J0260204 クロマグロの遊泳能力解析と魚ロボットへの応用

The thrust produced during an escape response (C-start) of a northern pike, Esox lucius (0.41 m total length, 0.398 kg), an acceleration specialist, is estimated using the Weihs model for fish fast-starts. High-speed cine film records (250 Hz) of pike C-starts were digitized and the angle of attack and displacement of all body sections determined. These parameters were incorporated into the model and thrust was calculated. A comparison of model predictions with values predicted from required forces found six of eight performance parameters to be within 22% for three fast-starts. A lack of significant difference between model estimates and required forces suggests that lift and acceleration forces are the major components of total thrust during C-type fast-starts. The caudal region, including the caudal, anal, and dorsal fins, contributes the most (>90%) to positive total thrust during the propulsive stage (stage 2). High velocities, large angles of attack, and large surface areas of these sections account for this. Approximately 77% of the positive total thrust during the propulsive stage is generated by the caudal fin and 28% by the anal and dorsal fins. Lift forces averaged over the fast-start are greater than average acceleration forces, but when positive acceleration forces of the propulsive stage only are considered, average lift and acceleration forces are similar (60 and 43% of total positive forces, respectively). Also, acceleration forces peak earlier than lift forces and contribute to an earlier escape response.

Four goldfish Carassius auratus morphotypes of similar length (50 mm): common (streamlined, full complement of paired and median fins, bifurcated caudal fin), comet ('common like' but with a long, deeply forked caudal fin), fantail (short, deep body with twinned caudal and anal fins) and eggfish (similar to the fantail but lacking a dorsal fin) were compared. Drag, steady swimming kinematics, energetics, fast-start performance, stability in yaw and roll and propulsive muscle ultrastructural characteristics were measured. A performance 'pairing' (common and comet; fantail and eggfish) was a recurrent theme for most performance variables. Fantail and eggfish drag were higher (requiring more thrust at any given velocity) than those for the more streamlined common and comet. This was reflected in kinematics; tailbeat frequency and stride length at any given velocity for the common and comet were lower and higher, respectively, than that of the fantail and eggfish. Common and comet fatigue times were not significantly different from those of their ancestor, crucian carp Carassius carassius, and higher than the fantail and eggfish. The cost of transport of the common and comet (c. 0. 6 mg O(2) kg(-1) m(-1)) was accurately predicted by the mass scaling relationship for fish, but values for the fantail and eggfish (c. 1. 3 mg O(2) kg(-1) m(-1)) were not. Rolling and yawing motions in eggfish (dorsal fin absent) during steady swimming were associated with significant energy losses. Eggfish maximum fast-start acceleration (c. 5 m s(-2)) was poor due to the absence of inertial and lifting contributions to thrust from the dorsal fin and energy wasting rolling motions. Common and comet fast-start performance (average velocity c. 0. 45 m s(-1), maximum velocity c. 1. 2 m s(-1), average acceleration c. 7. 5 m s(-2), maximum acceleration c. 35 m s(-2)) was similar to that of other locomotor generalists (e.g. rainbow trout Oncorhynchus mykiss). Artificially selected fishes can contribute to the understanding of form and movement in fishes and complement studies of the role of locomotor adaptations in natural systems.

In this paper, motion of fishes with a caudal fin with vertical phase differences are analyzed to identify the effect of this kind of a caudal fin, some numerical model for this motion was made and some analyses have been investigated. To do this, torque and thrust from the fish motion were calculated based on the theoretical backgrounds from previous other researches. The results of a conventional caudal fin and the proposed fin were compared and it was found that fish with the proposed caudal fin can decrease the sum of torque exerted on the body maintaining the thrust force, which helps fish to save energy to propel and stare at something more stably under water. Some experiments were also performed and those were well accordance with theoretical analysis.

In this paper we consider underwater snake robots (USRs) that may be equipped with additional added effectors along their body, including caudal, dorsal and pectoral fins, tunnel thrusters and/or a stern propeller. We propose a mathematical model for USRs swimming in a 2D plane, which includes the extra propulsion forces acting on each link from the added effectors. The resulting model is in closed form, making it well-suited for control design and analysis. We then consider the particular case when fins are added to one or more links to provide lift forces. We develop a quasi-static model for an oscillating and rotating foil, which is then combined with the model of the USR to provide a model of an USR with one or more fins along its body. This makes it possible to make a simulation-based comparison of the USR energy efficiency with and without fins. Simulation results presented in this paper show that there is a significant improvement in propulsion efficiency for the USR with a caudal (tail) fin compared to the results obtained for the USR without a caudal fin.

