271 research outputs found
Effect of Communication Delays on the Successful Coordination of a Group of Biomimetic AUVs
In this paper, the influence of delays on the ability of a formation control algorithm to coordinate a group of twelve Biomimetic Autonomous Underwater Vehicles (BAUVs) is investigated. In this study the formation control algorithm is a decentralized methodology based on the behavioural mechanisms of fish within school structures. Incorporated within this algorithm is a representation of the well-known and frequently used communication protocol, Time-Division-Multiple-Access (TDMA). TDMA operates by assigning each vehicle a specific timeslot during which it can broadcast to the remaining members of the group. The size of this timeslot varies depending on a number of operational parameters such as the size of the message being transmitted, the hardware used and the distance between neighbouring vehicles. Therefore, in this work, numerous timeslot sizes are tested that range from theoretical possible values through to values used in practice. The formation control algorithm and the TDMA protocol have been implemented within a validated mathematical of the RoboSalmon BAUV designed and manufactured at the University of Glasgow. The results demonstrate a significant deterioration in the ability of the formation control algorithms as the timeslot size is increased. This deterioration is due to the fact that as the timeslot size is increased, the interim period between successive communication updates increases and as a result, the error between where the formation control algorithm estimates each vehicle to be and where they actually are, increases. As a result, since the algorithm no longer has an accurate representation of the positioning of neighbouring vehicles, it is no longer capable of selecting the correct behavioural equation and subsequently, is unable to coordinate the vehicles to form a stable group structure
Modelling and simulation of a biomimetic underwater vehicle
This paper describes work carried out at the
University of Glasgow investigating biomimetic
fish-like propulsion systems for underwater
vehicles. The development of a simple
mathematical model is described for a
biomimetic fish like vehicle which utilizes a
tendon drive propulsion system. This model is
then compared with a model of a vehicle of
similar size but with a propeller for main
propulsion. Simulation results for both models
are shown and compared
Design and Evaluation of a Propulsion System for Small, Compact, Low-Speed Maneuvering Underwater Vehicles
Underwater vehicles used to perform precision inspection and non-destructive evaluation in tightly constrained or delicate underwater environments must be small, have low-speed maneuverability and a smooth streamlined outer shape with no appendages. In this thesis, the design and analysis of a new propulsion system for such underwater vehicles is presented. It consists primarily of a syringe and a plunger driven by a linear actuator and uses different inflow and outflow nozzles to provide continuous propulsive force. A prototype of the proposed propulsion mechanism is built and tested. The practical utility and potential efficacy of the system is demonstrated and assessed via direct thrust measurement experiments and by use of an initial proof-of-concept test vehicle. Experiments are performed to enable the evaluation and modelling of the thrust output of the mechanism as well as the speed capability of a vehicle employing the propulsion system
Design and Projected Performance of a Flapping Foil AUV
The design and construction of a biomimetic flapping
foil autonomous underwater vehicle is detailed. The vehicle was
designed as a proof of concept for the use of oscillating foils as
the sole source of motive power for a cruising and hovering underwater
vehicle. Primary vehicle design requirements included
scalability and flexibility in terms of the number and placement of
foils, so as to maximize experimental functionality. This goal was
met by designing an independent self-contained module to house
each foil, requiring only direct current power and a connection to
the vehicle’s Ethernet local area network for operation. The results
of tests on the foil modules in the Massachusetts Institute of
Technology (MIT) Marine Hydrodynamics Water Tunnel and the
MIT Ship Model Testing Tank are both used to demonstrate fundamental
properties of flapping foils and to predict the performance
of the specific vehicle design based on the limits of the actuators.
