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The application of tandem flapping foils propulsors to conventional aerial and underwater vehicles plays a most important role in the exploration of aerial and marine environments. The hydrodynamic study of fish schooling or birds flock when swimming/flying in fluid media and the application towards development of tandem flapping wing robots gaining more importance in the field of bioinspired vehicles. The advantages of tandem flapping wing configuration are improved thrust performance; maneuvering and less energy input as the downstream foils consumes less power compared to the single flapping foils. In thist study, the thrust of two flapping foils arranged in tandem mode subjected to pitching motion with different pitching amplitudes(A D ), Strouhal numbers (St D ), stream wise distance (S/c) and phase-lag ( $\varphi$ ) of foils are studied numerically using RANSE based CFD solver. This novel study mainly investigates the effects of Strouhal number and the dimensionless pitching amplitude on the thrust and efficiency of tandem foils. It is observed that the tandem foils generate higher efficiency at $\text{St}_{\mathrm{D}}=0.2$ and $\mathrm{A}_{\mathrm{D}}= 0.7$ . At this condition, the effects of stream wise distance and phase-lag of tandem foils are also investigated. When $\varphi$ is constant and S/c changes from 0.109 to 1, the efficiency of the upstream foil decreases and the efficiency of downstream foil increases. When S/c is constant and $\varphi$ changes from 0° to 180°, upstream foil efficiency increases and downstream foil efficiency decreases with increase in phase-lag. When $\varphi$ is 90°, total efficiency of the two foils gets the maximum value. In general, when S/c is 1 and $\varphi$ is 90°, the tandem flapping foils get the maximum propulsive efficiency. For achieving this condition, pitching amplitude, frequency and increased phase lag between the two foils plays a significant role compared to the stream wise distance(S/c) between the tandem foils.

The propulsive efficiency is one of the most important considerations for autonomous underwater vehicles (AUVs). Most efforts about improving efficiency of electric propeller focus on the optimal design of screw propeller and electric motor. However, these researches cannot ensure electric propeller operating in the most efficient way when the water flow velocity changes. Therefore, this paper proposes a maximum efficiency point tracker (MEPT) by analyzing the relationship of rotate speed, toque and efficiency for both screw propeller and electric motor under different water flow velocity values. The effectiveness of the proposed MEPT has been validated by simulation results with a simulated AUV electric propeller control system.

This work describes the architecture and evaluation of a turbo-electric distributed propulsion microgrid for ECO-150, a NASA funded 154 passenger subsonic fixed wing commercial transport aircraft concept for entry into service by 2035. Three different microgrid types are considered: ac synchronous distribution, dc distribution, and a hybrid approach. A high level architecture for each grid type is proposed, considering requirements for single point failure accommodation, redundancy and reconfigurability, and electrical protection. Component sizing models were developed for rotating electrical machines, power converters, distribution, and protection equipment, targeting a technology readiness level (TRL) of TRL-6 by 2025. These tools are combined to evaluate the mass and efficiency metrics for each microgrid type. Sensitivity sweeps on grid voltage and frequency were completed in order to determine optimal choices for both parameters. Results indicate that microgrid performance metrics are optimized for ECO-150 near 6 kilovolts (kV) and 1 kilohertz (kHz), with the dc and hybrid grids having a greater sensitivity to voltage than the ac grid. Advantages of the dc and hybrid grids include ability to provide powered yaw, and ability to incorporate energy storage. However, powered yaw control was investigated and determined to be less effective than a conventional tail on a per mass basis. After accounting for the mass of the associated thermal management system (TMS), the dc grid emerges as the lowest mass option above 3 kV, followed by the ac and the hybrid grid. However, ac grid achieves a transmission efficiency 2–3% higher than the dc grid, which will have system level effects on fuel burn, fuel weight, and overall propulsive efficiency. For near term practical implementation of turbo-electric distributed propulsion, the ac synchronous system should be considered seriously as a strong candidate.

Manta rays can achieve flexible movements underwater with high propulsive efficiency. Bionic manta ray robot has always been a hotspot in bio-robot research. In this paper, a novel bionic Manta Ray robot is proposed based on the synthetically biological observation of manta ray. Firstly, flexible mechanism and rigid support are integrated in the mechanical structure design of this robot and real flexible deformation of the pectoral fins can be well simulated. Secondly, central pattern generator (CPG) control approach is used to achieve the rhythmic biomimetic movement. Experiments with a demo prototype are conducted to validate the effectiveness and efficiency of proposed approaches.

