Modeling and propulsion methods of underwater snake robots

Multi-fin kinematics and hydrodynamics in pufferfish steady swimming

Full-link trajectory tracking control for underwater snake robot with vector thrusters in the presence of strong time-varying disturbances

A key evolutionary transformation of the locomotor system of ray-finned fishes is the morphological elaboration of the dorsal fin. Within Teleostei, the dorsal fin primitively is a single midline structure supported by soft, flexible fin rays. In its derived condition, the fin is made up of two anatomically distinct portions: an anterior section supported by spines, and a posterior section that is soft-rayed. We have a very limited understanding of the functional significance of this evolutionary variation in dorsal fin design. To initiate empirical hydrodynamic study of dorsal fin function in teleost fishes, we analyzed the wake created by the soft dorsal fin of bluegill sunfish (Lepomis macrochirus) during both steady swimming and unsteady turning maneuvers. Digital particle image velocimetry was used to visualize wake structures and to calculate in vivo locomotor forces. Study of the vortices generated simultaneously by the soft dorsal and caudal fins during locomotion allowed experimental characterization of median-fin wake interactions. During high-speed swimming (i.e. above the gait transition from pectoral- to median-fin locomotion), the soft dorsal fin undergoes regular oscillatory motion which, in comparison with analogous movement by the tail, is phase-advanced (by 30% of the cycle period) and of lower sweep amplitude (by 1.0 cm). Undulations of the soft dorsal fin during steady swimming at 1.1 bodylength s(-1) generate a reverse von Kármán vortex street wake that contributes 12% of total thrust. During low-speed turns, the soft dorsal fin produces discrete pairs of counterrotating vortices with a central region of high-velocity jet flow. This vortex wake, generated in the latter stage of the turn and posterior to the center of mass of the body, counteracts torque generated earlier in the turn by the anteriorly positioned pectoral fins and thereby corrects the heading of the fish as it begins to translate forward away from the turning stimulus. One-third of the laterally directed fluid force measured during turning is developed by the soft dorsal fin. For steady swimming, we present empirical evidence that vortex structures generated by the soft dorsal fin upstream can constructively interact with those produced by the caudal fin downstream. Reinforcement of circulation around the tail through interception of the dorsal fin's vortices is proposed as a mechanism for augmenting wake energy and enhancing thrust. Swimming in fishes involves the partitioning of locomotor force among several independent fin systems. Coordinated use of the pectoral fins, caudal fin and soft dorsal fin to increase wake momentum, as documented for L. macrochirus, highlights the ability of teleost fishes to employ multiple propulsors simultaneously for controlling complex swimming behaviors.

Relationships of mercury concentrations across tissue types, muscle regions and fins for two shark species

Automatic alignment of underwater snake robots operating in wakes of bluff bodies

This study aims to characterize the charcoal from the fins waste of the Kerandang fish, namely from the dorsal (DF), pectoral (PF), ventral (VF), anal (AF), and caudal fin (CF). The charcoal as a source of hydroxyapatite. Qualitative characterization used a Scanning Electron Microscope (SEM), Fourier Transfer Infra-Red (FTIR), and X-Ray Diffraction (XRD). The charcoal’s chemical composition consists of Carbon, Oxygen, Sodium, Magnesium, Phosphor, Sulfur, and Chlorine, Potassium, and Calcium. The highest carbon element was 67.74% in the caudal fins. The lowest chemical element in the element sulfur is 0.197% in the dorsal fins. SEM photos show that the charcoal from the caudal fins has more pores than the other fins. The FTIR results show that the functional groups contained in the charcoal from the fins are NH, OH, CO, C=O, C=C, S1-O, and CH groups, with wave numbers 1032-1036 cm−1. The absorption area of the S1-O group (silica), where the silica group from charcoal, has the highest intensity. XRD results showed that the charcoal from fish fins of Kerandang contained 100% hydroxyapatite.

Environmental Context. Surveys to assess the body burden of mercury in fish to support research or contamination advisory programs typically involve capturing and killing fish and analyzing muscle tissue for mercury. Lethal sampling may not be feasible in protected waters or in studies involving threatened or endangered species. We analyzed tail fin samples of two fish species for total mercury and compared results with muscle-tissue mercury and concluded that fin-Hg can be used as a predictor of muscle-Hg. This approach enables catch and release studies for mercury in fish. Abstract. The caudal (tail) fins from 17 walleye (Sander vitreus) and 12 northern pike (Esox lucius) from three northern Arizona lakes (Long Lake, Soldier Lake, and Upper Lake Mary) were analyzed for total-Hg by combustion–atomic absorption spectrometry. Results indicate that the fin contains measurable Hg that correlates with muscle-Hg concentrations. As the body burden of Hg increased, the concentration in the fin increased relative to the muscle. Mercury concentrations also increased with fish length and weight, although the relationship was lake- and species-dependent. Fish from Soldier Lake had the most efficient uptake of Hg, likely due to the trophic structure of the lake or the condition of the fish, but possibly due to an acute source of Hg. Overall, this study demonstrates that caudal fin clippings can be used as a non-lethal predictor of muscle-Hg concentrations, which can reduce the number of fish killed in routine monitoring programs.

