Fish Tail Research Articles

Online Hydraulic Stiffness Modulation of a Soft Robotic Fish tail for Improved Thrust and Efficiency.

This paper explores online stiffness modulation within a single tail stroke for swimming soft robots. Despite advances in stiffening mechanisms, little attention has been given to dynamically adjusting stiffness in real-time, presenting a challenge in developing mechanisms with the requisite bandwidth to match tail actuation. Achieving an optimal balance between thrust and efficiency in swimming soft robots remains elusive, and the paper addresses this challenge by proposing a novel mechanism for independent stiffness control, leveraging fluid-driven stiffening within a patterned pouch. Inspired by fluidic-driven actuation, this approach exhibits high bandwidth and facilitates significant stiffness changes. We perform experiments to demonstrate how this mechanism enhances both thrust and swimming efficiency. The tail actuation and fluid-driven stiffening can be optimized for a specific combination of thrust and efficiency, tailored to the desired maneuver type. The paper further explores the complex interaction between the soft body and surrounding fluid and provides fluid dynamics insights gained from the vortices created during actuation. Through frequency modulation and online stiffening, the study extends the Pareto front of achievable thrust generation and swimming efficiency.

A dynamic model of tensegrity robotic fish considering soft fish skin and tail

A dynamic model of tensegrity robotic fish considering soft fish skin and tail

Study on energy harvest performance of a flapping hydrofoil with swept leading edges by numerical methods

Inspired by the superior hydrodynamic performance of fish tails with swept shapes, whether a flapping hydrofoil with swept leading edges has higher energy harvesting efficiency attracts our great attention. By solving Reynolds-averaged Navier-Stokes equations with Spalart-Allmaras model, a numerical study on flapping swept hydrofoils was conducted. Results show that, compared to a flapping rectangular hydrofoil, a flapping swept hydrofoil has higher efficiency under almost all operating conditions. When the aspect ratio is 4.0, using a hydrofoil with a sweep angle of 10° increases the efficiency by nearly 9%. As the sweep angle increases, the efficiency increases first and then decreases, so there exists an optimal value. As the aspect ratio increases, the optimal sweep angle decreases. When the taper ratio is around 0.6, the efficiency is or is close to the maximum value. Compared with a single horseshoe vortex around flapping rectangular hydrofoils, the double horseshoe vortices around flapping swept hydrofoils and the advance of their formation time are the reasons for the efficiency improvement. The study confirms that a flapping swept hydrofoil turbine has higher efficiency than a flapping rectangular hydrofoil especially when the aspect ratio is from 2.0 to 5.0 and clarifies the reasons for the efficiency improvement.

Simulation Analysis and Experiment of Piezoelectric Pump with Tapered Cross-Section Vibrator

In order to meet the requirements of microfluidic transport in the fields of medical, health, and microelectromechanical integration, a valve-less piezoelectric pump with a tapered cross-sectional vibrator was designed according to the bionic principles of fish swimming. Through theoretical analysis, the pattern of fluid flow in the pump chamber caused by the vibration of the piezoelectric vibrator was derived. The flow field of the piezoelectric pump was analyzed through simulation based on multiple physical fields coupling using the software of COMSOL Multiphysics (version 6.1). The velocity field distribution and its change law were obtained, and the fluid disturbance and instantaneous motion suppression phenomena were acquired as well. Based on the analysis of flow field streamline, the rule of generating vortexes was found. Thus, the driving mechanism of the vibrator with the tapered cross-section, which was consistent with the swimming principle of a fish tail, was verified. A prototype pump was made, and the pump performance was tested. The experimental data showed that the tested flow rate changed in the same trend as the simulated flow rate. When the driving voltage was 150 V and the driving frequency was 588 Hz, the pump achieved a maximum output flow rate of 367.7 mL/min. These results indicated that the piezoelectric pump with the tapered cross-sectional vibrator has great potential of fluid transportation.