PurposeFor precisely presenting the swimming behavior of fish robots underwater and the practical implementation purpose, this paper aims to investigate a well-formulated fish robot model which integrates the nonlinear rigid body dynamics, kinematics and models of actuators.Design/methodology/approachThis fish robot model is mainly built up by three basic parts: a balance mechanism, a four-links vibrator and a caudal fin. In the fish robot’s head, there is a balance mechanism used to control the rotations in pitch and roll directions of the fish robot by moving two movable masses. The four-links vibrator with three active joints actuated by DC motors is designed to vibrate the fish’s body. In the end of the fish robot body, a caudal fin which connects with the passive joint is developed to generate hydrodynamic thrust forces to propel the fish robot.FindingsFrom the real stability tests and control verification, it is obvious that this proposed model can precisely present the swimming behavior of fish robots and possesses the potential to develop a fish-like robotic prototype.Originality/valueA well-formulated model with dynamics of actuators is integrated for presenting the swimming behavior of carangiform locomotion type fish robots in this investigation. From the simulation results and the practical test of a real fish robot, the feasibility of this proposed model for building up real fish robots can be proven, and this proposed model is accurate enough to effectively present the swimming behavior of fish robots.

The kinematics model based on the Slender-Body theory is proposed from the bionic movement of real fish. The Panel method is applied to the hydrodynamic performance analysis innovatively, with the Gauss-Seidel method to solve the Navier-Stokes equations additionally, to evaluate the flexible deformation of fish in swimming accurately when satisfying the boundary conditions. A physical prototype to mimic the shape of tuna is developed with the revolutionized technology of rapid prototyping manufacturing. The hydrodynamic performance for rigid oscillating hydrofoil is analyzed with the proposed method, and it shows good coherence with the cases analyzed by the commercial software Fluent and the experimental data from robofish. Furthermore, the hydrodynamic performance of coupled hydrofoil, which consisted of flexible fish body and rigid caudal fin, is analyzed with the proposed method. It shows that the caudal fin has great influence on trailing vortex shedding and the phase angle is the key factor on hydrodynamic performance. It is verified that the shape of trailing vortex is similar to the image of the motion curve at the trailing edge as the assumption of linear vortex plane under the condition of small downwash velocity. The numerical analysis of hydrodynamics for bionic movement based on the Panel method has certain value to reveal the fish swimming mechanism.

Experiment on the characteristics of 3-D vortex ring behind a flexible oscillating caudal fin

Fish swimming modes and the shape of both the fins and body are expected to affect their swimming ability under different flow conditions. These swimming strategies and body morphologies often correspond to distributional patterns of distinct functional groups exposed to natural and variable water flows. In this study, we used a swimming-respirometer to measure energetic costs during prolonged, steady swimming and while station holding in a range of simulated oscillatory wave-surge water flows, within the natural range of flow speeds and wave frequencies on coral reefs. We quantified the net cost of swimming (NCOS, metabolic costs above resting) for four reef fish species with differences in swimming mode and morphologies of the fin and body: a body and caudal fin (BCF) swimmer, the Hawaiian flagtail, Kuhlia xenura, and three pectoral fin swimmers, the kole tang, Ctenochaetus strigosus, the saddle wrasse, Thalassoma duperrey, and the Indo-Pacific sergeant major, Abudefduf vaigiensis. We found that the BCF swimmer had the highest rates of increase in NCOS with increasing wave frequency (i.e. increased turning frequency) compared with the pectoral fin swimmers. The wrasse, with a more streamlined, higher body fineness, had lower rates of increase in NCOS with increasing swimming speeds than the low body fineness species, but overall had the highest swimming NCOS, which may be a result of a higher aerobic swimming capacity. The deep-bodied (low fineness) pectoral fin swimmers (A. vaigiensis and C. strigosus) were the most efficient at station holding in oscillating, wave-surge water flows.

