Bionic Propulsion Research Articles

Experimental investigation on the hydrodynamic performance of a bioinspired manta-ray underwater vehicle in various forward propulsion modes

Bionic propulsion technology is revolutionizing underwater exploration by enabling underwater vehicles to navigate the oceans more efficiently. This research developed a scaled-down (10:1) experimental prototype of bionic manta-ray underwater vehicle, which has two degrees of freedom (2-DOF) pectoral fins: flapping and rotating. The impact of four different pectoral fin motion patterns (sinusoidal flapping and rotating, flapping frequency asymmetric, flapping amplitude offset, and rotating amplitude limitation) on the forward propulsion performance was investigated experimentally in a static water tunnel using a force/torque sensor and power analyzer. The results revealed that introducing asymmetry into the fin's flapping motion (asymmetric frequency or amplitude) significantly improved both average thrust and propulsive efficiency (the average thrust can be increased by more than 30%). Flapping with amplitude offset can effectively adjust its pitching moment without sacrificing much thrust. While the rotating motion of the pectoral fins contributes minimally to thrust generation compared to flapping, it plays an important role in enhancing both longitudinal stability and propulsive efficiency. Understanding the hydrodynamic performance of these various forward propulsion modes provides valuable insights for optimizing control strategies of bionic manta-ray underwater vehicles.

Underwater dynamic modeling and experiments of flexible structure with harmonic actuation of macro fiber composites

Flexible structures driven by smart actuators are promising alternatives for aquatic bionic propulsion vehicles. However, the hydrodynamic effects induced by viscous fluids on the dynamic response of flexible structures remain an ongoing challenge. Thus, this article presents a fluid-structure interaction dynamic model of a flexible underwater structure actuated by macro fiber composite actuators, and the underwater multimodal vibration characteristics are studied. The model is based on the extended Hamilton’s principle, which considers the effects of hydrodynamic forces. The segmented mode shape functions of the flexible structure are derived using the assumed mode method. The study shows that the first two mode shapes of the beam predicted by the model agrees with the experimental results. The underwater dynamic responses of the flexible structure in a board band covering the first two resonance frequencies are also investigated at different actuation levels. The underwater results indicate that the first two resonance frequencies are 1.05 and 6.1 Hz respectively, basically consistent with the simulation ones (1.07 and 6.61 Hz). Correspondingly, the maximum transverse deflections at the end of the beam are 4.81 and 1.31 mm respectively, which are slightly lower than the predicted values of 5.75 and 1.62 mm. Therefore, the validity of the proposed coupled dynamic model is verified, which can be utilized to predict the multimodal dynamic responses of underwater flexible structures actuated by MFC or other smart actuators.

Optimal design and development of a fast steering robot inspired by scallops.

The improvement of the steering performance of jet robots is challenging due to single inflexible jet aperture. Scallops provide a potential solution with hard shells and a double-hole jet propulsion, which are expected to achieve fast steering movement under water. Inspired by scallops, a bionic propulsion dynamic mesh is proposed in this article, and a three-dimensional computational model of scallops is established. We further calculated the scallop propulsion mechanism under the swing of shells with different shapes. The coupling of simultaneous swing of two shells and their coupling with velum are presented, revealing the unique movement mechanism of Bivalvia. Based on this, the advantages of the double-hole jet propulsion are applied to develop a scallop robot with excellent steering capabilities. Experiments are conducted to verify the steering performance of the scallop robot.

CMBUV: A Composite-Mechanism Bioinspired Underwater Vehicle Integrated With Elasticity and Shear Damping Possesses High-Performance Capability

