Pectoral Fin Propulsion Research Articles

Effects of motion parameters on the propulsion characteristics of flexible pectoral fins in bio-manta robots

Manta rays have emerged as excellent bionic objects due to their efficient and flexible propulsion. A thorough understanding of the propulsion characteristics of manta ray robot pectoral fins is highly important for optimizing pectoral fin design and guidance strategies. Based on the silhouette and kinematics of the manta ray, we designed flexible pectoral fins and a 2DoF bionic mechanism that couples the flapping and pitching movements. Blade element theory was used to conduct a dynamic analysis of the bio-manta pectoral fins. The Strouhal number is used as a key dimensionless number that affects the hydrodynamic characteristics of a bio-manta robot during periodic flapping, as well as the flexibility of the pectoral fins and the angle of attack. We describe a series of hydrodynamic experiments conducted to analyze the single and interactive effects of the motion parameters of pectoral fin propulsion and regression analysis. The results show that when St is [0.2,0.4], the CT (thrust coefficient) of the flexible pectoral fin increases rapidly. When St increased beyond 0.4, the growth trend slows and remains essentially unchanged after 0.8. The CT reaches its peak, the propulsion efficiency is highest when St is between [0.4,0.6]. The angle of attack and the CT show a negative inverse quadratic trend, reaching a peak at 6.5°, and their influence is weaker than that of the frequency. The flexibility and CT showed a cubic trend, and the influence of flexibility was more significant when swimming at medium and low speeds. When swimming slowly, flexibility has a significant interactive effect on the frequency and angle of attack. However, these interactive effects reduce at high speeds. When the bio-manta robot starts at 0 speed, it should maneuver at high frequency and large amplitude while ensuring sufficient structural strength. After reaching a certain speed, the device maintains a large amplitude and low-frequency flapping operation to continuously drive propulsion.

Pectoral Fin Propulsion Performance Analysis of Robotic Fish with Multiple Degrees of Freedom Based on Burst-and-Coast Swimming Behavior Stroke Ratio

The pectoral fin propulsion of a bionic robotic fish always consists of two phases: propulsion and recovery. The robotic fish moves in a burst-and-coast swimming manner. This study aims to analyze a pair of bionic robotic fish with rigid pectoral fin propulsion with three degrees of freedom and optimize the elliptical propulsion curve with the minimum recovery stroke resistance using computational fluid dynamics methods. Then, the time allocated to the propulsion and recovery phases is investigated to maximize the propulsion performance of the bionic robotic fish. The numerical simulation results show that when the time ratio of the propulsion and recovery phases is 0.5:1, the resistance during the movement of the robotic fish is effectively reduced, and the drag-reducing effect is pronounced. According to a further analysis of pressure clouds and vortex structures, the pressure difference between the upstream and downstream fins of the pectoral fin varies with different stroke ratios. The increase in recovery phase time helps to prevent premature damage to the vortex ring structure generated during the propulsion process and improves propulsion efficiency.

Propulsion curve analysis and optimisation of biomimetic pectoral fin with three degree of freedom based on multi-layer perception

This paper aims to improve the swimming efficiency of biomimetic robotic fish by optimising its propulsion curve with three degree of freedom (DOF), in which the key is to minimise the resistance during swing backstroke of the pectoral fin. For this purpose, a reference point on the pectoral fin is first selected, and then an 8-shaped propulsion curve is constructed to coordinate rowing and flapping motions. Meanwhile, a propulsion curve of feathering motion is also given correspondingly. On this basis, the overall curvature and curve offset are proposed as measurement parameters for the deformation of the propulsion curve and the proportion of abdominal/dorsal circles in the propulsion curve, respectively. As the motion law of feathering is given in a sinusoidal pattern, a data set of hydrodynamic parameters is obtained for pectoral fin propulsion under different motion parameter conditions by computational fluid dynamics(CFD) numerical simulation. Once again, a propulsion curve optimisation model is established based on multi-layer perception(MLP), which uses the hydrodynamic parameters data set as input. The results show that the resistance of swing backstroke reached the minimum when overall curvature is π/10 and curve offset is 0.4, which is enhanced by 30.13% and 33.33% at thrust and lift direction compared to the existing design, respectively. Furthermore, the flow field structure and hydrodynamic parameters around the robotic fish are calculated by CFD. The results show that two sets of vortex rings are generated around the fish body during a propulsion cycle. The vortex rings detached towards the lower and upper sides of the fish body such that the lift is minimal, the thrust direction is relatively stable, and the resistance is minimal during the swing backstroke. The experimental results indicate that it can raise propulsion efficiency during the pectoral fin propulsion process, verifying the effectiveness of this method.

