Research On Mechanism And Technical Of Active Noise Reduction For Sliding Bearing

As an important supporting part,sliding bearing is widely used in rotating mechanical products.It will inevitably produce noise due to vibration in the service process.This kind of noise has low frequency,strong cycle and easy to make people feel tired and worried.At present,there are two noise reduction methods: active noise reduction and passive noise reduction.Passive noise reduction is mainly used to reduce the middle and high frequency noise,but for the low frequency noise produced by rotating machinery,the effect of noise reduction is very small.Active noise reduction is mainly through real-time capture of the noise spectrum to obtain its characteristic signal,and then generate noise reduction sound wave.This method takes the noise itself as the research object,which is easy to be interfered by external signals,and it is difficult to implement and popularize effectively because of its weak pertinence.Therefore,this thesis takes the sliding bearing as the main research object and proposes an intelligent active noise reduction device.Considering the limited space,sliding bearing noise generated by the mostly comes from the rotor vibration,so if the rotor vibration problem of mapping after noise spectrum characteristics of sound waves,noise spectrum real-time capture problem is converted to the vibration mechanism of bearing rotor system or dynamic behavior research,through the real time to build the mapping relationship between vibration and noise,finally,the vibration signals processed(in opposite phase)are returned to the frequency spectrum of noise reduction source,which can realize adaptive and active noise reduction,and solve the problems that the existing noise reduction device is vulnerable to interference under the timevarying working condition of sliding bearings,and the noise reduction effect is difficult to meet the demand,etc.In this thesis,the dynamics of sliding bearing rotor system and the research status of active noise reduction at home and abroad are reviewed firstly,and the shortcomings of current noise reduction methods are analyzed.An intelligent active noise reduction device for sliding bearings was proposed to reduce the bearing noise,improve the enclosed space environment and improve the working experience of workers.The main points studied in this thesis are as follows:(1)The lubrication condition of the sliding bearing in the operation process is analyzed.Firstly,we analyze the motion of different sliding bearings under ideal conditions according to the Reynolds equation.Secondly,according to the dynamics theory,we analyze the change of shaft diameter with the environment under different working conditions.(2)The basic principle of active noise reduction was analyzed from the perspective of acoustics,and the vibration-noise coupling was carried out through the finite element analysis software to obtain the size of the noise generated by sliding bearing under different working conditions,which was expressed by the acoustic parameters of sound pressure level.The twophase flow oil film model of sliding bearing was established in Fluent fluid software,and the operating conditions of sliding bearing under non-ideal conditions were calculated.According to the oil film pressure obtained,the motion of journal was further calculated in MATLAB software.(3)The vibration and noise coupling analysis was carried out under ideal and non-ideal operating conditions respectively.In ideal condition,the influence law of structural parameters and working condition characteristic parameters of sliding bearing on sound pressure level was studied.The influence degree of lubricating oil viscosity,density,journal speed,external load amplitude and eccentricity on the sound pressure level was studied by orthogonal test method.At the same time,the influence of surface roughness of sliding bearing on the sound pressure level was studied.The results show that when the journal speed,external load,eccentricity and oil viscosity are reduced,the sound pressure level is reduced.Lubricating oil density has little effect on sound pressure level.The roughness can cause small fluctuations of journal displacement,but these small fluctuations have little effect on the sound pressure level.The orthogonal test results show that the external load has the greatest influence on the sound pressure level,followed by the eccentricity rate,the viscosity and velocity have similar influence trends on the sound pressure level,and the lubricant density has almost no influence on the sound pressure level.Under non-ideal condition,the influence of different contents of water,bubbles and solid particles in lubricating oil,including the diameter of oil inlet and the viscosity of lubricating oil under two-phase flow on the running condition of sliding bearing was studied.The results show that the noise increases with the increase of lubricating oil viscosity.With the increase of oil inlet diameter,the sound pressure level also increases,but the increasing trend decreases gradually.When the water content,gas content and particle content of the lubricating oil increase,the sound pressure level generated by the operation of the sliding bearing decreases.(4)The construction and fitting of noise reduction wave are carried out.According to the principle of acoustic interference,when two rows of sound waves of the same frequency meet at a certain point in space,the resultant sound pressure is related to the phase difference.Therefore,the effect of phase change on noise reduction is studied.The results show that when the phase difference is 0 degrees to 90 degrees,the noise does not decrease,but increases.When the phase difference is 90 degrees to 180 degrees,the noise reduction effect increases gradually.When the phase difference is 180 degrees,the noise reduction effect is the best,which is consistent with the active noise reduction theory.It shows that the adaptive active noise reduction method of intelligent sliding bearing proposed in this thesis is feasible to some extent.