The elliptical motion is proposed on a flapping hydrofoil for propulsion instead of the traditional two degrees of freedom motion, plunging/pitching motion. A synchronously periodic horizontal motion (surge) together with vertical motion (heave) and rotating motion (pitch) constitute the elliptical motion. A NACA0012 hydrofoil is placed in two-dimensional turbulent flow with the Reynolds number fixed at 40000. Two parameters are presented to describe different elliptical motions, the ratio of heaving amplitude and surging amplitude, the difference between surge and heave. The elliptical motion can significantly improve the thrust and propulsive efficiency compared with traditional motion. Besides, there exists an optimal parameter to get a maximum time-averaged thrust coefficient and efficiency. This study can provide a guidance for the engineering design of the motion trajectory on biomimetic underwater vehicles.

Flexible fins own outstanding advantages in robotic fish locomotion, especially in high propulsive efficiency. This paper proposes a mechanism for changing the moving direction of fish robots in two-dimensional planes using flexible pectoral fins. Firstly, a mathematical model of the fish robot equipped with non-uniform flexible pectoral fins is introduced. In this model, the influences of fluid inertia, and drag of the surrounding fluid exerting on the fin surface is considered as the Morison force. Based on the energetic method, the Assume Mode Method (AMM) and Rayleigh-Ritz method, the solution for the body motion and deformation of the points on the flexible fins is derived. Secondly, the mechanism for steering the direction of robot swimming motion is proposed. Due to the complex influence of lift forces which are generated by pectoral fins on the robot orientation, a fuzzy logic controller is designed to stabilize the angle trajectory of the fish robot. Finally, the numerical simulations, the movement performances, and the control effectiveness are illustrated.

The following paper presents the integration between the computational fluid dynamics (CFD) analysis of an oscillating foil and the design and fabrication of an ostraciiform swimming robot, a bio-inspired vehicle that consists of a rigid hull and an oscillating fin hinged to fore body through a revolute joint. Compared to other robotic fish, the aforementioned architecture has a lower propulsive efficiency but is capable of withstanding greater pressures with respect to other soft and piecewise-flexible propulsion systems. To generate the fin alternating motion a transmission mechanism based on a barrel cam was designed to replace the direct drive widely adopted in other biomimetic vehicles. In order to size the robot thruster and actuator, the forces acting on the oscillating fin were computed in Reynolds Averaged Navier-Stokes (RANS) equations implemented in a Discontinuous Galerkin (DG) solver. The numerical predictions were compared to analytic solutions provided in literature and the resulting model was then adopted to design an ostraciiform swimming robot and its navigation, guidance and control system. This vehicle will serve, in future work, as a test bench to validate the author's conclusions.

Propulsive performance of harmonically heaving and pitching foil is degraded by a breakdown in the angle of attack profile. In this paper, we build up a two-degree freedom harmonic motion in both heave and pitch motion as the baseline, and compare directly the performance obtained with specific angle of attack profiles and three-degree freedom harmonic motion. We set these profiles are: a square, a sawtooth wave and a cosine function. About three-degree freedom, we add a thrash motion on the base of two-degree freedom harmonic motion. The sawtooth angle of attack achieves the highest thrust coefficients over the other two cases of two-degree freedom motion. The three-degree freedom harmonic motion achieves a significant improve of thrust coefficients over other cases, but the efficiency is lower than the specific angle of attack profiles.

Bio-inspiration can lead to a significant improvement in propulsive efficiency and maneuverability of Autonomous Underwater Vehicles employed in large areas exploration. As a matter of fact, fish swimming capabilities are still far superior to what has been achieved by the modern nautical technology. In order to exploit the propulsive principles of fish swimming, a novel mechanism has been designed and prototyped to drive the thrust-generating caudal fin of the biomimetic underwater robot manufactured by the authors.