Benefiting from the potential advantages of low noise, high efficiency and little disturbance, bionic propulsion has attracted wide attentions. Compared with the rigid structure, the performance of the elastic propulsion structure such as flexible caudal fin and passive compliant joint has been improved, yet the effective frequency range is limited due to the single mechanism. The optimal propulsion can only be produced in a certain frequency range. In this article, a biological passive peduncle joint integrated with the composite mechanism of elasticity and shear damping is proposed, solving the problem of the narrow frequency range of effective propulsive capacity. Through the optimal regulation of the elastic function at a certain frequency range and characterization of the damping function which increases with frequency, the response features of the passive joint are optimized over a wide range of frequencies, thereby improving the propulsive performance of the composite-mechanism bioinspired underwater vehicle (CMBUV). A dynamic model is built and the deformation analysis of the compliant caudal fin is carried out. The propulsive efficiency is characterized, and the results indicate that the compliant caudal fin modulates the power transmission for enhancing thrust production. Extensive simulations and experiments reveal that the CMBUV achieves both high swimming speed with 4.42 body length per second and low cost of transport with 90.33 J kg <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{-1}$</tex-math></inline-formula> m <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{-1}$</tex-math></inline-formula> . Bioinspired propulsion from this study takes advantage of undulating propulsion of natural fish, offering valuable insights into performing marine tasks in ocean environments.

A novel miniature swimmer propelled by 36° Y-cut lithium niobate acoustic propulsion system

Self-propelled swimmers using ultrasonic transducers have been proposed and studied. The screw and bionic propulsion systems have dominated underwater robots. However, the complex structures make miniaturization difficult. The swimmers with ultrasonic transducers have no moving parts such as fins or propellers and can be driven by the nanomechanical-vibration in the surface of the transducer. Simple structure and high driving frequency make it easy to miniaturize. A 36° Y-cut lithium niobate (LN) thickness-vibration-mode transducer is used to investigate an underwater acoustic propulsion system. LN transducers are manufactured to 10 × 10 mm, 7 × 7 mm, and 4 × 4 mm square plates. The zero-speed propulsion and no-load speed are investigated to evaluate the swimmer performance. A mm-order swimmer is studied with a 4 × 4 mm LN transducer. At last, the multi-degrees-of-freedom swimmer driven by three 7 × 7 mm LN transducers is demonstrated with the advance and sway locomotion. In the future, a small-scale and agile self-propelled swimmer with an acoustic propulsion system can be expected for narrow and complex environment tasks, such as seagrass-prone areas and narrow pipelines.

Performance Optimization for Bionic Robotic Dolphin with Active Variable Stiffness Control.

Aquatic animals such as fish and cetaceans can actively modulate their body stiffness with muscle to achieve excellent swimming performance under different situations. However, it is still challenging for a robotic swimmer with bionic propulsion mode to dynamically adjust its body stiffness to improve the swimming speed due to the difficulties in designing an effective stiffness adjustment structure. In this paper, based on the special torque mode of a motor, we propose an active variable stiffness control method for a robotic dolphin to pursue better swimming speed. Different from a variable stiffness structure design, a torque control strategy for the caudal motor is employed to imitate the physical property of a torsion spring to act as the variable stiffness component. In addition, we also establish a dynamic model with the Lagrangian method to explore the variable stiffness mechanism. Extensive experiments have validated the dynamic model, and then the relationships between frequency and stiffness on swimming performance are presented. More importantly, through integrating the dynamic model and torque actuation mode-based variable stiffness mechanism, the online performance optimization scheme can be easily realized, providing valuable guidance in coordinating system parameters. Finally, experiments have demonstrated the stiffness adjustment capability of the caudal joint, validating the effectiveness of the proposed control method. The results also reveal that stiffness plays an essential role in swimming motion, and the active stiffness adjustment can significantly contribute to performance improvement in both speed and efficiency. Namely, with the adjustment of stiffness, the maximum speed of our robotic dolphin achieves up to 1.12 body length per second (BL/s) at 2.88 Hz increasing by 0.44 BL/s. Additionally, the efficiency is also improved by 37%. The conducted works will offer some new insights into the stiffness adjustment of robotic swimmers for better swimming performance.