As members of the derived teleost fish clade Scombridae, mackerel exhibit high-performance aquatic locomotion via oscillation of the homocercal forked caudal fin. We present the first quantitative flow visualization of the wake of a scombrid fish, chub mackerel Scomber japonicus (20-26 cm fork length, FL), swimming steadily in a recirculating flow tank at cruising speeds of 1.2 and 2.2FL s(-1). Thrust was calculated from wake measurements made separately in the horizontal (frontal) plane and vertical (parasagittal) planes using digital particle image velocimetry (DPIV) and compared with drag measurements obtained by towing the same specimens of S. japonicus post mortem. Patterns of flow indicated that the wake consisted of a series of linked elliptical vortex rings, each with central jet flow. The length of the minor axis (height) of the vortex rings was approximately equal to caudal fin span; the length of the major ring axis was dependent on swimming speed and was up to twice the magnitude of ring height. Profiles of wake velocity components were similar to theoretical profiles of vortex rings. Lift, thrust and lateral forces were calculated from DPIV measurements. At 1.2FL s(-1), lift forces measured relative to the X axis were low in magnitude (-1+/-1 mN, mean +/- S.D., N=20) but oriented at a mean angle of 6 degrees to the body axis. Reaction forces tend to rotate the fish about its center of mass, tipping the head down. Thus, the homocercal caudal fin of S. japonicus functions asymmetrically in the vertical plane. Pitching moments may be balanced anteriorly via lift generation by the pectoral fins. Thrust estimates for the two smallest fish based on DPIV analysis were not significantly different from drag measurements made by towing those same animals. At a speed of 1.2FL s(-1), thrust magnitude was 11+/-6 mN (mean +/- S.D, N=40). Lateral force magnitudes were approximately double thrust magnitudes (22+/-6 mN, mean +/- S.D., N=20), resulting in a mean mechanical performance ratio (thrust/total force) of 0.32 at 1.2FL s(-1). An increase in speed by a factor of 1.8 resulted in a mean increase in thrust by a factor of 4.4, a mean increase in lateral forces by a factor of 3, no change in the magnitude of lift produced and an increase in mean mechanical performance to 0.42. The relatively high lateral forces generated during swimming may be a necessary consequence of force production via propagated waves of bending.

Horizontal penetration in granular media is ubiquitous, from tunneling and geotechnical site investigation, to root growth and the locomotion of burrowing animals in nature. This contribution couples the discrete element method (DEM) with ant colony optimisation, a heuristic optimisation algorithm, to find the optimal tip shapes to minimise drag and lift forces during horizontal penetration. The tip which minimizes drag has a slender profile with a low tip curvature, to give a drag force that is $$15.6\%$$ 15.6 % lower compared to a conventional CPT intruder, however this shape induces a downwards force that increases with intruder depth. Conversely, the tip that minimizes lift is blunt, with a high tip curvature and short width, and reduces the drag and lift forces by $$4.5\%$$ 4.5 % and $$30.8\%$$ 30.8 % (respectively) compared to the CPT. The lift and drag forces are competing optimisation objectives, thus the tip shape with the optimal trade-off between drag and lift forces can be established using Pareto optimality. The Pareto optimal tip shape reduces the drag and lift forces by $$10.7\%$$ 10.7 % and $$19.4\%$$ 19.4 % respectively, and is strikingly similar to the profile of a sandfish. This contribution shows that when a common goal exists, bio-inspired solutions can offer an optimal solution to engineering applications. We also show the potential to integrate DEM simulations within an optimization framework to develop innovative design solutions.

Design and Implementation of Paired Pectoral Fins Locomotion of Labriform Fish Applied to a Fish Robot

A 3-D incompressible unsteady flow solver based on simple finite elements with adaptive remeshing and grid movement for both moving and deforming surfaces is described. We demonstrate the combination of adaptive remeshing techniques with the incompressible flow solver with the computation of flow past an eel in 2-D and a blue-fin tuna in 3-D. The flow past a swimming tuna was computed for two extreme cases of the caudal fin frequency and swimming speed. A grid refinement study was performed and a grid converged solution for the force produced by the caudal fin was obtained.