Snake Robots (SR) have been successfully deployed and proved to attain bio-inspired solutions owing to its capability to move in harsh environments, a characteristic not found in other kinds of robots (like wheeled or legged robots). Underwater Snake Robots (USR) establish a bioinspired solution in the domain of underwater robotics. It is a key challenge to increase the motion efficiency in underwater robots, with respect to forwarding speed, by enhancing the locomotion method. At the same time, energy efficiency is also considered as a crucial issue for long-term automation of the systems. In this aspect, the current research paper concentrates on the design of effectual Locomotion of Bioinspired Underwater Snake Robots using Metaheuristic Algorithm (LBIUSR-MA). The proposed LBIUSR-MA technique derives a bi-objective optimization problem to maximize the Forward Velocity (FV) and minimize the Average Power Consumption (APC). LBIUSR-MA technique involves the design of Manta Ray Foraging Optimization (MRFO) technique and derives two objective functions to resolve the optimization issue. In addition to these, effective weighted sum technique is also used for the integration of two objective functions. Moreover, the objective functions are required to be assessed for varying gait variables so as to inspect the performance of locomotion. A detailed set of simulation analyses was conducted and the experimental results demonstrate that the developed LBIUSR-MA method achieved a low Average Power Consumption (APC) value of 80. under δ value of 50. The proposed model accomplished the minimum PAC and maximum FV of USR in an effective manner.

The objective of this study was to taxonomically revise the 41 nominal species found within the Brachirus species complex (Order Pleuronectiformes; Family Soleidae). This complex is recognizable by a combination of characters: the structure of the supracranial portion of the dorsal fin which lack pterigiophores with their proximal ends directly over the cranium, by the joined dorsal, anal and caudal fins, and by the anterior tip of the dorsal fin almost reaching the upper jaw. This revision is based on the morphological and meristic examination of 34 type and 717 non-type specimens for all available nominal species. The type material was examined for twenty species. The remaining species were assessed from the original type description. It was found that the Brachirus species complex is made up of four genera including 19 valid species: Brachirus (14), Achiroides (1), Dexillus (3), and Paradicula (1). Eight of the nominal species do not belong to the Brachirus species complex and have been removed from the scope of this study. Achiroides, characterized by the rudimentary pectoral fins, contains a single valid species, A. melanorhynchus (Bleeker 1851) and three synonyms (Synaptura aenea Smith 1931, Anisochirus harmandi Sauvage 1878, and Plagusia leucorhynchos Bleeker 1851). Dexillus , characterized by the close proximity of the eyes, contains three valid species: D. macrolepis (Bleeker 1858), D. megalepidoura (Fowler 1934), and D. muelleri (Steindachner 1879). D. muelleri is a senior synonym of the nominal species Synaptura arafurensis Gunther 1880. Paradicula, unique in having the gill openings restricted to the base of the pectoral fins, contains a single valid species, P. setifer Paradice & Whitley 1927. The remaining Brachirus species cannot yet be defined as being monophyletic. Brachirus contains 14 valid species: B. aspilos (Bleeker 1852) (synonyms: Synaptura heterolepis Bleeker 1856, S. marmorata Bleeker 1853, and S. sorsongonensis Evermann & Seale 1907), B. sundaicus (synonyms: Bleeker 1870--75) (Synaptura cinerea De Vis 1883 and S. nigra MacLeay,1880), B. selheimi (Macleay 1882) (synonyms: B. salinarum Ogilby 1910, and Synaptura villosus Weber 1907), B. foliacea (Gunther 1862) (synonym: Synaptura filamentosa Sauvage 1878), B. siamensis (Sauvage 1878) (synonyms: Synaptura krempfi Durand 1940 and Chabanaudetta smithi Joglekar 1971), B. breviceps Ogilby 1910, B. cinerascens (Gunther 1862), B. fitzroiensis (De Vis 1882), B. orientalis (Bloch & Schneider 1801), B. pan (Hamilton 1822), B. panoides (Bleeker 1851), B. dicholepis Peters 1877, B. swinhonis Steindachner 1867, and B. canus Gray 1854. An identification key of valid species belonging to the Brachirus species complex is provided.