Ovipositional Preference of <i>Rhynchophorus ferrugineus</i> (Olivier) in Palm Species in Goa

Red palm weevil (RPW) Rhynchophorus ferrugineus (Olivier) (Coleoptera: Curculionidae) is devastating pest in commercial and ornamental palms. The study was conducted to find out ovipositional preference of R. ferrugineus in seven palm species. Result revealed that the fish tail palm (Caryota cumingii Lodd.) is highly preferred host for oviposition by R. ferrugineus followed by coconut (Cocos nucifera L.). Toddy palm (Borassus flabellifer L.) was found to be least preferred by R. ferrugineus for oviposition. The ornamental palm, cane palm Dypsis lutescens (H. Wendl.) Beentje and J. Dransf is found as new preferred host for oviposition in free choice test.

Light‐activated 3D printed fish‐like actuator

AbstractHydrogel‐based actuators are innovative materials that exhibit responsive and dynamic behavior in response to external stimuli, making them promising candidates for a wide range of applications in fields such as soft robotics. We employ 3D printing to create layered rectangles, using a passive ink composed of gelatin methacryloyl (GelMA) and an active ink consisting of GelMA and poly(N‐isopropylacrylamide) (PNIPAM). Our aim is to assess and compare the bending capabilities of these structures based on their layer arrangements in a buffer above the lower critical solution temperature. Therefore, an asymmetric rectangular structure is selected as the shape‐changing component in the tail of a 3D printed fish‐shaped hydrogel actuator. We show that gold nanostars integrated into the actuators serve as photothermal elements, enabling the fish tail to repeatedly bend when near infrared light is turned on and off. Our effort illustrates the potential of combining 3D printing, responsive hydrogels and photothermal elements with near infrared light towards soft robotic applications. This combination yields actuators capable of shape‐shifting without requiring localized light or transitioning between environments with varying temperatures.

Optimizing control for strike point sweeping using lower divertor coil in EAST

In 2021, EAST was equipped with a full-ring divertor coil to facilitate research on the fish tail divertor concept. Initially, it was observed that the coil current had a negligible ability to sweep the strike point. Conversely, when the amplitude and frequency of the alternating current were marginally increased, there was a significant interruption to plasma control. This perturbation was attributed to the poloidal control field’s limited response rate to the coil’s fluctuations. To address this issue, novel control methodologies were devised to ensure stable and effective sweeping of the strike point using the divertor coil. The devised methods are twofold: For high-frequency strike point control, a low-pass filter decoupling technique based on ISOFLUX control strategy enabled achieving a sweeping frequency of 100 Hz. This strategy allowed for consistent plasma management without compromising average stored energy or density regulation. Resulting from this proficient manipulation of the strike point, a reduction in the peak temperature of the divertor plate was observed. For low-frequency sweeping, a static multi-input multi-output decoupling approach was developed, facilitating concurrent sweeping of both the outer and inner strike points.

Drafting behaviors in fish induced by a local pressure drop around a hydrofoil model

Fish schooling has the improvement in hydrodynamic propulsive efficiency through the interaction of flow field induced by fish bodies and tail beat. Such energy-saving behaviors due to flow interactions also occur with changes in the flow field caused by structures. We examined the differences between a live fish swimming around a streamlined hydrofoil model prepared to represent fish body and swimming alone in a flow tank. We observed that the fish can remain in the same place without tail beating. It called “drafting” behavior. The analysis of fish drafting showed that fish obtained thrust using a local pressure drop caused by the high velocity flow even in the vicinity of the hydrofoil model at an angle of attack α of 10° to 20°without flow separation, and fish balanced forces by using an α of fish body. This tendency was confirmed in the model experiment using a two-axis load cell, and the forces acting on the fish body was the smallest value when the fish model was placed in the same conditions as a live fish experiment. We also confirmed by simulation and found that the α of fish body generated lift force and counteract the suction force. Above results indicate that a fish can balance the anterior–posterior and lateral direction forces by using a local pressure drop around a hydrofoil model as suction force, and using angle of attack on its body, thereby realizing drafting.

