Swimming Mode Research Articles

Metabolic trade-offs associated with homeostatic adjustments in pelagic and benthic cephalopods: Comparative evaluations of NH4+/H+ transport machinery in gills

Cephalopods are ancient mollusks that can be found in many different ecological niches in the ocean ranging from the intertidal zone to the deep-sea abyss. In order to adapt to a lifestyle in various habitats, cephalopods have evolved a variety of locomotory modes to accommodate their respective habitats. Most cephalopods have relatively high metabolic rates due to their less efficient swimming mode by jet propulsion. This lifestyle is characterized by a high level of energy expenditure, fueled exclusively by protein diets that are rapidly digested and may produce metabolic nitrogenous waste NH3/NH4 +accumulation and acid-base disturbances. This study observed that the NH4 +transport rate in pelagic bigfin reef squid (Sepioteuthis lessoniana) is two times faster than benthic common octopus (Octopus vulgaris). Inhibition of Na+/H+ exchangers (NHEs) showed significant disruption of NH4 + and H+ excretory processes in gills of octopus but not in squid. However, inhibition of vacuolar-type H+-ATPase (VHA) significantly disrupts NH4 + and H+ transport rates in gills of both animals. Accordingly, for NH4 + and H+ homeostasis, benthic octopus with lower aerobic respiration rates utilize both active and Na+-driven secondary transport machinery. In order to avoid NH4 + accumulated in the blood, pelagic squids with higher aerobic respiration rates prefer active NH4 + and H+ transport mechanisms that consume ATP intensively.

FIRST SKELETAL REMAINS OF <em>HELVETICOSAURUS</em> FROM THE MIDDLE TRIASSIC ITALIAN OUTCROPS OF THE SOUTHERN ALPS, WITH REMARKS ON AN ISOLATED TOOTH

The enigmatic marine reptile Helveticosaurus zollingeri, from the Middle Triassic Besano Formation of Monte San Giorgio, is known from three specimens found in Swiss territory. This paper describes the first skeletal remains of this taxon recovered from the corresponding Italian outcrops of Besano (Varese). An isolated tooth assigned to the same taxon and coming from the San Salvatore Dolomite, Rasa di Varese (Varese), is also redescribed herein. The skeletal remains have been CT scanned to inspect the preserved morphology of the bones hidden below the surface; CT data also allowed the identification of an associated ammonoid which has been crucial to determine the stratigraphic position of the studied material. The redescription of the tooth has been helped by a digital model of the specimen obtained through photogrammetry. With the additional new data obtained from the two specimens, the first skeletal reconstruction of Helveticosaurus is provided. This is followed by a phylogenetic test of the taxon, assessing its position among marine Triassic diapsids. Finally, in the light of recent studies we discuss the swimming mode and the possible ecological niche occupied by the animal: we suggest a distinction between the function of forelimbs and hindlimbs, and a distinction between different swimming styles likely performed by Helveticosaurus, depending on the speed of movements.

On an adaptation of the Reynolds number, applicable to body-caudal-fin aquatic locomotion

The Reynolds number, which describes the relative importance of viscous and inertial contributions is commonly used to analyze forces on fish and other aquatic animals. However, this number is based on steady, time-independent conditions, while all swimming motions have a periodic component. Here we apply periodic flow conditions to define a new non-dimensional group, which we name the “Periodic Swimming Number, P”, which rectifies this lacuna. This new non-dimensional number embodies the periodic motion and eliminates the arbitrariness of choosing a length scale in the Reynolds number for Body –Caudal-Fin (BCF) swimming. We show that the new number has the advantage of compressing known data on fish swimming to two orders of magnitude, vs. over six required when using the existing Reynolds number and can point to a new comparison of swimming effectiveness for swimming modes.

The Hydrodynamics of a Rod-Shaped Squirmer near a Wall

The hydrodynamic characteristics of a rod-shaped squirmer swimming near a wall were studied numerically using the immersed boundary-lattice Boltzmann method in the swimming Reynolds number range of 0.1 ≤ Res ≤ 2.0, where the number of assembled squirmers was 2 ≤ i ≤ 4 and the distance between two adjacent assembled squirmers was 0.75 d ≤ s ≤ 1.5 d (d is the diameter of a single squirmer). The effect of Res, i and s on the swimming mode of the squirmer was explored. The results showed that there are four swimming modes after the first collision between the rod-shaped squirmer and the wall. There are also four swimming modes when Res changes from 0.1 to 2.0. Puller, pusher and neutral squirmers showed different swimming modes when i changed, and the effect degree of the flow at the previous moment on the squirmer’s motion was different for different values of i. The change in s only affected the trajectory of the squirmer without changing its motion mode. Puller, pusher and neutral squirmers showed different swimming modes and velocity changes when s changed.

