Swimming Control Research Articles

Data-driven optimal control of undulatory swimming

Data-driven optimal control of undulatory swimming

A ray-inspired flexible robot fish with stable controllability actuated by photo -responsive composite hydrogels with poly(N-isopropylacrylamide) and multi-walled carbon nanotubes

Drawing inspiration from the movement behaviour of rays in nature, we have successfully developed a ray-inspired flexible robot fish driven by visible light. A composite made of poly(N-isopropylacrylamide) (PNIPAM) and multi-walled carbon nanotubes (MWCNTs) has excellent biocompatibility and photo-responsive deformability. The PNIPAM hydrogel flexible material of the robot fish was prepared by light curing printing technology. Under the control of visible light, the robot fish swims in a straight line at an average speed of about 0.42 mm/s. The photoinduced asymmetric deformation mechanism is used to control the deformation of the fins on both sides of the robot fish, so that the robot fish can turn and realize directional swimming control. These findings have important implications for the development of flexible bionic robots and provide valuable insights for the research of bionic robots driven by visible light.

Electromechanical enhancement of live jellyfish for ocean exploration.

The vast majority of the ocean's volume remains unexplored, in part because of limitations on the vertical range and measurement duration of existing robotic platforms. In light of the accelerating rate of climate change impacts on the physics and biogeochemistry of the ocean, the need for new tools that can measure more of the ocean on faster timescales is becoming pressing. Robotic platforms inspired or enabled by aquatic organisms have the potential to augment conventional technologies for ocean exploration. Recent work demonstrated the feasibility of directly stimulating the muscle tissue of live jellyfish via implanted microelectronics. We present a biohybrid robotic jellyfish that leverages this external electrical swimming control, while also using a 3D printed passive mechanical attachment to streamline the jellyfish shape, increase swimming performance, and significantly enhance payload capacity. A six-meter-tall, 13 600 l saltwater facility was constructed to enable testing of the vertical swimming capabilities of the biohybrid robotic jellyfish over distances exceeding 35 body diameters. We found that the combination of external swimming control and the addition of the mechanical forebody resulted in an increase in swimming speeds to 4.5 times natural jellyfish locomotion. Moreover, the biohybrid jellyfish were capable of carrying a payload volume up to 105% of the jellyfish body volume. The added payload decreased the intracycle acceleration of the biohybrid robots relative to natural jellyfish, which could also facilitate more precise measurements by onboard sensors that depend on consistent platform motion. While many robotic exploration tools are limited by cost, energy expenditure, and varying oceanic environmental conditions, this platform is inexpensive, highly efficient, and benefits from the widespread natural habitats of jellyfish. The demonstrated performance of these biohybrid robots suggests an opportunity to expand the set of robotic tools for comprehensive monitoring of the changing ocean.

Hydrodynamic interactions coordinate the swimming of two self-propelled fish-like swimmers

A muscle-contraction model of pre-strains is utilized to conduct a numerical investigation on the collective swimming of two self-propelled fish-like swimmers. To simulate the conscious swimming control exhibited by live fish, a PID control algorithm is integrated with the numerical simulation model. Specifically, in a scenario involving straight swimming, we conduct a comprehensive simulation study on the hydrodynamic interactions between the leading and following swimmers. The research focuses on the effects of phase difference and initial spacing between the two fish on their collective behavior. Notably, our simulation model considers both the alteration of muscular activities and the energy-saving effect during collective fish swimming. The results demonstrate that a simple PID controller can effectively imitate the conscious swimming control of live fish, ensuring the formation of collective mode of two freely swimming fish. By varying the initial spacing and phase difference, the two fish can attain the same swimming speed, and a similar steady flow field structure can be observed within a certain range of parameters. The passive hydrodynamic interactions, acting as both facilitators and impediments, aid in coordinating the swimming of fish individuals. Furthermore, for efficient swimming of the following fish, a ‘lazy’ strategy proves to be essential.

