| When the ship is actually sailing,it will be subjected to the action of wind and waves to produce swing motion.Its pitch can reach up to ±30°,and its roll can reach up to ±45°.When the ship swings,the shafting attached to the ship will also swing,resulting in more complex load on the stern tube bearing of shafting,the reliability of the stern tube bearing is critical to the shafting and even the entire ship.Therefore,the stern tube bearing will be the research object in this paper,the load on the stern tube bearing will be explored,and the establishment method of the bearing’s load spectrum will be studied,finally,the load spectrum that can be used to guide the bearing design and test is compiled.The research work of this paper is as follows:First,a mathematical model of the ship’s swing law is proposed based on the swing conditions,and the ship’s swing law model is connected with the wave shape parameters,then the ship’s swing law model is solved by the known wave shape parameters,after that the inertia force of the shafting under the swing condition is solved by the swing law model,that is,the calculation formula of the inertia force of the shafting is deduced from the mathematical model.The panel method based on the velocity potential is used to calculate the load on the propeller,first the surface of propeller and vortex are discretized into a series of hyperboloidal quadrilateral panels with constant source and sink and doublet distributions.The surface integral equation is established according to the Green formula,combined with the pressure Kutta condition,and the numerical solution of the equation is obtained by the Newton-Raphson iteration method.The velocity is determined by Yanagizawa method from the velocity potential on the surface,and then the pressure on the propeller surface is obtained by Bernoulli equation,finally the axial thrust and torque experienced by the propeller are obtain.The DTMB4119 propeller is selected as the calculation model for numerical calculation using the CFD simulation software FLUENT.First the coordinate conversion method is used to model the propeller by 3D modeling software Solidworks,then the sliding mesh model combined with the VOF method is used to calculate the hydrodynamic performance of the propeller.After verifying the feasibility of the numerical calculation method,the hydrodynamic performance of the propeller under different conditions are simulated,finally the force and torque values of the propeller under different conditions are obtained.A simplified model of the shafting is established using Solidworks software.And the various swing conditions are simulated in turn by ABAQUS.And angular displacement-time curve during the swing process which is the derived is used as the motion curve of the shafting to simulate the ship’s motion,this process can generate inertia force,and the load of the propeller obtained is applied to the shafting,and finally the load of the stern tube bearing is obtained.The establish process of the load spectrum is introduced.Firstly,the average/amplitude information of the load is obtained by MATLAB from the obtained load-time curve through data compression and cycle counting which is using rain flow counting method,and the average/amplitude distribution is respectively assumed,then the unknown parameters of the assumed probability density function are estimated and tested,finally the probability density function,distribution function and joint probability density function of the mean/amplitude value are established.Finally,the compiling methods of two-dimensional load spectrum and one-dimensional load spectrum are introduced,according to the obtained distribution function,the fluctuation center of the average and the maximum value of the amplitude are solved,and the amplitude is graded according to the ratio coefficient method.Then eight levels and one-dimensional load spectrum of axial force,radial force and torque are established for the stern tube bearing. |
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