Numerical investigation on the swimming mode and stable spacing with two self-propelled fish arranged in tandem

It is a long-held perception that fish may obtain a hydrodynamic advantage from clustering. This study attempts to determine whether all the fish in school gain the same energy advantage in different swimming modes. The numerical investigation based on two self-propelled fish arranged in tandem in carangiform, anguilliform, and sine curve swimming modes was conducted. It was found that fish could spontaneously form different steadily spaced queues, and discrete points of stable spacing were classified as proximity and wake interference points according to their swimming speed. The stable points were the result of the combined effect of wake impact and vortex modulation. From the carangiform to anguilliform to sine curve swimming modes, as the head amplitude increased, the vortex modulation of the rear fish gradually decreased, while the wake impact gradually increased. Therefore, the rear fish in carangiform swimming mode had lower energy consumption than that of the front, whereas the opposite was true in sine curve swimming mode. In addition, some interesting phenomena related to the vortex core arrangement were introduced at different stable points in these three swimming modes. The present results may enrich the scope of research on the hydrodynamic dominance of aquatic organisms in collective behaviour.

Robot Fish Caudal Propulsive Mechanisms: A Mini-Review

Researchers have developed numerous artificial fish to mimic the swimming abilities of biological species and understand their biomechanical subaquatic skills. The motivation arises from the interest to gain deeper comprehension of the efficient nature of biological locomotion, which is the result of millions of years of evolution and adaptation. Fin-based biological species developed exceptional swimming abilities and notable performance in highly dynamic and complex subaquatic environments. Therefore, based on research by the scientific community, this mini-review concentrates on discussing the mechanical devices developed to implement the caudal propulsive segments of robotic fish. Caudal mechanisms are of considerable interest because they may be designed to control inertial and gravitational forces, as well as exerting great dynamic range in robotic fish. This manuscript provides a concise review focused on the engineering implementations of caudal mechanisms of anguilliform, subcarangiform, subcarangiform, thunniform and ostraciiform swimming modes.

Trends in Stroke Kinematics, Reynolds Number, and Swimming Mode in Shrimp-Like Organisms.

Metachronal propulsion is commonly seen in organisms with the caridoid facies body plan, i.e. shrimp-like organisms, as they beat their pleopods in an adlocomotory sequence. These organisms exist across length scales ranging several orders of Reynolds number magnitude, from 10 to 104, during locomotion. Further, by altering their stroke kinematics, these organisms achieve three distinct swimming modes. To better understand the relationship between Reynolds number, stroke kinematics, and resulting swimming mode, Euphausia pacifica stroke kinematics were quantified using high-speed digital recordings and compared to the results for the larger E. superba. Euphausia pacifica consistently operate with a greater beat frequency and smaller stroke amplitude than E. superba for each swimming mode, suggesting that length scale may affect the kinematics needed to achieve similar swimming modes. To expand on this observation, these euphausiid data are used in combination with previously-published stroke kinematics from mysids and stomatopods to identify broad trends across swimming mode and length scale in metachrony. Principal component analysis (PCA) reveals trends in stroke kinematics and Reynolds number as well as the variation among taxonomic order. Overall, larger beat frequencies, stroke amplitudes, between-cycle phase lags, and Reynolds numbers are more representative of the fast forward swimming mode compared to the slower hovering mode. Additionally, each species has a unique combination of kinematics that result in metachrony, indicating that there are other factors, perhaps morphological, which affect the overall metachronal characteristics of an organism. Finally, uniform phase lag, in which the timing between power strokes of all pleopods is equal, in 5-paddle systems is achieved at different Reynolds numbers for different swimming modes, highlighting the importance of taking into consideration stroke kinematics, length scale, and the resulting swimming mode.