Study on visual localization and evaluation of automatic freshwater fish cutting system based on deep learning framework

ABSTRACT Pre-treatment processing technology plays a crucial role in the overall freshwater fish processing procedure, and automatic head and tail cutting stands out as a significant pre-treatment technique within the industry. The system for removing the head and tail of freshwater fish comprised a Cartesian coordinate manipulator, a fish transfer device, a control system, and an image acquisition device. In the vision system, five image segmentation methods were utilized for fish head and tail image segmentation comparison tests. These methods include U-Net (U-shaped Deep Neural Network), DeeplabV3, PSPNet (Pyramid Scene Parsing Network), FastSCNN (Fast Semantic Segmentation Network), and ICNet (Image Cascade Network), all of which were employed to evaluate their performance. Among the tested segmentation methods, the ICNet demonstrated the most excellent segmentation capability. The experimental results indicated a segmentation accuracy of 99.01%, a mean intersection over union (MIoU) of 82.50%, and an image processing time of 15.25 ms. The results showed that the fish head and tail were successfully cut off using this model for recognition with a circular knife. Consequently, the segmentation model employed in the machine vision system within this study has demonstrated successful applicability in automatically cutting the heads and tails of freshwater fish of various sizes.

Multi-physics coupling simulation and design of magnetic field-driven soft microrobots in liquid environments

Magnetic field-driven soft microrobots have widespread applications in biomedical science, microfluidic chips, nanoengineering, and various other domains. However, the existing methods for designing such magnetic-driven flexible robots largely rely on experimental trial and error or steady-state numerical simulated results, which fall short of meeting the intricate requirements for magnetic field editing and magnetic domain distribution. Addressing this issue, a multi-physics coupling numerical analysis method encompassing Magnetic-Fluid-Solid mechanics was developed. A complete process for transient numerical simulation resolution has been achieved. Utilizing this analysis method, the motion patterns of two typical prototypes of magnetic-driven miniature soft bionic robots, a bionic midge larvae robot, and a bionic jellyfish robot, have been analyzed. The central role of the magnetic field in driving these robotic designs—causing deformation in microrobots by designing magnetic domains and spinning the microrobots by controlling the magnetic field—has been revealed. We developed a theoretical model of a bionic fish tail fin robot driven solely by a rotating magnetic field and conducted comparative studies on the swimming efficiency, flexibility, stability, and relative advantages of the three types of robots. The impact of different magnetic domain distribution rules and different magnetic field driving methods on a robot's performance is analyzed, validating that higher swimming efficiency can be achieved by designing a robot's magnetic domains so that they undergo magnetic displacement under magnetic torque resulting in deformation. This innovative analysis method holds potential to provide valuable references for designing motion patterns of magnetically driven microrobots within liquid environments, thereby deepening our understanding toward various complex gait mechanisms involved in biological swimming.

A novel high energy density single-phase linear piezoelectric motor: design and experiment

The circuit simplification and simple structure of piezoelectric motor have become a major trend at present. Therefore, a novel, miniaturized, single-phase driven piezoelectric motor is proposed. The suggested piezoelectric motor employs a bending vibration mode of the first order, which is inspired by the motion patterns of fish tail fins. First, the motor’s operational principle and structure are explained. By analyzing the relationship between the working frequency and amplitude of the motor and the output power, the key parameters of the motor are determined, and the structure size of the motor is calculated. Next, the FEM model of the stator is utilized to conduct transient analysis in order to examine the movement path of the driving foot. Symmetrical right-diagonal or left-diagonal motions are formed by the driving foot during the first bending vibration, creating oblique elliptical movements. Finally, a prototype is made and its vibration and mechanical characteristics are tested. At a frequency of 15.6 kHz, the motor’s highest speed without any load is measured at 31.2 mm/s. Both forward and backward performance is identical. When the motor is supplied with a voltage of 140 Vpp and a preload of 2 N, it achieves a moving speed of 4.2 mm/s at 15.6 kHz, with an output thrust of around 0.9 N.