Foraging habitat determines predator-prey size relationships in marine fishes.

Predator-prey size (PPS) relationships are determined by predator behaviour, with the likelihood of prey being eaten dependent on their size relative to that of the consumer. Published PPS relationships for 30 pelagic or benthic marine fish species were analysed using quantile regression to determine how median, lower and upper prey sizes varied with predator size and habitat. Habitat effects on predator foraging activity/mode, morphology, growth and natural mortality are quantified and the effects on PPS relationships explored. Pelagic species are more active, more likely to move by caudal fin propulsion and grow more rapidly but have higher mortality rates than benthic species, where the need for greater manoeuvrability when foraging in more physically complex habitats favours ambush predators using pectoral fin propulsion. Prey size increased with predator size in most species, but pelagic species ate relatively smaller prey than benthic predators. As pelagic predators grew, lower prey size limits changed little, and prey size range increased but median relative prey size declined, whereas the lower limit increased and median relative prey size was constant or increased in benthic species.

Robot fish with two-DOF pectoral fins and a wire-driven caudal fin

This paper presents a robot fish with a wire-driven caudal fin and a pair of pectoral fins. First, the design of the robot fish is presented. The caudal fin is driven through wire-driven mechanism. The pectoral fins can perform two degrees-of-freedom motions, i.e. flapping (roll) and feathering (pitch). The pectoral fins can move in labriform mode for propulsion, or for other purposes such as turning and diving. Second, the propulsion analysis models for caudal fin propulsion and pectoral fins propulsion are derived. Finally, three types of experiments are conducted. Experiment results show that the swimming speed of caudal fin propulsion and pectoral fin propulsion match the model predictions. Moreover, with the caudal fin propulsion alone, the robot fish can swim up to 0.66 BL/s (body length/second); with the pectoral fin propulsion alone, the robot fish can swim up to 0.26 BL/s. The pectoral fins can significantly improve the maneuverability of the robot fish. Without using the pectoral fins, the turning radius of the robot fish is 0.6 BL; with the pectoral fins, the turning radius is reduced to 0.25 BL.

Biomechanical model of batoid (skates and rays) pectoral fins predicts the influence of skeletal structure on fin kinematics: implications for bio-inspired design

Growing interest in the development of bio-inspired autonomous underwater vehicles (AUVs) has motivated research in understanding the mechanisms behind the propulsion systems of marine animals. For example, the locomotive behavior of rays (Batoidea) by movement of the pectoral fins is of particular interest due to their superior performance characteristics over contemporary AUV propulsion systems. To better understand the mechanics of pectoral fin propulsion, this paper introduces a biomechanical model that simulates how batoid skeletal structures function to achieve the swimming locomotion observed in nature. Two rays were studied, Dasyatis sabina (Atlantic ray), and Rhinoptera bonasus (cownose ray). These species were selected because they exhibit very different swimming styles (undulation versus oscillation), but all use primarily their pectoral fins for propulsion (unlike electric rays or guitarfishes). Computerized tomography scans of each species were taken to image the underlying structure, which reveal a complex system of cartilaginous joints and linkages. Data collected from these images were used to quantify the complete skeletal morphometry of each batoid fin. Morphological differences were identified in the internal cartilage arrangement between each species including variations in the orientation of the skeletal elements, or radials, and the joint patterns between them, called the inter-radial joint pattern. These data were used as the primary input into the biomechanical model to couple a given ray skeletal structure with various swimming motions. A key output of the model is an estimation of the uniaxial strain that develops in the skeletal connective tissue in order for the structure to achieve motions observed during swimming. Tensile load tests of this connective tissue were conducted to further investigate the implications of the material strain predictions. The model also demonstrates that changes in the skeletal architecture (e.g., joint positioning) will effect fin deformation characteristics. Ultimately, the results of this study can be used to guide the design of optimally performing bio-inspired AUVs.

