Research On Optimization Design Of Main Bearings Of Megawatt Wind Turbines

With the increasing consumption of fossil energy and the global warming effect,the development of renewable clean energy has received wide attention from all over the world.Wind energy has been developed and utilized as an important new energy source.Double row tapered roller bearing is an important type of main bearing in direct drive wind turbines.On the one hand,its’ performance determines whether the wind turbines can operate effectively.On the other hand,the size of the bearing structure also affects the space of the entire wind turbine.At present,scholars’ research on the optimization design of large double row tapered roller bearings is still focused on how to increase the rated dynamic load per unit volume.Only the bearing geometry is used as an optimization constraint,and the influence of bearing contact stress and bearing life on bearing design under working load is not considered.When designing the shafting structure,it is often desirable to obtain a more compact shafting structure while ensuring the performance requirements of the bearing,and the optimization target of the above method is obviously inconsistent with this practical engineering problem.To solve this problem,this paper established an optimization design method with bearing volume as the optimization goal,and constrains the bearing geometry,roller contact stress and bearing life.The double-row tapered roller bearing which meets the stress and life requirements and the smallest volume under the given working condition load was obtained by genetic algorithm optimization.The specific research contents are as follows:(1)A static model of contact load for double row tapered roller bearings was established.The contact load of each roller was solved by converting the overall displacement of the bearing to the normal displacement of each roller to obtain the relationship between the contact load of the bearing external load roller.(2)Based on the Hertz contact theory,the finite-length contact problem was transformed into a point contact problem for the roller slice,and the stress distribution on the roller contour was iteratively obtained.The logarithmic curve modification was used to modify the shape of the roller contour to find the logarithmic curve modification parameter that minimized the maximum stress of the roller profile under the maximum roller contact load.(3)Two methods for calculating the bearing life of a fan were studied.Firstly,based on the life calculation method of the basic dynamic load rating,the life calculation was calculated from the capacity of the rolling bearing.Second,the life was calculated by analyzing the raceway contact.The fatigue load of the wind turbine(LDD)load processing method was studied.And calculated the equivalent life of the bearing by using the new load condition.(4)An optimized design method with bearing volume as the optimization target was established,which constrained the geometric relationship of the bearing,the roller contact stress and the bearing correction life.With this optimization method,the main bearing of a wind turbine was designed,and the design parameters of a double-row tapered roller bearing with minimum volume and meeting requirements of stress and life were obtained.After the volume of the optimized bearing was compared with that of the previously used bearing,it was found that the space volume of the bearing had decreased by 22.22%.(5)Taking the life of the bearing as the optimization target,the influence of the limit load and fatigue load on the bearing design parameters were considered,and the bearing under the fixed external dimension was optimized.In comparison with the bearing previously used,it was found that the design method increased bearing life by 10%.