Early-Life Fecal Transplantation from High Muscle Yield Rainbow Trout to Low Muscle Yield Recipients Accelerates Somatic Growth through Respiratory and Mitochondrial Efficiency Modulation.

Previous studies conducted in our lab revealed microbial assemblages to vary significantly between high (ARS-FY-H) and low fillet yield (ARS-FY-L) genetic lines in adult rainbow trout. We hypothesized that a high ARS-FY-H donor microbiome can accelerate somatic growth in microbiome-depleted rainbow trout larvae of the ARS-FY-L line. Germ-depleted larvae of low ARS-FY-L line trout reared in sterile environments were exposed to high- or low-fillet yield-derived microbiomes starting at first feeding for 27 weeks. Despite weight-normalized diets, somatic mass was significantly increased in larvae receiving high fillet yield microbiome cocktails at 27 weeks post-hatch. RNA-seq from fish tails reveals enrichment in NADH dehydrogenase activity, oxygen carrier, hemoglobin complex, gas transport, and respiratory pathways in high fillet yield recolonized larvae. Transcriptome interrogation suggests a relationship between electron transport chain inputs and body weight assimilation, mediated by the gut microbiome. These findings suggest that microbiome payload originating from high fillet yield adult donors primarily accelerates juvenile somatic mass assimilation through respiratory and mitochondrial input modulation. Further microbiome studies are warranted to assess how increasing beneficial microbial taxa could be a basis for formulating appropriate pre-, pro-, or post-biotics in the form of feed additives and lead to fecal transplantation protocols for accelerated feed conversion and fillet yield in aquaculture.

THE RUSSIAN FOLK “EGYPTOLOGY”

The paper deals with Russian folk legends about “pharaohs” - mythical creatures with a human torso and a fish tail, who inhabited the water element. The legends reflected the oldest layer of folk knowledge about the ancient Egyptian history. These ideas go back to the biblical story about Pharaoh's army that drowned in the Red Sea during the exodus of the Jews from Egypt. In Old Russia, the title “Pharaoh” became a symbol of a proud and wicked ruler. The legend about the mythical water people was first recorded by Vasily Poznyakov, who travelled to Egypt in 1558. At the end of the 16th century, his story was used by Trifon Korobeynikov, who was on a pilgrimage to the East. Thanks to this work, “pharaohs” and “pharaonic women” were formed as negative characters of the Christian legend and in the 18th - 19th centuries were firmly incorporated into Russian folklore, while the image of the mythical people itself received an eschatological sound. Images of these creatures became one of the motifs of folk decorative art in Nizhny Novgorod province and neighboring counties of Kostroma province. It had a negative meaning, which derived from the “negativity” of the Old Testament character of the same name and was projected onto one of the repulsive features of the local character.

Nonlinear dynamic analysis of anisotropic bimorph dielectric elastomer actuator for soft fish robots