The corrosion of grids in ion thrusters due to unsymmetrical leaks and beam dissipation which tends to decrease lifetime of thruster. Usage of cathode neutralizers have shown to decrease corrosion and effect the thrust vector of main electron beam. The existing neutralizer configurations reduce backfiring rate of flow to a minimal level, which has in turn limited the usage and lifetime of thrusters. Present work addresses the issue of this cathodic flow to effectively neutralize the beam by placing multiple cathodes radially and optimize design conditions to produce maximum propulsive efficiency and control the flow of cathodic ions which shouldn't cross main beam threshold. Changes in propulsive efficiency and thrust have been calculated which show an effective increase of 20%–25% and thrust increase of 36%, depending on number of probes, along with maintenance of effective mixing and neutralizing.

The sole means for conventional multirotor UAVs to achieve horizontal translation motion is by inducing changes in vehicle attitude. The lack of horizontal force control not only disallows full controllability in all 6 Degrees of Freedom (DoFs), but also limits the set of possible control solutions. One way of achieving horizontal force control is by mounting the rotors of a UAV under a fixed amount of tilt. Although this type of UAVs has been the topic of research in the past, there is still ample ground to cover in this area. Therefore, in this paper the maneuverability of a fully-actuated hexarotor is assessed. It is seen how a change in rotor tilt affects vehicle maneuverability and how propulsive efficiency is affected at the extremes. Furthermore, it is investigated what implications these results have for the high-level design process. Finally, it is seen how maneuverability is affected if one of the motors fails.

The development of multiple generations of robotic flapping pectoral fins has warranted a closer study of the relative thrusts and efficiencies exhibited by these fins. This paper describes the differences between the various fins - including stroke frequency, stroke amplitude, aspect ratio, and effective angle of attack - and investigates the effects these differences have on thrust generation and propulsive efficiency. Drawing from and building on previous fin results, both computational fluid dynamics (CFD) simulation results and experimental data are used to evaluate the thrust, power draw, and efficiency, and to find useful relationships between these values and parameters such as Strouhal number and advance ratio. This analysis has implication for future fin design and development of reduced order models for flapping propulsion mechanisms.

Robotic fish are widely studied for their high propulsive efficiency, maneuverability, speed, acceleration and stealth. Compared to the measurement of the speed and acceleration of robotic fish, the propulsion can hardly be detected because of the micro-force and the movement. In this paper, we designed a micro-force measuring apparatus consisting of a micro-force sensor and a fixing device for robotic fish. The sensor has an accuracy of 0.1mN and can transform the force to electronic signal which is convenience to measure. The designed fixing device can limit the lateral movements of robotic fish but have non drag force in the forward swimming direction. Through this apparatus we first measured different propelling models and then compared the propulsion of robotic fish with different shape and stiffness of caudal fins. Robotic fish designed with soft caudal fin can generate maximum propulsion when undulation in the carangiform model.

In this paper an attempt has been made for the conceptual design of an automatic fluid level controller for cryogenic tank lucratively for aerospace applications. An ideal design technique of the low temperature multi-phase fluid level control system for estimating the boil-off rate and/or the flow rate to facilitating the estimation of the total quantity of effective fluid available for completing the mission based on the use of microcontroller has been presented. The proposed control system model is mainly composed of microcontroller, level sensor, temperature sensors, pump and relay. This system could estimate the actual fluid volume of the low temperature cryogenic fluid for the evaluation of the effective propulsive efficiency of the entire aerospace vehicle. The preliminary sea level test results, using water as the base fluid, show that the system model being proposed is able to monitor the liquid level very effectively and accurately for estimating the total volume of the fuel and oxidiser for estimating the operating time of the aerospace vehicle lucratively.

A significant challenging task is to quantify the locomotor forces experienced by swimming animal because direct measurement of forces applied to the aquatic medium are not so feasible. It is advantageous to study the mechanics of animal locomotion for both engineers and biologists. An engineer can analyze motion and use in robotics field that approach also inform biologist to measure different parameters (e.g. muscle forces). Frogs are known as good swimmers and also webbed feet of frog help to swim efficiently in water. Living frogs propel in water by coordinated motion of their hindlimbs, achieving good propulsive efficiency and maneuverability. In this paper, a co-simulation technique to study the swimming locomotion of frogs is presented. Morphological data is collected from the living frog and used for developing the dynamic model. In this model, the body of the frog is modeled as ellipsoid and webbed feet are modeled as rigid flat trapezoidal plates to resemble the living frog. The dynamic behaviour of the swimming frog is simulated with multi-body dynamic co-simulation technique utilizing MSC ADAMS and Matlab/SIMULINK softwares. MSC ADAMS software is used to simulate the dynamics of the mechanical model whereas Matlab/SIMULINK is used to calculate the propulsive forces (drag force & added mass force) utilizing the kinematic information obtained from MSC ADAMS and mathematical models based on blade element theory. Different forces acting on the swimming frog are calculated and presented here.