The maximum speed of the vehicle is estimated based on the limitations
of the specific actuator and is shown to be a strong function
of the vehicle drag coefficient. When using four foils, the maximum
speed increases from 1 m/s with a vehicle Cd of 1.4 to 2 m/s when
Cd = 0.1, where Cd is based on vehicle frontal area. Finally,
issues of vehicle control are considered, including the decoupling
of speed and pitch control using pitch-biased maneuvering and the
tradeoff between actuator bandwidth and authority during both
the cruising and hovering operation
Hydrodynamics of Biomimetic Marine Propulsion and Trends in Computational Simulations
[Abstract] The aim of the present paper is to provide the state of the works in the field of hydrodynamics and computational simulations to analyze biomimetic marine propulsors. Over the last years, many researchers postulated that some fish movements are more efficient and maneuverable than traditional rotary propellers, and the most relevant marine propulsors which mimic fishes are shown in the present work. Taking into account the complexity and cost of some experimental setups, numerical models offer an efficient, cheap, and fast alternative tool to analyze biomimetic marine propulsors. Besides, numerical models provide information that cannot be obtained using experimental techniques. Since the literature about trends in computational simulations is still scarce, this paper also recalls the hydrodynamics of the swimming modes occurring in fish and summarizes the more relevant lines of investigation of computational models
Biomimetic oscillating foil propulsion to enhance underwater vehicle agility and maneuverability
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 2008Inspired by the swimming abilities of marine animals, this thesis presents "Finnegan
the RoboTurtle", an autonomous underwater vehicle (AUV) powered entirely by four
flapping foils. Biomimetic actuation is shown to produce dramatic improvements in
AUV maneuvering at cruising speeds, while simultaneously allowing for agility at
low speeds. Using control algorithms linear in the modified Rodrigues parameters to
support large angle maneuvers, the vehicle is successfully controlled in banked and
twisting turns, exceeding the best reported AUV turning performance by more than
a factor of two; a minimum turning radius of 0.7BL, and the ability to avoid walls
detected> 1.8BL ahead, are found for cruising speeds of 0.75BL/S, with a maximum
heading rate of 400
/ S recorded.
Observations of "Myrtle", a 250kg Green sea turtle (Chelonia mydas) at the New
England Aquarium, are detailed; along with steady swimming, Myrtle is observed performing
1800 level turns and rapidly actuating pitch to control depth and speed. Limb
kinematics for the level turning maneuver are replicated by Finnegan, and turning
rates comparable to those of the turtle are achieved. Foil kinematics which produce
approximately sinusoidal nominal angle of attack trace are shown to improve turning
performance by as much as 25%; the effect is achieved despite limited knowledge of
the flow field. Finally, tests with a single foil are used to demonstrate that biomimetically
inspired inline motion can allow oscillating foils utilizing a power/recovery style
stroke to generate as much as 90% of the thrust from a power/power stroke style
motion
Towards amphibious robots: Asymmetric flapping foil motion underwater produces large thrust efficiently
The development of amphibious robots requires actuation that enables them to crawl as well as swim; sea turtles are excellent examples of amphibious functionality, that can serve as the biomimetic model for the development of amphibious robots.
In this paper we have implemented the observed swimming kinematics of Myrtle, a green sea turtle Chelonia Mydas residing in the Giant Ocean Tank of the New England Aquarium, on the 1.5-meter long biomimetic vehicle Finnegan the RoboTurtle. It is shown that these kinematics result in outstanding performance in (a) rapid pitching, and (b) rapid level turning. The turning radius for the rigid hull vehicle is 0.8 body lengths, a remarkable improvement in turning ability for a rigid hull vehicle.
Still Finnegan’s performance lags the live turtle’s performance by about 20%. Careful observations have shown that turtles employ a fin motion in-line with the direction of locomotion; this degree of freedom was not available to the Finnegan fins, as presently designed. Experimental tests on a flapping fin equipped with this third degree of freedom have shown that the in-line motion enhances the fin’s performance.
This hydrodynamic result is doubly beneficial to an amphibious robot, because it allows for further enhancements in the hydrodynamic function of fins, while the in-line motion allows the same fins to be used for crawling on land.Massachusetts Institute of Technology. Sea Grant College Program; United States. Defense Advanced Research Projects Agency. Center of Excellence for Research in Ocean Science
3D locomotion biomimetic robot fish with haptic feedback
This thesis developed a biomimetic robot fish and built a novel haptic robot fish system based on the kinematic modelling and three-dimentional computational fluid dynamic (CFD) hydrodynamic analysis. The most important contribution is the successful CFD simulation of the robot fish, supporting users in understanding the hydrodynamic properties around it
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