| The harsh offshore working conditions and high maintenance costs restrict the development level of offshore wind power industry in China,which indicates the importance of reliability improvements of key components such as gearboxes for offshore wind power.The gearbox of a 5 MW offshore wind turbine is taken as the research object and the process of "parameter excitation characteristic analysisgear fault modeling and dynamic analysis-gearbox parameter optimization" is taken as the research idea.Multi-body dynamics,vibration theory,Hertz contact theory,lumped parameter method,genetic algorithm,modal analysis,orthogonal test and other methods are comprehensively applied in revealing the mechanism of gear failure and achieving optimal design schemes of offshore wind turbine gearbox based on reliability growth.The specific research and achievements are as follows:(1)The influence of parameters on the dynamic characteristics of gears.Taking the high-speed output parallel-stage gear-pair of a 5 MW offshore wind turbine gearbox as the research object,a 12-degree-of-freedom dynamic model considering its bending-torsion-axis-pendulum coupling is established.The influence of pressure angle,helix angle,tooth center distance and tooth backlash parameters on the dynamic characteristics of parallel gear-pairs are quantitatively explored under the rated speed condition.The research shows that the gear meshing force is relatively small at 25°pressure angle.The difference in the helix angles has a particularly significant effect on the vibration characteristics of the gear-pair,and the vibration is relatively weak at around 9° helix angle.Compared with the spur gear,the meshing stiffness of the helical gear is more sensitive to the change of the center distance.With the increase of the center distance,the meshing stiffness shows a downward trend as a whole.The change of the normal backlash has a more significant effect on the vibration characteristics of the spur gear.When the normal backlash is increased within a certain range,the vibration of the gear is weakened.(2)Modeling and dynamic characteristics analysis of local tooth surface uniform wearing fault.Taking the high-speed parallel-stage gear pair of 5 MW offshore wind turbine gearbox as the research object,an 8-DOF dynamic model of the gear transmission based on the lumped parameter method is established.The theoretical time-varying mesh stiffness models with/without wearing fault are obtained based on cantilever beam theory and potential energy method.The radian angle parameter θ is introduced to characterize the severity of wearing fault,and a geometry-parametric model of uniform wearing on the local tooth surface is established,after which the dynamic characteristics of the gearbox are analyzed at different speed and wearing severity conditions.The research shows that the gearbox vibrates more intensely with the increase of the input speed and the wearing severity.In the none-wearing meshing state,the main excitation source of the vibration acceleration of the housing is the frequency multiplication of the meshing frequency,which is 3fm,2fm,4fm,and 1fm in the descending order of amplitude.When tooth surface wearing fault occurs,the main excitation source changes into 2fm and the surrounding fault frequency.(3)Modeling and dynamic characteristics analysis of distributed tooth surface spalling fault based on tooth profile and friction coupling.Taking a high-speed parallel-stage gear pair of a 5 MW offshore wind turbine gearbox as the research object,a distributed tooth surface spalling fault modeling method based on tooth profile and friction coupling is proposed.The time-varying mesh stiffness model under different spalling degrees are established and substituted into the 8-DOF dynamic differential equation of the gearbox.The gearbox dynamics are simulated under different torque conditions,and the vibration characteristics under different wear severity and torque conditions are analyzed under time-frequency domain.The research shows the vibration of the gearbox and the torsional vibration of the gear become more severe with the increase of the tooth surface spalling severity and input torque.The vibration velocity and acceleration of the gearbox caused by tooth surface spalling are particularly significant in the vicinity of 40%rated torque.The main excitation frequencies that cause the pinion’s torsional vibration are sequenced by 1fm,2fm and 4fm,which doesn’t change with the spalling defect severity.However,the torsional amplitude values at higher-order excitation frequencies increase significantly with the degree of spalling.(4)Weight reduction optimization of large-scale offshore wind power multi-stage gearbox based on genetic algorithm.Taking a 5MW offshore wind turbine gearbox with a speed increase ratio of 97 as the research object,the optimized volume of the gearbox is derived from genetic algorithm after accurately designing the speed increase ratios and the arrangement of the number of planetary gears,which comprehensively considers constraints such as the strength of the transmission shaft and the tooth strength.After that,the speed increase ratio intervals of all stages of the optimized gearbox are decoupled,and the tooth number allocation schemes and the corresponding gearbox dynamics model of the bending-torsion-axis-pendulum coupled gearbox based on the zero-order optimization algorithm are established.Then,the quantitative statistical analysis is carried out on the load sharing characteristics and vibration characteristics of the gearbox under the rated speed condition.Taking the A5A3B gearbox as an example,when the three speed increase ratios are optimized from 4,5,and 4.85 to 3.778,5.4,and 4.755,the equivalent volume is reduced from nearly 7.214 m3 to about 6.444 m3,and the weight is reduced by about 10.7%.Taking an A3A3B gearbox as an example,when the teeth number of the sun gear,planetary gear,and ring gear are 29,28,and 85 in the first stage and 26,46,and 118 in the second stage,respectively,the teeth number of the large and small gear are respectively 111 and 25 in the third-stage,the gearbox shows good planetary-level load sharing characteristics and the high-speed output shaft has a stable transmission.It is a large-scale offshore wind turbine gear.(5)Research on multi-stage helix angle optimization of large offshore wind turbine gearbox based on orthogonal design.Firstly,taking a two-stage planetary and one-stage parallel gearbox of a 5MW offshore wind turbine as the research object,the three helix angles(A,B,C)in different stages are set as independent variable factors,and 5°,8°,11°,15° are set as corresponding four discrete levels,thus a 16-group orthogonal scheme is established.Secondly,the gearbox models with floating sun gears based on bending-torsion-axis-pendulum coupling corresponding to the orthogonal schemes are established,then the dynamic simulation are carried out.Mathematical statistical analysis on parameters such as load sharing coefficient and vibration signal is then performed,and evaluation of the factor-level effect is carried out.Finally,the validity of the results of the orthogonal test scheme is verified.Research shows the load sharing characteristics of any planetary stage are mainly related to the helix angle of its own stage.The larger first-stage helix angle and the 11° second-stage helix angle corresponds to better load-sharing characteristics.When the third-stage helix angle is around 8°,the vibration of the high-speed output shaft is weak.The modeling method for quantitative analysis of local tooth surface wearing and distributed tooth surface spalling faults provides an effective data reference for revealing gear fatigue fault characteristics.The gearbox parameter optimization method proposed in terms of vibration characteristics,load sharing characteristics,and weight reduction design provides necessary theoretical support for further improving the reliability of offshore wind turbine gearboxes.Some research results have been put into practical application and achieved good results. |
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