Adapting to the complex environment is significant for field robots. The field robots equipped with elliptic-curve legs which combine the advantages of legs and wheels, have achieved a good locomotion performance in terrain, while the leg-terrain dynamics has not been explored intensely, especially elliptic-curve legs passing through the soft substrate, such as muddy terrain. In this paper, an experimental platform for locomotion performances of elliptic-curve legs in muddy terrain is designed. With the platform, locomotion parameters of the elliptic-curve legs including forward speed, propulsion force, and torque output can be recorded and analyzed. The influences from the shapes of legs and the water content of muddy substrates are studied. The results indicate that the propulsive efficiency is higher when reducing the rotating speed of elliptic-curve legs in a higher water content substrate, and there are an optimal rotating speed for certain shapes of the legs to achieve a higher forward speed, which is meaningful for the mechanical design and the control of the field robots.

This study examines the propulsive efficiency of underwater vehicles which are driven by unsteady propulsors. The analysis is focused on vehicles utilizing a novel thruster which expels finite propulsive jets periodically. This analysis also applies to swimming squid and jellyfish (from which the thruster was inspired), and can be extended to any periodic unsteady propulsion. The vehicle trajectory is solved analytically to calculate the exact work output/input and it is observed that with unbounded forcing there is an optimal thruster duty cycle, λ = 0.31, which maximizes propulsive efficiency. This optimal duty cycle is very close to the actual jetting duty cycle observed in steadily swimming squid.

This paper examines a new type of thruster which, similar to squid and jellyfish, generates propulsive forces by cyclically ingesting and expelling jets of water. The thrust output of this device depends greatly on the nature of the expelled jet, with greater output occurring for jets which form a single coherent vortex ring rather than a vortex ring with a trailing wake. The average thrust output as well as the jetting efficiency are maximized with respect to the thruster's nozzle diameter and jet velocity program. The appropriate constraints of the problem are defined including a dynamic constraint to ensure that the propulsive jet forms a single vortex ring. It is shown that the average thrust output under these constraints reaches a maximum when the nozzle radius is set to a critical value, and that using an orifice nozzle decreases propulsive efficiency at low Reynolds numbers.

We report on the development of a single-propellant ElectroSpray (ES) microthruster able to: (a) cover a wide range of specific impulse (I sp ) and thrust at high propulsion efficiency, and (b) provide macroscopic thrust via micro-fabricated emitter arrays. The electrospray is a mature technology for the emission of fast nanodroplets at a propulsive efficiency larger than 50% over the full I sp range. The size of the droplets depends on the propellant flow rate and the physical properties of the electrolyte, especially the electric conductivity. To achieve a useful thrust one needs to multiplex the ES by operating many in parallel, which we achieve via silicon microfabrication of arrays of multiple and identical nozzles. The Multiplexed Electrospray (MES) micro-thruster is composed mainly of two electrodes: a nozzle-array and an extractor electrode, between which the electric field needed to form the ES is established. We tested nozzle arrays with up to 37 capillaries, that are spaced 1mm apart, with ID/OD = 10/30µm. The capillaries are filled with 2.01µm silicon dioxide beads to increase the hydraulic impedance and ensure uniform flow rate through the different emitters. A third electrode (accelerator) is mounted downstream the extractor to accelerate the droplets, thereby increasing the microthruster performance. The system is packaged in an alumina casing for electrical insulation and propellant feed. Tests run in a vacuum chamber at a pressure ≤10−5 mbar demonstrated reliable operation for several hours with a relatively high beam energy of 7.56kV. The 37-nozzle MES device was tested with the ionic liquid ethylammonium nitrate (EAN), at estimated total flow rates between 1.2 and 14 µL/h, emitted currents between 14.2 and 23.0 µA, specific impulse ranging between 710 and 1930s, and thrust ranging between 7.5 and 33 µN. EAN is well suited to cover a relatively broad range of charge/mass at an average propulsion efficiency of 66%. With further scale-up to a 600-MES system, the device would be suitable for micro-satellites missions such as attitude control and station keeping.

