Design Of Robotic Fish Research Articles

A Novel Variable‐Stiffness Tail Based on Layer‐Jamming for Robotic Fish

Fish have excellent swimming performance, and one key factor is their ability to autonomously adjust body stiffness, which can help them efficiently swim at different speeds and complex environments. At present, the variable‐stiffness design of robotic fish still suffers from structural complexity, severe deformation, and small variation range, which limits the application of variable‐stiffness theory in robotic fish. In this article, a variable‐stiffness tail is designed based on layer‐jamming for robotic fish, which can conveniently achieve online stiffness adjustment while maintaining the optimal stiffness distribution and the shape is unaffected. A modeling method for the tail is proposed by combining the mechanical characteristics of the layer‐jamming structure with the pseudo‐rigid body model. To validate the performance of the tail, a series of experiments are conducted, which show that the stiffness variation range of the tail is around 10 times, and the accuracy of the model in predicting the kinematics of the tail is also verified. Moreover, the thrust tests demonstrate that stiffness adjustment is beneficial for fish swimming at different frequencies. The proposed variable‐stiffness tail will promote the development of efficient underwater biomimetic robots.

Design and Analysis of a Novel Bionic Tensegrity Robotic Fish with a Continuum Body.

Biological fish exhibit remarkable adaptability and exceptional swimming performance through their powerful and flexible bodies. Therefore, designing a continuum flexible body is significantly important for the development of a robotic fish. However, it is still challenging to replicate these functions of a biological body due to the limitations of actuation and material. In this paper, based on a tensegrity structure, we propose a bionic design scheme for a continuum robotic fish body with a property of stiffness variation. Its detailed structures and actuation principles are also presented. A mathematical model was established to analyze the bending characteristics of the tensegrity structure, which demonstrates the feasibility of mimicking the fish-like oscillation propulsion. Additionally, the stiffness variation mechanism is also exhibited experimentally to validate the effectiveness of the designed tensegrity fish body. Finally, a novel bionic robotic fish design scheme is proposed, integrating an electronic module-equipped fish head, a tensegrity body, and a flexible tail with a caudal fin. Subsequently, a prototype was developed. Extensive experiments were conducted to explore how control parameters and stiffness variation influence swimming velocity and turning performance. The obtained results reveal that the oscillation amplitude, frequency, and stiffness variation of the tensegrity robotic fish play crucial roles in swimming motions. With the stiffness variation, the developed tensegrity robotic fish achieves a maximum swimming velocity of 295 mm/s (0.84 body length per second, BL/s). Moreover, the bionic tensegrity robotic fish also performs a steering motion with a minimum turning radius of 230 mm (0.68 BL) and an angular velocity of 46.6°/s. The conducted studies will shed light on the novel design of a continuum robotic fish equipped with stiffness variation mechanisms.

A Novel Untethered Robotic Fish with an Actively Deformable Caudal Fin

Based on the observation that live fish caudal fins exhibit softness, flexibility, and active deformation, which are essential for generating thrust, stability, and maneuverability, herein, a comprehensive study on a novel type of bionic robotic fish with an actively deformable caudal fin is presented. The article first presents the design of the robot. Next, the quasisteady model theory is used to establish the hydrodynamic force for modeling the deformable caudal fin. Furthermore, three deformation modes are studied and compared: the conventional nondeformable mode, the sine‐based mode, and the instantaneous mode. Finally, a series of extensive experiments are conducted to evaluate various performance metrics of this innovative untethered biomimetic robotic fish, including thrust, swimming speed, yaw stability, turning radius, and turning rate. The results demonstrate that the introduction of active deformation of the caudal fin significantly enhances the swimming performance in the aforementioned indices when compared to the conventional nondeformable mode. Notably, the instantaneous mode exhibits best performance in terms of thrust, swimming speed, turning radius, and turning rate, while the sine‐based mode demonstrates the best yaw stability. Consequently, this research contributes to the advancement of robotic fish design and the development of underwater biomimetic robots.

