Dimitrios P. Evgenidis
Investigation on the power efficiency of the Carangiform and Anguilliform LOCOmotion of an articulated robotic fish, by Dimitrios Evgenidis, MSc Marine Engineer
Abstract*
The nature of the project involves two versions- which differ in their locomotion pattern where the first pattern is angulliform, that resembles an eel, and carangiform, that resembles a tuna -of an articulated robot which have been examined in terms of energy consumption. By setting certain restrains and assumptions an ideal environment for the experiment has been set. The restrains and assumptions are that the robot is operated on a constant depth, therefore it is considered as 2-dimensional, swimming velocity cannot exceed 1.25 m/sec, which is the maximum speed for which data could be acquired and also it is assumed that the motion is only forward, and that each link vertically oscillates at a constant speed, as set by the Lagrange-Euler equations.
In anguilliform motion, it has been proven that the total energy of the system increases a large rate. Since Anguilliform motion is based on the motion of the whole body, in order generate thrust and, consequently, build up speed, all links have to undulate. The increment of the total energy is a result of the faster undulation of the links which create the propulsion force of the robot. According to obtained results, an Anguilliform swimming machine can only be used for usage in limited time operations. That issue it might be solved in robots of a larger scale but that would result into minimization of their manoeuvring abilities and limitation of operation areas.
In carangiform motion, the energy consumption is obviously low, as in biological carangiform swimmers. In order to generate thrust, the last two segments of the body undulate. Since the last link is equipped with a fin, it is able to generate and maintain thrust easily. Long distance traveling requires energy conservation and, consequently, the movements of the body should be at a minimum. The fin which is located in the last link allows the robot to displace much water and build up the thrust required to move at a certain speed and also maintain it. As the experimental procedure proved these characteristics minimise the total energy needed for operation. Obviously, it is the most efficient and effective movement when it is considered that in addition to the above, it also has only 2 moving parts, which means that there are fewer parts to maintain and service but it lacks in precision since the motion of the tailfin creates besides large thrust and a large vortex which affects the overall position of the robot in the liquid.
The results of the experimental procedure helped reaching a conclusion that anguilliform motion is more suitable when operating in tight and mazy areas in contrast with carangiform motion which is more suitable for long distance travelling or cases that manoeuvrability does not play an important role. Consequently, it can be said that a system that combines the two motions and will operate in two different modes has great advantages and can offer deliver some notable results. The system may comprise of 5 links and on the last link there will be a retractable tail fin. When the robot operates in anguilliform motion, the retractable tail will not be used and the 4 links will undulate, the same way they do in an anguilliform robot. When it operates in carangiform motion it will deploy the retractable tail, and the links will operate in pairs- link 1, the “head”, along with link2, then link 3 alone and link 4 and 5 together- in a similar configuration as the experimental.
All in all, bio mimetic systems as the experimental one have a long way in order to overcome the technical difficulties but in the long term these systems will be able to offer a more analytical insight in all kind of marine applications, such as ballast tanks and submerged hull inspection.
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Evgenidis Dimitrios Dissertation