Aerodynamic Analysis and Design Optimization of a Novel Flapping Wing Micro Air Vehicle in Hovering Flight

Inspired by the challenging and nimble flight dynamics of flying insects and birds, this research investigates bionic propulsion technology to develop an improved flapping wing micro air vehicle (FWMAV) design. Following the bionic formula, a prototype is preliminarily designed to achieve multi-attitude flight. Then, kinematic modeling is employed for further data analysis. A meshless particle hydrodynamics method is adopted to explore an optimized flapping driving mechanism and understand the influence of the flapping frequency, flapping amplitude, and quick-return characteristics of one side of the symmetrical mechanism on aerodynamic performance. Based on the aerodynamic model, force measurement experiments are developed to verify simulation availability and investigate the importance of wing flexibility. The numerical analysis results demonstrate that the average lift is approximately proportional to the flapping frequency, flapping-wing amplitude, and quick-return characteristics. Further optimization is conducted to find the best design parameters setting because of the complicated coupling relationship between the flapping wing amplitude and quick-return characteristics. Moreover, the optimized wing property supports high aerodynamic performance via experimental analysis in hovering flight.

Dynamics and hydrodynamic efficiency of diving beetle while swimming

Diving beetle, an excellent biological prototype for bionic underwater vehicles, can achieve forward swimming, backward swimming, and flexible cornering by swinging its two powerful hind legs. An in-depth study of the propulsion performance of them will contribute to the micro underwater vehicles. In this paper, the kinematic and dynamic parameters, and the hydrodynamic efficiency of the diving beetle are studied by analysis of swimming videos using Motion Capture Technology, combined with CFD simulations. The results show that the hind legs of diving beetle can achieve high propulsion force and low return resistance during one propulsion cycle at both forward and backward swimming modes. The propulsion efficiencies of forward and backward swimming are 0.47 and 0.30, respectively. Although the efficiency of backward swimming is lower, the diving beetle can reach a higher speed in a short time at this mode, which can help it avoid natural enemies. At backward swimming mode, there is a long period of passive swing of hind legs, larger drag exists at higher speed during the recovery stroke, which reduces the propulsion efficiency to a certain extent. Reasonable planning of the swing speed of the hind legs during the power stroke and the recovery stroke can obtain the highest propulsion efficiency of this propulsion method. This work will be useful for the development of a bionic propulsion system of micro underwater vehicle.

Residual Reinforcement Learning for Motion Control of a Bionic Exploration Robot—RoboDact

This paper aims to investigate the motion control method of a bionic underwater exploration robot (RoboDact). The robot is equipped with a double-joint tail fin and two undulating pectoral fins to obtain good mobility and stability. The hybrid propulsion mode helps perform stable and effective underwater exploration and measurement. To coordinate these two kinds of bionic propulsion fins and address the challenge of measurement noises and external disturbances during underwater exploration, a novel residual reinforcement learning method with parameter randomization (PR-RRL) is proposed. The control strategy is a weighted superposition of a feedback controller and a residual controller. The observation feedback controller based on active disturbance rejection control (ADRC) is adapted to improve stability and convergence. And the residual controller based on the soft actor-critic (SAC) algorithm is adapted to improve adaptability to uncertainties and disturbances. Moreover, the parameter randomization training strategy is proposed for adapting natural complicated scenarios by randomizing the partial dynamics of the underwater exploration robot during the training phase. Finally, the feasibility and efficacy of the presented motion control method are validated by comprehensive simulation tests and RoboDact prototype physical experiments.

Design and Control of an Underwater Robot Based on Hybrid Propulsion of Quadrotor and Bionic Undulating Fin

Stable, quiet, and efficient propulsion methods are essential for underwater robots to complete their tasks in a complex marine environment. However, with a single propulsion method, such as propeller propulsion and bionic propulsion, it is difficult to achieve high efficiency and high mobility at the same time. Based on the advantages of the high-efficiency propulsion of a bionic undulating fin and the stable control of the propeller, an underwater robot based on the hybrid propulsion of a quadrotor and undulating fin is proposed in this paper. This paper first introduces the mechanical implementation of the underwater robot. Then, based on kinematic modeling and theoretical derivation, the underwater motion and attitude of the robot are analyzed and the 6-DOF dynamic equation of the robot is established. Finally, the underwater motion performance of the robot is verified through field experiments. The experimental results show that the robot can realize the heave motion, surge motion, and in-situ steering motion independently and can hover stably. When the undulating frequency is 6 Hz, the maximum propulsion speed of the robot can reach up to 1.2 m/s (1.5 BL/s).