OpenFish: Biomimetic design of a soft robotic fish for high speed locomotion

We present OpenFish: an open source soft robotic fish which is optimized for speed and efficiency. The soft robotic fish uses a combination of an active and passive tail segment to accurately mimic the thunniform swimming mode. Through the implementation of a novel propulsion system that is capable of achieving higher oscillation frequencies with a more sinusoidal waveform, the open source soft robotic fish achieves a top speed of 0.85m/s. Hereby, it outperforms the previously reported fastest soft robotic fish by 27%. Besides the propulsion system, the optimization of the fish morphology played a crucial role in achieving this speed. In this work, a detailed description of the design, construction and customization of the soft robotic fish is presented. Hereby, we hope this open source design will accelerate future research and developments in soft robotic fish.

Design and implementation of a swimming robot with pectoral fins only

AbstractThe use of swimming robots has increased widely in recent years due to the need of using them in situations where human intervention is difficult or not allowed. Exploring depths of seas, military interventions, or entering areas where the amount of water pollution is high that may threaten the lives of divers. In such cases, the best alternative for humans is to use swimming robots. This paper presents a swimming robot based on Labriform swimming mode. First, it starts with an analytical study of the effect of the fins shape on the performance of a robotic fish. The suggested design of the pectoral fins is concave. The effect of such a design would help largely in achieving the highest thrust in comparison to flat designs provided in the literature. Secondly, a variation in the velocity between the power and recovery strokes is accomplished and a maximum thrust can be obtained when the velocity of the power stroke is three times the velocity of recovery stroke. Thirdly, the kinematics and dynamics of the swimming robot are derived and an evaluation of the total hydrodynamic forces that are exerted on the robot’s body is studied via the computational fluid dynamics method from SOLIDWORKS® platform. Finally, the obtained results are compared to other designs in the literature in terms of some dimensionless numbers of biological fish to examine the efficiency. The proposed design has been validated theoretically and examined experimentally. The results of the simulation and practical experiments confirmed the validity of the design.

Modeling of lophotrichous bacteria reveals key factors for swimming reorientation

Lophotrichous bacteria swim through fluid by rotating their flagellar bundle extended collectively from one pole of the cell body. Cells experience modes of motility such as push, pull, and wrapping, accompanied by pauses of motor rotation in between. We present a mathematical model of a lophotrichous bacterium and investigate the hydrodynamic interaction of cells to understand their swimming mechanism. We classify the swimming modes which vary depending on the bending modulus of the hook and the magnitude of applied torques on the motor. Given the hook’s bending modulus, we find that there exist corresponding critical thresholds of the magnitude of applied torques that separate wrapping from pull in CW motor rotation, and overwhirling from push in CCW motor rotation, respectively. We also investigate reoriented directions of cells in three-dimensional perspectives as the cell experiences different series of swimming modes. Our simulations show that the transition from a wrapping mode to a push mode and pauses in between are key factors to determine a new path and that the reoriented direction depends upon the start time and duration of the pauses. It is also shown that the wrapping mode may help a cell to escape from the region where the cell is trapped near a wall.

A new mode of swimming in singly flagellated Pseudomonas aeruginosa.

SignificanceThe monotrichous Pseudomonas aeruginosa was usually thought to swim in a pattern of "run and reverse" (possibly with pauses in between), where straight runs alternated with reverses with angular changes of swimming direction near 180°. Here, by simultaneously tracking the cell swimming and the morphology of its flagellum, we discovered a swimming mode in P. aeruginosa-the wrap mode, during which the flagellar filament wrapped around the cell body and induced large fluctuation of the body orientation. The wrap mode randomized swimming direction, resulting in a broad distribution of angular changes over 0 to 180° with a peak near 90°. This allowed the bacterium to explore the environment more efficiently, which we confirmed by stochastic simulations of P. aeruginosa chemotaxis.

Development of sensory organs and changes of behaviour in larvae Amur catfish, Silurus asotus

The development of morphology, sensory organs, and behavioural changes in larvae of Amur catfish (Silurus asotus) were described from 0 h after hatching (hAH) to 20 days after hatching (dAH) reared at 26.7 ± 1.3 °C under controlled conditions. The newly hatched larvae (4.71 ± 0.87 mm) had eyes that were only outlined and unpigmented, no taste buds, and free neuromasts with a demersal swimming mode associated with negative phototaxis and immediate rheotaxis responses. At 12 hAH (5.57 ± 0.25 mm), larvae had pigmented eyes, exhibited initial vertical and horizontal swimming behaviour, and switched to positive phototaxis and positive immediate rheotaxis responses. At 30 hAH (7.01 ± 0.41 mm), larvae with well-developed sensory organs began feeding for the first time, and cannibalistic behaviour was noted for the first time at this stage. At 5 dAH (12.12 ± 0.68 mm), larvae had enlarged taste buds and free neuromasts associated with active swimming behaviour. At 12 dAH (20.22 ± 0.09 mm), the Amur catfish entered the juvenile stage, and at 20 dAH (34.10 ± 0.89 mm), a pair of mandibular barbels degenerated and the fish preferred to remain on the substrate. This study concludes that the development of Amur catfish larval morphology, sensory organs, and behaviour are interrelated and progressively developed as larvae age.

