| In recent years,with the development of shipbuilding industry,the speed of surface vessels and submarines have been greatly enhanced,the effect of hydroelastic vibration on the hull strength and fatigue life has caused widespread concern in the shipbuilding industry.Fin stabilizer,hydrofoil ships and the rudder in submarine etc.wing structural components,once the design is inappropriate,vessels in high speed movements will encounter harmful vortex induced flutter,and even lead to structural damage.Therefore,use the results of hydroelasticity to analyze the vibration of oscillating hydrofoil in viscous fluid is important.Hydrofoil vibration is a typical hydroelasticity problem,is a cross discipline of hydrodynamics and mechanics of elasticity,to consider the coupling effect of three forces,which are hydrodynamic force,elastic force and inertial force,coupling the hydrodynamic and the elasticity equation to solve the problem.Based on the aeroelastics theoretical system,which is relatively mature,deduced two-dimensional hydrofoil Theodorsen theoretical solution of water and then solving elastic theory unstable boundary,however,two-dimensional theoretical model is obtained in the thin wing,potential flow theory under the simplified conditions,it is difficult to meet the needs of engineering.With the calculation of complex model,and the calculation method and hardware upgrade,numerical simulation has gradually become the mainstream.Numerical methods include non-coupling method,weak coupling and strong coupling,the commonly treatment methods are two-way flow solid coupling calculations of hydrofoil structure,get the time domain vibration,the shortcomings of this approach is the computational cost is large,and the processing method of dynamic grid requires very high.However hydrofoil as a rigid body,vibration amplitude in the water is not very big,influence on the flow field is also limited.Therefore,at present,the treatments mainly concentrated in non-coupling method of one-way fluid structure interaction(FSI),the hydrodynamic solved in flow field is taken into solid as the vibration source.Such as the hydrofoil unsteady method to draw on the wall pressure fluctuation can be used for solving the structural vibration or hydrodynamic noise,which is a neglected structural deformation effect on the flow field of the one-way coupling method.In this paper,the hydrofoil structure as the research object,first of all,the theoretical hydrodynamic analysis on two-dimensional wings section is held based on nonlinear approximation theory,Theodorsen unsteady model of thin wings in incompressible and inviscid flow is deduced,the relational between generalized force and generalized displacement can be drawn,Substituted into rigid body kinematic equations,and then the unstable boundary conditions can be solved.Secondly,hydrofoil vibration under FSI is studied.Large-eddy simulation method is used to calculate the flow field around hydrofoil,and Runge-Kutta method is applied to solve equations of rigid body motion.Flow results and motion results exchange data at the hydrofoil wall surface,by compiling a user-defined functions to control rigid body motion and flow field grid update.The influence of the hydrofoil parameters,i.e.attack angle,elastic axis position and flow velocity,on vibration are discussed.Once the velocity increase to a certain value,hydrofoil flutter phenomenon occurred.Also,discussion on time and frequency domain is held to investigate the flutter phenomenon.Then a three-dimensional hydrofoil structure as the object,vibration of threedimensional hydrofoil under FSI is analyzed,the hydrofoil's deformation and vibration are contrasted under the one-way and two-way FSI.Finally the submarine sail structure vibration and noise is studied,the modal analysis of the sail with and without rudder is carried out respectively,then the vibration and noise radiation under Point excitation and hydrodynamic calculated in CFD is studied. |
PDF Full Text Request