Research On The Self-propelled Swimming Of A Tuna-like Bio-mimetic Underwater Vehicle

Aquatic animals like fishes have great swimming performances of high efficiency,high speed and flexible maneuverability,which are the constant goals of unmanned underwater vehicles(UUVs).The bio-mimetic underwater vehicle has been an important development in underwater vehicle field.And the first concern is to explore the swimming mechanism of fishes.However,most of the previous investigations are based on the non-self-propelled swimming and simplified movement deformation equations,which are not deep enough on mechanism of swimming.In this thesis,under thunniform swimming and using Computational Fluid Dynamics(CFD)method,the self-propelled swimming mechanisms of a tuna-like bio-mimetic underwater vehicle in various movement patterns are studied.Firstly,in condition of determining the relationship between the pitch amplitude and Strouhal number,the maximal effective angle;numerical simulations of routine sinusoidal oscillating and adjusted non-sinusoidal oscillating are carried out by the Reynold average Navier Stokes(RANS)solver.Then,the trend of the hydrodynamic performance descent,the variation of the flow field and the effect of maximum angle of attack are analyzed in high Strouhal number for the routine oscillating.Further,for the adjusted oscillating,the results indicate that it can improve the thrust and efficiency of the hydrofoil in high Strouhal number effectively.And the different forms of the adjusted oscillating have great influences on thrust.Secondly,using the RANS solver and the dynamic interaction process which is based on the secondary development of the CFD,it will solve the dynamic equations coupledly,and the large deformation caused by ship motion will be manipulated through the integration of spring smoothing,remeshing and integrated grid movement technology.Based on the above,the numerical calculation model for the tuna-like bionic underwater vehicle with multi-degrees of freedom self-propelled swimming is established;numerical simulation of the acceleration process from static state to cruising state is completed,and comparing with the cruising experimental results,the effectiveness of self-propelled swimming model is verified.The changing of hydrodynamics,flow field and longitudinal motion,stability of transverse and heading motion in acceleration-cruise process are analysed in detail.The research shows that the heave amplitude,pitch amplitude,frequency have deep impact on acceleration-cruise process,and a suitable pitch angle cooperated with heaving can significantly enhance the propulsion and swimming efficiency.Thirdly,based on the self-propelled swimming with movement deformation equation of kick-gliding,numerical calculation of the swimming process in double tail-beat and half tail-beat of the tuna-like bionic underwater vehicle are completed.The results show that due to the rapid motion deformation,the efficiency is low in the kick stage,but the efficiency of energy utilization is improved by absorbing the inertial kinetic energy and the vortex energy in wake zone.If the gliding time is greater than a certain critical value,the kick-gliding saves more energy than the routine cruising,and the energy utilization efficiency in half tail-beat is higher than in double tail-beat.Hydrodynamic asymmetry change in kick-gliding makes the transverse and heading motion asymmetric,but it remains stable in a period.Finally,in the self-propelled swimming conditions,combining with the deformation equation of starting and turning motion,numerical calculations of maneuvering process of the tuna-like bionic underwater vehicle are accomplished,including the C shaped starting and turning.And the influences of the motion deformation parameters on the motion trajectory of starting and turning,turning angle,motion speed and hydrodynamic changing are analyzed in detail.The results show that the sharp fluctuation of the longitudinal force in earlier backswing is the main thrust source of accelerated motion when starting,and turning movement is mainly depends on the yawing moment from rapid deformation of forward swing.After completing starting and turning,the transverse and heading movement hasnt reached a steady state,and the starting motion is more unstable.The trajectory of the starting motion is usually hook shaped,and the trajectory of turning motion is deeply influenced by the yaw angle.The minimum turning radius happened when the yaw angle is about 180°.With appropriate motion and deformation parameters,it can keep the swimming speed when considerably yawing in turning motion.