Research shows that flexible pectoral fins can significantly improve the propulsive efficiency of the robotic fish. First, the paper introduces the study on the flexibility to promote the performance impact. Secondly, the chordwise flexible deformation model according to the movement characteristics of oscillating fins of cownose rays is built and the experimental platform of the oscillating fins for testing the flexible deformation effect is set up, and then the rectangular oscillating fins with aspect ratio AR = 2 is designed. Finally, the movement and deformation, thrust, input power and efficiency parameters of oscillating fins were measured through calculations and experiments, and the impact of the chordwise flexibility on the oscillating propulsion with different movement parameters is determined. The results can be used to determine the chordwise flexibility in designing the oscillating pectoral foils of robotic fish.

The propulsive efficiency is the key issue related to the practical application of the robotic fish. The negative work of the muscle of the biological fish reveals the efficient propulsion mechanism of swimming. In this paper, a distributed control system is presented for the robotic fish in an experiment platform. In order to study the relationship among the parameters, the negative work and the propulsive efficiency, this system can real time control each joint of the robotics fish and feedback the information. So the system is composed of three parts: the master-slave controller, the network and the driver of the joint motor. FPGA is chosen to accomplish the motor control and the data transition. Also the network based on LVDS has a high transfer rate to guarantee real-time and reliability of the system operation.

This paper describes the modeling, design, experimental testing and optimization of a flapping foil for use as an aquatic propulsive device on a robot capable of aerial and aquatic modes of locomotion. Motivation for the research stems from numerous avian species which use the same flapping mechanism as a means of propulsion in both mediums. The main aim of this research is to establish the optimal kinematic parameters during aquatic operations that maximise non-dimensionalised performance measures, such as propulsive efficiency. Optimization of said parameters enables the direct comparison between outstretched and retracted wing morphologies and permits scaling for future robotic vehicles. Static foils representing the wing in both an extended and retracted orientation have been manufactured and tested over a range of kinematics. The gathered results enable validation of previously developed numerical models as well as quantifying achievable performance measures. This research focuses on the mechanical propulsive efficiencies and thrust coefficients as key performance measures whilst simultaneously considering the required mechanical input torques and the associated thrust produced.

This paper investigates the hydrodynamic performance of flapping caudal fin by means of numerical simulation. Dynamic simulations of caudal fin with heaving and pitching motion are conducted to determine the relationship between the maximum angle of attack and difference of phase angle in terms of thrust coefficient and propulsive efficiency under low frequency. Combing 20°∼30°maximum angle of attack with 70°∼90°difference of phase angle, outstanding propulsive efficiency can be obtained. In addition, qualitative analyses are made to the wake vortex spacing. This study shows that wake spacing has interaction with the thrust coefficient and the propulsive efficiency.

This paper presents results detailing the performance of a flexible wing for use on a vehicle capable of both aerial and aquatic modes of locomotion, with primary focus on the aquatic substrate. The motivation for the research stems from the ability of avian species within the natural world demonstrating this multi-modal capability, utilsing a flapping mechanism as a means of propulsive generation. The fundamental aim is to capture the beneficial traits of a flexible wing and quantify any potential improvements in performance. We present a simplified numerical model which acts as an initial design tool prior to the fabrication of a flexible wing. This model aids in wing geometry selection so that under key kinematic parameters the wing passively deforms during aquatic operations in a beneficial manner, in an attempt to increase the maximum lift coefficient of the foil. Using the model we have fabricated a flexible wing and experimentally evaluated its performance in a range of tests, varying kinematic parameters relating to the flapping motion and forward velocities and compared this with a rigid wing model to investigate if the passive chord-wise flexibility leads to an increase in propulsive efficiency. We present the initial data set making this comparison, showing that the flexible wing was found to exhibit higher propulsive efficiencies at specific kinematic parameter sets. This modeling and experimental study will provide a foundation for the design of future vehicles capable of swimming and aerial locomotion, and help quantify the benefits of passively compliant structures in flapping wing propulsion.