Hydrodynamics and Musculature Actuation of Fish during a Fast Start

The fast start of fish is a rapid event that involves fast actuation in musculature and highly unsteady hydrodynamics. Fast-start capability is of great significance for fish to either hunt prey or escape from predators. In this study, we used a three-dimensional CFD model to study the hydrodynamics of a crucian carp during a C-type fast start. This study confirms the previous observations from both experiments and simulations that the jets are induced by the fast start for force generation, and the vortex rings generated in both the preparation and propulsion stages connect to each other. In addition, an obvious vortex ring generated by the head during the propulsion stage was observed, which potentially benefits the rotational motion during the fast start. According to the hydrodynamic information from CFD modeling, we established a model to analyze the internal torque, which represents the muscular actuation. The backward traveling speed of internal torque is 1.56 times the curvature speed, which confirms the existence of neuromechanical phase lag during the fast start of fish. This study potentially benefits the design of robot fish in terms of kinematics and driving mode.

Analysis of Heading Stability due to Interactions between Pectoral and Caudal Fins in Robotic Boxfish Locomotion

Investigating the interaction between fins can guide the design and enhance the performance of robotic fish. In this paper, we take boxfish as the bionic object and discuss the effect of coupling motion gaits among the two primary propulsors, pectoral and caudal fins, on the heading stability of the body. First, we propose the structure and control system of the bionic boxfish prototype. Second, using a one/two-way fluid–structure interaction numerical method, we analyse the key parameters of the prototype and discuss the influence of pectoral and caudal motion gaits on the hydrodynamic performance. Finally, effect of the pectoral and caudal interactions on heading stability of the prototype is systematically analyzed and verified in experiments. Results show that the course-deviating degree, oscillation amplitudes of yawing, rolling, and pitching exhibited by the prototype are smaller than that caused by single propulsor when the motion gaits of both pectoral and caudal fins are coordinated in a specific range. This paper reveals for the first time the effect of interactions between pectoral and caudal fins, on the stability of body's course by means of Computational Fluid Dynamics and prototype experiments, which provides an essential guidance for the design of robotic fish propelled by multi-fins.

Study on the mud swimming motion of Paramisgurnus dabryanus

In the context of the rapid development of bionic technology, inspired by the swimming behavior of fish, a variety of robotic fish have been designed and applied to different underwater works and even military applications. However, in some operations, such as detection and salvage, vehicles need to travel under mud, a medium that is different from fluids. This complicating factor put higher requirements on robotic fish design. In this study, Paramisgurnus dabryanus, a fish species adept at swimming into the mud, was taken as a research object to investigate its profile and mud swimming behavior. First, a three-dimensional (3D) image scanner is used for profile scanning to acquire the point cloud data of the profile features of the loach. After modification, data coordinate points are extracted and used to fit the profile curve of loach and build geometric and mathematical models by means of Fourier function fitting. The next step includes the analysis of the motion of loach, determination of main parameters of the wave equation, and establishment of the fish body wave curve of a loach in the swimming using MATLAB software. Saturated mud having a water content of 37% is adopted as an environmental medium to numerically simulate the swimming behavior in mud, identifying the distribution of vortex path, and velocity field of loach’s motion. The rationality of simulation results is verified by the loach mud swimming test, and the simulating results agree well with the experimental data. This study lays a preliminary foundation for the outer contour design of the robotic fish operating under mud and aims to carry out the drag reduction and accelerating design of the robotic fish. The robotic loach may be applied in fishery breeding, shipwreck salvage operations, and so on.

Trout-like multifunctional piezoelectric robotic fish and energy harvester

This work presents our experimental studies on a trout-inspired multifunctional robotic fish as an underwater swimmer and energy harvester. Fiber-based flexible piezoelectric composites with interdigitated electrodes, specifically macro-fiber composite (MFC) structures, strike a balance between the deformation and actuation force capabilities to generate hydrodynamic propulsion without requiring additional mechanisms for motion amplification. A pair of MFC laminates bracketing a passive fin functions like artificial muscle when driven out of phase to expand and contract on each side to create bending. The trout-like robotic fish design explored in this work was tested for both unconstrained swimming in a quiescent water tank and under imposed flow in a water tunnel to estimate the maximum swimming speed, which exceeded 0.25 m s−1, i.e., 0.8 body lengths per second. Hydrodynamic thrust characterization was also performed in a quiescent water setting, revealing that the fin can easily produce tens of mN of thrust, similar to its biological counterpart for comparable swimming speeds. Overall, the prototype presented here generates thrust levels higher than other smart material-based concepts (such as soft polymeric material-based actuators which provide large deformation but low force), while offering simple design, geometric scalability, and silent operation unlike motor-based robotic fish (which often use bulky actuators and complex mechanisms). Additionally, energy harvesting experiments were performed to convert flow-induced vibrations in the wake of a cylindrical bluff body (for different diameters) in a water tunnel. The shed vortex frequency range for a set of bluff body diameters covered the first vibration mode of the tail, yielding an average electrical power of 120 μW at resonance for a flow speed around 0.3 m s−1 and a bluff body diameter of 28.6 mm. Such low-power electricity can find applications to power small sensors of the robotic fish in scenarios such as ecological monitoring, among others.