Design and Hydrodynamic Experiment Research on Novel Biomimetic Pectoral Fins of a Ray-Inspired Robotic Fish

Bionic propulsion has certain advantages over traditional propellers. Much research on pectoral fins as bionic propellers for ray-inspired robots has been made, but rarely did they compare the hydrodynamic performance of different fins on the same platform to find out optimal balance. In this paper, the existing prototypes are categorized into three structure types, and a new bionic pectoral fin module used on a ray-inspired robotic fish was presented, together with a novel 2-DOF spatial parallel mechanism as the bionic propeller. Motion analysis of the mechanism agreed well with the pectoral fin kinematic model, providing a reliable basis to test different types of fins. Design and fabrication of the new bionic fin module as well as two traditional ones are also explained. Hydrodynamic experiment was conducted to study the differences between each fin type under various working conditions. Results indicate that the thrust generated by the fin oscillation is closely related to four parameters (amplitude, frequency, phase difference, and flow velocity), and there are optimal value ranges for better propelling performance when the frequency is around 0.5 Hz and phase difference is near 30°. Thanks to better profile preservation and hydro force interaction, the newly proposed pectoral fins had higher performance than the traditional ones in terms of thrust generation and controllability when the amplitude is higher than 30° and frequency is over 0.3 Hz. An average thrust of 2.98 N was recorded for the new fin module at the max amplitude of 60°, 11.6% and 16.4% higher than the other two comparative test groups, respectively.

Numerical investigations on bionic propulsion problems using the multi-resolution Delta-plus SPH model

The bionic propulsion has garnered increasing attention in both scientific and industrial communities of underwater bionic vehicles on account of its higher efficiency, less noise, and remarkable self-shelter capability. This paper is dedicated to investigating the propulsion mechanism of fish swimming using the Smoothed Particle Hydrodynamics (SPH) method. Two fish-like swimming problems, established with rigid flapping foils and deformable anguilliform swimmers respectively, are simulated using the δ+-SPH model under the laminar flow assumption. First of all, numerical benchmarks are implemented to validate the convergence and accuracy of the SPH model by comparing the SPH results with experimental data quantitatively and qualitatively. Furthermore, the mechanisms of the thrust generation of the bionic swimmers are investigated and discussed in detail from the viewpoint of vortex shedding patterns and several dimensionless parameters describing the motion characteristics. It is demonstrated that the thrust force is tightly related to the shape and scale of the vortex shedding in wakes, and that a higher Reynolds number or larger Strouhal number, as well as a larger motion amplitude, are in favor of improving the thrust. In addition, the numerical results also indicate that the SPH method possesses great potential for the simulation of bionic propulsion problems thanks to its Lagrangian and meshfree nature.

Design and Experimental Research on a Bionic Robot Fish with Tri-Dimensional Soft Pectoral Fins Inspired by Cownose Ray

Bionic propulsion has advantages over traditional blade propellers, such as efficiency and noise control. Existing research on ray-inspired robot fish has mainly focused on a single type of pectoral fin as bionic propeller, which only performed well in terms of pure speed or maneuverability. Rarely has the performance of different fin types been compared on the same platform to find an optimal solution. In this paper, a modularized robot fish with high-fidelity biomimetic pectoral fins and novel multi-DOF propelling mechanism is presented. A kinematic model of the pectoral fin based on motion analysis of a cownose ray is introduced as guidance for the propelling mechanism design. A high-fidelity parametric geo-model is established and evaluated based on statistical data. The design and fabrication process of the 3D soft bionic fins, as well as the robot platform, is also elaborated. Through experiments comparing the performance of different fin types constructed with different materials and approaches, it was found that the new soft fins made of silicon rubber have better performance than traditional fins constructed with a flexible inner skeleton and a permeable outer skin as a result of better 3D profile preservation and hydrodynamic force interaction. The robot ray prototype also acquires a better combination of high speed and maneuverability compared to results of previous research.