Sensorimotor control of swimming Polypterus senegalus is preserved during sensory deprivation conditions across altered environments

Control of locomotion involves the interplay of sensory signals and motor commands. Sensory information is essential for adjusting locomotion in response to environmental changes. A previous study using mathematical modelling of lamprey swimming has shown that, in the absence of sensory feedback, increasing fluid viscosity constrains swimming kinematics, limiting tail amplitude and body wavelength, resulting in decreased swimming speed. In contrast, previous experiments with Polypterus senegalus reported increased magnitude swimming kinematics (increased body curvature, body wave speed and frequency, and pectoral fin frequency) in high viscosity water suggesting that sensory information is used to adjust swimming form. It is not known what sensory systems are providing the necessary information to respond to these environmental changes. We tested the hypothesis that lateral line and visual input are responsible for the sensory-driven increase in swimming kinematics in response to experimentally increased fluid viscosity. The kinematics of five P. senegalus were recorded in two different viscosities of water while removing lateral line and visual sensory feedback. Unlike the mathematical model devoid of sensory feedback, P. senegalus with lateral line and/or visual senses removed did not reduce the magnitude of swimming kinematic variables, suggesting that additional sensory feedback mechanisms are present in these fish to help overcome increased fluid viscosity. Increases in swimming speed when both lateral line and visual sensory feedback were removed suggest that lateral line and visual information may be used to regulate swimming speed in P. senegalus, possibly using an internal model of predictions to adjust swimming form.

Size selectivity of a novel non-mesh codend (the Modular Harvesting System) in a New Zealand deepwater fishery

The Modular Harvesting System (MHS) is an inflatable membrane-like fabric tube with escapement holes that replaces the mesh codend of a trawl, and is designed to reduce damage to catch by providing fish a low-flow, low-turbulence environment that allows them to maintain swimming control and avoid compaction during trawling and haulback. The MHS gear is now used within New Zealand’s most valuable finfish fishery, deepwater hoki/blue grenadier (Merlucciidae, Macruronus novaezelandiae). This work presents the novel research used to estimate the size selectivity of the MHS gear, and to compare this to the selectivity of the conventional mesh trawl. Management objectives required estimates of the absolute size-selectivity of both the MHS and conventional gears, and also an estimate of their relative selectivity. An innovative statistical power analysis was developed to specify the required number of twin-trawl tows and number of fish to measure to ensure the desired statistical power to detect a meaningful difference between conventional and MHS gears. A novel twin-trawl experiment was employed whereby the conventional and MHS gears were each paired with a nonselective control, and then the conventional and MHS trawls were paired. All catch data were simultaneously analyzed in a hybrid selectivity model. The MHS and conventional gears had similar estimated size-selectivity curves, and they were not significantly different.

An early midbrain sensorimotor pathway is involved in the timely initiation and direction of swimming in the hatchling Xenopus laevis tadpole.

Vertebrate locomotion is heavily dependent on descending control originating in the midbrain and subsequently influencing central pattern generators in the spinal cord. However, the midbrain neuronal circuitry and its connections with other brainstem and spinal motor circuits has not been fully elucidated. Vertebrates with very simple nervous system, like the hatchling Xenopus laevis tadpole, have been instrumental in unravelling fundamental principles of locomotion and its suspraspinal control. Here, we use behavioral and electrophysiological approaches in combination with lesions of the midbrain to investigate its contribution to the initiation and control of the tadpole swimming in response to trunk skin stimulation. None of the midbrain lesions studied here blocked the tadpole's sustained swim behavior following trunk skin stimulation. However, we identified that distinct midbrain lesions led to significant changes in the latency and trajectory of swimming. These changes could partly be explained by the increase in synchronous muscle contractions on the opposite sides of the tadpole's body and permanent deflection of the tail from its normal position, respectively. We conclude that the tadpole's embryonic trunk skin sensorimotor pathway involves the midbrain, which harbors essential neuronal circuitry to significantly contribute to the appropriate, timely and coordinated selection and execution of locomotion, imperative to the animal's survival.

Learn to swim: Online motion control of an underactuated robotic eel based on deep reinforcement learning

As a typical underwater robot, the robotic fish has been a hot topic of research in terms of the swimming control method and the reduction of energy consumption. Body flexibility and passive designs have been proven to be effective approaches for improving the swimming performance of robotic fishes. However, the addition of passive structures or motions of these approaches makes it more difficult to control the movement of robotic fish. In this paper, we proposed a deep reinforcement learning-based method for online learning control of a robotic eel with multiple passive structures. First, we designed a robotic eel with two wire-driven segments and two complaint bodies made of elastic material. Second, a simulation model of the robotic eel was built and the validity of the model was tested. Following that, the neural network was trained in simulation and deployed directly on the robotic eel, which was controlled without an underlying control model or strategy and directly online by the neural network. Finally, extensive experiments verified the effectiveness of our control method, which offers a valuable and potential solution for robots difficult to model and control.