Multi-Objective Multidisciplinary Design Optimization of a Robotic Fish System

Biomimetic robotic fish systems have attracted huge attention due to the advantages of flexibility and adaptability. They are typically complex systems that involve many disciplines. The design of robotic fish is a multi-objective multidisciplinary design optimization problem. However, the research on the design optimization of robotic fish is rare. In this paper, by combining an efficient multidisciplinary design optimization approach and a novel multi-objective optimization algorithm, a multi-objective multidisciplinary design optimization (MMDO) strategy named IDF-DMOEOA is proposed for the conceptual design of a three-joint robotic fish system. In the proposed IDF-DMOEOA strategy, the individual discipline feasible (IDF) approach is adopted. A novel multi-objective optimization algorithm, disruption-based multi-objective equilibrium optimization algorithm (DMOEOA), is utilized as the optimizer. The proposed MMDO strategy is first applied to the design optimization of the robotic fish system, and the robotic fish system is decomposed into four disciplines: hydrodynamics, propulsion, weight and equilibrium, and energy. The computational fluid dynamics (CFD) method is employed to predict the robotic fish’s hydrodynamics characteristics, and the backpropagation neural network is adopted as the surrogate model to reduce the CFD method’s computational expense. The optimization results indicate that the optimized robotic fish shows better performance than the initial design, proving the proposed IDF-DMOEOA strategy’s effectiveness.

Hydrodynamic Analysis for the Morphing Median Fins of Tuna during Yaw Motions.

Tuna can change the area and shape of the median fins, including the first dorsal, second dorsal, and anal fins. The morphing median fins have the ability of adjusting the hydrodynamic forces, thereby affecting the yaw mobility of tuna to a certain extent. In this paper, the hydrodynamic analysis of the median fins under different morphing states is carried out by the numerical method, so as to clarify the influence of the erected median fins on the yaw maneuvers. By comparing the two morphing states of erected and depressed, it can be concluded that the erected median fins can increase their own hydrodynamic forces during the yaw movement. However, the second dorsal and anal fins have limited influence on the yaw maneuverability, and they tend to maintain the stability of tuna. The first dorsal fin has more lift increment in the erection state, which can obviously affect the hydrodynamic performance of tuna. Moreover, as the median fins are erected, the hydrodynamic forces of the tuna's body increase synchronously due to the interaction between the body and the median fins, which is also very beneficial to the yaw motion. This study indicates that tuna can use the morphing median fins to adjust its mobility and stability, which provides a new idea for the design of robotic fish.

Hydrodynamic Modeling and Design of Robotic Fish using Slender Body Theory

Design of bio-inspired robotic fish has been an important area of research for applications such as water quality monitoring, aquatic animal behavioral study and underwater exploration. The modeling of robotic fish requires high dimensional analysis, which increases the design complexity. To address this complexity, approximate models are preferred and frequently used in the design of robotic fishes. The accuracy of these models mainly relies on various hydrodynamic parameter identification of which drag coefficient estimation is highly challenging. This paper utilizes a simple deceleration motion model to estimate the drag coefficient effectively so that the linearization error is reduced. The non-linearity in the deceleration model is simplified and mapped as a linear model to predict the drag coefficient. The estimated drag coefficient is used for dynamic modeling of robotic fish using slender body theory. The dynamic model is validated through experimental setup using accelerometer and visual sensor data. The maximum swimming speed of 0.32 ms-1 is achieved at 1.2 Hz caudal fin oscillations.