Modeling, Trajectory Analysis and Waypoint Guidance System of a Biomimetic Underwater Vehicle Based on the Flapping Performance of Its Propulsion System

The performance of biomimetic underwater vehicles directly depends on the correct design of their propulsion system and its control. These vehicles can attain highly efficient motion, hovering and thrust by properly moving part(s) of their bodies. In this article, a mathematical modeling and waypoint guidance system for a biomimetic autonomous underwater vehicle (BAUV) is proposed. The BAUV achieves sideways and dorsoventral thunniform motion by flapping its caudal fin through a parallel mechanism. Also, an analysis of the vehicle’s design is presented. A thrust analysis was performed based on the novel propulsion system. Furthermore, the vehicle’s kinematics and dynamic models were derived, where hydrodynamic equations were obtained as well. Computed models were validated using simulations where thrust and moment analysis was employed to visualize the vehicle’s performance while swimming. For the path tracking scheme, a waypoint guidance system was designed to correct the vehicle’s direction toward several positions in space. To accurately obtain waypoints, correction over the propeller’s flapping frequency and bias was employed to achieve proper thrust and orientation of the vehicle. The results from numerical simulations showed how by incorporating this novel propulsion strategy, the BAUV improved its performance when diving and maneuvering based on the dorsoventral and/or sideways configuration of its swimming mode. Furthermore, by designing proper strategies to regulate the flapping performance of its caudal fin, the BAUV followed the desired trajectories. The efficiency for the designed strategy was obtained by comparing the vehicle’s traveled distance and ideal scenarios of straight-line trajectories between targets. During simulations, the designed guidance system presented an efficiency of above 80% for navigation tasks.

Magnetic Biohybrid Microrobot Multimers Based on Chlorella Cells for Enhanced Targeted Drug Delivery.

Magnetic micro-/nanorobots have been regarded as a promising platform for targeted drug delivery, and tremendous strategies have been developed in recent years. However, realizing precise and efficient drug delivery in vivo still remains challenging, in which the versatile integration of good biocompatibility and reconfiguration is the main obstacle for micro-/nanorobots. Herein, we proposed a novel strategy of magnetic biohybrid microrobot multimers (BMMs) based on Chlorella (Ch.) and demonstrated their great potential for targeted drug delivery. The spherical Ch. cells around 3-5 μm were magnetized with Fe3O4 to fabricate biohybrid microrobots and then loaded with doxorubicin (DOX). Using magnetic dipolar interactions, the microrobot units could reconfigure into chain-like BMMs as tiny dimers, trimers, and so forth via attraction-induced self-assembly and disassemble reversibly via repulsion. The BMMs exhibited diverse swimming modes including rolling and tumbling with high maneuverability, and the rolling dimer's velocity could reach 107.6 μm/s (∼18 body length/s) under a 70 Gs precessing magnetic field. Furthermore, the BMMs exhibited low cell toxicity, high DOX loading capacity, and pH-triggered drug release, which were verified by chemotherapy experiments toward HeLa cancer cells. Due to the remarkable versatility and facile fabrication, the BMMs demonstrate great potential for targeted anticancer therapy.

Shape optimization of a fish-like hyperelastic body vibrating with a swimming mode

Shape optimization of a fish-like hyperelastic body vibrating with a swimming mode

