Design And Research Of Key Technologies For A New AUV In Complex Sea Conditions

Modern autonomous underwater vehicle (AUV) is an intelligent unmannedplatform to perform a variety of military and civilian mission in complex marineenvironment, which can better meet the needs such as scientific research, militaryoperations and commercial applications and full utilize the marine resources. With themission needs of increasingly complex and diverse, the AUV is developing in thedirection of systematism, multifunction, and clustering technology. Existing AUV withsingle function has been unable to meet the needs of the current mission. Moreimportantly, the design theory of the AUV in complex sea conditions also need to befurther improved to adapt to the conceptual design of the AUV, which ensures that themulti-function AUV can resist environmental disturbances and be ability to completevarious tasks flexibly. Therefore, the overall design and the corresponding key technicalissues of a multi-moving state AUV in complex sea conditions has important theoreticalsignificance and engineering value for promoting the development of the domesticAUV. The international development forefront of the AUV is closely followed in thispaper. The smallness, modularity, economization and reliability are the design goals ofa new AUV. A multi-moving state AUV provided with the functions such as thesubmarine vectorial thrust, landing on the sea bottom, wheel driving on the ground andcrawling on the ground is developed and a number of key theoretical issues such askinematics and dynamics, navigation control and the ambient flow field in complex seaconditions are studied systematically, which provides an important theoretical basis andtechnical guidance for the further production of the experimental prototype. To sum up,the main results in this paper contain the following areas:(1) The overall design of a multi-moving state AUV is proposed. The main andaccessory structures adopt the separable form. The heave system, vectorial thruster,measurement and communication module, manipulation module and control system aredesigned. The structure and working principle of each system are made a detailedanalysis, which guarantees that the multi-moving state AUV has the functions such asthe submarine vectorial thrust, landing on the sea bottom, wheel driving on the groundand crawling on the ground. The piston-type heave system completes the distributionregulation of gravity and buoyancy. The vectorial thruster achieves four functions suchas wheels, legs, thrusters and course control. The measuring the communication moduleapplies the economical design reuse-conditioning systems. The manipulation moduleuses the orthogonal-design and high-precision transmission gear as drive mechanism.The control system uses the distributed control system architecture. The new AUV isequipped with rudders and vectored thrusters, which are combined to control the coursefor realizing multi-motion modes in different control modes of high speed and low speed respectively. The innovative design and kinematic analysis of each majormachine show that the new AUV designed in this paper is fully in accord with thedesign goals and functional requirements.(2) The parameterized design and mechanical properties of a new wheel propellerare studied. The propeller is a special kind of complex surface parts. The parametricvariables are defined according to the structural characteristics and process requirements,and then the coordinate transformation formula of transforming the local coordinates ofthe points on section planes to the global coordinates is deduced. The problem ofapplying different geometric parameter atlases to solid modeling is resolved usingMatlab process. Then demands of surface-loft, knit surface, thicken and so on are usedto complete the solid modeling. Two forms of modeling examples show that the processof parameterized design is simple and practical, which improves the efficiency of serialmodeling. On this basis, the computational fluid dynamics (CFD) method is applied toexplore the numerical methods of the propeller open-water performance by using theRANS equation and three different turbulence models including standard k-ε, standardk-w and RSM based on sub-domains hybrid meshes. The computational results ofopen-water performance of the propellers including DTMB4119, DTRC3745and D4-70are in good agreement with the experimental data, which verifies the correctness ofsolid modeling and numerical methods. The maximum error of RSM, standard k-ε andstandard k-w in the computational results of DTMB4119open-water performance are5.47%,7.41%and11.21%, which shows that the numerical method using RSM hasgood accuracy in the prediction of propeller open-water performance. This conclusionmay guide the selection of turbulence models in viscous flow computation aroundcomplex rotating machine. Some important viscous flow characteristics of the propellersuch as flow separation, tip vortex and trailing wake are got, which provides aneffective reference for the design of new efficient thruster. A new wheel propeller(WPD4-70) with the advantages of a large thrust, high structural strength, stablehydrodynamic performance and anti-blade flutter is present through a series of propelleropen-water performance computation and comparison under the guidance of thecharacteristic analysis of the ducted propeller and the contracted and loaded tip (CLT)propeller, which breaks the design bottleneck of the single function propeller. In orderto ensure the security and stability of the AUV when it is moving on the ground,nonlinear buckling analysis based on finite element method is used to compute themaximum allowable load of WPD4-70, the computational result is3975N. Meanwhile,the natural frequencies and vibration modes are got through the modal analysis ofWPD4-70, each natural frequency is less than the corresponding value of the model Ⅳ,which indicates that the ability of its vibration insulation in the driving state is enhanced.The past four vibration modes show that the first vibration mode (main vibration mode) is the distortion of the blades and the remaining modes are the radial stretching the edgeof the wheel. The final WPD4-70has preferable open-water performance and intensitycharacteristics, which can realize the functional requirements of the multi-moving stateAUV.