Effect of Reynold Number and Angle of Attack on the Hydrodynamic Forces Generated from A Bionic Concave Pectoral Fins

The pectoral fin shape, diameter and speed are the three main parameters for our robotic fish design. The influence of geometrical shape of pectoral fin in labriform mode swimming mechanism is evaluated with the aid of CFD method which is considered as a first step before building the complete design prototype. Two concave shape fins were designed precisely, each of them was attached to a servo motor arm which is in turn connected to a servo motor that is sliding on pair of shafts to work as robot straighter. The two servo motors along with their pectoral fins are placed in lm × 0.5m × 0.5m pool. Different number of angles of attack were tested and the results showed the optimum value is 50°. Further analysis based on Reynold number and its effect on the drag coefficient was investigated carefully. The hydrodynamic forces will be increases with the increasing of angle of attack for all Reynold numbers, which will in turn speed up the overall velocity of the body.

Optimization of Multibody fishbot undulatory swimming speed based on SOLEIL and BhT simulators

Robotic fish design is an upcoming and interesting research area with lot of challenging tasks due to the impulsive dynamics of water space. In this paper an evolutionary computational approach is performed to design caudal fins under carangi form and sub-carangi form swimming modes. Size and Shape with SOLEIL and multi-body evolutionary experiments were carried out using Euler-Lagrangian equation-based BhT tool to experiment and validate the hydrodynamic effects of caudal fin by avoiding complex and time consuming CFD simulations to achieve realistic motion. To improve average velocity of robotic fish two approaches have been suggested, one is a hill climbing algorithm to find optimal shape with standard stiffness whereas the second approach considers both shape and stiffness together in a genetic algorithm. Finally simulated fin models are compared against physical models to identify the correlation and performances of both to accurately approximate real world performances in a simulated environment leading to design optimised caudal fins for robotic fish.

CFD Studies of the Effects of Waveform on Swimming Performance of Carangiform Fish

Carangiform fish, like mackerel, saithe and bass, swim forward by rhythmically passing body waves from the head to the tail. In this paper, the undulating motions are decomposed into the travelling part and the standing part by complex orthogonal decomposition (COD), and the ratio between these two parts, i.e., the travelling index, is proposed to analyse the waveform of fish-like movements. To further study the relative influences of the waveform on swimming performance, a self-propelled model of carangiform fish is developed by the level set/immersed boundary (LS-IB) method, and the in-house code is tested by two cases of flow past a sphere and an oscillating cylinder, respectively. In this study, the travelling index is varied in ranges up to 50% larger or smaller than the biological data. The results show that carangiform fish seem to favour a fast and efficient swimming motion with a travelling index of around 0.6. Meanwhile, we study several numerical cases with different amplitude coefficients (0.5~1.1) and tail-beat frequency (2 Hz~5 Hz), and then compare their swimming performance with each other. We found that the forward speed is closely related to the travelling index and tail-beat frequency, while the swimming efficiency is increased with the tail-beat frequency and amplitude coefficient. These results are also consistent with biological observations, and they might provide beneficial guidance with respect to the future design of robotic fish.

Design and characterization of a miniature free-swimming robotic fish based on multi-material 3D printing

Research in animal behavior is increasingly benefiting from the field of robotics, whereby robots are being continuously integrated in a number of hypothesis-driven studies. A variety of robotic fish have been designed after the morphophysiology of live fish to study social behavior. Of the current design factors limiting the mimicry of live fish, size is a critical drawback, with available robotic fish generally exceeding the size of popular fish species for laboratory experiments. Here, we present the design and testing of a novel free-swimming miniature robotic fish for animal-robot studies. The robotic fish capitalizes on recent advances in multi-material three-dimensional printing that afford the integration of a range of material properties in a single print task. This capability has been leveraged in a novel design of a robotic fish, where waterproofing and kinematic functionalities are incorporated in the robotic fish. Particle image velocimetry is leveraged to systematically examine thrust production, and independent experiments are conducted in a water tunnel to evaluate drag. This information is utilized to aid the study of the forward locomotion of the robotic fish, through reduced-order modeling and experiments. Swimming efficiency and turning maneuverability is demonstrated through target experiments. This robotic fish prototype is envisaged as a tool for animal-robot interaction studies, overcoming size limitations of current design.

