Analysis Of Biomimetic Hydrofoil Propulsive Performance

The biomimetic propulsion, as a novel propulsion method different from the traditionalscrew propeller, offers a new idea for enriching propulsive method of underwater vehicles.The propulsive motion style of marine turtles’ hydrofoil is unique, and the attitude controlforms by limbs coordination are various. There are great significance and practical value tostudy the biomimetic hydrofoil propulsion technology of marine turtles for developing newtypes of underwater driving mode, enriching and perfecting underwater propulsive technology.Related research about the biomimetic hydrofoil propulsion technology has been done in threeaspects, namely, planning the motion pattern of the biomimetic hydrofoil, analyzing thepropulsive performance of the biomimetic hydrofoil and the numerical simulation of theunsteady flow field of the biomimetic hydrofoil.According to the monitoring results of marine turtles’ hydrofoil motion and theexperimental results of living marine turtles, bionic research has been conducted in theaspects of external morphology, limbs structure and motion characters of marine turtles. Theprofilogram of the biomimetic limbs are fitted in order to obtain the average chord and theaspect ratio. Motion characters of marine turtles’ hydrofoil are researched by studying the tiptrajectory character and the time ratio between the stroke and azimuth spin of the hydrofoil.That offers bionic foundation for planning motion parameters of the biomimetic hydrofoilpropulsion unit.Based on the two degree-of freedom biomimetic hydrofoil propulsion unit, thekinematics model of the biomimetic hydrofoil in segmented pattern of alternating stroke andazimuth spin motion is established. Propulsive performance of the hydrofoil in segmentedmotion pattern is studied by analyzing the hydrofoil tip trajectory, cycle thrust, propulsiveefficiency and the motion character of the biomimetic robot. The computational results in thisdissertation are verified through comparisons between the computational results and theexperimental results of the biomimetic robot in tank.Aiming at the problems of insufficient mechanism utilization and discontinuous thrust ofthe biomimetic hydrofoil in the segmented motion pattern of2degree-of freedom alternation, a new motion pattern of coupled stroke and azimuth spin is proposed. Integrating the azimuthspin, which does not produce efficient thrust, into the stroke spin, makes the thrust changescontinuously. Propulsive performance comparisons between the segmented and coupledmotion pattern are conducted from the aspects of average thrust, propulsive efficiency andmotion character of the biomimetic robot, to verify the effectiveness of the coupled motionpattern. Effect to the hydrofoil tip trajectory, cycle thrust and the propulsive efficiency ofchanged coupled motion parameters, such as motion cycle and the amplitude of the azimuthspin, are analyzed to offer theoretical basis for optimizing the coupled motion parameters.In order to analyze the cause of thrust produced by the hydrofoil in the view of fluid fieldchange, the unsteady fluid field of the biomimetic hydrofoil is simulated numerically.Relationships between the biomimetic hydrofoil thrust and the pressure as well as the velocityvector distribution of the fluid field are analyzed. Pressure data at the moment of largestpressure differential between the front and back faces of the hydrofoil is extracted as thedistribution load. Transformation and stress distribution of the biomimetic hydrofoil areanalyzed using the fluid-solid coupling technology. The strength of the biomimetic hydrofoilis verified by comparing the maximum stress of the biomimetic hydrofoil and the yield limitof the hydrofoil material.