The Research Of Biomimetic Sea Turtle’s Flexible Hydrofoils Propulsion Technology

AS one of the propulsion modes of marine animal, the sea turtle’s particular flexibleforelimb-hydrofoil propulsion has outstanding advantages of good yarage, less noise, highutilization ratio of eddy and particular attitude control method. If this propulsion technologycould be applied to the microminiature autonomous underwater vehicles which has small sizeand low Reynolds number, it will have significant theoretical research sense and practicalvalue for developing new underwater propulsion mode, improving the concealment andyarage of the underwater vehicles.Currently, the research of turtle hydrofoil propulsion is on the threshold, of which boththe hydrofoil flexible propulsion technology and the hydrofoil cooperation propulsiontechnology haven’t be studied enough. Whereas, these technology is the brief reason ofhydrofoil propulsion having the advantage of high efficiency and low noise, study thesetechnologies will be importance for understanding and mastering the hydrofoil propulsionprinciple, and expediting its practicability course about the underwater carrier technology.This thesis has researched the turtle hydrofoil flexible propulsion technology and hydrofoilcooperation propulsion technology from the studies of hydrofoil propulsion principle, and onthis basis the bionic carrier technology of hydrofoil propulsion was developed. At last, thepropulsive performance of flexible hydrofoil and control method of hydrofoils cooperationmotion were validate by the pool experiments about the bionic carrier.The principle and mechanical properties of turtle hydrofoil propulsion were researched.Through the biological prototype vivo experiments, the morphology and kinematicsparameters were acquired, and cyclical movement of hydrofoil could be divide into the twoDOF which were stroke spin and azimuth spin. The hydrofoil-tip motion trajectory could bedescribed as a three-dimensional “8” utilizing lemniscate of Bernoulli, and the hydrofoilkinematic models of stroke spin and azimuth spin could be established by harmonic motionequations. Based on this kinematic models, the numerical simulation of hydrofoil motion wasdone to study its outer force and flow field structure, and the experiments result showed thatthe resistance was superior near the hydrofoil shoulder but the thrust was superior near the tip,and the reverse Karman vortex street was appearing in hydrofoil wake. Utilizing the anatomy,hydrofoil’s skelecton and muscle mechanical properties were analyzed, and the conclusioncan be got that skelecton had marked viscous-elasticbehaviour and muscle was in the state ofisotonic contraction while hydrofoil moving.The bionic propulsion technology of turtle’s flexible hydrofoil was researched. Based on the principle analysis of hydrofoil motion, the driving force, deformation character and flowfield structure were studied, and then the hydrofoil’s trailing vortex Strouhal number beingbetween0.2and0.45, the Reynolds number being from3×102to4.5×104was calculated, theconclusion that trailing edge vortex’s accelerated shedding and leading edge vortex’s noshedding were the important reasons of hydrofoil’s high lift force (thrust) had been obtained.The viscoelastic constitutive property of turtle hydrofoil was studied, and the results showedthat the4parameters linear viscoelastic model could fit the viscoelastic characteristics ofhydrofoil’s trailing edge parenchyma preferably. Based on these, a half-iliac bionic flexiblehydrofoil was developed, and its tissue modal as well as numerical modal were analyzed tostudy its flexible deformation magnitude, deformation rapidity and deformation stress.Based on hydrofoil propulsion principle, the bionic carrier technology of hydrofoilpropulsion was developed. As the biological prototype to be bionic object, a bionic hydrofoilpropulsion experimental sample was developed, and then its three-dimensional motionhydrodynamic force was analyzed. The analysis showed that, there would be a vertical forcedisturbance in the sample’s straight navigation and the double hydrofoils yawing could notonly enhance the yawing torque but also increase the heeling moment rather than singlehydrofoil yawing. The amount external force of the sample during its pool experiments werestudied, and sample’s space motion equation was obtain pass by the matrix generalizedtransformation and Newton-Euler equation, which were providing the basis for abstractingsample’s dynamic model. Based on the kinematic model of bionic hydrofoil, the numericalsimulation tests of the sample’s hydrofoil were done, and the results showed that hydrofoilstroke spin angular velocity ω1and azimuth spin angle β playing an important role inadjusting hydrofoil thrust.Aim at the hydrofoil cooperation motion characteristics, the hydrofoil cooperationpropulsion technology was researched. The principle of turtle hydrofoil cooperation motionwas studied, and the analysis deduction was obtained that the hydrofoil trailing vortex strapcould be oversewed by the cooperation of hydrofoil’s stroke spin and azimuth spin, theaggregated vortex interference phenomenon would be eliminated by the cooperation motionof left and right hydrofoils. Then, the control system of the sample’s hydrofoil cooperationmotion was developed, both the subsection control method of hydrofoil’s two spincooperation motion and the angle velocity on-line adjustment method of double hydrofoilscooperation motion were proposed simultaneity, and the experiments of bionic sample’shydrofoil cooperation motion were conducted. The experiments results showed that, these twocontrol methods could realize sample doing hydrofoil’s two spin cooperation motion and double hydrofoils cooperation motion preferably.In order to validate the propulsive performance of flexible hydrofoil, the experimentalresearch of bionic sample moving in the static pool was done. First, the pool experimentalenvironment was built and the sample’s hydrofoil cooperation propulsion experiments weredone, and experiments results validated the analysis deduction that hydrofoil’s two spincooperation motion could increase sample’s portrait thrust and double hydrofoils cooperationmotion could enhance sample’s movement efficiency. Secondly, the sample’s straight aheadnavigation experiments were done, and it showed that hydrofoil stroke spin angular velocityω1and stroke spin angle a both had a monotonic increasing influence on sample’s speed, butthe hydrofoil azimuth spin angle β had a first high last low influence on the speed. Thesenavigation experiments results had validated the conclusion of hydrodynamic analysis andnumerical simulation about the hydrofoil motion. Thirdly, the sample’s yawing movementexperiments were done, and it showed that sample’s yawing velocity would be nonlinearincrease according to hydrofoil stroke spin angular velocity ω1. And the yawing experimentsresults also validated the conclusion that the double hydrofoils contrary phase differentialyawing not only increase the sample yawing velocity but also could reduce the sample yawingradius and moving stability rather than single hydrofoil yawing. At last, the propulsiveperformance contrast experiments of bionic sample with half-iliac flexible hydrofoil andwhole-iliac rigid hydrofoil were conducted, and it showed that the additional thrust functionof flexible hydrofoil would be embodied only at the high ω1value, but its damping effect ofsample speed was always existing and becoming more and more evident. These contrastexperiments validated the conclusion that flexible hydrofoil could improve the propulsiveperformance of the hydrofoil propulsion rather than the rigid one.