Electromechanical dynamics and optimization of pectoral fin–based ionic polymer–metal composite underwater propulsor

Ionic polymer–metal composites are soft artificial muscle-like bending actuators, which can work efficiently in wet environments such as water. Therefore, there is significant motivation for research on the development and design analysis of ionic polymer–metal composite based biomimetic underwater propulsion systems. Among aquatic animals, fishes are efficient swimmers with advantages such as high maneuverability, high cruising speed, noiseless propulsion, and efficient stabilization. Fish swimming mechanisms provide biomimetic inspiration for underwater propulsor design. Fish locomotion can be broadly classified into body and/or caudal fin propulsion and median and/or paired pectoral fin propulsion. In this article, the paired pectoral fin–based oscillatory propulsion using ionic polymer–metal composite for aquatic propulsor applications is studied. Beam theory and the concept of hydrodynamic function are used to describe the interaction between the beam and water. Furthermore, a quasi-steady blade element model that accounts for unsteady phenomena such as added mass effects, dynamic stall, and the cumulative Wagner effect is used to obtain hydrodynamic performance of the ionic polymer–metal composite propulsor. Dynamic characteristics of ionic polymer–metal composite fin are analyzed using numerical simulations. It is shown that the use of optimization methods can lead to significant improvement in performance of the ionic polymer–metal composite fin.

Median and Paired Fin Controllers for Biomimetic Marine Vehicles

This paper reviews the studies on the kinematics, hydrodynamics, and performance of median and paired fin (MPF) in fish and biomimetic mechanical systems from the viewpoint of enhancing the propulsive and maneuvering performance of marine vehicles at low speeds. Precise maneuverability and stability at low swimming speeds by use of MPF propulsion seem to be advantageous in complex habitats such as coral reefs. MPF propulsion in fish consists of undulatory fin motion and oscillatory fin motion. The kinematics of MPF in fish and mechanical systems in both groups is discussed. Hydrodynamic models and experimental data of undulatory and oscillatory motions of MPF in fish and mechanical system are reviewed. Pectoral fin propulsion has two categories which represent biomechanical extremes in the use of appendages for propulsion: drag-based and lift-based mechanisms of thrust production. The hydrodynamic characteristics of the two mechanisms are compared. The performance of fish and vehicles with MPF is reviewed from the viewpoint of maneuverability. Especially, performance of a recently developed fish-like body with a pair of undulatory side fins, a model ship with a pair of ray-wing-type propulsors, and an underwater vehicle with two pairs of mechanical pectoral fins are discussed.

Diversity of pectoral fin structure and function in fishes with labriform propulsion

Aquatic propulsion generated by the pectoral fins occurs in many groups of perciform fishes, including numerous coral reef families. This study presents a detailed survey of pectoral fin musculoskeletal structure in fishes that use labriform propulsion as the primary mode of swimming over a wide range of speeds. Pectoral fin morphological diversity was surveyed in 12 species that are primarily pectoral swimmers, including members of all labroid families (Labridae, Scaridae, Cichlidae, Pomacentridae, and Embiotocidae) and five additional coral reef fish families. The anatomy of the pectoral fin musculature is described, including muscle origins, insertions, tendons, and muscle masses. Skeletal structures are also described, including fin shape, fin ray morphology, and the structure of the radials and pectoral girdle. Three novel muscle subdivisions, including subdivisions of the abductor superficialis, abductor profundus, and adductor medialis were discovered and are described here. Specific functional roles in fin control are proposed for each of the novel muscle subdivisions. Pectoral muscle masses show broad variation among species, particularly in the adductor profundus, abductor profundus, arrector dorsalis, and abductor superficialis. A previously undescribed system of intraradial ligaments was also discovered in all taxa studied. The morphology of these ligaments and functional ramifications of variation in this connective tissue system are described. Musculoskeletal patterns are interpreted in light of recent analyses of fin behavior and motor control during labriform swimming. Labriform propulsion has apparently evolved independently multiple times in coral reef fishes, providing an excellent system in which to study the evolution of pectoral fin propulsion.