This article describes the initial design of a biomimetic cuttlefish robot. The robot has a similar streamlined shape as cuttlefish, propelled by the complex of the biomimetic undulatory level pectoral fin and the water-jetting. Firstly, the morphology and swimming theory of cuttlefish is analyzed. Secondly, the overall structure of the biomimetic cuttlefish robot is designed and the three-dimensional model is simulated by software FLUENT. Finally, the biomimetic level pectoral fin and the biomimetic mantle actuated by SMA wires are designed. The propulsive thrust and the propulsive efficiency are analyzed. The results show that the robot has good hydrodynamic performance, can achieve slow swimming speed with high efficiency by the level pectoral fin. When the swimming speed is 0.18 m/s, the propulsive fore is 0.047 N, the propulsive efficiency is 89 %. It can also achieve high swimming speed relying on jetting propulsion. The maximum propulsive force is 0.79 N and the maximum swimming speed is above 0.6 m/s, the propulsive efficiency is 31 %.

The SQX-500 AUV is currently under joint development by Marport Canada Inc, the Institute for Ocean Technology of the National Research Council Canada, and Memorial University of Newfoundland. With a twin-hull design, and a novel propulsion and control system, the SQX-500 provided several unique challenges during the design and development process. In order to characterize the hydrodynamic performance of this vehicle for various operating conditions, a complete set of hydrodynamic experiments was carried out. These experiments included 0.88 scale model tow tank testing, full scale testing of a custom propeller, passive stability verification, and several tests to characterize the vehicle propulsion system. Together these experiments determine the overall propulsive efficiency of the vehicle under various operating conditions. In addition, analysis of the results from these experiments was used to determine which tests should be performed on future vehicle designs., Autonomous Underwater Vehicle (AUV) 2010 Conference, 1-3 September 2010, Monterey, CA, USA

This paper described our work in probing into fish robot with pectoral fin propulsion. The aim of this project is to develop a robot fish mimicking cownose ray that swims with flexible pectoral fins in oscillation motion. According to the analysis of cownose ray'motion, a novel robot fish prototype propelled by pectoral fins was designed, The effect of flapping parameters (frequency and amplitude) and flexibility of fins on the propulsive performance was studied through a series of experiments underwater. Experiments showed that the velocity was almost in linear relationship with flapping frequency and amplitude below 2.0Hz, and the propulsive efficiency without chord-wise or span-wise ribs is higher than that with ribs. The conclusion is deduced that if the flexibility was selected properly, the pectoral fins with flapping mode would be an efficient propulsion mode for underwater vehicles.

Water-jet propulsion system is widely used to high speed marine vessels by virtue of high propulsive efficiency, good maneuverability, and less vibration. The flow through the water-jet inlet will be analysed in more detail. In order to validate the computational method the CFD results are compared with experimental data for a model scale water-jet inlet duct. During the validation process, the effects of the confinement of the flow due to the cavitation tunnel walls are also addressed. The CFD results can be used to visualise the flow behaviour in more detail.

This paper investigates the three dimensional hydrodynamics of a fishlike robot swimming in the straight forward way under self-propulsion. The unsteady flow fields associated with swimming robot is computed by using Navier-Stokes equation. Both the user defined function and dynamic mesh technique are applied to track the robot motion. The results show that the mean magnitudes of net thrust force and net lift force approach to zero for one cycle. The variation trends of thrust force, swimming power and propulsive efficiency over time are in sine function. The computed flow fields clearly reveal the evolution of two pairs of pressure cores traveling along the robot as it swims. A positive pressure gradient around the tail is in competition with negative pressure gradient in the head; thrust forces is produced when the positive pressure gradient dominate the negative one. The findings help reveal the propulsive mechanism of the fishlike robot propulsion and benefit the fishlike robot design.

This paper presents the design of an Autonomous Surface Vehicle (ASV) used for marine environment monitoring or hydrologic survey. A catamaran is used to improve stability against waves, and the shape of high-speed ship is exploited to reduce the resistance. The characteristics of resistance, electric motor and propeller are optimally matched, so that the battery power is saved and the endurance is improved. By using wireless local loop based on IP, the reliability of remotely operated system is increased and distance of effective communication is extended. All the compartmentalized cabins are modularized and configured with universal data interfaces to facilitate connecting various instruments. Tests on near sea show that the ASV can do both fixed-spot observation as a moored buoy and cruise observation as a survey vessel. In addition, it can reach shallow areas where a survey vessel cannot access. Therefore, it can be widely used on water surface of river, lake and ocean for environment monitoring, survey and exploration.