Nonsinusoidal motion effect on a self-propelled heaving foil

In order to explore the mechanism of bionic propulsion and bionic robots, to make up for the limitations of traditional propulsion with a uniform incoming flow, numerical methods are used to couple fluid dynamics and flapping foil motions, and a flapping-fluid coupling self-propulsion calculation model is established in this paper. K is used as the waveform adjustment parameter to change the waveform from triangle wave to sine wave and square wave. The self-propulsion performances of non-sinusoidal heave motion under two frequency-heaving amplitude combinations are numerically simulated to study the influence of different motion waveforms on self-propulsion velocity, efficiency and flow field structure in still water. The results show that the non-sinusoidal waveform has a great influence on the self-propulsion. With the increase of K, the closer to the square wave, the more violent the speed oscillation, the faster the starting acceleration, the greater the forward displacement and the average speed, as K decreases, self-propulsion efficiency and energy utilization continue to increase. The results of this study have certain guiding significance for the design of bionic underwater vehicles.

Propulsive performance of a newly conceptual design of flapping foil with fixed gurney plate- A numerical study

In order to improve the propulsive performance of flapping foil, a new conceptual design of flapping foil device is proposed in current study by adding a pair of fixed gurney plates to the trailing end of flapping foil. The two-dimensional transient numerical study has been carried out to analyse the propulsive performance of current flapping foil at a Reynolds number of 1.0 × 106. In addition, the effect of non-dimensional flapping frequency (St number), the gurney plate length as well as the gurney plate position along the chord length direction of the foil has also been conducted. The numerical results reveal that the current flapping foil with fixed gurney plate exhibits better propulsive performance than the conventional one by increasing the thrust force within the whole motion period. Similar with the conventional one, the St number is also a dominant parameter in evaluating the propulsive efficiency and the optimum value leading to highest propulsive efficiency varies around 0.3. The simulation results indicate that the geometric parameter of gurney plate length does not always play a positive role in improving propulsive efficiency and there exists optimal gurney plate length corresponding to highest propulsive efficiency. The numerical results also demonstrates that the more closer the gurney plate is to the trailing edge of flapping foil, the better the propulsive performance of flapping foil will be. Conclusions acquired in this study may provide some guidance for the design of bionic propulsion device or vehicle.

Observation and analysis of diving beetle movements while swimming

The fast swimming speed, flexible cornering, and high propulsion efficiency of diving beetles are primarily achieved by their two powerful hind legs. Unlike other aquatic organisms, such as turtle, jellyfish, fish and frog et al., the diving beetle could complete retreating motion without turning around, and the turning radius is small for this kind of propulsion mode. However, most bionic vehicles have not contained these advantages, the study about this propulsion method is useful for the design of bionic robots. In this paper, the swimming videos of the diving beetle, including forwarding, turning and retreating, were captured by two synchronized high-speed cameras, and were analyzed via SIMI Motion. The analysis results revealed that the swimming speed initially increased quickly to a maximum at 60% of the power stroke, and then decreased. During the power stroke, the diving beetle stretched its tibias and tarsi, the bristles on both sides of which were shaped like paddles, to maximize the cross-sectional areas against the water to achieve the maximum thrust. During the recovery stroke, the diving beetle rotated its tarsi and folded the bristles to minimize the cross-sectional areas to reduce the drag force. For one turning motion (turn right about 90 degrees), it takes only one motion cycle for the diving beetle to complete it. During the retreating motion, the average acceleration was close to 9.8 m/s2 in the first 25 ms. Finally, based on the diving beetle's hind-leg movement pattern, a kinematic model was constructed, and according to this model and the motion data of the joint angles, the motion trajectories of the hind legs were obtained by using MATLAB. Since the advantages of this propulsion method, it may become a new bionic propulsion method, and the motion data and kinematic model of the hind legs will be helpful in the design of bionic underwater unmanned vehicles.