Antifatigue effects of the composition of Moringa oleifera leaves and Polygonatum polysaccharide and its mechanisms

Objective: To investigate the anti-fatigue effects of composition of Moringa oleifera leaves and Polygonatum polysaccharide, and to explore the mechanisms. Methods: Thirty male Kunming mice were randomly divided into control (C) and composition of Moringa oleifera leaves and Polygonatum polysaccharide group (MP). There were 15 mice in each group. Group C was given distilled water and the group MP was given composition intragastriclly every day. The volume was 0.5 ml. After 14 days of treatment, weight-bearing swimming experiment was conducted, and exhaustive swimming time was recorded. The bearing weight was 3% of the body weight. In another experiment, 48 male Kunming mice were randomly divided into quiet control group (QC), swimming control group (SC) and composition group (MP). There were 16 mice in each group. The QC and SC groups were given distilled water intragastrically, and the group MP was treated with composition every day for 14 days. The volume was 0.5 ml. On the day 15, 30 minutes after intragastriclly administration of distilled water, blood, liver and hind leg muscle of the QC group were collected immediately. The SC and MP groups were subjected non-weight-bearing swimming experiment, and blood, liver and hind leg muscle were collected after swimming. The fatigue related indexes, oxidant/antioxidant parameters and energy metabolism indicators in serum and tissues were determined by commercial kits. Results: The exhaustive swimming time of mice in MP group was significantly longer than that in the C group (P<0.05). Compared with the control group, non-weight-bearing swimming decreased the contents of serum glucose and GSH, the contents of hepatic glycogen and ATP, the hepatic activities of SOD, LDH and ATPase, and muscle activity of GSH-Px (P< 0.05). However, serum levels of BUN and MDA were increased (P<0.05). Compared with the SC group, the composition remarkably increased the contents of serum glucose and hepatic glycogen, increased serum content of GSH, enhanced hepatic activities of SOD, LDH and ATPase and muscle activity of GSH-Px, and increased the hepatic content of ATP (P<0.05). However, the serum level of BUN was decreased (P<0.05). Conclusion: The Moringa oleifera leaves and Polygonatum polysaccharide composition possesses anti-fatigue effects. Anti-oxidant and improving energy metabolism could be the important mechanisms.

Real-time parametric estimation of periodic wake-foil interactions using bioinspired pressure sensing and machine learning

Periodic wake-foil interactions occur in the collective swimming of bio-inspired robots. Wake interaction pattern estimation (and control) is crucial to thrust enhancement and propulsive efficiency optimization. In this paper, we study the wake interaction pattern estimation of two flapping foils in tandem configurations. The experiments are conducted at a Reynolds number of 1.41 × 104 in a water channel. A modified wake-foil phase parameter Φ, which unifies the influences of inter-foil distance L x , motion phase difference Δφ and wake convection velocity U v , is introduced to describe the wake interaction patterns parametrically. We use a differential pressure sensor on the downstream foil to capture wake interaction characteristics. Data sets at different tandem configurations are collected. The wake-foil phase Φ is used to label the pressure signals. A one-dimensional convolutional neural networks (1D-CNN) model is used to learn an end-to-end mapping between the raw pressure measurements and the wake-foil phase Φ. The trained 1D-CNN model shows accurate estimations (average error 3.5%) on random wake interaction patterns and is fast enough (within 40 ms). Then the trained 1D-CNN model is applied to online thrust enhancement control of a downstream foil swimming in a periodic wake. Synchronous force monitoring and flow visualization demonstrate the effectiveness of the 1D-CNN model. The limitations of the model are discussed. The proposed approach can be applied to the online estimation and control of wake interactions in the collective swimming and flying of biomimetic robots.

