Others Example - BioInspiration

Hello lovely readers! We hope you are doing well. Our small turtles are doing as fine as ever.

This week we will be covering about an example by other studies that have performed on turtles. One of them is the Design and Implementation of a Biomimetic Turtle Hydrofoil for an Autonomous Underwater Vehicle, as mentioned in the previous post. The team of researchers for this study investigated on the design and possibility of implementation of a turtle hydrofoil for an Autonomous Underwater Vehicle to replace the old propeller usually used for ships. Due to the agility of how turtles can easily move underwater, it would be beneficial for submariners if they posses the same degree of manoeuvrability for their submarines. 

In National University of Singapore (NUS), researchers created turtle-inspired robots for various underwater purposes. These very nimble and maneuverable robots can perform dangerous underwater tasks that are too hazardous for humans, such as detecting nuclear wastes and also at depths that are too high in pressure. Unlike typical diving vehicles such as submarines, these turtles do not have any ballast system, hence it is smaller and lighter, and able to carry bigger payloads so that it can perform complicated tasks such as surveillance in water quality of Singapore's reservoir. It can dive vertically, by using front and himb limb gait movements, similar to real turtles. 

Figure 1. The biomimetic turtle-inspired robot designed by NUS.

Another study on biomimetics of turtles is from the paper "Towards Amphibious Robots: Asymmetric Flapping Foil Motion Underwater Produces Large Thrust Efficiently" by Stephen Licht, Martin Wibawa, Franz S Hover and Michael S Triantafyllou from Massachussets Institute of Technology. They studied the swimming kinematics of a green sea turtle Chelonia Mydas and applied to the biomimetic vehicle the called Finnegan. The vehicle is 1.5 m long and 0.55 mm wide and propelled by four independently controlled high aspect ratio fins. After modification, the turning radius of Finnegan is 0.8 of its body length, which is a remarkable improvement. The fins of Finnegan were designed so that it is capable of moving in a two-degree of freedom motion. However the study found out that turtles has a third degree of motion but the researchers could not apply it onto Finnegan.

Literature Review

Hello again fellow readers!

Leo and Ralph are doing fine, they are in fact doing great! Both tortoises appear healthy and energetic. Also, we just changed the container that we used to keep them both.

One of them is inside the small purple container.

Anyway, in conjunction with the module's blog schedule, in this post we will see biomimetics studies that have been done by researchers that were inspired from turtles. One interesting study is the Design and Implementation of a Biomimetic Turtle Hydrofoil for an Autonomous Underwater Vehicle, by Davinia Font, Marcel Tresanchez, Cedric Siegentahler, Tomas Palleja, Merce Teixido, Cedric Pradalier and Jordi Palacin.

Basically, the study is about the design and implementation of a turtle hydrofoil for an Autonomous Underwater Vehicle (AUV). The most common AUV propulsion system is usually using propellers, however propellers are not suitable for some conditions, such as low flow conditions, in confined spaces, near the surface, and in unsteady flow. Hence, propulsion based on 'fins' are of great interest for maneuverability. The authors proposed turtle's propulsion methods.

An example of an AUV used by United States Navy.

Turtle's fins have a hydrofoil shape. The skeleton of the fin, which consists of thick humerus and radius, are short in length, while the phalanx is comparatively very long. These characteristics create a streamlined hydrofoil that is adapted to swim efficiently, as the resistance from the hydrofoil dynamic swirl is reduced. In addition to the fin's shape, the turtle's head has a pointy shape, able to reduce the forward resistance by adapting the position of its head relative to the navigation path. In other words, the head helps 'cut' through the water.

a) Oval path followed by the legs of a freshwater turtle.

b) Figure-of-eight path followed by the hydrofoils  of a sea turtle.

They conducted three experiments to study the feasibility of the concept. They performed computer simulations as well as physical experiments to determine the optimum angle of attack, propulsion path of hydrofoil, and the profile of water speed generated by the displacement of hydrofoil.The study concluded that the design of AUV can be further improved when using this biomimetic inspiration, specifically from turtles.