In this paper, a robotic fish which has a novel fin structure conceived and designed to be as a propulsor is proposed. The ultimate goal of this project is to provide an insight into the methodology of designing and controlling a propulsion system underwater, which is employed at low speeds, offering greater maneuverability, better propulsive efficiency. The whole process of design, construction and control of a prototype is presented; the experiments are performed to study performances of the fin and to verify the feasibility for further development as an alternative propulsion method for underwater vehicles.

This paper reveals a new phenomenon of the body side-sway for rigid robot fish and proposes three effective restraining methods. The body side-sway problem is produced by the lateral component of hydrodynamic force and inertial force, while influenced by mass distribution of fish body and oscillating rules of caudal fin. Considering the body side-sway, a virtual prototype for two-joint robot fish, which is the simplified form of multi-joint robot fish, is established in MSC-ADAMSreg to conduct the simulation. Simulation results indicate that the body side-sway can reduce the amplitude of tail peduncle and change the attack angle of caudal fin, and then affect the thrust and the propulsive efficiency. To inhibit the harmful body side-sway which also contributes to the energy loss, we last summarize three restraining methods: attaching dorsal fin and pelvic fin, using the vibration absorber and building two parallel tail mechanisms.

This paper proposes a new way for improving the swimming efficiency of fishlike robots. The approach is based on the observation of natural fishes whose muscle tendons play the role of ldquobiological springsrdquo. These springs allow the fish to recover a part of the energy usually lost (by dissipation in the actuators). Mechanically, this energy is produced by the negative work of inertial forces. This principle is here applied to the swim through a spring located between the body and the tail of the robot. More than qualitatively exploring this way, the article proposes a computation of the ldquooptimal valuerdquo of the spring stiffness based on the use of a simple efficiency criterion. The results deduced from this study are physically interpreted, and applied through first simulations, where the propulsive efficiency is improved of 12%.

Bionic undulating fin is a new bionic underwater propulsor based on propulsive mode of undulating fin which has high propulsive efficiency, maneuverability and stability. The structure and locomotive model of the bionic undulating fin system were analyzed, and a control system which fits several undulating modes was put forward in this paper. Locomotion simulation was done based on the Matlab/Simulink model. Results indicate that the control system can response to multiple undulating modes and locomotive parameters accurately, thus gets the desired waves.

We present experimental data elucidating the effects of hydrodynamic coupling on the propulsive efficiency of an array of three oscillating hydrofoils. We simulate this system using an inviscid flow model; this model duplicates certain key features of our experimental data but fails to consider the effects of wake vortex generation and interaction. We present a qualitative model for the role played by wake vortex dynamics in the cooperative locomotion of fish schools, and derive a mathematical model in the form of a nonlinear control system describing the interaction of a single deformable body with a single nearby vortex. We present simulations based on the latter to illustrate the capture of vortices shed from one fish in a school by a second, trailing fish; vortex capture in this sense is the control problem central to cooperative swimming.

This paper presents a three-dimensional, dynamic model of robotic fish which synthesizes both the carangiform and anguilliform swimming modes. The designed robotic fish is composed of three parts: stiff anterior body with a pair of pectoral fins for up-and-down motion, flexible rear body, and an oscillating lunate caudal fin. We use unsteady flow theory to analyze the motion of the anterior part and the links, and adopt experimental result from oscillating foil for the caudal fin. So the dynamic equation of each part can be obtained, and by summing up these equations, the dynamic equation for total swimming robot can be derived. The desired propulsive characteristics including forward velocity, sway velocity, pitch velocity, three velocity of Eulerian angles of the stiff anterior body, motion trajectory as well as propulsive efficiency can then be obtained by solving ordinary differential equation. The circular motion, based on asymmetrical kinematics of flexible rear body, can be achieved by adding different deflections to the oscillatory links. Comparisons between simulation results and real experiments are then conducted and discussed. A good agreement on dynamic characteristics demonstrates the validity of the proposed model.