A review study on bio-inspired robotic fish

The paper presents a comprehensive review of design, modelling and performance parameters of robotic fish. Bio-robotics capitalises on the natural behaviours of biological systems to facilitate new designs for robots. The propulsion mechanism employed by natural fishes is imitated for designing of robotic fishes. Fishes have two locomotion modes, body and/or caudal fin (BCF) mode and median and/or paired fin (MPF) mode. These modes have been studied in this paper, so as to facilitate easy selection of a specific mode according to the application. A robotic fish system includes different subsystems (such as mechanical unit, control unit and actuation unit). These along with various materials and components used in these subsystems have been overviewed. Further study has been carried out to understand the dynamic characteristics of a robotic fish model. Performance parameters of the robotic fish are discussed in this paper. Various innovative approaches towards designing of robotic fish and the issues that need to be resolved are also discussed.

Infiltrating the zebrafish swarm: design, implementation and experimental tests of a miniature robotic fish lure for fish–robot interaction studies

Robotic fish are nowadays developed for various types of research, such as bio-inspiredrobotics, biomimetics and animal behavior studies. In the context of our research on the social interactions of the zebrafish Danio Rerio, we developed a miniature robotic fish lure for direct underwater interaction with the living fish. This remotely controlled and waterproof device has a total length of 7.5 cm with the same size ratio as zebrafish and is able to beat its tail with different frequencies and amplitudes, while following the group of living animals using a mobile robot moving outside water that is coupled with the robotic lure using magnets. The robotic lure is also equipped with a rechargeable battery and can be used autonomously underwater for experiments of up to 1 h. We performed experiments with the robot moving inside an aquarium with living fish to analyze its impact on the zebrafish behavior. We found that the beating rate of the tail increased the attractiveness of the lure among the zebrafish shoal. We also demonstrated that the lure could influence a collective decision of the zebrafish shoal, the swimming direction, when moving with a constant linear speed inside a circular corridor. This new robotic fish design and the experimental results are promising for the field of fish---robot interaction.

A Survey on Undulatory Motion Based Robotic Fish Design

A B S T R A C T Robotic fish design (Biomimetic) is an upcoming research area in which undulation motion has its own set of parameters to decide its efficiency. To analyse its swimming efficiency several existing robotic models using undulation motion have been thoroughly studied and few critical parameters such as fin size, shape, flexibility of material, fin flapping rate etc., have been identified. After simulating the above critical parameters using a MATLAB based CFD tool, mainly to design prototypes for research purpose which concentrates on optimizing its swimming efficiency. Several combinations of critical parameters are discussed for robotic fish prototype design by identifying critical parameters and maximizing the swimming efficiency of robotic fish based on the above properties. The fin models have been tested using Matlab based CFD tool through simulation and the swimming speed, direction have also been tested for various models. An improved benchmark for designing robotic fish model is proposed in order to simplify selection of components, architecture, and cost involve.

Design of Robotic Fish for Aquatic Environment Monitoring

In this paper, smartphone based aquatic debris monitoring robot design is proposed and discussed. Regularly monitoring aquatic waste or debris is of more interest to the environments, aquatic life, human health, and water transport. This paper presents the design of a robotic fish system that integrates an Android smartphone and a robotic fish for debris monitoring. The smartphone based aquatic robot can accurately detect debris in the presence of various environments.

The Mechanism and Transmission Design of Robotic Fish in Coal Mine

After coal mine flooding accident, the complexity mine environment caused rescue difficult, the paper proposed using robotic fish in the accident to do the detection. The basic configuration of the robotic fish was designed based on the fish propulsion mechanism, and the transmission mechanism was especially designed. Then, the mechanism kinematic analysis, and the mechanism motion curves were simulated using MATLAB, and a detail analysis of the transmission process of caudal fin system and the check of the motor torque were accomplished.

Robotic Fish Design and Control based on Biomechanics

This paper presents a theoretical framework on the design, modelling and control of a robotic fish inspired by the carangiform mode of swimming. The physical design of the robotic fish is obtained by trying to mimic the external anatomical features of a Tuna. To mimic the undulation of the fish posterior, a novel combination of manipulator link mechanism and a flexor-extensor mechanism has been used. The paper emphasizes the design and the modelling of this link mechanism and provides a kinematics model for the same. Dynamics modelling of the robotic system is based on Lagrangian methods. Finally we simulate a simple controller based on surface-swimming approximation of the developed dynamics model.