Lagrangian analysis of bio-inspired vortex ring formation

Pulsatile jet propulsion is a highly energy-efficient swimming mode used by various species of aquatic animals that continues to inspire engineers of underwater vehicles. Here, we present a bio-inspired jet propulsor that combines the flexible hull of a jellyfish with the compression motion of a scallop to create individual vortex rings for thrust generation. Similar to the biological jetters, our propulsor generates a nonlinear time-varying exit velocity profile and has a finite volume capacity. The formation process of the vortices generated by this jet profile is analysed using time-resolved velocity field measurements. The transient development of the vortex properties is characterised based on the evolution of ridges in the finite-time Lyapunov exponent field and on local extrema in the pressure field derived from the velocity data. Special attention is directed toward the vortex merging observed in the trailing shear layer. During vortex merging, the Lagrangian vortex boundaries first contract in the streamwise direction before expanding in the normal direction to keep the non-dimensional energy at its minimum value, in agreement with the Kelvin–Benjamin variational principle. The circulation, diameter and translational velocity of the vortex increase due to merging. The vortex merging takes place because the velocity of the trailing vortex is higher than the velocity of the main vortex ring prior to merging. The comparison of the temporal evolution of the Lagrangian vortex boundaries and the pressure-based vortex delimiters confirms that features in the pressure field serve as accurate and robust observables for the vortex formation process.

Intermittent swimming of two self-propelled flapping plates in tandem configuration

Intermittent swimming and schooling individually offer the possibility of energy economy for fish. To study the role of the simultaneous use of both behaviors, the intermittent swimming of two self-propelled plates in tandem configuration is investigated numerically. Two intermittent swimming modes, i.e., the multiple-tail beat (MT) mode and the half-tail beat (HT) mode, are considered. For solitary plate swimming intermittently while maintaining fixed bout period, the propulsion velocity and energy consumption decrease monotonically as the duty cycle increases, consistent with the prediction of the reduced-order model. A pair of plates swimming with independent duty cycle can form orderly configurations, without separating or colliding, when their duty cycles are similar. For the MT mode, the asymmetric wake of the leader enhances the drag on the following plate by inducing an additional oncoming flow against it, making the follower harder to follow. For the HT mode, the symmetric wake of the leader reduces the drag on the follower, making it easier to follow. No significant difference was found in the propulsive performance of intermittent swimming between the leading plate in orderly configurations and solitary plate. The results of efficiency indicate that the HT mode is more economical than the MT mode for the follower. Usually, the smaller the equilibrium gap spacing is, the more efficient the follower is. The results of the cost of transport show that the follower achieves better energy economy for higher propulsion velocity. The results provide some insight into the collective intermittent swimming of fish and are helpful for bionic design.

Multiple Bio-Inspired Father-Son Underwater Robot for Underwater Target Object Acquisition and Identification.

Underwater target acquisition and identification performed by manipulators having broad application prospects and value in the field of marine development. Conventional manipulators are too heavy to be used for small target objects and unsuitable for shallow sea working. In this paper, a bio-inspired Father–Son Underwater Robot System (FURS) is designed for underwater target object image acquisition and identification. Our spherical underwater robot (SUR), as the father underwater robot of the FURS, has the ability of strong dynamic balance and good maneuverability, can realize approach the target area quickly, and then cruise and surround the target object. A coiling mechanism was installed on SUR for the recycling and release of the son underwater robot. A Salamandra-inspired son underwater robot is used as the manipulator of the FURS, which is connected to the spherical underwater robot by a tether. The son underwater robot has multiple degrees of freedom and realizes both swimming and walking movement modes. The son underwater robot can move to underwater target objects. The vision system is installed to enable the FURS to acquire the image information of the target object with the aid of the camera, and also to identify the target object. Finally, verification experiments are conducted in an indoor water tank and outdoor swimming pool conditions to verify the effectiveness of the proposed in this paper.

Performance analysis of bio-inspired transformable robotic fish tail

We simulate, validate and analyze the performance of a transformable tail of an adaptive robotic fish based on the propulsion of three bio-inspired body deformations similar to those of the big-eye trevally, the butterfish, and the boxfish. The objective is to enable robotic fish operation in rapidly changing underwater environments that may require transitions between swimming modes. The bio-inspired propulsion tail consists of a passive caudal fin attached to three articulated segments each actuated by a servomotor to produce desired deformations. Representing these deformations by analytical functions, the linkage lengths of the three segments are optimized using Simscape. A testing platform, equipped with a load cell and a distance laser sensor, is developed to measure and validate the predicted thrust and forward speed over a range of undulation frequencies and amplitudes of lateral oscillations. Static thrust values are also compared to their theoretical counterparts obtained from Lighthill's theory of elongated bodies' propulsion. The results show that the locomotion modes alone can impact the swimming performance over an unchanging morphology. The experimental results further indicate that synchronicity of locomotion parameters found in nature has a greater effect on the overall thrust than varying a specific parameter.

Numerical study of complex modal characteristics in anguilliform mode of fish swimming

Numerical study of complex modal characteristics in anguilliform mode of fish swimming