Electric fields when applied to smart materials like dielectric elastomers (useful for biomimetic creatures), provide a greater amount of mechanical actuation, but concerns with various drawbacks of isotropic dielectric elastomers whereas by imparting anisotropy through reinforcing soft fibers in such materials is used to overcome the drawbacks associated with it. Thus, in this study, nonlinear dynamic analysis of anisotropic visco-hyperelastic convex tapered bimorph dielectric elastomer actuator is reported to mimic actual fish tail by providing flaps through actuation. Experimental stress relaxations of the elastomer at different temperatures are performed using dynamic mechanical analysis (DMA 8000) to determine shear moduli (relaxed and unrelaxed) and relaxation time. The thermo-electro-visco-hyperelastic behavior of such actuators is represented by the Gent model of hyperelasticity in conjunction with the new relaxation model of viscoelasticity based on the obtained experimental data. Thereby, the governing equation of motion is derived based on Euler Lagrangian principle and solved through MATLAB and Simulink to analyze the nonlinear dynamics of active layer for such anisotropic actuators. For this present analysis, the fiber angles of the reinforcement, the taper ratio, and the temperatures are altered to study the effects of these parameters on the time series and frequency responses. The frequency spectrum shows generation of different frequencies which are linear combination of natural and excitation frequencies. The stretch histories, deflections, phase planes, Poincaré maps along with hysteresis loops and bifurcation diagram are attained to represent the physical behavior of nonlinear dynamics. Then from the responses it is inferred that with an increase in temperature and taper ratio, the stretch and deflection also increases, since the natural frequency and stiffness decreases for particular fiber angle. From the phase portraits, the quasi-periodic nature of the system is evident at dominant spike and the hysteresis loop indicates energy dissipation. From the bifurcation diagram analysis, sub or super of the dominant amplitude of frequency exists. At low frequency it is found that the stretch histories are chaotic.

Key point detection method for fish size measurement based on deep learning

AbstractAccurate fish size measurement in breeding areas is crucial for the fishing industry. Unlike acoustic methods with high equipment cost and low measurement accuracy, current image‐based methods offer a promising alternative. However, these image‐based methods still face challenges in selecting measurement points. To address this issue and achieve precise measurements of individual fish, this paper introduces an automatic fish size measurement method based on key point detection. We established a Fish‐Keypoints dataset and utilized deep learning techniques for the detection of fish and their key points. Using a binocular camera system, we reconstruct a three‐dimensional coordinate system to measure key points at the fish's head and tail, facilitating fish length calculation. The detection model achieves an accuracy of 85.1% in key point detection. The proposed method is tested in both land and underwater environments, demonstrating a relative measurement error of approximately 7% for fish in pools. This confirms the proposed method's ability to accurately detect measurement points, offering superior accuracy compared to other methods.

Acoustic predation in a sailfish-flying fish cloak

When a sailfish circles to corral a school of flying fish in a vortex near the ocean surface, a tiny patch of arced surface waves confined to oppositely placed 70° sectors appears dispersing coherently, but why? It is modeled that, when the fish motions stop suddenly, the corralled school compacts, the tail shed propulsion vortices touch, break and radiate the pressure released from the centrifugal vortex rotation creating an acoustic monopole. The surface-wave patch is a section of the sphere of radiation. The oppositely placed curved bodies of the sailfish and the flying fish act as concave acoustic mirrors about the monopole creating a reverberating bell-shaped cloak in between which vibrates the ear bones and bladders of the flying fish disorienting them. A cup of water firmly struck on a table induces a similar vibration of a purely radial mode. The sailfish circles around the school at a depth where the wind induced underwater toroidal motion in the vertical plane becomes negligible such that the flying fish is unable to sense the tailwind direction above, limiting the ability to swim up and emerge in the right direction to glide. Experiments confirm that the flying fish tail rigidity is too low for a quick ballistic exit, which is not called for either.

Study of lift enhancing mechanisms via comparison of the flapping trajectory of tandem flapping foil

Designing an aero/hydrovehicle that mimics natural swimmers such as fish is a challenging task. In the present study, an attempt has been made to mimic the fish tail motion that generates the lift energy. Two fishtail trajectories are replaced with two National Advisory Committee for Aeronautics 0012 foils in a tandem configuration for energy extraction. The energy induced due to lift force of the hind wing while flapping along fishtailed trajectory in single and tandem configurations is determined and compared with that of the simple flapping foil having heave and pitch motion only. The impact of various factors such as foil gap (G), phase angle (φ), and influence of Strouhal number (St) on the energy extraction performance is also investigated at a Reynolds (Re) number of 1173. The results show that a fishtail motion trajectory and foil gap ratio of 3c–4c (c being chord length) would enhance the energy extraction performance of the hindwing. The present research provides a new vision for the improvement of biomimetic power generators, as it aims to improve energy efficiency through the use of wake vortices.

