| Forage crushing machine is a kind of forage processing equipment developed independently in China.The main disadvantages are high noise and strong vibration.Noise does great harm to people’s hearing,nerve and digestive system,and also affects people’s work efficiency.The problem of noise and vibration seriously hinders the further popularization and development of the forage crusher.In order to better control the noise and vibration of the crusher,it is necessary to test,analyze and optimize the coupling noise.In order to predict and optimize the coupling noise of the forage crusher in the design stage,the no-load noise and load noise of the forage crusher were tested by multi-point measurement method based on sensor array.The collected data were analyzed by self-spectrum and wavelet analysis to identify the noise source accurately.On this basis,the analysis of unbalanced rotor flow field in the rubbing mill-shell vibration response,the vibration transfer characteristics between the acoustic analogy theory to establish kneading crusher aerodynamic noise and unbalanced rotor caused by the body vibration noise coupled acoustic model,and use more coupled noise model based on proven island genetic algorithm for structural optimization design.Research shows that:(1)No-load and load noise spectrum structure is similar,mainly composed of discrete spectrum and continuous spectrum,in which the discrete noise generated by rotating rotor hammer striking airflow and material is the main component of the noise of the crushing machine.The closer the measuring point is to the feed port and the discharge port,the greater the noise pressure level is.The maximum noise of no-load and load appeared at the measuring point near the inlet front.(2)Compared with no load,the amplitude of the sound pressure level at the measuring point near the feed outlet increases after adding the material,while the amplitude of the sound pressure level at the measuring point near the discharge outlet decreases.The maximum difference between load and no-load A-weighted total sound pressure level is 1.30 d B(A).It can be seen that the main noise source of the forage crusher is the aerodynamic noise generated by the disturbed airflow of the rotor hammer.(3)According to the wavelet packet frequency band energy analysis of the noise signals,the noise energy at the fundamental frequency generated by the vibration excitation caused by the hammer disturbing the gas-solid two-phase flow field when the rotor rotates accounts for 58.32% of the total energy,which is the main noise source.The energy at triple frequency is the next,accounting for 9.15% of the total energy.In addition,the noise generated by the fundamental frequency of the unbalanced rotor excitation accounts for 7.05% of the total energy and is also the main noise source of the coupled noise.(4)By comparing the measured and numerical results of noise,it can be seen that the variation law of measured and simulated sound pressure levels at each measuring point is basically the same,and the maximum measured and simulated pressure levels both appear at the front of the feed inlet close to the top of the feed inlet.The measured sound pressure level is slightly higher than that of the simulation,and the maximum difference of the total sound pressure level between the simulation and the test is 1.6 d B(A).It can be seen that the established coupling noise model of the crushing machine is basically accurate and the numerical prediction results are reliable.(5)After optimization,the maximum noise was reduced from 102.60 d B(A)to87.56 d B(A),lower than the national standard of 90 d B(A).The optimization results are feasible,which provides a method basis for low noise design of forage crusher. |
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