Flow pattern investigation of bionic fish by immersed boundary–lattice Boltzmann method and dynamic mode decomposition

The investigation of fish swimming is prevalent in the fields of biomimetic hydrodynamics and is important for research on the temporal–spatial evolvement of vortex structures around fish, the design and development of propulsion systems, the shape and structural design of bionic robot fish, and the energy-saving control of schooling robot fish swimming. Conventional numerical simulations of fish swimming depend on mesh establishment and testing. However, the deforming body of a swimming fish largely affects local grids and results in low simulation accuracy due to the uncertainties of mesh resolution and structures. The immersed boundary method adopted in this paper has many advantages, it can efficiently capture the details of the complex dynamics of solid surfaces. Through this method, the fish surface is discretized into Lagrangian points with dynamic coordinates for the performance of complicated dynamic motions. In this work, the immersed boundary–lattice Boltzmann method algorithm with a multi-direct forcing scheme based on Palabos is tested with the cases of flow past a sphere to validate its precision. Then, a function of harmonic oscillation is coupled with fish surface points to perform the level swimming of the RoboTuna fish at different Reynolds numbers. The evolvements of vortex structures around the fish body are analyzed on the basis of the Q-criterion. The processes of the deformation of streamlines around the fish tail into local swirling by tail paddling are revealed, and an angle of approximately 30° between the outer edges of the velocity contour and the line cross of the fish head emerges after the fluid domain develops into a stable state. Then, the data of the fluid fields are subjected to dynamic mode decomposition (DMD), wherein the single mode reveals the presence of up-and-down and axisymmetric patterns behind the fish body. Reconstruction and error calculation are performed to validate the accuracy of the DMD model, then DMD prediction is performed to obtain the flow pattern in the future state and error analysis is conducted. In this work, the mutual effects of the swimming fish and the fluid fields, the formation processes of the vortical fields around the fish tail, and the temporal–spatial evolvements of the structural dynamics of the fluid fields behind the fish body are investigated to provide fundamental information to investigations on propeller systems, flexible propulsion devices, the mechanisms of energy extraction from fluids by the fish tail, and the energy-saving strategies of fish schooling.

Anti-fatigue and anti-oxidant effects of curcumin supplementation in exhaustive swimming mice via Nrf2/Keap1 signal pathway

Demands for dietary supplements with anti-fatigue effects are growing fast due to increasing societal demands. Moreover, in highly physically active individuals, there are also significant needs for supplements to improve exercise performance. The present study evaluated the potential anti-fatigue and anti-oxidant effects of curcumin in mice using exhaustive swimming test. Male C57BL/6J mice were randomized into six groups: blank control (Rest), swimming control (Con), Vitamin C (Vc), low-dose curcumin (C50), middle-dose curcumin (C100), and high-dose curcumin (C200). After a 4-week intervention, the mice in all groups except the Rest group were subject to an exhaustive swimming test. Then, mice were sacrificed to examine serum biochemical markers and fatigue-related enzymes. Moreover, the gene and protein expressions of signal transduction factors involved in the Nrf2/Keap1 signaling pathway were measured. The results indicated that curcumin significantly enhanced the exercise tolerance of mice in the exhaustive swimming test. Particularly, the swimming time of mice in the C100 group was increased by 273.5% when compared to that of mice in the Con group. The levels of blood urea nitrogen, blood ammonia, lactic acid, creatine kinase and lactate dehydrogenase in the C100 group were decreased by 13.3%, 21.0%, 18.6%, 16.7% and 21.9%, respectively, when compared to those of mice in the Con group. Curcumin alleviated exercise-induced oxidative stress and significantly enhanced the activities of superoxide dismutase, catalase and glutathione peroxidase by activating the Nrf2 signaling. These findings indicated that curcumin supplementation exerted remarkable anti-oxidant and anti-fatigue effects in mice, providing additional evidence supporting the use of curcumin as functional food, especially by those engaged in sports-related activities.

