【作者】 王娟；

【导师】 王春光；

【作者基本信息】 内蒙古农业大学 ， 农业机械化工程， 2010， 博士

【摘要】 揉碎机是我国近年来研制出的一种新型饲草料加工设备,它是介于铡切与粉碎两种机械加工技术之间的一种新型加工方式。经揉碎后的秸秆为柔软、蓬松的丝状物,具有适宜的长度和粗细度,因而对于直接饲喂反刍家畜以及干燥、粉碎、制粒、压块(饼)、化学处理、生物处理等后续加工都极为有利。但是,揉碎机和大部分旋转机械一样,存在噪声高、振动强烈的缺点,严重阻碍了其进一步的推广和发展。本文针对揉碎机的空气动力性噪声和机械噪声展开研究,结合理论分析、数值模拟和试验研究对其噪声产生机理和特性进行了分析研究,主要内容有以下：(1)依据国家标准GB6971-86《粉碎机试验方法》和GB3768-83《噪声源声功率级的测定一简易法》分别对空载和负载下9R-40型揉碎机5个测点的噪声进行试验研究。得出空载和负载的主要噪声源都是空气动力性噪声,且都是旋转噪声。(2)基于MATLAB提供的小波工具包,结合小波技术和频谱分析技术对揉碎机的噪声源进行识别。用db4小波基对采集的空载和负载第5测点的噪声信号进行尺度为6的小波分解,获得了7个频带的能量分布和百分含量。(3)以导流板、齿板、锤片、风扇及其组合为试验因素进行揉碎机噪声分离研究,通过分析获得到影响揉碎机的噪声大小的主、次因素,即风扇旋转产生的空气动力性噪声是影响揉碎机噪声的主要噪声源,其次是锤片,导流板对噪声的影响不大,齿板具有吸声作用。(4)获得了对噪声影响较大的转速、锤片数与声压级之间的关系：转速越高,噪声越大,且转速在2400-2800r/min范围内,最佳转速应选择2600r/min左右；锤片的数量只影响噪声幅值,对主要频率影响较小。(5)通过振动试验得到揉碎机的主要零件的主要实际振动频率都集中在100-500Hz以内,而且转子存在严重的动不平衡,在x、y、z三个方向上的振动能量都很大,这对轴承的寿命,以及整机的振动都有严重的影响。(6)基于结构力学和振动理论,运用有限元分析软件ANSYS对9R-40型揉碎·机上、下机壳的固有频率及振型进行分析。结合振动试验结果和模拟结果,从刚度角度提出结构优化方案,为揉碎机的改进和性能优化提供参考。(7)为了对揉碎机空气扰动噪声源的产生机理、噪声特性及其规律进行研究,运用计算流体力学软件Fluent对9R-40型揉碎机内部的流场进行了三维模拟,直观显示了揉碎机腔体内的流场特性和流动状态。并且对计算所得的风速曲线和试验测得的值进行对比,结果表明,二者最大相对误差小于8%,且得到了转速为2800r/min运动时揉碎机流场的压力分布和内部流场速度分布。通过气流流场模拟结果分析表明,低速气流从进气口经高速旋转的转子作用后,产生了旋转噪声和涡流噪声；另外,在出料直管内形成一个回流区,易造成出料口堵塞,也会产生噪声。更多还原

【Abstract】 Rubbing and breaking machine is a new type of forage processing equipment, which is developed in China in recent years. It is a new processing method which is between cutting and crushing process technologies. The rubbed straws are soft and fluffy filaments, which have appropriate length and coarseness. As a result, it is extremely beneficial for directly feeding、smashing、drying、grinding、granulating、briquetting (cake)、chemical processing、biological treatment and other subsequent processing However, the rubbing and breaking machine are the same as the most rotating machines that have the disadvantages of high noise and strong vibration, which seriously impedes the further promotion and development of rubbing and breaking machine. This paper is a study of aerodynamic noise and mechanical noise, which combined with theoretical analysis, numerical simulation and experimental study on the mechanism of its noise generation and characteristics, the main contents are as follow:(1) According to national standard GB6971-86《mill test methods》and GB3768-83《noise source power level measurement method for simple》, the experiment had been conducted on five measurement points around 9R-40 rubbing and breaking machine under no-load and load conditions, The result is that aerodynamic noise is the main noise source whether it is no-loaded or loaded.(2) Based on wavelet tools package provided by MATLAB software, the main noise sources are identified using the technology of wavelet and spectrum analysis. The noise signals which are obtained on the no-load and load conditions are decomposed with db4 wavelet in the scale of 6, for the fifth measurement points.then the decomposed coefficients in seven different frequency band were obtained. According to the energy distribution of the 7 different frequency bands noise signals of the 9R-40 rubbing and breaking machine, the result is that the main signal of the rubber noise is mid-frequency noise.(3) The separation study is carried out that take deflector、toothed plat、hammer and fan and combination of them as main factors. The result obtained that is aerodynamic noise was mainly caused by rotating fan, and secondary factors were hammers.Deflector has little effect on the noise, but tooth plate has an effect of sound absorption.(4) The relationship between sound pressure level and rotating speed、the number of hammer which have great impact on the noise were obtained. The higher the speed is, the greater the noise is. And in the range of speed from 2400 r/min to 2800r/min, the optimum speed should be about 2600r/min. The numbers of hammer pieces are more related to noise size, but less related to noise frequency.(5) By vibration testing, the actual vibration frequencies of the main parts of the rubbing and breaking machine focused on the range of 100-500Hz. Besides there was seriously rotor dynamic imbalance, and the vibration energy of bearing in the three directions of x, y, z are large, which has a lot of critical effects on the life of bearings and vibration of the whole machine.(6) Based on structural mechanics and vibration theory, the natural frequency and vibration mode of the upper and lower shell of 9R-40 rubber were analyzed using the finite element analysis software ANSYS, combining with vibration test results and simulation results, the structural optimization program was purposed on the point of stiffness, which provide a theoretical reference for improving machine and performance optimization.(7) For studying principle, property and law of producing air disturbulance noise, three dimensional inner flow fields were simulated with Fluent software. Properties and state of the flow fields were showed directly. Comparing numerical simulation curves with experiment data, the maximum relative error was indicated less than 8%. The distribution of pressure and velocity of flow fields were obtained from the simulation results at 2800 r/min. By analyzing the simulation results of flow field, both rotation noise and eddy current noise were produced when low airflow from inlet was affected by high rotating rotor. In addition, a reversed flow is formed in the outlet, which can cause a block and produce noise.更多还原