(3) The nonlinear dynamics of the new AUV is studied in complex sea conditions.Euler angles representation is applied to establish six-DOF nonlinear kinematic modelaccording to the structural characteristics and motion characteristics of the new AUV. Inorder to achieve the satisfactory performance with arbitrary angles, the quaternionmethod is used to solve the especial singularities when the pitch angles are±90o. TheNewton second law and Lagrangian approach are used to deduce the vectored thrusterAUV’s nonlinear dynamic equations with six degrees of freedom (DOF) respectively incomplex sea conditions based on the random wave theory, the dynamic models of thetwo methods are same, which shows that the dynamic model of the vectored thrusterAUV is accurate. On this basis, the mathematical model of the new AUV’slow-frequency motion and high-frequency motion in complex sea conditions areestablished. The Runge-Kutta arithmetic is used to solve the dynamic equations, whichnot only can simulate the motions such as cruise and hover but also can describe thevehicle’s low-frequency and high-frequency motion, so this method clears up thedifficulties of computation and display of the coupled nonlinear motion equations incomplex sea conditions. The kinematic model and dynamic model are proved to bevalid through the computation and analysis of its spatial motion’s performance ininterference-free environment and the analysis of the integrated signals includinglow-frequency motion signal and high-frequency motion signal in environmentaldisturbance, which shows that the maneuverability of the vectored thruster AUVequipped with rudders and vectored thrusters is enhanced. Furthermore, it is necessaryto filter the measurement of the new AUV’s position and orientation signal in complexsea conditions, and the low-frequency motion signal control can effectively avoid theproblem of energy waste and propeller wear.(4) The trajectory tracking control problem of the new AUV in complex seaconditions is studied. The fastness and stability of the new AUV in complex seaconditions need the control system with strong robustness to complete. In order to solvethe nonlinear term and unmodeled dynamics existing in the new AUV’s attitude controland the disturbances caused by the external marine environment, a second-order slidingmode controller with double-loop structure that considering the dynamic characteristicsof the rudder actuators is designed. Then Lyapunov stability theory is used to verify thestability of the controller. the impacts of system parameters, rudder actuator’sconstraints and boundary layer on the sliding mode controller are computed andanalyzed to verify that the sliding mode controller based on dynamic boundary layer can effectively resolve sliding mode loss in the attitude control caused by the rudderactuator amplitude and rate limiting and avoid the control failure caused by that thedesign theory does not match with the actual application conditions. According to thesubmarine theory, six-DOF motion equations of the new AUV are decomposed into twomutually non-coupled subsystems, namely the horizontal plane subsystem and thevertical plane subsystem. As the yaw angle and yaw angle rate rather than thedisplacement of the new AUV can be measured directly in the horizontal plane, thesliding mode control algorithm combining cross track error method and line of sightmethod is used to fulfill its high-precision trajectory tracking control in different seaconditions, which ensures the robustness and accuracy of the sliding mode controllerwhen the heading error is too large. As the vertical displacement of the new AUV canbe measured, a stable sliding mode controller is designed based on the single-inputmulti-states system，which takes into account the characteristic of the hydroplane andthe amplitude and rate constraints of the hydroplane angle. Moreover, the using ofdynamic boundary layer improves the robustness and control accuracy of the system,which realizes the accurate tracking of time-varying depth signal with the desiredattitude in different sea conditions. The impacts of currents and waves on the slidingmode controller of the new AUV are analyzed qualitatively and quantitatively bycomparing the trajectory tracking performance of the new AUV in different seaconditions, which provides an effective theoretical guidance for the control systemdesign of the new AUV in real complex environment.(5) The hydrodynamic characteristics of the viscous flow field around the newAUV in complex sea conditions are studied. The CFD method is used to simulatenumerically the unsteady viscous flow around the new AUV with propellers innon-environmental interference conditions by using the RANS equations, SST k-wmodel and pressure implicit with splitting of operators (PISO) algorithm based onsliding mesh. The computational results have good convergence, which reflects well thereal ambient flow field of the new AUV with propellers. The interaction between AUVhull and wheel propellers is predicted qualitatively and quantitatively by comparing thehydrodynamic parameters such as resistance, pressure, velocity and so on that fromintegral computation and partial computation of the viscous flow around the AUV withpropellers in non-environmental interference conditions, which provides an effectivereference to the optimization design, vibration and noise of the AUV hull and propellersin real environment. The communication tasks usually require the new AUV to navigateon the sea surface in complex sea conditions. Therefore, the movement forms and flowfield characteristics of the new AUV navigating in head sea at high speed are necessaryto be studied. The mathematical model of the high-speed AUV in head sea isestablished with considering the hydrodynamic lift based on strip theory according to the motion characteristics of the new AUV in waves, which is solved to get the heaveand pitch of the AUV by Gaussian elimination method. Then the motion processes ofthe AUV’s heave and pitch are realized in the numerical computation of the flow fieldaround the AUV based on the dynamic mesh that driven by the UDF function sourcecode compiled with DEFINE_CG_MOTION macro. According to the coordinatetransformation principle of AUV’s longitudinal motion theory and the technique ofpurely numerical wave based on the UDF function source code compiled with DEFINEmacro, the three-dimensional numerical wave of the computational field is realizedthrough defining the unsteady inlet boundary condition. On this basis, the CFD theory isused to establish the mathematical model of the unsteady viscous flow around the AUVwith considering free surface effort by using the RANS equations, SST k-w model andVOF model. The hydrodynamic parameters of the AUV such as drag, lift, pitch torque,velocity, pressure, and wave profile are got by numerical computation, which predictwell the real flow field around the high-speed AUV in head sea. The computationalwake of the AUV is in good agreement with the experimental phenomenon of awave-piercing surface vehicle, which verifies effectively the correctness of thenumerical method.