Ilex paraguariensisA. St.-Hil. (Yerba Mate) Differently Regulates the Lipid Mobilization and, Irisin and Lactate Levels in Sedentary and Chronic Swimming Mice

Healthy mice were submitted or not to daily chronic swimming and/or daily yerba mate (YM) infusion intake and had their bloods analyzed after four weeks. We hypothesized that daily intake of YM may act differently on lipid mobilization and, on the creatine, lactate and irisin levels in sedentary mice and those submitted to chronic exercise. The groups were (n=48): YM-non-treated control (NTC), YM-non-treated swimming control (NSC), non-roasted YM (NRY), roasted YM (RY), swimming plus non-roasted YM (SNRY), swimming plus roasted YM (SRY). No significant (P&gt;0.05) difference was observed concerning creatine phosphoskinase (CPK) value. Lactate level decreased significantly (P&lt;0.05) for SNRY and SRY, suggesting accelerated lipid mobilization and glycogen sparing potential. There was significant (P&lt;0.05) body weight loss in all, except for NTC. Higher weight loss in NRY, RY, SNR and SRY indicated greater lipid mobilization. Thiobarbituric acid reactive substances (TBARS) and irisin had significantly (P&lt;0.05) higher values for RY. This is first report that deals with the effect of YM consumption on serum irisin level. Major amounts of caffeic acid derivatives, slightly increased caffeine and less amount of rutin may be responsible by accelerated lipoperoxidation in sedentary healthy mices chronically treated with roasted YM. Chronically consumed YM plus swimming aid in healthy weight loss. Sedentary lifestyle plus roasted YM chronic consumption may cause accelerated lipid mobilization and increased TBARS production via irisin overexpression leading to an increase in lipoperoxidation.

Fluid–structure interaction analysis on motion control of a self-propelled flexible plate near a rigid body utilizing PD control

Inspired by a previous experimental study of fish swimming near a cylinder, we numerically investigate the swimming and station-holding behavior of a flexible plate ahead of a circular cylinder whose motion is controlled by a proportional–derivative (PD) controller. Specifically, the deformation of this two-dimensional plate is actuated by a periodically varying external force applied on the body surface, which mimics the fish muscle force to produce propulsive thrust. The actuation force amplitude is dynamically adjusted by a feedback controller to instruct the plate to swim the desired distance from an initial position to a target location and then hold the station there. Instead of directly using the instantaneous position signal, an average speed measured over one force actuation period is proposed with the inclusion of instantaneous position information to form the tracking error for the PD control. Our results show that the motion control of swimming and station holding has been achieved by this simple but effective feedback control without large overshoot when approaching the target at different flow conditions and actuation force formulas. Although the swimming distance remains the same, a plate whose initial position is closer to the cylinder requires less energy expenditure to swim to the target location and hold the station there. This is because the low-pressure zone near the trailing edge of the plate is reduced in size, which provides drag reduction, contributing to reduced swimming energy. A higher Reynolds number also leads to energy savings. Under the same control strategy, the swimming performance is more affected by the force-frequency while the phase shift of the actuation force has a less significant impact.

Effect of Interval Swimming Training on Iron Storage and Hepcidin Level in Adolescent Boys Aged 13-15 Years Old

Background and Objectives: Iron has a substantial role in growth of children. Regarding importance of iron metabolism and the role of hepcidin in this process, we aimed to evaluate the impact of a single period of interval swimming exercise on iron storage content and plasma hepcidin level in adolescent boys. Subjects and Methods In present semi-experimental study, 30 swimmers were selected by targeted sampling, and randomly allocated into two groups (each with 15 members) of swimming interval training (13.70±0.70) and control (13.75±0.88). Training protocol included eight weeks of interval swimming exercise, three sessions (50-60 minutes) per week of swimming interval training with 60-80% heart rate reserved, and rest to training ratio 1:1. Fasting blood sampling was performed in pre-test and post-test. Paired and independent t tests were used for data analysis at significant level of P≤0.05. Results After eight weeks of training, a significant reduction was found in levels of hemoglobin (P=0.001), serum iron (P=0.008) and ferritin (P=0.012, while hepcidin level (P=0.040) showed a significant increase respective to control group. Conclusion Considering our results, eight weeks of interval swimming exercise can reduce iron storages (in physiologic levels) and increase plasma hepcidin in adolescent boys.

Beyond the Kármán gait: knifefish swimming in periodic and irregular vortex streets.