Numerical study on hydrodynamic behavior of flexible multi-stage propulsion foil

To examine mechanisms of the high speed and efficiency of propulsion of aquatic animals and to apply the findings to the design of underwater vehicles, this study uses dolphins as an example. The motion of aquatic animals is divided into three stages for the convenience of analysis of bio-propulsion: the oscillation of one-third of the rear body, the oscillation of the caudal fin, and the deformation of the caudal fin. We call the case multi-stage propulsion when all the stages are contained in a bio-propulsion. We investigate the effects of the phase difference between oscillations of the first and second stages φ on hydrodynamic performance and the chordwise deformation factor δc0 on hydrodynamic performance. The results show that when the phase difference was 90°, the propulsion efficiency was the highest and an appropriate caudal chordwise deformation could increase the propulsion efficiency, which was consistent with the result of previous studies. The key part of this paper is the comparative study between different propulsion modes in terms of fluid mechanism from multiple perspectives, such as the force generated by the oscillating motion, the shedding frequency of the wake vortex, and the spacings of vortices induced by different propulsion modes. The aim of this paper is to understand the mechanism supporting a larger thrust and higher efficiency of multi-stage propulsion and provide reference for the improvement and optimization of bionic propulsion in the future.

The Analysis of Biomimetic Caudal Fin Propulsion Mechanism with CFD.

In nature, fish not only have extraordinary ability of underwater movement but also have high mobility and flexibility. The low energy consumption and high efficiency of fish propulsive method provide a new idea for the research of bionic underwater robot and bionic propulsive technology. In this paper, the swordfish was taken as the research object, and the mechanism of the caudal fin propulsion was preliminarily explored by analyzing the flow field structure generated by the swing of caudal fin. Subsequently, the influence of the phase difference of the heaving and pitching movement, the swing amplitude of caudal fin, and Strouhal number (St number) on the propulsion performance of fish was discussed. The results demonstrated that the fish can obtain a greater propulsion force by optimizing the motion parameters of the caudal fin in a certain range. Lastly, through the mathematical model analysis of the tail of the swordfish, the producing propulsive force principle of the caudal fin and the caudal peduncle was obtained. Hence, the proposed method provided a theoretical basis for the design of a high-efficiency bionic propulsion system.

Bionic Flapping Pectoral Fin with Controllable Spatial Deformation

This paper presents the design of a bionic pectoral fin with fin rays driven by multi-joint mechanism. Inspired by the cownose ray, the bionic pectoral fin is modeled and simplified based on the key structure and movement parameters of the cownose ray’s pectoral fin. A novel bionic propulsion fin ray composed of a synchronous belt mechanism and a slider-rocker mechanism is designed and optimized in order to minimize the movement errors between the designed fin rays and the spanwise curves observed from the cownose ray, and thereby reproducing an actively controllable flapping deformation. A bionic flapping pectoral fin prototype is developed accordingly. Observations verify that the bionic pectoral fin flaps consistently with the design rule extracted from the cownose ray. Experiments in a towing tank are set up to test its capability of generating the lift force and the propulsion force. The movement parameters within the usual propulsion capabilities of the bionic pectoral fin are utilized: The flapping frequency of 0.2 Hz–0.6 Hz, the flapping amplitude of 3°–18°, and the phase difference of 10°–60°. The results show that the bionic pectoral fin with actively controllable spatial deformation has expected propulsion performance, which supports that the natural features of the cownose ray play an important role in designing and developing a bionic prototype.

The mechanism of flapping propulsion of an underwater glider

To develop a bionic maneuverable propulsion system to be applied in a small underwater vehicle, a new conceptual design of the bionic propulsion is applied to the traditional underwater glider. The numerical simulation focuses on the autonomous underwater glider (AUG)'s flapping propulsion at by solving the incompressible viscous Navier-Stokes equations coupled with the immersed boundary method. The systematic analysis of the effect of different motion parameters on the propulsive efficiency of the AUG is carried out, including the hydrofoil's heaving amplitude, the pitching amplitude, the phase lag between heaving and pitching and the flapping frequency. The results obtained in this study can provide some physical insights into the propulsive mechanisms in the flapping -based locomotion.