Several physico-mechanical designs evolved in fish are currently inspiring robotic devices for propulsion and maneuvering purposes in underwater vehicles. Considering the potential benefits involved, this paper presents an overview of the swimming mechanisms employed by fish. The motivation is to provide a relevant and useful introduction to the existing literature for engineers with an interest in the emerging area of aquatic biomechanisms. The fish swimming types are presented, following the well-established classification scheme and nomenclature originally proposed by Breder. Fish swim either by body and/or caudal fin (BCF) movements or using median and/or paired fin (MPF) propulsion. The latter is generally employed at slow speeds, offering greater maneuverability and better propulsive efficiency, while BCF movements can achieve greater thrust and accelerations. For both BCF and MPF locomotion, specific swimming modes are identified, based on the propulsor and the type of movements (oscillatory or undulatory) employed for thrust generation. Along with general descriptions and kinematic data, the analytical approaches developed to study each swimming mode are also introduced. Particular reference is made to lunate tail propulsion, undulating fins, and labriform (oscillatory pectoral fin) swimming mechanisms, identified as having the greatest potential for exploitation in artificial systems.

In this work, we developed a mathematical model and a simulation platform for a fish-inspired robotic template, namely Magnetic, Modular, Undulatory Robot <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(\mu \text{Bot})$</tex> . Through this platform, we systematically explored the effects of robot design and fluid parameters on swimming performance via reinforcement learning. The mathematical model was composed of two interacting subsystems, the robotic dynamic model and the hydrodynamic model. The hydrodynamic model consisted of the reactive components (added-mass force and pressure forces) and the resistive components (drag and friction forces). These components were nondimensionalized for deriving key "control parameters" of the robot-fluid interaction. The <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mu\text{Bots}$</tex> were actuated via magnetic actuators controlled with harmonic voltage signals, which were optimized via EM-based Policy Hyper Parameter Exploration (EPHE) to maximize forward swimming speed. By varying the control parameters, a total of 36 cases with different robot template variations (Number of Actuators (NoA) and stiffness) and hydrodynamic parameters were simulated and optimized via EPHE. Results showed that the wavelength of the optimized gaits (i.e., backward traveling wave along the body) was independent of template variations and hydrodynamic parameters. Higher NoA yielded higher speed but lower speed per body length, suggesting a diminishing gain from added actuators. Body and caudal-fin dynamics were dominated by the interaction among fluid added-mass, spring, and actuation torque, with negligible contribution from fluid resistive drag. In contrast, thrust was dominated by the pressure force acting on the caudal fin, as steady swimming resulted from a balance between resistive force and pressure force, with minor contributions from added-mass force and body drag forces. Therefore, added-mass force only indirectly affected the thrust generation and forward swimming speed via the caudal fin dynamics.

A comprehensive understanding of flow resistance is essential for understanding the hydrodynamical functioning of a river channel and predicting its evolution within the landscape. It governs the distribution of shear stress along the channel's boundaries, which in turn impacts the extent and distribution of erosion on the riverbed and banks. Flow resistance in steep mountain streams is primarily form drag and they exhibit high relative roughness. They tend to exhibit complex bed morphologies due to presence of large immobile boulders, aggregates of sediment particles, and specific bed or channel configurations. This roughness leads to the development of intricate three-dimensional flow patterns that may modify lift and drag forces acting on bed sediment. These alterations in forces can, in turn, impact water velocities and sediment fluxes within the stream. Despite extensive research, there is a lack of widely accepted theory addressing flow resistance in rough channels. Empirical evidence has established that conventional statistical description of bed morphology prove insufficient in fully describing riverbed roughness. This is why it is important to establish whether the morphology of riverbeds could exhibit a degree of inherent organization rather than appearing random. If this were to be true, riverbed morphology would exhibit a degree of consistency across different rivers and environments, enabling the formulation of generally applicable expressions for surface roughness that can be implemented in flow-resistance equations. Recent advances in uncrewed aerial vehicle (UAV) based structure from motion (SfM) allow for centimeter accurate measurement of the 3D morphology of river channels over hundreds of meters of river length. Obtaining accurate representation of the river channel's 3D topography serves as the starting point for examination of channel geometry and river bed roughness. Taking advantage of this, we have developed a workflow to characterize the geometry of natural river reaches, including shape metrics, estimates of hydraulic geometry, and grain size and location distributions based on automated image segmentation. We present our findings from a number of river channels in Taiwan. However, the most relevant way to characterize the geometry of a riverbed is through the interaction with the flow. The application of 3D flow modeling has proven to be of great importance in understanding flow patterns and sediment transport. We present plans to conduct 3D flow modelling over the measured river reaches in an effort to understand the most relevant aspect of the riverbed geometry to flow resistance.&amp;#160;