Neotropical freshwater fishes such as knifefishes are commonly faced with navigating intense and highly unsteady streams. However, our knowledge on locomotion in apteronotids comes from laminar flows, where the ribbon fin dominates over the pectoral fins or body bending. Here, we studied the 3D kinematics and swimming control of seven black ghost knifefish (Apteronotus albifrons) moving in laminar flows (flow speed U∞≈1-5 BL s-1) and in periodic vortex streets (U∞≈2-4 BL s-1). Two different cylinders (∼2 and ∼3 cm diameter) were used to generate the latter. Additionally, fish were exposed to an irregular wake produced by a free oscillating cylinder (∼2 cm diameter; U∞≈2 BL s-1). In laminar flows, knifefish mainly used their ribbon fin, with wave frequency, speed and acceleration increasing with U∞. In contrast, knifefish swimming behind a fixed cylinder increased the use of pectoral fins, which resulted in changes in body orientation that mimicked steady backward swimming. Meanwhile, individuals behind the oscillating cylinder presented a combination of body bending and ribbon and pectoral fin movements that counteract the out-of-phase yaw oscillations induced by the irregular shedding of vortices. We corroborated passive out-of-phase oscillations by placing a printed knifefish model just downstream of the moving cylinder, but when placed one cylinder diameter downstream, the model oscillated in phase. Thus, the wake left behind an oscillating body is more challenging than a periodic vortex shedding for an animal located downstream, which may have consequences on inter- and intra-specific interactions.

Recent progress on motion control of swimming micro/nanorobots

AbstractSwimming micro/nanorobots attract considerable attention due to their considerable promises in various fields ranging from environmental remediation to biomedicine. However, the control system for optimal trajectory and precise localization is an exciting yet challenging for the existing swimming micro/nanorobots. Researchers have used different actuation systems allowing multiple degrees of freedom to actuate swimming microrobots with various motion control methods from well‐controlled physicochemical processes to achieve autonomous movement along the gradient of various chemical or physical fields. Furthermore, with the advance of intelligent technology, machine learning strategies have been considered for intelligent control of swimming microrobots. In this paper, we summarized directly manual control and autonomous tactic motion of swimming micro/nanorobots. The application of reinforcement learning in controllable motions of swimming microrobots was also elaborated.

Developing Biohybrid Robotic Jellyfish (Aurelia aurita) for Free-swimming Tests in the Laboratory and in the Field.

Biohybrid robotics is a growing field that incorporates both live tissues and engineered materials to build robots that address current limitations in robots, including high power consumption and low damage tolerance. One approach is to use microelectronics to enhance whole organisms, which has previously been achieved to control the locomotion of insects. However, the robotic control of jellyfish swimming offers additional advantages, with the potential to become a new ocean monitoring tool in conjunction with existing technologies. Here, we delineate protocols to build a self-contained swim controller using commercially available microelectronics, embed the device into live jellyfish, and calculate vertical swimming speeds in both laboratory conditions and coastal waters. Using these methods, we previously demonstrated enhanced swimming speeds up to threefold, compared to natural jellyfish swimming, in laboratory and in situ experiments. These results offered insights into both designing low-power robots and probing the structure-function of basal organisms. Future iterations of these biohybrid robotic jellyfish could be used for practical applications in ocean monitoring.

An untethered soft robotic fish using SMA wires and its performance analysis

The authors have developed a bionic robotic fish having a soft tail by employing intelligent materials as actuators. Two sets of shape memory alloy (SMA) wires are stitched to the two sides of the soft tail, allowing the tail to bend on either side. The designed structure is expected to have the ability to mimic the straight swimming posture of a real fish in the water, and also to turn left and right using the soft body and caudal fins (BCF propulsion). The body and the head part are designed by a 3D CAD software, whose streamline ability is verified through the fluid simulation, and are printed by a high-precision 3D printer. A micro Arduino computer is set inside the fish body for the total swimming control. The infrared (IR) communication is also installed for the detailed analysis of the swimming motion and the speed. By studying the relationship between the control signals and the swimming behaviour of the robotic fish, the performance of the swimming motion was examined for determining the parameter values to realise real-fish swimming.

Lead-lag Swimming Control of Robot Fish Using Color Detection Algorithm

Lead-lag Swimming Control of Robot Fish Using Color Detection Algorithm