion of active SiO2-Pt Janus particles (JPs) in a two-dimensional bath of smaller silica tracers dispersed with varying areal densities. Our observations indicate that when an active JP undergoes a collision with an isolated tracer, their interaction can have a significant impact on the swimmer's motion. However, the overall impact of tracers on the active JPs' motion (translation and rotation) depends on the frequency of collisions and also on the nature of the collision, which is marked by the time-duration for which the particles maintain contact during the collisions. Further, in the high-density tracer bath, our experiments reveal that the motion of the active JP results in a novel organizational behavior of the tracers on the trailing Pt (depletion of tracers) and the leading SiO2 (accumulation of tracers) side. In laboratory frame the emergence and the subsequent vanishing of the depletion zone are discussed in detail.

Changes in rays\u2019 swimming stability due to the phase difference between left and right pectoral fin movements

Swimming motions of rays that swim using undulation locomotion are not always symmetrical; there may be a phase difference between the left and right pectoral fins. However, few studies on the swimming of rays have mentioned left and right pectoral fin movements. Moreover, the effects of movements of the left and right pectoral fins on swimming have not been clarified. This paper describes a computational study of phase differences of pectoral fin movements in the swimming of rays with the validity of fluid analysis methods. The movement and shape of the ray were made based on previous biological research and pictures. An overset grid was used to reproduce the ray’s complex motions. The analysis was performed under four phase difference conditions: 0 T (T is the period), 0.25 T, 0.5 T, and 0.75 T. The results show that a phase difference between the left and right pectoral fin movements affects swimming stability and maneuverability but not propulsive efficiency. We suggest that the phase difference in pectoral fin movements is essential for the swimming of rays, and rays adjust the phase difference between the movement of the left and right pectoral fins to suit their purpose.

Effects of rapid yawing on simple swimmer models and planar Jeffery's orbits

Over a sufficiently long period of time, or from an appropriate distance, the motion of many swimmers can appear smooth, with their trajectories appearing almost ballistic in nature and slowly varying in character. These long-time behaviours, however, often mask more complex dynamics, such as the side-to-side snakelike motion exhibited by spermatozoa as they swim, propelled by the frequent and periodic beating of their flagellum. Many models of motion neglect these effects in favour of smoother long-term behaviours, which are often of greater practical interest than the small-scale oscillatory motion. Whilst it may be tempting to ignore any yawing motion, simply assuming that any effects of rapid oscillations cancel out over a period, a precise quantification of the impacts of high-frequency yawing is lacking. In this study, we systematically evaluate the long-term effects of general high-frequency oscillations on translational and angular motion, cast in the context of microswimmers but applicable more generally. Via a multiple-scales asymptotic analysis, we show that rapid oscillations can cause a long-term bias in the average direction of progression. We identify sufficient conditions for an unbiased long-term effect of yawing, and we quantify how yawing modifies the speed of propulsion and the effective hydrodynamic shape when in shear flow. Furthermore, we investigate and justify the long-time validity of the derived leading-order solutions and, by direct computational simulation, we evidence the relevance of the presented results to a canonical microswimmer.

Effects of short-term sub-lethal diazinon® exposure on behavioural patterns and respiratory function in Clarias batrachus: inferences for adaptive capacity in the wild

ABSTRACT The potentials for neurotoxicity and respiratory distress under 96 h acute diazinon exposures was examined using behavioural indices and opercular movement respectively in walking catfish, Clarias batrachus. Diazinon exposure concentrations were correlated with toxicological (lethal and sublethal) endpoints. The LC50 values and 95% confidence limits at 24, 48, 72 and 96 h, were 21.85 (19.09- 28.199 mg/L), 19.081 (17.15-21.65 mg/L), 16.07 (14.49- 17.86 mg/L) and 12.85 (10.92-14.39 mg/L) respectively. Concentration-dependent mortality and altered behavioural responses including uncoordinated swim movements, excessive mucus secretion, imbalanced and erratic swimming patterns and brief inactivity prior to mortality was observed. The altered behavioural patterns reflecting neurotoxicity, and increased opercular movement indicating respiratory distress in the catfish increased proportionally with elevated levels diazinon and exposure time. The inactive and almost non-motile state prior to death indicates paralysis and muscle seizure typical in the late stages of cholinergic toxicity. The severity of behavioural and respiratory effects on adult C. batrachus, a hardy species, portends catastrophic consequences for less hardy and more susceptible aquatic taxa like fish in the field, including considerable loss of adaptive ability.

How to keep up with the analysis of classic and emerging neurotoxins: Age-resolved fitness tests in the animal model Caenorhabditis elegans - a step-by-step protocol.

The global chemical inventory includes neurotoxins that are mostly interrogated concerning the biological response in developing organisms. Effects of pollutants on adults receive less attention, although vulnerabilities can be expected throughout the entire life span in young, middle-aged and old individuals. We use the animal model Caenorhabditis elegans to systematically quantify neurological outcomes by application of an age-resolved method. Adult hermaphrodite worms were exposed to pollutants or non-chemical stressors such as temperature in liquid culture on microtiter plates and locomotion fitness was analyzed in a whole-life approach. Cultivation at 15, 20 or 25 °C showed that worms held at 15 °C displayed an enhanced level of fitness concerning swimming movements until middle age (11-days-old) and then a decline. In contrast, C. elegans cultivated at ≥ 20 °C continually reduced their swimming movements with increasing age. Here, we provide a step-by-step protocol to investigate the health span of adult C. elegans that may serve as a platform for automation and data collection. Consistent with this, more neurotoxins can be investigated with respect to vulnerable age-groups as well as contributing non-chemical environmental factors such as temperature.