In this paper, we show the simulation result to find the suitable fish swimming modes (especially BCF swimming) for fishlike underwater robot system. To find the suitable swimming modes, we assume that they have the same length, volume, and weight, but they have the different numbers of actuator (joint). And we use the minimum number of joint for each swimming mode. We derive the dynamic equation for each system using Kane’s method and these results are compared by the result of DADS. We present the optimal solution of swimming mode for some aquatic locomotion, especially faster (high propulsive efficiency) and more maneuverable (quick turning motion).

Within median and/or paired fin (MPF) propulsion, many fish routinely use the long-based undulatory fins as the sole means of locomotion. In this paper, the long-based undulatory fin of an Amiiform fish "G. niloticus" was investigated. A simplified physical model was brought forward, which makes up of N equal thin rods and a rectangular elasticmembrane connecting them together. With light mass, small stiffness and low natural vibration frequency, the long-based fin undulating and fluid loading may induce large flexible distortion of their long-based fins when swimming. We established a kinematic model of the long-based undulatory fin on the basis of analyzing the long-based dorsal fin locomotion and considering the fluid-structure interaction. Further, the equilibrium equations of the undulatory fin were obtained by applying the membrane theory of thin shells in which the geometrical non-linearity of the structure is taken into account. Last, we apply the derived the kinematic model and equilibrium equations of the undulatory fin to analyze the thrust and propulsive efficiency varying with the aspect ratio of the fin and the maximum swing amplitude.

This paper presents a dynamic model of robotic fish which synthesizes both the carangiform and anguilliform swimming modes. The designed robotic fish is divided into three parts: stiff anterior body, flexible rear body, and an oscillating lunate caudal fin. We use unsteady flow theory to analyze the motion of the anterior part and the links, and adopt basic airfoil theory for the caudal fin. By summing up the longitudinal force, lateral force and yaw moment on each propulsive component, the kinematic and dynamic equations of the swimming robotic fish can be derived. The desired propulsive characteristics including forward velocity, sway velocity, angular speed, motion trajectory as well as propulsive efficiency can then be obtained via solving ordinary differential equation. Comparisons between simulation results and real experiments are then conducted and discussed. A good agreement on dynamic characteristics demonstrates the validity of the proposed model.

The space power research engine (SPRE), a free-piston Stirling engine with a linear alternator, is being tested as a candidate high-capacity power supply for space systems. Results of baseline engine tests at design and off-design operating conditions are presented. The test results are compared with HFAST code model predictions and show fairly good agreement. The trends in measured data generally follow the same trends as the code predictions. The code, however, does not account for effects of gas bearing flows and mass transport between volumes of the engine. >

The use of appropriate propulsion devices for autonomous underwater vehicles (AUVs) is important from the point of view of higher propulsive efficiency and directional stability. In this paper, a design methodology for a propeller/stator combination behind an autonomous unmanned underwater vehicle is described. The design procedure is presented based on the three dimensional flow around the vehicle and the lifting line theory of propeller action with the associated formulation. The effect of variation of the axial distance between the propeller and stator and the number of the stater blades on the propulsor characteristics are systematically investigated. From the application of this method to a typical AUV the improvements in torque balance and propulsive efficiency are demonstrated.

Various kinds of flip-flop linear motors (FFLM) are discussed in comparison with linear synchronous motors (LSM), from the view point of propulsive efficiency. The essential difference between them exists in the waveforms of the current flowing in the ground coils. They are rectangular with various conduction angles for FFLMs and sinusoidal for LSM. The typical circuit configurations of the FFLMs for 180/spl deg/, 120/spl deg/, 90/spl deg/ and 60/spl deg/ conduction modes are described. The magnetic fields caused by the periodical arrangement of permanent magnet pairs which are assumed to be mounted on vehicles are then analysed for the respective conduction modes. Considerations on the economical aspects of both the actuators and the driving circuits are also described. The optimum arrangement of the magnet pairs is concluded to depend on the current conduction modes. It is also concluded that if the total length of the actuator is given and higher power is required, 120/spl deg/ FFLM is preferable and if least vehicle weight or most efficient magnet use are required, 60/spl deg/ FFLM is preferable particularly for high frequency traffic. >