Recent kinematic and hydrodynamic studies on fish median fins have shown that dorsal fins actively produce jets with large lateral forces. Because of the location of dorsal fins above the fish's rolling axis, these lateral forces, if unchecked, would cause fish to roll. In this paper we examine the hydrodynamics of trout anal fin function and hypothesize that anal fins, located below the fish's rolling axis, produce similar jets to the dorsal fin and help balance rolling torques during swimming. We simultaneously quantify the wake generated by dorsal and anal fins in brook trout by swimming fish in two horizontal light sheets filmed by two synchronized high speed cameras during steady swimming and manoeuvring. Six major conclusions emerge from these experiments. First, anal fins produce lateral jets to the same side as dorsal fins, confirming the hypothesis that anal fins produce fluid jets that balance those produced by dorsal fins. Second, in contrast to previous work on sunfish, neither dorsal nor anal fins produce significant thrust during steady swimming; flow leaves the dorsal and anal fins in the form of a shear layer that rolls up into vortices similar to those seen in steady swimming of eels. Third, dorsal and anal fin lateral jets are more coincident in time than would be predicted from simple kinematic expectations; shape, heave and pitch differences between fins, and incident flow conditions may account for the differences in timing of jet shedding. Fourth, relative force and torque magnitudes of the anal fin are larger than those of the dorsal fin; force differences may be due primarily to a larger span and a more squarely shaped trailing edge of the anal fin compared to the dorsal fin; torque differences are also strongly influenced by the location of each fin relative to the fish's centre of mass. Fifth, flow is actively modified by dorsal and anal fins resulting in complex flow patterns surrounding the caudal fin. The caudal fin does not encounter free-stream flow, but rather moves through incident flow greatly altered by the action of dorsal and anal fins. Sixth, trout anal fin function differs from dorsal fin function; although dorsal and anal fins appear to cooperate functionally, there are complex interactions between other fins and free stream perturbations that require independent dorsal and anal fin motion and torque production to maintain control of body position.

Locomotion in tetraodontiform fishes (puffers and relatives) involves the use of multiple fins for propulsion during swimming. A variety of tertraodontiform swimming modes have been defined, but the contributions of pectoral, dorsal, anal, and caudal fins to the propulsion in these fish remain largely unknown. We used video analysis to study swimming behaviour of the striped burrfish ( Chilomycterus schoepfi ). Burrfish swam in a flow tank at speeds of 0.5–6.3 standard body lengths per second, during which all fins oscillated at all speeds. The oscillation frequency range of all fins was 2.1–9.2 Hz, increasing with velocity. Pectoral fins were always out of phase, usually by 180 degrees (alternate left and right beats). Reduced frequency parameters for all fins were high (0.65–12.1) indicating that acceleration reaction is the dominant mechanism of thrust. Phase lag between anal and caudal fins assumed three distinct states which suggests that burrfishes alter the patterns of fin motion in discrete stages analogous to gaits. Rapid oscillation of five fins in various degrees of asynchrony is a mechanism to produce relatively constant thrust from multiple periodic motions.

In this paper, we present a joint controller for stabilizing a swimming gait for underwater snake robots. The controller is based on energy-shaping control, and it is shown to render the gait exponentially orbitally stable for a range of control parameters. In addition to shaping the energy of each joint oscillation, the phase differences between them are stabilized to a desired phase shift. The result is a set of synchronized, shifted oscillations, constituting the swimming gait. Furthermore, a simulation study is conducted, in which the proposed controller is found to exhibit significantly greater robustness to disturbances than an existing joint controller from the literature.

The ontogeny of the developmental stages of the hake Merluccius hubbsi is described. Fish larvae and post-transitional juveniles were collected in the Nor-Patagonian area from 1989 to 2004. The opening of the mouth and the pigmentation of the eyes are coincident with yolk resorption, finishing the yolk-sac stage. This species presents pigmentation on the head, trunk and tail typical of gadiform larvae. Pectoral fin development is completed during the transformation stage. The post-transitional juvenile stage begins when the fin-ray complements are complete and squamation begins. The fins become fully formed in the following sequence: pelvic fins, first dorsal fin, second dorsal and anal fins together, caudal fin and pectoral fins. The caudal complex is totally developed in larvae of 22.0-23.0 mm standard lengths (L(S)) and all vertebral elements are first observed in larvae of 8.5 mm L(S). The rate of development of M. hubbsi observed in this study could be faster than the rates reported for other species of Merluccius by different authors.

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.