Acute toxicity of fluoride and aluminium on the freshwater fish, &lt;em&gt;Cyprinus carpio&lt;/em&gt; L

Fluoride is a trace element which has beneficial effect at lower concentration but detrimental at higher concentration. The fluoride contamination in ground water is a major global problem. Similarly, aluminium is the most abundant metal of the earth, highly toxic to all organisms. In the present study, we investigated the acute toxicity of fluoride and aluminium on three month old fingerlings of Cyprinus carpio L. in hard water (Hardness 125 mg/L of CaCO3) under static renewal bioassay. The 96 h LC50 value of the fluoride and aluminium were 675.615 and 224.214 mg/L, respectively. There was a significant correlation (P <0.01) between mortality rate of C. carpio with all concentrations of fluoride as well as aluminium. The exposure time (24, 48, 72 and 96 h) and different concentration of fluoride (680, 684, 686 and 692 mg/L) and aluminium (228, 229, 231 and 232 mg/L) was also significantly correlated (P <0.05). The different abnormal behaviour displayed by the fluoride and aluminium exposed fishes were erratic swimming movements, rapid opercular activity and excessive secretion of mucous. The safe level of concentrations of fluoride and aluminium were 6.75 and 2.24 µg/L, respectively. The LC50 values of fluoride and aluminium of the present study may be useful in deriving water quality standards in West Bengal.

An Inertial Sensing-Based Approach to Swimming Pose Recognition and Data Analysis

In this paper, inertial sensing is used to identify a swimming stance and analyze its swimming stance data. A wireless monitoring device based on a nine-axis microinertial sensor is designed for the characteristics of swimming motion, and measurement experiments are conducted for different intensities and stances of swimming motion. By comparing and analyzing the motion characteristics of various swimming stances, the basis for performing stroke identification is proposed, and the monitoring data characteristics of the experimental results match with it. The stance reconstruction technology is studied, PC-based OpenGL multithreaded data synchronization and stance following reconstruction are designed to reconstruct the joint association data of multiple nodes in a constrained set, and the reconstruction results are displayed through graphic image rendering. For the whole system, each key technology is organically integrated to design a wearable wireless sensing network-based pose resolution analysis and reconstruction recognition system. Inertial sensors inevitably suffer from drift after a long period of position trajectory tracking. The proposed fusion algorithm corrects the drift of position estimation using the measurement of the visual sensor, and the measurement of the inertial sensor complements the missing measurement of the visual sensor for the case of occlusion of the visual sensor and fast movement of the upper limb. An experimental platform for upper-limb position estimation based on the fusion of inertial and visual sensors is built to verify the effectiveness of the proposed method. Finally, the full paper is summarized, and an outlook for further research is provided.

The effect of ankle flexibility on the relationship between knee isokinetic strength and the speed of underwater dolphin kicks in male competitive swimmers

BACKGROUND: Lower-extremity muscle strength and ankle flexibility play key roles in underwater swimming movements. OBJECTIVES: To investigate the relationship between knee isokinetic strength and the speed of underwater dolphin kicks (UDK-S) in competitive male swimmers and identify whether ankle flexibility affects the association between knee isokinetic strength and UDK-S. METHODS: Fifty-two highly trained male swimmers participated in this study. The speed at which the participants travelled 15 m performing UDKs was calculated as UDK-S. Knee flexor and extensor concentric isokinetic strength at fast (240∘/s) and slow (60∘/s) velocities and ankle flexibility were evaluated. Bayesian framework analysis was conducted to examine the relationship between these variables and determine whether this relationship is influenced by ankle flexibility. RESULTS: There was strong-to-extremely strong evidence (Bayes factor = 24.4 to 198.3) that knee extensor (60∘/s) and knee flexor (60∘/s and 240∘/s) strength are positively and generally moderately correlated with UDK-S. Ankle plantar flexion flexibility was identified to be a moderator between knee extensor strength (60∘/s) and UDK-S. CONCLUSIONS: Knee extensor and knee flexor strength were significantly correlated with UDK-S, and the relationship between knee muscle strength and UDK-S was influenced by ankle plantar flexion flexibility in male competitive swimmers.

Swimming dynamics of a self-propelled droplet

Chemically active droplets often show intriguing self-propulsion behaviour in a surfactant solution. The drop motion is controlled by the nonlinear coupling among chemical transport in the bulk fluid, consumption of surfactant at the drop surface, and the fluid flow driven by the self-generated Marangoni stress. To quantify the underlying hydrodynamics, this work investigates the swimming motion of a two-dimensional drop that is determined by two dimensionless parameters, the Péclet number ($Pe$) and Damköhler number ($Da$). The weakly nonlinear analysis shows that near the instability threshold, the drop undergoes a supercritical bifurcation with velocity $U\sim \sqrt {Pe-Pe_c}$, where $Pe_c$ is the critical Péclet number for the onset of dipole mode. In the highly nonlinear regime, the drop transits from steady translation of pusher swimming to unsteady motion of mixed pusher–puller swimming along zigzaging trajectories of quadrangle and/or triangle waves. Mode decomposition shows that the zigzag motion is directly related to the interaction between the secondary wake of low surfactant concentration and the primary wake.