An innovative divertor concept, the fish tail divertor, for reducing the surface temperature on the divertor target plate in EAST tokamak experiments

An innovative divertor concept, the fish tail divertor, is proposed in this paper, aimed at reducing the surface temperature on the tokamak divertor plate as well as that due to the edge localized modes. This new concept has been implemented in experiments to demonstrate its capability of strike point sweeping on the plate at a frequency range from 10 to 100 Hz by using an oscillating magnetic field. A strike point movement of 5–6 cm is achieved by applying a coil current of several percent of plasma current, leading to a significant reduction of divertor surface temperature. The result indicates a possible application in a fusion reactor.

High Linearity, Low Hysteresis Ti3C2Tx MXene/AgNW/Liquid Metal Self‐Healing Strain Sensor Modulated by Dynamic Disulfide and Hydrogen Bonds

AbstractFlexible wearable strain sensors have received extensive attention in human–computer interaction, soft robotics, and human health monitoring. Despite significant efforts in developing stretchable electronic materials and structures, developing flexible strain sensors with stable interfaces and low hysteresis remains a challenge. Herein, Ti3C2Tx MXene/AgNWs/liquid metal strain sensors (MAL strain sensor) with self‐healing function are developed by exploiting the strong interactions between Ti3C2Tx MXene/AgNWs/LM and the disulfide and hydrogen bonds inside the self‐healing poly(dimethylsiloxane) elastomers. AgNWs lap the Ti3C2Tx MXene sheets, and the LM acts as a bridge to increase the lap between Ti3C2Tx MXene and AgNWs, thereby improving the interface interaction between them and reducing hysteresis. The MAL strain sensor can simultaneously achieve high sensitivity (gauge factor for up to 3.22), high linearity (R2 = 0.98157), a wide range of detection (e.g., 1%–300%), a fast response time (145 ms), excellent repeatability, and stability.In addition, the MAL strain sensor before and after self‐healing is combined with a small fish and an electrothermally driven soft robot, respectively, allowing real‐time monitoring of the swinging tail of the small fish and the crawling of the soft robot by resistance changes.

Comparative Analysis of the Hydrodynamic Performance of Arc and Linear Flapping Hydrofoils

In order to improve the hydrodynamic performance of flapping hydrofoils and solve the problem of insufficient hydrodynamic force in plain river network areas, in this study, we consider the more realistic swing of fish tails and propose an arc flapping method, the coupled motion of which has three degrees of freedom: heave, pitch, and lateral displacement. Two flapping methods, positive arcs and negative arcs, were derived on the basis of the lateral displacement direction. By using the finite volume method (FVM) and overlapping grid technology, a numerical simulation was conducted to compare and analyze the pumping performance of three types of flapping hydrofoil, namely, linear, positive arcs, and negative arcs, in order to further provide guidance for the structural optimization of bionic pumping devices. The results showed that the wake vortex structures of the three flapping modes all had anti-Kármán vortex streets, but the wake vortex of linear flapping deflected upward, and the wake vortex of positive arc flapping tended to be further away in the flow field. In one cycle, thrust was always generated by the positive arc flapping hydrofoil and the linear flapping hydrofoil, but the thrust coefficient curve of the positive arc flapping hydrofoil was more stable than that of the linear flapping hydrofoil, and the peak value was reduced by 46.5%. In addition, under the conditions of a flow rate of 750 L·s−1 and an average head of 0.006 m, the pumping efficiency of the positive arc flapping hydrofoil reached 35%, thus showing better pumping performance than the traditional linear flapping hydrofoil under conditions with ultra-low head.