Locomotion in sturgeon: function of the pectoral fins.

Pectoral fins are one of the major features of locomotor design in ray-finned fishes and exhibit a well-documented phylogenetic transition from basal to derived clades. In percomorph fishes, the pectoral fins are often used to generate propulsive force via oscillatory movements, and pectoral fin propulsion in this relatively derived clade has been analyzed extensively. However, in the plesiomorphic pectoral fin condition, exemplified by sturgeon, pectoral fins extend laterally from the body in a generally horizontal orientation, have been assumed to generate lift to balance lift forces and moments produced by the heterocercal tail, and are not oscillated to generate propulsive force. The proposal that pectoral fins in fishes such as sturgeon generate lift during horizontal locomotion has never been tested experimentally in freely swimming fishes. In this paper, we examine the function of pectoral fins in sturgeon swimming at speeds from 0.5-3.0 L s(-)(1), where L is total body length. Sturgeon were studied during steady horizontal locomotion as well as while sinking and rising in the water column. Pectoral fin function was quantified using three-dimensional kinematics to measure the orientation of the fin surface, digital particle image velocimetry (DPIV) was used to describe flow in the wake of the fin and to estimate force exerted on the water, and electromyography was used to assess pectoral fin muscle function. Sturgeon (size range 25-32 cm total length) swam horizontally using continuous undulations of the body with a positive body angle that decreased from a mean of 20 degrees at 0.5 L s(-)(1) to 0 degrees at 3.0 L s(-)(1). Both the angle of the body and the pectoral fin surface angle changed significantly when sturgeon moved vertically in the water column. Three-dimensional kinematic analysis showed that during steady horizontal swimming the pectoral fins are oriented with a negative angle of attack predicted to generate no significant lift. This result was confirmed by DPIV analysis of the pectoral fin wake, which only revealed fin vortices, and hence force generation, during maneuvering. The orientation of the pectoral fins estimated by a two-dimensional analysis alone is greatly in error and may have contributed to previous suggestions that the pectoral fins are oriented to generate lift. Combined electromyographic and kinematic data showed that the posterior half of the pectoral fin is actively moved as a flap to reorient the head and body to initiate rising and sinking movements. A new force balance for swimming sturgeon is proposed for steady swimming and vertical maneuvering. During steady locomotion, the pectoral fins generate no lift and the positive body angle to the flow is used both to generate lift and to balance moments around the center of mass. To initiate rising or sinking, the posterior portion of the pectoral fins is actively moved ventrally or dorsally, respectively, initiating a starting vortex that, in turn, induces a pitching moment reorienting the body in the flow. Adjustments to body angle initiated by the pectoral fins serve as the primary means by which moments are balanced.

Motor patterns of labriform locomotion: kinematic and electromyographic analysis of pectoral fin swimming in the labrid fish Gomphosus varius

Labriform locomotion is a widespread swimming mechanism in fishes during which propulsive forces are generated by oscillating the pectoral fins. We examined the activity of the six major muscles that power the pectoral fin of the bird wrasse Gomphosus varius (Labridae: Perciformes). The muscles studied included the fin abductors (arrector ventralis, abductor superficialis and abductor profundus) and the fin adductors (arrector dorsalis, adductor superficialis and adductor profundus). Our goals were to determine the pattern of muscle activity that drives the fins in abduction and adduction cycles during pectoral fin locomotion, to examine changes in the timing and amplitude of electromyographic (EMG) patterns with increases in swimming speed and to correlate EMG patterns with the kinematics of pectoral fin propulsion. EMG data were recorded from three individuals over a range of swimming speeds from 15 to 70 cm s-1 (1­4.8 TL s-1, where TL is total body length). The basic motor pattern of pectoral propulsion is alternating activity of the antagonist abductor and adductor groups. The downstroke is characterized by activity of the arrector ventralis muscle before the other abductors, whereas the upstroke involves nearly synchronous activity of the three adductors. Most EMG variables (duration, onset time, amplitude and integrated area) showed significant correlations with swimming speeds. However, the timing and duration of muscle activity are relatively constant across speeds when expressed as a fraction of the stride period, which decreases with increased velocity. Synchronous recordings of kinematic data (maximal abduction and adduction) with EMG data revealed that activity in the abductors began after maximal adduction and that activity in the adductors began nearly synchronously with maximal abduction. Thus, the pectoral fin mechanism of G. varius is activated by positive work from both abductor and adductor muscle groups over most of the range of swimming speeds. The adductors produce some negative work only at the highest swimming velocities. We combine information from pectoral fin morphology, swimming kinematics and motor patterns to interpret the musculoskeletal mechanism of pectoral propulsion in labrid fishes.

