| Wave-driven vehicle is a kind of surface unmanned vehicle driven by ocean wave energy.It has the advantages of strong ocean survivability,endurance and self-supporting.At present,it has been applied to marine meteorological monitoring,marine resource exploration and military fields,and has become one of the research hotspots of marine unmanned equipment.Wave-driven vehicle belongs to multi-body dynamic system in structure.According to the connection mode between hull and hydrofoil,it can be divided into rigid connection type and flexible connection type.Self-propulsion performance is one of the important indexes of multi-body system of wave-driven vehicle.The so-called "self-propulsion" refers to the process of wave-driven vehicle from static state to stable autonomous navigation driven by wave energy.Self-propulsion performance directly reflects the capture ability and rapidity of wave-driven vehicle to ocean wave energy.However,there are many difficulties in the study of its self-propulsion performance,including the complex multi-body dynamic model of wave-driven vehicle,the difficulty of modeling,the difficulty of CFD numerical calculation on the premise of unknown kinematic response of wave-driven vehicle,and the high accuracy of CFD numerical calculation.These difficulties make the previous research results unsatisfactory.Based on the existing research,this topic studies the self-propulsion performance of the multi-body system of wave-driven vehicle:Firstly,the numerical flow field of two-phase flow is established in OpenFOAM-v2006.The overlapping grid method is used to simulate the self-propulsion process of wave-driven vehicle in regular and irregular waves.Through the method that the background grid moves with the overlapping grid,on the premise of ensuring the calculation accuracy,the number of grids is effectively reduced,the calculation efficiency is improved,and the unbounded navigation of the vehicle driven by waves in the numerical simulation is realized.For irregular waves,the frequency spectrum of coastal waves in China is used to generate waveforms,and Particle Swarm Optimization algorithm is used to optimize them.Secondly,the limitations of step-by-step integration method in the numerical solution of multibody dynamics are described,and then a MBD generalized displacement direct solution method with iterative convergence in unit time step is proposed.By directly solving the generalized displacement in each time step and ensuring the iterative convergence of generalized displacement in unit time step,this method avoids the problem of speed and position default in the numerical integration of multibody dynamics,It also avoids the problem of stiffness of equations generated by step-by-step integration method,so as to realize the stable solution of nonlinear dynamic problems.Combined with CFD method,the dynamic and kinematic response of a multi-body system of a wave driven vehicle in regular waves is simulated to verify the effectiveness of the solution method.Thirdly,the numerical calculation method of self-propulsion process of wave-driven vehicle based on the combination of MBD and CFD is proposed.Among them,for the multi-body dynamic model of the flexible connected wave-driven vehicle,based on the rigid connected model,the solution model of tensile force of the flexible umbilical cable is established.According to the structural characteristics of the flexible connected model,the moving velocity with the moving background grid is assigned as the sailing velocity of the glider of the flexible connected wave-driven vehicle.On this basis,the self-propulsion process of rigid connected and flexible connected wave-driven vehicles in regular waves is numerically simulated,and the dynamic and kinematic response laws of the two structural forms of vehicles are analyzed.Then,the influence of wave parameters,wave encounter angle,structural parameters including the umbilical length,distance between adjacent hydrofoils and the installation position of hydrofoils on the self-propulsion performance of the two type of wave-driven vehicles is analyzed,and the structural parameters of the two wave-driven vehicles are optimized based on the analysis results.After completing the numerical simulation in regular waves,the self-propulsion process of the two vehicles in irregular waves is numerically simulated.Finally,the test prototypes of rigid connected and flexible connected wave-driven vehicles are developed,and the tank test and ocean test of the self-propulsion process of the two kinds of wave-driven vehicles are completed.The test results show that the accuracy of the numerical simulation results is high.The numerical simulation method of MBD and CFD proposed in this subject has strong effectiveness and accuracy,which lays a foundation for the research and development of the same type of ocean wave-driven vehicle in the future. |