Kinematic and electromyographic analysis of steady pectoral fin swimming in the surfperches

The musculoskeletal mechanism of pectoral fin propulsion was investigated in representatives of the two subfamilies of the Embiotocidae (surfperches). Kinematic and electromyographic records of steady swimming by the open-water cruiser Amphistichus rhodoterus and the benthic maneuverer Embiotoca lateralis were compared at 80 % of the species' respective pectoral­caudal gait transition speeds. Synchronized records of fin movement and the intensity of pectoral muscle activity allowed previous hypotheses of muscle function, based on anatomical lines of action, to be tested. Divisions of the pectoral musculature inserting on the central and trailing- edge fin rays serve simple functions of abduction and adduction. Muscles controlling the fin's leading edge, by contrast, play more complex roles during the fin stroke, including deceleration of the fin at the downstroke­upstroke transition and rotation of the adducted fin during the non-propulsive period between fin beats. In spite of their phylogenetic and ecological divergence, the surfperches exhibit a number of mechanistic similarities which probably characterize the family. The timings of kinematic events and the maximal excursions of the fin tip, as well as the temporal order of muscle activation and the time to peak activity, are largely conserved. The predominant dorsoventral component of fin movement during the stride is consistent with a lift-based mechanism of propulsion. E. lateralis exhibits a greater anteroposterior range of motion and a more continuous period of fine motor control of the fin than A. rhodoterus, differences which may correspond to the species' respective capacities for maneuvering. Mechanistic variation in the family is associated with rather minor structural differences (in fin shape and fin base orientation). Owing to the similar functional demands placed on the pectoral fins of many fishes, it is probable that the mechanistic details of embiotociform swimming are widely distributed within the Perciformes.

Pectoral Fin Locomotion in Fishes: Testing Drag-based Models Using Three-dimensional Kinematics

Paired fin propulsion in fishes has classically been divided into two categories which represent biomechanical extremes in the use of appendages for propulsion: lift-based and drag-based mechanisms of thrust production. Theoretical models predict that fishes using drag-based propulsion should have wedge-shaped fins with relatively blunt distal edges, a fin beat cycle that is oriented along the anteroposterior (x) axis, feathering of the fin to reduce drag during the protraction phase, and maximal fin area during the retraction phase as the fin sweeps posteriorly perpendicular to the body. In this paper we use a three-dimensional analysis of pectoral fin propulsion in the largemouth bass, Micropterus salmoides , to (1) evaluate the extent to which bass pectoral fin kinematics fit predictions of drag-based propulsion, and (2)demonstrate the complexity of fin movement when the traditional two-dimensional analysis is extended into three dimensions. We attached small markers to visualize the diaphanous distal fin edge, and we videotaped lateral and ventral views from which we could measure x, y, and z coordinates from the fin and body. We divided the fin into two triangular elements for which we calculated planar (three-dimensional) angles relative to each of three reference planes (XY, YZ and XZ) during the fin beat cycle. We show how angles of attack based only on two-dimensional data may result in gross errors that severely compromise understanding of the mechanics and hydrodynamics of pectoral propulsion. Furthermore, three-dimensional analysis revealed that bass fin kinematics are much more complex than expected on a rowing model of drag-based propulsion, and that the pectoral fins may produce drag-based thrust even during protraction. Three dimensional kinematic data are critical to understanding the hydrodynamics of aquatic animal propulsion. Such data are a necessary foundation for reconstructing patterns of movement, modeling (both theoretical and empirical), and for assessing the extent to which motion is under active control or a passive consequence of fluid resistance.